Study On Failure Mechanism Of Fabric-Unidirectional Prepreg Hybrid Laminates With Open-Hole

With the continuous development of the aerospace field,the requirements for material properties continue to increase,and hybrid composite materials have become one of the hot research directions due to their excellent comprehensive properties.Fabric-unidirectional prepreg hybrid laminate with excellent static properties and good environmental adaptability is mainly used in the aircraft body part,and the development prospect is very broad.So it is of great significance for its research.In this paper,experimental research and finite element analysis were carried out on the mechanical properties,moist heat behavior and failure mechanism of fabricunidirectional prepreg hybrid laminates with open-hole.The unidirectional compression test of fabric-unidirectional prepreg hybrid openhole laminate in wet and dry environments was carried out,and the influence of environment and layer structure on mechanical properties was analyzed by comparing the two test results.Damage patterns are analyzed by combining the results of the fracture scan of the test piece and the acoustic emission signal.The results show that the fabric-unidirectional prepreg hybrid open-hole laminate can maintain good mechanical properties in the humid and hot environment.The failure process mainly includes fiber breakage,matrix cracking and delamination failure.The degree of dispersion and the proportion of layer have a significant impact on the mechanical properties of compression.The moisture absorption process and heat conduction process of fabricunidirectional prepreg hybrid open-hole laminate were analyzed by finite element software,and the moisture absorption mechanism and humid heat effect were analyzed by combining theoretical calculations.The results show that the moisture absorption process of fabric-unidirectional prepreg hybrid open-hole laminate conforms to Fick’s law.The heat transfer process is faster than the hygroscopic process,and the increase in temperature promotes the diffusion process of water molecules.Humidity and temperature can cause free strain of humid heat and change the mechanical properties of component materials,so as to affect the macroscopic overall properties of fabricunidirectional prepreg hybrid open-hole laminates.A multi-scale analysis of fabric-unidirectional prepreg hybrid open-hole laminate is carried out,and the macroscopic mechanical properties of fabric and unidirectional prepreg laminate are predicted by establishing a fiber filament cell model and a twodimensional fiber bundle cell model.According to the predicted properties parameters,the progressive damage model was established,and the results of the simulation analysis were in good agreement with the experimental results.By analyzing the model results,the failure evolution mechanism of three types of damage: fiber damage,matrix damage and delamination damage is obtained.Combined with the characteristics of layer structure,several different layer structure schemes are designed to analyze the influence of dispersion degree and layer ratio on the mechanical properties of fabricunidirectional prepreg hybrid open-hole laminate.The results showed that fiber damage,matrix damage and delamination damage occurred sequentially.All three forms of damage begin in the area of stress concentration at the edge of the hole.Delamination damage only occurs at the interface between the fabric and the unidirectional prepreg.The method of reducing the dispersion degree of fabric and unidirectional prepreg and increasing the proportion of 0° unidirectional prepreg can effectively improve the compressive failure load.