## 2 DIC Used in Impact Studies to Measure Target Deformation
The authors reported that the foam acted as an insulating material for both thermal transition and penetration of the laser light, significantly increasing the resistance of the structure to laser damage [25]. With advances in camera resolution and frame rate, obtaining an optimized speckle pattern becomes more important. [PERSON] and [PERSON] [26] designed a rig to hold a permanent marker in a custom fixture with a 3 axis milling machine providing accurate location control. Their custom fixture allowed for precise creation of a pre-generated speckle pattern, with specified speckle size. This control allows for the production of speckle patterns that give both 3 pixels per speckle and 50/50 black to white coverage. Using this rig, the authors were able to make patterns with about 3% spatial resolution (about 50 \(\upmu\)m), sized from 0.2 mm to 4 mm and coverage areas of 10 mm \(\times\) 10 mm to 200 mm \(\times\) 200 mm. Two Specialised Imaging Kiranas cameras, recording at 2 million FPS, were used to obtain the imagery for the 3D DIC. To test the speckle patterns with 3D DIC, the authors impacted 6.35 mm thick aluminium plates with, 12.7 mm diameter copper spheres at 1.2 km/s. The authors recorded a bulge of 18 mm in diameter and displaced nearly 9 mm prior to failure of the plate (which occurred in less than 15 \(\upmu\)s). Through the 3D DIC image processing, the authors were able to calculate the von Mises, radial tensile and radial compressive strains throughout the impact of the projectile into the plate [26]. [PERSON] [27] continued their work in 2019, by evaluating the underlying elements of uncertainty that affect collected data, during high-strain rate mechanical testing [27]. To test this, 3D DIC was conducted on a 6.35 mm thick aluminium disk, being impacted by a 6.25 mm diameter steel sphere with a velocity of approximately 500 m/s. The authors used a pair of Shimadzu HPV-X2 cameras (Shimadzu, Kyoto, Japan) operating at up to 10 million FPS. The DIC system was tested prior to the ballistic testing, investigating warm-up error, and displacement error. During the initial warmup (30-60 min), the cameras exhibited a sharp increase in temperature, leading to in-plane and out-of-plane errors of up to 60 \(\upmu\)m and 30 \(\upmu\), respectively. By 60 min of warmup, the error had decreased to 5 to 10 \(\upmu\)m and had decreased to 1 \(\upmu\)m by the 120-minute mark. Once the cameras had fully warmed up, [PERSON] examined the measurement error of the system, by displacing speckled target distances of 1-13 mm in increment of out-of-plane steps of 0.1, 0.2, 0.5 and 1.0 mm steps. The authors show that the error was in the range of 5-11 \(\upmu\)m (0.5-6% of the measured step size, respectively). As the step size decreased, the percent error increased as the precision limit of the DIC system was approached. The ballistic tests conducted on the 6.35 mm thick aluminium disk showed a peak surface displacement and velocity of 3 mm and 40 m/s when impacted by the steel sphere at 536 m/s, with an average interframe displacement of 120 \(\upmu\)m. The error for this range of displacement was taken by [PERSON] as being between 0.5% and 6% [27]. [PERSON] et al. [28] used 3D DIC to examine ballistic impact loading on carbon fibre materials, with a thickness of 6.35 mm and 25.4 mm. The authors used two different carbon fibre layup architectures,one being 2D layups laminated into a single panel and the other with a complex 3D panel. The 2D carbon fibre panel was laid up in a [0\({}^{\circ}\)/45\({}^{\circ}\)/-45\({}^{\circ}\)/90\({}^{\circ}\)] stacking sequence with 2 stacks used for the nominal thickness of 6.35 mm, and 8 stacks were used and for the 25.4 mm thickness. The 3D panels had a complex weave, with differing architecture between the 6.35 mm and 25.4 mm thickness panel. Both the 2D and 3D panels, with a nominal thickness of 6.35 mm, had an areal density of 0.97 kg/m\({}^{2}\), and the 2D and 3D panels with a nominal thickness of 25.4 mm had an areal density of 3.9 kg/m\({}^{2}\).