激光冲击强化钛合金圆角构件的残余应力分布及其抗疲劳研究

发布时间：2018-01-18 03:15

本文关键词：激光冲击强化钛合金圆角构件的残余应力分布及其抗疲劳研究　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

【摘要】：机械领域中零部件大多带有复杂的曲面特征,如结构圆角、沟槽等,这些曲面结构的临界区曲率变化较大,往往存在应力集中,在外载荷的作用下易萌发疲劳裂纹,进而发生断裂,是疲劳薄弱区,而激光冲击强化能有效提高曲面部件的疲劳寿命。但激光冲击诱导曲面结构残余应力的分布规律不能基于平面结构获得的趋势进行预测,因此研究曲面结构激光冲击强化的残余应力分布,提高曲面构件疲劳性能,具有重要的意义。本文通过理论分析、数值模拟以及试验验证等手段,以TC4-DT钛合金圆角构件为研究对象,探讨了激光冲击强化对曲面结构残余应力分布及其疲劳性能的影响。本文主要研究工作如下:(1)论述了激光诱导冲击波的产生及其与材料相互作用过程,分析了冲击波作用下残余应力场的形成机制,探讨了激光冲击作用下曲面结构残余应力产生的机理以及曲率与残余应力之间存在的可能关系;采用ABAQUS有限元分析软件建立了凹面、平面和凸面三种几何模型,研究了激光多点搭接冲击下曲面结构的几何效应。结果表明,三种几何模型之间的残余压应力大小及影响层深度存在以下关系:凹面平面凸面。对于凹面结构,残余压应力随曲率半径的增大而减小,最后趋于平面结构;而对于凸面结构,残余压应力随半径的增大而增大,最后趋于平面结构;对于圆角构件,R3模型表面的残余压应力分布要优于R6模型。(2)基于ABAQUS有限元分析软件对圆角结构在不同激光冲击参数下残余应力的分布规律进行了研究。结果表明:对于圆角结构,残余压应力大小随峰值压力的增大而增大,但存在一个饱和值,而残余压应力影响层深度一直增加;随着激光脉宽的增大,各路径上残余压应力呈增大的趋势,残余压应力影响层深度也随之增加;冲击次数增加到一定次数后作用不明显,甚至起反作用,而冲击次数对深度方向上的残余应力分布影响较小。(3)对TC4-DT钛合金R3、R6圆角双联试样进行了激光冲击强化试验和疲劳拉伸试验。结果表明,试样经激光冲击强化后,疲劳寿命大幅增加,虽然不同条件下疲劳增益各不相同,但R3和R6试样的疲劳增益却相差无几。(4)通过对疲劳断口形貌的微观分析发现,比较冲击前后:在疲劳源区,试样未冲击端断口上疲劳源均位于圆角根部相切处,而冲击端疲劳源向冲击深度方向转移,且均位于侧面;在疲劳稳定扩展区,相同位置处冲击端断口上的疲劳条带间距明显小于未冲击端,说明激光冲击强化能有效抑制疲劳裂纹的扩展;在最终瞬断区,试样冲击端瞬断区上的韧窝尺寸较未冲击端大。通过对激光冲击强化改善圆角结构抗疲劳特性的研究发现:激光冲击通过引入残余压应力来减小裂纹尖端有效应力强度因子幅,抑制疲劳裂纹的扩展,达到提高圆角构件疲劳寿命的目的;而曲率半径则通过对集中应力和残余应力分布的共同作用来影响圆角构件的疲劳性能。
[Abstract]:In the field of mechanical parts with the most complex surface feature, such as the structure of the trench, rounded, critical curvature changes of the surface structure is large, there is stress concentration, it was easy to fatigue crack under external loading, and fatigue fracture is the weak area, and laser shock peening can improve the fatigue life of surface the distribution of components. But not laser shock induced surface residual stresses in plane structure trend based on the forecast, so the research on surface structure of the residual stress distribution of laser shock strengthening, improving fatigue properties of surfaces, is of great significance. In this paper, through theoretical analysis, numerical simulation and experimental verification method based on TC4-DT the rounded titanium alloy component as the research object, discusses the laser shock stress distribution and fatigue properties of surface residual structure. This paper mainly research The work is as follows: (1) discusses the shock wave induced by laser and its interaction with the process of the material, analyzes the formation mechanism of shock wave under the action of the residual stress field, discusses the mechanism of laser shock surface structure under the effect of residual stress and curvature and residual stress exist in the relationship between the force is established; concave using finite element analysis software ABAQUS, and the three plane convex geometry model, the geometric effect of surface structure of multi point laser lap under the impact. The results showed that three kinds of residual geometric model between compressive stress size and influence depth has the following relations: concave convex concave plane. The structure, the compressive residual stress the force decreases with the increase of the radius of curvature, and finally tends to planar structure; for convex structure, the residual compressive stress increases with the increase of the radius, and finally tends to planar structure; for fillet component, R3 model The surface residual stress distribution is better than the R6 model. (2) based on finite element analysis software ABAQUS on distribution of fillet structure under different laser shock parameters of residual stress were studied. The results show that: for the fillet, the residual compressive stress with the size of the peak pressure increased, but there is a a saturation value, and the residual stress influence depth has been increased; with the increase of pulse width, the path of the residual compressive stress increases, the compressive residual stress influence depth increases; the impact number increased to a certain number of aftercrop is not obvious, or even counterproductive, and impact times on the residual stress distribution in the depth direction has little influence. (3) of TC4-DT titanium alloy R3, R6 double fillet samples by laser shock test and fatigue tensile test. The results show that after laser shock peening, the fatigue life significantly Although the gain increase, fatigue under different conditions are different, but the fatigue gain R3 and R6 samples but not much difference between. (4) through microscopic analysis on the fatigue fracture morphology found that: in the comparison before and after the impact fatigue source region, the sample fracture fatigue impact end source are located in the root of the fillet tangent at the impact end the impact of fatigue source transfer to the depth direction, and are located in the expansion zone on the side; fatigue and stability, at the same position of impact fatigue fracture end on band spacing is significantly lower than that of non impact end, which indicates that the extended LSP can effectively inhibit the crack; in the final fracture zone, specimen fracture zone on the end of the impact toughness nest size is not large. The impact end by strengthening the research on improving the fatigue resistance of the fillet on laser shock: laser shock by introducing compressive residual stress near the crack tip to reduce the effective stress intensity factor range, inhibition of fatigue crack The purpose of improving the fatigue life of fillet members is to expand, while the radius of curvature influences the fatigue performance of fillet members by the combined action of concentrated stress and residual stress distribution.

【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG665

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