Directionality of yield point in strain-aged steels: The role of polar dislocations
- 作者：V. Taupin ; S. Varadhan ; C. Fressengeas ; A.J. Beaudoin
- 关键词：Yield point ; Static aging ; Bauschinger effect ; Dislocation structures ; Strain gradient plasticity
- 刊名：Acta Materialia
- 出版年：2008
- 期刊代码：1_13596454
- 类别：ms
- 出版时间：August 2008
- 卷：56
- 期：13
- 页码：3002-3010
- 文件大小：1086 K
摘要
The directionality of the sharp yield point in strain-aged steels has been investigated by modeling tension/compression and forward/reverse torsion tests separated by accelerated aging. The occurrence of a Bauschinger effect and the absence of a yield point after a forward straining–aging–reverse straining sequence are interpreted within the framework of a field dislocation theory coupling the evolution of statistical and polar dislocation densities with that of point defects due to strain aging. The polar dislocation density reflects lattice incompatibility and long-range internal stresses. By assisting yielding in reverse straining, the associated back-stress is seen as the origin of the Bauschinger effect. By also promoting dislocation unlocking, the back-stress is found to be responsible for the absence of a yield point in reverse straining. Polarized dislocation structures formed in forward straining in association with back-stress build up may annihilate and inverse polarization occur in reverse straining. This microstructure evolution translates into an inflexion of strain hardening after strain path reversal.