Residual Stresses VII, ICRS7

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Authors: Feng Zhao, Hua Chen Liu
Abstract: Because of the particularity of distribution of the residual stress of cold-formed thin-wall steel members, now there has not yet been a proper method for directly considering the influence of the residual stress in calculating the reliable capacity of carrying load of cold-formed thin-wall steel members, and such is the typical case in China’s National Technical Specification of Cold-formed Thin-wall Steel Structures GB50018-2002. With the cold-formed thin-wall channel steel taken as specific object in this study as well as assumed to be ideal elastic-plastic body, their finite modular models are set up in ANSYS. According to the tested results and the distributing rules of residual stress, the models of the residual stress of cold-formed thin-wall channel steel are established close to the factual data, and also the initial stress file is set up that can describe the magnitude and distribution of the residual stress. The file has two features: first, it is likely to find out about the rules of the cold-steel residual stress varying in the direction of thickness by using the values of residual stress at some integral points in thickness direction of a specified module , and second, it is applicabled to simulate various distributions of residual stress. So the ultimate load of the member can be worked out and elastic-plastic calculating problem of cold-formed thin-walled steel sections can be easily solved by introducing the initial stress file into the stability analysis of ANSYS.
Authors: Yoshiaki Akiniwa, Keisuke Tanaka, Hidehiko Kimura
Abstract: Single-edge-notched specimens of ultrafine-grained steel were fatigued. The mean grain size of the steel is about 2 micrometers. Propagation behavior of fatigue cracks was observed with the crack closure. The resistance of the crack propagation of ultrafine-grained steel was larger than that of conventional steels. The crack closure acted as an important role for the larger resistance of fatigue crack propagation. After fatigue tests, stress distribution near the fatigue crack was measured by monochromatic X-rays from synchrotron radiation. The irradiated area was 100 µm x 100 µm. Residual and loading stress distributions ahead of the crack tip and on the crack wake was measured at the maximum stress intensity factor and zero applied load. The stress was determined by sin2ψ method. The measured stress was compared with the value calculated by FEM and the fatigue crack propagation model. The stress distribution at the maximum load and residual stresses agreed very well with the calculated results. The crack opening stress calculated by the residual stresses agreed with the experimental result.
Authors: Manuel François, C. Ferreira, Ronald Guillén
Abstract: The global uncertainty, in X-ray stress analysis, is due to many factors but one of the most important is the uncertainty on peak positions due to counting statistics and other random errors on peak positions. Although a lot of work has been done to estimate the latter, very little work has been devoted to its propagation through the least square regression. This work presents some analytical results in the general case of triaxial stress state (elliptic curve fit) and proposes approximate formulae to easily compute the uncertainty on normal and shear stress components from acquisition parameters such as the number N of y tilts and the maximum y value. It was found that the latter only influences significantly the uncertainty on the normal stress component and that the dependency of the uncertainty on N does not necessarily follow a 1/ N relation.
Authors: Jean Michel Sprauel, H. Michaud
Abstract: X-ray diffraction is used to analyse the fatigue behaviour of carbo-nitrided steel layers. Measurements are therefore carried out on the two major phases of the material, i.e. the martensite (a') and the retained austenite (g). On such gear material, X-ray residual stress evaluations are particularly difficult for three reasons. First, the studied material is multiphase. For that reason, in each phase, the stress component in the direction normal to the surface is non negligible. Second, the diffraction peaks obtained on the martensite are broadened, due to the overlap of different reflections of the tetragonal structure. Third, the material contains also carbide and nitride clusters, which lead to incoherent and diffuse scattering of X-rays thus making quantitative phase determination difficult. In our paper the methods used to solve these problems are presented. The development of a new quantitative phase analysis method which accounts for the variation of diffuse scattering of X-rays is shown first. The second part deals with an iterative micromechanical model implemented for the evaluation of the carbon content and the residual stress components of each phase. These methods are used for analysing the evolution with cycling fatigue of all the parameters derived from our enhanced analysis (phase volume fraction, carbon content, stress components, peak width).
Authors: Arnold C. Vermeulen
Abstract: The sensitivity of various combinations of optics to alignment errors is investigated. A large number of tests with varying specimen displacements and incident beam misalignments are performed for both line and point focus residual stress optics combinations. This investigation includes experiments with mixed combinations of typical “focusing beam optics” and “parallel beam optics”. It is verified if the peak positions are either sensitive to height errors like for the focusing beam geometry or insensitive like for the parallel beam geometry. The peak position sensitivity is classified for all combinations of incident beam and diffracted beam optics modules.
Authors: Shin Ichi Ohya, Koichi Akita, Yuichi Shitaba, Mitsutoshi Yoshikawa
Authors: Chedly Braham, Andrzej Baczmanski, Wilfrid Seiler, N. Shiraki
Abstract: The X-ray diffraction measurements based on the grazing incident geometry were applied to determine lattice strains in polycrystalline materials. This method enables a non-destructive measurement at chosen depth below the sample surface. The volume, for which the stress is measured, is well defined and it does not vary during experiment. The multireflection method was used for analysis of the experimental results since the interplanar spacings were measured for various orientation of the scattering vector as well as for various crystallographic planes {hkl}. Applying two different wavelengths of X- ray radiation and various incident angles non-destructive measurements of the residual stresses in function of penetration depth were performed. The variation of stresses in plastically deformed surface layers of steel samples was successfully determined and the values of the stresses were confirmed by standard diffraction measurement.
Authors: Bruno Lavelle, L. Vendier, O. Auriol
Abstract: X-rays transmission stress analysis was tested on a 2mm thick steel sheet using energy dispersive X-rays diffraction (EDXD) and an industrial radiography equipment as X-ray source. A complex state of residual stresses was created in the sheet before the test and modified during the experiment by the way of a in-situ tensile test. In the diffracted beam spectrum, the energy peak displacement was related to macroscopic stresses using the elementary Mohr’s circle formalism for plane stress analysis. The change in the stresses thus analyzed is compared with the applied stress.
Authors: Jun Peng, Vincent Ji, Wilfrid Seiler
Abstract: Residual stresses levels and their distributions in thin films have an important effect on their mechanical properties. The non-destructive analysis by pseudo-grazing incidence X-ray diffraction (GIXRD) allows us to define residual stresses gradients as a function of thin film depth. In case of pseudo-GXRD, we must take into account the effects due to surface roughness on residual stress analysis. We have investigated firstly a set of carbon steel specimens with different surface roughness (RZ varies from 4.2µm to 9.5µm) obtained by grinding. All specimens were tempered to eliminate the residual stresses due to machining. With K radiation of Chromium, Bragg peak positions were determined with various incidence angles  (varies from 1° to 78°) for each specimen. Secondly, a carbon steel specimen containing 4 zones with different surface roughness was loaded elastically in tension, pseudo-GIXRD has used for stress analysis on the loaded specimen with various incidence angles. The peak shifts due to the surface roughness were studied as function of different roughness and different incidence angles. The stress relaxation due to surface roughness was then studied.
Authors: Sophie Berveiller, Pascal Dubos, Karim Inal, André Eberhardt, Etienne Patoor
Abstract: We have developed a new convenient tool for local stress and strain analysis in the scanning electron microscope. It is based on the Kossel diffraction, physical phenomenon that is known for a long time because of its high accuracy for lattice constant determination in micron regions. The pattern is recorded on a CCD camera allowing a fast and reliable analysis. This technique has been applied to several materials. In-situ tensile tests were performed on a shape memory alloy. During loading, we observe clearly a shift of Kossel lines on the diagram, whose magnitude depends on the (hkl) crystallographic planes. The stress can be deduced from the diffracting plane strain measurement using a single crystal stress analysis.

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