Fatigue Crack Analysis of Magnesium ZK60 V-Notched Specimen Using X-Ray Tomography

Abstract

Magnesium alloys are attractive lightweight structural materials that have the potential to be used in aerospace, automotive and medical industries. However, fatigue is a major cause of failure in structural components. It is also known that notches, which are unavoidable, have a detrimental effect on fatigue resistance. Fatigue damage is associated with the formation of crack(s). Therefore, it is necessary to understand the fatigue crack growth behavior for better design analysis. In this research, a V-notched specimen machined from ZK60 magnesium extrusion is tested under cyclic axial loading. Fatigue experiment was performed under completely reserved force-controlled loading with an amplitude of 12 kN and under standard laboratory conditions. The fatigue test was interrupted 14 times in order to perform ex-situ x-ray tomographic analysis using the Nikon XTH 225 ST system. The sample failed after 184,005 cycles. A gray-level thresholding process was performed using MATLAB on the selected slices to convert each pixel to either white or black color. Then, these slices were stacked using imaging software to make 2D representations of the crack surface at different cycles. As a result, the areas of the crack surfaces were measured for all scans. The result suggests an exponential relationship between the crack surface area and the number of cycles.