Abstract
Shape memory alloys (SMAs) are a relatively new class of functional materials, exhibiting special thermomechanical behaviors, such as shape memory effect and superelasticity, which enable their applications in seismic engineering as energy dissipation devices. This paper investigates the properties of superelastic NiTi shape memory alloys, emphasizing the influence of strain rate on superelastic behavior under various strain amplitudes by cyclic tensile tests. A novel constitutive equation based on Graesser and Cozzarelli’s model is proposed to describe the strain-rate-dependent hysteretic behavior of superelastic SMAs at different strain levels. A stress variable including the influence of strain rate is introduced into Graesser and Cozzarelli’s model. To verify the effectiveness of the proposed constitutive equation, experiments on superelastic NiTi wires with different strain rates and strain levels are conducted. Numerical simulation results based on the proposed constitutive equation and experimental results are in good agreement. The findings in this paper will assist the future design of superelastic SMA-based energy dissipation devices for seismic protection of structures.
Highlights
Shape memory alloys (SMAs) are a unique class of materials that have the ability to undergo large deformations, up to 8∼10%, that is, at least one order of magnitude greater than common metals and alloys, and revert back to their original and undeformed shape or dimension through either applications of heat, that is, the shape memory effect (SME), or removal of stress, that is, the superelastic effect.The particular properties of SMAs were first discovered by Chang and Read in 1951; it was not until after 1962 when Buechler and his colleagues found the shape memory effect in nickel-titanium (NiTi) at the Naval Ordnance Laboratory that both in-depth research and practical applications emerged
This paper investigates the properties of superelastic NiTi shape memory alloys, emphasizing the influence of strain rate on superelastic behavior under various strain amplitudes by cyclic tensile tests
SMAs have been wildly implemented in biomedical, aerospace, mechanical, and civil engineering areas [1,2,3,4,5], making it necessary to have a precise understanding of the special mechanical behavior of SMAs in order to fully develop and exploit their potential
Summary
Shape memory alloys (SMAs) are a unique class of materials that have the ability to undergo large deformations, up to 8∼10%, that is, at least one order of magnitude greater than common metals and alloys, and revert back to their original and undeformed shape or dimension through either applications of heat, that is, the shape memory effect (SME), or removal of stress, that is, the superelastic effect.The particular properties of SMAs were first discovered by Chang and Read in 1951; it was not until after 1962 when Buechler and his colleagues found the shape memory effect in nickel-titanium (NiTi) at the Naval Ordnance Laboratory that both in-depth research and practical applications emerged. Shape memory alloys (SMAs) are a unique class of materials that have the ability to undergo large deformations, up to 8∼10%, that is, at least one order of magnitude greater than common metals and alloys, and revert back to their original and undeformed shape or dimension through either applications of heat, that is, the shape memory effect (SME), or removal of stress, that is, the superelastic effect. The unique mechanical behaviors of SMAs are made possible by reversible martensitic phase transformation (MPT) induced by temperature or mechanical stress between the austenitic phase (A) and martensitic phase (M). In the stress-free state, the material is characterized by four transition temperatures, namely, martensite start temperature Ms, martensite finish temperature Mf, austenite start temperature As, and austenite finish temperature Af. Below the martensite finish temperature, Mf, residual deformations induced by the martensite reorientation due to applied stresses can be recovered by heating the material above the austenite finish temperature, Af, resulting in the shape memory effect (SME). The austenite finish temperature, Af, martensite is formed associated with forward MPT
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