钻孔法测量残余应力过程中钻孔附加应变的研究（Ⅱ）

本文应用弹塑性理论研究了被测试样的屈服强度、应力场对钻孔法测量残余应力过程中钻孔附加应变的影响,使用简化的理论模型推导了低速旋转钻头钻孔产生附加应变的一般表达式.结果表明钻孔引入的附加应变与被测试样的原始残余应力状态有关,随应力水平增加而增大,在压应力减小到某一临界值σ时,钻孔附加应变为零。在 Ly12铝合金上的实验测量结果与理论结果一致。     

钻孔偏心下的应变释放系数及残余应力

用钻孔应变释放法测残余应力的基本理论导出在任意钻孔偏心下应变释放系数[A],[B]的精确公式.揭示了各传统近似方法(丝栅中心应变法、纵向线积分平均应变法及有效面积上积分平均应变法)的应变释放系数随r_м/а的变化规律。并采用数值逼近法求解了钻孔偏心时的应变释放系数及残余应力.结果表明,偏心对残余应力影响很大。     

钻孔偏心对松弛应变和残余应力的影响

用盲孔释放法测残余应力的基本理论导出在任意钻孔偏心下应变释放系数 A、B 的精确公式.同时通过用偏心公式和不偏心公式计算得到的残余应力值的比较,说明钻孔偏心量对残余应力值影响很大.     

用激光散斑剪切干涉法及钻孔释放法测定残余应力

本文用激光散斑剪切干涉法及钻孔释放法直接测取释放应变,进而计算残余应力.用模拟铝合金试件测取残余应力,条纹清晰,试验结果与理论解一致性较好。     

云纹干涉与钻孔法测量残余应力的实验方法与系统

应变片钻孔法是工程中应用最广的残余应力测量方法之一，由于应变片只能得到其长度范围内的平均应变，测量误差比较大，本文提出用云纹干涉法测量的位移信息代替应变片测量的应变信息来确定残余应力，用有限元建立位移与残余应力之间的关系，基于以上理论，开发了一种可以进行现场残余应力测量的便携式云纹干涉钻孔系统，并用该仪器进行了铝合金激光焊接接头的残余应力测量，得到了焊缝中心残余应力值。     

非中心钻孔时残余应力的分析

当钻孔位置不在应变花中心或者应变片任意排布时,联系松弛应变与残余应力之间足够简单的一般关系式至今还没有见到。Sandifer及Hsin-Pang Wang都推导过这方面的关系式,但是,他们的关系式相当复杂,很难在一般钻孔位置的情况下求解。     

用中心钻孔公式计算残余应力时偏心钻孔造成的误差分析

本文应用钻孔时联系松弛应变与残余应力之间的一般关系式,在应力状态、几何布置较为广泛的组合范围内,分析了当用中心孔公式计算由于钻孔偏心而造成的分析误差。计算结果表明,以往在个别情况下作出的分析,大大低估了偏孔造成的分析误差。     

钻孔法测量残余应力的现状

一、钻孔法的基本原理零件表面总可以看成是主应力为σ_1,σ_2的二向残余应力状态,见图1.如果在测量处钻一个直径为α的小孔,就成为二向应力状态下的孔边应力集中问题.预先在孔边粘贴应变片测出应变数值后,就可以由弹性理论公式算出残余应力σ_1,σ_2的数值。通常在0°,45°,90°三个方向粘贴应变片,见图2.图中角是0°方向的应变片与主应     

钻孔法测量残余应力中几个问题的探讨

本文针对钻孔法测量残余应力中一些不能用“释放”理论解释的问题,通过对钻孔法基本测量原理的分析和与其它传统电测方法对比,认为常用于测量残余应力的电测方法中钻孔法应定义为“干扰法”,切条法和套孔法为“释放法”,Sach＇s镗削法则为“干扰-释放法”.根据实验结果推荐公式=(λ-1)~(1/2)为预测钻孔深度的经验公式.同时应用“干扰”理论分析了压痕法测量残余应力的基本特性,提出压痕法与电测法结合将发展成为一种近似无损的测量残余应力的新方法.     

云纹干涉与钻孔法测量搅动摩擦焊接头的残余应力

搅动摩擦焊是90年代出现的一种新型焊接技术,特别适用于熔化焊接性差的有色金属等材料.搅动摩擦焊接头的残余应力分别具有高应力梯度的特点,传统的应变片钻孔法不能满足测量要求.本文结合云纹干涉法与钻孔法的技术,得到了铝合金薄板搅拌摩擦焊接头残余应力沿深度和沿垂直焊缝方向的分布.     

Residual stress determination using blind-hole drilling and digital speckle pattern interferometry with automated data processing

A combined system of blind-hole drilling and digital speckle pattern interferometry that performs automated data analysis is used to determine the magnitude of the residual stress induced in an aluminum plate subjected to uniaxial tension. The authors perform a finite element analysis of the blind-hole drilling process to adjust the analytical model commonly used for residual stress determination. The relieved displacement field due to the introduction of the blind hole is determined by the evaluation of the optical phase distribution. Using more than 300 values of this displacement field, the magnitude of the residual stress is determined and compared with the applied stress value.     

Brief investigation of induced drilling stresses in the center-hole method of residual-stress measurement

Results of experiments to measure induced drilling stresses in the center-hole method of residual-stress measurement are described. Five specimens of different metals were specially prepared in an attempt to relieve malerial residual stress. Surface-residual-stress measurements were then performed by the center-hole method with a conventionally used (low-speed) end mill and an ultra-high-speed drill. For each specimen, the relieved strains due to the hole drilling were significantly higher for the low-speed end mill than for the ultra-high-speed drill. Preliminary conclusions are that the ultra-high-speed drill would be much superior to the conventional low-speed end mill in the measurement of residual stress by the center-hole method.     

Residual Stress Determination Using Hole Drilling and 3D Image Correlation

In recent years, the hole drilling method for determining residual stresses has been implemented with optical methods such as holographic interferometry and ESPI to overcome certain limitations of the strain rosette version of hole drilling. Although offering advantages, the interferometric methods require vibration isolation, a significant drawback to their use outside of the laboratory. In this study, a 3D image correlation approach was used to measure micron-sized surface displacements caused by the localized stress relief associated with hole drilling. Residual stresses were then found from the displacements using non-dimensional relations previously derived by finite element analysis. A major advantage of image correlation is that it does not require interferometric vibration isolation. Experiments were performed to check the ability of this new approach for uniaxial and equi-biaxial states of stress. Stresses determined by the approach were in good agreement with computed values and those determined by hole drilling using holographic interferometry.     

Analysis of the Influence of the Thickness and the Hole Radius on the Calibration Coefficients in the Hole-Drilling Method for the Determination of Non-uniform Residual Stresses

Experimental Mechanics - The Hole-Drilling method is a semi-destructive technique useful for obtaining residual stress distributions by drilling and measuring relieved strains. The standard for...     

Displacement Determination by Holographic Interferometry for Residual Stress Analysis in Elastic Bodies

A method is developed for determining the three displacement components by the method of holographic interferometry from two interferograms used to measure residual stresses by hole drilling. The displacements are determined at the intersection points of the principal axes and the hole boundary. The method is experimentally validated by measuring the stress state of a plate under uniaxial tension __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 8, pp. 111–117, August 2005.     

Investigation of shrinkage-induced stresses in stereolithography photo-curable resins

An experimental study has been undertaken to investigate the shrinkage characteristics of acrylic-based and epoxy-based stereolithography (SL) photopolymer resin systems after they have been laser cured and post-cured under ultraviolet (UV), and thermal exposure. The induced residual stresses and strains were determined by the shadow moiré and the hole-drilling strain-gage methods. Out-of-plane displacements (warpage) of acrylic-based post-cured resin plates were recorded by means of the shadow moiré method and correlated to the shrinkage strains by theoretical analysis. The induced residual stresses in the epoxy-based cylindrical resin specimens were determined from strains of three-element strain-gage rosettes of the blind-hole drilling method. Results are presented for the shrinkage stresses and strains for both material systems as a function of the post-curing process (UV, thermal). It was found that the shrinkage strains in the acrylic-based photopolymer resin were of considerable magnitude, while thermal post-curing resulted in higher shrinkage stresses for both material systems. The values of the shrinkage stresses compare well with those of the existing literature.     

Three-dimensional stress relief displacement resulting from drilling a blind hole in acrylic

Analyses of optically based, hole-drilling stress measurements require accurate knowledge of the three-dimensional relaxation displacements induced by the drilling of a blind hole into the surface of a stressed object. These displacements are calculated using two closed-form solutions proposed earlier and a numerical finite element technique. Double exposure holographic fringe patterns calculated from the analytic displacements are in poor agreement with those observed in a controlled laboratory calibration experiment on a block of acrylic subject to a known uniaxial compressive stress. However, the fringe positions predicted by the finite element modeling match those obtained from the observed fringe pattern using image-processing procedures, although some drilling-related discrepancies remain near the stress-relieving hole. The stressstrain behavior of acrylic is extremely temperature sensitive; the discrepancies near the stress relief hole may result from drilling induced heat. Despite these near hole disagreements between the predicted and observed fringe patterns, the overall correspondence indicates that the finite element method adequately provides the desired three-dimensional relaxation displacements necessary for determination of stress magnitudes in some blind hole drilling measurements employing coherent optical recording.     

Hybrid experimental-numerical concept of residual stress analysis in laser weldments

The concept, methodology and instrumentation for hybrid experimental-numerical residual stress analysis in a laser weldment are presented. Grating interferometry and digital speckle photography are applied as complementary experimental methods for the determination of the initial model of residual strains and of the material properties at the various zones of a laser weldment. These data inserted into a finite element model enable one to analyze the formation of the residual stress state of the object, which is compared and modified by means of experimental data in a closed iterative loop. This full hybrid approach is tested successfully on a laser-welded steel specimen in uniaxial tensile tests.     

A Study on Hydraulic Autofrettage of Thick-Walled Cylinders Incorporating Bauschinger Effect

Pressure vessels which are subjected to cyclic external or internal high pressure are used in many fields of industry and need to be sure of reliability and safety. To ensure of reliability and safety, thick-walled cylinder, such as a cannon or nuclear reactor, is autofrettaged to induce advantageous residual stresses. The compressive residual stress which was introduced by autofrettage process acts to offset the tensile residual stress induced by internal pressure. It increases operating pressure and restrains crack initiation and crack propagation. As the autofrettage level increases, the magnitude of compressive residual stress at the bore also increases. However, the Bauschinger effect reduces the compressive residual stresses with prior tensile plastic strain, and decreases the beneficial autofrettage effect. There are some differences between theoretical solution considering elastic-perfectly material behavior and real autofrettage process results. The purpose of the present paper is to predict the accurate residual stress of SNCM 8 high strength steel using the Kendall model which was adopted by ASME Code. The tensile and uniaxial Bauschinger effect tests of SNCM 8 were performed to evaluate Bauschinger effect factor(BEF), thereafter this constant was used in calculating the residual stress. The residual stress distribution which is considering the Bauschinger effect was profiled using Kendall model, and the results were compared with the analytical and Finite Element analysis. The results were found that residual stress incorporating the Bauschinger effect at bore was smaller than ideal calculation. These results should be considered in designing pressure vessels.     

Application of X-ray diffraction, micromagnetic and hole drilling methods for residual stress determination in a ball bearing steel ring

A basic understanding of distortion problems requires the analysis of a complete manufacturing process including an almost complete overview of residual stress states in the component during each production step. To reduce the measurement time in the future, three measurements methods (X-ray diffraction, micromagnetic and blind hole drilling methods) have been used to analyze residual stress states in machined AISI 52100 ball bearing rings. X-ray diffraction was used as a state-of-the-art method for machining induced residual stresses with pronounced gradients. The ring exhibited a complex residual stress state with high tensile residual stresses at the surface, a strong gradient in depth, and also showed some variation along the outer circumference due to a superimposition of machining induced residual stresses and effects from the clamping device process. Due to this surface state, micromagnetic signals depend on the analyzing frequency. A calibration of the signals was only possible with the X-ray diffraction data. The results of the three different measurement methods correlate reasonably well.