The effect of fiber undulation on the strain field for pinned composite/titanium joints under tension

The way fiber undulation around pins affects pinned composite/titanium joints' stiffness and strength properties is illustrated for double-lap-shear joints under quasi-static tensile loading. 3D digital-image-correlation techniques were employed to measure in-plane strain distribution on the surface of the composite joint member. Pinned joints with formed holes and three different composite stacking sequences were manufactured and compared to joints with drilled holes. Whereas in the case of joints with formed holes, the process of inserting the pin into uncured prepreg material created undulations, joints with drilled holes are characterized by a uniform fiber direction but partly broken fibers. Due to homogenization of the strain field within the load-carrying 0° layers, pinned composite/metal joints with formed holes proved to significantly outperform joints with drilled holes in terms of tensile stiffness and strength.