Enhanced CAE Methodology to Predict Bolt Shear Failure using Multi-Layer Approach

Automotive seat system is one of the most complex systems in vehicle for its technical and functional requirements. Seat is designed to meet all regulatory requirements subjecting it to multiple tests with loading patterns which caters to the occupant safety. Varied loading and load path for different test requirements cause seat bolts to experience tensile, compressive, bending moments and shear loading. Shearing along bolt length is one of the common failure modes observed during design validation by physical tests. In the world of CAE, there is an industry approach to find the bolt failures at nut and head for all kind of loads. But shear failures along bolt lengths are not accurately predictable as multiple sheet metal parts will transfer loads unevenly onto bolt length and it becomes challenge to find which component is leading to shear failure. Hence by adding multiple rupture layers across the bolt length shear and its location could be predicted. Further, to resolve the bolt shear issues, engineers generally try to modify the component design for better energy absorption, but our research found that, only by increasing the clearance around bolt hole or by converting the hole to full slot or half slot (based on the bolt movement in forwards/upward/downward direction) will resolve the bolt shear issues. During one of such failures, a new approach of adding multiple rupture layers along bolt length was used which predicted the shear failure modes and location of shear as observed in physical tests. The CAE bolt model thus updated with new procedure for all such future bolt shear failure prediction in seat structure models.