Application of computational plasticity to the analysis of vehicle cab frames

The application of computational plasticity to the very practical engineering problem of crash‐worthiness of vehicle safety cab frames during impact and rollover incidents is described. The resulting behaviour of these structures cannot be determined solely by strict elastic analyses as plastic behaviour is intrinsic to the problem. The importance of predicting the deformations of the cab structure under extreme loadings lies in a consideration for the safety of its occupants. Physical testing is extremely valuable here but is costly and time‐consuming. The role of the computer is thus evident in producing rapid estimates of cab collapse modes, loadings and deformations. Three main causes of non‐linearity are identified in the behaviour of ductile framed structures under static loading, i.e. the effects of plasticity in the structural material, the effects of axial forces and the effects of large displacements of the structure under load. The paper describes and compares two computer programs which have been used to model the behaviour of vehicle cab frames when subjected to roof crush loading in a static test. Both programs employ non‐linear beam finite elements to model the behaviour of a framed structure. One program runs in an iterative fashion while the other runs in an incremental fashion.