Search Results

With electric vehicles (EVs) and hybrid electric vehicles (HEVs) set to grow in the coming years, design optimizations of electric motors for automotive applications are receiving more attention. Under demanding duty cycles, the moving part within a motor, the rotor, may experience high and varying stresses, which may lead to fatigue failure. Therefore, engineers are facing challenges in designing efficient and durable motors, especially for interior permanent-magnet (IPM) motors, in which the rotors have embedded magnets with small "bridges" of laminated electrical steel to keep the magnets in place. Cost-effective stators and rotors are made from electrical steels, with high magnetic permeability and low power losses. However, national and international standards for electrical steels do not specify mechanical properties. Steel producers would normally state typical mechanical properties only, and no fatigue properties are available in published literature.

Durability assessment of automotive structures with resistance spot welds is an important part of automotive development. Down-gauging of vehicle body structures permitted by high strength steels brings added challenges to joint design. As a result, more accurate fatigue life analysis of joints is called for by automotive engineers, especially as part of the computer-aided engineering (CAE) evaluations in the early stage of model development. This paper will review, evaluate and compare spot-weld fatigue assessment techniques suitable for use in the CAE environment. Particular attention is paid to the process of generating technique-specific spot-weld fatigue property curves. The focus is then switched to two of the most promising techniques, which are evaluated in detail. The validity of the two techniques and the associated fatigue data are then demonstrated on fatigue life predictions of simple and complex components.

This paper summarizes the results of a recent study on a fatigue predictive technique for spot-welded automotive structures. The technique makes use of an equivalent stress intensity factor (Keq) as fatigue parameter for life predictions. A series of fatigue tests were conducted by using different types of fatigue specimens and weld arrangements. Using the raw test data collected, fatigue properties were processed in the form of ΔKeq versus fatigue life by a fracture mechanics based stress intensity factor technique. It is demonstrated that the fatigue properties are consistent among all the specimens tested and relatively geometry-independent. With the stress intensity factor based fatigue properties, the predictive technique was applied to more complex specimens with non-symmetric weld configurations and non-uniform loading conditions (resulting in mixed-mode loading on each weld). The results indicate good correlation between life predictions and test data.