Interfacial Mechanical Properties Of Shape Memory Alloy Composite

Shape memory alloy as a kind of smart material is widely applied in aerospace, civil engineering and medical engineering due to its unique shape memory effect and superelasticity. Shape memory alloy composite which is fabricated by embedded shape memory alloy wires, trips and particles has been one of research hotspots and emphases. Shape memory alloy fiber-reinforced composites can achieve many special functions that traditional composites cannot. Therefore, shape memory alloy composites have a wide application potential. However, the weak interface between shape memory alloy fiber and its surrounding matrix limits its development and application. Therefore, it is necessary to study the mechanical properties of shape memory alloy composite interface.In present thesis, the mechanical properties of the interface between shape memory alloy (SMA) fiber and its surrounding matrix was studied by theoretical analysis, finite element simulation and experimental methods. The main contents are list as follows:Stress function method and principle of minimum complementary energy are utilized to solve the internal stress of SMA composite in the condition of different thermomechanical loading. A subroutine is coded based on the constitutive equation that is used for theoretical analysis and implemented into the commercial finite element software Msc.marc to analyze the internal stress distributions in SMA composite embedding pre-strained SMA wire under mechanical or/and thermal loading and the results are compared with each other.Based on the energy criterion in fracture mechanics, energy release rate for single fiber pull out test of SMA composite is deduced and a debond criterion between fiber and matrix is obtained. The expression of fiber pull out stress is given according to the criterion and the influence of temperature, prestrain value of fiber and fiber embedded length on pull out stress is analyzed. In addition, fiber pull out process is simulated with finite element method, which matches well with theoretical results.Interface strength of SMA composite is improved by experimental methods. Different methods are used to improve the interfacial strength, including different kind of surface treatments, adding coupling agent and nano SiO2. The results indicate that all the methods can improve the interface strength of SMA composite, especially the anodization in HF.Influence of recovery stress on interfacial properties of SMA composite is studied. Interfacial debonding behavior under different thermomechanical loadings is studied by embedding SMA wires with different prestrain value into epoxy resin. The comparison between experimental and theoretical results indicates the theoretical analysis validation.