An investigation on fatigue crack growth rates through a designed nonsymmetric crack growth test

A nonsymmetric fatigue crack growth (FCG) test is specially designed and performed to study whether FCG test data from nonsymmetric cracking which is unavoidable in practice can be used to determine valid FCG rate information for fatigue life evaluation. Two types of alloys were used in this test and the FCG data were obtained via visual measurements. The effects of boundary conditions and central hole were examined using FEA software and the results showed that within engineering allowable error margin, the theoretical solution of stress intensity factors (SIFs) under the remote uniform tension is valid for nonsymmetric crack in this test. As a result, a method for analyzing the FCG rate of nonsymmetric through-thickness crack is proposed. It is found that the FCG rate parameters in the stable stage have no difference between two crack tips and the crack growth data can be used together to determine the Paris parameters. The proposed method, if supported by further research, can be adopted to validate FCG test data involving nonsymmetric cracking in standard tests.