Effects of assembly loads on fatigue failure of bimetallic tapered joints

In this investigation, an aluminium disk specimen with a steel tapered stud is designed to represent a typical tapered steel stud and aluminium knuckle assembly. The steel stud and the aluminium disk are assembled together by interference fit. Experiments are conducted to determine the relationship between the assembly parameters of draw load and draw distance for coated and uncoated steel studs. These experimental results are compared to the corresponding computational results to determine the effective coefficient of friction needed in computational simulations of the assembly process and subsequent service loads. The results for the coefficients of friction from the combined experimental and computational analysis are then used to analyse the thread fatigue failure of bimetallic tapered joint assemblies under cyclic service loads with consideration of assembly loads. The computational results show that for bimetallic tapered joints under cyclic service loads with different assembly draw loads, the equivalent completely-reversed stress amplitude for the material element of interest near the first thread of the stud is higher for cases with smaller assembly draw loads. These results correlate with the experimental observations that lower assembly loads tend to decrease the fatigue initiation life near the first stud thread root in tapered bimetallic joints under cyclic loading conditions.