A method to predict residual strength and fatigue life of impact damaged carbon/epoxy laminates

Nonvisible impact damage reduces static and residual strength of cfrp-composite structures. Fatigue loading of impacted laminates in compression causes damage growth. The stress condition that inflicts the degradation is generated by the buckling deflection. Observed phenomena were utilized to conceive a method for the analytical prediction of compressive strength of composite structure after impact and after impact and fatigue. The draft of such a prediction method uses laminate plate theory, stability theory and linear elastic fracture mechanic. Necessary input data such as material strength properties and stiffness reduction curves (indicating damage growth) require only standard testing. A three dimensional damage model and a formula describing the typical relation between delamination growth and increase in compliance measured during fatigue are subjects of continued research.