## 2 DIC Used in Impact Studies to Measure Target Deformation
[24] used multiple high-speed cameras to perform 3D DIC simultaneously, on both the front and back of composite panels constructed of [0\({}^{\circ}\)/90\({}^{\circ}\)] cross py layups of Dyneema HB26 and Spectra Shield 3124 UHMWPE fibres. The authors used a combination of pairs of cameras including the Phantom v711, Phantom v12 and Phantom v16 (Vision Research Inc., Wayne, NJ, USA), running at between 21,000 to 82,000 FPS. To ensure that the photography was synchronized, all of the cameras ran off a common trigger and common time reference [24]. The authors extended the speckle pattern onto the rig, holding the samples to identify if it moved during the experiment. The projectiles used to test the samples were 20 mm diameter steel and copper fragment simulating projectiles fired at a velocity of up to 1.2 km/s. The initial tests carried out were V50 tests and found that the ballistic limit for the Dyneema HB26 composite panel was around 700 m/s for both projectiles and about 600 m/s for the Spectra Shield 3124 impacted with the steel projectile and 700 m/s for the copper projectile. The 3D DIC on the front face of the Spectra Shield 3124 revealed that a certain part of the front face material experienced an inelastic deformation, but only experienced less than 1% tensile strain during the impact event, regardless of impact velocity. It also revealed that a bright flash, circular in shape, occurred during the instance of projectile-panel impact. This flash changed to a peanut shape as the projectile began to penetrate the panel. After the flash had dissipated, melted material was ejected from the sides of the projectile chiselled nose. After the impact, the 3D DIC revealed that the panels underwent in-plane motion before out-of-plane motion, due to the sonic velocity along the Dyneema fibres being significantly higher than the transverse velocity through the panel. This in-plane motion takes the form of wrinkles propagating towards the edge of the panel. Overall, the authors show that the Dyneema HB26 undergoes smaller out-of-plane displacements than the Spectra Shield 3124. In addition, the in-plane area of deformation for the Spectra Shield 3124 panels is significantly smaller than the Dyneema, likely due to a higher shear strength and stiffness in the Dyneema. As for 3D DIC conducted on the back face of the panels, the authors demonstrated that the primary and secondary  
Figure 3: Schematic diagram of the target used in [PERSON] et al. [22] Reproduced from [PERSON] et al. [22], with permission from Elsevier. yarns at the back of the panel did not experience more than 2% throughout most of the measured length, regardless of strike velocity. The primary yarns experienced the greatest strain throughout their lengths immediately after the flash at the front face vanished [24]. Given the recent increased threat of laser based systems, [PERSON] et al. [25] conducted a study using 3D DIC of the interaction between a high powered laser and carbon and glass fibre structural materials. For the 3D DIC, the authors used a pair of Optronis CR3000 cameras (Optronis, Kehl, Germany) running at 500 FPS and the VIC-3D software (Correlated Solutions, Inc., Irmo, SC, USA) to process the images and a single FLIR SC 7500 camera (FLIR Systems, Inc., Wilsonville, Oregon, USA) for infrared imagery. This study tested two different sample geometries, a thin carbon or glass laminate with 1.5 mm of foam core and a thick carbon or glass laminate with 5 mm foam core. The laser was a Nd:YAG type with a wavelength of 1.06 \(\upmu\)m, 10 Hz impulse frequency and an impulse duration of 2 ms. Each single impulse had 5 J of energy and was focused onto the target by a lens that gave an impact circle of 2 mm diameter. Each sample was impacted by 10 pulses. The results of their 3D DIC indicated that the internal pressure increased significantly, due to thermal degradation of the matrix and foam.