Theoretical Study On Temperature Dependent Ultimate Tensile Strength And Fracture Toughness Of Metal Matrix Composites

With the development of modern science and technology,the mechanical properties of materials at high temperature are more and more strict in various fields.After a lot of research and development,short fiber and particle reinforced metal matrix composites have become a commonly used engineering material,it combines the properties of metal materials(ductility and toughness)and ceramic materials(high strength and high modulus),so that it has higher shear and tensile / compressive strength at high temperature.Therefore,it is widely used in automotive industry,aerospace and other fields.Short fiber and particle reinforced metal matrix composites will inevitably suffer from different temperature environments when applied in the above fields.In view of its temperature dependence mechanical properties directly affect the safety and reliability of service parts,which reasonable characterization and improvement of its mechanical properties at high temperature have become the focus of the research field of metal matrix composites.Thus,fully understanding and quantitatively characterizing the variation law of mechanical properties of short fiber and particle reinforced metal matrix composites with temperature is of great scientific significance for its preparation,application and safety and reliability evaluation.This thesis focuses on the temperature dependent ultimate tensile strength of short fiber reinforced metal matrix composites and the temperature dependent fracture toughness of particle reinforced metal matrix composites,the specific research contents are as follows:(1)For short fiber reinforced metal matrix composites,combining the mixture law and taking into account fiber strength,load transfer,dispersion strengthening,residual thermal stress,dislocation strengthening,the mechanical properties of the matrix and their evolution with temperature.A temperature dependent ultimate tensile strength model of short fiber reinforced metal matrix composites without fitting parameters was established.The prediction results of the model are in good agreement with all the available experimental data,which provides a method for conveniently predicting the temperature dependent ultimate tensile strength of short fiber reinforced metal matrix composites.Then,the contribution of each strengthening mechanism to the ultimate tensile strength of short fiber reinforced metal matrix composites and its evolution with temperature were analyzed.The results show that adding short fiber with high temperature strength is an effective method to improve the ultimate tensile strength of short fiber reinforced metal matrix composites at high temperature.Furthermore,the quantitative effect of the evolution of Young’s modulus of fiber and matrix with temperature on the ultimate tensile strength of short fiber reinforced metal matrix composites were analyzed within the scope of applicability of the model.The results show that increasing the Young’s modulus of matrix can effectively improve its ultimate tensile strength at high temperature.Finally,the effects of fiber volume fraction and fiber strength evolution with temperature on the ultimate tensile strength of short fiber reinforced metal matrix composites were quantitatively analyzed.The results show that the ultimate tensile strength at high temperature can be improved by strengthening fiber strength and increasing fiber volume fraction This study provides some technical guidance and basic theory for the production,preparation and design of short fiber reinforced metal matrix composites.(2)For particle reinforced metal matrix composites,the Young’s modulus,yield strength and their evolution with temperature are considered.A temperature dependent fracture toughness model of particle reinforced metal matrix composites without fitting parameters was established.The predicted results of the model are in good agreement with all the available experimental results.The model provides a simple method to predict the temperature dependent fracture toughness of particle reinforced metal matrix composites.Then,the quantitative effects of particle volume fraction and diameter on fracture toughness of particle reinforced metal matrix composites were analyzed within the applicable range of the model,the analysis results show that an appropriate increase in particle diameter and decrease in particle volume fraction can effectively improve the fracture toughness at high temperature.This study provides some suggestions for the design and preparation of particle reinforced metal matrix composites at different temperatures.