TRIDENT Postshot Report:
Flyer Impact Experiments on NiTi and NiAl,
March 2002 - "Flying Pig"

Contents

• Introduction
• Objectives
• Calendar
• Targets
• Diagnostics
• Drive beam
• Shots
• Observations
• Log of notable events
• Results
• Conclusions
• Acknowledgements
• References

Introduction

Objectives

The specific objectives of these experiments were:

• To perform flyer impact experiments on samples of NiTi.
• To perform flyer impact experiments on samples of NiAl.

Calendar

Event	Plan	Actual
Start of TRIDENT time	11 Mar	4 Mar
First shot	11 Mar	5 Mar
Last shot	21 Mar	7 Mar

Table 1. Calendar of events.

	Plan	Actual	Comments
Duration	2 weeks	1 week
Laser available	8 days	4 days
Shots (time after set-up)	7.5 days	3 days

Table 2. Period, availability and usage.

Targets

Flyers were NiTi, NiAl, or copper. As before, the copper flyers were punched from Goodfellow foils.

NiTi samples of two compositions (batch codes 5B and 6B) were again 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. Compared with the previous samples, where the relatively dull finish caused problems with VISAR signals, the samples used here were polished to a near-mirror finish on the side facing the VISARs. The velocimetry signals were correspondingly better.

Samples of NiAl crystal cut along (100) and (110) planes were provided by K. McClellan and J. Brooks (MST-8). These were irregularly-shaped pieces, ~100 to 400 µm thick, and included samples large enough to be used as flyers.

Each flyer was attached to its 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.

A small number of shots at the start of the series were dedicated to verifying that the acceleration history of the flyer was essentially as measured in December, and hence that the barrel length required to reach the maximum speed could be calculated in the same way without needing additional characterisation shots.

All final assembly was performed in-house at TRIDENT.

Diagnostics

Timing markers were incorporated 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.

The following types of target were used:

• Window impact: flyer of the sample material impacting a window. LiF was used as the window for these experiments; its impedance is much higher than that of the PMMA used in December, giving a higher impact pressure for a given flyer speed.
• Copper flyer into free-standing target of sample material. The copper flyer was punched by the drive beam from a foil generally of much larger diameter. To reduce the uncertainty in `barrel' length from the uncertainty in the thickness of the glue bond between the flyer and the substrate, the sample was mounted on a pillar or holder of shim stock, glued directly to the surface of the copper. This technique was used successfully in previous shots [2] with no apparent motion of the sample from early shocks travelling up the pillars. In the present experiments, a few shots showed some sign of early motion; this could have been caused by pillars which were larger than intended in lateral extent, pillars which slipped closer to the centre of the flyer before the glue had set, or if some of the epoxy had formed a fillet between the sample and the flyer.

These experimental designs were chosen based on practical experiences in calculating mechanical properties from the different types of experiment used in December [3,4]. This time, no effort was made to recover samples.

Drive beam

Shots

Topic	Shots		Comments
	Plan	Actual
Diagnostic timing	3	4
NiTi 5B	10	3
NiTi 6B	20	4
NiAl (100)	10	9
NiAl (110)	20	9
Total	63	29
Shots per day	8	10	actual: 6, 9, 14

Table 3. Shot statistics.

Table 4 summarizes the configuration of each shot.

Shot	Flyer	Barrel	Target	Energy	Line VISAR		Point VISAR		Comments
		(µm)		(J)	sweep	delay	sweep	delay
					(ns)	(ns)	(ns)	(ns)
5 Mar
14376	Cu, 105 µm	300 (pink)	LiF	11	1000	2363	3000	10000	point late, line OK
14377	Cu, 105 µm	300	LiF	10	1000	2363	3000	2000	point OK but timebase too long, line too early (wanted to catch impact; we changed the wrong delay)
14378	Cu, 105 µm	300	LiF	11	1000	3300	3000	2000	point: ~1 W for ~150 mV pk/pk; no line record, point good - a little early
14379	NiTi 6B, 160 µm	300 (brown + transp)	LiF	11	1000	3300	3000	2750	point: 100 mW for 400 mV pk/pk; line late, point good; accelerating on impact
14380	NiTi 6B, 164 µm	300 (brown + transp)	LiF	14	1000	2500	3000	2750	point: signal low (didn't check alignment under vacuum) but prob OK; line: caught accel, missed impact, looks like plasma leaked from sides
14381	GE-NiAl- D5-1-100-100-1, 94 µm	300 (brown + transp)	LiF	12	1000	3000	3000	2750	point: 200 mW for 200 mV pk/pk; point data prob OK (early ringing); line didn't show much - plasma again?
6 Mar
14383	Cu, 55 µm	350 (pink)	LiF	13	1000	2400	3000	2750	point: 75 mW for 400 mV pk/pk; point signal good (early ringing again); line OK: accel + impact
14384	NiTi 6B, 106 µm	300 (pink)	LiF	14	1000	2800	3000	2750	point: 10 mW for 400 mV pk/pk; point good; line looks like plasma leak
14385	NiTi 6B, 203 µm	200 (pink)	LiF	11	1000	2800	3000	2750	point: good; line: ?plasma leak
14386	NiTi 5B, 160 µm	240 (pink)	LiF	11	1000	2800	3000	2750	point: good; line: low contrast (rough flyer) but accel + impact
14387	GE-NiAl- D5-1-110-250-1, 228 µm	150 (pink)	LiF		1000	2800	3000	2750	9 point: good; line: accel + impact + ring down
14388	GE-NiAl- D5-1-110-250-2, 262 µm	120 (pink)	LiF		1000	2800	3000	2750	10 point: good; line: accel + impact + ring down
14389	GE-NiAl- D5-1-100-350-10, 375 µm	140 (blue on flyer surf)	LiF	11	1000	2800	3000	2750	point: looks good; line: accel + impact + ring down
14390	GE-NiAl- D5-1-100-350-6, 389 µm	140 (blue on flyer surf)	LiF	11	1000	2800	3000	2750	point looks OK; line: accel but no clear impact, low contrast
14391	Cu, 105 µm	260 (brown on flyer surf)	GE-NiAl- D5-1-001-200-2, 221 µm	10	1000	2800	3000	2750	point: good flyer accel; line: looks like a slow accel; no sign of a shock breakout
7 Mar
14393	Cu, 105 µm	260 (brown on flyer surf)	GE-NiAl- D5-1-110-250-4, 264 µm	10	1000	2800	3000	2750	point: good flyer accel; line: looks like a slow accel; no sign of a shock breakout
14394	Cu, 55 µm	400 (pink on flyer surf)	NiTi 5B, 104 µm	12	1000	2800	3000	2750	point: nice accel; line: end of accel + shock breakout (tilted)
14395	Cu, 55 µm	400 (pink on flyer surf)	NiTi 5B, 93 µm	20	1000	2800	3000	2750	point: nice accel; line: end of accel + shock breakout
14396	Cu, 55 µm	140 (blue on flyer surf)	GE-NiAl- D5-1-110-250-3, 260 µm	5	1000	3200	3000	2750	point: nice accel; line: probe failed
14397	Cu, 55 µm	140 (blue on flyer surf)	GE-NiAl- D5-1-110-250-5, 242 µm	6	1000	3200	3000	2750	point: nice accel; line: probe weak but caught shock
14398	Cu, 55 µm	260 (brown on flyer surf)	GE-NiAl- D5-1-110-250-7, 229 µm	11	1000	2400	3000	2750	point: nice shock breakout; line: nice accel + reasonable shock breakout (tilted)
14399	Cu, 55 µm	260 (brown on flyer surf)	GE-NiAl- D5-1-001-200-1, 198 µm	11	1000	2400	3000	2750	point: nice shock breakout; line: nice accel, ?plasma across sample => no clear shock
14400	Cu, 105 µm	260 (brown on flyer surf)	GE-NiAl- D5-1-110-250-6, 268 µm		1000	2400	3000	2750	point: nice flyer accel; line: nice accel but missed shock (too early)
14401	Cu, 105 µm	260 (brown on flyer surf)	GE-NiAl- D5-1-001-350-2, 348 µm	10	1000	3100	3000	2750	point: nice flyer accel; line: flyer accel, sample v early precursor then shock
14402	Cu, 250 µm	140 (blue on flyer surf)	GE-NiAl- D5-1-001-400-3, 393 µm	11	1000	3400	3000	2750	point: looks OK for flyer accel; line: v early precursor then shock
14403	Cu, 250 µm	140 (blue on flyer surf)	GE-NiAl- D5-1-100-400-1, 391 µm	9	1000	3400	3000	2750	point: looks OK for flyer accel; line: v early precursor then shock
14404	Cu, 105 µm	260 (brown on flyer surf)	GE-NiAl- D5-1-110-250-4, 253 µm	11	1000	3100	3000	2750	point: nice flyer accel; line: sample v early precursor, dark region, then shock
14405	GE-NiAl- D5-1-110-400-3, 392 µm	150 (yellow)	LiF	10	1000	3200	3000	2750	point: looks good; line: OK accel; impact at end of record
14406	GE-NiAl- D5-1-001-350-4, 350 µm	150 (yellow)	LiF	11	1000	3400	3000	2750	point: looks good; line: accel ~OK, then messy - plasma leak?

Table 4. Summary of all shots.

In all cases, the spot diameter was ~5 mm, the drive laser delivered energy at 1.054 µm (IR), the dynamic diagnostic was VISAR velocimetry, the drive pulse was ~600 ns long, and the streak trigger delayed 500 ns from the probe laser trigger. Unless stated, all flyers were launched from a substrate of PMMA/C/Al/Al₂O₃/Al, to which they were glued with epoxy. Where used, LiF windows were ~1020 µm thick.

Observations

1. Point VISAR on Cu flyers: over ~200 mW, the signal return dropped sharply after the shutter was opened.

Log of notable events

• 1 Mar: go-ahead definite ~7 p.m. (a Friday)
• 2 Mar: ~5 hrs work on target assembly + scoping changes to optics
• 3 Mar: ~2 hrs of changes to optics
• 4 Mar: changes to optics, line VISAR timing
• 5 Mar: first shot ~10:00, next ~11:00; arc reported ~11:30; Trident reported out till ~13:30; at 13:30 extended till ~15:30; actually up ~14:40; last shot ~17:20.
• 6 Mar: Randy found polariser on Verde moved beam orientation, giving more signal for less power; from ~15:30 probe laser playing up; 16:05: static sample shot waiting for probe laser; probe back up ~16:50 (looking very nice).
• 7 Mar: apparently record for Trident shots/day (14 beat previous 13, Pete Walsh, higher energy but when working days were longer, and simple targets)

Results

For both NiTi (two compositions) and NiAl (two orientations), we collected data from a flyer of the sample material impacting a LiF window, and data from a copper flyer impacting the sample material. A range of impact speeds was used, up to a few hundred metres per second. In the case of the window impact data, the data collected were the flyer acceleration history and the deceleration on impact. For the copper flyer experiments, the data were flyer acceleration history and the free surface velocity history of the sample. The experiments concentrated on the sample types for which less (or no) data were obtained in December.

It should be possible to extract further EOS and strength data on NiTi and NiAl from these experiments.

Conclusions

Detailed analysis of the VISAR data is in progress.

We would like to have further TRIDENT time to complete the planned measurements on NiAl, 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.C. Swift, TRIDENT Postshot Report: Flyer Impact Experiments on NiTi and NiAl, December 2001 - "Pink Flamingo", LA-UR in preparation (2002).
2. 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).
3. D.C. Swift and R. Hackenberg, Laser-launched flyer experiments on nickel -- titanium alloy, LA-UR-02-1658 (2002).
4. D.C. Swift and K. McClellan, Laser-launched flyer experiments on nickel -- aluminium alloy, LA-UR in preparation (2002).

Distribution