|Title:||Study on deformation behavior in micro-scaled plastic deformation of copper|
|Advisors:||Fu, Mingwang (ME)|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
|Department:||Faculty of Engineering|
|Pages:||xvi, 91 pages : color illustrations|
|Abstract:||Micro-forming is one of the promising approaches to fabricate micro parts for its high productivity, low production cost and good mechanical properties. The material deformation behavior in micro-forming, however, is different from the one in macro-forming. The macro-forming knowledge is not applicable to the design and development of micro parts. It is thus necessary to investigate the size effect on deformation behaviors and the physics behind in micro-scaled plastic deformation. In this research, the micro-compression and torsion test was conducted to investigate the size effect on material flow behavior, surface roughness evolution and flow stress. In this research, the cold-drawn and annealed pure copper with two different geometry sizes and single crystal copper with three different orientations including <100>, <110> and <111> was used. It is found that the inhomogeneous material flow occurs, surface roughness and flow stress changes with the decrease of specimen size and the increase of grain size from polycrystalline copper to the single crystal copper. In this dissertation, Hall-Petch relationship was used to explain the grain size effects on micro deformation behavior. Surface layer model was used to explain geometry size effects in compression test of polycrystalline copper. In torsion test, strain gradient effect was introduced to explain the higher flow stress of smaller specimen. The FE simulation for both single crystal copper and polycrystalline copper was conducted via ABAQUS/CAE by using the established UMAT subroutine based on the widely accepted crystal plasticity finite element method. For the modeling of polycrystalline material, the 3D Voronoi model is generated by using Neper software in this study to simulate the specimen with different grain size. The simulation result is basically consistent with experimental results, thus the deformation details can be analyzed from plastic strain distribution, surface roughness, inhomogeneous deformation. This research thus provides an in-depth understanding of the deformation behavior in micro-scaled plastic deformation.|
|Rights:||All rights reserved|
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