A New Failure Criterion for Laminated Safety Glass

The prediction of the head injurie criterion (HIC) for pedestrian protection in automotive applications is still a great challenge. In particular, the simulation of the head impact on windshields requires a reliable FE-modelling technique as well as predictive material laws including the constitutive behaviour up to fracture. In the present work, a new failure criterion for laminated safety glass under low velocity impact is presented. The model is implemented as a user defined material model for shell elements in LS-DYNA. In order to represent the stress intensity in the vicinity zone of a crack tip, a mixture of the element erosion technique and a decrease of strength in the direction of cracks is considered. By that there is no need to determine the current stress intensity factor. The used failure prediction is similar to a major stress criterion and the fracture strength depends on the stress rate and, in addition, on the fracture state of the neighboring elements. The basic strength is derived from the first region of the crack-velocity dependency which is approximated by an empirical power law. The reduction of element strength in crack direction depends on the element size which allows the use of a regular, coarse mesh. Experimental results of head impact tests under different configurations are used for the validation of the present model.