Study on the influence of preload on the three-point bending limit load of CFPR countersunk bolt connections

Abstract

Countersunk bolts are one of the main methods for joining carbon fiber-reinforced matrix composites (CFPR) in the aerospace field. In this paper, a study on the failure form and damage process of bending fracture behavior is carried out for the countersunk bolt connection structure of CFPR. Different preload forces were applied to the structure to study the three-point bending ultimate load and bending stiffness of the laminate, and it was found that the effect of preload on the bending stiffness and ultimate load of the specimen was nonlinear, and there existed a specific value of preload that made the bending stiffness and ultimate load of the structure reach the maximum value; the distribution of structural fracture cracks when different preload forces were applied was studied, and it was found that the increase of preload helped to suppress the lower laminate fiber direction. It was found that the increase of preloading force could help to suppress the parallel cracks in the fiber direction of the lower ply, but the effect on the vertical cracks was not significant. The main reasons for the increase in transverse cracks were also discussed.