INERTIA-SENSITIVE IMPACT ENERGY-ABSORBING STRUCTURES .2. EFFECT OF STRAIN-RATE

By employing the elastic-plastic structural model introduced in part I [1], which contains four compressible bars and four elastic-plastic ' 'hinges'' of finite length, the entire dynamic deformation history of Type II structures is traced. In contrast to part I, strain-rate effec ts are incorporated into the analysis throughout the entire response o f the structure. The Cowper-Symonds relation is adopted and the yield stress varies with the current strain-rate during the dynamic response of the model. The numerical examples presented show that the strain-r ate effect plays an equally important role to that of inertia on the d ynamic behaviour of this kind of energy-absorbing structure if the mat erial of the structure is rate-sensitive, e.g. made of mild steel. Com pared with the corresponding quantities in the quasi-static case, the combined effects of strain-rate and inertia make the peak load much hi gher and the final displacement much smaller. It is also found that be cause the increase of the yield stress due to strain-rate sensitivity expands the range of elastic deformation, the elastic strain energy st ored in the structure made of rate-dependent material is notably large r than that in the structure made of rate-independent material. This i mplies that when strain-rate effects are taken into account in the ana lysis, elasticity must play a more significant role and should not be neglected.