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 Michel.arrigoni@ensta-bretagne.fr Soft Targets Protection – Prague – 19th October 2018 Soft Targets Protection – Prague – 19th October 2018 1

Context Ballistic and terrorist threats : Armoured vehicules and ballistic protections are heavy ! Light weight armour and ballistic protections ! Soft Targets Protection – Prague – 19th October 2018 2

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 2018 3

Composite materials Performance evaluation by Ashby method: [Cunniff 2002, 23rd Army conf.] Fibre behavior Soft Targets Protection – Prague – 19th October 2018 4

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 2018 5

Tensylon® UHMWPE Manufactured by Dupont® Pre-pregs of 2 plies oriented [0,90°]n + hot pressing Soft Targets Protection – Prague – 19th October 2018 6

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 2018 7

Terminal ballistics in UHMWPE Multi delamination by plate impact at 236 m/s on Dyneema HB26 [Lässig 2017] Soft Targets Protection – Prague – 19th October 2018 8

Laser shock as delaminator Extensive studies about LASer Adhesion Test (LASAT) : [Ehrhart, 2014, PhD dissertation] Soft Targets Protection – Prague – 19th October 2018 9

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 2018 10

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 2018 11

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

Experimental results HV signal for 1,15 mm thick Tensylon® @ 1,8 GW/cm² Soft Targets Protection – Prague – 19th October 2018 13

Discussion From spallation signature to stress and strain rate evaluation Spall strength : [Gay, 2014 ] Strain rate: Soft Targets Protection – Prague – 19th October 2018 14

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 2018 15

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 2018 16

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 2018 17

Questions … ? Soft Targets Protection – Prague – 19th October 2018 18