On predicting the behaviour of an iron‐based shape memory alloy with the Ramberg‐Osgood model

Iron‐based shape memory alloys (Fe‐SMAs) exhibit the particular characteristic of remembering their initial shape after a phase transformation from austenitic to martensitic. This property, along with the high strength and ductility, recommends such materials for strengthening existing structures and designing highly efficient pre‐stressed structural elements. To achieve this, pre‐strained strips or rods made of Fe‐SMA are anchored to a parent structure in the first step. Afterwards, the activation of the Fe‐SMA is triggered through heating, and the material strives to return to its initial shape. Due to the anchoring, a tensile stress is generated in the Fe‐SMA upon cooling back to room temperature, while in the parent structure, a compressive stress field is obtained. The material behaviour of the Fe‐SMA under uniaxial loading is characterized by a rounded stress‐strain relationship without a pronounced yield point, similar to cold‐formed steels. Moreover, in many currently existing applications, the material is used both in the martensitic phase (pre‐strained form before activation) and in the austenitic phase (after activation). This contribution addressed the suitability of the two‐stage Ramberg‐Osgood model for predicting the uniaxial stress‐strain response of the Fe‐SMA. The key parameters were derived based on uniaxial tensile tests and the suitability of the proposed stressstrain curves for use in advanced finite element simulations was emphasized by simulating these tests.