TRIDENT Postshot Report: Flyer Impact Experiments on NiTi and NiAl, December 2001 - "Pink Flamingo"

Contents

• Introduction
• Objectives
• Calendar
• Targets
• Diagnostics
• Drive beam
• Shots
• Results
• Conclusions
• Acknowledgements
• References

Introduction

An abbreviated version was submitted as an LA-UR for classification in early 2002 but disappeared into the ether. This memo is a replacement.

Objectives

The specific objectives of these experiments were:

• To measure flyer speeds and acceleration curves for copper flyers ~50 to 200 µm thick on PMMA substrates, using deposited flyer launch layers.
• To perform flyer impact experiments on samples of NiTi, with sample recovery.
• To perform flyer impact experiments on samples of NiAl, with sample recovery.

Calendar

Event	Plan	Actual
Start of TRIDENT time	~10 Dec	17 Dec
First shot	~11 Dec	17 Dec
Last shot	~20 Dec	20 Dec

Table 1. Calendar of events.

	Plan	Actual	Comments
Duration	2 weeks	0.75 weeks
Laser available	8 days	3.5 days
Shots (time after set-up)	8 days	3 days

Table 2. Period, availability and usage.

Targets

Copper foils were purchased from Goodfellow Corp; most flyers were punched from this stock. The foils had distinct striations and machining marks. We attempted to remove these from the surface to avoid the generation of interference patterns which might interfere with the laser velocimetry measurements, by polishing the surface manually using diamond paste. This was only partially successful.

NiTi samples of two compositions were provided by R. Hackenberg (MST-7). These included flyers, ~100 to 200 µm thick and 5 mm in diameter, and semicircular targets, ~100 to 400 µm thick. The previous NiTi samples had a near-mirror finish, and the velocimetry signal was not obscured by window reflections. This time, we had agreed to try less polished samples to see whether less time could be spent preparing the samples. Adequate signals were obtained from bare samples, but the reflection from (uncoated) PMMA windows was slightly stronger than from the samples.

Samples of NiAl crystal cut along (100) planes were provided by K. McClellan (MST-8). These were irregularly-shaped targets, ~100 to 400 µm thick.

The flyer was attached to the substrate with five-minute epoxy, the flyer being pressed down to minimize the thickness of the glue layer. Spacer rings, punched from plastic shim stock, were inserted between the substrate and the target assembly (i.e. the window) to allow space for the flyer to accelerate. The distance from the free surface of the flyer to the impact surface of the sample is referred to as the barrel length. The complete assembly was screwed together in a target holder. Some shots in the series were dedicated to measuring the acceleration history of the flyer and hence the barrel length required to reach the maximum speed. We had anticipated that, between the uncertainty in laser energy delivered and the uncertainty in the barrel length, there might be a significant uncertainty in the impact time, particularly for the thicker flyers driven with lower energies. In the limited time available, we did not measure the thickness of the glue bond; this was potentially a cause for concern. In practice, the energy delivered was very close to the value requested, and the barrel length was also reproducible (indicating that the glue bond in the flyer was thin and reproducible), so the impact time could be predicted with reasonable accuracy.

All final assembly was performed in-house at TRIDENT.

Diagnostics

We had planned to image the target into the line VISAR and then to the streak camera. In the event, Randy Johnson developed his previous technique of imaging the target straight through the VISAR (i.e. focused at infinity) to the camera to make better use of the full width of the camera. He also incorporated timing markers on the streak record. As before, the probe laser was made to produce a long (~1.5 µs) pulse to be able to capture the acceleration and impact of the flyer.

Since the P-24 point VISAR was not complete, we used the Sandia VISAR borrowed for the preceding experiments. The P-24 Verde laser was used.

We had intended to assemble the experiments so that the PMMA window was split, with half coplanar with the impact surface of the sample. This would provide a time fiducial for the arrival of the flyer. The PMMA semicircles did not arrive until after the start of the experimental session, so early experiments were performed with a full disc of PMMA. The VISAR recording window was usually not long enough to capture the impact of the flyer directly with the window, so this time fiducial -- and thus the direct measurement of shock speed - was not available in these experiments.

We investigated the use of an alternative technique, attaching the sample to a copper disc ~50 µm thick, as in flyer plate experiments at Z [2]. The shock breakout in the copper provided the time fiducial. This technique was not suitable for `symmetric impact' experiments where the flyer and sample were the same material.

We intended to perform all experiments so that the target was in contact with a PMMA window, providing a well-characterised loading history and facilitating sample recovery. Because of the relatively low reflectivity of the NiTi samples, and to make assembly simpler with a fiducial for shock arrival, some shots were fired with a bare sample. In these cases, the sample was lost.

Drive beam

Shots

Topic	Shots		Comments
	Plan	Actual
Diagnostic timing	5	2
Flyer acceleration	12	9
Impact timing	2	0
NiTi	15	14	Plan: per composition.
NiAl	12	8	Plan: per orientation.
Total	46	33	Plan: excludes some data shots.
Shots per day	8	11

Table 3. Shot statistics.

Only two shots were required to time in the diagnostics, thanks to the work performed during Dennis Paisley's flyer development experiments immediately beforehand. Usable data were obtained from both VISARs in every other experiment, except for one NiTi shot in which the line VISAR record was obscured by window reflection. (There was considerable interference in other NiTi experiments, but the record was still usable.) Excellent flyer acceleration records were obtained for copper flyers of different thickness and using different energies. We decided to omit corresponding acceleration shots for NiTi flyers, and used an areal mass scaling instead. To save more time, we omitted copper/copper impacts to verify the barrel length, and proceeded directly with NiTi.

The target numbering for NiAl and NiTi samples is shown in Tables 4 to 6, and the complete list of shots in Table 7.

No.	Flyer	Barrel	Target	Windows
1	Cu, 105	300	NiAl GE (001), 200	PMMA disc
2	Cu, 105	300	NiAl GE (001), 217	PMMA disc
3	Cu, 105	200	NiAl GE (001), 217	PMMA disc
4	Cu, 250	150	Cu, 55 um / NiAl GE (001), 398
5	Cu, 250	150	Cu, 55 um / NiAl GE (001), 398
6	Cu, 250	150	Cu, 55 um / NiAl GE (001), 398
7	Cu, 250	150	NiAl GE (001), 398	PMMA step-disc
8	Cu, 250	150	NiAl GE (001), 398	PMMA step-disc

Table 4. NiAl samples.

Code	Composition
5B	52.5 at % Ni
6B	55.6 at % Ni

Table 5. NiTi compositions.

No.	Flyer	Barrel	Target	Windows
1	NiTi 5B, 90/80-85 edge	300	NiTi 5B, 191/181 edge	PMMA disc
2	NiTi 5B, 102/92-100 edge	300	NiTi 5B, 197/188 edge	PMMA disc
3	NiTi 5B, 108/101-106 edge	200	NiTi 5B, 202/192 edge	PMMA disc
4	NiTi 5B, 201/195 edge	150	NiTi 5B, 403/388 edge	PMMA step-disc
5	NiTi 5B, 207/204 edge	150	NiTi 5B, 404/399 edge	PMMA step-disc
6	NiTi 5B, 209/202 edge	150	NiTi 5B, 419/404 edge	PMMA step-disc
7	NiTi 5B, 154/148 edge	375	NiTi 5B, 300/290 edge	PMMA half-disc over flyer
8	NiTi 5B, 156/148 edge	375	NiTi 5B, 305/295 edge	PMMA half-disc over flyer
9	Cu, 55	200	NiTi 5B, 88/85 edge	PMMA half-disc over flyer
10	Cu, 55	500	NiTi 5B, 91/89 edge	PMMA half-disc over flyer
11	Cu, 55	500	NiTi 5B, 95/85 edge	PMMA half-disc over flyer
12	Cu, 55	575	NiTi 6B, 113/107 edge	PMMA half-disc over flyer
13	NiTi 6B, 90/86 edge	200	NiTi 6B, 211/208 edge	PMMA half-disc over flyer
14	NiTi 6B, 222/216 edge	80	NiTi 6B, 414/410 edge	PMMA half-disc over flyer

Table 6. NiTi samples.

Shot	Flyer	Barrel	Target	Energy	Line VISAR		Point VISAR		Comments
		(um)		(J)	sweep	delay	sweep	delay
					(ns)	(ns)	(ns)	(ns)
17 Dec
14117	Cu, 105 µm	1600	PMMA	10	2000	800	3000	3300	point late, line ?early, recovery OK
14118	Cu, 105 µm	1600	PMMA	9	2000	100	3000	2200	Little motion. RPP shield discoloured => ?drive too low.
14119	Cu, 105 µm	1600	PMMA	10	2000	100	3000	2200	Beautiful acceleration to ~280 m/s. Noticed misty sheen to beam area of RPP.
14120	Cu, 105 µm	1600	PMMA	5	2000	100	3000	2200	Beautiful acceleration to ~160 m/s. Misty sheen no worse.
14121	Cu, 105 µm	1600	PMMA	20	2000	100	3000	2200	Beautiful acceleration to ~350 m/s. Flyer escaped through PMMA window. Misty sheen no worse.
18 Dec
14123	NiTi, 90 µm	300	NiTi, 191 µm / PMMA	10	2000	100	3000	2200	NiTi #1
14124	NiTi, 102 µm	300	NiTi, 197 µm / PMMA	20	2000	100	3000	2200	NiTi #2
14125	NiTi, 108 µm	200	NiTi, 202 µm / PMMA	5	2000	100	3000	2200	NiTi #3
14126	Cu, 105 µm	300	NiAl 001, 200 µm / PMMA	11	2000	100	3000	2200	NiAl #1
14127	Cu, 105 µm	300	NiAl 001, 217 µm / PMMA	20	2000	100	3000	2200	NiAl #2
14128	Cu, 105 µm	200	NiAl 001, 217 µm / PMMA	4	2000	100	3000	2200	NiAl #3
14129	Cu, 55 µm	1600	PMMA	11	2000	100	3000	2200	Accelerated to ~470 m/s
14130	Cu, 55 µm	1600	PMMA	19	2000	100	3000	2200	Accelerated to ~630 m/s
14131	Cu, 55 µm	1600	PMMA	5	2000	100	3000	2200	Accelerated to ~310 m/s
14132	Cu, 250 µm	1600	PMMA	11	2000	100	3000	2200	Accelerated to ~130 m/s
19 Dec
14134	Cu, 250 µm	1600	PMMA	24	2000	100	3000	2200	Accelerated to ~220 m/s
14135	Cu, 250 µm	1600	PMMA	5	2000	100	3000	2200	Accelerated to ~80 m/s
14136	Cu, 250 µm	150	Cu, 55 µm / NiAl 001, 398 µm	11	2000	1600	3000	3700	NiAl #4 (Cu baseplate)
14137	Cu, 250 µm	150	Cu, 55 µm / NiAl 001, 398 µm	19	2000	1600	3000	3700	NiAl #5 (Cu baseplate)
14138	Cu, 250 µm	150	Cu, 55 µm / NiAl 001, 398 µm	15	2000	1600	3000	3700	NiAl #6 (Cu baseplate)
14139	Cu, 250 µm	150	NiAl 001, 398 µm / PMMA	11	2000	1100	3000	2200	NiAl #7 (PMMA step-disc)
14140	Cu, 250 µm	150	NiAl 001, 398 µm / PMMA	20	2000	1100	3000	2700	NiAl #8 (PMMA step-disc)
14141	NiTi, 201 µm	150	NiTi, 403 µm / PMMA	11	2000	1100	3000	2700	NiTi #4 (PMMA step-disc)
14142	NiTi, 207 µm	150	NiTi, 404 µm / PMMA	19	2000	700	3000	2700	NiTi #5 (PMMA step-disc)
14143	NiTi, 209 µm	150	NiTi, 409 µm / PMMA	16	2000	1100	3000	2700	NiTi #6 (PMMA step-disc)
14144	NiTi, 154 µm	375	NiTi, 300 µm	10	2000	1600	3000	2700	NiTi #7 (PMMA impact fiducial)
20 Dec
14146	NiTi, 156 µm	375	NiTi, 305 µm	22	2000	1600	3000	2700	NiTi #8 (PMMA impact fiducial)
14147	Cu, 55 µm	200	NiTi, 88 µm	12	2000	600	3000	2700	NiTi #9 (PMMA impact fiducial)
14148	Cu, 55 µm	500	NiTi, 91 µm	21	2000	1100	3000	2700	NiTi #10 (PMMA impact fiducial) Fringes not clear.
14149	Cu, 55 µm	500	NiTi, 95 µm	17	2000	600	3000	2700	NiTi #11 (PMMA impact fiducial)
14150	Cu, 55 µm	580	NiTi, 113 µm	20	2000	600	3000	2700	NiTi (new comp) #12 (PMMA impact fiducial)
14151	NiTi, 90 µm	200	NiTi, 211 µm	10	2000	600	3000	2700	NiTi #13 (PMMA impact fiducial)
14152	NiTi, 222 µm	100	NiTi, 414 µm	11	2000	600	3000	2700	NiTi #14 (PMMA impact fiducial)

Table 7. Summary of all shots. In all cases, the spot diameter was ~4 mm and the drive laser produced radiation of 1.054 µm (IR), VISAR velocimetry was used, and the drive pulse was ~600 ns long. Unless stated, all flyers were launched from a PMMA/C/Al/Al₂O₃/Al substrate, glued with epoxy.

Results

We collected NiTi data including histories for interface speed and free surface speed as a function of impactor speed. The data included some measurements of shock speed, but the uncertainty in this quantity may be quite large,

The NiAl data were similar, though fewer shots were fired; the sample finish was smoother, so the fringe contrast in the line VISAR was very high.

It should be possible to extract EOS and strength data on NiTi and NiAl from these experiments. The recovered samples are also available for metallographic analysis, if desired.

Conclusions

Detailed analysis of the VISAR data is in progress.

We would like to have further TRIDENT time to complete the planned measurements on both materials, as well as to perform follow-up work.

Acknowledgements

This work was performed in part under the auspices of the U.S. Department of Energy under contract # W-7405-ENG-36.

References

1. D.L. Paisley, D.C. Swift, R.P. Johnson, J.C. Lashley and J.G. Niemczura, Flyer plates launched with long laser pulses, LA-UR-01-5814 (2001).
2. D.C. Swift, Uniaxial shocks in beryllium: preshot calculations for experiments at Z, LA-UR-01-341 (2001).

Distribution