Analysis On Improving The Property Of Bending And Low-velocity Impact Response Of Composite Material Laminate Using The Pseudo-elasticity Of SMA

It is well known that composite materials have advanced characteristics such as high strength-to-weight ratio, high stiffness-to-weight ratio, high corrosion resistance and the capability of flexible design and fabrication. They have been extensively applied in aerospace structures, automobiles, military and civil engineering. However, composite structures are vulnerable to low-velocity impact. In certain circumstances, delamination, expanding crack, the fiber fracture can occur in the composite structures due to impact force. Presence of such internal damages will reduce the strength of composite structures up to fifty percent, and even lead to collapse of the structures. Thus, research on the impact response of composite structures has gained much attention in recent years. It is needed to improve the low-velocity impact response property of composite structures in engineering.SMA(Shape Memory Alloy) has been widely used in aerospace, industrial automation, energy, civil engineering, medical and mechanical manufacturing areas due to their unique shape memory and pseudo-elastic effects. In recent years, the subject of improving the bending and low-velocity impact response properties of composite structure by using SMA has been research, and the research is focused on the use of shape memory effect of SMA to improve the mechanical property of composite structures, and the research subject on improving the mechanical property of composite structures by using of pseudo-elastic effects of SMA is rarely concerned. In this dissertation, according to the project for science and technology study of Ministry of Education of China " The finite element and experiment study of dynamic response of SMA reinforced composite structure under low velocity impact", the pseudo-elastic effects of SMA on the bending and low-velocity impact response properties of composite laminates have been studied comprehensively, and some significant results have been obtained. Some important works are described as follows. (1) Based on the classical mixture law of single fiber reinforced composite structure, the formulae calculating the material coefficients of SMA hybrid composite structure are deduced out, and the constitutive relations of SMA hybrid composite thin plate are given out.(2) Based on the characteristic of the hysteresis loop of pseudo elastic SMA, the piecewise linear model of SMA pseudo-elastic stress-strain relation is established. The characteristic of energy absorbability of SMA is studied.(3) Using Rayleigh-Ritz method, the improvement of bending response of SMA hybrid composite laminates by using the pseudo-elastic and the characteristic of energy absorbability of SMA is analyzed. The study results show that pseudo-elastic SMA can more effectively improve the bending deflection and stress of SMA hybrid composite laminates.(4) Based on the piecewise linear model of SMA pseudo-elastic stress-strain relation, according to the energy balance principle, the low-velocity impact response property of SMA hybrid composite laminates is analyzed by using piecewise energy balance method. The study results show that pseudo-elastic SMA can effectively improve the low velocity impact response property of SMA hybrid composite laminates, and that the more the martensite fraction induced by stress is, the better the effect of improving the low velocity impact response property of composite laminates is. In addition, the results show that the effect of improving the low velocity impact response property of composite laminates by using the characteristic of energy absorbability of SMA is better than the effect by using the martensite transformation induced by stress.(5) In order to compare with calculated results of the energy method, in this dissertation, the finite element method is used to stduy the low-velocity impact response property of SMA hybrid composite laminates too. The Newmark direct integration method is used, and the modified Hertz's contact law is given out, in addition, because of the calculation of stiffness matrix of finite element dynamic equation is difficult, a method for calculating the stiffness matrix is used, in which by using the linearized increasing constitutive relations of SMA, the Young's modulus of SMA is computed iteratively. For verification of the capability and applicability of the proposed method for low velocity impact response analysis, a classical impact problem of plate (Karas,1939) is calculated and compared with previously published works, the compared results show that a very good agreement is achieved. All the numerical results show that SMA can effectively improve the low velocity impact response property of composite laminates.