Identification of Aging Aircraft Electrical Wiring

Woolrich Engineering Consulting Firm

Final Report

Group Members: Robert Beremand – Project Manager Chad Hanak – Senior Engineer Melissa Straubel – Senior Engineer

Sponsors: Dr. R. O. Stearman Marcus Scott Kruger

May 5, 2003

Woolrich Engineering Consulting Firm Austin, TX 78705

May 5, 2003 Dr. R.O. Stearman Department of Aerospace Engineering and Engineering Mechanics College of Engineering, University of Texas at Austin Dear Sir: The attached report contains a description of Woolrich Engineering Consulting Firm’s efforts in evaluating wire aging experiments and the effect of aging on the triboelectric effect. Within the report are background information, theory, a description of the experimental setup and laboratory specimen, results of our work, a list of work that Woolrich Engineering recommends for the next team, and a description of the cost analysis. The background information discusses the history of the problem, recommended solutions to the problem, and also presents technical background including the types of wire failures. A description of the triboelectric effect and frequency response are presented in the theory portion of the report. In subsequent sections, descriptions of the wire used in our experiments, as well as an explanation of the test setup, are discussed. We then further explain what we have discovered in the last four months of our work, and present our recommendations for the team that continues. We conclude with a cost analysis of the work we have completed. While we were not able to simulate the aging of the wires, Woolrich Engineering was successful in obtaining wire, parameterizing the test setup, and testing previously aged wires for triboelectric response. The attached report contains the semester’s work; however, if you have any questions or comments, please feel free to contact us via email at beremand@mail.utexas.edu. Sincerely, Melissa Straubel Robert Beremand Chad Hanak Senior Engineer Project Manager Senior Engineer

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Abstract

The analysis techniques and results developed in this project were motivated by a need to find a nondestructive method of determining the quality of aircraft electrical wiring. Deteriorating insulation on electrical wiring is considered a significant safety hazard in aviation. An aircraft’s wiring can only be visually inspected by disassembling the craft, which is not a feasible option. Therefore, an indirect method of gauging the condition of a wire’s insulation is required. This study builds upon the research of previous studies by attempting to use the triboelectric effect in wiring to determine the condition of the wire. Woolrich Engineering hopes to find that a wire excited by a vibration of known frequency and amplitude will produce a predictable triboelectric response that varies with the condition of the wire.

Wire specimen aging techniques from previous studies were evaluated and modified to yield better (faster) results. A freezer and an incubator have been acquired for this purpose, but are not yet operational. Consistency problems with the wire analysis test setup used by previous studies have also been addressed. It was discovered that the EMI emitted by the shaker accounted for nearly all of the responses previously recorded. It was also discovered that surrounding the shaker with grounded foil essentially eliminated this interference. In addition, it was discovered that the coax cable that had been used for the majority of the testing was partially bad. With a new wire, Woolrich Engineering was able to obtain more consistent results. Unfortunately, these advancements in the setup were realized only recently and have not yet been fully incorporated into the testing process. Woolrich Engineering is, however, optimistic that the recent developments will allow future groups to make further, significant progress.

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Acknowledgements

Woolrich Engineering would like to thank our sponsors for this project, Dr. R.O.

Stearman and Marcus Kruger. Dr. Stearman, who is an aerospace engineering professor

at the University of Texas at Austin, was instrumental in acquiring several major

components for this project. These components included an incubator for conducting

heat and humidity tests and a freezer for conducting our cold tests. Marcus Kruger, an

aerospace engineering graduate student, provided his knowledge and guidance in the

setup of this project. Woolrich Engineering met with him during weekly consultation

sessions in which we analyzed the experimental setup and methods for testing.

Woolrich Engineering would also like to thank Frank Wise, the onsite electrician

for the Aerospace Engineering and Engineering Mechanics Department. He offered his

expertise to assist the team in researching and obtaining the wire that was used in this

project.

Without the contributions of these individuals, the work conducted by Woolrich

Engineering would have been difficult and time consuming.

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Table of Contents

List of Tables and Figures ................................................................................................ v 1.0 Introduction........................................................................................................... 1

1.1 History of the Problem ..................................................................................... 1 1.2 Previous Work................................................................................................... 2 1.3 Methodology ...................................................................................................... 2 1.4 Report Overview ............................................................................................... 4

2.0 Technical Background.......................................................................................... 6 2.1 Types of Wire Failures ..................................................................................... 6 2.2 Current Methods Used to Detect Faulty Wiring............................................ 6

3.0 Theory .................................................................................................................... 7 3.1 Triboelectric Effect ........................................................................................... 7 3.2 Triboelectric Effect: A Project-Specific Analysis .......................................... 8 3.3 Frequency Response ....................................................................................... 11 3.4 Statistical Sampling ........................................................................................ 12

4.0 Laboratory Specimen ......................................................................................... 14 5.0 Laboratory Aging................................................................................................ 16

5.1 Data Collection Cycle ..................................................................................... 16 5.2 Aging Processes ............................................................................................... 18 5.3 Aging Equipment ............................................................................................ 20 5.4 Anticipated Results ......................................................................................... 22

6.0 Age Analysis ........................................................................................................ 23 6.1 Experimental Setup ........................................................................................ 23

6.1.1 Signal Analyzer/Computer........................................................................ 24 6.1.2 Data Acquisition System........................................................................... 24 6.1.3 Amplifier................................................................................................... 25 6.1.4 Electromagnetic Shaker ............................................................................ 25 6.1.5 Electromagnetic Interference (EMI) Reduction........................................ 26

6.2 Review of Previous Results ............................................................................ 29 6.3 Anticipated Results ......................................................................................... 30

7.0 Results .................................................................................................................. 32 7.1 Acquisitions ..................................................................................................... 32 7.2 Laboratory Aging............................................................................................ 32 7.3 Test Setup Repeatability/Verification ........................................................... 33 7.4 Aged Wire Tests .............................................................................................. 34 7.5 Important Discoveries .................................................................................... 37

8.0 Recommendations ............................................................................................... 42 8.1 Laboratory Aging Equipment ....................................................................... 42 8.2 Electromagnetic Interference (EMI) Shielding............................................ 42 8.3 Use of Bare Wires............................................................................................ 43 8.4 Used Aviation Wire......................................................................................... 43

9.0 Task Distributions............................................................................................... 44 10.0 Cost Analysis ....................................................................................................... 45 11.0 Conclusion ........................................................................................................... 46

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12.0 Works Cited......................................................................................................... 47 13.0 Appendix A – Timeline ....................................................................................... 48 14.0 Appendix B – Raw Data ..................................................................................... 49

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List of Tables and Figures Figure 1: Wreckage from TWA Flight 800 [3] 1

Figure 2: Relative movement between insulating and conducting surfaces induces a current [5]

7 Figure 3: Wire/Electromagnetic Shaker System 9

Figure 4: Differences in Redox Reaction Rates Can Create an Electric Potential Between Two Materials [9]

10 Figure 5: Alpha Wire Spools 15

Table 1: Wire Specifications [10] 15

Figure 6: Data Collection Cycle Comparison 17

Figure 7: Aged Wire Samples [4] 19

Figure 8: Freezer Donated by UT-Austin Zoology Department 22

Figure 9: Signal Analyzer, Amplifier, and shaker [4] 23 Figure 10: Shaker/Stinger/Chessboard System [4] 26

Figure 11: Plastic Tabs Holding a Wire in Place on the Chessboard 27

Figure 12: Shaker and Chessboard Shielded with Grounded Foil 28

Table 2: BSS Engineering, Inc. Testing Results [4] 29

Figure 13: Sample Mean Responses for Three Nominal Alpha Wire 1632 Specimens 34

Figure 14: Sample Mean Responses of Two Wires Aged for Different Periods of Time in Jet-A Fuel

35 Figure 15: Sample Mean Responses of Five Oven-Aged Alpha Wire 1632 Specimens

36

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Figure 16: Measured Background Noise without a Wire Attached (No Shaker Excitation) 38

Figure 17: Measured Background Noise with a Wire Attached (No Shaker Excitation)

39 Figure 18: Measured Response of a Bare Wire (Shaker Turned On) 40 Figure 19: Measured Response of an Insulated Wire (Shaker Turned On) 41

Figure 20: Diagram labeling the distribution of tasks 44

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1.0 Introduction

1.1 History of the Problem

Since the 1980s, the Navy and Air Force have documented problems with aircraft

electrical wires exposed to prolonged high heat, moisture, chemicals, and vibration

during aircraft operation. Faulty electrical wire insulation has caused in-flight fires and

electrical failures in addition to control connection failures. This has caused

malfunctions in aircraft spoilers, and has triggered inadvertent autopilot commands, or

disabled the autopilot completely [1].

Similar problems have occurred in the commercial airplane industry. More than

half of the world’s passenger jets contain potentially problematic wire insulation [2].

Two high profile accidents, TWA Flight 800 and Swiss Air Flight 111, were blamed on

faulty electrical wiring.

In both commercial and military arenas, Kapton has been the wire under question.

Because of the evident problem that aging wires pose, Dr. R.O. Stearman has asked ASE

463Q teams, beginning in the summer of 2002, to investigate the relationship between the

age and condition of a wire and its triboelectric response.

Figure 1: Wreckage from TWA Flight 800 [3]

2

1.2 Previous Work

The ASE 463Q fall 2002 team at UT Austin, BSS Engineering, Inc., performed

laboratory aging tests on Alpha Wire 1632 specimens in order to simulate the aging of

the wires. They concluded that heat and humidity tests did not properly age the wire

specimens. Visual and touch inspections of wires aged over 7 ½ weeks showed no

changes in the wire’s physical characteristics. The previous team felt that this result was

due its inability to increase the temperature imposed upon the wire specimens above

120°F. They also felt that the laboratory aging experiments would be more efective if

conducted over a longer amount of time. BSS Engineering, Inc. also exposed the Alpha

wire to saltwater and Jet-A fuel and found that these solutions corroded and tarnished the

wire, and bonded the copper strands together. Physically handling the wire also revealed

that it was noticeably more brittle. Visual inspection of wire submerged in Jet-A Fuel

showed that the rubber insulation had expanded in diameter and length. [4]

Though the previous team was successful in simulating the aging of the wire, they

were unsuccessful in identifying a relationship between the aged wire and its triboelectric

response. Single frequency tests were performed on the aged wires, but no trend could be

determined from data points that were taken. BSS Engineering, Inc. suspected the

inaccurate data were due to electromagnetic interference caused by the electromagnetic

shaker because of its proximity to the wire circuit [4].

1.3 Methodology

This study attempted to build on the work of the previous design team who examined

this problem. In particular, three tasks were given a great deal of attention:

• Redesigning and validating the age analysis laboratory setup

3

• Enhancing the thermal wire aging technique and setup

• Searching for qualitative evidence that the triboelectric response of a wire

deteriorates with age by analyzing previously aged wires.

Previous design teams, notably BSS Engineering, Inc. (fall 2002), reported that the

current age analysis laboratory setup was not capable of consistently reproducing a

characteristic triboelectric response from a nominal piece of wire [4]. Without the

capability to reproduce nominal results in a controlled test setup, the testing of actual

aged wire specimens was of no real value. Thus, it was important for Woolrich

Engineering to first modify and validate the laboratory analysis setup before attempting

to generate any triboelectric response data.

Another difficulty encountered by previous design teams involved the thermal

aging techniques employed to deteriorate the wires’ insulation. Past thermal aging

techniques involved placing wires in an environmental chamber in Ernest Cockrell, Jr.

Hall, which is under the administration of the Civil Engineering Department at the

University of Texas at Austin. This technique proved to be ineffective, however, because

ongoing civil engineering experiments that also resided in the chamber required a

constant temperature of 120°F [4]. Such a temperature is well within the operating range

of the wire insulation, and, therefore, did little to deteriorate the insulation over the 7 ½

week duration of the study. In order to more effectively thermally age the wire

specimens, Woolrich Engineering decided it was necessary to obtain our own equipment.

This removed the constraints that kept the previous design team from successfully

thermally aging their wire specimens.

Because of difficulties in obtaining our own equipment, Woolrich Engineering

did not age wires in the lab, though we did spend a great deal of time creating a new

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aging process. The technique Woolrich Engineering planned to use to thermally age

wires was a thermal cycling process. Wire specimens were to be placed in the

environmental chamber and subjected to a temperature of 170°F. After 24 hours of heat,

the specimens were to be removed from the chamber and placed in a freezer for 24 hours.

The cycle then repeated for the duration of the study. Other aging techniques that were to

be employed by Woolrich Engineering were identical to those employed by BSS

Engineering, Inc., namely one set of wire specimens was to be soaked in saltwater, and

another set was to be soaked in Jet-A fuel.

Finally, Woolrich Engineering decided it would be desirable to use wire that had

seen years of service in actual aircraft to search for qualitative evidence that the

triboelectric response of a wire changes as the wire ages. The limited amount of time in

which this study was to be conducted meant that it would be possible to age wire

specimens by only a small amount. The controlled aging techniques, however, would

allow Woolrich Engineering to search for a quantitative trend that defines the change in

the triboelectric response of a wire with time. Since this result was not at all apparent at

the start of our work, it was deemed prudent to collect documented wires of various ages

from an aviation scrap yard and analyze their triboelectric responses to see if a qualitative

trend could indeed be observed.

1.4 Report Overview

This report presents the theory behind the triboelectric effect that motivated this

study. The results of previous design teams, and their effects on current undertakings, are

also discussed. All modifications to the previous laboratory analysis setup and aging

techniques are noted in detail. The report culminates with the results and conclusions

5

arrived at by Woolrich Engineering. Finally, recommendations for further investigations

into wire age analysis are presented.

6

2.0 Technical Background

2.1 Types of Wire Failures

When wires deteriorate, the insulation can begin to chafe and crack. This may be

a result of prolonged exposure to harsh temperature, humidity, corrosion, and/or vibration.

Kapton (see Introduction) appears to be particularly vulnerable to this. When the

insulation chafes and cracks, the risk of electrical fires increases. Also, chafed and

cracked wire insulation can cause control malfunctions. By far, the most dangerous wire

failure is a phenomenon called arcing, in which “an exposed wire comes in contact with

[another] metal object, [typically] the frame of [the] aircraft or another exposed wire, to

create a short circuit" [4]. When this happens, it creates large amounts of heat, which

can ignite the insulation. The fire can then travel down the wire consuming more

insulation and exposing more wire. Obviously, any system in which this occurs will fail.

Worse yet, the effect can potentially spread to other systems, causing them to fail as well.

"Other less significant electrical system problems involve open circuits, bolted short

circuits, intermittent open circuits, and degraded shielding. Nevertheless, even these

minor failures could prove to be catastrophic, should they occur on critical systems" [4].

2.2 Current Methods Used to Detect Faulty Wiring

Unfortunately, there is currently no widely accepted, widely available method for

detecting faulty wiring. However, some industry experts believe the triboelectric

response may be usable to determine the condition of a wire.

7

3.0 Theory

The theory describing the triboelectric effect is presented in this section, as well

as a project-specific discussion of the effect, the theory behind signal response, and a

brief summary of some finite statistics utilized in this report.

3.1 Triboelectric Effect

The triboelectric effect is more commonly known as static electricity. It occurs

when two materials slide against each other. In the case of electrical wiring, the two

materials are the insulating and conducting materials of a wire. As seen in the figure

below, a frictional force from the two materials sliding against each other causes

electrons from one material to separate and reattach themselves to the second material.

This creates a charge imbalance between the two surfaces, and the current induced from

this imbalance creates unwanted noise and interference. To a certain extent, this is

unavoidable in a signal.

Figure 2: Relative movement between insulating and conducting surfaces induces a

current [5]

8

The magnitude of the triboelectric effect is dependent upon numerous factors, such as:

• material composition

• the humidity to which the material is exposed

• the strength of the frictional forces

• the rate at which the electrons separate from one material and reattach themselves

to the other

A general equation for the current induced between two materials is [6]:

DMQC

DkMvi

n

+= (3.1)

where

k = proportionality constant, which is unique to the material M = mass flow rate D = average particle diameter v = particle velocity n = exponent, which is unique to the material Q = charge on contacting particles i = triboelectric signal C = proportionality constant

The relationship given in this equation may be applicable to a straightforward situation,

such as a single particle running along a surface, but is difficult to apply to more

complicated problems, such as quantifying the aged state of a wire with electrical current.

Because these factors will change with the age of the wire, Woolrich Engineering did not

find it necessary to attempt to quantify each parameter. However, it was still expected to

find a relationship between the state of the wire and its triboelectric response.

3.2 Triboelectric Effect: A Project-Specific Analysis

Exhaustive analysis of the mechanics behind the triboelectric effect in a wire have

led Woolrich Engineering to model the excited conductor/insulator interface in a wire as

9

an AC voltage source. The shaker transfers kinetic energy into the wire system, a portion

of which is transmitted to the conductor/insulator interface as friction. A rough

approximation of this friction energy can be derived from analyzing the work done by the

insulation as it moves past the conductor a length dx , as illustrated in Figure 3.

Figure 3: Wire/Electromagnetic Shaker System

The force normal to the surface of the conductor is equal to some function of the hoop

stress applied by the insulation, multiplied by the surface area of the conductor. The

force of friction is then given by multiplying the normal force by the coefficient of

kinetic friction. Then the frictional force multiplied by the relative axial displacement of

the two objects, dx , gives the energy imparted on the system by friction. This result is

summarized by the following equation:

(3.2)

dx

Shaker

Wire

V

L

R

( )( ) dxrLfE khoop µπσ 2=

10

This energy input causes electrons to be stripped from both the insulation and the

conductor. Much like a redox reaction, one of the materials loses electrons at a faster rate

than the other given the same rate of energy input [7]. This idea is illustrated by Figure 4,

where the magnesium electrode is clearly more negative than the copper electrode.

Figure 4: Differences in Redox Reaction Rates Can Create an Electric Potential Between Two Materials [8]

Thus, there is a net movement of electrons from one material to the other. This will

either create a surplus or a dearth of negative charge in a localized area of the conductor.

Since the charge has remained the same in the parts of the conductor that are not

experiencing vibration, an electric potential now exists along the conductor. This will in

turn induce a current. As the motion resulting from the shaker changes direction, the rate

of energy addition into the system decreases, and the potential between the insulation and

the conductor can no longer be maintained. The local equilibrium is reestablished,

creating an electric potential in the conductor that is opposite in polarity from the original

potential. This causes current to be induced in the opposite direction, thus creating

alternating current.

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Based on the above discussion and the friction energy equation derived earlier, it

was expected that the amplitude of the voltage induced as a result of the triboelectric

effect would vary with the coefficient of kinetic friction, and the rate at which each

material loses electrons, given a specified rate of energy addition ( insulationR and conductorR ).

Thus

(3.3)

Woolrich Engineering believed that the material constants in the above equation

would change in a predictable manner as a wire ages, and so the voltage should also vary

with the age of the wire. Woolrich Engineering hoped to find an empirical formula that

described this variation in the voltage produced through the triboelectric effect as a

function of a wire’s age/physical condition.

3.3 Frequency Response

Frequency response is a system’s response characteristics to a wide range of input

frequencies and it is usually discussed in terms of gain and phase. The general transfer

function of the system is expressed as [6]

)()(

)( 0

fGfG

fHi

= (3.4)

where

H(f) = system transfer function )(0 fG = frequency spectrum of the output signal )( fGi = frequency spectrum of the input signal

( )

= conductorinsulation

k RRdt

dEVV ,,µ

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There are two methods for analyzing the frequency response of a system:

• A single frequency signal is applied to the system and the amplitude of the

resulting output is measured. To determine the gain of the system, which is the

ratio of output and input amplitudes, this process is repeated for a range of

frequencies.

• A random noise signal is applied to the system and its instantaneous response is

measured. This is performed in order to simultaneously test all frequencies in

question. For this method, the frequency response is the ratio of the cross

spectrum and the autospectrum of the input [6].

3.4 Statistical Sampling

When taking measurements of a dynamical system, one must realize that it is

often impossible to account for every noise that might convolute said measurements. In

order to get a better idea of the true value of such a measurement, it is usually necessary

to take a number of measurements that, when analyzed together, give a better description

of the phenomenon under examination. The following summary of some basic finite

statistics was paraphrased from [8]. The sample mean,

(3.5)

calculated from N measurements of the same phenomenon, provides the “most probable

estimate of the true mean value, 'x ” [8]. The sample variance,

∑=

=N

iix

Nx

1

1

13

(3.6)

yields information about the precision of the measurement. The interval, with respect to

the sample mean, in which the true mean value of a measurement lies can be determined,

with %P accuracy, to be

(3.7)

where Pt ,υ is the t-estimator, and 1−= Nυ denotes the degrees of freedom of the

measurement system. Consequently, one can represent the true mean value of a

measurement as

(3.8)

In this study, each wire was measured 15 times, which yields a t-estimator value of 2.977

if P = 99% accuracy is desired [8].

( )∑=

−−

=N

iix xx

NS

1

22

11

2/1, NSt x

Pυ±

2/1,'

NStxx x

Pυ±=

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4.0 Laboratory Specimen

To provide some constancy with the previous work done on this project, Woolrich

Engineering decided to continue to work with ALPHA Wire 1632. This wire has rubber

insulation and was initially suggested to previous teams by Frank Wise, the department

electrician, as a type of wire that might deteriorate quickly. It was also decided to cut this

wire into segments of the sized used by BSS Engineering, Inc. Woolrich Engineering

purchased red wire to help distinguish the newer wire from the black wire used in fall

2002.

In addition, Dr. Stearman suggested that Woolrich Engineering test a wire with

Teflon insulation, as it is a more common insulator in industry. Teflon is tougher than

rubber and is more resistant to corrosion and temperature extremes. Also, it has a much

lower coefficient of friction, and, therefore, presumably, has a less pronounced

triboelectric effect [9]. ALPHA Wire 5852 was selected for its low price, Teflon coating,

and because its other characteristics seemed to be average. In order to compare this to

the Alpha Wire 1632, a smaller diameter, higher gauge, was chosen for the Teflon wire,

based on the fact that a narrower wire has a greater surface area to volume ratio.

Woolrich Engineering was confident that this would make it more susceptible to

corrosion than a similar, thicker wire. In addition, Woolrich Engineering predicted that

its high surface area to volume ratio would cause it to have a more pronounced

triboelectric effect than a similar, thicker wire. Although we have been unable to find

literature to either support or refute this theory. Also, a narrow wire has the added benefit

of being less expensive. This allowed the team to make longer segments of wire, which

were believed to be beneficial. It stands to reason that shaking a long section of wire

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would generate more current than shaking a small section of wire. Spools of these wires

can be seen in Figure 5 below.

ALPHA 1632 ALPHA 5852

Figure 5: Alpha Wire Spools

Some additional specifications for the wires Woolrich Engineering used are presented in

Table 1.

Table 1: Wire Specifications [10]

Alpha Wire 1632

• Hook-Up wire, Test Lead wire • 20 Gauge (thick) • Stranded, Tinned Copper • Rubber Insulation • -30o to 90o C

Alpha Wire 5852 • Hook-Up wire • 28 Gauge (thin) • Stranded, Silver-plated Copper • Teflon insulation • -60o to 105o C • Low Friction • High Chemical Resistances

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5.0 Laboratory Aging

The following is a description of the aging process Woolrich Engineering created

and had hoped to employ. Because Woolrich Engineering was not able to obtain the

proper aging equipment during the work period this semester, no wires were actually

aged using this proposed process.

5.1 Data Collection Cycle

In order to improve the size of the aged wire data sets, the Woolrich Engineering

team deemed it necessary to restructure the data collection procedures. BSS Engineering,

Inc. was limited to collecting one point of data at any given time during the aging

processes, because of their collection methodology. They began aging all their wire

segments at the same time. Then, periodically, they would remove one sample at a time

from each aging process, test it, mark it, and not return it to the aging process afterwards

[4]. In order to avoid such limitations, Woolrich Engineering instead proposed to

remove every sample simultaneously at every collection time. All the samples would be

tested, and then returned to the aging process afterwards to perpetuate the study. In this

way, data yield at a given time would be increased ten fold as there would be ten wire

samples for each aging process.

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Figure 6: Data Collection Cycle Comparison

In addition to increasing the size, and thus the robustness, of the data sets, there

would have been other side effects of this new method. One positive side effect would

have been that, because the samples would always have been returned after testing, a set

date would not have been required for the end of the aging process. Thus, the team that

will continue this project in the summer of 2003 would have been able to continue further

aging of the same samples immediately should they have chosen to do so. A negative

side effect would have been the loss of the ability to retest data at a later date. Because

the samples would have been effectively recycled, there wouldn’t have been a way to

recheck the previous conditions of the samples once they were returned to the aging

process. Should a problem in the testing have been discovered later, it would have been

impossible to correct. Thus, if this technique is used in the future, great care must be

taken to make sure that the samples are evaluated correctly before aging is resumed.

Also, due to the extra burden of testing so many samples at once, Woolrich Engineering

proposed taking data every week or every other week rather than every half-week, as

BSS Engineering, Inc. did. In addition, visual inspections would have been impacted by

the new procedures. The previous team stripped the ends of the insulation off the wire

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samples when they were removed from aging [4]. Stripping was necessary to allow the

wire samples to be hooked up to electronics. It also provided visual data of what had

happened to the wire underneath the insulation. If the samples were to be repeatedly used,

they would need to be stripped from the beginning. The exposed ends would have had to

be protected with removable covering of some sort, and would not have been a good

representation of the rest of the wire. However, a simple solution to this problem was

formulated. A group of short wire segments, perhaps only two inches, cut from surplus

wire, were to be added for the sole purpose of providing visual data. These mini-samples

were to be removed one at a time, partially stripped, tagged, and preserved for side by

side comparison. After considering the possible ramifications, it was decided that the

benefits of the new data collection procedures outweighed their trade-offs.

5.2 Aging Processes

The aging processes Woolrich Engineering proposed to explore this semester fell

into two general categories: temperature plus humidity; and corrosion. The previous

team performed temperature and humidity processes separately. They were unable to

realize the desired results from heat alone, but attributed this to an inability to achieve

adequate heat due to facility restrictions [4]. By acquiring its own equipment, the

Woolrich Engineering team had hoped to reach higher temperatures. The team also

decided to examine the effects of cold temperatures. Coincidentally, both TWA 800 and

Swiss Air 111, probably victims of wire failure, flew in cold conditions [4]. Furthermore,

the team firmly believed in the potential of cycling back and forth between temperature

extremes. Although the previous team found only minimal results from humidity alone,

Woolrich Engineering believed the presence of moisture would be an important

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component of the temperature plus humidity aging processes, especially when cycling

between hot and cold. Adding water would generate periods of freezing and thawing

which would apply mechanical aging on a microscopic level.

The corrosion aging processes would simply involve exposing the wire samples to

corrosive solutions by means of soaking. The two corrosives to be used were the same as

those used by the previous team: Jet-A fuel and salt-water solution. The previous team

found that both corrosives yielded some results. The saltwater solution had corroded the

conductor and fused the strands together. Also, the wire exposed to saltwater became

noticeably more brittle.

Figure 7: Aged Wire Samples [4]

The Jet-A fuel had a definite visible effect on the rubber alpha wire, particularly in

significant swelling of the insulation [4].

The disconcerting potential side effect from using corrosive soaks, is the extent to

which any residue that might be left behind might alter the triboelectric response. To

illustrate this concern, consider that, to reduce the triboelectric effect, some wires are sold

with graphite lubricant in between the insulator and the conductor. The graphite serves to

reduce friction and therefore reduce the triboelectric effect [10]. Thus, the presence of

another form of matter can alter the triboelectric effect without altering the age and

condition of the wire. Therefore, it may be possible that salt deposits or residual Jet-A

20

fuel, could upset the data. One solution would be to remove the foreign material before

testing. Salt could probably be partially removed by a brief, fresh water wash or soak.

Jet-A fuel residue might be more challenging to deal with. Fortunately, if residue does

have a significant effect, we believe it should affect the data consistently. Thus, if

residue is important, the initial application would result in a dramatic change, and then a

constant, unchanging affect.

In addition, Woolrich Engineering planned on having a group of wires that cycle

through all the different tests. The team also considered the possibility of having groups

of wires that were under tension while aging. In an email to the previous team, Ronald

Galvez of the NASA Integrated Wire group mentioned that wires under tension tend to

age more quickly [11].

Though vibration was specifically mentioned as a potential cause of wire

deterioration, it was not considered for use in the above age processes because its effects

were deemed too difficult to accelerate.

5.3 Aging Equipment

Certain equipment was necessary to age the wires. The corrosive tests merely

required the corrosive agent, and a large enough bucket. Temperature and humidity tests,

however, required a more elaborate setup.

Several options were examined for a heating element. Commercial, kitchen ovens

were eliminated because one could not be found that was rated safe for continuous use.

Drying ovens were quickly ruled out because they are designed to remove humidity.

After a good deal of searching, incubators were also ruled out initially, because one could

not be found with sufficient heating abilities. Thus, Woolrich Engineering began to

21

consider environmental chambers. The environmental chambers showed some promise.

They were capable of both hot and cold temperatures beyond the team’s needs. Many

could control humidity, and several were programmable. Programmability would be

particularly nice as it would allow the temperature cycling to be automated and, thus,

more frequent. Finding adequate information on the specifications and prices of

environmental chambers was difficult, and could only be accomplished with calls to

companies. Unfortunately, Woolrich Engineering could not find a model within the

project’s reduced budget. Two units were found for about $7,000, but these were

refurbished, and only came with a three to four month warranty. Even these were too

expensive. The UT surplus on Pickle campus was contacted, but they had had auctions a

few weeks earlier, and did not have any useful equipment on hand.

Fortunately, Dr. Stearman discovered that the Zoology department had an old

incubator and an old freezer (Figure 8) that they no longer had a use for. He was able to

secure this equipment for Woolrich Engineering free of charge. Furthermore, it was his

understanding that the incubator, a Labline model, was capable of generating the levels of

heat desired. Once the freezer, formerly used to store dead animals, is cleaned by the

university, and a Labline technician can come out to inspect the incubator, the Aerospace

Department will be able to take possession of the equipment.

22

Figure 8: Freezer Donated by UT-Austin Zoology Department

The freezer was not designed to control humidity; thus, something must be done

to retain moisture during the cold treatment. The most likely option is placing the wires

in small, sealed containers. Also, if wires are to be placed under tension during aging,

some type of apparatus, perhaps a rack, will be needed for that purpose.

5.4 Anticipated Results

It was expected that, as the wire deteriorates, its material properties will change.

As the insulation loses its elasticity and corrodes, its texture, friction characteristics,

impedance, and/or ability to retain or absorb charge may change. In addition, the

conductor may corrode or develop cracks, and its material properties could, therefore,

change as well. It was expected that these changes would result in trends in the wires’

triboelectric responses.

23

6.0 Age Analysis

Though attempts to assemble a quality laboratory wire aging setup didn’t quite

come to fruition, Woolrich Engineering was able to analyze several wire samples aged

during previous studies. Additionally, some rudimentary aging was conducted by heating

wires in a conventional oven. The testing results, though inconclusive on the question of

how a wire’s triboelectric response varies with age, provided valuable information on the

nature of the test setup itself.

6.1 Experimental Setup

The experimental setup had four major components: signal analyzer/computer,

data acquisition system, signal amplifier, and electromagnetic shaker. The latter three

components are pictured in Fig. 9. Everything was connected in the manner utilized by

the previous wiring team.

Figure 9: Signal Analyzer, Amplifier, and Shaker [4]

24

6.1.1 Signal Analyzer/Computer

A Dell computer controlled the entire experiment through the software interface

provided by Hewlett Packard (HP) to operate the data acquisition system. The HP

program was used to generate a known harmonic signal to excite the wire. The electric

response from the wire was then acquired by the program, plotted, and analyzed.

Specifically, the wires were subjected to a sinusoidal signal with a frequency of 1kHz and

an amplitude of approximately 100mV. Testing each wire with the same excitation

signal enabled Woolrich Engineering to determine the effect of a wire’s physical

condition on its triboelectric response at a given frequency. That is, the manner in which

a wire’s triboelectric response varies as the wire deteriorates.

It is worthy to note that Woolrich Engineering had initially intended to utilize the

IDEAS program as the test setup’s computer interface. It is a more elaborate program

than the Hewlett Packard program that was actually used, and supposedly has better data

file exporting capabilities. The IDEAS program was sidelined, however, when Woolrich

Engineering discovered a problem in the program that prevented it from actually

acquiring data from the data acquisition system. Initial attempts to contact MTS Systems

Corporation to rectify the situation were abandoned when the testing team was notified

that a newer version of IDEAS was soon to be installed on the lab’s computer.

6.1.2 Data Acquisition System

The Hewlett Packard 3566A/67A Data Acquisition System served as the interface

between the computer and the wire/electromagnetic shaker setup. The device was

necessary to convert the digital signal that the computer generated to the analog signal

that was needed to operate the electromagnetic shaker. Additionally, the analog signal

25

generated by the triboelectric response of the wire needed to be converted into a digital

format before it was sent to the computer.

6.1.3 Amplifier

The analog signal outputted by the data acquisition system was not powerful

enough to operate the electromagnetic shaker. Thus, the signal needed to travel through a

MB Electronics 125V Power Amplifier. Following the precedent set forth by the

previous team, the amount of amplification was kept constant (setting 1 on the amplifier)

and all changes in the amplitude of the excitation signal were made via the computer

interface [4].

6.1.4 Electromagnetic Shaker

The electromagnetic shaker was powered directly by the signal output from the

power amplifier. It vibrated in the axial direction according to the amplitude and

frequency specified in the computer interface. A stinger was used to protect the shaker

by indirectly connecting it to the chessboard that held the wire specimen under

examination. Should the motion of the system have approached the safety limits of the

shaker, the stinger would’ve fail before the shaker was harmed. The initial configuration

of the shaker/stinger/chessboard system is shown in Fig. 10.

26

Figure 10: Shaker/Stinger/Chessboard System [4]

The shaker was initially arranged, and the repeatability properties of the test

system verified, in the vertical direction as depicted in Fig. 10. However, after concern

arose about the transverse motion of the chessboard atop the stinger, the entire setup was

repositioned in a horizontal direction, and the chessboard was bolted to a stabilizing

platform that only allowed motion in said direction. Though it was unclear whether or

not this change resulted in a significant reduction of the noise seen in the responses

generated by the wires, it did reduce their magnitudes. Woolrich Engineering

hypothesized that magnitude reduction was due to the fact that gravity no longer acted to

hold the wires against the chessboard, so the percentage of the shaker’s signal that was

transferred from the chessboard to the wires decreased with the move to a horizontal

setup.

6.1.5 Electromagnetic Interference (EMI) Reduction

Results from the previous team suggested that electromagnetic interference (EMI)

may have originated from and influenced the various components of their test setup [4].

27

It is believed that this interference generated a large amount of noise that was erroneously

incorporated into the response signal from a wire. Such an effect would help to explain

why the team was not able to reproduce a response from a single wire specimen with any

acceptable degree of accuracy. Consequently, several methods for reducing EMI in the

laboratory area were utilized for this study.

Before any testing took place, the data acquisition system and the power

amplifier were separated in order to limit the effect an electromagnetic field generated by

one unit might have on the other. During the aforementioned study, these two units were

located one on top of the other. The shaker was also isolated as much as possible from

the other test components.

Initial testing indicated that the orientation of the wire under examination with

respect to the chessboard (which remained fixed) had a significant effect on the

magnitude of the wire’s measured response. In an effort to eliminate this undesirable

variable, plastic tabs were purchased and placed at various positions on the chessboard in

order to insure that all wires placed on the chessboard would have a fairly uniform

geometry. These tabs are visible on the chessboard in Fig. 11.

Figure 11: Plastic Tabs Holding a Wire in Place on the Chessboard

28

A significant drop in the scatter of the measured response of a particular wire was

witnessed after the tabs were installed.

After some considerable testing had been conducted, the shaker and chessboard

were placed inside separate grounded foil enclosures as a means of shielding the wire

being examined from EMI (depicted in Fig. 12).

Figure 12: Shaker and Chessboard Shielded with Grounded Foil

This was suggested by many sources, including the Alpha Company, which provided the

wire that was used for this study [12]. The grounded foil shielding had an enormous

effect on the measured responses of the wires. Electromagnetic interference accounted

for nearly all of the magnitude of the responses measured prior to installing the shielding.

Responses to the 1kHz, 100mV excitation signal fell from the 2-8 mV range to the 20-40

µV range.

Realizing the need for a sturdier shielded test setup, Woolrich Engineering

concluded that the wire under examination should be placed inside a grounded section of

metal pipe. The pipe could then be connected to the shaker, providing a straight and rigid

29

platform via which the wire could be both vibrated and shielded from EMI. This

apparatus was constructed, but Woolrich Engineering lacked sufficient time to

incorporate it into the test setup.

6.2 Review of Previous Results

BSS Engineering, Inc was the previous group that was assigned the task of testing

aged wire to determine whether or not the triboelectric response of the wire varied with

age. They aged wires in saltwater, humidity, and Jet-A fuel, among other things, and

some of their results are presented in Table 2.

Table 2: BSS Engineering, Inc. Testing Results [4]

The data presented for the five tests of both Nominal wires 1 & 2 appears very random,

and there doesn’t seem to be any correlation between the amount of time a wire was aged

in a humid environment and its triboelectric response. Based on these results, BSS

Engineering concluded that their data was too random to be of any value. They attributed

this randomness, in large part, to electromagnetic interference (EMI).

Wire Response to 1KHz, 100mV sinusoid input (mV)

Nominal 1 2.116 0.142 0.677 0.131 1.928

Nominal 2 0.738 0.145 2.355 0.222 0.432

Humidity 1 (3.5 days)

1.970

Humidity 5 (17.5 days)

2.063

Humidity 10 (35 days)

1.720

30

6.3 Anticipated Results

Woolrich Engineering, while reviewing BSS Engineering’s final report, decided

to investigate whether or not some valuable information might actually be extracted from

a test setup that appeared to generate such random data. Woolrich engineers

hypothesized that the seemingly random data generated by the test setup (which had not

yet been shielded with grounded foil) actually behaved like a random variable with a

fixed mean and a Gaussian distribution about that mean. The large difference between

consecutive measurements could then be attributed to a large variance. If this were true,

then even though the measurements were very noisy, it might be possible to see trends in

the sample mean and/or sample variance of the triboelectric response of a wire as it

deteriorated with age.

This line of thinking was further buoyed by the idea that, although EMI could

make up a large part of the measured response of each wire, it should be a constant part.

This would mean that, despite the fact that the magnitude of a wire’s triboelectric

response could not be determined, any change seen in its measured response could be

largely attributed to a change in its triboelectric response. The assumption of the

constancy of the EMI in the measured response arose from the fact that most of the EMI

that the wire being tested saw originated from the shaker, which always operated at the

same frequency and amplitude. Additionally, every wire had the same geometry with

respect to the shaker, so they should all have received the EMI originating from shaker in

the same manner.

Each wire specimen of interest was tested 15 times in order to generate a pool of

data from which to calculated the wire’s sample statistics. This approach was used to

31

verify the consistency of the test setup, as well as to look for trends in a wire’s

triboelectric response as the wire aged.

32

7.0 Results

In contrast to the first half of this study, which was focused on research and

design, the last half was oriented toward verifying the test setup and generating results.

A few items were also acquired.

7.1 Acquisitions

Woolrich Engineering, with the assistance of Dr. R. O. Stearman, acquired a

freezer and an incubator (capable of varying heat and humidity) free of charge from the

Zoology Department at the University of Texas at Austin. However, these units are not

yet ready to be used for the purpose of aging wire specimens. The freezer was used to

hold biological specimens, and so must be sterilized and inspected by University

authorities. The incubator must be inspected by a technician from Labline (the

incubator’s manufacturer) before it is put back into service.

Additional purchases included foil for use in the construction of shielded

enclosures for the various laboratory devices used in the age analysis test setup. Metal

pipe was obtained for the construction of the wire testing/shielding enclosure. Also,

several spools of Alpha Wire were purchased for aging and testing, as specified in section

4.0 of this report.

7.2 Laboratory Aging

Although much of the necessary laboratory equipment was acquired, as

mentioned above, it was never certified for use. As a result, the only wires that were

aged were subjected to temperatures between 300°F and 400°F in a conventional oven for

33

various amounts of time. Though this method did significantly age the five wires that

were subjected to it, the actual aging process was not very scientific. Both the aging time

and the temperature were varied during this process, meaning only qualitative

observations could be taken from the data generated from the wires in question.

7.3 Test Setup Repeatability/Verification

Verifying the test setup’s ability to consistently reproduce the same result when

testing identical wires under identical operating conditions was a priority during this

study. In order to do this, three Alpha Wire 1632 segments of about 2.5 ft were cut from

different spools and tested 15 times each. The test setup was not yet shielded with

grounded foil and was oriented vertically. The plastic tabs had been installed to insure

each wire would have the same orientation relative to the rest of the test setup. In

between each of the 15 tests for a wire, the wire was removed from the chessboard and

replaced. This was done so that any differences in orientation that may still have existed

due to bends in the wires, orientation of the ends, etc. would be averaged out over the 15

tests. After each wire had undergone its 15 tests, the entire test setup was shutdown and

restarted before testing the next wire. The results, shown in Fig. 13, indicated that the

test setup, even in this unshielded arrangement, was capable of producing fairly

consistent results.

34

8

8.05

8.1

8.15

8.2

8.25

8.3

8.35

0 1 2 3 4

Nominal Wire Number

Mea

n R

espo

nse

Am

plitu

de (m

V)

Figure 13: Sample Mean Responses for Three Nominal Alpha Wire 1632 Specimens

The error bars in Fig. 13 are just the precision intervals in which the

measurement’s true mean must lie. They are further defined in section 3.4 of this report.

By examining these error bars, one can see that there is a good probability that the true

mean response of each of the three wires coincides with a reasonable degree of accuracy.

7.4 Aged Wire Tests

After the tests setup’s ability to produce consistent results had been verified,

Woolrich Engineering began to retest wire specimens that had been aged by BSS

Engineering, Inc. in the fall of 2002. Specifically, a few specimens from the wires aged

in saltwater and those aged in Jet-A fuel were examined. Neither examination produced

any statistically significant trends. It is important to note that the test setup had

35

transitioned to its horizontal position (but was not yet shielded) by the time this testing

occurred, which would account for the difference in response amplitudes between Fig. 13

and Figs. 14-15. The results from the tests of the wires aged in Jet-A fuel are shown in

Fig. 14.

2.54

2.56

2.58

2.6

2.62

2.64

2.66

2.68

2.7

2.72

0 2 4 6 8 10 12

Wire Aging Sequence

Mea

n R

espo

nse

Am

plitu

de (m

V)

Figure 14: Sample Mean Responses of Two Wires Aged for Different Periods of Time in Jet-A Fuel

The two wires examined in this case were the first and last wires to be removed from the

Jet-A fuel. These wires should have shown the largest discrepancy between their

measured responses, yet the difference shown in Fig. 14 is not statistically significant.

After examining the error bars defining the precision intervals, one realizes that there’s a

greater chance that the true mean responses of the two wires coincide than there is that a

trend exists. Due to this result, no intermediately-aged wires were tested.

36

The five wires aged in a conventional oven by Woolrich Engineering appeared to

be considerably more deteriorated than the wires aged in Jet-A fuel or saltwater. A

glance at Fig. 15 shows that these five wires also provide more indication that an age-

dependent trend might actually exist than anything tested previously by groups working

on this project.

2.3

2.35

2.4

2.45

2.5

2.55

2.6

2.65

2.7

0 1 2 3 4 5 6

Wi r e A gi ng S e que nc e

Figure 15: Sample Mean Responses of Five Oven-Aged Alpha Wire 1632 Specimens

Four of the five wires appear to indicate that a wire’s triboelectric response decreases

with age. Wire #3, however, is an outlier that cannot be ignored in such a small data set.

As such, this part of the study must be deemed inconclusive. More data points would be

needed to state with any confidence that such an age-dependent trend does indeed exist.

37

7.5 Important Discoveries

Towards the end of the project, a couple of important discoveries were made by

Woolrich Engineering. The first discovery occurred when the horizontally-oriented test

setup was shielded with grounded foil. The shielding was extremely effective, as it

eliminated nearly all of the electromagnetic interference (EMI) present in a wire’s

measured response to the shaker’s input. This lead to the realization that the wire

responses that had been measured previously were almost entirely dominated by EMI.

The response signal dropped from a strength of 2-8 mV to one of 20-40 µV. This result

didn’t necessarily invalidate the ideas put forth in section 6.3 of this report concerning a

constant EMI signal. However, it does appear like it would be a good idea to verify the

results of sections 7.3-4 with the grounded foil shielding in place.

The second discovery came about as a result of the first. When the shielding was

first install, the measured response signal appeared to be unaffected by whether or not the

shaker was turned on or off. Noise was all that could be detected. Consequently, another

coaxial cable was strung between the data acquisition system and the shaker/chessboard

setup. When this new coaxial wire was used to measure the response of the wire under

examination, the response showed much less background noise and a peak at the

excitation frequency. This meant that the initial coaxial cable that was used to generate

the data presented in sections 7.3-4 was partially bad. It appeared that the cable added

noise to the signal that was in the microvolt range. This would have had the effect of

artificially inflating the variance of the data presented in the aforementioned sections.

The last discovery concerned the triboelectric response of a bare wire.

Specifically, the fact that it didn’t have a response because there was no insulation for the

conductor to rub against. Thus, a bare wire was used to verify the presence and

38

approximate magnitude of the triboelectric response of a segment of Alpha Wire 1632 to

the input specified in section 6.1.1 of this report. This is illustrated by the following

sequence of screen shots of the Hewlett Packard signal analyzer software:

Figure 16: Measured Background Noise without a Wire Attached (No Shaker

Excitation)

Figure 16 shows the background noise picked up by the good coaxial cable in the vicinity

of the chessboard when no wire was attached to it and the shaker was off. The noise

generally ranged from 0-5 µV. The vertical white trace indicates the 1 kHz excitation

frequency, which is the frequency of interest when viewing these screen shots. The value

39

of the 1 kHz response signal, which was transient, is shown at the bottom of Fig. 16 as

the Y variable.

Figure 17: Measured Background Noise with a Wire Attached (No Shaker

Excitation)

In Fig. 17, a wire has been attached to the coaxial cable, and is acting as an antennae.

The transient noise has increased in magnitude to between 0 and 10 µV, and the response

signal at 1 kHz generally ranged from 3-8 µV. The shaker was still off.

40

Figure 18: Measured Response of a Bare Wire (Shaker Turned On)

Now the shaker has been turned on at 1 kHz and bare wire has been place on the

chessboard and attached to the coaxial cable. A triboelectric response was not expected

and did not ocurr, which is apparent in Fig. 18. The noise was at approximately the same

level as that depicted in Fig. 17, and response value at 1 kHz remained virtually

unchanged.

41

Figure 19: Measured Response of an Insulated Wire (Shaker Turned On)

Finally, Fig. 19 depicts the measured response of an insulated wire with the shaker turned

on. Though the background noise was at the same level as that shown in Fig. 18, there

was a clear peak a 1 kHz that could only be attributed to the triboelectric response

generated by the insulation on the wire under examination. This response was transient,

and was observed to range between 20 and 40 µV.

42

8.0 Recommendations

Though Woolrich Engineering was unable to verify any age-related trends in a

wire’s triboelectric response, the team did formulate several suggestions that might aid

future groups in this endeavor.

8.1 Laboratory Aging Equipment

Although a freezer and an incubator were obtained by Woolrich Engineering for

use in aging wire specimens, neither was ever brought back into safe operating condition.

The freezer needs to be inspected by University of Texas at Austin safety officials,

cleaned, and partially painted. The incubator must be inspected by a technician from

Labline (the manufacturer) before it is brought back into service.

8.2 Electromagnetic Interference (EMI) Shielding

The grounded foil enclosures that shield the wire under examination from the

EMI generated by the shaker were hastily constructed. As such, the quality of the

structures is lacking. With little effort, these enclosures could be redesigned so that they

are more robust and do a better job of completely shielding the test setup. Additionally,

the acquisition of an EMF meter would allow future groups to determine the amount of

EMI that remains inside the grounded foil enclosure that shields the wire/chessboard test

setup.

Woolrich Engineering was unable to find an EMF meter with the desired range in

frequencies that could interface with a computer, so real-time monitoring of EMI was

required during triboelectric testing.

43

8.3 Use of Bare Wires

The Hewlett Packard signal analyzer program described in section 6.1.1 has the

ability to capture a brief time history of multiple measurements and export these histories

to Matlab files. Recalling that the response of the bare wire described in section 7.5 is

essentially identical to that of the insulated wire sans the triboelectric response, it appears

possible to measure both a bare and insulted specimen simultaneously and subtract one

signal from the other to be left with a nearly noiseless triboelectric response. If both

wires are of the same length and oriented in the same direction on the chessboard, then

the EMI induced in them should nearly agree in both phase and magnitude. Thus, a

measurement time history could be captured from both wires, exported to Matlab,

differenced, and a fast fourier transform performed on the resulting signal. The transform

should result in a magnitude vs. frequency plot that is nearly zero everywhere except at 1

kHz, where there should be a peak corresponding to the magnitude of the triboelectric

response.

8.4 Used Aviation Wire

Every effort should be made to acquire some documented used wire from planes

residing in the aviation scrapyard in Lancaster, TX (near Dallas). Some of the planes in

the scrapyard are more than 30 years old, and analyzing the wire found within could

provide valuable qualitative insight into the nature of the age-dependent variation of a

wire’s triboelectric response.

44

9.0 Task Distributions

At the start of our project, Woolrich Engineering elected Robert Beremand as the

project manager. His responsibility included organizing the team and its work, and

making sure all components of the project were implemented. All three members of

Woolrich Engineering contributed equally to the project, though each specialized in one

of two major segments – wire aging and age analysis. These technical areas were divided

so as to increase the proficiency of the work performed by the team. Robert Beremand

was responsible for researching and designing the laboratory aging tests. The design of

the test setup and analysis of the process that were utilized to acquire a signal response

were the responsibility of Chad Hanak and Melissa Straubel. All members of Woolrich

Engineering contributed and participated equally to the project, and all were present

during each of these phases. The Figure below gives a schematic representation of task

distributions.

Project Manager: Robert Beremand

• Research of lab aging • Design of lab aging

processes

Senior Engineer: Melissa Straubel

• Design of test setup for age analysis

Senior Engineer: Chad Hanak

• Analysis of signal response method

Figure 20: Diagram labeling the distribution of tasks

45

10.0 Cost Analysis

The laboratory experiments and tests conducted in the second half of the semester

required a minimal budget. Woolrich Engineering was fortunate to obtain an incubator

from the Zoology Department at no cost. Zoology also donated a freezer, which future

teams will be able to use for cold tests. Obtaining these two pieces of equipment at no

charge greatly reduced Woolrich Engineering’s expenses. The Jet-A fuel and saltwater

solutions to be used for lab aging were left over from previous teams. Also, the

Aerospace Engineering Department at the University of Texas at Austin already

possessed the laboratory equipment necessary for age analysis: a signal analyzer, a data

acquisition system, a wave amplifier, and a shaker.

The only purchase Woolrich Engineering made during the study was that of the

wire itself. One 1000 ft spool of Alpha Wire 5852 was purchased at $120.90. Also, five

100 ft spools of Alpha Wire 1632 were purchased at $36.88 for each spool. The total

cost of purchases, therefore, totaled $305.30.

Woolrich Engineering also obtained foil, cardboard, and metal pipe to construct

the shielding enclosures, but these were all donated items. Therefore, the total cost to

conduct this project was relatively inexpensive.

46

11.0 Conclusion

Significant progress was made in the area of test setup research and design, as

well as in the procurement of necessary materials. The ability of the unshielded test setup

to reproduce reasonably consistent results was verified, and the electromagnetic

interference (EMI) present in the vicinity of the test setup was quantified and largely

eliminated. The presence of a triboelectric effect in an insulated wire was verified, and

its magnitude approximately measured. Processes were developed for isolating and

analyzing a wire’s triboelectric response. These included the statistical approach

suggested in section 6.3 of this report and the bare wire technique for signal isolation

outlined in section 8.3.

Necessary laboratory aging equipment was obtained, but still needs to be

refurbished. The only major item that was not acquired was the used airplane wire from

the aviation scrap yard in Dallas. The results and recommendations of this study should

greatly assist future groups in their attempts to determine how a wire’s triboelectric

response varies with its age/physical condition.

47

12.0 Works Cited

[1] Furse, C. & Haupt, R. (2001). “Down to the Wire.” IEEE Spectrum Online. http://www.spectrum.ieee.org/WEBONLY/publicfeature/feb01/wire.html (25 January 2003).

[2] Stoller, G. “Wired For Trouble.” USA Today. 09 November 1998. pgs 1B-3B. [3] Barr, E. “TWA Flight 800: What Happened to the 747?” Free Republican.com. http://www.freerepublican.com/forum/a3873a5167f9b.htm (3 March 2003). [4] Steinbarger, S., Bryant, D., and Shinagawa, Y. “Identification of Aging Aircraft

Electrical Wiring.” ASE 463Q Final Report. 6 December 2002. pgs 22-38. [5] Stearman, R. (2003). “A Study on the Insitu Identification of the Aging of Aircraft

Electrical Wiring.” (Project Quad-Sheet) University of Texas at Austin. [6] “Frequency Response.” National Instruments.

http://zone.ni.com/devzone/nidzgloss.nsf/ webmain/B5EAD6A10F1950258625686A0078B847?OpenDocument (6 March 2003).

[7] Clark, J. (2002). “An Introduction to Redox Equilibria and Electrode Potentials.”

Chemguide. http://www.chemguide.co.uk/physical/redoxeqia/introduction.html#top (6 March 2003).

[8] Figliola, R. S., and Beasley, D. E. Theory and Design for Mechanical Measurements.

Third Edition. John Wiley & Sons, Inc. New York. 2000. pgs. 121-141. [9] "Hook-Up Wire" Alpha Wire Company. http://www.alphawire.com/pages/pdf/176.pdf (6 March 2003). http://www.alphawire.com/pages/pdf/173.pdf (6 March 2003). [10] "High Resistance Measurements" http://216.239.33.100/search?q=cache:KBNb-

PoWQ8sC:www.keithley.com/kei_assets/downloads/6584.PDF+graphite+wire+triboelectric+friction&hl=en&start=8&ie=UTF-8 (cached in www.google.com, site presently down)

[11] NASA email to wiring group of fall 2002. Located in WRW 202 [12] “Technical Data: Shielding.” Alpha Wire Company.

http://www.alphawire.com/pages/342.cfm (6 March 2003).

48

13.0 Appendix A – Timeline

The following chart documents the timeline of work performed by Woolrich

Engineering over the last four months.

Date Jan. 13 - 31 Feb. 1 - 15 Feb. 16 - 30 Mar. 1 - 15 Mar. 16 - 31 April 1 - 15 April 16 - 30 May 1 - 14Objective Group Meetings Preliminary Presentation Research Write Introduction Introduction Due Continue Research Evaluate Progress Write Mid-semester Report Mid-Semester Presentation Edit Mid-Semester Report Mid-Semester Report Due Continue Research Lab and Age Analysis Setup Data Collection and Analysis Final Report & Presentation Preparation Final Presentation Write Final Report Final Report Due

Note: indicates important dates

49

14.0 Appendix B – Raw Data

This section contains the raw data from the tests that were summarized in section

7.0 of this report.

Figure B.1: Test Setup Repeatability/Verification Data: Vertical, Unshielded Test Setup with a 1 kHz, 100 mV Excitation Signal

Test Number Wire #1 Wire #2 Wire #3

1 8.28077 7.81701 8.20883 2 8.33191 8.17022 8.13221 3 8.2099 8.07357 8.03002 4 8.26521 8.1571 8.14576 5 7.9958 8.2122 8.27704 6 7.98147 8.22263 8.17848 7 8.29096 8.06933 8.07058 8 8.16511 8.25663 8.41046 9 8.10701 8.14717 8.38432

10 8.12298 7.93213 8.09243 11 8.2225 8.44921 8.21667 12 7.99562 8.03029 8.0684 13 8.10623 8.43819 8.36429 14 8.20179 8.07538 8.24302 15 8.21081 8.41833 8.38461

std dev 0.1119683 0.1798712 0.1273786 mean 8.1658713 8.164626 8.213808 Pooled Data mean 8.1814351 std dev 0.1427303 Precision interval = 0.0860653 0.1382594 0.0979106

50

Figure B.2: Previously Aged Wires (Jet-A Fuel): Horizontal, Unshielded Test Setup with a 1 kHz, 100 mV Excitation Signal

Test Number Wire #1a Wire #11a 1 2.64053 2.563192 2.6441 2.717033 2.56821 2.644194 2.63929 2.701295 2.58344 2.627046 2.61701 2.666777 2.58678 2.653188 2.61416 2.544249 2.54758 2.59136

10 2.61635 2.6416711 2.69775 2.5568712 2.78192 2.5483513 2.71132 2.5333314 2.60468 2.6769615 2.74684 2.65301

mean = 2.6399973 2.621232std. dev. = 0.0669355 0.0604418

51

Figure B.3: Oven-Aged Wires (Variable Time and Temperature): Horizontal, Unshielded Test Setup with a 1 kHz, 100 mV Excitation Signal

Test Number Wire #1 16 min. @ 300°F

Wire #2 36 min. @ 300°F

Wire #3 55 min. @ 300°F

Wire #4 55 min. @ 300°F & 25 min. @ 400°F

Wire #5 55 min. @ 300°F & 55 min. @ 400°F

1 2.38263 2.5339 2.43892 2.54029 2.42962 2.52091 2.45061 2.45388 2.49244 2.439653 2.5436 2.40981 2.56753 2.59705 2.351024 2.57911 2.41374 2.52682 2.31025 2.381555 2.62804 2.45966 2.5822 2.32474 2.327536 2.59896 2.47481 2.61736 2.37078 2.326917 2.60784 2.42438 2.61151 2.51469 2.352538 2.60301 2.58256 2.58654 2.57594 2.378969 2.60414 2.41191 2.59439 2.38847 2.33784

10 2.60542 2.43011 2.55746 2.50253 2.3239211 2.61314 2.41976 2.5319 2.51102 2.3151312 2.62493 2.55264 2.63675 2.38172 2.3472413 2.60597 2.4434 2.5523 2.3602 2.3311914 2.63349 2.48305 2.5946 2.42182 2.3344415 2.62741 2.43115 2.5471 2.35549 2.32443

mean = 2.58524 2.4614327 2.5599507 2.443162 2.3534627std. dev. = 0.0640655 0.0545982 0.0557496 0.0945435 0.0381485 precision interval = 0.0492445 0.0419673 0.0428524 0.0726716 0.0293232