Prediction of the net-tension strength of single bolt joint using the 0° ply strength and fracture toughness

This paper puts forward a new method to predict the net-tension strength of single blot joint based on the Finite Fracture Mechanics (FFM) model. Instead of using the tensile strength and fracture toughness of the laminates, only the properties of the 0° ply are used to obtain the failure stress and critical crack length by considering the relation between mode I fracture toughness of laminates and that of 0° ply. While the tensile strength of the 0° ply can be easily obtained through uniaxial tensile tests, the size effect law of double edge notched specimens is incorporated for the determination of the crack resistance curve of the ply. After validating the proposed method by the experimental results of central-notched IM7/8552 laminates, a 3D finite element model is established and the secondary bending is taken into consideration to find the maximum stress distribution of 0° ply around the bolt hole of the single bolt joint. It is concluded that the predicted strength by the semi-analytical method suits well with the experimental results. The secondary bending and the crack resistance curve, which can be seen as improvements of the Finite Fracture Mechanics model, have an influence on the predicted value.