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|Title:||Modeling of deformation behavior of metal matrix composites in laser forming||Authors:||Liu, Furong||Keywords:||Hong Kong Polytechnic University -- Dissertations
Metallurgy -- Laser use in
Metals -- Formability
|Issue Date:||2007||Publisher:||The Hong Kong Polytechnic University||Abstract:||Laser forming is a cost-effective rapid prototyping technique which bends the work piece by thermal stresses induced by laser irradiations without the assistance of any external force. A considerable amount of experimental and numerical work has been carried out to investigate the process. However, most of the work still focuses on monolithic alloys, and relatively little has been done on laser forming of composite materials. In this project, the deformation behavior of the A16092/25SiCp composite is experimentally and theoretically investigated. The experimental results reveal that the composite can be deformed to a large bending angle despite the poor thermo-physical properties of its aluminum matrix. A linear relationship between the bending angle and the number of laser irradiations is observed and no pronounced strain hardening is found in the composite. An analytical model is developed to predict the bending angle of the composite sheet by laser forming based on Vollertsen's two-layer model. It is found that the trend of the predictions is in good agreement with the experimental results, and a higher bending angle is observed for the composite sheet than for its matrix material. By modeling the changes of the thermo-physical properties of the composite including absorption coefficient, coefficient of thermal expansion (CTE), specific heat, thermal conductivity, yield stress and elastic modulus, the effect of reinforcements on the final bending angle is also analyzed.
In order to further investigate the deformation behavior of composite materials in laser forming, a new microstructure integrated finite element model is developed. A unit cell model is built up to obtain thermo-physical properties of the composite with the assumptions that particles are linearly elastic materials, the matrix is an elastic-plastic material, and the interface is perfectly bonded. Based on the predicted thermo-mechanical properties of the composite, the thermal and structural fields of the composite in laser forming are modeled. The simulated bending angles show a reasonable agreement with the experimental results, and the factors leading to the discrepancies are discussed. In the project, the effect of volume fraction, morphology, and distribution of reinforcement on the deformation behavior of the composite in laser forming is also studied. With the consideration of the effect of interface debonding on the deformation behavior of the composite in laser forming, a new damage-coupled finite element model is further developed. A periodic multi-particle cell model is used to determine the damage evolution of interfacial decohesion under uniaxial tensile loading, where the onset of damage is assumed to follow a maximum normal stress criterion. The simulation results are shown to be in reasonably good agreement with the experimental findings, and it is found that interfacial decohesion has a significant effect on the deformation behavior of the composite in laser forming. The present project is an important attempt to carry out an in-depth investigation of laser forming on composite materials. The findings of the present project may open up a potential industrial application for laser forming, and will lead to better understanding of deformation mechanisms of composites in laser forming.
|Description:||xx, 233 leaves : ill. ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577P ISE 2007 Liu
|URI:||http://hdl.handle.net/10397/3142||Rights:||All rights reserved.|
|Appears in Collections:||Thesis|
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