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A B S T R A C T Aluminium is a lightweight material with high strength and good corrosion resistanceamong other beneficial properties. Thanks to these properties, aluminium is more extensively used in the vehicle industry. High-pressure die casting of aluminium is a manufacturing process that makes it possible to attain complex, multi-functional components with near-net shape. However, there is one disadvantage of such castings, that is, the presence of various defects such as porosity and its effect on mechanical properties. The aim of this work was to investigate the influence of porosity on the fatigue strength of high-pressure die cast aluminium. The objective was to derive the influence of defect size with respect to the fatigue load, and to generate a model for fatigue life in terms of a Kitagawa diagram. The aluminium alloy used in this study is comparable to AlSi9Cu3. Specimens were examined in X-ray prior to fatigue loading and classified with respect to porosity level and eventually fatigue tested in bending at the load ratio, R, equal to −1. Two different specimen types with a stress concentration factor of 1.05 and 2.25 have been tested.It has been shown that the fatigue strength decreases by up to 25% as the amount of porosity of the specimen is increased. The results further showed that the influence of defects was less for the specimen type with the higher stress concentration. This is believed to be an effect of a smaller volume being exposed to the maximum stress for this specimen type. A Kitagawa diagram was constructed on the basis of the test results and fracture mechanics calculations. A value of 1.4 Mpa m 1/2 was used for the so-called stress intensity threshold range. This analysis predicts that defects larger than 0.06 mm 2 will reduce the fatigue strength at 5 × 10 6 cycles for the aluminium AlSi9Cu3 material tested. A = area of the defect a = 'crack length', defect radius da d N = crack growth rate N = number of cycles to failure K = stress intensity factor K t = elastic stress concentration factor R = stress ratio (=σ min /σ max ) K = stress intensity range K th = stress intensity threshold range at approximately 10 −9 m/cycles σ n = nominal stress range σ an = nominal stress amplitude σ FL = fatigue strength at N = 5 × 10 6 cycles

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The fatigue strength of spot‐welded stainless sheet steels has been investigated. The main part of the fatigue tests was performed on a cold rolled austenitic stainless sheet steel (AISI304) in air at ambient temperature. For comparison, a duplex stainless steel (SAF2304) of similar yield strength as AISI304 was also incorporated into the test programme. Since the fatigue strength of spot‐welded joints depends on the mode of loading, both shear‐loaded and peel‐loaded joints were tested. The fatigue strength of the spot‐welded stainless steels was found to decrease with decreasing sheet thickness. Furthermore, the fatigue strength for peel‐loaded joints is lower than that of shear‐loaded joint for sheets of equal thickness. The local loading conditions at the weld edge have been analysed in terms of finite element calculations and fracture mechanics. A design parameter derived from a fracture mechanics analysis was defined for spot‐welded stainless sheet steels. It was shown to predict the fatigue life of the present steels and joint configurations in a satisfactory way.

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