Spatial Distribution Of Residual Stress Research Articles

Mathematical modeling of diagnostics of residual stresses in a layered medium

The work is devoted to the use of mathematical modeling in the framework of the problems of non-destructive testing of structural materials. A mathematical formulation of a three-dimensional problem of diagnostics for elastic layered medium is constructed, which makes it possible to determine the spatial distribution of residual stresses from the values of displacements measured on the surface of a layered half-space, which arose as a result of a specially initiated wave process. Under the assumption of weak inhomogeneity and anisotropy of the layers, a transition is made to a linearized (which is ill-posed) problem, the procedure for solving which is constructed using the method of stationary basic processes. As an example, the case of diagnosing a one-dimensional (depending only on the distance to the surface) distribution of residual stresses is considered.

Evaluation of Tensile Residual Stress in Welded Steel Plates Using Acoustically Stimulated Electromagnetic Response.

Residual stress is one factor involved in the degradation and damage of industrial products. It is important to understand the magnitude and distribution of residual stress to maintain the integrity of a product. Magnetic measurements are a potential nondestructive method for evaluating residual stress in steel because the hysteresis properties are sensitive to stress. In recent years, spatial mapping of local magnetic hysteresis loop has been performed by using the acoustically stimulated electromagnetic (ASEM) method, which obtains the conversion coefficients from local hysteresis parameters to tensile stress. In this study, we demonstrate the evaluation and spatial imaging of tensile residual stress through local hysteresis parameters using welded steel specimens. We confirm that local coercivity can be used for evaluating residual tensile stress in the high-stress region. In addition, the spatial distribution of residual stress is well visualized by imaging the ASEM response signals due to remanent magnetization.

Diffraction-Based Residual Stress Characterization in Laser Additive Manufacturing of Metals

Laser-based additive manufacturing methods allow the production of complex metal structures within a single manufacturing step. However, the localized heat input and the layer-wise manufacturing manner give rise to large thermal gradients. Therefore, large internal stress (IS) during the process (and consequently residual stress (RS) at the end of production) is generated within the parts. This IS or RS can either lead to distortion or cracking during fabrication or in-service part failure, respectively. With this in view, the knowledge on the magnitude and spatial distribution of RS is important to develop strategies for its mitigation. Specifically, diffraction-based methods allow the spatial resolved determination of RS in a non-destructive fashion. In this review, common diffraction-based methods to determine RS in laser-based additive manufactured parts are presented. In fact, the unique microstructures and textures associated to laser-based additive manufacturing processes pose metrological challenges. Based on the literature review, it is recommended to (a) use mechanically relaxed samples measured in several orientations as appropriate strain-free lattice spacing, instead of powder, (b) consider that an appropriate grain-interaction model to calculate diffraction-elastic constants is both material- and texture-dependent and may differ from the conventionally manufactured variant. Further metrological challenges are critically reviewed and future demands in this research field are discussed.

Distribution of residual stress in an asymmetric T-section beam by stretch-bending

Residual stress is frequently induced during quenching of aluminium alloys, and even following stress relief, it can cause distortions in the subsequent manufacturing processes. Evaluating the spatial distribution of residual stress in safety-critical aeronautical structures is of practical importance. For this purpose, the residual stress distribution of a 2026-T3511 aluminium alloy asymmetric T-section beam under displacement-controlled stretch-bending is investigated. A two-step numerical simulation is performed to predict the residual stress superposition in the quenching and subsequent mechanical processes. Moreover, a multiple-cut contour method is used to measure the stress variations on three distinct cutting planes. The results reveal that bending merely alters the distribution pattern of the residual stress rather than reducing the magnitude, whereas stretch-bending offers the advantages of shape forming and stress relief, which are validated by fabricating a long, asymmetric T-section beam.

Spatial distribution of residual stress in similar and dissimilar laser welding

Spatial distribution of residual stress in similar and dissimilar laser welding

Spatial distribution of residual stresses in glass-ZrO2 sphero-cylindrical bilayers

Residual stresses arising from inhomogeneous cooling after sintering have shown to play a preponderant role in the higher incidence of chippings observed for glass-zirconia dental prostheses. Still, current descriptions of their nature and distribution have failed to reconcile with clinical findings. Therefore, an axisymmetric sphero-cylindrical bilayer model was used in this study to determine the effect of the cooling rate on the final spatial distribution of residual stresses. Zirconia frameworks with two different radii (1.6 and 3.2mm) were CAD/CAM fabricated. Subsequent glass overlays with two different thickness ratios (1:1 and 2:1) were generated and heat pressed onto the zirconia substrates. The obtained structures were submitted to a last firing process and fast- (45°C/s) or slow-cooled (0.5°C/s) to room temperature. Unbonded bilayers were produced by firing glass overlays onto boron nitride coated zirconia. Thin sagittal and transversal sections were obtained from the specimens to assess residual stress distribution by means of light birefringence. The applied cooling rates did not affect distribution or magnitude of radial residual stresses (sagittal sections), whereas increased hoop stress magnitudes were measured (transversal sections) in fast-cooled specimens. A distinct stress nature was observed for the hoop stress component of unbonded overlays after fast cooling. Interaction between stress components seems to govern the final stress distribution, highlighting the importance of a multiaxial assessment of this problem in three-dimensional structures.

An accurate method for determining residual stresses with magnetic non-destructive techniques in welded ferromagnetic steels

The scope of the present research work was to investigate the proper selection criteria for developing a suitable methodology for the accurate determination of residual stresses existing in welded parts. Magnetic non-destructive testing took place by the use of two magnetic non-destructive techniques: by the measurement of the magnetic Barkhausen noise and by the evaluation of the magnetic hysteresis loop parameters. The spatial distribution of residual stresses in welded metal parts by both non-destructive magnetic methods and two diffraction methods was determined. The conduction of magnetic measurements required an initial calibration of ferromagnetic steels. Based on the examined volume of the sample, all methods used were divided into two large categories: the first one was related to the determination of surface residual stress, whereas the second one was related to bulk residual stress determination. The first category included the magnetic Barkhausen noise and the X-ray diffraction measurements, while the second one included the magnetic permeability and the neutron diffraction data. The residual stresses determined by the magnetic techniques were in a good agreement with the diffraction ones.

Spatial distribution of residual stress in diamond-silicon carbide composites

Raman spectroscopy and x-ray diffraction whole profile analysis were used to analyze strain in diamond crystals in diamond-silicon carbide composites. The composites were obtained by the infiltration technique from diamond and silicon powders at 8 GPa and 2173 K. Frequency shifts of Raman peak of diamond were used to calculate residual stress and then to draw maps of stress distribution on the surface of diamonds. Large stresses were formed near contact points between diamond crystals. Analysis of profiles of three x-ray reflections of diamond provided information on dislocations and crystallites sizes. After sintering crystallites which scattered x-ray coherently had small sizes which depended on the dimensions of diamond crystal used in the sintering process.

Measurement of laser peening residual stresses

Laser peening is an emerging surface treatment for metals that imparts compressive residual stress near the surface by introducing cold work. The present paper describes two residual stress measurement techniques that are well suited for the measurement of residual stresses induced by laser peening. Since residual stress is a key outcome of the laser peening process, its measurement is an important process diagnostic. The two residual stress measurement techniques described are the slitting method and the contour method. In the present research, the slitting method is used to establish relationships between various laser peening parameters (irradiance, pulse duration, number of layers, etc.) and the residual stress profile (residual stress versus depth) in flat plate coupons that have been uniformly peened on one surface. This helps to identify an effective set of laser peening parameters for the given material. Next, laser peening is applied to a specimen(s) with representative geometry and the contour method is used to measure the spatial distribution of residual stress around critical geometric features. The information gathered from the contour method measurement(s) is used to identify an effective laser peening pattern (coverage area) for the given geometry. This two step procedure is illustrated using recent measurements on sample Alloy 22 (UNS N06022) welds for the Yucca Mountain Project. Details of both measurement procedures are given including representative results for each.

Spatially Resolved Characterization of Residual Stress Induced by Micro Scale Laser Shock Peening

Single crystal aluminum and copper of (001) and (110) orientation were shock peened using laser beam of 12 micron diameter and observed with X-ray micro-diffraction techniques based on a synchrotron light source. The X-ray micro-diffraction affords micron level resolution as compared with conventional X-ray diffraction which has only mm level resolution. The asymmetric and broadened diffraction profiles registered at each location were analyzed by sub-profiling and explained in terms of the heterogeneous dislocation cell structure. For the first time, the spatial distribution of residual stress induced in micro-scale laser shock peening was experimentally quantified and compared with the simulation result obtained from FEM analysis. Difference in material response and microstructure evolution under shock peening were explained in terms of material property difference in stack fault energy and its relationship with cross slip under plastic deformation. Difference in response caused by different orientations (110 and 001) and active slip systems was also investigated.