喷丸强化TC4 ELI钛合金的残余应力深度敏感压痕测试与有限元模拟研究

发布时间：2018-05-09 13:47

本文选题：TC4 + ELI钛合金　；参考：《浙江大学》2015年硕士论文

【摘要】：TC4钛合金由于具有密度低、屈强比高等一系列优点而被广泛应用于航空航天等领域。在实际应用中,大量服役中的工程装备常常承受复杂的交变载荷作用,仅仅依靠材料本身的疲劳抗力有时难以满足工程装备的长服役寿命和高可靠性等技术要求。喷丸处理作为有效的表面强化处理方法,已被广泛应用于提高材料及其构件的疲劳强度和疲劳寿命。因此,为了促进钛合金在航空航天等领域中的更好应用,系统研究喷丸处理后钛合金材料表面强化层的残余应力场和力学性能分布规律,进而研究喷丸工艺参数与残余应力分布特征的相关性,并进一步研究喷丸强化残余应力场的定量评估方法等,将具有重要的工程实际意义。本文主要采用深度敏感压痕测试和金相组织检查,并结合有限元数值模拟方法,系统研究了TC4 ELI钛合金光滑试样和单边缺口试样喷丸强化层的残余应力分布和力学性能变化规律。首先,采用深度敏感压痕技术,结合M.Dao等人提出的逆向算法确定出喷丸强化层材料力学性能的变化特征。结果表明：喷丸撞击引起的材料非均匀形变硬化和延性耗散提高了喷丸强化层材料的刚度特性和变形抗力,但降低了强化层材料的塑性与韧性性质。上述材料力学性能的变化规律与喷丸强度相关。其次,应用显微分析术研究发现：喷丸强化层内材料产生了明显的滑移带,喷丸撞击引起材料表面位错密度的提高导致了变形层的循环硬化,使喷丸强化层内的显微组织趋于等轴化且诱发了β相向α相的转变。同时,基于深度敏感压痕测试,采用Suresh修正模型确定出不同喷丸强度下光滑与缺口试样的残余应力分布特征。结果表明：喷丸引入的残余应力场由表层的压残余应力区向次表层的拉残余应力区过渡。喷丸强度的提高增大了压残余应力区域,但对其最大压残余应力的影响很小。喷丸强化残余应力场的分布规律与喷丸强度相关。基于本文提出的残余应力定量评估方法得到的结果与其深度敏感压痕测试获得的残余应力场两者基本一致。最后,论文还采用有限元数值模拟方法研究了喷丸强化光滑试样的残余应力分布特征,并与深度敏感压痕测试得到的残余应力场进行了对比。结果表明：数值模拟得到的喷丸强化残余应力场与深度敏感压痕测试得到的结果取得了很好的一致性。
[Abstract]:TC4 titanium alloys are widely used in aeronautics and spaceflight due to their low density and high yield ratio. In practical application, a large number of engineering equipment in service often bear complex alternating loads, and it is sometimes difficult to meet the technical requirements of long service life and high reliability of engineering equipment only by relying on the fatigue resistance of the material itself. As an effective method of surface strengthening, shot peening has been widely used to improve the fatigue strength and fatigue life of materials and their components. Therefore, in order to promote the better application of titanium alloy in aerospace and other fields, the distribution of residual stress field and mechanical properties of the strengthened layer on the surface of titanium alloy after shot peening is studied systematically. Furthermore, it is of great practical significance to study the correlation between the parameters of shot peening and the distribution characteristics of residual stress, and to further study the quantitative evaluation method of the residual stress field strengthened by shot peening. In this paper, the depth sensitive indentation test and metallographic examination are used, and the finite element numerical simulation method is used. The distribution of residual stress and the change of mechanical properties of shot peening strengthened layers of TC4 ELI titanium alloy smooth and unilateral notched samples were systematically studied. Firstly, the depth sensitive indentation technique and the reverse algorithm proposed by M.Dao et al are used to determine the characteristics of mechanical properties of shot peening strengthened layer. The results show that the inhomogeneous deformation hardening and ductility dissipation caused by shot peening increase the stiffness and deformation resistance of the shot peening strengthened layer, but decrease the plasticity and toughness of the strengthened layer. The change of mechanical properties of the above mentioned materials is related to the shot-peening strength. Secondly, it is found by microanalysis that there are obvious slip bands in the peening strengthened layer, and the increase of dislocation density on the surface of the material caused by shot peening results in cyclic hardening of the deformed layer. The microstructure in the shot peening strengthened layer tends to be equiaxed and the transformation of 尾 phase to 伪 phase is induced. At the same time, based on the depth sensitive indentation test, the residual stress distribution characteristics of smooth and notched specimens under different shot peening strength were determined by Suresh modified model. The results show that the residual stress field induced by shot peening is transferred from the compressive residual stress zone to the tensile residual stress zone. The increase of shot peening strength increases the area of compressive residual stress, but has little effect on the maximum compressive residual stress. The distribution of the residual stress field of shot peening is related to the shot peening strength. The results obtained based on the quantitative evaluation method of residual stress proposed in this paper are basically consistent with the residual stress field obtained by the depth sensitive indentation test. Finally, the residual stress distribution of shot peening smooth specimen is studied by finite element method, and compared with the residual stress field obtained by depth sensitive indentation test. The results show that the results obtained by numerical simulation are in good agreement with those obtained by depth sensitive indentation test.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG668

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