A fatigue design parameter for spot welds

The development of fatigue cracks in galvanized low carbon and high-strength-low-alloy tensile-shear-spot weldments was investigated using the AT & T Microhmeter. The boundaries between the three stages of the fatigue life were determined based on the resistivity measurements of the Microhmeter. Subsequently, the effects of sheet thickness, specimen width, and nugget diameter on the total fatigue life as well as its stages were studied. Sheet thickness was found to have the largest effect on fatigue life while the nugget diameter had the least. The galvanized low carbon tensile-shear specimens outperformed the corresponding high-strength-low-alloy specimens in the long life regime.The finite element analyses together with the displacement match technique were used to determine the stress intensity factors for the tensile-shear specimen. Several geometries were analyzed and the effects of the sheet thickness, nugget diameter, specimen width and free length on the stress intensity factors were determined. The stress intensity factors determined from the linear three dimensional finite element analyses failed to correlate the fatigue data of tensile-shear specimens with different dimensions.Consequently, an empirical K$\sb{\rm i}$ parameter based on the experimental fatigue data was derived. The K$\sb{\rm i}$ parameter collapsed the fatigue data of different spot welded specimens into a narrow band for which a best-fit was obtained. The best-fit equation help estimate the fatigue life while the K$\sb{\rm i}$ parameter provide the designer with a useful tool for designing the spot welds against fatigue and studying the effects of varying any of the design variables on the fatigue performance of the spot welded joint without having to resort to extensive testing.U of I OnlyETDs are only available to UIUC Users without author permissio