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.     

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.     

The Role of Residual Stresses in the Performance and Durability of Prestressing Steel Wires

Residual stresses developed during wire drawing influence the mechanical behavior and durability of steel wires used for prestressed concrete structures, particularly the shape of the stress–strain curve, stress relaxation losses, fatigue life, and environmental cracking susceptibility. The availability of general purpose finite element analysis tools and powerful diffraction techniques (X-rays and neutrons) has made it possible to predict and measure accurately residual stress fields in cold-drawn steel wires. Work carried out in this field in the past decade, shows the prospects and limitations of residual stress measurement, how the stress relaxation losses and environmentally-assisted cracking are correlated with the profile of residual stresses and how the performance of steel wires can be improved by modifying such a stress profile.     

The Potential for Assessing Residual Stress Using Thermoelastic Stress Analysis: A Study of Cold Expanded Holes

Thermoelastic stress analysis (TSA) is a well established tool for non-destructive full-field experimental stress analysis. In TSA the change in the sum of the principal stresses is derived, usually when a component is subjected to a cyclic load. Therefore the mean stress or any residual stress in a component cannot be obtained from the thermoelastic response. However, modifications to the linear form of the thermoelastic equation that incorporate the mean stress may provide a means of establishing the residual stresses. It has also been shown that the application of plastic strain modifies the thermoelastic constant in some materials, causing a change in thermoelastic response, which may also be related to the residual stress. The changes in response due to plastic strain and mean stress are of the order of a few mK and are significantly less than those expected to be resolved in standard TSA. Recent developments in infra-red detector technology have enabled these small variations in the thermoelastic response to be identified, leading to renewed interest in the use of TSA for residual stress analysis in realistic components. The component studied in this work is an aluminium plate that contains a cold expanded hole, hence providing an opportunity to examine any changes in thermoelastic response caused by the residual stress in the neighbourhood of the hole. The variations in thermoelastic response due to residual stress are shown to be measurable and significant; validation of the residual stress field is provided by laboratory X-ray diffraction. The potential for a TSA based approach for residual stress analysis is revisited, and the feasibility of applying it to components containing realistic residual stress levels is assessed.     

Inverse Eigenstrain Analysis of the Effect of Non-uniform Sample Shape on the Residual Stress Due to Shot Peening

This paper deals with the analysis of elastic strain and eigenstrain in non-uniformly shaped shot-peened 17-4PH stainless steel samples. Based on residual strain measurements by synchrotron X-ray diffraction, the finite element (FE) models are established for the inverse problem of eigenstrain analysis in slice conical sample. The eigenstrains obtained in the slice are then implemented into the FE model of the solid conical sample. It is found that the dependence of elastic strain distributions on the peening intensity and sample shape/thickness could be elucidated via the understanding of underlying permanent strain, or eigenstrain. The effect of the peening process is therefore best described in terms of the induced eigenstrain. The proposed framework is useful for the predictive modelling of residual stresses in non-uniformly shaped shot-peened materials, in that it allows efficient reconstruction of complete residual stress states. In addition, it provides an excellent basis for developing predictive tools for in service performance and design optimisation.     

Microstructure Effect on the Lcr Elastic Wave for Welding Residual Stress Measurement

The ultrasonic residual stresses measurement is based on the acoustoelastic effect that refers to the change in velocity of the elastic waves when propagating in a stressed media. The experimental method using the longitudinal critically refracted (Lcr) waves requires an acoustoelastic calibration and an accuracy measurement of the time-of-flight on both stressed and unstressed media. The accuracy of this method is strongly related to that of the calibration parameters, namely the time-of-flight at free stress condition (t₀) and the acoustoelastic coefficient (K). These parameters should be obtained on a free stress sample that has an identical microstructure to that of the stressed media. Our study concerns the ultrasonic evaluation of the welding residual stresses. This assembly process induces three distinct microstructures in the weld seam: the melted zone (MZ), heat affected zone (HAZ) and the parent metal (PM). Previously, the residual stresses evaluation in the steel welded plates, by the use of the Lcr wave method, was only possible in the MZ and in the PM zones. While in the HAZ, the residual stresses were incorrectly evaluated due to its small width impeding the extraction of the calibration sample. In this paper, we propose an original approach to solve this problem, which consists of reproducing the microstructure of this zone using a specific heat treatment. For the experimental part, P355 steel welded plates were used and the three zones were probed. The results compared with those obtained by the hole-drilling reference method show a proven potential of the ultrasonic method using the Lcr waves. The Lcr wave residual stresses measurements were made with sufficient accuracy, such as the variability of repeated measures was estimated on the order of ± 36 MPa.     

Mapping Multiple Components of the Residual Stress Tensor in a Large P91 Steel Pipe Girth Weld Using a Single Contour Cut

The contour method is applied in an innovative manner to measure the distribution of hoop residual stress in a large martensitic-ferritic steel pipe containing a multi-pass girth weld. First, a novel one-step wire electro-discharge machining cut is conducted to divide the pipe lengthways into two halves. The deformation of the cut halves is then measured and analysed in a way that simultaneously gives maps of hoop stress across the wall thickness on both sides of the pipe and automatically accounts for through-thickness hoop bending effects and how they may vary along the pipe. Finally the contour method results are combined with X-ray diffraction residual stress measurements using the principle of superposition to determine the distribution of the axial and radial residual stresses in the pipe. It is thereby demonstrated how the distribution of three direct components of the residual stress tensor in a welded pipe can be readily determined using a “hybrid” contour measurement approach.     

Determination of residual stresses by an optical correlative hole-drilling method

In conjunction with the incremental hole-drilling method, a new evaluation procedure is presented for determining the residual stress state in components. In contrast to the classical method, the whole displacement field around the drilled hole is measured using the electronic speckle pattern interferometry technique. The displacement patterns, measured without contact to the surface, are then correlated with those obtained by finite-element simulations using statistical methods. The simulated displacement patterns, used for calibration purposes, result from the application of properly defined basic loads. In this way, the values and the orientation of the residual stresses can be determined by superposition of these properly scaled and shifted basic loads. Even complex states of stress can be evaluated. The theoretical background and experimental results are presented.     

Plasticity Effects in the Hole-Drilling Residual Stress Measurement in Peened Surfaces

The incremental hole-drilling technique (IHD) is a widely established and accepted technique to determine residual stresses in peened surfaces. However, high residual stresses can lead to local yielding, due to the stress concentration around the drilled hole, affecting the standard residual stress evaluation, which is based on linear elastic equations. This so-called plasticity effect can be quantified by means of a plasticity factor, which measures the residual stress magnitude with respect to the approximate onset of plasticity. The observed resultant overestimation of IHD residual stresses depends on various factors, such as the residual stress state, the stress gradients and the material’s strain hardening. In peened surfaces, equibiaxial stresses are often found. For this case, the combined effect of the local yielding and stress gradients is numerically and experimentally analyzed in detail in this work. In addition, a new plasticity factor is proposed for the evaluation of the onset of yielding around drilled holes in peened surface layers. This new factor is able to explain the agreement and disagreement found between the IHD residual stresses and those determined by X-ray diffraction in shot-peened steel surfaces.     

Evaluation of Residual Stresses Induced by Robotized Hammer Peening by the Contour Method

Welded components suffer from high tensile residual stresses close to the weld beads. These stresses seem to be the origin of premature cracking which could result in a catastrophic rupture during operation and a reduction of the lifespan of these components. In this context, the Hydro-Québec’s Research Institute (IREQ) developed a technique of residual stresses relaxation by robotized hammer peening which makes it possible to release stresses close to surface and preserve the mechanical and dimensional properties of manufactured components. Robotized hammer peening was used to induce compressive residual stresses on initially stress free samples of austenitic stainless steel 304L. Hammer peening layers from one to nine were performed and the resulting residual stresses were evaluated thanks to the contour technique. Complete 2D residual stress fields on samples cross sections were obtained. The ability of hammer peening to relax residual stresses within welded plates was then quantified on austenitic stainless steel 304L plates welded with a 308 steel and hammer peened. These tests show the efficiency of hammer peening as a method to relax tensile residual stresses and induce compressive ones to a depth of a few millimetres. Process parameters were optimized such as the number of hammer peening layers to be applied to reduce processing time and maximization of the intensity and spatial distribution of the compressive residual stresses.     

Thermal Stress Measurement in Continuous Welded Rails Using the Hole-Drilling Method

The absence of expansion joints in Continuous Welded Rail has created the need for the railroad industry to determine the in-situ thermal stress levels for rail buckling and breakage prevention. This paper explores the hole-drilling method as a possible solution to this problem. A new set of calibration coefficients to compute the stress field relieved by fine hole depth increments required by the high strength steel was determined. The new calibration coefficients were experimentally validated on an aluminum plate subjected to a known uniaxial load. The thermal stress levels of constrained rails were estimated after compensation for the residual stress components, based on statistical relationships developed experimentally between the longitudinal and the vertical residual stresses. The results showed that the hole-drilling procedure, with appropriate calibration coefficients and residual stress compensation, can estimate the in-situ rail thermal stresses with an expected accuracy that is within the industry acceptable levels.     

Measurement of Torsionally Induced Shear Stresses in Shrink-Fit Assemblies

Shear stresses along the shaft/hub interface in shrink-fit components, generated by torsional loads, can drive premature failure through fretting mechanisms. It is difficult to numerically predict these shear stresses, and the associated circumferential slip along the shaft/hub interface, due to uncertainties in frictional behaviour and the presence of steep stress gradients which can cause meshing problems. This paper attempts to provide validation of a numerical modelling methodology, based on finite element analysis, so the procedure may be used with confidence in fitness-for-purpose cases. Very few experimental techniques offer the potential to make measurements of stress and residual stress interior to metallic components. Even fewer techniques provide the possibility of measuring shear stresses. This paper reports the results of neutron diffraction measurements of shear stress and residual shear stress in a bespoke test specimen containing a shrink-fit. One set of measurements was made with a torsional load ‘locked-in’. A second set of measurements was made to determine the residual shear stress when the torsional load had been applied and removed. Overall, measurement results were consistent with numerical models, but the necessity for a small test specimen to allow penetration of the neutron beam to the measurement locations meant the magnitude of shear stresses was at the limits of what could be measured experimentally.     

Evaluation of residual stresses and strains using the Eigenstrain Reconstruction Method

The study of residual stress has long been an important research field in science and engineering, due to the fact that uncontrolled residual stresses are detrimental to the performance of products. Numerous research contributions have been devoted to the quantification of residual stress states for the purpose of designing engineering components and predicting their lifetime and failure in service. For the purposes of the present study these can be broadly classified into two main approaches, namely, the interpretation of experimental measurements and process modelling. In this paper, a novel approach to residual stress analysis is developed, called here the Eigenstrain Reconstruction Method (ERM). This is a semi-empirical approach that combines experimental characterisation, specifically, residual elastic strain measurement by diffraction, with subsequent analysis and interpretation based on the eigenstrain theory. Three essential components of the ERM, i.e. the residual strain measurement, the solution of the inverse problem of eigenstrain theory, and the Simple Triangle (SIMTRI) method, are described. The ERM allows an approximate reconstruction of the complete residual strain and stress state in the entire engineering component. This is a significant improvement compared to the experimentally obtained limited knowledge of stress components at a selected number of measurement points, or to the simple interpolation between these points.     

Comprehensive numerical analysis of a three-pass bead-in-slot weld and its critical validation using neutron and synchrotron diffraction residual stress measurements

The current paper presents a finite element simulation of the residual stress field associated with a three pass slot weld in an AISI 316LN austenitic stainless steel plate. The simulation is split into uncoupled thermal and mechanical analyses which enable a computationally less expensive solution. A dedicated welding heat source modelling tool is employed to calibrate the ellipsoidal Gaussian volumetric heat source by making use of extensive thermocouple measurements and metallographic analyses made during and after welding. The mechanical analysis employs the Lemaitre–Chaboche mixed hardening model. This captures the cyclic mechanical response which a material undergoes during the thermo-mechanical cycles imposed by the welding process. A close examination of the material behaviour at various locations in the sample during the welding process, clearly demonstrates the importance of defining the correct hardening and high temperature softening behaviour. The simulation is validated by two independent diffraction techniques. The well-established neutron diffraction technique and a very novel spiral slit X-ray synchrotron technique were used to measure the residual stress–strain field associated with the three-pass weld. The comparison between the model and the experiment reveals close agreement with no adjustable parameters and clearly validates the used modelling procedure.     

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.     

Residual-stress distributions produced by strain-gage surface preparation

Abrasion of a metallic surface to improve bonding during strain-gage installation is generally thought to produce negligible effect on the measurement of residual stresses by blind hole drilling. However, residual stresses induced by surface abrasion may affect residual-stress measurements in shallow subsurface layers of residual-stress fields produced by processes such as grinding and shot peening.The residual-stress and cold-work distributions produced by four methods of abrasive surface preparation and etching were studied by X-ray diffraction in fully annealed AISI 1018 steel. The surface residual stresses produced by abrasion ranged from tension to compression with magnitudes as high as 80 percent of the yield strength. Cold work was induced to depths of 20 to 60 m. Etching produced low magnitude surface stresses and negligible cold work.Paper was presented at the 1986 SEM Spring Conference on Experimental Mechanics held in New Orleans, LA on June 8–13.     

Improvement of the Contour Method for Measurement of Near-Surface Residual Stresses from Laser Peening

A study was conducted to develop a methodology to obtain near-surface residual stresses for laser-peened aluminium alloy samples using the contour method. After cutting trials to determine the optimal cut parameters, surface contours were obtained and a new data analysis method based on spline smoothing was applied. A new criterion for determining the optimal smoothing parameters is introduced. Near-surface residual stresses obtained from the contour method were compared with X-ray diffraction and incremental hole drilling results. It is concluded that with optimal cutting parameters and data analysis, reliable near-surface residual stresses can be obtained by the contour method.     

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 stress prediction and determination in 7010 aluminum alloy forgings

Precipitation-hardened aluminum alloys gain their high strength through heat treatment involving a severe quenching operation, which can have the adverse effect of introducing residual stresses. The finite element code ABAQUS is used to simulate the quenching of aluminum alloy 7010 in an attempt to predict the residual stress distribution that develops in simple shapes. The rate of heat transfer from the material is determined using the finite element method to predict the heat transfer coefficient from surface cooling curves achieved experimentally. The flow stress of the material is assumed to be strain rate dependent and to behave in a perfectly plastic manner. The predicted residual stress magnitudes and directions are compared to values determined using the holedrilling strain gage method and the X-ray diffraction technique.     

Measuring Inaccessible Residual Stresses Using Multiple Methods and Superposition

The traditional contour method maps a single component of residual stress by cutting a body carefully in two and measuring the contour of the cut surface. The cut also exposes previously inaccessible regions of the body to residual stress measurement using a variety of other techniques, but the stresses have been changed by the relaxation after cutting. In this paper, it is shown that superposition of stresses measured post-cutting with results from the contour method analysis can determine the original (pre-cut) residual stresses. The general superposition theory using Bueckner’s principle is developed and limitations are discussed. The procedure is experimentally demonstrated by determining the triaxial residual stress state on a cross section plane. The 2024-T351 aluminum alloy test specimen was a disk plastically indented to produce multiaxial residual stresses. After cutting the disk in half, the stresses on the cut surface of one half were determined with X-ray diffraction and with hole drilling on the other half. To determine the original residual stresses, the measured surface stresses were superimposed with the change stress calculated by the contour method. Within uncertainty, the results agreed with neutron diffraction measurements taken on an uncut disk.