Study On Static Delamination Of Z-pin Reinforced Composite Laminates

The amount of composite materials used in the new generation of aircraft is a key indicator to measure structural advancement.Composite laminates are a typical structural in engineering applications,but the interlaminar fracture toughness of composite laminates is relatively weak,which severely restricts their applications in the main bearing structure of aircraft.Z-pin reinforcement technology has great significance as a toughening method that can significantly improve the interlaminar mechanical properties of composite materials.Previous research on Z-pin reinforcement technology mostly focused on the Z-pin diameter,volume fraction and other factors,and the research on Zpin fiber materials also has important scientific value.Although there are some research results on the delamination expansion behavior of Z-pin reinforced composite laminates in this file,there are still many deficiencies,and further study is needed before the Z-pin reinforced laminates in engineering applications can be meet the design requirements.This paper focuses on the influence of Z-pin fiber material on the static delamination expansion behavior of composite materials.A series of work has been carried out on the Z-pin reinforcement mechanism and the following research results have been obtained:(1)Considering the influences of Z-pin fiber on the static delamination expansion behavior,designed two different Z-pin fiber-reinforced laminate test pieces,and set a blank laminate without Z-pin as a control,and Mode I and Mode II static delamination tests are carried out: the R-curve of different specimens in the course of Mode I and Mode II delamination expansion are obtained;The failure mechanism of Z-pin reinforced composites is revealed by observing the micro-morphology of the delamination interface.(2)According to the Z-pin toughness mechanism in the delamination process of Zpin reinforced laminates,the Z-pin resistance mechanism is abstracted as a kind of bridging behavior between crack surfaces,and the cohesion model bilinear intrinsic structure relationship combined with nonlinear spring unit is used to realize the Mode I and Mode II static delamination simulation considering the influence of Z-pin.The good applicability of the numerical model is verified by comparing the prediction results of different models with the experimental results,and the predictive research of Z-pin parameter on delamination expansion behavior is further carried out.(3)In the consideration of the Z-pin toughness mechanism of laminate delamination and the typical fibrosis bridging junction model of single-track plates is elongated to Zpin reinforced laminates while the bilateral reversed force mechanism of Z-pin is embedded into the CZM frame that introduces the concept of fracture wrinkle surface bridging in fracture mechanics where Z-pin bridging conjunction is proposed Z-pin bridging model described by the law.The assurance rule of the Z-pin bridging conjunction is based on the method of the reversed fracture toughness data.Profoundly construct the trilinear constitutive relation of reflection the authentic mechanism of laminate delamination in realizing the effective simulation of the Mode I of Z-pin toughness synthetic material laminate delamination extension behavior to verify the adaptability of the proposed Z-pin bridging conjunction model.In summary,this thesis has carried out systematic experimental study on the delamination behavior of Z-pin reinforced composite laminates and has carried out indepth experimental research and numerical simulation research on the Z-pin bridging mechanism in delamination expansion behavior,the strengthening mechanism of Z-pin on the interlaminar fracture toughness of composite laminates is revealed to some extent.The work of this paper can provide theoretical guidance and technical support for the application of Z-pin reinforcement technology in composite materials.