Analysis For Ductile Matrix Composites Under Cyclic Thermomechanical Loading

Continuous fibers reinforced metal matrix composites (MMCs) have been in wide use today. The future of MMCs in turbine generator and ultrasonic aerocraft is inspiring. These equipments always work under thermomechanical fatigue loading, for the fail-safe design and reliable use of the equipments made of continuous fibers reinforced metal matrix composites, an important task is to understand the thermomechanical fatigue characteristic of MMCs.In this paper, as the prophase work, we study the composite stress under cyclical thermo mechanical load. The governing ordinary differential equations of composite stress are given by using shear-lag theory. Two questions were solved: it is considered for matrixes to sustain axial load and matrixes not to sustain axial load. When study the problem that matrixes sustain axial load, we consider the stress of 3D composite with a single broken fiber and debonding around the breaks. When study the problem that matrixes don't sustain axial load, we consider the stress of 2D composites with multiple broken fibers, basing on the conclusion with an influence superposition method, we build the simple model for multiple fiber breaks with shear-lag theory to compute the stresses and displacements in 2D unidirectional fiber composites, we consider the shear layers between fibers and matrixes. By studying the characteristics of ductile matrix composites, we find the quantificational fundamental relation between local cyclic plasticity,fiber volume fraction,matrix volume fraction and the interface of fibers and matrixes. The conclusion establishes the base for study thermomechanical fatigue (TMF).The results show that: (1) Under the equal range thermomechanical loading, there is a new steady cyclic plasticity zone of matrixes around the broken fiber. With the increase of load, cyclic plasticity zone becomes long, then the fiber and matrix go on debonding, as the influence of friction, the composites will reach a balance state if the load is unchanged.(2) With the increase of load, shear layers take place the local yield before matrixes, in the same condition, the length of shear layers is longer than matrix's. (3)The influence of temperature to the composite stress is very complex, it relates to initial temperature,temperature range and the way to give loads.The solutions obtained may be used for the fatigue of MMCs caused by the fiber breakage and the thermomechanical behavior of the fiber/matrix interface.