Improving Composite Bolted Joint Efficiency by Laminate Tailoring

Abstract

The objective of tailoring the laminate in a composite bolted joint is to uncouple the local bearing capacity from the influence of the laminate axial strain level. This can be accomplished by partitioning the laminate into two distinct regions, each serving a specific purpose. The primary region of the laminate typically contains a fairly high percentage of 0-deg plies and thus carries a high percentage of the overall axial load. The bearing region, in contrast, contains no 0-deg plies and thus carries only a small portion of the overall axial load. As a result, the bearing region is insensitive to the amount of axial load in the joint and can continue to serve the function of introducing the bolt loads into the laminate even at high levels of axial strain. This concept has been validated by static tests of single-fastener coupons, multiple-fastener joints, and full-scale components. Even at the complexity level of the full-scale component, the tailored laminate approach provided a 24 percent increase in weight efficiency and a 62 percent increase in axial strain level compared to a companion component utilizing nontailored laminates.