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A general failure criterion for spot welds is proposed with consideration of the plastic anisotropy and the separation speed for crash applications. A lower bound limit load analysis is conducted to account for the failure loads of spot welds under combinations of three forces and three moments. Based on the limit load solution and the experimental results, an engineering failure criterion is proposed with correction factors determined by different spot weld tests. The engineering failure criterion can be used to characterize the failure loads of spot welds with consideration of the effects of the plastic anisotropy, separation speed, sheet thickness, nugget radius and combinations of loads. Spot weld failure loads under uniaxial and biaxial opening loads and those under combined shear and twisting loads from experiments are shown to be characterized well by the engineering failure criterion.

Experiments to obtain the failure loads of spot welds are first reviewed under combined opening and shear loading conditions. A failure criterion is then presented for spot welds under combined opening and shear loading conditions based on the results from the experiments and a lower bound limit load analysis. In order to account for spot welds under more complex loading conditions, another lower bound limit load solution is presented to characterize the failure loads of spot welds under combinations of three forces and three moments. Based on the limit load solution, an engineering failure criterion is proposed with correction factors determined by different spot weld tests. The engineering failure criterion can be used to characterize the failure loads of spot welds with consideration of the effects of sheet thickness, nugget radius and combinations of loads.

Recent design characteristic changes in a small segment of production passenger car front seats have focused attention on the influence of seat back strength on occupant kinematics and potentially injurious loads placed on occupants during rear end collisions. The National Accident Sampling Study database from the years of 1980 to 1993 was interrogated to determine the relationship between vehicle change in velocity, and the nature and severity of injuries sustained by passengers occupying those seats in rear end collisions. The results of the NASS data analysis show that the yielding seats in most current automobiles perform well as a passive restraint system. When the yielding passenger car seats are compared to the stiffer seat/cab, the passenger car seats offered improved protection. Additionally, the data indicate that the three point restraint system provides protection and restraint for front seat occupants in rear impact.