Comparison of FEA and Experimental Fatigue Testing Methods for Wire Z-Specimens: Insights from Constant Life Curves, Load Analysis, Metallography and Fractography

This study outlines an investigation into the ultra high cycle fatigue behavior of nitinol wire Z-specimens by integrating finite element analysis (FEA) results with metallographic inclusion measurements and experimental fatigue test results. The study compares the outcomes of Z-specimen fatigue tests from two different laboratories, emphasizing the influence of testing parameters such as grip distance and setup configuration. Notable differences between FEA predictions and experimental results are discussed in the context of these procedural variations and differences in cycles to fracture for similar test levels. Preliminary analysis of constant life curves derived from the Z-specimen tests is presented and contrasted with existing data from rotary bend wire fatigue experiments to assess consistency and reliability across methodologies with differing mean strain.

Further, the research includes an evaluation of load (force) data as a function of the number of fatigue cycles, providing insights into the mechanical response and endurance characteristics of the specimens under cyclic loading. Fractographic analysis supplements the quantitative findings by revealing underlying failure mechanisms and surface features associated with the testing. Collectively, this work aims to deepen the understanding of fatigue performance in drawn nitinol materials and inform the development of standardized testing protocols especially in the 100 million to billion cycle fatigue regime for future applications.