Model Composites: A Novel Approach for the Evaluation of Micromechanical Behavior Available to Purchase

Microlevel damage events in composite materials are extremely important issues when addressing the remaining strength and life of the system. These events include fiber fractures, matrix cracks, and fiber end effects. Development of accurate representations of these phenomena at the local level is difficult and until this time unverifiable. An experimental procedure is suggested which involves a macromodel composite to generate data that are utilized to validate (or invalidate) current and proposed micromechanical analysis of composite materials containing damage. Quantitative experimental data on the perturbed strain field are measured with embedded strain gages and internal Fabry Perot fiber optic strain sensors, while qualitative measurements are accomplished with data obtained from a birefringent matrix. The majority of the tests described herein are representative of continuous fiber composites containing a fiber fracture. A controlled fiber fracture is achieved in the model composite at a predetermined location. Stress concentration and ineffective length (i.e. size of the perturbed stress field) measurements are experimentally determined for different fiber volume fractions and interphase coatings (i.e. on fiber). Initial results suggest that crack propagation plays a significant role in the stress redistribution which occurs in the vicinity of a fiber fracture. We suggest that the interphase region affects the formation and propagation of cracks in the composite. The methodology described in this paper allows a researcher to systematically study the effect of various physical parameters, such as fiber volume fraction, constituent properties, and interphases, on the local stress state in a material system.