Experimental Investigation Of Fatigue Properties For The Ceramic Matrix Composite At Elevated Temperature

In the hypersonic environment,the safety of the aircraft will be affected by the thermal environment,and the performance of thermal protection material has significant influence on the safety of the aircraf,so it is very important to study the mechanical properties of thermal protective materials.The ceramic matrix composites have the advantages of high temperature resistance and good stability,as a result they are the most important thermal protection materials for hypersonic vehicles.In this paper,the mechanical properties and mechanism analysis of two kinds of ceramic matrix composites(2D C/SiC ceramic composite,mullite fiber-reinforced silica aluminum matrix composites)were researched by MTS material testing machine.In this paper we establish mesoscopic mechanics model and predict ultimate strength of the two kinds of ceramic matrix composites with the shear lag theory and mixture ratio.The uniaxial tensile experiments for the specimens of two kinds of material were conducted at elevated temperature(800oC).The data of the two kinds of material were processed,and the stress-strain curves of the tensile test were drawn.Mechanical properties such as elastic modulus and ultimate stress of the materials were carried out.Constitutive relation under two conditions of uniaxial tension was summarized.We start the low frequency(5Hz)tension-tension fatigue test for two materials at stress ratio R is 0.1 in the high temperature,and adopts lifting method to obtain material cut-off limit fatigue life under conditions of five hundred thousand.Experimental parameters are given double the fatigue life of the two materials under high temperature model,analyzed the fatigue characteristics of the two different materials.Experiment studies of the mechanical properties of materials under high temperature variation with cycles,and founds that with the increase of the cycle,the strained material is gradually increased,there has been a significant material creep behavior.At last,observe the fracture surface of the representative specimen by SEM.Observe the characteristics of fracture surfaces form different fracture form.The same and different characteristics of the fracture surfaces were analyzed.Then,discuss the damage evolution of the material under tensile loading and the damage evolution of the failure.