Fatigue life prediction of composite material based on micromechanics of failure

Abstract

In the present effort experimental work has been carried out as confirmatory tests for a fatigue life prediction model which is based on micromechanics of failure. A micromechanics based methodology is considered superior because of being able to provide a detailed insight in to the failure mechanism of composite material and hence better fatigue life prediction. The development of this methodology necessitates the determination of the properties of matrix and fibers separately. A separate failure criteria is used for each constituent and fatigue life prediction model developed. FEM simulation of tubular specimen subjected to torque is carried out. Pure torsion load is applied to the specimens in these experiments. Torsion specimens are prepared using L135i resin and in house manufacturing facilities. Molds and tabs are designed and manufactured to prepare the specimen. Manufacturing steps of torsion specimen are quite time taking and laborious. Static torsion and fatigue torsion tests are performed on in house developed torsion testing equipment. Static torsion tests are performed to estimate the shear strength of resin. The fatigue tests are performed on 80%, 70% and 60% load levels of the shear strength of resin. A comparison of the results of torsion fatigue tests and the predicted fatigue life using SN curve shows a good agreement. Effective stress is used to generate the proposed SN curve of resin. Well matching experimental results with predictions shows that the micromechanical model for fatigue life prediction of resin is better predicting the failure mechanism and life.