鈍化裂縫前端彈塑性變形之探討

王俊文(June-Wen Wang)

指導教授 ： 蔣長榮

國立清華大學/工學院/動力機械工程學系/碩士(2006年)

摘要

本文採用工程軟體『Ansys』來分析一含裂縫之彈塑性材料，假設其裂縫前端是一初始曲率半徑為0.5mm的鈍化裂縫，在受第I型負載模式(Mode I)及小尺度塑變條件下，應力強度因子(Stress Intensity Factor) 與材料的應變硬化率對裂縫前端的應力，應變與塑性區分布所造成的影響。材料特性以雙線性(Bilinear)塑性力學模型及隨動硬化規則(Kinematic Hardening)為主。
由文中結果可知，因為裂縫前端為鈍化的關係，在材料本身的應變硬化率(千分之3.585)下，應力強度因子為2300時，裂縫前端Y向應力最大值發生在距裂縫前端1.649 mm處，而且裂縫前端Y向應力值在應變硬化率大於0.02會達到最大值；在塑性區的範圍內，材料的應變硬化率對應力和應變的分布影響很大。

關鍵字

破裂力學 ； 應力強度因子 ； 滑移線場理論 ； 隨動硬化規則 ； 裂縫

並列摘要

This thesis is analyzed an elastic-plastic material with a crack by using Finite Element Method simulation, and suppose there is a blunt crack with a curvature radius which is equal to 0.5mm. For the model I loading and the small scale deformation, the stress intensity factor KI and strain hardening of material influence caused toward stress strain and plastic zone distribution of the crack tip. The material property relies primarily on bilinear-plasticity mechanics model and kinematics hardening law.
From the result of this work, because of the blunted crack tip (ρ=0.5mm), the position of the maximum value of stress of y direction is equal to 1.649 mm measured from crack tip, when the original strain hardening law of material is equal to 0.003585 and the stress Intensity Factor KI is equal to 2300 MPa . The strain hardening rate is greater than 0.02 and will reach the maximum in the stress of y direction of crack tip. In the range of plastic zone, the strain hardening rate of material strongly influences the distribution of stress and strain.

並列關鍵字

fracture mechanics ； stress intensity factor ； slip line theory ； Kinematic Hardening ； crack

參考文獻

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