Monotonic and Fatigue Response of Co-cured Composite Lap Joints with Modified Interfaces

This paper examines the performance of co-cured composite single lap joints with modified interfaces under monotonic and fatigue loading. The configuration examined is a quasi-isotropic lay-up with a unidirectional interface. However the modified interface designs are applicable to all lay-ups. The objective is to improve the static and fatigue strength of the joint while keeping alterations of a predetermined base design to a minimum. Two design improvements are considered: The Nested Overlap and the Half Slice Overlap. An experimental approach which consists of testing single lap joint composites with altered and unaltered interfaces in monotonic and fatigue loading is adopted. Comparison of ultimate strengths is indicative of the effectiveness of the proposed concepts. Progression of failure is characterized by acoustic emission measurements. The numbers of acoustic events prove to be sensitive indicators of failure initiation. Ultrasonic scanning provides additional insight into the progress of damage and correlate well with visual observations. Test results are compared with a Finite Element Analysis.