Interacting Stress Analysis Of Multiple Fibers Breaks In Ductile Matrix Composites Under Thermomechanical Ioading

In this paper, we study the influence of the broken fibers in composites under cyclical thermomechanical load. The distribution of composite stress is given in paper. We study two questions: the stress of 3D composite with a single broken fiber; the stress of 2D composites with multiple broken fibers. The governing ordinary differential equations of composite stress are given by using shear-lag theory.In the 3D geometrical model of composite, the equations are adapted to one-dimensional cylindrical geometry with the cell of composite is hexagonal array. Matrixes around the broken fiber only sustain shear stress. The constitution relationship of matrix is perfect elastic-plastic. Under cyclical thermomechanical load the stress of fibers and matrixes is given around the broken fiber. The effect is different under the in-phase thermomechanical loading with under the out-of-phase thermomechanical loading. It is because the yield stress declines with the rising temperature. Under the equal range thermomechanical loading, there is steady cyclic plasticity zone of matrixes around the broken fiber. The range of plastic shear strain is steady before fiber and matrix debonding. The range of plastic shear strain is important to fatigue of composite. After some cyclical thermomechanical load, fiber and matrix will debond in the cyclic plasticity zone. Then, the new cyclic plasticity zone will appear. The broken fiber will be pulled out after mostly segment of the broken fiber debond to matrix.When the stress of composites with multiple broken fibers is studied, it is considered for matrix to sustain axial load. Shear layer lay between fiber and matrix. We develop a shear-lag model and an influence superposition technique to compute the stresses and displacements in 2D unidirectional fiber composites in response to multiple fiber breaks. There are three states around broken fibers: matrix yielding, shear layer yielding , matrix and shear layer yielding. The stress of composite with multiple broken fibers is transformed to the superposition of much stress of composites with a single broken fiber or a single broken matrix. After computing the stress of composite with Al matrix and Be fiber, it is found that the influencing area of fiber breaking is about ten fibers. The intension of composite little varies after fibers breaking. The stress of shear layers greatly changes due to fiber breaking.