1. Soft Targets Protection – Prague – 19th October 2018
Delaminiation of UHMWPE composite materials by laser induced shock waves
L.-C. ALIL, M. ARRIGONI, M. ISTRATE, A. N. KRAVCOV, G. TAHAN, J. LE PAVIC
Soft Targets Protection – Prague – 19th October 2018
Soft Targets Protection – Prague – 19th October

2. Context Ballistic and terrorist threats :
Armoured vehicules and ballistic protections are heavy !
Light weight armour and ballistic protections !
Soft Targets Protection – Prague – 19th October

3. Content Composite materials for light weight armours
Terminal ballistic in UHMWPE & Tensylon®
Laser shock as delaminator
Laser shock and terminal ballistic
Experimental results
Conclusions
Prospects
Soft Targets Protection – Prague – 19th October

4. Composite materials Performance evaluation by Ashby method:
[Cunniff 2002, 23rd Army conf.]
Fibre behavior
Soft Targets Protection – Prague – 19th October

5. Terminal ballistics in UHMWPE
Penetration failure mechanisms of UD UHMWPE laminates
h/d = target thickness / projectile diameter
Quantitative relations of different stages for varied ratio of h/d.
[D. Zhang 2014, Materials and Design]
8,4 mm
16,92 mm
25,24 mm
thicknesses
Stage I : Penetration
Stage II : Damage
Stage III : Delamination
Thickness h increases => energy is disspated by stage III :
delamination
Soft Targets Protection – Prague – 19th October

6. Tensylon® UHMWPE Manufactured by Dupont®
Pre-pregs of 2 plies oriented [0,90°]n + hot pressing
Soft Targets Protection – Prague – 19th October

7. Terminal ballistics in UHMWPE
Impact of FMJ 7,62 mm at 700 m/s on Tensylon UHMWPE
[Alil, 2018, Express Polymer Letters]
23mm
Delamination is more than 20 times the caliber
Multi delamination observed, also reported by Lässig on Dyneema HB26 [Lässig 2017]
Soft Targets Protection – Prague – 19th October

8. Terminal ballistics in UHMWPE
Multi delamination by plate impact at 236 m/s on Dyneema HB26 [Lässig 2017]
Soft Targets Protection – Prague – 19th October

9. Laser shock as delaminator
Extensive studies about LASer Adhesion Test (LASAT) :
[Ehrhart, 2014, PhD dissertation]
Soft Targets Protection – Prague – 19th October

10. Laser shock / Ballistic impact
Pressure loading P:
Laser shock
Ballistic impact
[Berthe, 1999]
Power dens. ϕ (GW/cm²)= Emax(J)/(τ(s).S(cm²))
Power dens. and materials:
6-7 GPa Wa Cf / 100 Gpa vac
Impact velocity and materials :
1 – 10 Gpa for 800 m/s
Impact diameter 2 to 5 mm
Imapct diameter 5 to 13 mm
Max rep rate 10 Hz
Max rep rate 10 Hz
Laser shock provides P of same order of magnitude as ballistic impact !
Soft Targets Protection – Prague – 19th October

11. Laser shock / Ballistic impact
Duration τ:
Laser shock
Ballistic impact
[Arrigoni, 2008]
Time ns
200 1
Vacuum / air τ = 15 ns
Confined pulse τ = 30 ns
Laser pulse τ = 10 ns
τp = π.ωp with ωp = (1/r)√(3Pmax/2ρ)
[Hutchings, 1983] for spherical projectile
τp =52 µs for Mark IV bullets at 610m/s
[Hopkinson, 1914]
Cible
rprojectile = 3.5 mm
V0 = 800 m/s
V0 = 400 m/s Al
τp(µs)
4.2
6.3
Pmax (GPa)
9.0
4.0 PE
τp (µs)
8.0
12.6
2.5
1.0
τ can be tuned by flyer technique but in detriment to impact velocity …
Laser shock provide τ /1000 of what obtained by ballistic impact !
Soft Targets Protection – Prague – 19th October

12. Experimental setup
Laser induced shock waves on UHMWPE [Alil 2018, Materiale Plastice]
Soft Targets Protection – Prague – 19th October

13. Experimental results
HV signal for 1,15 mm thick 1,8 GW/cm²
Soft Targets Protection – Prague – 19th October

14. Discussion
From spallation signature to stress and strain rate evaluation
Spall strength : [Gay, 2014 ]
Strain rate:
Soft Targets Protection – Prague – 19th October

15. In agreement with 50 MPa given by Lässig 2015 for Dyneema
Discussion
HV signal for Tensylon® and referred spall strength and strain rates :
Sample
Thick. [mm]
ΔU [m/s]
Δt [s]
σrupt [MPa]*
𝜺 [s-1]*
T-1
1.15
46.3
93.7 58
-3.65E+06
T-2
40.2
124 48
-1.97E+06
T-3 60
120
-8.74E+06
T-5
2.45 18
80.8 32
-1.37E+06
T-9 57
210 46
-2.21E+06
T-10 80
185 33
-2.34E+06
Mean rupture stress
45.8
*ρ=0.94 g/cm3 and C0=1797 m/s
In agreement with 50 MPa given by Lässig 2015 for Dyneema
Soft Targets Protection – Prague – 19th October

16. Conclusions
Material evaluation showed UHMWPE as good candidate material for ballistic protection,
Preliminary experiments showed Tensylon® is able to stop 7,62*39 at 700 m/s,
Literature review tells that delamination plays a major role for thick tarkets,
Laser shock experiments with HV records evidenced delamination at high strain rate (> 2e6 s-1) for an interply strength of 45 MPa, close to that observed on Dyneema®,
Tensylon® is transparent to the laser wavelength,
Difficulties to make cross section observations by cutting,
Xray µtomography did not allow measuring the delamination,
Soft Targets Protection – Prague – 19th October

17. Prospects
Delamination strength dependance : ageing / T° / strain-rates,
Out of plane characterisation [Matache 2018],
Numerical modelling of experiments :
Laser-Matter interaction to have a suitable loading
FEM explicit with damage model
Soft Targets Protection – Prague – 19th October

18. Questions … ?
Soft Targets Protection – Prague – 19th October