Stress concentrations in composites with interface sliding, matrix stiffness and uneven fiber spacing using shear lag theory

The stress concentrations near a single fiber break in a unidirectionally reinforced fiber composite are investigated using a shear lag theory within the framework of finite elements. A model for uniformly spaced, well bonded fibers embedded in a matrix that cannot carry axial loads that was formulated previously is first introduced. The solution of this problem involves Fourier transforms and requires only a two-dimensional numerical integration. The work described in the current paper characterizes the stress concentrations around a single fiber break in the presence of fiber/matrix interface sliding, axial matrix stiffness and uneven fiber spacing. Due to the introduction of these complicating factors, the model no longer lends itself to the simple Fourier transformation solution method. For the case of interface sliding a new method is developed to handle sliding in any shear lag system. For the cases of axial matrix stiffness and uneven fiber spacing a finite element code specifically written for this problem is used to determine the fiber stresses. The results are discussed in the context of global versus local load sharing, and the effects on composite failure.

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