Nondestructive Methods and Special Test Instrumentation Supporting NASA Composite
Overwrapped Pressure Vessel Assessments
AIAA-2007-2324
Regor Saulsberry1 and Nathanael Greene2
NASA Johnson Space Center White Sands Test Facility, Las Cruces, New Mexico, 88012
Ken Cameron3 and Eric Madaras4 NASA Langley Research Center, Hampton, Virginia 23681-2199
Lorie Grimes-Ledesma5 Jet Propulsion Laboratory, Pasadena, California, 91109
John Thesken6 Ohio Aerospace Institute-NASA Glenn Research Center, Cleveland, Ohio, 44135
Leigh Phoenix7 Cornell University, Ithaca, New York, 14853
Pappu Murthy8 and Duane Revilock9 NASA Glenn Research Center, Cleveland, Ohio, 44135
Many aging composite overwrapped pressure vessels (COPVs), being used by the National Aeronautics and Space Administration (NASA) are currently under evaluation to better quantify their reliability and clarify their likelihood of failure due to stress rupture and age-dependent issues. As a result, some test and analysis programs have been successfully accomplished and other related programs are still in progress at the NASA Johnson Space Center (JSC) White Sands Test Facility (WSTF) and other NASA centers, with assistance from the commercial sector. To support this effort, a group of Nondestructive Evaluation (NDE) experts was assembled to provide NDE competence for pretest evaluation of test articles and for application of NDE technology to real-time testing. Techniques were required to provide assurance that the test article had adequate structural integrity and manufacturing consistency to be considered acceptable for testing and these techniques were successfully applied. Destructive testing is also being accomplished to better understand the physical and chemical property changes associated with progression toward “stress rupture” (SR) failure, and it is being associated with NDE response, so it can potentially be used to help with life prediction. Destructive work also includes the evaluation of residual stresses during dissection of the overwrap, laboratory evaluation of specimens extracted from the overwrap to evaluate physical property changes, and quantitative microscopy to inform the theoretical micromechanics.
1 Project Manager, NESC Independent Technical Assessment NDE Lead, Laboratories Office, P.O. Box 20/201LD. 2 Project Manager, Laboratories Office, P.O. Box 20/201LD. 3 NESC COPV Independent Technical Assessment Leader, NASA Langley Research Center, Hampton, Virginia. 4 Ph.D., NDE Test Office, NASA Langley Research Center, Hampton, Virginia. 5 Ph.D., NESC COPV Team Leader, 4800 Oak Grove Drive. 6 Ph.D., 21000 Brookpark Road. 7 Professor, Cornell University, Ithaca, New York. 8 Deputy Structural Fellow, NESC, NASA Glenn Research Center, Cleveland, Ohio. 9 Project Manager, Structures and Acoustics Division, NASA Glenn Research Center, Cleveland, Ohio.
https://ntrs.nasa.gov/search.jsp?R=20070010588 2020-04-03T12:07:55+00:00Z
I. Introduction ASA is engaged with recertification and life extension of the many aging Kevlar®* composite overwrapped pressure vessels (COPVs). The COPVs have varying criticality, usage histories, damage and repair histories,
time at pressure, and number of pressure cycles. When NASA reviewed the COPVs, a concern was raised with respect to “stress rupture” (SR) life predictions.
Similarly, concerns arose regarding the graphite (carbon) epoxy COPVs also used in newer systems. A Nondestructive Evaluation (NDE) Super Problem Resolution Team (SPRT) was formed to provide NDE competence for the necessary technical assessment. The NDE SPRT evaluated the data available and established observations and recommendations; however, immediate application of NDE to COPVs was found limited by the “state of the art” and specific experience base. Additionally, assisted by observations of the SPRT, the NASA NDE Working Group (NNWG) recognized the need for development of NDE specifically applicable to COPVs, some of which is actively underway.
As a resolution to the life prediction issue, a COPV test project was initiated at NASA Johnson Space Center White Sands Test Facility (WSTF) to better understand where these vessels stood in their available life. Additionally, carbon COPV SR test programs have been ongoing at WSTF for several years, and recent investigations have been supported by the SPRT. Pretest NDE was needed and applied to screen the COPVs prior to testing, and NDE technology was also needed and applied during testing to gather critical test data. Since validated processes were not always available, “best practices” were applied. This effort is producing very valuable results.
II. Assessment of NDE Applicable to COPVS NDE techniques were reviewed to identify those applicable to the COPVs of concern. Traditional and mature
techniques had been used successfully to find isolated or discrete mechanical damage (e.g., impact damage) in COPVs;1 however, methods that may help characterize global degradation or damage resulting in creep and/or SR were not as well documented. An in-depth research program would be necessary to determine the COPV material properties undergoing degradation leading to SR. A technology assessment of NDE for SR degradation in COPVs was accomplished and published in November 2004 by a COPV NDE SPRT subcontractor, the Department of Defense (DOD) Nondestructive Testing Information Analysis Center (NTIAC); and it represents a good compilation of technology that is applicable and leads to further work in this area.2 The SPRT recognized that a comprehensive research and development program was needed to further identify potential NDE methods and evaluate their potential to monitor SR in COPVs.
III. Methods for Characterizing Global Damage As of this study, no NDE technique is currently known to be directly applicable to prediction of SR and other
life-dependent COPV issues. For life issues, we still need to better identify the only partially defined physical attributes or phenomena producing failure to allow appropriate NDE techniques to be down-selected from the list of potential candidate methods. These down-selected methods will then need to be further developed and applied.
Since essentially all current and future NASA spacecraft utilize COPVs subject to SR, this creates a major concern that needs to be addressed. In response to this, the NDE SPRT identified and ranked possible candidate NDE methods that may potentially be used to assess the COPV material properties that are undergoing degradation leading to SR, and information was collected to delineate future research needs. In addition, the NTIAC technology assessment of NDE for SR degradation in COPVs represents a useful compilation of current technology that may be applicable in the future, but requires further work as described in the formal report. A study is currently being undertaken by the NASA NDE Working Group (NNWG) to help understand the degradation process leading to SR, so as to target and develop NDE that may be useful in detection. It is noted that the NNWG SR NDE research effort does not have adequate funding to fully resolve this issue, and other synergistic funding and complementary efforts are being sought to fill this important need for future NASA space programs.
IV. Methods for Locating Isolated Damage Although detection of delaminations in COPVs has been successfully accomplished by various methods,
detection of small fibers that have previously broken, independently of matrix damage, is far more difficult, and success is limited. Discontinuities in the extremely small fibers (typically only a few micrometers) are very difficult
* Kevlar® is a registered trademark of E. I. Du Pont de Nemours and Co., Wilmington, DE.
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to detect with direct imaging techniques. New developments such as high resolution x-ray computed tomography (XCT) hold some promise for laboratory-level analysis. Additionally, the acoustic emissions method allows detection of the origin and monitoring of active defect growth in COPVs under load. Generally, significant acoustic emissions only occur when new peak pressures are reached, and the vessels are generally acoustically silent at pressure variations below the last peak pressure. However, even with this limitation, it is effective in identifying new impact damage or areas where fiber has been strained to the point of damage or breakage. Also as discuss later in this paper, Shearography has also been found effective in identifying delaminations, impact damage, and localized variations in stress fields in COPVs.
One if the largest issues was also noted to be the general lack of a correlation between the specific NDE response and specific loss in structural integrity of the vessel. This is another area the NNWG has started looking at. An initial project to establish a correlation between calibrated inpacts, NDE response, and specific reduction in burst strength of certain carbon bottles is in progress.
V. Brief NNWG “Stress Rupture” NDE Project Overview The NNWG Stress Rupture NDE started in late 2005 and is currently continuing. The objective of the NNWG
project is to advance the state-of-the-art by developing NDE techniques that are capable of assessing SR degradation in COPVs in either a health-monitoring mode or a traditional remove-and-inspect mode. NDE techniques resulting from this effort will be a challenge to field and it will likely take several years.
The general approach is to determine the feasibility of a selected number of candidate NDE techniques for detecting degradation leading to SR in COPVs in either a health-monitoring mode or a traditional remove-and-inspect mode. This is done by submitting specimens of various SR age to many different type of NDE and evaluating for response that can be correlated. In parallel, destructive analysis (DA) is used to better understand SR failure signatures so as to better target NDE techniques.
The study is using Kevlar as the model COPV SR system for initial study, due to the substantial knowledge base in literature and numerous test specimens. An extensive number of Kevlar test articles with varying amount of actual age and time at stress are available for NDE evaluations. Additional, accelerated aging is being accomplished and the NDE response compared to the old Kevlar specimens. After knowledge is gained from the Kevlar study, it will be applied to COPVs made from carbon new and emerging fibers.
Kevlar composite specimens were developed by overwrapping aluminum-lined cylinders and aged to simulated long term stress rupture degradation. The accelerated aging efforts were accomplished using two different approaches: 1) by elevated stress levels, and 2) separately by stepped increases in temperature ASTM D 69923 to provide sets of test specimens (cylinders and coupons made from cylinders) for evaluation by NDE and destructive analysis. These methods provide test specimens with creep degradation without the complexities that result from oxidation, moisture, and ultraviolet light. During the aging, In addition to temperature and pressure transducers, Fiber Bragg grating (FBG) strain sensors and Acoustic Emission (AE) sensors were use in an effort to correlate their respective response to the stress rupture age progression and help develop data for later health monitoring applications. The FBG were predominantly surface-bonded, although a few were embedded to compare surface strain near the liner. Due to their extensive experience with ASTM D 6992, the Texas Research Institute accomplished the aging of the specimens in consultation with researchers at Cornell University, and NASA is accomplishing most of the NDE.
Aging has gone as anticipated and interesting relationships are being observed in the data FBG, AE, and temperature data. This data will be assemble and reported following data analysis. Each of the cylinder specimen sets will now be evaluated by each NDE technique and also by destructive assay. The most likely candidates for health monitoring are thought to be acoustic emission, eddy current sensors to evaluate composite and liner thinning through changes in stand-off, Bragg gratings, and other conventional strain sensing techniques. Following this, all NDE and DA results are to be analyzed and the most promising NDE methods selected. Various fleet leader specimens (virgin, aged, and failed) will then be evaluated with down-selected NDE and DA to determine capability of NDE and DA methods on complex specimens with “real” age.
VI. NDE for WSTF Experimental Carbon Bottle Burst Testing The NDE SPRT supported the commercially available† Carbon COPV Bottle Burst Testing at WSTF in 2004
and the project provided an excellent example of successful applications of pretest NDE and optical FBGs. The objectives were to screen for detectable impact damage or manufacturing defects, assess any notable tank-to-tank
† Manufactured by Luxfer® Inc., Riverside, CA.
manufacturing variance, and assess the potential use of multiple FBG strain sensors for COPV ground test monitoring and/or flight COPV health monitoring purposes. Pretest NDE included ultrasonic testing (UT), eddy current testing (ET), flash thermography, and shearography. Following pretest NDE, 18 FBG sensors were bonded to the COPVs and monitored during the testing.
A. Pretest NDE NDE SPRT members at the Aerospace Corporation (El Segundo, California) accomplished the UT and ET. For
UT, the COPVs were filled with water and immersed. The cylindrical region of each COPV was subjected to pulse-echo testing at 25-MHz using a commercial system. Reflected radio frequency wave trains were digitized and stored for each point on a 0.05-in. axial by 2-degree circumferential grid. These data were analyzed in a number of ways to reveal potential delaminations between the overwrap layers, unbonds between the overwrap and liner, and potential wind anomalies.
For ET, a commercial 2.5-MHz anisotropic probe was held in dry contact with the cylindrical surface of the COPV. Data were accumulated on a 0.05-in. axial by 2-degree circumferential grid. Scans were then performed for two orientations of the probe: with the induced current 1) perpendicular and 2) parallel to the hoop fiber direction. The results reflected variations in the overwrap (fiber conductivity, fiber density, wind anomalies, etc.).
For example, there was one prominent indication (in bottle No. 1894) evident in both the UT and ET results. The material was at least one ply thinner on one side of the indication and at least one ply thicker on the other side; therefore, it appeared that a ply had slipped. There was nothing to indicate that a ply was twisted (no local high spot). This was not thought to have a significant effect on the burst data, and proved not to since it had the second-highest burst pressure of the lot.
Flash thermography was performed at NASA Marshall Space Flight Center (MSFC) using a thermal wave imaging data acquisition system running EchoTherm®‡ software and an Indigo Merlin§ infrared camera. The bottles were prepared for the thermographic test by painting with water-soluble flat black paint and applying temporary 0.125-in. square lead tape markers placed on 60-degree centers. The thermographic evaluation was relatively quick, taking approximately 1 h per bottle, including setup. Thermography provided a screening for handling damage (delaminations) and process variations (such as porosity or misplaced fibers/tows) that may be present in the vessels. Enhanced thermography images were made by subtracting the pre-trigger image from the images acquired after flash heating. Many small regions of porosity, voids, or low consolidation were noted. These regions show up as small white “hot” patches in the thermograms. The regions were noted to be scattered and numerous, but not thought to be significant enough to affect the structural integrity of the vessels.
Shearography was also performed at MSFC using a Laser Technology, Inc. (LTI) (Norristown, Pennsylvania) SC-5100 system (Figure 1). The bottles were prepared for testing by coating them with water-washable penetrant developer. The bottles were pressurized to less than 5 psig during the shearography test. This evaluation was nearly as quick as the thermography, with surface preparation for each vessel taking less than 0.5 h each and the actual test taking no more than 1 h for each vessel. Shearography provided a measure of the expected strain field generated during pressurization, but at a very low proof level. Variations in the strain field will show in the out-of-plane surface deformation that shearography measures. The test locates regions of the vessel that have lower stiffness properties as a result of handling damage, manufacturing/process variations, or aging. No indications were noted in raw data or wrapped or unwrapped phase maps. The NDE testing helped ensure that the data collected during burst testing were not biased by poor bottle quality.
B. Fiber Bragg Grating Strain Sensors The NDE SPRT used FBG sensors to monitor the stress strain relation in the carbon fiber/matrix during the
testing at WSTF with consultation from MSFC staff. Twelve FBG sensors were laid out and attached to the bottle surface as described below.
VII. Sensor Layout and Installation Figure 2 shows the layout orientation of the sensor strings on the bottle. Four sensor strings (three sensors in
each string, two strings to a channel) were adhered to the bottle surface with the fiber along the bottle axis, and two sensor strings were aligned with the fiber along the hoop direction.
‡ EchoTherm® is a registered trademark of Thermal Wave Imaging, Inc., Ferndale, MI. § Merlin® is a registered trademark of Indigo Systems Corporation, Santa Barbara, CA.
When looking down at the bottle from the pressure port, the origin is designated to be at the transition from curved surface to the bottle flat directly below the first digit of the serial number on the bottle pressure port (see Figure 2), the axial sensors are centered in the flat along the y direction (along the bottle axis) with 2.5 in. between sensors, and are placed every 90 degrees in the φ (hoop) direction. The hoop sensors were placed as close as possible to six of the axial sensors.
VIII. Sensor Interrogator Setup The sensor interrogation unit consisted of a tunable laser module, beam coupling optics, wavelength reference,
light detectors, and a personal computer with a high-speed data acquisition card. An optical diagram of the interrogation unit is shown in Figure 3. Light emitted from the tunable laser was split equally into four paths: three sensor channels and one reference channel. In each sensor channel the light was split equally into each of two sensor strings. The sensor reflections passed back through the 2 x 2 coupler to the detector. In the reference channel, light passed through a gas reference cell in which it was absorbed at a series of well-known wavelengths. As the laser swept through its wavelength range, the channel waveforms were collected by an external computer using a high-speed analog-to-digital (A/D) data acquisition card that monitored the voltages output by the detector amplifier modules. Each channel supported six sensor wavelengths, three each on two strings. A spare A/D channel was used to collect the pressure transducer voltage so that the FBG sensor strain values could be directly plotted with bottle pressure.
IX. Experimental Procedure and Results For each of the ten commercial Carbon bottles that were tested, the pressure was ramped up at 50 psi/s to
roughly 2000 psi, held constant for roughly 3 min, allowed to drop to 0 psi and held for another 3 min. Then the pressure was ramped at 50 psi/s to 2000 psi and held for one min, then ramped up at the same rate until the bottle burst. The baseline strain readings were taken at time = 0 s.
After the bottles were burst and removed from the test chamber, the burst locations were recorded. The burst locations for each bottle are depicted in Figure 4 and listed in Table 1. All of the burst locations were within 1 in. of the center of the bottle in the axial direction, and were well distributed in the hoop direction.
Figure 1. Shearography setup.
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Figure 2. FBG sensor layout.
Tunable Laser Sensor Strings
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Figure 3. Sensor interrogation unit.
The graphs in Figures 5 through 9 depict the data corresponding to the 50-percent pressure cycle and burst
cycle. The plots display the ramp up to 2000 psi, the 3-min hold, the ramp back down to 0 psi, and the following 3-min hold. The plots are of the sensor strains as a function of time. These plots are useful when looking for creep during the 50-percent load cycle: creep is indicated if the sensor strains do not return to their starting position. An example of this effect is depicted in Figures 5 and 6: the strain curves during the 50-percent load cycle for the hoop sensors for a previously cycled bottle, No. 2179, and a pristine bottle, No. 2139. The hoop strains all return to within 15 microstrains of their starting strain for the previously exercised bottle, but remain as much as 600 microstrains above their starting strain for the pristine bottle, indicating residual fiber stress.
For an elastic material, assuming that the bottle stress is proportional to bottle pressure, the strain-versus-pressure plots should be linear, and should not show any appreciable gap between the rising and falling pressure curves. Most of the well-conditioned bottles exhibit elastic behavior during the 50-percent pressure cycle, as shown in Figure 7. However, a similar plot for a pristine bottle exhibits a far larger degree of hysteresis (Figure 8), indicative of material stretching in the hoop direction during the load cycle. There is also a difference in onset of non-elastic behavior during the burst testing between the pristine and well-conditioned bottles. Although the burst pressures for bottle Nos. 2179 and 2139 were different by only 220 psi (4430 psi versus 4210 psi, respectively),
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Figure 4. Bottle burst location depicted on the same plot as sensor location.
Table 1. Hoop and Axial Coordinates of the Burst Locationa
Bottle Number φ
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2189 45 4.75 2052 210 4.25 2099 20 3.75 2139 10 4.00 1903 350 4.50 2175 100 4.75 2179 120 3.75 2069 40 4.00 2176 285 4.00 1894 240 4.25
a Bottle numbers are listed in the order they were burst
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Figure 5. Strain as a function of time during the 50-percent load cycle for the channel 3 sensors (all in the hoop direction) for bottle No. 2179.
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Figure 6. Strain as a function of time during the 50-percent load cycle for the channel 3 sensors (all in the hoop direction) for bottle No. 2139.
Figure 9 shows that a large increase in slope of the strain curve occurs at approximately 3700 psi for the well-conditioned bottle (left), but close to 2300 psi for the pristine bottle (right). This increase in slope is likely a first indication of fiber and liner realignment of load sharing characteristics. This occurs at different pressures depending on the previous stress state of the bottle. Figure 9 also shows the first attempt to model the bottles and compare it with the actual measurement. This was done using ANSYS®** failure analysis software, without taking plastic behavior of the aluminum liner into account; hence it did not predict the liner’s behavior at the point of rapid strain transfer to the fiber.
A second model, constructed using the GENOA Progressive Failure Analysis (PFA)†† software, applied nonlinear elastic/plastic behavior for the liner material and micromechanics modeling of the fiber/matrix composite layers based on the manufacturing wind patterns. This particular model was only performed using data for a pristine vessel. The GENOA model indicates the onset of plastic behavior and the subsequent shift of stress to the composite layers. A plot of the stress at the surface in the hoop direction near the equator of the vessel is shown in Figure 10. The lower curve represents the stress in the composite, while the upper curve is the computed stress in the fibers themselves. The plot supports the assessment of the knee occurring near the same point as measured by the Bragg sensor.
X. General FBG Experimental Conclusions Since the testing was performed on the ten articles, interesting trends and repeatable measurements were made
showing in the strain fields during initial pressurization to 2000 psi and then from ambient to burst pressurization up to burst. Clear differences were seen in the behavior of virgin versus previously pressurized vessels that could be correlated with a structural analysis of the tanks. Additionally, the FBG results were instrumental in determining the true stress ratio. This resulted in substantial upward revisions to the actual stress ratios that were present in the
** ANSYS® is a registered trademark of Swanson Analysis Systems, Inc., Houston, PA. †† GENOA-PFA is licensed by Alpha STAR Corp., Long Beach, CA.
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Figure 8. Strain as a function of pressure during the 50-percent load cycle for the channel 3 sensors (all in the hoop direction) for bottle No. 2139.
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Figure 7. Strain as a function of pressure during the 50-percent load cycle for the channel 3 sensors (all in the hoop direction) for bottle No. 2179.
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Figure 9. Strain as a function of pressure during the burst cycle for the channel 3 sensors (all in the hoop direction) with predictions made with ANSYS software.
WSTF SR testing. One of the vessels was first thought to have ruptured at a problematic 52-percent stress ratio
and the FBG system provided the data necessary to correct the stress ratio to 58 percent. Many of the FBGs also indicated valuable information on fiber load redistribution and matrix micro cracking. This, like acoustic emissions data, helps give the location of active areas of load redistribution and needs more study to better utilize the capability. The method also shows promise for longer-term monitoring of other bottles during testing at WSTF and for potential flight application.
XI. NDE Supporting Current WSTF Kevlar COPV Testing A test program is in progress at WSTF with the objective of providing data that can be used to better predict the
reliability of certain Kevlar COPVs types that have been in use for many years, and hopefully extend their useful life. Volumetric/strain testing and associated laboratory analysis are being accomplished to understand composite/liner interaction, the “through-wall” stress gradient, and evaluate other strain and volume changes as the as COPVs are pressure cycled and then finally burst. Age and environmental related material degradation are also being evaluated. Stress rupture testing may also be accomplished to evaluate the life prediction model. To effectively accomplish this testing, both pretest NDE to verify the structural integrity of the test articles and real-time NDE are being used during testing to develop critical data.
Table 2 indicates the typical NDE and test instrumentation being applied, with a brief indication of what is being measured. Pretest NDE and other NDE used to gather test data are discussed in more detail in the following sections (such as eddy current used to determine composite thickness change with pressurization).
A. Overview of COPV FBG Strain Measurement The basic FBG system and sensor interrogation unit is the same as discussed previously under NDE for the
earlier WSTF Experimental Carbon Bottle Burst Testing; however, additional strain sensors are utilized. The FBG sensor attachment area on the Kevlar COPV was cleaned and the surface conditioned. The sensor strings were routed to the dome section of the bottle, where they were taped in place and terminated to the fiber optic connector block using double-sided adhesive foam tape. The sensors were all placed on the bottom hemisphere, under the rationale that the bottle was symmetrical about the equator, the sensors would be more out of the way on the bottom side, and the fiber cables could be more easily mounted to a connector block near the bottom pressure port for patching and routing.
Most of the sensors were aligned in the direction of the tow that makes up the wrap, since this should be the direction of the critical strain that would determine when the wrap will fail; but a few sensors were also oriented perpendicular to the tow orientation. The FBG were routed to avoid the location of several acoustic emission sensors, and none of the fibers were allowed to pass over the bottle equator, since two “belly band” wire
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Figure 10. Strain plots using the Genoa software to predict structural failure.
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Table 2. Typical WSTF COPV Test NDE and Instrumentation.
Method Measurement
Visual inspection (pretest) External inspection of overwrap. Indication of gross damage
Flash thermography (pretest) Heat signature decay. Sub-surface ply delamination
Borescope inspection (pretest) Internal inspection of liner. Indication of damage or buckling
IR heat soak thermography (pretest) Heat signature decay. Sub-surface ply delamination
Shearography (pretest) Differential strain resulting from anything that would cause it (e.g., impacts, delaminations, broken fiber)
Fiduciary marking (pre/posttest) Measurement of distance between marks
Pressure, temperature (test) Time, pressure, and temperature
Cabled girth linear variable displacement transducer (LVDT) (test)
Circumferential displacement measured at 0, 45, and 80 degrees
Boss LVDT (test) Axial displacement
Conventional Strain gauge (test) Change in length. Fiber strain
Fiber Bragg grating (test) Change in length. High resolution
Acoustic emission (test) Acoustic noise. Fiber breakage or delamination
Volume displacement (load cell and supply weight)
Vessel test fluid mass. Strain and fiber creep (weighed from supply and expulsion volumes)
Full field digital image correlation Vessel strain
Eddy current probes Composite thickness change
Raman Spectroscopy – portable Residual stress and stress changes while pressurizing
displacement sensors were installed there to measure the bottle diameter as a function of pressure. After the FBG sensors were installed, foil strain gauges were installed adjacent to them to allow comparison of data. It was found that the method of attachment was much more critical for application of surface mount FBG and in general the data
as not as accurate or repeatable as the conventional strain gauges.
. Eddy Current Composite Thickness Measurement During pressurization, a thinning of the Kevlar composite of the COPVs was predicted. Eddy current techniques
rovide a means to measure this change in composite thickness, and have been implemented for the pressurization nd burst tests at WSTF. Additionally, it was determined that liner thickness variations could also be evaluated by sing both the horizontal and vertical component of the signal. NASA Langley Research Center (LaRC), in onjunction with WSTF, has instrumented a COPV eddy current composite thickness gauging measurement system. brief description of the inspection system and anticipated results are discussed in the following paragraphs.
Eddy current techniques are primarily designed to operate based upon the electromagnetic induction of current nto a conducting object due to the applied alternating magnetic field of a test coil. The induced current acts to ppose changes in the applied field, and results in a change in impedance of the test coil. Eddy current instruments re designed to measure these changes in the test coil impedance, which are then correlated with physical properties uch as the conductivity of the material under test and lift-off distance (test coil to conductor spacing). For COPV omposite thickness inspections, eddy current lift-off measurements can be performed to measure the probe-to-liner pacing. With the probe bonded to the Kevlar surface, this effectively measures the thickness of the Kevlar omposite.
Figure 11 displays the system supporting the WSTF COPV studies. A commercial Zetec MIZ-27®‡‡ SI eddy urrent instrument is used to simultaneously drive four custom-wound eddy current coils on the Kevlar COPV and
‡‡ MIZ® is a registered trademark of Zetec, Inc., Issaquah, WA.
eight on the larger gaseous helium tanks. The coils, shown in the right-hand side of Figure 11, are each enclosed in a housing 1-in. in diameter and 0.75-in. tall. Each coil has been placed on an insulating surface (Delrin®§§ sheet) over a stainless steel conductor. In this laboratory environment, the simple geometry mimics the Kevlar composite over a COPV with a metal. A laptop computer is used to acquire and archive the data in real-time during testing. In the figure, the normalized impedance of the four coils is displayed in the four dots in the center of the MIZ-27 screen. The signals have been nulled, or balanced, at the respective composite thicknesses seen by each probe and rotated such that a change in lift-off results in a vertical deflection of the eddy current signal. The probe response is digitized and stored on the laptop computer, while the vertical components of the signals are displayed in a strip chart on the computer screen. A separate analog input channel is reserved to acquire timing information from the pressurization tests.
In order to determine the voltage change caused by a given change in composite thickness, calibration of the probes and equipment is needed. This is performed using nonconductive shim material to measure the change in probe output for a known thickness change. The calibration range should encompass the range-of-thickness change anticipated during the test. In Figure 12, the computer display for the removal of a 0.001-in. plastic shim over the 0.25-in. insulator block is shown. For these tests, a 15-kHz drive signal was supplied to the test coils. A unit drop in the voltage measured when the shim was removed was clearly well above the background variation of the system. The sensitivity of the measurement is dependent upon the nominal composite thickness and is typically inversely proportional to probe-to-conductor spacing. Table 3 shows the voltage change corresponding to a 0.001-in. change in composite thickness at nominal composite thickness values of 0.25, 0.375, 0.5, and 0.75 in.
0mttn
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Figure 12. Screenshot of data in Plot 2 shows voltage change associated with change in thickness from 0.251 to 0.250 in. as a 1-mil shim is removed from probe 2 at T ~ 100. All other channels remained at nominal coating thicknesses.
Figure 11. Eddy current inspection system for COPV composite thickness measurement
Table 3. Eddy Current System Response for Various Nominal Lift-Off Values. Nominal Composite
Thickness 0.25 in. 0.375 in. 0.5 in. 0.625 in. 0.75 in.
∆V/mil 0.35 V/mil 0.18 V/mil 0.12 V/mil 0.065 V/mil .04 V/mil
The noise floor of the system has been measured at about 0.02 V, providing an absolute sensitivity of near
.5 mil for the 0.75-in. composite thickness, and greater sensitivities at smaller composite thicknesses. In reality, the easurable composite thickness change is likely to be limited by external system noise and instrumentation drift. In
he open laboratory, sensor outputs were seen to drift by approximately 0.1 V over a 1-h time period, due in part to emperature variations. An equivalent value for sensors bonded onto a COPV configured for pressurization testing is ot currently available.
After laboratory validation at the NASA-Langley Research Center, the eddy current system was shipped to STF for installation on a COPV vessel. Figure 13 shows an example COPV with the eddy current sensors
ttached. One of the sensors is clearly visible just above the equatorial belly band.
§§ Delrin® is a registered trademark of E. I. Dupont de Nemours, Wilmington, DE.
F
cycleand 1compaccomcurrecurrehas in
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Figure 13. Eddy current sensors installed on COPV.
ollowing laboratory calibration, COPVs were installed on at the pressurization facility. Various pressurization s were applied while the composite overwrap thickness was measured with the eddy current sensors. Figures 14 5 display resulting composite and liner thickness change in a sample final ramp to burst. A decrease in the osite and liner thickness is measured on all channels as the pressure increases. An x-ray correlation was plished on the first vessel to help validate the eddy current thickness measurements and found the eddy
nt measurements to be accurate to the resolution of the x-ray technique. Although data from up to eight eddy nt sensors per COPV was sometimes a bit time consuming to reduce and analyze, it has been instrumental and dicated how the composite and liner strain together through yield and all the way to burst.
igital Image Correlation igital image correlation (DIC) was accomplished using ARAMIS software. This technology uses the
iples of 3D image correlation photogrammetry that gives full-field displacement and strain measurements. The principles of 3D image correlation photogrammetry have been known for about 15 years.4 The particular 3D e correlation system being utilized, ARAMIS, has been commercially available for about 10 years. he system requires spraying random high-contrast dot patterns onto a sample; this pattern is then tracked in
MIS by thousands of unique correlation areas known as facets. The center of each facet is a measurement point an be thought of as a 3D extensometer. Arrays of them form in-plane strain rosettes. The facet centers are ed in each successive pair of images, with accuracy up to one-hundredth of a pixel.5
For the typical WSTF COPV installation (Figure 16)a resolution of 512 x 512 pixels, giving a recording speedspeeds were used for some tests due to the negative heatinsurface mounted instrumentation. The Phantom cameras aARAMIS software can take measurements. The volume vcamera setup consisted of 35-mm lenses with the camerasvolume of 1060 mm/875 mm/875 mm. To calibrate for thpixels, and a 1200 mm NIST-traceable calibration cross wsensor. After successful computation, the calibration devithan the 15 degrees required for a successful calibration. Ttime for synchronization, which provided accuracy withinthe vessel consisted of a white background with 0.25-in. bFigure 16. The system was particularly useful in indicatinthe COPV pressurization range as indicated in Figure 17 aalso provided excellent strain data in areas where conventto these, as indicated in Figure 18, except where cables or
*** Phantom® is a registered trademark of Vision Research
Figure 16. Digital image correlation camera view o
Figure 15. Example Liner thickness reduction with pressure.
Figure 14. Example Composite thickness reduction with pressure.
, digital high-speed Phantom®*** v7.0 cameras were used at ranging from 100 to 3000 frames per second (fps). Lower g affect that supplemental lighting had on other COPV ct as a stereo pair to create a volume of area in which the aries with the calibration method and field of view. This at a typical angle of 15.7 degrees, giving a measuring is volume, the camera resolution was set at 800 x 1200 as rotated and moved in specified locations to calibrate the
ation was below 0.04 and the angle variance was larger he cameras used inter-range instrumentation group (IRIG) 1 microsecond between images. The pattern sprayed on lack dots sprayed on the surface viewed, as noted in g overall principal strain fields that developed higher in nd indicating surface fiber failure near burst. The system ional strain gauges were not installed and correlated well other instrumentation interfered.
, Inc., Wayne, NJ.
f COPV (Black dots sprayed over area of interest).
Figure 17. Digital image correlation Full Field Principal Strain .
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
Pressure (psi)
Stra
in (m
s)
h SG-13 0°h SG-37 120°h SG-24 240°DIC ARAMIS
Figure 18. Digital image data correlation to conventional strain gauges
S
train
(ms)
D. 40-in. COPV Pretest NDE Shearography To help verify the integrity of a large 40-in. COPV prior to test, shearography was utilized as shown in
Figure 19. This testing was accomplished under the guidance of John Newman††† and with equipment supplied by NASA Kennedy Space Center. This approach, in combination with heat soak thermography, was deemed to give an excellent pretest health check of the 40-in. COPV. A general discussion of the system follows. Subsequent testing of 24 additional spherical Kevlar and spherical and cylindrical carbon COPVs was then accomplished in September 2006 and provide excellent results.
The shearography camera uses a Michelson-type interferometer with two essential modifications. First, one mirror is precisely tilted to induce an offset, or sheared image, of the test part with respect to a second image of the part. Second, the sheared amount is a vector with an angle and a displacement amount. The shear vector, among other factors, determines the sensitivity of the interferometer to surface displacement derivatives.
The two laser speckle images of the test part, offset by the shear vector, interfere at every paired point over the surface in the field of view. The single frequency laser light from the two sheared images of the part is focused onto the camera array of photosensitive pixels. Light from pairs of points in each sheared image interfere. Each video frame, comprised of the complex addition of these two sheared images, can be subtracted from a stored reference image. The absolute difference yields a fringe pattern observed on the monitor. The second mirror in the Michelson interferometer may be phase-stepped using a piezoelectric device and the images combined to create a phase map (Figure 20). Further processing using any number of unwrapping algorithms may be used to generate fringe-free images of local surface deformation derivates.
In practice, each step in creating a shearogram is performed automatically using image-processing macros constructed by combining each processing function in a sequence. Shearography system operators perform a test with a single keystroke.
††† John Newman is the president and founder of
background information on shearography. He hNDT methods since 1970. Mr. Newman foundeshearography system in the mid 1980s. Mr. Newcurrent Chairman.
LTI/NASA Kennedy Figure 19. LTI SC-5100 system bein
Pressure Supply Panel COPV Support and Rotation Bearing
Laser Technology, Inc. in Norristown, PA, and author of the as worked in the field of holography, shearography, and laser d LTI in 1977 and led the development of the first electronic man initiated the ASNT Laser Methods Committee and is the
Space Center Shearography Test Team Photo
g applied to Kevlar COPV.
COPV Pressure Gauge G1 LTI-5100 ShearographyCamera
E. Quantitative Shearography Measurements Precision calibration of the shearogram image scale (pixels/in.) and the shear vector allows further processing of
shearography data to determine defect indication dimensions, area, and the deformation of the material. The digital measurement of the deformation derivative may be integrated to show the shape of the target surface deformation as well as the magnitude of the deformation at any location, as in Figure 20. Shearography can be used to measure the deformation response of a structure to an applied load and as a means for deriving material properties.
An example of composite shearography images of a Kevlar test tank is shown in Figure 21. The pressure was cycled between 70 and 90 psi to create a delta strain for each image. The sensitivity is noted by very slight strain indicated in the overwrap pattern and from tank features such as the girth weld area. Minor delaminations are also indicated in the upper right where wrap patterns cross. However, no impact damage was noted as seen on the impact standard image shown on the lower right. Shearography of a carbon test COPV is also shown in Figure 22. In this figure, damage from calibrated impacts are clearly imaged and the sensitivity of the system is indicated by the less substantial and unexpected un-programmed damage noted on the lower left.
Figure 20. A phase map shearogram with horizontal shear vector yields a fringe pattern showing the first derivative of the out-of-plane deformation, ∂w/ ∂x. Using an unwrapping agorithm, the image at right shows the positive (white) and negative (black) slope change. The metal plate with a 4.0-inch diameter flat-bottomed hole was deformed by 7.0 µm.
Strain Concentration at the equator over liner circumferential girth weld.
Quilted deformation pattern due to tape placement and thinner composite between wraps.
Minor tape delamination Near end boss.
Impact damage on a COPV at WSTF. Damaged areas are 1.3 in. diam. compared to the 0 .25 in. visual dent on the surface.
COPV Test Standard
Figure 21. Example Shearography image of Kevlar COPV as compared to a damage standard.
F. Thermography Experimental Setup NASA LaRC developed the WSTF IR thermography system that was used for single-sided data acquisition on
the 40-in. Kevlar COPV, shown in Figure 23. The IR imager is a commercial radiometer with a cooled 256 H x 320 V-element InSb (indium - antimonide) focal plane array detector. The radiometer’s noise equivalent temperature difference (NE∆T), cited by the manufacturer, is 0.025 °C when operating the detector in the 3 to 5 µm wavelength range. The radiometer produces images at both 30 fps output (video frame rate, in an RS170 format compatible with standard video equipment) and 60 fps output in a 12-bit, RS422 digital format. External optics, consisting of a wide-angle lens using germanium optical elements, were used to increase the system field-of-view by a factor of approximately two. The expanded field-of-view of this lens is 41 degrees horizontally and 31 degrees vertically.
Heating of the inspection surface is produced by focusing two 500-W quartz lamps on the inspection area, using parabolic reflectors. The heating time for the COPV was 90 s, and temperature data were acquired during the cool-down for 10 min (a reduced frame rate of 5 fps was achieved by sub-sampling). Because of the large thermal mass of these specimens, the surface temperature rise during heating was less than 10 °C. Although the surface of the specimen was somewhat reflective, it was not necessary to apply any emissivity enhancing coating since data were only acquired during the cool-down.
XII. Experimental Results Only one minor indication, possibly a small near-surface ply disband or resin lean area, was noted real-time
during data collection (Figure 24). However, additional heat soak thermography and ultrasound were done of the area and it was deemed not to be a concern.
Un-programmed Damage Figure 22. Shearography Inspection of Impact Damaged Carbon COPV
XIII. Acoustic Emissions Overview Technical support for the AE test support was provided by the NASA Langley Research center. AE sensors
were installed typically in 5 locations on smaller COPVs and 12 positions on larger COPVs. Three were installed on the upper boss, three others on the lower boss and six were installed around the equator. Using this configuration, sensors were used to triangulate the source locations for the acoustic activity. Sample data is shown super imposed on the 2D symbolic view of a spherical COPV shown in Figure 25. Lighter indications depict activity locations on the lower side. An example of the total number of acoustic events plotted during a pressurization and hold is indicated in Figure 26. In this case it is significant to note that acoustic activity continued during the pressure hold from 1500 to 2000 seconds. At lower pressure holds, this acoustic activity did not continue. This may be indicating that damage is profligating and the overwrap may be slowly failing. As more data is added to the COPV AE database, this type of data may be very valuable for COPV in situ health monitoring. During the WSTF COPV testing, a timeline of all COPV failure events was assembled and AE data was reviewed in detail and was extremely useful for correlation to DIC and other measurement techniques to substantiate and map locations of fiber breakage and fully characterize COPV performance.
Figure 23. Heat soak thermography application to Kevlar COPV.
Indication
Reflection
Figure 24. Example Kevlar COPV heat soak thermography images.
Figure 25. Example Unfiltered AE COPV Data - All Events
Events Count vs. Time and Pressure vs. Time
0
1000
2000
3000
4000
5000
6000
7000
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Time (s)
No.
of E
vent
s
EventsPressure
7000
6000
5000
4000
3000
2000
1000
0
Pres
sure
(PSI
)
MEOPTest
Figure 26. Example AE Events vs. Time during a pressurization and hold
Pres
sure
(psi
)
XIV. Conclusions The NASA COPV assessments started by the NESC in 2004 led to the evaluation of NDE applicable to COPVs
and the follow-on work is still in progress. Reasonably mature NDE methods were identified for application to detect impact and other localized damage. However, NDE response has not been quantitatively related to a specific reduction of structural integrity. Additionally, no NDE methods were found available for evaluation of global material property changes that could be related to progression toward stress rupture or that could aid in life predictions. Therefore, detailed recommendations for a stress rupture NDE program were provided by the NESC NDE SPRT, but the new NDE will likely take years to field. The NNWG is currently proceeding with the recommendations to the extent that funding is available, but more work needs to be done in this area.
The applications of several NDE methods to pretest screening of Kevlar and other carbon COPVs undergoing testing at WSTF have demonstrated their effectiveness. Additionally, NDE techniques applied real-time during COPV testing is providing excellent test data and helping to provide critical rationale to continue flying aging vessels. Due to the magnitude of these efforts, these applications are provided as an overview only and the paper serve as a pathfinder for other who may want to collaborate on COPV NDE.
XV. References 1. Johnson, E. C. and J. P. Nokes. “NDE Techniques Assessment for Gr/EP Composite Overwrapped Pressure
Vessels.” Proceedings of the Ninth International Symposium on Nondestructive Characterization of Materials, Sydney, Australia, June 28-July 2, 1999.
2. Nondestructive Evaluation for Stress-rupture Degradation in Composite Overwrapped Pressure Vessels. Prepared by the Nondestructive Testing Information Analysis Center, a DOD Information Analysis Center. Sponsored by the Defense Technical Information Center (DTIC). Prepared for the NASA Engineering and Safety Center, Contract SPO700-97-D-4003, Delivery Order No. 0033, TAT No. NT-04-0005/0038, November 2004.
3. ASTM 6992, Standard Test Method for Accelerated Tensile Creep and Creep-Rupture Of Geosynthetic Materials Based on Time-Temperature Superposition Using the Stepped Isothermal Method, American Society for Testing of Materials, West Conshohocken, PA, 2003. Method applied by J. S. Thornton, Texas Research Institute, TRI/Austin, Inc., 9063 Bee Caves Road, Austin, Texas 78733, U.S.A.
4. Kahn-Jetter, Z. L. and T. C. Chu. “Three-dimensional Displacement Measurements Using Digital Image Correlation and Photogrammetric Analysis,” Experimental Mechanics, Vol. 30:1, pp. 10-16, March 1990.
6. Schmidt, T., J. Tyson, D. M. Revilock, Jr., and M. Melis. “Full-field dynamic deformation and strain measurements using high-speed cameras.” SPIE 26th ICHSPP, September 2004.
48th
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raph
y, u
ltras
ound
, sh
earo
grap
hy, a
nd a
cous
tic e
mis
sion
s (c
oin
tapp
ing)
.–
Det
ectio
n of
fibe
rs th
at h
ave
prev
ious
ly b
roke
n in
depe
nden
t of m
atrix
da
mag
e is
diff
icul
t, an
d su
cces
s is
lim
ited
in th
is a
rea.
•E
xtre
mel
y sm
all f
iber
s (ty
pica
lly o
nly
a fe
w m
icro
met
ers)
are
ver
y di
fficu
lt to
eva
luat
e w
ith d
irect
imag
ing
tech
niqu
es.
•S
ome
rece
nt im
prov
emen
ts in
ND
E m
etho
ds p
erm
it en
hanc
ed
dete
ctio
n an
d ch
arac
teriz
atio
n of
del
amin
atio
n, fi
ber b
reak
age,
an
d m
atrix
cra
ckin
g no
t det
ecta
ble
in e
arlie
r CO
PV
ND
E s
urve
ys.
•H
igh-
reso
lutio
n X
-ray
Com
pute
d To
mog
raph
y (X
CT)
als
o ho
lds
som
e de
gree
of p
rom
ise
for l
abor
ator
y-le
vel a
naly
sis.
•A
cous
tic e
mis
sion
s m
etho
d al
low
s de
tect
ion
of th
e or
igin
and
m
onito
ring
of a
ctiv
e de
fect
gro
wth
in C
OP
Vs
unde
r loa
d.–
Acou
stic
em
issi
ons
of in
tere
st o
nly
occu
r whe
n ne
w p
eak
pres
sure
s ar
e re
ache
d, b
ut m
ay b
e an
indi
cato
r tha
t rup
ture
is im
min
ent.
8
Met
hods
for C
hara
cter
izin
g G
loba
l Dam
age
•N
o N
DE
tech
niqu
e is
cur
rent
ly k
now
n to
be
dire
ctly
ap
plic
able
for p
redi
ctio
n of
str
ess
rupt
ure
and
othe
r life
-de
pend
ent C
OPV
issu
es.
–Fo
r life
issu
es: w
e ne
ed to
iden
tify
yet u
ndef
ined
phy
sica
l attr
ibut
es
or p
heno
men
a pr
oduc
ing
failu
re in
ord
er to
app
ly a
ppro
pria
te N
DE
.•
For K
evla
r: th
e po
ssib
ility
of “
cree
p”an
d/or
acc
umul
ated
“mic
ro-
crac
king
”or s
low
fibe
r che
mic
al d
egra
datio
n m
ay b
e ar
eas
to
targ
et fo
r dev
elop
men
t.•
For
carb
on fi
ber:
accu
mul
ated
mic
ro d
amag
e m
ay b
e a
fact
or,
alon
g w
ith th
e po
ssib
ility
of e
xtre
mel
y sl
ow c
reep
.–
Var
iatio
ns in
fibe
r res
idua
l stre
ss o
r stre
ss c
once
ntra
tions
may
also
co
ntrib
ute
to C
OP
V fa
ilure
: If s
ome
fiber
s ex
perie
nce
high
er lo
ads
than
ot
hers
, onc
e th
e m
ore
high
ly s
tress
ed fi
bers
fail,
a c
hain
reac
tion
may
re
sult
in th
e tra
nsfe
r of e
ver-
incr
easi
ng s
tress
to th
e re
mai
ning
fibe
rs,
lead
ing
to C
OP
V fa
ilure
.•
Sev
eral
CO
PV
ND
E te
chni
ques
hav
e be
en id
entif
ied
to
pote
ntia
lly a
sses
s th
e de
grad
atio
n of
fibe
r tha
t wou
ld le
ad to
st
ress
rupt
ure,
but
thes
e te
chni
ques
hav
e ye
t to
be a
dequ
atel
y ev
alua
ted.
–S
umm
ariz
ed in
the
back
up c
harts
–N
NW
G p
roje
ct ta
rget
s ev
alua
tion
of th
ese
9
NN
WG
CO
PV S
tres
s R
uptu
re N
DE
Goa
l•
To a
dvan
ce th
e st
ate-
of-th
e-ar
t by
deve
lopi
ng N
DE
te
chni
ques
that
are
cap
able
of a
sses
sing
stre
ss-
rupt
ure
degr
adat
ion
in K
evla
r CO
PV
s in
eith
er a
he
alth
-mon
itorin
gm
ode
or a
trad
ition
al re
mov
e-an
d-in
spec
tmod
e–
ND
E te
chni
ques
from
this
effo
rt w
ill ta
ke s
ever
al y
ears
to fi
eld.
Obj
ectiv
e•
Det
erm
ine
the
feas
ibili
tyof
can
dida
te N
DE
tech
niqu
es in
det
ectio
n of
deg
rada
tion
lead
ing
to
stre
ss ru
ptur
e in
Kev
lar C
OP
Vs
•In
par
alle
l, ut
ilize
des
truct
ive
anal
ysis
to b
ette
r un
ders
tand
stre
ss-r
uptu
re fa
ilure
sig
natu
res
so a
s to
be
tter t
arge
t ND
Ete
chni
ques
10
NN
WG
Tec
hnic
al A
ppro
ach
•U
sing
Kev
lar a
s th
e in
itial
CO
PV
stre
ss-r
uptu
re
syst
em fo
r ND
E s
tudy
-Sub
stan
tial k
now
ledg
e ba
se in
lite
ratu
re-D
ocum
ente
d to
resp
ond
to a
ging
tech
niqu
es-M
any
Kev
lar t
est a
rticl
es a
nd fl
eet l
eade
rs w
ith
“rea
l”ag
e ar
e av
aila
ble
for c
ompa
rison
-A fo
unda
tion
for f
ollo
w-o
n ef
forts
for C
OP
Vs
utili
zing
ca
rbon
and
em
ergi
ng c
omm
erci
al fi
bers
(e.g
., P
BO
(Z
ylon
); M
-5; a
nd h
ybrid
izin
g fib
ers
(car
bon
and
PB
O)
•A
test
pop
ulat
ion
of 1
00 K
evla
r spe
cial
test
CO
PV
s ha
ve b
een
wra
pped
and
will
be
used
to e
xam
ine
vario
us N
DE
tech
niqu
es u
nder
acc
eler
ated
agi
ng
cond
ition
s
11
NN
WG
Tec
hnic
al A
ppro
ach
(con
t.)
•A
ccel
erat
ed a
ging
is b
eing
acc
ompl
ishe
d by
two
met
hods
w
hich
use
prim
arily
ele
vate
d st
ress
(at h
igh
ambi
ent
tem
pera
ture
) and
sep
arat
ely
elev
ated
tem
pera
ture
to
prov
ide
sets
of t
est s
peci
men
s–
An
envi
ronm
enta
l cha
mbe
r has
bee
n co
nstru
cted
whe
re p
ress
ure
and
tem
pera
ture
are
con
trolle
d in
depe
nden
tly–
Req
uire
s bu
rsts
of 8
bot
tles
at 2
0 de
g. C
and
rupt
ure
of 2
6 ea
chun
der t
he tw
o ac
cele
rate
d ag
ing
cond
ition
s•
10 s
pare
bot
tles
are
rese
rved
for r
epla
cem
ents
as
need
ed.
•Th
e ag
ing
proc
ess
mon
itore
d w
ith F
BG
stra
in g
ages
and
A
E s
enso
rs b
oth
to fa
cilit
ate
agei
ng a
nd to
obt
ain
ND
E
data
12
NN
WG
Tec
hnic
al A
ppro
ach
(con
t.)
•U
se e
ach
ND
E te
chni
que
and
dest
ruct
ive
anal
ysis
to e
valu
ate
coup
on
and
cylin
der s
peci
men
set
s an
d do
cum
ent r
esul
ts
•A
naly
ze a
ll N
DE
and
DA
resu
lts a
nd s
elec
t mos
t pro
mis
ing
ND
E
met
hods
.
•E
valu
ate
vario
us e
xist
ing
spec
imen
s (v
irgin
, age
d an
d fa
iled)
with
do
wn-
sele
cted
ND
E a
nd D
A to
det
erm
ine
capa
bilit
y of
ND
E a
nd D
A
met
hods
on
mor
e co
mpl
ex s
peci
men
s w
ith “r
eal”
age.
13
Kev
lar T
est P
roje
ct O
bjec
tives
(Pig
gyba
ck)
•P
rovi
de d
ata
that
can
be
used
to e
valu
ate
and
pote
ntia
lly
exte
nd th
e us
eful
life
of t
he fl
ight
CO
PV
s –
Vol
umet
ric/s
train
test
ing
and
asso
ciat
ed la
bora
tory
ana
lysi
s: to
unde
rsta
nd c
ompo
site
/line
r stra
in in
tera
ctio
n an
d cl
arify
the
“thro
ugh-
wal
l”st
ress
gra
dien
t (co
mpl
ete)
–S
tress
rupt
ure
test
ing:
to d
eter
min
e if
relia
bilit
y m
odel
s pa
ram
eter
s ar
e co
nser
vativ
e –
Mat
eria
l deg
rada
tion
eval
uatio
n•
Bur
st te
st re
pres
enta
tive
CO
PV
s to
det
erm
ine
if bu
rst
pres
sure
has
dec
reas
ed, a
nd a
ccom
plis
h co
upon
s/st
rand
te
stin
g th
at w
ill h
elp
with
an
unde
rsta
ndin
g of
mat
eria
l de
grad
atio
n
14
NN
WG
Pro
gres
s to
Dat
e
•In
itial
Kev
lar P
iggy
back
Cam
pain
com
plet
ed w
ith e
xten
sive
ND
E d
evel
opm
ent
and
new
insi
ghts
(esp
ecia
lly fo
r stre
ss ru
ptur
e m
onito
ring)
–La
bora
tory
cha
ract
eriz
atio
n an
d fa
ilure
pre
curs
ors
note
d•
New
Agi
ng c
ham
bers
set
up a
t TR
I (pr
imar
ily T
RI R
&D
fund
s)•
Kev
lar C
OP
V A
ging
suc
cess
fully
com
plet
ed–
Age
d C
OPV
s an
d fa
iled
resi
dual
read
y fo
r “ro
und
robi
n”N
DE
ana
lysi
s•
TIM
hel
d at
TR
I to
shar
e da
ta: T
RI,
GR
C, U
of C
, WS
TF, o
ther
s•
Sig
nific
ant i
nsig
hts
gain
ed w
ith re
al-ti
me
ND
E d
urin
g ag
ing
–AE
dat
a vs
tim
e, k
nee
in th
e cu
rve
and
grow
ing
ampl
itude
pot
entia
lly w
arns
of f
ailu
re
to c
ome
–Th
erm
al e
last
ic a
ffect
at K
evla
r stra
nd fa
ilure
–La
RC
pro
vide
d A
E, W
STF
FO
BG
sys
tem
, MS
FC te
ch s
uppo
rt an
d fu
ndin
g•
Gre
at p
rogr
ess
at b
oth
GR
C U
nive
rsity
of M
isso
uri (
at C
olum
bia)
in D
A/N
DE
–
Fibe
r lev
el fa
ilure
mod
es n
oted
and
thro
ugh
the
thic
knes
s ef
fect
s of
voi
ds e
tc.
–R
aman
spe
ctro
scop
y •
Ext
ensi
ve d
ocum
enta
tion
from
GR
C o
n R
aman
for s
tress
mea
sure
men
ts a
nd e
arly
co
rrel
atio
ns o
f sam
ples
with
stre
ss ru
ptur
e ag
e•
Pap
er g
ener
ated
on
Ram
an in
sigh
ts fr
om U
of M
•
WS
TF p
rocu
red
mic
ro-lo
ad fr
ame
and
AE
sys
tem
/FO
BG
read
y to
sta
rt S
EM
te
stin
g to
imag
e st
ress
rupt
ure
of s
trand
s an
d ob
tain
AE
sig
natu
res
15
Typi
cal C
OPV
Inst
rum
enta
tion,
ND
E, a
nd D
A
Met
hod
Mea
sure
men
t V
isua
l Ins
pect
ion
(Pre
test
)Ex
tern
al in
spec
tion
of o
ver w
rap.
Indi
catio
n of
gro
ss d
amag
e
Flas
h Th
erm
ogra
phy
(Pre
test
)H
eat S
igna
ture
Dec
ay S
ub-s
urfa
ce P
ly D
elam
inat
ion
Bor
esco
pe In
spec
tion
(Pre
test
)In
tern
al in
spec
tion
of li
ner I
ndic
atio
n of
dam
age
or b
uckl
ing
IR H
eat S
oak
Ther
mog
raph
y (P
rete
st)
Hea
t Sig
natu
re D
ecay
Sub
-sur
face
Ply
Del
amin
atio
n
Shea
rogr
aphy
(Pre
test
CO
PV o
nly)
Diff
eren
tial s
train
resu
lting
from
any
thin
g th
at w
ould
cau
se it
(e.g
., im
pact
s, de
lam
inat
ions
, bro
ken
fiber
, etc
.)
Fidu
ciar
y M
arki
ng (P
re/P
ostT
est)
Mea
sure
men
t of d
ista
nce
betw
een
mar
ks
Pres
sure
, Tem
pera
ture
(Tes
t)Ti
me,
Pre
ssur
e, a
nd T
empe
ratu
re
Cab
led
Girt
h LV
DT
(Tes
t)C
ircum
fere
ntia
l dis
plac
emen
t mea
sure
d at
0, 4
5, a
nd 8
0 de
gree
s
Bos
s LV
DT
(Tes
t)A
xial
dis
plac
emen
t
Stra
in G
auge
(Tes
t)C
hang
e in
leng
th. F
iber
stra
in
Fibe
r Bra
gg G
ratin
g (T
est)
Cha
nge
in le
ngth
. Hig
h re
solu
tion
Aco
ustic
Em
issi
on (T
est)
Aco
ustic
noi
se. F
iber
bre
akag
e or
del
amin
atio
n
Vol
ume
Dis
plac
emen
t(L
oad
Cel
l and
Sup
ply
Wei
ght)
Ves
sel t
est f
luid
mas
s. St
rain
and
fibe
r Cre
ep (w
eigh
ed fr
om su
pply
and
ex
puls
ion
volu
mes
)
Full
Fiel
d D
igita
l Im
age
Cor
rela
tion
Ves
sel s
train
Eddy
Cur
rent
Pro
bes
Com
posi
te th
ickn
ess c
hang
e
Porta
ble
Ram
an S
pect
rsco
pyR
esid
ual S
tress
/iden
tific
atio
n of
stre
ss g
radi
ents
16
Hea
t Soa
k Th
erm
ogra
phy
App
licat
ion
1
2
4
3
65
Figu
re 1
Sect
ione
d C
OPV
with
def
ects
for u
se a
s a
stan
dard
•1
–4:
del
amin
atio
ns o
f Kev
lar f
iber
s•
Def
ects
5 &
6: h
ole
drille
d in
to th
e lin
er
Hea
t soa
k/co
ol-d
own
ther
mog
raph
y
17
Pret
est H
eat S
oak
Ther
mog
raph
y
•Tw
o 50
0-W
qua
rtz la
mps
wer
e fo
cuse
d on
the
insp
ectio
n ar
ea u
sing
par
abol
ic re
flect
ors.
–H
eatin
g tim
e fo
r the
CO
PV
was
90
s, a
nd te
mpe
ratu
re d
ata
was
ac
quire
d du
ring
the
cool
-dow
n fo
r 10
min
(a re
duce
d fra
me
rate
of 5
fp
s w
as a
chie
ved
by s
ub-s
ampl
ing)
.–
Bec
ause
of t
he la
rge
ther
mal
mas
s of
thes
e sp
ecim
ens,
the
surfa
ce
tem
pera
ture
rise
dur
ing
heat
ing
was
< 1
0 ºC
.–
Alth
ough
the
surfa
ce o
f the
spe
cim
en w
as s
omew
hat r
efle
ctiv
e, it
was
not
nec
essa
ry to
app
ly a
ny e
mis
sivi
ty e
nhan
cing
coa
ting
sinc
e da
ta w
as o
nly
acqu
ired
durin
g th
e co
ol-d
own.
18
Hea
t Soa
k Th
erm
ogra
hy
of S
pher
ical
CO
PV Indi
catio
n
Ref
lect
ion
Clo
se-u
p
19
Gen
eral
The
rmog
raph
y C
oncl
usio
n
•H
eat s
oak
Ther
mog
raph
y pe
rform
ed w
ell a
s an
in
spec
tion
tool
for t
he re
lativ
ely
thic
k w
all C
OP
Vs
–A
ppro
ach
finds
def
ects
dee
per t
han
conv
entio
nal F
lash
Th
erm
ogra
phy
–C
ompl
ete
insp
ectio
ns w
ere
perfo
rmed
rapi
dly.
•Th
erm
ogra
phy
used
in c
ombi
natio
n w
ith S
hear
ogra
phy,
w
as d
eem
ed to
giv
e an
exc
elle
nt h
ealth
che
ck o
f the
C
OP
V o
f con
cern
.
20
CO
PV S
hear
ogra
phy
•S
hear
ogra
phy
was
als
o re
cent
ly u
sed
to h
elp
verif
y th
e in
tegr
ity o
f 24
CO
PV
prio
r to
test
.–
Acc
ompl
ishe
d un
der t
he g
uida
nce
of J
ohn
New
man
, pr
esid
ent/f
ound
er o
f Las
er T
echn
olog
ies,
Inc.
(LTI
)–
Use
s a
Mic
hels
on ty
pe in
terfe
rom
eter
with
two
esse
ntia
l mod
ifica
tions
•O
ne m
irror
pre
cise
ly ti
lted
to in
duce
an
offs
et
(she
ared
) im
age
of th
e te
st p
art w
ith re
spec
t to
a se
cond
imag
e of
the
part
•S
hear
ed a
mou
nt is
a v
ecto
r with
an
angl
e an
d a
disp
lace
men
t am
ount
21
Sche
mat
ic D
iagr
am o
f a M
iche
lson
Typ
e Sh
earo
grap
hy In
terf
erom
eter
22
Shea
rogr
aphy
Tes
t Set
Up
–C
OPV
Insp
ectio
n CO
PVPr
essu
reG
age
G1
LTI-5
100
Shea
rogr
aphy
Cam
era
GN
2 Fl
owC
ontr
ol P
anel
CO
PV S
uppo
rtan
d R
otat
ion
Bea
ring
LTI/N
ASA
Kenn
edy
Spac
e C
ente
r She
arog
raph
y Te
st T
eam
Pho
to
23
Shea
rogr
aphy
Tes
t Set
-Up
for C
OPV
Tes
ting
Pneu
mat
ic O
pera
tion/
Shea
rogr
aphy
Dat
a C
aptu
re
Rig
id C
OPV
Sup
port
Fr
ame
allo
ws
tank
rota
tion.
CO
PV P
ress
ure
Gag
e0-
120
psi.
150
psi.
GN
2 Su
pply
Vent
V1 V2 1.V1
ope
ned,
pre
ssur
e ra
ised
to 7
0psi
., V1
clo
sed.
2.
Shea
rogr
aphy
refe
renc
e im
age
capt
ured
@ 7
0 ps
i.3.
V1 o
pene
d, p
ress
ure
rais
ed to
90p
si.,
V1 c
lose
d.4.
Shea
rogr
aphy
Str
esse
d im
age
capt
ured
@ 9
0 ps
i.5.
Fina
l she
arog
raph
y im
age
com
pute
d.
24
Exam
ple
Shea
rogr
aphy
Imag
es
•She
arog
raph
y sh
ows
surf
ace
defo
rmat
ion
deriv
ativ
es d
ue to
pre
ssur
e ch
ange
in ta
nk.
•Whi
te a
reas
are
sur
face
s sl
opin
g to
war
ds th
e ca
mer
a, d
ark
area
sar
e sl
opin
g aw
ay fr
om th
e ca
mer
a.•D
evia
tion
from
a n
eutr
al g
ray
valu
e of
128
(8-b
it, 2
56 g
ray
leve
ls) d
eter
min
e de
form
atio
n am
plitu
de.
•Fea
ture
s yi
eldi
ng a
str
ain
resp
onse
due
to lo
w in
tern
al p
ress
ure
chan
ge: T
ape
dela
min
atio
n,
impa
ct d
amag
e, C
OPV
des
ign
stra
in c
once
ntra
tions
Min
or ta
pe d
elam
inat
ion
Nea
r end
bos
s.
Stra
in C
once
ntra
tion
at th
e eq
uato
r ove
r lin
er c
ircum
fere
ntia
l gi
rth
wel
d.
Qui
lted
defo
rmat
ion
patte
rn d
ue to
tape
pl
acem
ent a
nd th
inne
r co
mpo
site
bet
wee
n w
raps
.
Impa
ct d
amag
eon
a C
OPV
at W
STF.
Dam
aged
are
as
are
1.3
in. d
iam
.co
mpa
red
to th
e 0.
25 in
. vis
ual
dent
on
the
surf
ace.
CO
PV T
est S
tand
ard
25
Car
bon
CO
PV S
hear
ogra
phy
Insp
ectio
n-1
0 ps
id
Dam
age
unde
tect
able
vis
ually
26
Cor
rela
tion
of S
hear
ogra
phy
Res
pons
e to
Im
pact
dam
age
•P
rovi
des
exce
llent
imag
e an
d ef
fect
ive
dam
age
area
to
com
pare
with
impa
ct c
hara
cter
istic
s
27
Cor
rela
tion
of S
hear
ogra
phy
Res
pons
e to
Im
pact
dam
age
Con
’t
27 ft
-lbs
15 ft
-lbs
23 ft
-lbs
•D
etec
ts a
reas
no
t rev
eale
d by
vi
sual
insp
ectio
n•
Dam
age
area
s fo
r diff
eren
t im
pact
ene
rgie
s vi
sual
ly e
vide
nt•
Dam
age
area
in
crea
ses
with
im
pact
ene
rgy
for a
ll C
OP
Vs
Dam
age
Area
(in2 )
05
1015
20
Impact Energy (ft-lbs)
010203040506070
Sm. C
yl.
Lg. C
ylin
der
28
Com
posi
te/L
iner
Thi
ckne
ss M
easu
rem
ent
Eddy
cur
rent
sys
tem
for r
eal-t
ime
CO
PV c
ompo
site
thic
knes
sN
ASA
Lang
ley
Res
earc
h C
ente
r
29
Eddy
Cur
rent
Sys
tem
X-r
ay V
erifi
catio
n
30
Exam
ple
Ove
rwra
p Th
ickn
ess
Eval
uatio
n by
Ed
dy C
urre
nt
31
Exam
ple
Line
r Thi
ckne
ss E
valu
atio
n by
Ed
dy C
urre
nt
32
Dig
ital I
mag
e C
orre
latio
n
•D
igita
l im
age
corr
elat
ion
is a
ccom
plis
hed
usin
g A
RA
MIS
so
ftwar
e –
3D im
age
corr
elat
ion
give
s fu
ll-fie
ld d
ispl
acem
ent a
nd s
train
m
easu
rem
ents
–S
yste
m w
as d
evel
oped
by
GO
M m
bh (B
raun
schw
eig,
Ger
man
y)•
Req
uire
s sp
rayi
ng ra
ndom
hig
h-co
ntra
st d
ot p
atte
rns
onto
a
sam
ple;
this
pat
tern
is th
en tr
acke
d in
by
thou
sand
s of
uni
que
corr
elat
ion
area
s (fa
cets
)•
Mea
sure
men
t poi
nts
from
cen
ter o
f eac
h fa
cet,
whi
ch c
an b
e th
ough
t of a
s 3D
ext
enso
met
er a
rrays
, for
m in
-pla
ne s
train
ro
sette
s
33
Dig
ital I
mag
e C
orre
latio
n Se
tup
Dur
ing
Bur
st T
ests
NAS
A G
RC
DIC
Tes
t Tea
m P
hoto
N
ASA
GR
C D
IC T
est T
eam
Pho
to
Blac
k do
ts s
pray
ed o
ver a
rea
of in
tere
st
34
Dig
ital I
mag
e C
orre
latio
n Vi
deo
Gre
en to
Red
ar
ea in
dica
ting
as
ymm
etric
st
ress
fiel
d du
ring
pres
suriz
atio
n (a
rea
of
acce
lera
ted
S
tress
Rup
ture
an
d gr
eate
r fa
ilure
risk
)
35
Nor
mal
ized
Str
ain
vs. P
ress
ure,
Hoo
p W
rap
on N
ASA
CO
PV T
est
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
1000
0
1100
0
1200
0
010
0020
0030
0040
0050
0060
0070
0080
00
Pres
sure
(psi
)
Strain (ms)
h SG
-13
0°h
SG-3
7 12
0°h
SG-2
4 24
0°D
IC A
RAM
IS
Strain (ms)
Pres
sure
(psi
)
36
Gen
eral
Sch
emat
ic o
f CO
PV F
BG
St
rain
Mea
sure
men
t Sys
tem
Tu
nabl
e La
ser
Sens
or S
trin
gs
Gas
Cel
l Ref
eren
ce
37
Exam
ple
Unf
ilter
ed A
E D
ata
-All
Even
ts(E
ric M
adar
as h
as d
etai
ls)
Zero
Mer
idia
n
Are
as o
f int
eres
t
Top
Vie
w
38
Exam
ple
AE
Even
ts V
s Tim
e
Even
ts C
ount
vs.
Tim
e an
d Pr
essu
re v
s. Ti
me
500
1000
1500
2000
2500
3000
3500
4000
450
Tim
e (s
)
Yie
ldin
g
Con
tinuo
us
yiel
ding
and
pr
ogre
ss to
war
d fa
ilure
(sto
pped
pr
ior t
o fa
ilure
oc
curr
ing)
39
FBG
Dis
clos
ed L
oad
Red
istr
ibut
ion
4550
4560
4570
4580
4590
4600
4610
4620
4630
4640
4650
4660
4670
4680
4690
4700
4710
4720
010
0020
0030
0040
0050
0060
0070
0080
00
Pres
sure
(psi
g)
Tank Volume (in3)
Pres
sure
(psi
g)
Tank Volume (in3)
40
OM
S R
uptu
re D
IC V
ideo
41
AC
CEL
ERA
TED
AG
ING
OF
KEV
LAR
-EPO
XY C
OPV
s
Twin
CO
PV
Tes
t Cha
mbe
rsL
= 31
o C, 0
.80
SR
R
= 8
1oC
, 0.6
5 S
R
Tem
pera
ture
and
Str
ess
Agi
ng
Test
Cha
mbe
rs
42
EXA
MPL
E A
GIN
G A
PPR
OA
CH
ES0
12
34
0.80
0.75
0.70
0.65
0.60
STRESS RATIO
TIM
E, H
RS
(Life
time
Scal
e Pa
ram
eter
, Log
Sca
le)
330
300
3000
1010
010
00
25C
40C
60C
80C
100C
Ada
pted
from
Pho
enix
18-
Aug
-06
SR
= 0
.80,
T =
31o C
SR
= 0
.65,
T =
81o C
0.85
NA
SA
/slp
/isoc
hron
al a
ging
par
amet
ers
2.xl
s
Stre
ss A
ging
Step
ped
Ther
mal
Agi
ng
43
NN
WG
Pro
gram
to Id
entif
y N
DE
met
hods
for d
etec
ting
onse
t of
Cre
ep-R
uptu
re in
Com
posi
te S
truc
ture
s
•A
E in
dica
tions
beg
in to
acc
umul
ate
wel
l bef
ore
rupt
ure
occu
rs.
The
sync
hron
izat
ion
of th
ese
data
with
the
stra
in a
nd te
mpe
ratu
re in
dica
tions
w
ill b
e ac
com
plis
hed
in th
e ne
xt p
hase
of o
ur
proj
ect.
44
Exam
ple
AE
RES
ULT
SB
ottle
82:
AE
EVEN
TS P
RO
VID
E N
OTI
CE
OF
RU
PTU
RE
S/N
82
FAIL
UR
E.x
ls
21 D
ecem
ber 2
006
0
200
400
600
800
1000
1200
1400
1600
1800
Number of AE Events
RU
PTU
RE
TIM
E: 9
1 hr
s
AD
VA
NC
E N
OTI
CE
: 1.9
8 hr
s
45
Exam
ple
Aco
ustic
Em
issi
on D
ata
Even
ts v
s Ti
me
0
100
200
300
400
500
600
050
0010
000
1500
020
000
2500
0
Sec
onds
Acoustic Emission Events
46
Exam
ple
Aco
ustic
Em
issi
on C
umul
ativ
e Ev
ent E
nerg
ies
050
0010
000
1500
020
000
2500
030
000
3500
040
000
4500
0
1
29
57
85
113
141
169
197
225
253
281
309
337
365
393
421
449
477
505
Aco
ustic
Em
issi
on E
vent
#
Cumulative Energy(all channels)
47
NN
WG
ND
E of
Cre
ep-R
uptu
re N
DE
Prel
imin
ary
Find
ings
•A
ccel
erat
ion
fact
ors,
ATσ
, of t
he o
rder
105
are
bei
ng
achi
eved
by
incr
easi
ng s
tress
and
tem
pera
ture
ove
r av
erag
e le
vels
exp
erie
nced
in s
ervi
ce.
•A
E in
dica
tions
beg
in to
acc
umul
ate
wel
l bef
ore
rupt
ure
occu
rs.
The
sync
hron
izat
ion
of th
ese
data
with
the
stra
in
and
tem
pera
ture
indi
catio
ns w
ill b
e ac
com
plis
hed
in th
e ne
xt
phas
e of
our
pro
ject
. •
Act
ive
stra
in, t
empe
ratu
re a
nd A
E m
easu
rem
ents
app
ear t
o be
giv
ing
sign
als
of im
pend
ing
rupt
ure.
Giv
en o
ur A
T x
Aσ
prod
uct,
a ye
ar o
r mor
e of
not
ice
of im
pend
ing
rupt
ure
may
be
feas
ible
usi
ng a
ctiv
e se
nsor
s.
48
Con
clus
ions
•N
AS
A C
OP
V a
sses
smen
t sta
rted
in 2
004
led
to th
e ev
alua
tion
of
ND
E a
pplic
able
to C
OP
Vs.
–R
easo
nabl
y m
atur
e N
DE
wer
e id
entif
ied
for a
pplic
atio
n to
det
ect
impa
ct a
nd o
ther
loca
lized
dam
age.
•N
DE
resp
onse
not
effe
ctiv
ely
rela
ted
to a
spe
cific
redu
ctio
n in
st
ruct
ural
inte
grity
.–
Littl
e N
DE
was
foun
d av
aila
ble
to e
valu
ate
glob
al m
ater
ial p
rope
rty
chan
ges
poss
ibly
rela
ted
to p
rogr
essi
on to
war
d st
ress
rupt
ure
orth
at
coul
d ai
d in
life
pre
dict
ions
.•
Det
aile
d re
com
men
datio
ns fo
r a s
tress
-rup
ture
pro
gram
wer
e pr
ovid
ed
to a
dvan
ce th
e st
ate-
of-th
e-ar
t, bu
t will
take
sev
eral
yea
rs to
fiel
d.•
The
NN
WG
is c
urre
ntly
mak
ing
exce
llent
pro
gres
s in
this
are
a.
•A
pplic
atio
ns o
f sev
eral
ND
E m
etho
ds to
pre
test
scr
eeni
ng K
evla
r an
d ca
rbon
CO
PV
s, in
test
at W
STF
ove
r the
last
two
year
s, h
ave
dem
onst
rate
d th
eir e
ffect
iven
ess
–N
DE
app
lied
real
-tim
e du
ring
test
ing
is a
lso
prov
idin
g ex
celle
nt te
st
data
, hel
ping
to p
rovi
de ra
tiona
le to
con
tinue
flyi
ng s
ome
vess
els
49
Add
ition
al A
ctiv
ities
Pla
nned
•E
valu
ate
and
valid
atin
g N
DE
that
can
be
inte
grat
ed in
to
man
ufac
turin
g to
ens
ure
sign
ifica
nt fl
aws
do n
ot e
xist
and
ens
ure
man
ufac
turin
g co
nsis
tenc
y.–
Pre
vent
man
ufac
turin
g is
sues
and
ens
ure
clos
er g
roup
ing
of p
hysi
cal
prop
ertie
s.•
Dev
elop
Com
posi
te N
DE
Sta
ndar
ds a
pplic
able
to C
OP
Vs
–N
AS
A to
p le
vel s
tand
ard
and
guid
es s
ite A
STM
and
con
sens
us s
tand
ards
–A
STM
ND
E s
tand
ard
Gui
de a
nd 5
sta
ndar
ds o
f pra
ctic
e in
dev
elop
men
t•
Impl
emen
t add
ition
al re
al-ti
me
ND
E d
urin
g te
stin
g to
pro
vide
an
enha
nced
und
erst
andi
ng o
f the
CO
PV
incl
udin
g lin
er a
nd C
ompo
site
inte
ract
ion:
–Fu
rther
dev
elop
men
t of S
hear
ogra
phy
appl
icat
ion
to p
rovi
de s
ensi
tive
in-
plan
e st
rain
val
ues
–C
orre
latin
g S
hear
ogra
phy
and
Aco
ustic
Em
issi
ons
(AE
) ND
E–
Ref
inem
ent o
f AE
freq
uenc
y co
nten
t to
prov
ide
a di
ffere
ntia
tion
betw
een
fiber
vs.
mat
rix c
rack
ing
and
othe
r dam
age/
prog
ress
ion
–R
efin
emen
t of e
ddy
curr
ent t
o pr
ovid
e pr
ecis
e co
mpo
site
and
line
r th
ickn
ess
varia
tion
at th
e C
OP
V is
cyc
led
(hor
izon
tal a
nd v
ertic
al
com
pone
nt)
50
Bac
kup
Cha
rts
51
CO
PV P
oten
tial A
cous
tic N
DE
Met
hods
Met
hod
Prop
erty
Mea
sure
d Pr
iorit
y
Aco
ustic
Em
issi
on
Act
ive
dam
age
grow
th d
urin
g lo
adin
g su
ch a
s m
atrix
cra
ckin
g, d
elam
inat
ion
or fi
ber b
reak
ing
Hig
h
Con
vent
iona
l Pul
se
Ech
o U
ltras
onic
s M
acro
mod
ulus
A
ttenu
atio
n M
icro
crac
king
Hig
h
Aco
usto
-Ultr
ason
ics
Aco
ustic
Atte
nuat
ion
Hig
h
Lam
b W
aves
/Pla
te
Wav
es
Aco
ustic
Pro
perti
es/M
odul
us M
icro
crac
king
Hig
h
Lase
r Ultr
asou
nd
Mac
rom
odul
us
Atte
nuat
ion
Mic
rocr
acki
ng
Hig
h
52
CO
PV P
oten
tial E
lect
rom
agne
tic M
etho
ds
Met
hod
Prop
erty
Mea
sure
d Pr
iorit
y
Edd
y C
urre
nt
Ele
ctric
al C
ondu
ctiv
ity -
prop
ertie
s
Hig
h
Mic
row
ave
Die
lect
ric P
rope
rties
Hig
h
Ter
aher
tz
Die
lect
ric P
rope
rties
H
igh
One
Sid
ed N
MR
C
hem
ical
Bon
ding
/Pol
ymer
ic S
truct
ure
Of
Kev
lar
Hig
h
MR
I C
hem
ical
Stru
ctur
e Lo
w
53
CO
PV P
oten
tial O
ptic
al M
etho
ds
Met
hod
Prop
erty
Mea
sure
d Pr
iorit
y
Lase
r spe
ctro
scop
y C
hem
ical
Bon
ding
Low
Ram
an s
pect
rosc
opy
Che
mic
al B
ondi
ng a
nd
Res
idua
l Stre
ss
Med
ium
1
Four
ier T
rans
form
P
hoto
acou
stic
S
pect
rosc
opy
Inte
rlam
inar
She
ar S
treng
th
Med
ium
1
FTIR
C
hem
ical
Bon
ding
Med
ium
1
Ligh
t sca
tterin
g R
efra
ctiv
e In
dex/
Terte
ry S
truct
ure
Hig
h
Infra
red
Spe
ctro
scop
yC
hem
ical
Bon
ding
M
edum
1
Infra
red
Imag
ing
Cha
nges
In T
herm
al T
rans
fer
Pro
perti
es
Low
Vib
ro-th
erm
ogra
phy
Det
ectio
n O
f Mic
rocr
acki
ng o
r Lo
caliz
ed D
amag
e Lo
w
1 -W
ill w
ait f
or d
estru
ctiv
e an
alys
is re
sults
?-W
ait f
or o
ther
ND
E re
sults
sin
ce th
ese
tech
niqu
es a
re th
ough
t to
be lo
w to
med
ium
in p
riorit
y
54
CO
PV P
oten
tial S
trai
n M
easu
rem
ent M
etho
ds
Met
hod
Prop
erty
Mea
sure
d Pr
iorit
y D
istri
bute
d St
rain
Sen
sing
(FBG
)
Stra
in
Hig
h
Bond
ed M
echa
nica
l Stra
in G
auge
s
Stra
in
Hig
h
Bel
ly B
and
LVD
T
Dis
plac
emen
t H
igh
Sub
-Pix
el V
ideo
Imag
e C
orre
latio
n
Stra
in fi
eld/
full
field
st
rain
H
igh
Lase
r Pro
filom
etry
Stra
in
Hig
h
Moi
re in
terfe
rom
etry
Stra
in
Hig
h
Whi
te L
ight
Pro
filom
etry
Stra
in
Hig
h
Spe
ckle
Inte
rfero
met
ry
S
train
H
igh
PZT
Pat
ch
S
train
Lo
w
She
arog
raph
y
Stra
in
Hig
h
Pho
toel
astic
Coa
tings
S
train
H
igh
55
CO
PV P
oten
tial P
enet
ratin
g R
adia
tion
ND
E M
etho
ds
Met
hod
Pr
oper
ty M
easu
red
Pr
iorit
y
X-ra
y D
iffra
ctio
n
Deg
ree
of C
ryst
allin
ity, L
attic
e S
paci
ng, R
esid
ual S
tress
Hig
h
X-ra
y To
mog
raph
y
Den
sity
Cha
nges
Cau
sed
by
Mic
rocr
acki
ng
Low
Neu
tron
Rad
iogr
aphy
Den
sity
Var
iatio
n Lo
w
X-ra
y R
adio
grap
hy
D
ensi
ty V
aria
tions
Lo
w
56
CO
PV P
oten
tial D
estr
uctiv
e A
naly
sis
Expl
orat
ory
Inve
stig
atio
ns o
f ND
E Id
entif
ied
Reg
ions
of I
nter
est
Pote
ntia
l Ana
lytic
al T
echn
ique
s
Frac
ture
Sur
face
s: m
atrix
cra
ckin
g, fi
lam
ent
brea
ks a
nd s
plits
, mic
rocr
acks
in fi
lam
ents
•
Opt
ical
Mic
rosc
opy
• S
cann
ing
Ele
ctro
n M
icro
scop
y •
Tran
smis
sion
Ele
ctro
n M
icro
scop
y
Deg
ree
of C
ryst
allin
ity, C
hang
es in
Cry
stal
linity
an
d O
rient
atio
n
• X-
ray
Diff
ract
ion
Evi
denc
e of
UV
Deg
rada
tion,
Oxi
datio
n an
d or
H
ydro
lysi
s; O
ther
Che
mic
al S
peci
es
• M
icro
Fou
rier T
rans
form
Infra
red
Spe
ctro
scop
y •
Four
ier T
rans
form
Infra
red
Spe
ctro
scop
y •
Tim
e of
Flig
ht S
econ
dary
Ion
Mas
s S
pect
rosc
opy
• E
nerg
y D
ispe
rsiv
e X-
ray
Spe
ctro
scop
y •
Ram
an S
pect
rosc
opy
• P
orta
ble
X-ra
y
Mec
hani
cal P
rope
rties
in R
egio
ns N
ear a
nd
Aw
ay fr
om th
e Id
entif
ied
Reg
ions
• M
ini-t
ensi
le, S
hear
Tes
ting
Mol
ecul
ar W
eigh
t
• W
et C
hem
istry
-Rel
ativ
e V
isco
sity
Kev
lar M
olec
ular
Wei
ght
• S
olut
ion
Vis
cosi
ty (c
onc.
HsS
O4 )
57
Firs
t Acc
eler
ated
Tes
t Bed
(con
t.)
Task
8•
Dis
tribu
te s
ampl
e se
ts o
f spe
cim
ens
for c
hara
cter
izat
ion
by N
DE
tech
niqu
es a
nd
iden
tifie
d or
gani
zatio
ns.
Mak
e N
DE
mea
sure
men
ts a
nd d
ocum
ent r
esul
ts.
Task
9•
In a
par
alle
l effo
rt to
Tas
k 8,
dis
tribu
te s
ets
of fl
at s
ampl
es fo
r cha
ract
eriz
atio
n by
de
stru
ctiv
e an
alys
is (D
A) t
o id
entif
ied
orga
niza
tions
.–
Mak
e D
A m
easu
rem
ents
and
doc
umen
t res
ults
.Ta
sk 1
0•
Ana
lyze
all
resu
lts fr
om N
DE
and
DA
mea
sure
men
ts a
nd d
own-
sele
ct b
est N
DE
and
D
A m
etho
ds.
–R
epla
n co
ntin
uing
pro
ject
as
need
ed.
58
CO
PV T
est P
rogr
ams
–W
STF/
Mul
ti-C
ente
r
Kev
lar®
CO
PVS
tress
Rup
ture
/Bur
st(N
NW
G N
DE
Pig
gyba
ck)
Car
bon
CO
PVS
tress
Rup
ture
/B
urst
(Pre
test
& re
al-
time
ND
E)
PBO
CO
PVS
tress
Rup
ture
Bur
st
Car
bon
Fibe
r CO
PV
Im
pact
Dam
age
Stu
dy
Car
bon
Fibe
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yper
golic
Fue
lC
ompa
tibilit
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tudy
Sub
scal
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OP
VS
tress
Rup
ture
Stu
dy
Sub
scal
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OP
V S
tress
Rup
ture
/B
urst
Flui
dsC
ompa
tibilit
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urst
Cyc
le B
urst
Stre
ssR
uptu
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Vac
uum
, H
umid
ityan
d Sh
elf L
ifeS
tress
Rup
ture
Vacu
umB
urst
Adva
nced
CO
PVFe
asib
ility
Eval
uatio
ns -
CEV
NN
WG
CO
PVPr
ojec
ts
Stre
ss R
uptu
reN
DE
Kevl
ar®
and
Car
bon C
orre
latin
gN
DE
Res
pons
eto
Bur
stR
educ
tions
Inte
grat
ing
ND
E
Into
Man
ufac
turin
g an
d M
onito
ring
FY07
New
Sta
rt
Cha
ract
eriz
atio
n Th
roug
h th
e W
all
Stre
ss G
radi
ent