THICKNESS CONSTRAINTS IN COMPOSITE JOINTS

摘要

Mechanical fasteners are commonly used for composite joining. However, only twodimensionalconfigurations are commonly investigated in the study of composite joining. This studyinvestigates the effects of three-dimensional scaling on the strengths of composite joints. Double-lapsingle-pin joints made of glass/epoxy composite laminates were used in the investigations. Experimentalresults revealed that the joint strengths decreased as the joint sizes increased. However, as the joint sizeincreased, the damage mode of composite joints also changed from initial bearing damage followed byfinal net-section failure for small joint sizes to direct catastrophic net-section failure for large joint sizes.It was found from experiments that the constraints in the thickness direction played a key role in thedamage processes. Three factors were identified to be responsible for the constraints in the thicknessdirection. They were composite thickness, bonding strength through the laminate thickness and clampingforce from bolting. Composite joints with low thickness constraints tended to have fiber buckling anddelamination which resulted in initial bearing damage before final net-section failure. Since they showedlarger displacement to failure and higher energy absorption during damage processes, composite jointshaving initial bearing damage followed by final net-section failure were more ductile than thoseexperienced direct catastrophic net-section failure.