【作者】 武敬伟；

【导师】 花银群；

【作者基本信息】 江苏大学 ， 机械制造及其自动化， 2007， 硕士

【摘要】 本文从激光冲击波诱导残余应力场的机理出发,对激光冲击强化Fe-Ni合金残余应力场进行了数值模拟,并对Fe-Ni合金进行了激光冲击强化的试验研究,主要取得了如下研究成果:阐述了激光冲击波的形成机制,分析了约束模式下的Fabbro模型及其修正模型,根据弹塑性动力学、冲击波理论,探讨了激光冲击波的传播机理和材料在一维应变压缩下的本构关系。结合材料在一维应变压缩下的本构关系分析了激光冲击波诱导残余应力场的形成过程,探讨了残余应力场的主要影响因素。以ANSYS/LS-DYNA为平台,建立了激光冲击强化Fe-Ni合金的有限元分析模型,阐述了激光冲击强化数值模拟的有限元理论基础,讨论了建模过程中的几个关键问题,分析了模拟得到的冲击波的传播和残余应力场的分布情况,对激光冲击参数对残余应力场的影响进行了数值模拟研究。模拟结果表明:在激光功率密度小于一定阀值时,表面残余压应力最大值随着激光功率密度增加而增加,超过阀值之后,表面残余压应力最大值减小,同时在激光功率密度增加的整个过程中,残余压应力层深度则是一直增加的;表面残余应力最大值和残余压应力层深度随着脉宽的增加而增加,增加脉宽对残余应力场在表面以及深度方向上均有一定程度的改善,特别是长脉宽的改善更为明显;通过增加光斑半径对残余压应力场的改善主要体现在表面残余应力场的改善上,而在深度方向上效果相对有限:多次连续冲击强化对残余应力场的改善不仅体现在峰值残余压应力的提高上,更体现在残余压应力层深度的增加上,可以通过增加冲击次数来改善残余应力场在表面和深度方向上的分布,特别是对后者的改善更为明显。对Fe-Ni合金进行了激光冲击强化的试验研究,实验结果表明冲击区硬度平均值比基体部分提高了16%,冲击区发生了马氏体相变,产生了高密度胞状位错和孪晶,对比残余应力场的实验与数值模拟结果,两者取得了较好的一致。更多还原

【Abstract】 Based on the mechanism of LSP inducing residual stress field, in this paper, the residual stress field of Fe-Ni alloy was simulated and then experimental research was made on LSP of Fe-Ni alloy. The main contents were as following:The mechanism of laser shock wave was described. Fabbro model and its corrected model in the confined mode were analyzed. According to the theory of plastic-elasticity dynamics and the theory of shock wave, the constitutive equations of material were analyzed when laser shock wave propagated in material in one dimension strain compress.Combined with the constitutive equations in one dimension strain compress , the forming processing of residual stress field induced by LSP was analyzed. Then the main influencing factors of residual stress field were analyzed, especially the shock parameter.Based on ANSYS/LS-DYNA software, the FEA analysis model was founded, considering the finite element theory. Some key problems were discussed. The results of numerical simulation were analyzed. The effects of laser shock parameters on the residual stress field of Fe-Ni alloy were studied by numerical simulation, which indicated that:The peak surface residual compressive stress increased as the laser power density increased when the laser power density was below a fixed value, and then decreased. At the same time, the depth of the residual compressive stress was increasing all the time. The maximum and the depth of the residual compressive stress increased as the laser pulse duration increased, which showed it could improve the residual compressive stress field by increasing the laser pulse duration. The simulated results also revealed that increasing the laser spot size could resulted in an increase in the maximum and the depth of the residual compressive stress, especially the latter.Experimental research was made on LSP of Fe-Ni alloy, the results of the experiment were analyzed. The results indicated that the average microhardness of the shock zone of the samples increased by about 16%. The results also showed LSP induced martensitic transformation、cellular dislocation of high density and twin. In contrast with FEA and experimental data, the simulated data of residual stress field was well consistent with the experimental data.更多还原