Mechanical Behavior Study On Advanced Composite Materials And Structures In Different Temperatures

Fiber-reinforced composite materials and corresponding lattice structures have been widely used in aerospace,transportation,construction,national defense and other fields due to their high specific stiffness and specific strength.In recent years,with the in-depth development of the aerospace industry,civil aviation aircraft,hypersonic vehicles,satellites,space stations and other structures are in service in complex temperature conditions.Therefore,the application of materials and structures in different temperature conditions and lightweight design issues have become increasingly prominent.There are many studies on polymer matrix composites,but characterizing their nonlinear behavior remains a challenge.As one of the candidate materials for thermal structure,ceramic matrix composites behave high nonlinear with complicated deformation mechanism.However,due to the difficult preparation technology and high development costs of ultra-high temperature experimental equipment,there exits no reports about ultra-high temperature constitutivetheory.The research of lightweight ultra-low-conductivity C/C composites mainly focuses on material preparation and performance characterization.Due to its complex microstructure,model reconstruction is a major problem in numerical simulation.In addition,the research on lattice structures mainly focus on metal and polymer matrix composites.The research on lattice structure of ceramic matrix composites is still in its infancy.This paper mainly studies the mechanical behavior of advanced composite materials and structures at different temperatures.We derived the nonlinear constitutive model of fiber-reinforced composites in theory,and systematacially studied the mechanical and thermal properties fiber-reinforced composites from preparation technology to experimental characteization and numerical analysis.An elastoplastic damage coupled phenomenological constitutive model was established for unidirectional fiber reinforced polymer matrix composites?UD FRPC?.The constitutive model considered that the nonlinear deformation process of UD FRPC includes plastic hardening and plastic damage coupled softening processes.Firstly,a four-parameter yield criterion was proposed to judge whether the material entered the plastic hardening stage.The criterion considered the transverse isotropy,tension-compression asymmetry and the effect of shear yield strength increase due to transverse compression.Then Puck failure theory was used to judge whether the material had been damaged.The return mapping algorithm was used to ensure that each stress iteration felt on the plastic yield surface.The constitutive model could be applied to numerical simulation analysis of braided polymermatrix composites.In addition,the unified theory of yield and failure for UD FRPC was derived,which predicted the failure envelope of the matrix exactly.For C/SiC braided composites,the anaerobic ultra-high temperature nonlinear phenomenological constitutive theory was established for the first time.The theory considered the tension-compression asymmetry,unilateral crack closure effect,orthotropy and thermal hardening effect.The proposed theory considered that the nonlinearity of C/SiC braided composites originated from the generation and propagation of microcracks inside the material.In the anaerobic ultra-high temperature environment,when the temperature is less than a certain value,the temperature has little effect on the crack density,and the formation and evolution of cracks were only related to the stress state.The compressive stress suppressed nonlinearity?crack propagation?,while the tensile or shear stress component lead to nonlinear behavior.In an anaerobic environment,when the temperature riseed to a certain value,the nonlinearity of the C/SiC braided composite material was reduced,i.e.,the thermal hardening effect.Carbon bonded carbon fiber?CBCF?compositeand carbon-bonded carbon fiber composites impregnated with Al₂O₃-SiO₂ aerogel?CBCF/Si-Al aerogel composite?were prepared.The thermal and compressive properties of CBCF and CBCF/Si-Al aerogel composites at high temperatures were tested.The SEM observations and experimental results showed that the CBCF composite had significant anisotropy in microstructure,thermal conductivity and mechanical properties.The elastic modulus and compressive strength of the CBCF composite in xy direction are higher than those in z direction,whereas the thermal insulation performance was just the opposite.The mechanical properties and thermal insulation properties of CBCF/Si-Al aerogel composites were significantly improved.In addition,this paper also proposed an algorithm for generating a three-dimensional random fiber network with a fiber aspect ratio exceeding 100,which could reconstruct the microstructure of the CBCF composite in reality.The heat transfer analysis was performed using the CBCF model reconstructed by the algorithm.C/SiC lattice sandwich panels with different core inclinations were prepared by hot press forming and PIP process.Mechanical?in-plane compression,out-of-plane compression and three-point bending?and thermal experimental tests were performed on C/SiC lattice sandwich panels.The failure behaviors and failure modes of C/SiC lattice structure in in-plane and out-of-plane compressions were systematically studied in theory and in numerical simulations.The C/SiC lattice thermal protection system was designed to realize the integrated design of thermal insulation.The concept of structural efficiency was proposed as an indicator for evaluating the thermal and mechanical properties of lattice thermal protection system.The results show that the lattice thermal protection system had the best comprehensive performance when the core inclination angle is 30°.