Fatigue Characteristics of Fe-Based Shape-Memory Alloys

This study reports the details of an experimental study of fatigue behavior of two types of Fe-based shape-memory alloys (Fe–SMAs). The two types of Fe–SMAs developed for this study were used to prepare specimens according to ISO 12106 standards. All fatigue tests were conducted under a constant frequency of five hertz using a universal testing machine with a capacity of 100 kN. The stress ratio applied to the test was zero, and the fatigue tests were conducted until the number of loading cycles exceeded two million, by reducing the stress range from 700 MPa by 100 MPa for each test. At stress range of 700 MPa, the number of loading cycles that has a large ultimate elongation, was greater for the B-type alloy than the A-type alloy. On the other hand, the number of loading cycles at the low stress range below the yield strength was found to be higher in the A-type alloy, which had a higher yield strength than in the B-type alloy. Additionally, by analyzing the S–N relationship and performing a first order regression analysis for the test results, it was confirmed that the fatigue limits of the A-type and B-type alloys are 473 MPa and 330 MPa, respectively.