A Study On Fatigue Crack Propagation Of Q345R Steel Subjected Multiple Overloads

Overload often appear in the fatigue,when Engineering components in the actual service process bear the complex fatigue loading.The influence of material fatigue crack propagation is not the same on different forms of overload,therefore,the study of fatigue crack propagation behavior subjected multiple overloads has great academic value and engineering significance.The crack propagation experiments and approaches of fatigue crack growth modeling are used to study behavior of Q345 R steel.The specific research content and conclusions are as follows:The crack propagation experiments under two overloads conducted using compact tension speciment of Q345 R steel.The retardation effect increases at first and then decreases with increase of the overload interval under the same R-ratio,overload applying crack length and overload ratio due to applied two overloads,and the retardation effect of overload is the most obvious when the overload interval is half cycles of a single tensile overload retardation zone.Retardation stage of previous overload is covered by the next overload influence area due to interaction between multiple overloads.Retardation stage appears after increasing overload interval.Modified Wheeler model including overload interaction parameters or no overload interaction parameter is used to predict fatigue crack growth behavior subjected two overloads.To contrast of the two models predicted results,including overload interaction parameters modeling prediction results are better with the test results.Two modified Wheeler models are used to predict fatigue crack growth behavior subjected periodic overload.Overload interaction is produced between two or more overloads,when overload interval is small.So,the gap is made between the prediction results and the experimental results.The approach for crack growth developed by Jiang and co-workers is used to predict the crack growth rate under two overloads.The prediction results are better with the test results.Then,using the model predicts the crack growth rate under periodic overload.The prediction results are better with the test results,compered with the results of modified Wheeler model.The prediction results validate the model.