The Effect of Bending Overload and Overloaded Crack Length toward Life Time of Solid Shaft

Abstract

Several theories have assumed that the stress applied to a structure or component is constant (magnitude and direction). However, what happens in reality may not be the case. So, many component from metal are damaged due to stress changes both magnitude and its direction, called fatigue failure. Skinner (2001) shown that failures caused by fatigue as high as 50-90 percent of all failures in a mechanical mechanism.

This study uses a true experimental method fatigue testing in carbon steel ST 70 by using parameters without overload, overload of 70 N and 105 N as the independent variable, the length of cracks and crack propagation rate (da/dN) as the dependent variable, and the number of cycles given during normal loading 50,000 cycles and 15,000 cycles when overload, and overloaded cracks length are 1.15 mm and 1.65 mm as the variable control. The data obtained using graphs and theoretical analysis. It was found that the overload and overloaded crack length influences the crack growth behavior.

The results of this study shown that overload and overloaded crack length affect the plastic zone at the crack tip and the residual stress. If the plastic zone increase and the occurrence of compressive residual stress then the fatigue life will be increase, respectively. This is due to the delay in the crack propagation rate (da/dN). In addition, different levels of overload will affect a number of delay cycles. The longest delay cycles with overload 70 N and overloaded crack length 1.65 mm in 900,000 cycles. So, the longest fatigue life with overload 70 N and overloaded crack length 1.65 mm in 4,015,000 cycles.

Keywords: Overload, Crack Length, Fatigue Life, Delay Cyclic, Plastic Zone, Residual Stress.