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DoD MEMS Fuze Reliability Evaluation
58th Annual NDIA Fuze Conference, Baltimore, MD Thursday, July 9th 2015, Open Session VA, 14:00
Presented by Daniel Lanterman (NSWC IHEODTD) for:
Taylor T. Young
NSWC IHEODTD
Jeffrey Smyth U.S. Army ARDEC Picatinny Arsenal
RDAR-MEF-F Fuze Division
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MEMS Safe and Arm Chip
Set-back Lock
Command Lock
Slider
Initiator
Arming Micro Motor
Micro Detonator
Shown in Safe (unarmed) Position
Setback Lock
Command Lock Command
Armed Slider Front
Back
Micro-Detonator
Cup
MEMS based fuzing offers the potential for small volume, low cost, and low energy.
NSWC IHEODTD has been investigating silicon based MEMS for over a decade.
Can use either command arm/lock release motors or built in environmental sensors.
All non-explosive components fabricated on SOI wafers using established semi-conductor processes.
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MEMS Applications Hypervelocity Projectile 40 mm Grenade
High Reliability DPICMS Replacement (HRDR)
HRDR brief by Daniel Pines at 4:40 today in US only session
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Explosive Train Overview • Based on micro-detonator technology
developed at NSWC IHEODTD – Demonstrated to TRL6 in 40 mm
Grenade configuration
• Initiator fabricated onto the cap chip – Vaporizing metal foil bridge
• Pressed silver azide pellet assembled with the MEMS S&A chip
• Silver azide drives a flyer to initiate a lead
• Lead make 90° turn and initiates a booster
• Energetic components packaged in a metal fixture that is attached to an electronic PCB μDetonator Package
Output to Booster
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Navy Explosive Train (Basics)
MEMS Microdetonator 6 mg - φ2 mm Silver Azide
Booster Charge – RSI-007/PBXN-5
Lead –EDF-11
MEMS Chip Base Chip
Cap Chip
Secondary Lead (EDF-11)
RSI-007
Flyer Plate
HE-to-HE or
Flyer Contact
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Army Explosive Train (Basics)
MEMS Microdetonator
Energetic Ink
Booster Charge – EDF-11
Lead – EDF-11
MEMS Chip
Base Chip
Cap Chip
Lead (EDF-11)
Booster
(ED
F-11)
HE-to-HE Contact
Flyer Plate
Both detonators use stainless steel flyer plates
US Army AREDEC also has a MEMS Fuze effort.
Uses LIGA metal MEMS processes.
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Explosive Train Reliability
• MEMS intentionally pushes the lower limits of explosive component size. We want the smallest size detonators and leads that will work reliably.
• Target programs have strict reliability requirements. This is particularly true for HRDR which must comply with OSD’s policy of >99% reliability for cluster munitions.
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Brute force methods
Brute force demonstrations requires excessive number of shots to prove reliability. 99.9% Reliability @ 95% CL: 3000 Shots
0.7
0.75
0.8
0.85
0.9
0.95
1
10 100 1000 10000 100000
Rel
iabi
lity
Number of Shots Without Failures
0.00001
0.0001
0.001
0.01
0.1
1
1 10 100 1000 10000 100000 1-
Rel
iabi
lity
Number of Shots Without Failures
Binomial Reliability at 95% Confidence Level (one sided)
100 shot test series only demonstrates reliability to 97% (@ 95% CL)
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Background – Traditional Estimation Methods
Traditional Reliability Methods have imposed penalties on the system. These penalties are large enough to produce an observable failure rate. Reliability is obtained by extrapolating to zero penalty. Penalties take the form of gaps (Varigap testing), reductions in donor output either through reducing its density or using less powerful explosives (Varidrive testing) or using less sensitive acceptor explosives (Varicomp testing).
All of these methods are problematic at the MEMS scale. Varidrive and Varigap change the shock curvature generated. Changes to explosives in Varidrive and Varicomp are not advisable since MEMS systems are near critical diameter.
Flat Shock Curved Shock
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Background – A New Approach
• Separate response of donor and accepter at each interface.
Variation in Response of Acceptor
Variation in Response of Donor
Overlap – Probability of Failure
•Data can better be used to evaluate a family of similar designs.
•Data also provides more insight into the system and can be used to optimize design
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Background – Probabilistic Hugh James Space
0 0.5 1 1.5 2 2.5 30
0.5
1
1.5
2
2.5
3
3.5
4
Σ = u2/2
E=P
u τ
50% reliability1% reliability99% reliability
Increasingreliability
1/J=Ec/E+Σc/Σ
Ec (critical minimum energy) & Σc (critical minimum ‘power’) are defined by the acceptor explosive material. E & Σ can be calculated from variable flyer and gap tests and inherent explosive properties. These methods were developed at AWE and LLNL and implemented at AFRL.
Hugh James formalism can be used to map out statistical response of acceptor explosive
0 0.5 1 1.5 20
0.2
0.4
0.6
0.8
1
JP
roba
bilit
y
Normal distrubution about thresholdProbability of detonation transfer
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Detonator Characterization
MEMS flyer velocities can be measured with PDV
Variability will be present in any system Need to shoot a sufficient number (100+) to fit to a statistical distribution. Exact number of shots needed depends on how quickly tails of distribution die off.
PDV system can also be used to measure pressure time histories for contact detonation interfaces.
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PDV Measurements Navy Army
PMMA
Barrel
SS Flyer
MEMS Initiator
AgN3
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PDV Results - Navy
14
0
1
2
3
4
5
6
7
8 Co
unt
Bin
20 shots analyzed to date. Additional shots planed.
Standard deviation 4.7% of mean value.
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EDF-11 HJ Parameterization • Electric gun will be used to make
EDF-11 sensitivity measurements. • Conduct threshold testing at several
flyer thicknesses (0.5, 1, 2 & 3 mils Kapton)
• 1.6mm square flyer. Based on computer models of the flat section of MEMS flyer.
• Limited number of previous measurements at EFI relevant length scales, but spot size dependent.
Need to have Hugh James Initiation data at MEMS scales
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Flyer Measurements in HJ Space
E
Σ
Navy MEMS Data
Army MEM data
Remember: the Navy design uses a larger diameter flyer
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Previous EDF-11 Threshold Measurements
E
Σ
Navy MEMS Data
Army MEM data
EDF-11 Threshold Data
LLNL has made previous threshold measurements on EDF-11
These measurements were made at EFI length scales, and would be lower at larger spot sizes.
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Fit ill-defined E
Σ
Navy MEMS Data
Army MEM data
EDF-11 Threshold Data
These two points do not well define a hyperbolic fit.
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Proposed Measurement Paths E
Σ
Navy MEMS Data
Army MEM data
EDF-11 Threshold Data Threshold FIt
.5 mil flyer
1 mil flyer
2 mil flyer
3 mil flyer
Each flyer thickness defines a path through HJ space.
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Upcoming • Finish detonator experiments and fit distribution
function • Multiple threshold test series of EDF-11 in a
MEMS relevant Hugh James Space – 0.5,1,2, and 3 mil thick Kapton
• Transfer lead output test series – PDV measurements of lead output
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Conclusions • New explosive trains require new methods of analysis.
• These new methods can better aid intelligent design.
• We believe we have a reasonable path to demonstrate
reliability.
• Both and the Navy and Army are committed to ensuring that MEMS fuzing achieves the highest degrees of reliability possible.
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Acknowledgments Section: Thanks to the Joint Fuze Technology Program (JFTP) for funding this work.
Thanks to Chadd May and Lawrence Livermore National Labs (LLNL) for the loan of the
electric gun.
Thanks to those who have helped work on the project:
ARDEC Roger Cornell
Charlie Robinson Brian Fuchs
NSWC IHEODTD G. Shane Rolfe Jason Brindle Daniel Pines
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