Fracture Mechanics Approach to the Interaction Between Fiber and Matrix in Composite Materials.

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1. The damage model with shear resistance along the fiber-matrix boundary was applied to the microscopic failure processes in composite materials using the shear lag analysis. The focused materials were the broken fiber reinforced composites, hybrid composites, and short fiber composites. The effects of the geometrical and material constants were obtained. One of the interesting results is as follows. If the Griffith type of energy equation is the dominant condition for the propagation of debonding, it propagates gradually at first and beyond some critical value of debonding length it propagates catastrophically to the final failure of short fiber composites. This critical value is dependent on both the fiber aspect ratio and the Young's modulus ratio.2. Three-dimensional elastic analysis was applied to the interaction between the fiber and crack in composite materials. The integral equation was formulated to yield the effect of fiber on the stress intensity factor of a penny shaped cr … More ack in composite materials under Mode <III> loading. The nearest fibers have the dominant effect on the stress intensity factor than any other fiber.3. An approximate analytical solution was obtained for the microscopic stress distribution in unidirectional composites. It has strong relation to the debonding and shear resistance between the fiber and matrix. The increased fiber volume fraction was found to change the normal stress at the boundary from the compressive to tensile one in the real composite system under axial tensile loading.4. An numerical process to treat the integral equation for the T-shaped crack was found to yield the resonable stress intensity factor of the boundary crack between different materials.5. The experimantal models for the above 2 and 4 were made to insure the analytical solutions. A Charpy type impact test was performed to obtain the fracture mode and energy in case of 2. The caustic method was used to obtain the stress intensity factor at the debonding tip in case of 4. Less