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Finite Element Analysis of SiCp/AlSi3 Composites Thermal Residual Stress
Author: TianYu
Tutor: LiDongCheng
School: Jilin University
Course: Materials Processing Engineering
Keywords: Thermal residual stress Finite element analysis Metal matrix composites Porosity
CLC: TB331
Type: Master's thesis
Year: 2009
Downloads: 173
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Abstract
SiCp/Al composites is bound to generate thermal residual stress during cooling process, because the thermal expansion coefficient is significant different between matrix and reinforcement. Thermal residual stress in materials also has an impact on many properties (yield strength, tensile strength and thermal expansion coefficient, etc.), The study about thermal residual stress of SiCp/Al composites is very necessary.Researchers have a certain degree of research on the generation and influencing factors of thermal residual stress in composite materials, and have also been a lot of finite element simulation and experiments, but most of which focused on fiber and short fiber reinforced composites. Unlike fiberreinforced composites, the thermal residual stress is rather complicated in particle reinforced composites, so the study is usually used in finite element software for numerical calculation. Researchers usually use different shape, size, content of SiCp/Al composites to create different models, most of which are twodimensionalbased and circular or square particle shape models, and the study is limited.This thesis is mainly about thermal residual stress of SiC particle reinforced aluminum matrix composites during the process of cooling, CATIA software is used to create threedimensional model of SiCp / Al composites, which is analyzed by ABAQUS software. The change of SiCp/Al composites thermal residual stress is observed by changing the SiC particle size, shape and content, and affect on matrix and particles. The phenomenon will be studied that porosity and external stress impact thermal residual stress. The main conclusions of the paper are as followed.1. It was found that thermal elastoplastic FEM results is quite close to reality compared with thermal elasticity FEM results, and using thermal elastoplastic finite element theory to simulate the actual situation is more closer to the real material internal stress state.2. Particle size dose not affect the particlematrix interface residual stress, but it directly determines the field of the thermal residual stress generated. Large particles have a larger residual stress fields, small particles have a small residual stress field. The direct proportion relationship exists between them.3. At the same percentage of particle volume fraction, the more flat or thin the particle shape is, the larger the particlematrix interface thermal residual stress and strain is, and the nearer the location of maximum curvature the particleâ€™s largest stress and strain is. When shape of particles is close to the spherical particle, the particlematrix interface thermal residual stress and strain tends to a constant.4. In the actual preparation, SiC particles are not spherical, most of which have angularity, the angularity directly affect the matrix residual stress. In three regular polyhedron models (tetrahedron, hexahedron, octahedron), the tetrahedron model angularity location exists the largest thermal residual stress, and the octahedron model angularity location exists the smallest one. Stress concentration of the angularity location easily lead to the particles fracture, result in cracks in matrix and affect the overall performance of the materials.5. Through analysis from different volume percentage particles of the models, we can find that the particlematrix interface stress is changed with the increase in particle content. This impact is likely to increase or decrease the interface stress, but not very significant. Therefore the particlematrix interface stress is not changed seriously when the particle content is low. The matrix thermal residual stress increase sharply with the particle content increasing, but this trend is not unlimited, when the particle content exceed 10%, the increase of matrix stress becomes slow.6. When pores exist, residual stress distribution of the matrix residual changed. The matrix between particles and porosity appears stress relaxation phenomenon. Residual stress of the matrix near porosity rises after a decline and forms a "depression". This is because that the heat shrinkable imbalance leads to stress concentration of the matrix around particles.7. Pores size of composites affects residual stress significantly. Large pores relax the matrix particles residual stress more obviously, and the stress "depression" is more close to particles. The distance between particles and pores also affects the matrix residual stress. The shorter the distance is, the more obvious the stress relaxation effect is, and the lower the minimum stress is.8. Actually, pore shapes can not be spherical, and some are needlelike, The irregular shapes are easier to lead to stress concentration and crack generation around pores, resulting in the decline of composites strength.9. External stress on the spherical particle composite models affects the thermal residual stress significantly. It changes the residual stress value and distribution at a certain extent. When external stress is lower, stress concentration phenomenon is relaxed at the particlesmatrix interface. However, when the stress is the larger, even beyond the yield limit of the matrix, the matrix stress rise rapidly, external stress becomes matrix suffered major stress.10. For porosityparticle composite model, when the direction of tensile or compressive stress parallel to the line through the center of the particles, the changes of matrix stress are not obvious, this is because pores hinder external stress transfer. The direction of tensile or compressive stress is perpendicular to the line through the center of the particles, the thermal residual stress of the matrix around particles drops rapidly, and the stress around pores drops firstly and then rise even over the stress before the imposed external stress. This shows that external tensile or compressive stress replace the thermal residual stress and become the major stress of the composites.11. Both tensile stress and compressive stress can cause stress concentration around the pores for the porosity  particle composite model. the stress concentration around pores is conducive to the formation and expansion of the matrix crack. As the matrix around the particles also exist a higher residual stress, cracks can easily be extended to particlesmatrix interface, and result in particle debonding and fracture. Mechanical properties of composites is declined.

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