Interface Mechanical Design Of Aramid Fiber Composites

< p > composite materials are widely used in military and civil aircraft abroad. For example, composite materials in EF2000 account for 40%, and composite materials used in B787 even account for 50%.

It can be said that composite material is the future of aerospace structure, and also the key material of the future aerospace power system. It is one of the symbols of the advanced nature of aerospace weapons and equipment.

As an advanced composite material, aramid fiber has better performance than glass fiber composite material, and it is an ideal material for aerospace vehicles such as aircraft, rockets, satellites, spacecraft and so on.

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< p > however, there are still some deficiencies in the research of aramid fiber, such as lack of design of fiber / matrix interface, lack of effective experimental characterization methods to monitor curing stress, lack of research on crack resistance mechanism of matrix cracks, lack of effective experimental characterization, and less analysis of fatigue properties of 3D braided composites.

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< p > based on this, we carry out three main research experiments: 1., fiber matrix gradient interface design. In fiber composites, there is a pitional area between fiber and matrix, commonly referred to as interface phase. The interface phase can be designed to gradient distribution to solve the interfacial stress due to the mismatch of elastic constants and thermodynamic constants of two materials.

A fiber / matrix interface phase with elastic modulus distributed along radial gradient is proposed. The Navier equation of the gradient interface of fiber / matrix in different gradient forms is established, and the thickness of the interface phase is optimized by correlation analysis.

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Experiment and Simulation of interface curing deformation of < p > 2. were carried out. The stress gradient evolution of resin during curing process was measured by DGS method, and the effect of fiber bundle on curing stress was analyzed.

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< p > 3. matrix crack fiber interaction caustics analysis based on Esheby equivalent inclusion theory, the stress field near the crack tip is obtained, and the control equation of the crack caustics near the fiber is derived. The influence of the elastic constants of the fiber bundle, the thickness of the fiber bundle and the distance from the fiber bundle to the crack tip on the focal line are analyzed, and the theoretical derivation results are verified by the static and dynamic caustics test.

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< p > generally speaking, the study is the theoretical solution and experimental verification of mechanical problems such as damage and fatigue of fiber matrix gradient interface under thermal mechanical coupling load in fiber composites, the infiltration process of resin, the interaction between fiber and resin, and the experimental characterization of curing stress and deformation of fabric composites, the interaction of matrix crack fiber bundle under fatigue loading, the crack resistance of fiber to fatigue crack growth and the effect on fatigue life.

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