Full-Field Deformation Measurements of Aluminum Plates Under Free Air Blast Loading

Assessment of the structural dynamic response caused by an explosion is complex due to the high velocity impact, the transient nature of the deformation and the interactions between the structure and the pressure wave. This paper deals with full-field measurements of aluminum plates under free air blast loading conditions. Forty grams of explosive material C4 is detonated at a stand-off-distance of 250 mm and two synchronized high-speed cameras in a stereoscopic setup are used to capture the plate response with an inter frame rate of 6,000 fps. The transient deformation fields are calculated using a three-dimensional digital image correlation technique. The observations appeared to be interesting and somewhat counter intuitively. Results show that a free air blast load induces a highly localized, rapid material response which can be essentially divided in two different stadia. First, when the shock impulse occurs, all particles are forced to move out-of-plane and provided with initial velocities. Secondly, when the pressure wave has vanished, the deformation is further driven by this imparted momentum. This paper shows that a 3D high-speed DIC system is a powerful tool for the assessment of the dynamic response of a structure subjected to extreme loading conditions such as explosions and that this system is capable of accurately measuring surface displacement and deformation data at high rates. Moreover, a free air blast load makes it possible to load a plate specimen at different strain rates in different zones. This makes the test suitable for future material identification using inverse methods, which profit from heterogeneous displacement and strain fields.