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The fatigue property of dissimilar spot welds between an aluminium alloy (AA5052) and a magnesium alloy (AZ31) was studied in this research. The AA5052 and AZ31 coupons were resistance spot welded together by using an interlayer of Sn-coated steel between the two coupons. The fatigue test results revealed that the Mg/Al joints had the same level of fatigue strength as Mg/Mg resistance spot welds. It was found that within the life range of Nf < 105 cycles, Mg/Al welds degraded faster than Mg/Mg joints. This was attributed to the larger bending moment on the plane of fatigue failure in the Mg/Al welds. Three failure modes were observed under different cyclic loading regimes: Al/steel interfacial failure, Mg coupon failure and Al coupon failure. Fatigue fracture surface of Mg/Al welds consisted of two distinct regions: crack propagation region with brittle morphology and final rupture with ductile morphology. [ABSTRACT FROM AUTHOR]

This article proposes a thermal facture model of sandwich structures occupying a functionally graded interlayer with thermal resistance inside the crack region introduced. The crack surfaces are partially thermally insulated with thermally insulated crack and thermally conductive crack as limiting cases. A system of singular integral equations in thermo-elastic field is reduced and solved numerically by using the collocation methods with higher asymptotic terms in order to improve the convergence and accuracy. For a special case, exact solution is derived to validate the theoretical analysis and numerical computation. Numerical analyses are conducted to reveal the influences of the graded interlayer size, graded parameter and dimensionless thermal resistance on the temperatures along the crack plane and the stress intensity factors. [ABSTRACT FROM AUTHOR]

Fatigue crack propagation (FCP) behaviour of 4003 ferritic stainless steel was investigated using infrared thermography. Four stages of superficial temperature evolution were observed during the FCP tests: an initial temperature decrease stage, a temperature equilibrium stage, a slow temperature increase stage and an abrupt temperature increase stage; a thermal model is developed to explain the observed temperature evolution. The experimental results indicate that: when the range of stress intensity factor (Δ K) is at a low level where the crack is located in slow propagation region, thermoelastic effect will be in dominant status; when the Δ K is at a high level where the crack is located in stable propagation region, the temperature rise can be used to describe FCP rate. The fatigue fracture surfaces were examined using scanning electron microscope (SEM) in order to understand the effect of the fatigue mechanisms on temperature variation. [ABSTRACT FROM AUTHOR]