Study Of Interlaminar Fracture Toughness Of Composite Laminates Type Ⅰ Based On Fiber Bridging Theory

Composite materials are widely used in mechanical processes and aerospace structure design due to their excellent properties.As composite materials are anisotropic materials,there are differences in mechanical properties between longitudinal and transverse directions.Since laminates are mostly manufactured by gluing process,the interlaminate properties are relatively weak and prone to delamination damage,resulting in a significant reduction in the strength and stiffness of structural members.Therefore,the interlaminar properties become a key factor to be studied in the design of laminate structures.For multi-directional laminates with more complex delamination expansion mechanism,large scale fiber bridging,matrix fracture and crack leap often occur in delamination expansion,making the study of type I interlaminar fracture and delamination expansion more complex and requiring more in-depth research.On the basis of existing studies,an in-depth study is conducted in this paper,and the main findings are summarized as follows:(1)A nonlinear delamination prediction model based on fiber bridging theory is proposed.Considering the nonlinear degradation of bridging stress and the influence of fibers on matrix damage,analyzing the functional relationship between strain energy release rate and crack tip opening displacement,combining cohesion model and its principle,proposing a nonlinear delamination prediction model based on fiber bridging theory;revealing the fracture toughness change law and bridging stress distribution law during delamination expansion,and improving the prediction accuracy of delamination.(2)A steady-state fracture toughness prediction model based on fracture theory is established.Consider the irregularity of the crack expansion path and the effect of the change of interface angle near the crack on the stress distribution at the crack tip.The effects of resistance work and matrix fracture work caused by breaking fiber bridging are also considered,and the numerical relationship with fracture work in the delamination process is established to propose a steady-state fracture toughness prediction model based on fracture theory.Combined with the fracture mechanics theory,the steady-state fracture toughness values of the specimens under various interface angles are predicted to provide theoretical support for the crack leap phenomenon.(3)Study on the toughening mechanism of mode Ⅰ interlaminar fracture toughness of composite materials.The effects of three working conditions,namely,specimen thickness,layup interface angle and initial crack length,on the interlaminar fracture toughness of mode Ⅰ composites are studied.The crack expansion paths and layered expansion laws of different laminates are analyzed.