Development of a Novel Approach for Fatigue Life Prediction of Structural Materials

摘要

Experiments were conducted to study the fatigue initiation and crack growth of four structural materials: aluminum 7075T651 alloy, stainless steel AL6-XN, stainless steel 304L, and Aerospace Steel 4340. It was confirmed that fatigue can occur under compression-compression loading for the aluminum alloy. Results from multiaxial fatigue experiments revealed that the fatigue cracking behavior was material and loading amplitude dependent. Under cyclic pure shear loading, the S-N curves of aluminum alloy and the stainless steel AL6-XN displayed a distinct kink that was related to a change in the cracking behavior. The R-ratio affected the crack growth of all the four materials under investigation. For the 7075T651 and AL6-XN, a single overload resulted in an immediate reduction in the crack growth rate in the subsequent loading. For the AISI 304L alloy and 4340 steel, a short-lived increase in crack growth was observed right after the application of an overload. A new approach was found to be promising for the prediction of the crack growth from a notch, the R- ratio effect, and the effect of the overload.