【作者】 李超；

【导师】 陈旭；

【作者基本信息】 天津大学 ， 化工过程机械， 2009， 硕士

【摘要】 材料在循环载荷作用下产生的塑性变形的逐渐累积现象称为棘轮效应。棘轮问题的危害性引起了国内外学者的广泛重视,其研究已经成为热点方向。对于材料低周疲劳行为,绝大多数的实验及理论研究都是在应变循环控制下加载,对于有平均应力存在的应力控制循环加载下的低周疲劳行为研究较少,特别是关于材料全寿命棘轮效应的研究更少。为了研究和预测16MnR钢及焊缝金属的棘轮效应,完成室温下压力容器常用钢16MnR钢及焊缝金属的应变对称循环实验和一系列全寿命的单轴棘轮效应实验。实验结果表明:16MnR钢是一种循环稳定材料;焊缝金属由于本身组织的不均匀性,焊缝金属内部存在缺陷,而在循环载荷的作用下,焊缝金属内部的缺陷损伤会进一步增加,降低了材料的强度,因此焊缝金属表现出了循环软化特性。在单轴棘轮效应实验中,随着平均应力和应力幅值的增加,棘轮应变增加;在循环过程中,棘轮应变不能达到饱和,即棘轮应变随循环次数的增加而持续增加。同时,不断增加的棘轮效应带来了附加的疲劳损伤,缩短了疲劳寿命。利用Chen和Jiao提出的基于O-W模型的改进模型,通过单轴棘轮效应实验,确定了符合16MnR钢及焊缝金属的常数,该模型很好的预测了16MnR钢及焊缝金属的单轴棘轮应变。更多还原

【Abstract】 The ratcheting of materials corresponds to progressive inelastic deformation under cyclic stressing. The ratcheting effect has arisen abroad recognition by scholars and the research on the ratcheting has become a hotspot. For the low cycle fatigue of materials, most of the experimental studies concern strain–controlled loading. Ratcheting, a cyclic accumulation of inelastic deformation, will occur under asymmetrical cyclic stressing. It is extremely necessary to consider the ratcheting effect on fatigue life.In order to realize and predict the uniaxial ratcheting of 16MnR steel, a seris of experiment study was performed on the uniaxial strain cycling and uniaxial ratcheting deformation on the based metal and weld joint of 16MnR under asymmetrical stress cyclic loading at room temperature. The experiment results have shown that 16MnR steel is a cyclic stable material. As weld metal has defects inside and the defects will increase under the cyclic loading, which would reduce the strength of material, thus weld metal shows clear cyclic softening. The uniaxial ratcheting behaviors of the materials were studied in detail under cyclic stressing. The effects of stress amplitude and mean stress on the ratcheting were discussed under uniaxial asymmetrical stress cycling. It shows that ratcheting increases with mean stress and stress amplitude increasing. At the same time, the increasing ratcheting brought fatigue damage, which reduced fatigue life of the materials.In this paper, the modified model based on Ohno-Wang model by Chen and Jiao was used. The results show that the modified model predict the uniaxial ratcheting of 16MnR steel well.更多还原