htn-123001-0006-draft sma ring clamps test...

HTN-123001-0006 3/28/2002

Shape Memory Alloy Ring Clamps for a Large Compton Imager - Test Report

Eric Ponslet

3/28/2002

Name: Phone & E-Mail Signature:

Main Author: Eric Ponslet 505-661-3000, ext. 15 [email protected]

Approved:

Abstract

Shape memory alloy ring clamps are being considered as a key feature in the assembly of a large Compton imager. Those rings would provide the mechanical clamping force to couple silicon detector trays to cooling tubes. Tests were performed to gain experience with those rings, establish practical assembly techniques, and evaluate their effectiveness in the wide temperature range to be survived by the design. This report summarizes these activities and the test results. The idea was found practical, and a reliable assembly technique was developed. The clamping force achieved with prototype subassemblies fell short of the required levels due primarily to inadequate machining tolerances. It is expected that clamping forces will be sufficient given carefully controlled tolerancing of the mating pieces.

D E S I G N E N G I N E E R I N G

A D V A N C E D C O M P O S I T E A P P L I C A T I O N S

U L T R A - S T A B L E P L A T F O R M S

1 10 E A S T G A T E D R .

L O S A L A M O S , N M 8 7 5 4 4

P H O N E 5 0 5 6 6 1 • 3 0 0 0

F A X 5 0 5 6 6 2 • 5 1 79

W W W . H Y T E C I N C . C O M

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Revision Log

Rev. Date Author(s) Summary of Revisions/Comments - 03/28/01 E. Ponslet Initial release.

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Table of Contents

1. Definitions ............................................................................................................................. 4 2. Introduction ........................................................................................................................... 4 3. Design Concept ...................................................................................................................... 4 4. Required Holding Load.......................................................................................................... 6 5. Purpose of the Tests ............................................................................................................... 7 6. Test Items and Setup.............................................................................................................. 7

6.1 SMA Rings .................................................................................................................................. 7 6.2 Test Samples................................................................................................................................ 8 6.3 Ring Shrinking Technique........................................................................................................... 9 6.4 Friction Release Test Setup....................................................................................................... 10

6.4.1 Room Temperature .............................................................................................................................10 6.4.2 Reduced/Elevated Temperature...........................................................................................................11

7. Results.................................................................................................................................. 13 7.1 General Notes ............................................................................................................................ 13 7.2 Temperature Rise from Resistive Heating of Rings.................................................................. 14 7.3 Room Temperature Tests (Samples #1 to #3) ........................................................................... 15 7.4 Low and Elevated Temperature Tests (Sample #4 and #5) ...................................................... 17

8. Conclusions.......................................................................................................................... 21 8.1 Practical Aspects ....................................................................................................................... 21 8.2 Friction Release Force (measurement technique)...................................................................... 21 8.3 Friction Release Force (value)................................................................................................... 21 8.4 Recommendations for Future Work.......................................................................................... 21

9. References............................................................................................................................ 22 Appendix A. Drawings ............................................................................................................. 23

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1. Definitions • SMA: Shape Memory Alloy, a class of metal alloys that exhibit "shape memory" through

thermally or mechanically induced phase changes. • RT: Room Temperature, nominally 21ºC. • OD: outer diameter. • ID: inner diameter. • LN2: Liquid Nitrogen.

2. Introduction

In earlier work[2,3,4] for the Naval Research Laboratory, HYTEC proposed a design concept for a large Compton imager that relies on SMA ring clamps to assemble the supporting structures of silicon trays to a network of cooling tubes. These ring clamps shrink by about 4% when heated above a transition temperature. That transition is irreversible and can be used to produce very high clamping forces with very lightweight rings.

The SMA rings are an essential feature of the design. They provide low-mass structural connections between substructures and ensure intimate thermal contact between heat dissipating trays and cooling tubes. The design concept is described in detail in [4] and summarized in the following section.

The concept relies on its ability to generate enough friction between trays and cooling tubes to resist design accelerations of 20g. The rings selected are theoretically capable of generating clamping forces many times larger than necessary. However, several practical factors contribute to lower actual clamping forces. These are: dimensional tolerances of the mating features (OD of cooling tubes, ID of clamp blocks, OD of clamp seats, and ID of rings), compliance of the cooling tubes, stiffness of the clamp blocks, and temperature variations.

To demonstrate the feasibility of the concept, a series of tests were planned to directly measure the friction load between a section of cooling tube and a clamp block equipped with two SMA rings. The tests are performed at room temperature and at the upper and lower ends of the survival temperature range for the design (-60ºC and +40ºC).

In addition, the test program was to provide a better understanding of the practical issues with the use of SMA rings and help develop appropriate assembly procedures.

3. Design Concept

The baseline design for a large Compton imager consists of an array of 4 by 4 by 24 individual modules, called trays. Each tray is a self-contained detection module and consists of a "slab" of 4x4 double-sided silicon strip detectors (each nominally 66×66×7mm), edge-bonded together and to a structural and cooling frame made of aluminum alloy. The frame also supports a pair of printed circuit boards with front-end electronics for the top and bottom strip chains. Figure 1 shows a schematic of a tray module.

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thick silicon detectors (4x4), edge-bonded into

"slab" with rigid epoxy corner block with SMA clamp

printed circuit board, bonded to frame with

conductive tape

structural/thermal frame

power and data

connectors

frame side plate (aluminum)

shape memory alloy (SMA) ring clamp

passing hole for aluminum cooling tube

partially split corner block (aluminum) clamps on cooling tube

silicon detector "slab" edge-bonded to structural frame with RTV (4 sides)

Figure 1: Thick silicon tray concept; bottom detail shows a

corner block with SMA ring clamps.

To form the complete instrument, trays are first stacked into towers of 24 units (Figure 2). Sixteen such towers are then assembled in a 4×4 pattern onto a common base to complete the instrument. In each tower, the trays are stacked on top of one-another around four ¼" cooling tubes that run vertically through corner blocks in the trays frames. The tubes provide liquid cooling to the trays but also constitute the primary structural element of a tower. Each tray is held tightly clamped onto the tubes by a set of eight SMA rings (2 at each corner). The corner blocks are split (Figure 1) so that a clamping pressure is produced between the inner bore of the block and the outer diameter of the tubes when the rings are shrunk. This pressure, together with the high coefficient of friction between clean aluminum surfaces, keeps the trays in place along the cooling tubes.

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¼" OD aluminum cooling tubes (2 in, 2 out)

cooling tube elbow (removable)

tower-to-tower anchor frames (2 places)

aluminum cooling tube

SMA ring clamps

Structural frame

(aluminum) guide tubes for tigthening cables (plastic)

stack of 24 identical active trays, two passive end frames, and two mid-tower anchor frames

end frame (top and bottom)

Figure 2: An assembled tower module.

4. Required Holding Load

A fully assembled tray is expected to have a total mass of 1.275 kg[4]. Subjected to our design static acceleration of 20g[2], this induces a total load of 250 N (56 lbf). Assuming that this inertial load is evenly reacted by all four tubes, the load to be resisted in friction at each corner of the tray is 63N (14 lbf). If we take a safety factor of 3.0 on that last number, we conclude that a corner-block to tube interface should be able to resist 188 N (42 lbf), at any temperature between -60ºC and +40ºC[2].

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5. Purpose of the Tests

The goals of this test program are: 1) Establish the practical feasibility of the design in terms of handling, assembly, etc. 2) Develop tools and procedures for assembly and shrinkage of the SMA rings. 3) Measure the amount of friction produced between the tube and the corner block

a) at room temperature, b) at –60ºC, c) at +40ºC.

6. Test Items and Setup

6.1 SMA Rings

The shape memory allow rings used in these tests are made by Intrinsic Devices, Inc. of San Francisco, CA[5]. They are machined from solid bars of Nitinol Alloy H (see Table 1) and "trained" to an expanded diameter at room temperature. The expanded shape is retained up to about 50ºC, at which point an unrestrained ring will begin to recover its smaller diameter "memorized" shape. If unrestricted, the ring will be fully recovered at about 100ºC. However, since the shape memory effect is also stress dependent, full recovery of a restrained ring requires heating to 165ºC. Thermochromic paint marks on the ring clearly indicate when this temperature has been reached (paint changes from light blue to dark brown). The recovery is instantaneous, so that heating for longer durations or to higher temperatures brings no benefit.

Property Value Composition Ti 38%, Ni 48%, Nb 14% Density 6900 kg/m3 (0.25 lb/in3)

Recovery Temperature (start) 50ºC (122ºF) Recovery Temperature (full clamping) 165ºC (330ºF) Melting point 1300ºC (2370ºF) Thermal conductivity 18 W/mK (10.4 BTU/hr.ft.ºF) Specific heat 837 J/kg.K (0.2 BTU/lb.ºF) Coeff. of thermal expansion 11×10-6 /K (6.1×10-6 /ºF) Poisson's ratio 0.33 Electrical resistivity 90×10-6 ohm.cm Yield strength at 20ºC 480 MPa (70 ksi) Tensile strength at 20ºC 830 MPa (120 ksi) Elongation to failure 25% Hardness 68 Ra Young's Modulus 75 GPa (11 Msi)

Table 1: Typical properties of Intrinsic Devices shape memory alloy H[5].

Those rings can be shrunk by heating them any number of ways. We opted for direct resistance heating where the rings are very rapidly heated by passing a high intensity electrical current through them. This technique minimizes heat input to the rest of the structure. See Section 6.3 below for details.

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The particular ring used is model number AHM0833-0056-0183. Nominal characteristics of that model are listed in Table 2.

Quantity Value ID as supplied (min) > 8.33 mm (.328") ID after free recovery (max) < 8.01 mm (.315") Thickness as supplied 0.53 to 0.59 mm (.021" to .023") Length as supplied 1.72 to 1.94 mm (.068" to .076") Nominal Clamping Force1 1160 N (260 lb) Nominal shrinkage 4.5%

Table 2: Nominal characteristics of SMA ring Intrinsic Devices UniLok® #AHM0833-0056-0183[5].

The clamping force generated by an SMA ring also depends on temperature, through the combined effects of differential CTE and temperature dependant properties of the SMA. Contacts with the manufacturer led us to expect a reduction in load of about 35% at -60ºC and an increase of about 50% at +40ºC, compared to room temperature values. In addition, variations in friction properties at those temperatures could affect the friction load measured in the tests.

Note that, at room temperature, assuming no clearance, rigid substrates, and a friction coefficient of 1.15 (aluminum on aluminum), these rings are theoretically capable of inducing almost 300 lbf of friction release load, or about 7 times our required value (Section 4).

6.2 Test Samples

A total of five test samples were machined and assembled. Each sample consists of a short section of cooling tube with a fixture block welded at one end (Figure 3, top left), a corner block with machined lips to receive the rings, and two SMA rings. The lips on the corner blocks feature a slightly raised edge to hold the rings in place before they are shrunk during assembly (barely visible in the top left of Figure 3). Both the corner block and the fixture blocks at the end of the tubes have holes drilled in two opposing sides for load transfer during the pull tests. The corner blocks are hard coated to electrically insulate the rings from the rest of the structures (also see Section 6.3).

1 The nominal clamping force is the integrated value of the radial clamping force exerted by the fully recovered ring on a perfectly rigid substrate and without pre-recovery clearance. It is equal to the contact area multiplied by the contact pressure. It can only be used as an indication of clamping strength of one ring relative to another, since clamping force is highly dependant on substrate compliance and diameter clearance.

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Figure 3: Components of test specimen showing corner

piece, SMA rings, and cooling tube section (top left), close-up on hard-coated corner piece with rings installed (top

right), and assembled specimen (bottom) before shrinking the rings (note the light blue thermochromic paint marks

on the rings).

Fabrication drawings for all those parts can be found in Appendix A. Note that the parts were unfortunately not machined to the tight tolerances shown on the drawings: clearances between the tubes and the corner block bores and between the rings and the lips were substantially larger than specified. Actual dimensions were not measured for lack of time and equipment.

6.3 Ring Shrinking Technique

The SMA rings are shrunk by briefly heating them to 165ºC. The heat is provided by direct resistance effect. A high intensity electrical current is circulated through both halves of the ring between contacts at diametrically opposed points. The electrical current is supplied by a high amperage constant-current laboratory supply (Lambda ZUP6-130[6], Figure 4). A programmable waveform generator is used to trigger the power supply and provide a well-timed pulse of current through the ring.

To avoid conduction through the structure instead of the ring, the aluminum corner pieces were hard-coated to produce a highly insulating surface layer. This conversion coating process produces a surface "buildup" of about .001" that must be accounted for in designing parts. The inside of the ¼" bore was masked during the coating operations, leaving bare aluminum alloy in those areas for maximum friction with the tubes.

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A custom electrode system was built to provide consistent contacts with the ring (Figure 4). The electrode is made from Chromium Copper alloy and is configured as a spring-loaded clamp. For assembly, the electrode clamp is simply positioned across the ring (Figure 7), before the power supply is triggered. This provides a very clean current supply to the ring, free of any arcing. The power supply produces a well-controlled pulse with smooth ramp up and no overshoot.

The required intensity and duration of the current pulse depends on the ring dimensions, the heat sinking properties of the substrate and electrodes, and the ambient conditions. Initial information obtained from the ring manufacturer suggested 60A for 1.5 seconds as a starting point. Trial and error tests showed that a pulse of 120A for 2 seconds was required to consistently produce full shrinkage of the rings when installed on the corner blocks and tubes (as evidenced by the thermochromic paint marks). Total voltage drop through the cables, electrodes, and ring is about 2.3 V wit approximately 3 foot long AWG10 supply cables.

Figure 4: Custom, spring-loaded electrode clamp (left),

and high intensity power supply and timing setup (right).

6.4 Friction Release Test Setup 6.4.1 Room Temperature

The samples were tested on a small Dillon load frame. The holes in the corner blocks and the fixture blocks on the tubes are caught by pins which transfer the load into glass/epoxy fixture plates and from there into adapter blocks for the load cell and frame. A 500 lbf load cell measures the pull load, and a 0.0001" resolution caliper measures the motion of the moving beam of the load frame. All signals are interfaced to a PC and logged into files using a custom LabView VI.

All tests were conducted with a constant pull velocity of approximately 0.001"/second (25 microns/second). For room temperature tests, the samples were set in the fixtures an allowed to equilibrate with the ambient air before the test was started.

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6.4.2 Reduced/Elevated Temperature

For high and low temperature tests, the sample was enclosed in a small insulated chamber made from ½" Styrofoam board. A hole was cut near the bottom of that chamber to receive either a LN2 supply line (for cold tests) or a flexible metal tube ducting hot air from an air gun (for warm tests). The 4" long, glass/epoxy fixture plates provide thermal insulation to limit heat conduction to/from the ambiance and prevent large temperature swings on the load cell (the load cell is temperature compensated to better than ±0.01% of FS/ºC, or in this case ±0.05 lbf/ºC).

The samples used in these tests (#4 and #5) were equipped with two type-T thermocouples, bonded with epoxy into 0.8 mm diameter holes drilled in the corner block and the tube.

After the sample was installed in the fixtures, the LN2 or hot air supply was started at a slow flow setting. This would bring the sample from RT to –60ºC in about 10 minutes and from RT to 40ºC in about 5 minutes. The samples were soaked at the target temperature for 3 to 6 minutes before starting the tests. After soak, the temperatures measured by the thermocouples on the tube and corner block were typically within one to 4ºC of each other. The test temperature was taken as the average of the tube and block temperatures, and was never more than 1.5ºC from the target temperature.

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Figure 5: Low/elevated temperature test setup.

Figure 6: Test samples #4 and #5 were equipped with thermocouples bonded in Ø0.8mm holes in the corner

block and tube.

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7. Results

7.1 General Notes

As mentioned above, the parts received from the shop did not appear to achieve the required tolerances. For lack of time and inspection equipment, they were used for the tests nonetheless. This caused the ring-block-tube assemblies to exhibit significantly more clearance than designed. Because of this, a large fraction of the shrinkage of the SMA clamps was used-up in closing those clearances, leaving only a portion to build up pressure. This likely explains the low friction loads measured in the tests. It is expected that much higher clamping forces will be achieved by closely controlling actual dimensions of parts prior to assembly.

In addition, we may also elect to split the corner blocks in two orthogonal directions (instead of just one) to increase their compliance, again leaving more of the shrinkage force to produce actual contact pressure between tube and block. Finally, a ring with slightly larger cross section could be used to increase contact force even further. Note however that the final design should be determined through further testing as there is a risk of overstressing the cooling tube in compression (see Section 8.4).

Table 3 gives specific observations about each sample.

# Notes Tests Performed 1 Rings snapped in place nicely.

Tube and corner cleaned with rubbing alcohol. First ring was heated twice to achieve proper temperature (first attempt @ 80A × 2 seconds, then @ 100A × 2 seconds). Corner was accidentally made to slip before data taking. Slip tests performed back-and-forth over same tube section.

Room temperature slip.

2 One ring snapped in place nicely, other somewhat loose. Tube abraded with ScotchBrite. Tube and corner cleaned with rubbing alcohol. Resistive heating OK (100A × 2 seconds). Slip tests performed back-and-forth over same tube section.

Maximum temperature from resistive heating measured with clamped thermocouple. Room temperature slip.

3 One ring somewhat loose, other completely loose. Tube abraded with ScotchBrite. Tube and corner cleaned with rubbing alcohol. Resistive heating OK (100A × 2 seconds). Slip tests performed back-and-forth over same tube section.

Temperature history from resistive heating measured with surface-bonded RTD. Room temperature slip.

4 Both rings completely loose. Tube abraded with ScotchBrite. Tube and corner cleaned with rubbing alcohol. Resistive heating OK (100A × 2 seconds). Slip tests performed in succession (one direction only).

Maximum temperature from resistive heating measured with embedded thermocouple. Room, low, and high temperature slip.

5 Both rings completely loose. Tube abraded with ScotchBrite. Tube and corner cleaned with rubbing alcohol. Resistive heating OK (100A × 2 seconds). Slip tests performed in succession (one direction only).

Maximum temperature from resistive heating measured with embedded thermocouple. Room, low, and high temperature slip.

Table 3: Miscellaneous notes about the five test samples.

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7.2 Temperature Rise from Resistive Heating of Rings

Shrinking the rings by resistive heating introduces a fixed amount of heat into the ring and the surrounding structures. The resulting temperature rise could be a concern for the sensitive detectors and electronics nearby. To evaluate this concern, the temperature of the corner block was measured during shrinkage operations. A miniature RTD probe was bonded near the center of one face of a corner block and temperature readings were logged at 0.1 second intervals. Starting from room temperature, the first ring was actuated and the temperature history recorded. After the assembly had cooled back down to RT, the same process was repeated for the second ring. Figure 8 shows the measured temperature histories. The peak temperature was 42 to 46ºC. Note that when assembling an actual tower, the heat will tend to flow into much larger structures and will likely lower the peak further. An option to lower the peak even further would consist of running coolant in the tubes during ring shrinkage operations, in which case the temperature rise would become negligible (but the electrical current required would likely increase to well above 200A).

The peak temperature was also measured with thermocouples during assembly of samples 2 (one ring), 4 (both rings), and 5 (both rings). Those peaks were measured at 40, 45, 47, 46, and 49ºC, respectively. In the first measurement, a plastic clamp was used to hold the thermocouple against the corner block (as opposed to using bonded thermocouples); the last measurement was started from a temperature of 32ºC (10ºC above RT).

Figure 7: measurement setup for temperature rise due to

ring actuation.

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Figure 8: Measured temperature histories of corner block

during and after actuation of SMA rings on sample #3; peak temperature was less than 46ºC; note that corner

block was pressed against work bench during ring 1 actuation and in air (no contact) during ring 2 actuation.

7.3 Room Temperature Tests (Samples #1 to #3)

The first three samples were used for RT tests only. In each test, the block was pulled from its "as-assembled" position on the tube to near the end of the tube. The block was then forced back to near the as-assembled position before running the next test. This implies that only the first test on each sample gives a true reading of initial friction release force. Subsequent tests measure friction on already rubbed surfaces.

Figure 9 shows the results of those tests. Note first the very wide scatter between release forces in the various tests. Also note that the friction force consistently increases from one test to the next on any given sample, likely due to cold welding effects from the repeated friction. Most curves show a classic dry friction phenomenon where the load increases elastically at first, reaches a high point (the static friction release) then drops by a few percent and settles to a kinematic friction value. Variations, both from sample to sample and from a steady kinematic friction load are likely explained mostly by differences in initial clearances in the assemblies and small variations of the tube diameter along its length.

Sample #1 was unfortunately caused to slip during setup, before the first test was started. The static friction release loads for samples 2 and 3 were 44 and 20 lbf, respectively. This is larger than the inertial load per corner (14 lb) but too low to guarantee the desired safety factor of

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three. These low values are thought to be due to larger clearances than designed. Better tolerance control on the parts is expected to improve on this.

Table 4 and Figure 10 summarize the initial static release loads from all room temperature tests (see next section for details about tests performed on samples 4 and 5).

0

50

100

150

200

250

300

0.00 0.05 0.10 0.15 0.20 0.25

displacement (inch)

load

(lb

f)

Sample 1, RT Test 2Sample 1, RT Test 3Sample 1, RT Test 4Sample 1, RT Test 5Sample 2, RT Test 1Sample 2, RT Test 2Sample 2, RT Test 3Sample 3, RT Test 1Sample 3, RT Test 2

Figure 9: results from room temperature tests on sample

assemblies 1, 2, and 3; note that sample 1, test 1 is not available because that sample was accidentally made to

slip before data recording was started.

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Sample #

Test # Notes Friction Release Load

(lbf) 1 1

2 3 4 5

not available same tube section same tube section same tube section same tube section

- 72.6 64.2

154.0 173.5

2 1 2 3

initial release same tube section same tube section

44.4 167.8 266.8

3 1 2

20.0 98.2

4 1 2 3 4

23.3 30.8 21.5 33.8

5 1 2

25.3 16.3

Table 4: Friction release loads measured at RT on the five samples.

1 2 3 4 5

1

2

3

4

5

0.00

50.00

100.00

150.00

200.00

250.00

300.00

initial release

load (lbf)

sample #

release test #

Figure 10: Measured release loads for successive RT tests on all samples; note that for samples 1 to 3 successive tests

were performed over the same tube section by repositioning the corner block before each test.

7.4 Low and Elevated Temperature Tests (Sample #4 and #5)

Samples 4 and 5 were used for low and elevated temperature tests. With the experience gained on the RT tests, the procedure was modified to avoid successive rubbing of the same tube section:

a) Assemble samples with block leaving >0.5" of exposed tubing available for pull

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b) Set sample in pull fixtures c) Pull at RT for <0.1" d) Install chamber and cool sample to -60ºC; soak for a few minutes. e) Pull at -60ºC for <0.1" f) Remove chamber and let sample come back to RT g) Reinstall chamber and heat sample to +40ºC; soak for a few minutes. h) Pull at +40ºC for <0.1" i) Remove chamber and let sample come back to RT

This procedure allows two or more tests at each temperature on each sample before reaching the end of the tube.

Sample #4 was tested first. For practical reasons, the procedure above was modified slightly to add an additional RT test (test #6). Sample 5 was tested per the above procedure, repeated twice. The results are summarized in Figure 11 and Figure 12. Note again the well-defined static release load in most tests and the kinematic friction region that follows. As mentioned above, the fact that the kinematic friction load is not constant after release can likely be explained by cold welding effects and slight variations in tube diameter.

Note that the release loads are even lower than measured on samples 1 to 3, likely because of even wider clearances (see Table 3). Note also that high temperature tests do not appear to show higher release loads than RT as was expected. Low temperature tests however show markedly reduced release loads. This is more visible in Figure 13 and Figure 14 where the post-release loads are plotted versus the test temperature.

0

5

10

15

20

25

30

35

40

0 100 200 300 400 500 600 700 800time (sec) / displacement (mil)

slip

pag

e lo

ad (

lbf)

Test 1, RT

Test 2, LT

Test 3, HT

Test 4, RT

Test 5, LT

Test 6, RT

Test 7, HT

Test 8, RT

Figure 11: Load histories for sample #4 at various

temperatures.

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0

5

10

15

20

25

30

35

40

0 100 200 300 400 500 600

time (sec) / displacement (mil)

slip

page

load

(lb

f)

Test 1, RT

Test 2, LT

Test 3, HT

Test 4, RT

Test 5, LT

Test 6, HT

Figure 12: Load histories for sample #5 at various

temperatures.

0

5

10

15

20

25

30

35

40

-80 -60 -40 -20 0 20 40 60

temperature (degree C)

slip

page

load

(lb

f)

Test 1, RT

Test 2, LT

Test 3, HT

Test 4, RT

Test 5, LT

Test 6, RT

Test 7, HT

Test 8, RT

Figure 13: Sample #4 post-release loads versus

temperature.

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0

5

10

15

20

25

30

35

40

-80 -60 -40 -20 0 20 40 60

temperature (degree C)

slip

page

load

(lb

f)

Test 1, RT

Test 2, LT

Test 3, HT

Test 4, RT

Test 5, LT

Test 6, HT

Figure 14: Sample #5 post-release loads versus

temperature.

y = -0.0027x2 + 0.0767x + 24.69

y = -0.003x2 + 0.1049x + 25.512

0

5

10

15

20

25

30

35

40

-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50

Temperature (degree C)

Load

(lb

f)

initial release loadaverage load after release2nd order fit (initial relase load)2nd order fit (average load after release)

Figure 15: Initial release load and average load after

release as a function of temperature (samples 4 and 5).

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Finally, Figure 15 summarizes the temperature dependence effects. The figure shows the static release loads and the average loads after release as a function of temperature. Second order trend lines are also shown. It is interesting to note that the expected increase in release load at high temperature does not show at all in the data; reasons for this are unknown.

On the other hand, the expected reduction in release load at low temperature is clearly seen and amounts to about 55%.

8. Conclusions

8.1 Practical Aspects

The SMA ring clamp concept was found quite practical in real-world assembly trials. The resistive heating of the rings is well controlled and consistent, once adjusted for the particular configuration and conditions. Peak temperatures observed in structures around the ring remain very reasonable (45 to 50ºC) due to the rapid heating of the ring (2 seconds @ 120 Amps). Lower peak temperatures could be achieved if necessary with liquid cooling of the tubes and/or even shorter, more intense current pulsed (1 second at about 200 Amps for example). If a constant current power supply is used, the current pulse can be tightly controlled without high frequency oscillations so that electro-magnetic influence on the front-end electronics should be negligible. Note also that the aluminum structures are completely insulated electrically from the power supply by a .002" hard-coated layer on the corner block.

8.2 Friction Release Force (measurement technique)

The fixturing and simple thermal chamber used in the tests was found to perform well. The procedure used for the temperature dependence tests was quite effective at producing substantial amounts of data from a single sample. The scatter in the data was large but still small enough to clearly identify the loss of clamping force at low temperature.

8.3 Friction Release Force (value)

The disappointing aspect of this test program is the very low values of friction release forces measured in the tests. This is believed to be the result of excessive clearances between tube, corner block, and ring, which cause most of the shrinkage to be used-up in closing those clearances as opposed to building contact pressure. Evidence of inaccurate machining was found although a detailed inspection of the parts was not performed before assembly.

8.4 Recommendations for Future Work

In view of the low release loads measured in these tests, we recommend the following actions:

1. Consider modifying the corner block design to incorporate a second set of slots at 90 degrees from the first. This would increase the compliance of the corner block, leaving more of the SMA force for pressure buildup.

2. Review detailed drawings with particular attention to minimizing clearances between tube, block, and ring.

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3. Consider increasing the ring cross section as much as possible within current corner block envelope.

4. Produce another set of parts and perform QA inspection of all clearance-critical dimensions.

5. Repeat tests using procedure from Section 6.4.2.

9. References 1. J. Kurfess and B. Phlips, “Compton Imager Mechanical Design Study - Statement of Work,”

Naval Research Laboratory, March 22, 2001, full text included in Appendix A. 2. E. Ponslet, "Simplified Mechanical and Thermal Design Requirements for Conceptual Design

Studies of an Advanced Compton Imager," doc. HTN-123001-0001-B, HYTEC Inc., Los Alamos, NM, October 1st, 2001.

3. E. Ponslet, "Thermo-mechanical Feasibility of an Advanced Compton Detector: Bounding Calculations and Trend Studies," doc. HTN-123001-0002, HYTEC Inc., Los Alamos, NM, February 14, 2002.

4. E. Ponslet, "Thick Silicon Advanced Compton Detector: A Design Concept," doc. HTN-123001-0003-A, HYTEC Inc., Los Alamos, NM, February 14, 2002.

5. Intrinsic Devices, Inc., 2353 Third Street, San Fransisco, CA 94107-3108, Tel (415) 252-5902, Fax (415) 252-1624, www.intrinsicdevices.com .

6. Lambda EMI, 405 Essex Road, Neptune, NJ 07753, Tel (732) 922-9300, Fax (732) 922-9334, www.lambda-emi.com .

HTN-123001-0006 3/28/2002

23

Appendix A. Drawings

Final fabrication drawings for the test samples and fixtures are included in the following pages.

3

22

1 1

1

2

2

1

3

4

5

7

6

6

8

8

9

9

10

10

THIRD ANGLE PROJECTION

UNLESS OTHERWISE SPECIFIED: DIMENSIONS ARE IN INCHES -TOLERANCES-

DECIMALS ANGULAR = +/- 30'.X = +/- .1.XX = +/- .01.XXX = +/- .005 SURFACE FINISH = 250

C

B

AA

B

CAD GENERATED DRAWING,DO NOT MANUALLY UPDATEDO NOT SCALE DRAWING

SCALE

DWG. NO.

DSHEET NO.

REVISION



FINISH

123-TCT-02-1009

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8 7 6 5 4 3 2 1

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678

1 of 1PART NO.

123-TCT-02-1009-12:1

SIGNATURE DATE

Designer Roger L. Smith 1/29/2002

Drawn Roger L. Smith 1/29/2002

Checked Eric Ponslet 1/29/2002

Engineer Eric Ponslet 1/29/2002

Approved Eric Ponslet 1/29/2002

REVISIONS

REV DESCRIPTION DATE APPROVED

ACT 2PULL TEST

FIXTURE ASSEMBLY

ITEM QTY PART NO. DESCRIPTION MATERIAL

1 4 123-TCT-02-1010-1 Spreaded Plate2 4 123-TCT-02-1011-1 G10 Pull Bar3 2 123-TCT-02-1012-1 Fixturing Block4 1 123-TCT-02-1013-1 Pull Tube Weldment5 1 123-TCT-02-1014-1 Corner Block6 4 123-TCT-02-1015-1 Pivot Screw7 2 Clamping Ring8 8 Pin, .25 (1/4) diam. X 1.25 lg SST9 8 Soc Hd Screw, #8-32 UNC-2A X .31 (5/16) lg SST10 2 Thredded Stud, M12 X .31 (5/16) lg SST

PARTS LIST

2X .194 - .004+.002

1.18

.50

.188 .808

.250

.012 M A B C

B

C

.13 A

MATERIAL: 6061-T6 AL




C

B

AA

B


SCALE

DWG. NO.

DSHEET NO.

REVISION



FINISH

123-TCT-02-1010

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SIZE

TITLE

678

1 of 1PART NO.

123-TCT-02-1010-14:1

NOTES: UNLESS OTHER WISE SPECIFIED

1. ALL DIMENSIONS IN INCHES2. DIMENSIONS AND TOLERANCING PER ASME Y14.5M-19943. SURFACE TEXTURE PER ANI/ASME B 46.1-19854. REMOVE ALL BURRS AND BREAK SHARP EDGES TO A MAXIMUM OF .0155. ALL INSIDE CORNERS TO BE .015 RADIUS MAX6. COUNTERSINK 82 DEGREES ALL TAPPED HOLES TO MAJOR DIAMETER7. COUNTERSINK 82 DEGREES APPROXIMATELY .03/.06 DEEP ALL DRILLED HOLES8. PARTS TO BE THOROUGHLY CLEANED TO REMOVE ALL OIL, GREASE, DIRT AND CHIPS9. PART NUMBER (DRAWING NO., DASH NO., REVISION NO., SERIAL NO.) TO BE CLEARLY MARKED ON THE PART ITSELF.

SIGNATURE DATE






REVISIONS


ACT 2PULL TEST

SPREADER PLATE

.38

2.00

#8-32 UNC-2B, THRU

.188

1.750

.017 M A B C

A

.75

.250 - .000+.002

1/4-20 UNC-2B, THRU

.375

1.625

.375 .375

.017 M A B C

.012 M A B C

B

C

MATERIAL: G10 or G11 PLATE STOCK




C

B

AA

B


SCALE

DWG. NO.

DSHEET NO.

REVISION



FINISH

123-TCT-02-1011

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SIZE

TITLE

678

1 of 1PART NO.

123-TCT-02-1011-14:1



SIGNATURE DATE






REVISIONS


ACT 2PULL TEST

G10 PULL BAR

.38

4.00

#8-32 UNC-2B, THRU

.188

3.750

A3

A2

.017 M A B C

A

.75

.250 - .000+.002

1/4-20 UNC-2B, THRU

.375

3.625

.375 .375

A1

.017 M A B C

.012 M A B C

B

C

A





C

B

AA

B


SCALE

DWG. NO.

DSHEET NO.

REVISION



FINISH

123-TCT-02-1011

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1 of 1PART NO.

123-TCT-02-1011-14:1



SIGNATURE DATE






REVISIONS


A SEE ECN# D972103-A FOR CHANGE LIST 03/06/02 Eric Ponslet

ACT 2PULL TEST

G10 PULL BAR

.75

.250 - .000+.002, THRU

.375

.375

.012 M A B C

A

B

2X .88

1.88

.16

.433 - .005+.000

2X R .03

.75

C

M12 X .75

.375

.375

.017 M A B C

MATERIAL: SST




C

B

AA

B


SCALE

DWG. NO.

DSHEET NO.

REVISION



FINISH

123-TCT-02-1012

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SIZE

TITLE

678

1 of 1PART NO.

123-TCT-02-1012-14:1



SIGNATURE DATE






REVISIONS


ACT 2PULL TEST

FIXTURING BLOCK

THRU ITEM 1 ONLY .188 - .000

+.002

.250

1

2

.005 M A B C

.06

.50

3.00

1/16

.63

.433

.250±.002,THRU ITEM 1

.313

.217

.015 M A B C




C

B

AA

B


SCALE

DWG. NO.

DSHEET NO.

REVISION



FINISH

123-TCT-02-1013

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SIZE

TITLE

678

1 of 1PART NO.

123-TCT-02-1013-14:1



ITEM QTY DESCRIPTION MATERIAL

1 1 Upper Pull Block 6061-T6 AL2 1 Cooling Tube 6061-T6 AL Tube, .25 OD X .058 wall

PARTS LIST

SIGNATURE DATE






REVISIONS


ACT 2PULL TEST

PULL TUBE WELDMENT

.016 - .002+.000

.098 - .000+.002

.984

2X .322±.002

2X .328±.002.010 M A B C

.010 M A B C

A

.250 - .002+.006 THRU

.433

.433

.020

.217

.217

A

A

.010 M A B C

B

C

.492

.188 - .000+.002 THRU

.010 M A B C

.453

.453

2X FULL R

2X .020

.079

SECTION A-A

MATERIAL: 6061-T6 ALUMINUM




C

B

AA

B


SCALE

DWG. NO.

DSHEET NO.

REVISION



FINISH

123-TCT-02-1014

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SIZE

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1 of 1PART NO.

123-TCT-02-1014-14:1



SIGNATURE DATE






REVISIONS


ACT 2PULL TEST

CORNER BLOCK

.465

.365

.188 - .002+.000

Modify SST, Soc Hd Screw, 1/4-20 UNC-2A




C

B

AA

B


SCALE

DWG. NO.

DSHEET NO.

REVISION



FINISH

123-TCT-02-1015

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SIZE

TITLE

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1 of 1PART NO.

123-TCT-02-1015-18:1



SIGNATURE DATE






REVISIONS


ACT 2PULL TEST

PIVOT SCREW

1

2

3

4

5

6

7




C

B

AA

B


SCALE

DWG. NO.

DSHEET NO.

REVISION



FINISH

123-TCT-02-1016

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SIZE

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1 of 1PART NO.

123-TCT-02-1016-14:1

SIGNATURE DATE






REVISIONS


ACT 2POWER CLAMP

ASSEMBLY

ITEM QTY PART NO. DESCRIPTION MATERIAL

1 1 123-TCT-02-1017-1 Positive Side Jaw2 1 123-TCT-02-1018-1 Negative Side Jaw3 2 123-TCT-02-1019-1 Bridge4 1 62118617 MSC Spring Plunger5 1 Dowel Pin, .1875 (3/16) diam. X .50 (1/2) lg. SST6 4 Button Hd Screw, #4-40 UNC-2A X .19 (3/16) lg7 2 Button Hd Screw, #10-24 UNC-2A X .38 (3/8) lg

PARTS LIST

.10

65.0°

R .188

2X #4-40 UNC-2B, THRU

1.963 .375

2.900

.177

.198

.017 M A B C

.013 M A B C

.122

.069

2.50

3.00

2X R .25

#10-24 UNC-2B, THRU2X #10-32 UNf-2B, THRU

.156

.375

1.400

.017 M A B C.017 M A B C

.375

.313

MATERIAL: C18200 CHROMIUM COPPER




C

B

AA

B


SCALE

DWG. NO.

DSHEET NO.

REVISION



FINISH

123-TCT-02-1017

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1 of 1PART NO.

123-TCT-02-1017-14:1



SIGNATURE DATE






REVISIONS


ACT 2POWER CLAMP

POSITIVE SIDE JAW

R .188

.188 - .000+.001

.10

65.0°

3.000

2.150

2.900

.198 .177

.012 M a b c

.017 M a b c

A

C

#10-24 UNC-2B, THRU

2X R .25

.122

.069

2X 2.50

.375

.156

.017 M a b c

.38

.31

B

MATERIAL: C18200 CHROMIUM COPPER




C

B

AA

B


SCALE

DWG. NO.

DSHEET NO.

REVISION



FINISH

123-TCT-02-1018

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SIZE

TITLE

678

1 of 1PART NO.

123-TCT-02-1018-14:1



SIGNATURE DATE






REVISIONS


ACT 2POWER CLAMP

NEGATIVE SIDE JAW

.188 - .002+.004

.136 - .002+.004

.65

1.10

2X .20

2X .38

.138 .375

.177

.927

.325

2X.06 X 45 CHAMFER

.013 M A B C

.017 M A B C

B

C

.06

A





C

B

AA

B


SCALE

DWG. NO.

DSHEET NO.

REVISION



FINISH

123-TCT-02-1019

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8 7 6 5 4 3 2 1

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D D

HYTEC,INC

SIZE

TITLE

678

1 of 1PART NO.

123-TCT-02-1019-14:1



SIGNATURE DATE






REVISIONS


ACT 2POWER CLAMP

BRIDGE

htn-123001-0006-draft sma ring clamps test...

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