Photoelastic determination of stresses in the tube plate of a 70-mw steam generator

This article describes the examination, by three-dimensional photoelasticity, of the tube plate of a sodium steam generator. The tube plate is flat on the side of the tube bundle (121 tubes) and spherical (concave) on the other side. The photoelastic model was made by precision casting, there being no glued joints at the points which are important from the point of view of stresses, such as the tube-tube plate junctions. Both the stress distribution along important sections and the stress concentrations in different types of tube-tube plate junctions due to the internal pressure were determined. The investigation described in this article was carried out in the framework of the Association—Euratom TNO/RCN on Fast Reactors, on behalf of the TNO—Neratoom Sodium Technology Project.     

Photoelastic investigation of a channel cover of bleed condenser

This paper describes the investigation on an epoxy model of a channel cover of bleed condenser, by three-dimensional photoelasticity. The channel cover is a thick plate with two nozzles which are connected on one side to pipes carrying water vapor/water under high pressure. A flat tube plate is connected on the other side by means of sixteen bolts around the periphery with high initial bolt forces. The photoelastic model of the channel cover was made by machining a cast epoxy block (Araldite CT200). The stress distribution along critical sections of the model and the regions of maximum stresses and their values were determined. The prototype stresses were calculated from experimentally obtained values of model stresses, using simiilitude laws.     

Analysis of axially symmetrical residual stresses in bars and tubes

A new method has been developed for the determination of residual stresses in a cylinder. Boring out or removing layers from outside induces changes in the length and diameter of the remaining bar. The initial distributions of the stresses are derived from measurements of the length change only. Details of equations required for the calculations are described. The method rests on an assumption that the radial displacement just below a surface is equal to the radial displacement at a new surface after removal of the surface layer of material. This assumption leads to relations between the three residual-stress components. The numerical calculations of these relations agree well with the experimental data for quenched cylinders obtained by using the Sachs method in other investigations. A brief general discussion is given on the equilibrium conditions of the residual stresses determined.     

Repeatability of the Contour Method for Residual Stress Measurement

This paper describes the results of a residual stress measurement repeatability study using the contour method. The test specimen is an aluminum bar (cut from plate), with cross sectional dimensions of 50.8 mm?×?76.2 mm (2 in?×?3 in) with a length of 609.6 mm (24 in). There are two bars, one bar with high residual stresses and one bar with low residual stresses. The high residual stress configuration (±150 MPa) is in a quenched and over-aged condition (Al 7050-T74) and the low residual stress configuration (±20 MPa) is stress relieved by stretching (Al 7050-T7451). Five contour measurements were performed on each aluminum bar at the mid-length of successively smaller pieces. Typical contour method procedures are employed with careful clamping of the specimen, wire electric discharge machining (EDM) for the cut, laser surface profiling of the cut faces, surface profile fitting, and linear elastic stress analysis. The measurement results provide repeatability data for the contour method, and the difference in repeatability when measuring high or low magnitude stresses. The results show similar repeatability standard deviation for both samples, being less than 10 MPa over most of the cross section and somewhat larger, around 20 MPa, near the cross section edges. A comparison with published repeatability data for other residual stress measurement techniques (x-ray diffraction, incremental hole drilling, and slitting) shows that the contour method has a level of repeatability that is similar to, or better than, other techniques.     

An assessment of residual-stress measurements around cold-worked holes

An X-ray diffraction technique was employed to determine the residual stresses introduced by cold working a fastener hole in a 6-mm thick 2024-T351 aluminum plate. The radial and tangenital residual stresses were measured at both faces of the plate and the measurements compared with the results from a two-dimensional axisymmetric finite-element model. The comparisons were favorable, although modifying the finite-element model to simulate the X-ray process provided better agreement. Experimental determinations of residual stresses showed differences between the two faces of the plate. This feature was attributed to the directional nature of the cold-working process. Paper was presented at the 1994 SEM Spring Conference on Experimental Mechanics held in Baltimore, MD on June 8–10.     

On thermal stresses and displacements in finned-tube panels

The end stresses in a finned-tube panel subjected to transverse temperature gradients are shown to be substantially different than those of a flat plate. Important differences occur due to the local bending of the tube and the extension of the tube beyond the end of the fin. On the other hand, stresses not near the ends and the in-plane deflections of a finned-tube panel are similar to those of a flat plate. These results are obtained by means of a review of flat-plate analysis and comparison with measurements made on two finned-tube panels with a step-transverse temperature gradient.     

Residual surface stresses in laminated cross-ply fiber-epoxy composite materials

Residual (curing) stresses in a cross-ply laminated plate are related to the strains released when individual plies are separated. Released displacements are determined using high-sensitivity moiré interferometry and linearized strain-displacement equations are used to determine residual strains. Elastic orthotropic stress-strain relations are used to calculate residual stresses remote from free-edges of a [90₂₀/0₂₀/90₂₀] graphite-epoxy cross-ply panel. The measured strains compare favorably with those predicted by laminated plate theory. In a second example, the circumferential and radial residual strains and stresses at the end-section of a thick-walled cross-ply graphite-epoxy cylinder are determined. Paper was presented at the 1992 SEM Spring Conference on Experimental Mechanics held in Las Vegas NV on June 8–11.     

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.     

Effect of decoupled fluid loading on nonlinear vibration of a flat plate

Numerical simulations of nonlinear responses of a flat plate subject to decoupled fluid loading are carried out. Under clamped boundary conditions and subject to forced vibration at its natural frequency corresponding to the (5,1) mode, the various response modes of the plate are determined. It is found that increasing the excitation amplitude, the response changed from periodic to chaotic. In addition, the fluid-wall shear stresses are found to change the response from linear to nonlinear and vice versa depending on their magnitudes. When a static pressure load is combined with fluid-wall shear stresses and low excitation amplitude, the resulting response was chaotic.     

Measurement and Prediction of Residual Stresses in Quenched Stainless Steel Components

Austenitic stainless steel cylinders and rings are spray water quenched to create residual stresses at or greater than the yield strength. The residual stresses are measured using neutron diffraction, and two mechanical strain relaxation methods: deep hole drilling and incremental centre hole drilling. This paper compares the measurements with predictions of quenching using finite element analysis. Also finite element analysis is used to mimic deep hole and incremental centre hole drilling methods and to reconstruct residual stresses as if they have been measured. The measurements reveal similar trends to the predictions but there is only limited agreement between their magnitudes. However, there is better agreement between the reconstructed stresses and the measurements. Both the two mechanical strain relaxation methods reveal that large discrepancies occur between measurements and predictions arise because of plasticity. Irrespective of this and surprisingly there is good agreement between deep hole drilling and neutron diffraction measurements.     

爆炸处理消除大型柱壳结构环焊缝残余应力实验研究

为探讨大型耐压柱壳结构对接环焊缝焊接残余应力消除方法,根据耐压柱壳结构环焊缝焊接工艺,设计并制作了大型耐压柱壳结构对接环焊缝模拟焊接模型,并采用沿焊缝条状布药,分别进行了单、双面布药爆炸处理消除大型耐压柱壳结构对接环焊缝焊接残余应力模型实验。结果表明:大型耐压柱壳结构对接环焊缝存在较大的焊接残余应力;单、双面爆炸处理均能有效调整、消除焊接残余应力,残余应力分布明显均匀化;焊后残余应力越大,爆炸处理效果越明显,当焊接残余应力大于0.5s时,单面爆炸处理后残余应力m下降幅度在40%以上,双面爆炸处理后残余应力m下降幅度在60%以上;采用沿焊缝条状布药,爆炸处理能有效消除沿焊缝的纵向残余应力;双面爆炸处理效果优于单面爆炸处理效果。     

Flat vs. Stacked rosettes

Special four-element flat rosettes were used to measure residual stresses and stress concentrations. The resulting data indicated that flat strain-gage rosettes are sometimes quite inadequate for measuring principal stresses. Since all equations used to determine principal stresses from strain-gage rosettes assume a single-point measurement for all elements, it was decided to evaluate, experimentally, both flat and stacked rosettes when used in different types of stress fields. The two rosette types were found to perform equally well in constant stress fields. In nonconstant stress fields where the stress gradient was linear and of moderate level, both rosette types again performed satisfactorily. When these rosettes were subjected to nonlinear stress gradients, the data from the stacked rosette were much superior. Even a small nonlinearity in the stress gradient across a flat rosette caused significant errors in the results. A mathematical model is used to evaluate the performance of flat rosettes subjected to theoretical linear and nonlinear stress gradients. The theoretical sets of strain readings were programmed into a computer in the same manner as would be done with sets of actual test data. The theoretical data agreed quite well with the experimental data obtained and also provided information on flat-rosette performance under loading conditions difficult to simulate in the laboratory.     

Formation of the residual stress field under local thermal actions

The one-dimensional process of material deformation due to local heating and subsequent cooling is analyzed in the framework of the classical theory of elastoplastic deformations. The problem of formation of residual stresses in a thin plate made of an elastoplastic material under a given thermal action is solved. The graphs of fields of residual stresses and displacements are constructed.     

Path dependency in hybrid structures with simultaneous ductile and brittle connections and materials

This article considers a steel–stud–concrete hybrid structure with a Fibre Reinforced Polymer plate adhesively-bonded to the steel member. Owing to the combination of ductile and brittle materials and connections present, the failure behavior of such a structure can be influenced by residual stresses, which in turn depend on the plasticity-inducing load paths previously experienced by the structure. Plasticity of only the stud connections generates a different residual stress pattern from plasticity of only the steel member, and an understanding of the mechanics of residual stress generation in each case is fundamental to the development of a framework of ideas on path dependency in such structures. Measurements of deformation do not necessarily permit faithful reconstruction of residual stress profiles, as these measurements typically give total (elastic plus plastic) deformations from the times that the measurements start, while the residual stresses are related to the elastic components of deformation from the times that the structural components were manufactured. Numerical work is thus needed to determine residual stresses. To that end, a verified finite element program is here used to investigate residual stress patterns in the above hybrid structure due to plasticity of either the studs or the steel member. For yield of the steel, the effects on the residual stresses of initial self-equilibrating stresses in the steel member are investigated. Crucial to the success of the analyses are curvilinear or multi-linear loading/unloading constitutive relationships not only for the materials, but also for the connections. The residual stress profiles from the steel yield and stud yield analyses are examined and compared, and ideas for extension of the work are suggested.     

Residual-stress analysis of an epoxy plate subjected to rapid cooling on both surfaces

This paper presents theoretical and experimental methods of finding the residual stress in an epoxy plate subjected to rapid cooling on both surfaces. The theoretical residual-stress distributions in a plate are calculated by using the fundamental equations based on the linear viscoelastic theory. The specimens in the experiment are subjected to rapid cooling. The residual stresses are measured by the layer-removal method. The theoretical and experimental results are compared and discussed.     

基于断裂力学理论的表面淬火齿轮疲劳寿命的数值计算

基于二维线性断裂力学理论，提出了一种表面淬火齿轮的弯曲疲劳寿命预测方法，并开发了相应的计算程序。在程序中，用权函数法估计应力强度因子，运算速度快，节省了计算时间。在估计应力强度因子时，考虑了热处理后产生的残余应力的影响。用开发的软件对表面淬火齿轮的弯曲疲劳寿命作了预测，并与试验数据进行了比较。预测值与试验结果基本相符，特别是高应力时，二者符合的更好。     

X-ray Diffraction Technique with Imaging Plate for Detecting Surface Distribution of Residual Stress in Diaphysis of Bovine Femurs

Stress measurements of bone are essential for evaluating the risk of bone fracture, the cure of bone diseases (e.g., osteoporosis), and the bone adaptation. Previously, a method using X-ray diffraction (XRD) was used to assess the presence of residual stress in the diaphysis of bovine and rabbit extremities. However, the previous method required a complicated experimental setup, long irradiation time, and limitations of the sample size. To profoundly enhance the understanding of distribution and biomechanical implications of bone residual stresses, it is necessary to develop an alternative method that features a simple setup without limitations on the sample size and shape. An imaging plate (IP) can obtain the two-dimensional distribution of hydroxyapatite crystal deformation and has the potential to resolve the previously mentioned issues. The aim of this study was to develop a measurement system using an XRD technique with an IP for obtaining the surface distribution of residual stress in the diaphysis of extremities. A mid-diaphysis specimen taken from an adult bovine femur was irradiated with characteristic Mo-Kα X-rays under no external forces and the diffracted X-rays were detected by an IP in the reflection side. The residual stress in the bone axis was calculated from the XRD pattern. As a result, tensile residual stresses were detected at the diaphyseal surface, corresponding to the results of the previous method. The developed system reduced the irradiation time by two thirds and the limitations of the sample size were removed.     

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.     

Laser surface-contouring and spline data-smoothing for residual stress measurement

We describe non-contact scanning with a confocal laser probe to measure surface contours for application to residual stress measurement. (In the recently introduced contour method, a part is cut in two with a flat cut, and the part deforms by relaxation of the residual stresses. A cross-sectional map of residual stresses is then determined from measurement of the contours of the cut surfaces.) The contour method using laser scanning is validated by comparing measurements on a ferritic steel (BS 4360 grade 50D) weldment with neutron diffraction measurements on an identical specimen. Compared to lower resolution touch probe techniques, laser surface-contouring allows more accurate measurement of residual stresses and/or measurement of smaller parts or parts with lower stress levels. Furthermore, to take full advantage of improved spatial resolution of the laser measurements, a method to smooth the surface contour data using bivariate splines is developed. In contrast to previous methods, the spline method objectively selects the amount of smoothing and estimates the uncertainties in the calculated residual stress map.     

NUMERICAL PREDICTION OF PROCESS-INDUCED RESIDUAL STRESSES IN GLASS BULB PANEL

A numerical simulation model for predicting residual stresses which arise during the solidification process of pressed glass bulb panel was developed. The solidification of a molten layer of glass between cooled parallel plates was used to model the mechanics of the buildup of residual stresses in the forming process. A thermorheologically simple thermoviscoelastic model was assumed for the material. The finite element method employed was based on the theory of shells as an assembly of flat elements. This approach calculates residual stresses layer by layer like a truly three-dimensional calculation, which is well suited for thin pressed products of complex shape. An experimental comparison was employed to verify the proposed models and methods.