Fatigue design of weld part in non-combustible magnesium alloy based on fracture mechanics

Abstract

Fatigue design of weld part in non-combustible magnesium alloy has been studied. Specimens for fatigue test were produced by TIG welding with different welding conditions. According to result of fatigue strength tests, all weld specimens tested in the present study were broken at the weld prat, and a weld defect was found as a fatigue fracture origin. Fatigue life was well arranged by effective stress intensity factor calculated with a size of weld defect played as a fracture origin and applied stress. Therefore, it is speculated that fatigue strength of weld part is depending on a size of weld defect and threshold stress intensity factor at the weld part. Size of weld defect and value of threshold stress intensity factor possibly changed by welding condition. Therefore, relationship between heat input during welding process and threshold stress intensity factor was studied by conducting fatigue crack growth test at the weld part. The value of threshold stress intensity factor range increased with increase in heat input of welding process. However, values for threshold stress intensity factor range almost coincided when the crack growth curves were arranged by effective stress intensity factor range. Difference in threshold stress intensity factor range due to difference in heat input of welding process was mainly induced by change in crack closure effect. It is proposed that effect of crack closure depending on mechanical property of weld part should be taken into account on fatigue design of weld part in non-combustible magnesium alloy.