Application of Crack Propagation Simulation of Windshield to Roof Strength Analysis

This paper describes a new modeling method to represent the crack propagation of windshield, namely the laminated safety glass. In the roof strength analysis used for vehicle development process, it is not easy to accurately predict crack propagation paths with existing modeling method, e.g., improving material properties. If the windshield cracks in a test using a prototype vehicle, the body deformation in the simulation and that in the test might not match, resulting in a less accurate simulation of force transfer to vehicle frames through the windshield. Therefore, prediction of crack propagation in a windshield is significant in accurately estimating the deformation and improving the accuracy of roof strength simulation results. The new modeling method to represent the crack propagation of the windshield was applied using tied overlapping shell technique, one of the modeling methods for material fracture, which has been developed by Kojima et al. The tied overlapping shell technique consists of element groups made of base elements and overlapping elements which are rotated 45 degrees in the normal direction. The base and the overlapping elements are connected using tied contact. The physical laminated safety glass windshield is constructed by placing an adhesive polyvinyl butyral (PVB) interlayer between two glass panes, outer glass and inner glass. In this study, double overlapping shell parts and a PVB interlayer part were applied to a windshield model to represent the crack propagation of the glass. Consequently the model has three layers with five mesh plates. Each part is modeled with shell elements and positioned corresponding to the neutral location of each layer thickness respectively. Four-point bending tests using specimens cut out of windshield glass were carried out to determine the critical fracture strain of glass considering the loading mode in roof strength analysis. Thereafter, application of the windshield glass model developed in this study to a roof strength analysis model was carried out to validate against test data. This paper summarized the application of new modeling method to represent the crack propagation of windshield glass in a roof strength analysis. It was found that the first two cracks propagation and the maximum force of the roof strength could be simulated. In the model the first two cracks propagated in the same shape as seen in the test. However, the number of crack propagation paths observed in the simulation was just two while there were many crack paths observed in the test. In addition, the difference in the maximum force of the roof strength between in the simulation and in the test was approximately 1%. However, after the cracks occurred, the force dropped more rapidly in the simulation than in the test. With this consideration there may be room for correction of the elimination methods.