Relaxation Methods for Measuring Residual Stresses: Techniques and Opportunities

Relaxation methods, also called “destructive” methods, are commonly used to evaluate residual stresses in a wide range of engineering components. While seemingly less attractive than non-destructive methods because of the specimen damage they cause, the relaxation methods are very frequently the preferred choice because of their versatility and reliability. Many different methods and variations of methods have been developed to suit various specimen geometries and measurement objectives. Previously, only specimens with simple geometries could be handled, but now the availability of sophisticated computational tools and of high-precision machining and measurement processes has greatly expanded the scope of the relaxation methods for residual stress evaluation. This paper reviews several prominent relaxation methods, describes recent advances, and indicates some promising directions for future developments.     

A Novel Cutting Strategy for Measuring Two Components of Residual Stresses Using Slitting Method

An exact knowledge of residual stresses that exist within the engineering components is essential to maintain the structural integrity. All mechanical strain relief (MSR) techniques to measure residual stresses rely on removing a section of material that contains residual stresses. Therefore, these techniques are destructive as the integrity of the components is compromised. In slitting method, as a MSR technique, a slot with an increasing depth is introduced to the part incrementally that results in deformations. By measuring these deformations the residual stress component normal to the cut can be determined. Two orthogonal components of residual stresses were measured using the slitting method both experimentally and numerically. Different levels of residual stresses were induced into beam shaped specimens using quenching process at different temperatures. The experimental results were then compared with those numerically predicted. It was shown that while the first component of residual stress was being measured, its effect on the second direction that was normal to the first cut was inevitable. Finally, a new cutting configuration was proposed in which two components of residual stresses were measured simultaneously. The results of the proposed method indicated a good agreement with the conventional slitting.     

Superposition and Destructive Residual Stress Measurements

The paper describes destructive measurement of residual stress profiles across two perpendicular planes in a single coupon. Several established destructive measurement techniques can determine the residual stress locked in a coupon of interest, but in general, only a single measurement can be taken without releasing stress and affecting subsequent measurements. However, when the first measurement determines a stress profile across an entire plane, the released stress can be determined, through a supplemental stress analysis incorporating results from the first measurement, and then accounted for in a subsequent measurement. To demonstrate the capability, we describe measurements of residual stress profiles across two perpendicular planes in aluminum compact tension coupons. Residual stress was introduced into the coupons by laser shock peening, and measurements were performed using the slitting method. For each coupon, the measured stress profile on the first plane was used to compute stress released on the second plane. By adding this released stress to measured stress for the second plane, we obtain a stress profile for the second plane in the original configuration. Results of a numerical model that predicts residual stress due to laser shock peening are presented, and agreement between the model and experimental results gives confidence in the superposition method applied.     

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.     

Experimental Methods for Determining Residual Stresses and Strains in Various Biological Structures

Over the years, an assortment of methods for determining residual stresses has been developed in the field of experimental mechanics. Adaptations of those methods to study residual strains and stresses in various biological structures found in humans, other mammals, viruses and an insect are reviewed. Methods considered include deflections from release of residual stresses, hole drilling and ring coring, strains upon dissection, the contour method, slitting (crack compliance), X-ray diffraction, photoelasticity, and membrane and shell displacements. Sources of residual stresses and strains are summarized and examples of their physiological role noted.     

钻孔法和光栅应变花测试复合材料的残余应力

残余应力对材料、结构的疲劳强度和使用寿命等性能的影响早已为人们所熟知,由于它的大小、方向和分布随制造加工或处理方法不同而有很大的随机性,国内外对它的研究很重视。对于各向异性的复合材料,随着加上生产制造过程及工艺参数的不同,其中的残余应力的大小、方向等就更加复杂。从国内外对残余应力的研究中,可以看出大多数都着重于实验研究。本文应用钻孔法和云纹干涉技术的成果,针对残余应力测试中的特点,尤其是在利用钻孔法和云纹干涉技术测试残余应力时存在的问题,在目前绝大多数云纹干涉技术所使用的正交光栅的基础上,提出并研制出一种三个方向的光栅,即在原来 0°、90°两个方向光栅上,再加上一个 45°方向的光栅,在进行云纹干涉测试时,一次加载时就可以同时测试出三个独立的位移场:u场、v场和s场,利用这三个位移场就可以得到相应的三个应变:ε0、ε90和ε45,进而可以计算得到相应的应力。     

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.     

Measurement of Applied Stresses and Residual Stresses on a Residual Stress Model by Applying Two Different Loads

Applied stresses on a residual stress model have previously been obtained by measuring the residual stresses and the resultant stresses generated by applying a load. The present paper reports that the applied stresses and the residual stresses on the residual stress model can be obtained by measuring two resultant stresses generated by applying loads of two different magnitudes. In the proposed method, the residual stresses need not be obtained from the residual stress model before applying a load. The residual stress model used to test the proposed method is a circular disk with frozen stresses that is subjected to a diametral compressive load at a certain angle. The applied stresses and the residual stresses on a residual stress model were experimentally and precisely obtained by digital photoelasticity using linearly polarized light.     

Residual Stresses from Incremental Hole Drilling Using Directly Deposited Thin Film Strain Gauges

Experimental Mechanics - Commonly, polymer foil-based strain gauges are used for the incremental hole drilling method to obtain residual stress depth profiles. These polymer foil-based strain...     

A New Procedure to Measure Near Yield Residual Stresses Using the Deep Hole Drilling Technique

Mechanical strain relief techniques for estimating the magnitude of residual stress work by measuring strains or displacements when part of the component is machined away. The underlying assumption is that such strain or displacement changes result from elastic unloading. Unfortunately, in components containing high levels of residual stress, elastic-plastic unloading may well occur, particularly when the residual stresses are highly triaxial. This paper examines the performance of one mechanical strain relief technique particularly suitable for large section components, the deep hole drilling (DHD) technique. The magnitude of error is calculated for different magnitudes of residual stress and can be substantial for residual stress states close to yield. A modification to the technique is described to allow large magnitudes of residual stress to be measured correctly. The new technique is validated using the case of a quenched cylinder where use of the standard DHD technique leads to unacceptable error. The measured residual stresses using the new technique are compared with the results obtained using the neutron diffraction technique and are shown to be in excellent agreement.     

A Procedure to Measure Biaxial Near Yield Residual Stresses Using the Deep Hole Drilling Technique

Deep Hole Drilling (DHD) is a mechanical strain relief technique used to measure residual stresses within engineering components. Such techniques measure strains or displacements when part of the component is machined away and typically assume elastic unloading. However, in components containing high levels of residual stress, elastic–plastic unloading can occur which may introduce substantial error. For the case of the DHD technique, a modification to the technique referred to here as the incremental or iDHD technique has been developed to allow such high levels of residual stress to be measured. Previous work has demonstrated the accuracy of the iDHD technique, although only for axisymmetric residual stress distributions. In the present investigation, the application of the iDHD technique has been extended to the general case of biaxial residual stress fields. Finite element simulations are first carried out to demonstrate the ability of the iDHD technique to measure biaxial residual stress. Experimental measurements were then made on shrink fit components and ring welded components containing biaxial residual stress to investigate the performance of the technique in practice. Good agreements between iDHD measurements, neutron diffraction measurements and FE predictions of the residual stresses were obtained, demonstrating the generally improved accuracy of the iDHD technique compared to the standard DHD approach.     

压力机焊接残余应力的状态分析

对 ２０００ｋ Ｎ 及 １５００ｋ Ｎ 压力机焊后残余应力状态进行了测试分析,并对用振动法和热处理两种方法进行消除残余应力的效果进行了现场测试及对比分析。     

Determination of Residual Stresses in High Speed Milled Aluminium Alloys Using a Method of Indent Pairs

An improved method of indent pairs is utilised to determine residual stresses in high speed milling specimens of AA 6082-T6 and AA 7075-T6 aluminium alloys. To carry out the measurement procedure, this approach does not need specific equipment but only requires a universal measuring machine and an oven. An indentation device is incorporated to the measuring machine, which allows reducing the absolute error of measurement to just ±0.9 MPa. The geometry of the tool and cutting parameters are selected to evaluate the sensitivity of the method. The residual stress distributions generated by high speed milling are exhaustively evaluated taking into account orthogonal components of cutting speed and tangential force, which are parallel and perpendicular to feed direction.     

再生器、沉降器残余应力状态分析

对炼油厂催化系统的再生器、沉降器残余应力状态进行现场测试分析,并对出现缺陷处、装置焊接成型过程中的强力组装处等典型部位进行测试,分析了出现缺陷的原因。     

SMA复合材料在热载条件下的残余应力分析

本文基于三相复合圆柱模型发展了增量型的分析方法,讨论在ＳＭＡ复合材料中由于ＳＭＡ材料相变以及各相材料热特性随温度变化引起的残余应力。研究基体与过渡恸介面和纤维与过渡界面间的残余应力,同时讨论由于基体相的变化对残余应力的影响。特别研究了涂层和复合材料基体间界面处的残余应力受纤维体积比、涂层厚度、纤维最大相变应以及基体中纤维取向等影响,而且讨论了计及应力对相就运动方程的影响时对ＳＭＡ复合材料相变温度和     

三维电子散斑干涉法在检测残余应力中的应用

本文提出一种新的大错位三维电子散斑干涉法,并将其和钻 法检测残余应力技术结合起来,其特点一是利用三个激光器,从不同的方向照射被测物体,二是在被测物附近放置一参考物,利用大错位棱镜,使物体表面的信息和参考物上的信息都进及ＣＣＤ中,可以得到与三个位移场有关的电子散斑干涉条纹图,并可以运算和分离获得独立的ｕ,ｖ和ｗ场信息,本文介绍了大错位三维电子散斑干涉法的原理、方法和系统,并将其应用于钻孔法释放残余应     

抽油杆表面感应淬火引起的残余应力

本文讨论了抽油杆通过感应线圈和水冷装置时的温度场和由温度场引起的相变。在有限元计算中，通过与实验数据对比，认为考虑温度对弹性模量有影响的计算模型更合理，并用此模型计算了由温度和相变共同作用的弹塑性应力场，及最终的残余应力。结果表明淬火层超过一定厚度后，残余应力分布的合理性降低；淬火前抽油杆的强度与残余应力的大小关系较弱。