## 3 3D DIC in Blast and Shock Loading  
One of the earliest studies utilizing 3D DIC to measure the dynamic deflection of plates loaded through explosive blasts was a study by [PERSON] et al. [37] This study examined the response of aluminium 6061 sheets (\(356\times 406\times 1.6\) mm) to sub-surface detonations with a fixed stand-off distance. Two depths were used for the explosive, 7.6 mm and 25.4 mm, with a stand-off distance of 28.7 mm. [PERSON] et al. used a pair of Phantom V7.1 high-speed cameras (Vision Research Inc., Wayne, NJ, USA) to capture the images. The authors used a field of view of \(75\times 75\) mm and a frame rate of 61,538 FPS for the shallow depth detonations and a field of view of \(150\times 150\) mm and 26,143 FPS for the deeper detonations. Their results demonstrate that a shallow explosion causes a vertical deformation in the plate which is twice as large as the deep explosion, with similar trends in vertical velocity and vertical acceleration. The shallow plate experienced a maximum velocity of 230 m/s during the early stages of the blast loading. The 3D DIC also provided information regarding the strain rates experienced by the aluminium plates. The shallow detonation caused higher strain rates, but these were sustained over a shorter period of time than the deeper detonations [37]. [PERSON] et al. [38] conducted a study looking at the response of sandwich panels (back and front face sheets of glass-fibre reinforced polymer with a styrene acrylonitrile foam core) to explosive blasts in free air. The face sheets consisted of two plies of [0\({}^{\circ}\)/90\({}^{\circ}\)/\(\pm\)45\({}^{\circ}\)] e-glass each and the foam core had thickness of 40 mm. The explosive used in that study was 30 kgs of C4 with standoff distances of 8 m and 14 m. The intent of the 8 m standoff was to cause significant damage to the sandwich panels, while the 14 m standoff was to impart a pressure of \(\sim\)200 kPa to the sandwich panel and take them to their elastic limit, with no visible blast damage effects on the front face. The 3D DIC images were taken with a pair of Photron SA3 cameras (Photron USA, Inc., San Diego, CA, USA) sampling at 2000 FPS with a resolution of \(1024\times 1024\) pixels. The authors used the ARAMIS software (GOM GmbH, Braunschweig, Germany) for DIC image processing. To verify the 3D DIC results, the authors used a laser gauge as a secondary displacement measurement device, focused on the centre of the panel. With the larger standoff distance, the results show that there was a uniform and symmetrical response of the panel, up until the maximum out-of-plane displacement of 63 mm. Both the laser gauge and DIC data correlated well, up until the point of maximum deflection. After this point, vibrations transmit through the isolation mounts to the camera arrangement, changing their position relative to their original positions. There was no evidence of damage to the panel shown by their DIC analysis in terms of magnitude or distribution of strain. In comparison, the closer standoff distance resulted in significant damage to the panels. Initial damage occurs in the top left-hand edge of the panel and propagates down that side of the target. The displacement curve flattens around the time of the first indication of damage and peaks at a value of 131 mm, corresponding to a maximum strain of approximately 3%. At 3% strain, the front face sustained inter-laminar skin failure and front-ply fibre breakage, whilst the core suffered cracking from skin to skin, with the rear skin remaining intact. The severity of the failure increased towards the centre of the panel. The 3D DIC results showed the discontinuity in the strain field distribution caused by a separation of skin and core, as well as allowing the shifts in the deformed shape to be observed. From this it can be concluded that 3D DIC can be a powerful tool for monitoring structural integrity and identifying damage mechanisms in even extreme loading cases [38].