Maximizing Cross Tension Impact Properties of Spot Welds in 1.5mm Low Carbon, Dual-phase, and Martensitic Steels

Investigating dynamic spot weld behavior for computer modeling of automotive structures is an important topic for discussion. However, current FEA efforts to model spot welds as part of larger structures during impact are hampered by the availability of appropriate dynamic data. This is partly due to the traditionally specified test methods and apparatus used. In this study, an instrumented accelerated drop weight tower is used to monitor the dynamic impact behavior of individual spot welds under normal loading. A new specimen geometry is introduced. Welds in 1.5mm thick steels with approximate tensile strengths of 315, 440, 700, 966, 1170, 1330, and 1550 MPa were investigated using a systematic arrangement of electrode force, weld time, hold time, button size, and impact velocity. Load-displacement curves were analyzed for curve shape, peak load, and impact energy absorbed by the weld. This data was used to identify weld schedules that maximize impact performance. The influence of steel tensile strength and interfacial fractures on weld impact properties and strain rate sensitivity were also assessed. A relationship between absorbed energy and dynamic peak load was found that delineated the influence of steel family on weld behavior, which has implications to weld pitch and automotive design concepts.