Determination And Adjustment Of Matrix Residual Stress In Continuous Alumina Fiber-reinforced Aluminum Composites

Continuous alumina fiber-reinforced aluminum matrixcomposite((Al2O3)f/Al）has excellent specific stiffness and strength in fiberdirection, high fatigue resistance and relatively high electrical conductivity.This composite material is mainly used in aerospace, automobile andpower transmission. In the power transmission, as the reinforced core, thismaterial is expected to replace the traditional steel reinforced core tobecome the ideal material for the long-distance power transmission. As weknow, the (Al2O3)f/Al composites have to bear complex loadings oftensile stress, gravity and nature force during installation and service. Thusit is necessary to get to know the influence curve of pretension load onfatigue life of (Al2O3)f/Al composites, and reveal fatigue damagemechanisms. In this passage, the relation of fatigue life of (Al2O3)f/Alcomposites and pretension load was discussed with experimental andsimulations methods from the view of thermal residual stress.The experimental results show that the thermal residual stress in(Al2O3)f/Al composites o tensile stress, around25MPa. The results offinite-element method (FEM) show that the equivalent Von-Mises stress inmatrix reaches the maximum at the interface and reduced along the radicaldirection. The experimental results show that the influence of pretensionload on residual stress of composites is obvious. As the pretension loadincreases, the tensile thermal residual stress in matrix decreases rapidly first, and change to compressive residual stress when pretension loadreaches around80MPa. After that, the matrix residual stress increasesslightly as the pretension load increases. When the pretension load is highenough (higher than~300MPa), the residual stress stay the same. FEM andequi-strain theoretical model was used to give quantifiable analysis of theinfluence of the pretension load. They present the same result withexperimental. In the FEM results, the mechanism of pretension load effecton residual stress is uncovered with the residual stress evolution ofcomposites in the process of loading-unloading. The results show thatduring process of unloading the fibers tend to recover to their virgin length,and the matrix can only partly recovered, then the fibers will apply areverse compression to matrix. At lower pretension loads, on unloading thematrix can only elastic recovered. When the pretension load is high enough,on unloading the matrix reverse plastic deformation occurs with arelatively small rate of the strain-hardening exponent of the pure aluminummatrix, leading to the gradual change in matrix residual stress withpretension load.On the base of tensile-compressive cyclic loading method, anothermethod with only unidirectional tensile or compressive loading isestablished by the author. The results from these two methods are almostthe same. Therefore, the later method is believed to be another reliableapproach to test the residual stress of fiber-reinforced composites.Besides, in this paper we discuss the influence of annealing treatmenton the adjustment of matrix residual stress. The results show that theresidual stress is related to annealing temperature. Residual stressdecreased with the increase of annealing temperature. These can beexplained that the defect (like dislocation) decreases during the annealingprocedure.