The fact that helmets can prevent head injury is well-established. This paper describes the use of a dynamic, inelastic and large deformation finite element code LS-DYNA3D to simulate the impact response of motorcycle helmets. In order to verify the accuracy of the model, the simulation results of helmet drop on steel anvils were compared with experiments. The numerical predicted results matched experimental data very well. We then study the effects of ventilation holes. EPS shell with ventilation holes absorbed shock better than intact one when impacting the flat anvil, but not when impacting the hemi-sherical anvil. Next, a full FEM model which contain Hybrid III head, neck, and chest has been developed and couple with helmet FEM model for analyzing the kinematics of the neck motion and the associated dynamic transient response of the head subjected to various impact angles. The critical characteristics such as head C.G. acceleration, section forces and moments at the head-neck section and neck-chest section are investigated for each cases. Thus we have established a reliable 3D finite element model which can help us to better design the helmet.
The shear localization phenomena during serrated chip formation in high speed orthogonal metal cutting process have been studied by using the explicit finite element analysis. A three dimensional computational model has been developed for analyzing dynamic thermomechanical deformations of a thermally softening viscoplastic workpiece material subjected to various tool cutting speeds and tool rake angles. The shear band characteristics such as temperature contour, effective plastic strain, effective plastic strain rate, propagating speed and orientation are investigated for each cases. Cutting forces can be estimated by this 3D model. The predictions of the finite element analysis are shown that above a critical high cutting speeds the secondary shear of the chip on rake surface appear to be a negligible effect which indicated the chip segments can be separate completely due to extensive shear in the primary shear zone; this phenomena agreed well with the experimental observations. The numerical model presented here can easily applied to study the oblique cutting process.
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