应用云纹干涉法测量冷挤压孔周残余应力分布

本文就冷挤压加工后紧固孔周的残余应力测量问题进行了研究。文中提出了径向切割法以释放欲求剖面的周向残余应力;采用高灵敏度的云纹干涉法测量残余应力释放后引起的附加变形;用载波错位法获得高反差的应变条纹图。     

循环载荷下冷挤压孔宏观残余应力的松弛效应

本文对应用云纹干涉法测量冷挤压孔周残余应力分布作了简要的论述，并应用该技术研究了冷挤压孔周残余应力在循环应力作用下的松弛问题，还探讨了残余应力的构件疲劳过程的相互作用，最后绘出不同循环应力次数作用后残余应力高周疲劳效应的几组实验结果。     

铰孔和疲劳对冷挤压孔周残余应力的影响

应用干涉云纹测量了冷胀孔周残余应力分布，并用实验方法研究了铰孔和疲劳对残余应力的影响。介绍了测试技术和原理，提供了典型的实验结果，并讨论了误差原因     

激光反射全息干涉法现场测量残余应力的实验研究

本文根据激光反射干涉法的基本原理，采用钻盲孔释放残余应变的手段，提出一种新颖的残余应力激光全息现场测量的方法，推导出该光学测量方法３种计算公式．解决了激光全息干涉法不能进行现场实测的难题．     

激光反射全息干涉法现场测量残余应力的实验研究

本文根据激光反射干涉法的基本原理，采用钻盲孔释放残余应变的手段，提出一种新颖的残余应力激光全息现场测量的方法，推导出该光学测量方法３种计算公式．解决了激光全息干涉法不能进行现场实测的难题．     

基于弹性理论的残余应力反演和变形计算

毛坯在制造过程中,材料力学性能的非均匀性导致其内部产生残余应力.残余应力会造成结构破坏,在工件的切削去除过程中,残余应力会逐渐释放并引起变形.采用有限元的“生死单元”技术模拟材料的切削去除过程,并转化为残余应力的释放,基于板壳理论、小变形理论、弹性理论和叠加原理,将径向基函数插值法与几何方程、物理方程相结合,开发出一种新的解析方法,反演残余应力场并计算变形.结果表明解析方法的理论解与有限元解高度吻合,能够用于判断残余应力分布并计算残余应力弹性释放引起的变形.     

冷拔无缝钢管残余应力测量的杂交实验方法

提出了一种数值模拟和实验杂交的实验方法,测量了钢管内表面的残余应力。采用非线性有限元法模拟了冷拔钢管的成型过程,得到了钢管脱模以后的残余应力,通过释放切口处单元的刚度模拟了含有残余应力钢管的切割过程,研究了切割方法对残余应力的影响,数值计算和实验结果表明切割方法对二次残余应力有很大影响。采用X射线测量仪测量了钢管内表面的残余应力。研究结果表明,计算结果基本符合实验结果,误差可以被工程接受。     

硅基底多层薄膜结构材料残余应力的微拉曼测试与分析

针对MEMS器件制备中两种典型的硅基底多层薄膜结构的残余应力问题,本文提出了利用微拉曼光谱技术测量其残余应力的方法,分析并给出了硅基底多层薄膜结构中的残余应力分布规律。实验结果表明,在硅基底和薄膜内存在较大的工艺残余应力,残余应力在基底内靠近薄膜两侧部分呈非线性变化,在基底内主要呈线性变化,并引起基底整体翘曲。基于实验结果分析,提出了硅基底多层薄膜结构的分层结构模型。本文工作表明微拉曼光谱技术是测量与研究硅基底多层薄膜结构残余应力的一种有力手段。     

大错位量散斑干涉法测量残余应力

本文提出大错位量激光散斑干涉法结合钻孔法测量残余应力,对单向拉伸残余应力进行了测量,试验结果与理论解非常吻合,并且实现了对真实构件表面残余应力的测量.     

聚晶金刚石复合片热残余应力分布规律实验研究

利用改进的应力释放法、X射线衍射法以及Raman光谱,对平面界面结构金刚石复合片表面热残余应力分别进行了实验研究,得到了金刚石层表面热残余应力值及其分布规律,同时得到了基体厚度与热残余应力的相关关系.研究结果表明,采用应力释放法、X射线衍射法及Raman光谱法测试PDC表面热残余应力,其测试结果均与有限元分析结果相吻合,证明了这三种方法的有效性.其中,X射线衍射法测试结果的误差最大,应力释放法其次,Raman光谱法最为精确.由于应力释放法应变片尺寸及X射线衍射法光斑照射范围的限制,无法在试样表面上取较多的测试点,因此难以得到理想的热残余应力分布曲线.而Raman光谱法中所采用的激光光斑仅5μm,可以取更多的测试点,因此其结果更能真实的反映金刚石层表面热残余应力的分布规律.本文的研究结果为精确测试PDC热残余应力,从而为优化PDC界面结构、提高PDC使用性能提供了理论和实验依据.     

Residual Stresses Induced by Cold Expansion of Adjacent and Cut-Out Holes

Fatigue life of fastener holes can be enhanced via a cold-expansion process to introduce a compressive residual stress field around the hole edge and to reduce crack growth propagation. Considering that aerospace components contain multiple rows of holes, the present investigation focuses on the evaluation of the three-dimensional residual stress distribution in adjacent cold-expanded (CE) holes. The redistribution of residual stresses caused by a cut introduced between two adjacent holes was also investigated. Finite element (FE) analysis and experimental technique were used to assess the residual stress distribution in a 6082-T6 aluminum plate with two adjacent holes expanded sequentially at 4 % nominal interference. The influence of center-to-center distance between holes was explored to assess the optimal level of separation between adjacent holes. Results suggested that residual stresses near second CE hole are markedly lower than those of first CE hole and that a cutting process does not affect the beneficial compressive residual stress around CE holes. These effects may delay fatigue crack propagation from CE holes or cut-out holes.     

Interference fasteners for fatigue-life improvement

This paper describes use of interference-fit fasteners for improving fatigue life. Experiments showed substantial improvements in life for constant amplitude and spectrum loading, even where high loading introduced plastic deformation. Tests conducted at low stresses on single-shear butt joints showed but little improvement, because high bending stresses caused failure at edges of washers instead of through fastener holes. On the other hand, axial-loaded specimens containing unloaded interference fasteners showed marked increases in life at all stress levels.     

A new analytical-numerical method for calculating interacting stresses of a multi-hole problem under both remote and arbitrary surface stresses

Based on the elementary solutions and new integral equations, a new analytical-numerical method is proposed to calculate the interacting stresses of multiple circular holes in an infinite elastic plate under both remote stresses and arbitrarily distributed stresses applied to the circular boundaries. The validity of this new analytical-numerical method is verified by the analytical solution of the bi-harmonic stress function method, the numerical solution of the finite element method, and the analytical-numerical solutions of the series expansion and Laurent series methods. Some numerical examples are presented to investigate the effects of the hole geometry parameters (radii and relative positions) and loading conditions (remote stresses and surface stresses) on the interacting tangential stresses and interacting stress concentration factors (SCFs). The results show that whether the interference effect is shielding (k <1) or amplifying (k> 1) depends on the relative orientation of holes (α) and remote stresses (σ_x^∞, σ_y^∞). When the maximum principal stress is aligned with the connecting line of two-hole centers and σ_y^∞ <0.5σ_x^∞, the plate containing two circular holes has greater stability than that containing one circular hole, and the smaller circular hole has greater stability than the bigger one. This new method not only has a simple formulation and high accuracy, but also has an advantage of wide applications over common analytical methods and analytical-numerical methods in calculating the interacting stresses of a multi-hole problem under both remote and arbitrary surface stresses.     

Z-pin复合材料细观模型固化残余应力研究

针对植入Z-pin后碳纤维增强复合材料的微观结构，通过施加Z-pin周期性边界约束条件，建立了Z-pin复合材料单层板单胞细观模型．考虑固化过程中树脂体积收缩、弹性模量随固化度变化和纤维因Z-pin进入偏转因素，运用有限单元法计算了单胞结构在固化成型工艺过程中树脂和纤维应力发展和分布，并研究了Z-pin直径和分布密度对单层板面内残余应力的影响．结果表明：凝胶点之前，树脂模量和残余应力很小，凝胶点之后，树脂模量和残余应力增加较快；残余应力分布与纤维偏转有关；Z-pin直径和分布密度增加会使固化残余应力增大．     

Experimental and numerical study of residual stresses caused by cold expansion of adjacent holes

Cold expansion is a useful process for imposing compressive residual stresses around the holes in riveted and bolted connections. These stresses increase the fatigue life of holed parts. Distribution and amount of exerted residual stress dependent on various parameters as material, distance of adjacent holes, hole diameter, cold expansion ratio and plate thickness. In this study, experimental and numerical results for two different aluminum alloys and various holes distances are investigated and compared. Effects of mentioned parameters on the residual stress are studied.     

Stress Distribution in an Orthotropic Plate with Circular Holes under Impulsive Loading

The photoelastic method is used to analyze the stress–strain state induced by an impulsive load in an orthotropic plate with circular holes. The distribution of dynamic stress concentration factors along the periphery of the holes is studied, and stresses and strains in representative sections are determined     

On the measurement of residual-stress gradients in aluminum-alloy specimens

The assessment or prediction of fatigue life or strength improvement due to residual stresses requires knowledge of their magnitude and distribution. This paper presents an extension of the modified hole-drilling technique (MHDT) to the measurement of stress gradients in a biaxial-residual-stress field. This is achieved by taking a series of ‘point’ measurements and evaluating the stress profile with due consideration to the effects of hole location, the interaction between holes and the redistribution of stress due to hole drilling. An application to the measurement of residual stresses induced in 2024-T3 aluminum-alloy specimens by edge-dimpling technique is described and the method of compensation for the effect of redistribution of stress is explained. The experimental results are shown to be in good agreement with those obtained elsewhere by an analytic-numerical solution.