基于压痕隆起量的残余应力测试方法与实验研究

发布时间：2018-08-27 05:46

【摘要】：在机械加工过程中,外力和温度变化引起的不均匀塑性变形是产生残余应力的主要原因,残余应力对材料的力学行为和使用寿命有着重大的影响。压痕法因具有操作简单、快捷、微损伤的特点,在测量材料的力学性能和残余应力方面得到了较为广泛的应用。但到目前为止,压痕测量法只能获得一个测点的平均应力,无法获得残余应力的应力分量及其方向。因此,本文从实验与仿真两个方面探索新的压痕检测分析技术,以测量一般应力状态下残余应力的大小和方向。在压痕试验中,由于材料的塑性变形,压痕周围会出现材料的堆积和沉陷。通过分析发现,压痕卸载后的变形量,特别是压痕周边的最大隆起量,与残余应力的大小和方向有关。为获得最大隆起量与残余应力的定量关系,本文首先采用有限元分析方法,对球形压痕条件下不同的残余应力组合进行了大量的分析计算,拟合出了残余应力大小与隆起量的双线性定量关系,得到了拉伸残余应力使隆起量变小,压缩残余应力使隆起量变大的一般规律。在残余应力方向的研究方面,发现最大隆起量出现的方向与平面最大应力方向相同,与最大隆起量方向垂直的方向即为平面最小应力方向。另外,通过提取压痕周边离面位移数据,根据干涉原理形成了模拟干涉条纹图,与相关文献的实验干涉条纹图进行了对比,在形状上高度吻合。为验证仿真结果的正确性,本文设计制造了一个可以施加单轴与双轴应力的实验装置。在对试件施加已知应力后,在压痕试验机上用直径为2.5mm的布氏压头和大小恒定的压力对试件中部位置进行静态压痕实验。卸载后,采用高精度的激光共聚焦方法对压痕表面轮廓进行了非接触式测量。实验验证了理论与仿真的结果,即残余应力与隆起量的双线性关系。实验表明可以运用卸载后压痕隆起量来表征残余应力。另外,本文运用中科院KJS-3型冲击压痕产生装置,对不同应力状态下的试件进行了冲击压痕试验,然后用光学方法测量卸载后的轮廓。结果表明,冲击压痕状态下卸载后压痕隆起量与残余应力之间也存在和静态压痕类似的规律。根据理论仿真和实验分析的结果,本文提出了压痕隆起量与二维残余应力之间的一般经验公式,据此公式可以直接根据压痕试验后的隆起量来计算二维残余应力的方向以及各分量的大小。本文提出的方法的精确度很大程度上取决于三维轮廓测量的精确度,故本文研究了三种非接触式的全场轮廓测量方法:激光三角法,层析聚焦法和投影条纹法。运用光学方法来精确测量卸载之后压痕周围的隆起量。本文以布氏压痕试验为基础,提出了一种新的完整测量二维残余应力的新方法。该方法可以快捷准确的测定物体内部的残余应力,其精度可以满足工程应用的需要,为构件的表面性能和剩余寿命的评价提供了一种的新的测量与分析技术。
[Abstract]:In the process of machining, the inhomogeneous plastic deformation caused by the change of external force and temperature is the main cause of the residual stress, and the residual stress has a great influence on the mechanical behavior and service life of the material. The indentation method has been widely used in measuring the mechanical properties and residual stresses of materials because of its advantages of simplicity, rapidity and microdamage. But up to now, the indentation method can only obtain the average stress of one measuring point, and can not obtain the stress component and direction of the residual stress. Therefore, in this paper, a new indentation detection and analysis technique is explored from the aspects of experiment and simulation to measure the magnitude and direction of residual stress in general stress state. In indentation test, due to the plastic deformation of the material, there will be material accumulation and subsidence around the indentation. It is found that the amount of deformation after indentation unloading, especially the maximum uplift around the indentation, is related to the magnitude and direction of residual stress. In order to obtain the quantitative relationship between the maximum uplift quantity and the residual stress, the finite element analysis method is used to analyze and calculate the different residual stress combinations under the spherical indentation condition. The bilinear quantitative relationship between the residual stress and the uplift is obtained. The general rule that the tensile residual stress makes the uplift smaller and the compressive residual stress makes the uplift larger is obtained. In the research of the direction of residual stress, it is found that the direction of maximum uplift is the same as the direction of plane maximum stress, and the direction perpendicular to the direction of maximum uplift is the direction of plane minimum stress. In addition, by extracting the off-plane displacement data of indentation periphery, the simulated interference fringes are formed according to the principle of interference, which are compared with the experimental interference fringes of related literature and are highly consistent in shape. In order to verify the correctness of the simulation results, an experimental device which can apply uniaxial and biaxial stresses is designed and manufactured. After applying the known stress to the specimen, the static indentation experiment was carried out on the indentation machine with a Brinell indenter with diameter of 2.5mm and a constant pressure. After unloading, the contours of indentation surface were measured by high precision laser confocal method. The theoretical and simulation results are verified by experiments, that is, the bilinear relationship between residual stress and uplift. The experimental results show that the residual stress can be characterized by indentation uplift after unloading. In addition, the impact indentation test was carried out on the specimens under different stress states by using the KJS-3 impact indentation generating device of the Chinese Academy of Sciences, and then the contours after unloading were measured by optical method. The results show that there is a similar rule between the amount of indentation uplift and the residual stress after unloading under the condition of impact indentation and static indentation. Based on the results of theoretical simulation and experimental analysis, a general empirical formula between indentation uplift and two-dimensional residual stress is presented in this paper. Based on this formula, the direction of two-dimensional residual stress and the size of each component can be calculated directly from the uplift of indentation test. The accuracy of the proposed method depends largely on the accuracy of 3D contour measurement. Therefore, three non-contact full-field contour measurement methods, namely laser triangulation method, tomography focusing method and projection fringe method, are studied in this paper. The optical method is used to accurately measure the uplift around the indentation after unloading. Based on Brinell indentation test, a new complete method for measuring two-dimensional residual stress is presented in this paper. This method can quickly and accurately measure the residual stress inside the object, and its precision can meet the needs of engineering application. It provides a new measurement and analysis technique for the evaluation of the surface performance and residual life of the components.
【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG115

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