Lifetime Predictions of Actuation Fatigue for Shape Memory Alloy Notched Members

Shape Memory Alloy (SMA)-based solid state actuators are an attractive alternative to conventional actuators when a small volume and/or large force and stroke are required. These alloys have the unique characteristic of being able to accommodate large recoverable strains through repeated martensitic-austenitic phase transformation. Insufficient understanding of the SMA "actuation" fatigue properties and lack of theoretical models for accurate prediction of fatigue life are the main limiters for their wider acceptance in engineering applications. The efficiency of the Smith-Watson-Topper model combined with the field intensity approach in estimating fatigue life for loaded notched SMA members undergoing thermal cycling is demonstrated. The field intensity approach adopted, which characterizes damage over a critical region where failure mechanisms are highly active rather than at a single point, is more reasonable from the point of view of fatigue failure mechanisms and more comprehensive from the point of view of explaining fatigue phenomena.