Investigation of ductile fracture in microforming via experiment and FE simulation

Pao Yue-kong Library Electronic Theses Database

Investigation of ductile fracture in microforming via experiment and FE simulation

 

Author: Wang, Chengyang
Title: Investigation of ductile fracture in microforming via experiment and FE simulation
Degree: M.Sc.
Year: 2012
Subject: Metals -- Microstructure.
Metals -- Fracture.
Metals -- Ductility.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: xv, 122 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2516577
URI: http://theses.lib.polyu.edu.hk/handle/200/6554
Abstract: Because science and technology are developing extremely fast, especial1y the rapid progress of electronic industry and micromachine, microparts are highly demanded in the last decade and their technical requirements are higher and higher. Nowadays, the microforming technology has been partially used in electronic industry for producing the microparts like micro screws, contact springs and IC socket etc. With the continuous development of technologies, applied fields of microforming are rapidly extended to machinery, chemical industry, aerospace, biology, etc, and its status is more and more important in these fields. Metal forming is a traditional and promising industry because of its high productivity, high material usage and good mechanical properties. But when the deformation processes are scaled down to micro-scale from conventional macro-scale, the deformation propertied of material changes, since the ratio between the dimensions of a part and parameters of the microstructures or surface changes with miniaturization. This is the so-called size effects, which prevent the transfer of knowledge about design and development from macro- to micro-forming. Therefore, it is necessary to investigate the size effect phenomena. In this thesis, Al-alloy cylinder billets with diameter from 2 mm to 0.5 mm were prepared. The size effect was investigated mainly from material behavior and scatter. The occurrence of ductile fracture is often a limiting factor in metal forming processes. Prediction of ductile fracture initiation allows prior modification of the process, which can result in a defect-free final product with financial savings. In this thesis, different shape and geometry specimens in micro-scale were prepared. The specimens were upset to investigate the fracture strain and fracture location. The commercial software DEFORM was used to simulate the forming progress. Six different criterions were built-in in the FE-simulation. The criterions were evaluated to get the most accurate one for Al-alloy.

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