沉头螺接复合材料接头失效预测强度包线法

Failure envelope is usually employed to assess the strength and failure modes of multi-bolt jointed composite structures in engineering design and analysis. The current failure envelope method is only applicable to convex head bolt jointed structures, but not applicable to countersunk head bolt jointed structures. A finite element model of the countersunk head bolt jointed composite structure with sleeves was established. The tensile properties of the 3-bolt joint were analyzed, and the model was verified against test results. The effect of the sleeve was studied with this model. On this basis, the failure envelope method is proposed to predict the strength and failure mode of countersunk head bolt jointed composite structures. The results show that the sleeves can significantly slow down the expansion of hole edge damage and prevent violent variation of the joint bolt load ratio in tensile process, compared with bolt interference assembly only. The introduction of sleeves improves load carrying capacity and stiffness of the joint. The 2% off-set load, ultimate load and stiffness of the joint with sleeves are 14.08%, 5.21% and 6.04% greater than those of the joint without sleeves, respectively. By examining a small number of single bolt joints, the new failure envelope of multi-bolt jointed structure with corresponding design parameters can be drown, which can be used to predict the strength and failure mode of countersunk and convex head bolt jointed composite structures.