Comparing the behavior of homogeneous vs. fluid filled solid headforms under blunt impact loading conditions

A single point acceleration measurement at the center of gravity (C.G) of the rigid headform has been typically used to assess the head injuries under the blunt loading conditions. The head protective equipment (e.g. Helmets) used in sports, vehicles and defense fields are developed and tested based on this single point acceleration. This raises two critical questions; 1) can a homogeneous rigid headform represent the heterogeneous skull-brain complex; 2) If not, which is the critical point of measurement in the compliant headform. To answer these questions, compliant (acrylic gel complex) and rigid (aluminum body) head surrogates with an identical mass are subjected to similar blunt loading conditions. Target surfaces of different stiffness and an impact velocity of 1 m/s are employed to evaluate the critical difference in the head surrogates. Acceleration (C.G) and shell strain (impact location) in the compliant surrogate and acceleration (C.G) and the impact force in the rigid surrogate are experimentally measured. Experimental and computational studies illustrate that the acceleration field in the gel-filled case varies from coup to counter-coup region; however, the acceleration field in the rigid headform is uniform. The variation in the acceleration field is influenced by the shell deformation that in turn depends on the stiffness of the target surface. In deformable target surfaces, theacceleration and head injury criterion (HIC) values are higher inthe compliant surrogate than the rigid surrogate; the effect is reversed for rigid target surfaces.