Experimental investigation of a strain softening approach to predicting failure of notched composite laminates

• Main Author: Kongshavn, Ingrid A.
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/4484

This work describes an experimental investigation of a strain softening approach to the prediction of fracture in notched composite laminates. This approach has been found to more accurately predict fracture of large notched coupons or structures than traditional approaches. Strain softening accounts for the effect of damage in front of the notch tip, by the post-peak region of a strain softening curve. This region is traditionally defined by a stress that decreases with increasing strain. A physical understanding of the post-peak region of the curve is required to better examine the predictive capabilities of strain softening. For this to be achieved, a detailed physical understanding of the damage in the process zone is required. In this study, two carbon fibre reinforced laminate material systems were examined. An overheight compact tension (OCT) specimen was developed to grow damage in a stable manner. The displacements in front of the notch tip indicated the progression of damage across the specimen width throughout the test. A detailed physical description of the damage, which consisted of a crack and process zone were obtained. The sequence of damage growth in the process zone was determined. Tensile specimens cut from the process zones indicated a preliminary shape of the strain softening curves for the two material systems. Finally, the experimental results were used to calibrate a preliminary F E M strain softening analysis of the OCT specimens. The preliminary F E M results suggest that a strain softening material response is necessary to capture the progressive damage growth across the specimen width.