Thesis 23

A Study of the Effect of Mean Load and Load Amplitude on the Fatigue Crack Growth Rate for the AISI 4140 Steel.

by Mr. Jirapong Kasivitamnuay (1996) ;Master degree thesis *(The Full Text view in Thai Language only)*

ABSTRACT

    AISI 4140 steel was tested under constant amplitude cyclic loading at various conditions of mean load and load amplitude, based on ASTM E 647-93 standard. The objectives of this research are to study the fatigue crack growth behavior, to analyse the condition of load simulation from actual loading to testing condition and to find the fatigue crack growth rate equation.

    From the experiment under conditions of load ratio range from 0.3 to 0.8 show that the crack growth behavior is independent of load ratio. Moreover, at the same load ratio, tests at different value of maximum load range from 1.600 tons to 4.000 tons show that crack growth behavior is independent of maximum load. Thus load ratio can be used as a parameter for setting the testing condition which the result can be applied to any component under actual loading. Additionally testing condition can be specified to give suitable for the capacity of testing machine and specimen size.

    Fatigue crack growth rate equation, obtained from the experiment, is expressed by da/dn = 5.32x10-9(K)3.06 and has the coefficient of determination equals to 0.97. This equation is an important data for calculating the fatigue life and designing any component. Computer program for calculating the fatigue life of a circular shaft under cyclic bending moment was also written to present the application of crack growth rate equation.

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