## 3 3D DIC in Blast and Shock Loading
The air blast panels had a size of 1.6 m \(\times\) 1.3 m and the underwater panels had a size of 0.4 m \(\times\) 0.3 m. The authors sized the air blast panels to represent full-scale face panels of comparable magnitude to real naval structures and sized the underwater panels to allow for sufficient rigid edge restraint/support during the tests. The air blast was created by 30 kgs of C4 plastic explosive, at a standoff distance of 8 m and 14 m. The 14 m standoff distance was setup to expose the panels to an approximate shock pressure of 200 kPa and take the panels to their elastic limit, while the 8 m standoff distance was chosen to inflict damage to the panels. Notably, 3D DIC was only used for the air blast experiments and the authors used a pair of Photron SA3 cameras (Photron USA, Inc., San Diego, CA, USA) running at 2000 FPS, to obtain the high-speed imagery. The high-speed imagery was processed using the ARAMIS software (GOM GmbH, Braunschweig, Germany) package and the results were verified by use of a laser gauge on the centre of the target. Their results show excellent correlation between the 3D DIC and laser gauge of less than 1% error. For the 14 m standoff, the sample with a 40 mm core deflected by 63 mm (1% major principle strain) and the sample with a 30 mm core deflected by 78 mm (1.25% major principle strain). The 3D DIC did detect signs of mild sub-surface core cracking from early discontinuities in the major principle strain plots. To determine the failure diagnostic capabilities of the 3D DIC technique, a panel with a 40 mm thick core and 8 m standoff distance was used. The authors reported a flattening in the displacement curve near the maximum deflection (131 mm out-of-plane displacement with a 3% strain) that corresponded to crack formation in the skin of the panel. Their results demonstrated that 3D DIC can be a very powerful tool for monitoring the structural integrity of various materials and identifying damage mechanisms occurring even when subjected to extreme loading cases [41]. [PERSON] et al. [42] investigated sandwich structures with e-glass composite skins, SAN foam cores and polyurea interlayers. The e-glass composite skins had woven fibres laid up in a [0\({}^{\circ}\)/45\({}^{\circ}\)/90\({}^{\circ}\)/\(-\)45\({}^{\circ}\)] orientation and were 5 mm thick. The SAN foam cores consisted of 3 layers of foam with low, mid-range and high density, with an overall thickness of 38 mm. The first two layers of the core were low and mid-range density and had a thickness of 12.7 mm, with the third being high density and 6.35 mm thick. The authors had two configurations, (i) one located at the polyurea layer just behind the front face sheet, and (ii) the other located it just in front of the back sheet. [PERSON] et al. exposed the configurations to two loading conditions, an incident peak pressure of 1 MPa and wave speed of approximately 1000 m/s and an incident peak pressure of 1.5 MPa and a wave speed of approximately 1300 m/s. The high-speed imagery was captured with a pair of Photron SA1 cameras (Photron USA, Inc., San Diego, CA, USA) operating at 20,000 FPS and no information was given regarding the software used to process the 3D DIC imagery. The authors show that both configurations exhibited maximum deflection in the low-density foam layer, but configuration (i) had a more uniform load distribution and exhibited maximum compression later in the deformation history. This maximum compression later in the deformation history leads to less transmission of the load to the medium density foam layer. The 3D DIC shows that configuration (i) exhibited a maximum strain of approximately 2.6% across the central region and a maximum out-of-plane velocity of 30 m/s, compared to configuration (ii), which had a maximum strain of approximately 1.625% and a maximum out-of-plane velocity of 24.375 m/s. This shows that configuration (ii) had about 35% less maximum strain and 15% less maximum out-of-plane velocity. [PERSON] et al.