Impact on a head-neck structure

Abstract

An analytical and experimental study was executed involving non-destructive, axisymmetric impact on a fluid-filled shell constrained by a viscoelastic, artificial neck—a system intended to simulate a human head-neck structure. The shel material was considered to be homogeneous, isotropic and elastic, while the fluid was regarded as inviscid and compressible with its motion irrotational. The artificial neck was represented analytically by a linear viscoelastic cantilever beam that was rigidly connected to the shell. The physical model consisted of a water-filled uniform spherical thin-walled shell composed of lucite attached to an artificial neck developed by the Biomedical Laboratories of the General Motors Corporation. The system was loaded by the impact of a spherical aluminum shell with an o.d. of 7·4 in. that formed part of a simple pendulum. The impact force in both the analytical and experimental studies consisted of a half-sine pulse with a duration of 2·5 msec. The analytical solution first required the determination of the interaction forces and moments at the head-neck junction, which were ascertained from continuity conditions and an assumed rigid shell. These quantities, in turn, were applied simultaneously with the impact force to the deformable fluid-filled shell. yielding a boundary value problem that was solved on a digital computer. The resultant predictions of circumferential shell strain, fluid pressure, and displacement of the junction were found to be in good agreement with the experimental data. Implications of the results for head injury are discussed.