Materials Science Forum Vols. 524-525

Abstract: The paper presents the results of residual stress measurements on a ferritic steel plate containing a repair weld. The repair was considered representative of that found in the secondary circuit piping in power plant. The paper primarily uses the deep hole drilling (DHD) technique, but compares results found by this technique with those obtained using neutron diffraction. Both sets of measurements confirmed that highly tensile residual stresses exist in the repair weld. The two measurement techniques produced results that were in acceptable agreement, but the neutron diffraction results were consistently higher than the deep hole drilling results. It was thought this was due to the use of a constant stress-free lattice parameter d0 .

Abstract: An algorithm of the layer growing/removing method for computing of the residual stresses in thin orthotropic inhomogeneous circular disc is presented. The stresses are calculated from strain measurements on the free stationary contour or on the lateral surface, or from X-ray diffraction measurements on the disc’s moving contour. The suggested algorithm is programmed for PC. Two illustrative examples are presented.

Abstract: As part of the European project “high and ultrahigh temperature heat exchangers” (HITHEX) the prediction and experimental assessment of the lifetime behaviour, characterisation and qualification of particular CMC materials, including carbon fibre reinforced carbonsiliconcarbides (C/C-SiC), has been executed. Part of the programme of the HITHEX project was the measurement of the strain development within the C/C-SiC tubular specimens from room to high temperature, the results of which are presented here. Residual strains have been determined in several specimens by neutron diffraction at the High Flux Reactor (HFR) of the Joint Research Centre in Petten, The Netherlands. At the HFR two facilities are available for residual strain investigations. Both instruments were utilised in the investigations. The first facility at beam tube HB5, the combined stress and powder diffractometer, employs a constant neutron wavelength of 0.257 nm, and the second facility at HB4, the Large Component Neutron diffraction facility, LCNDF, has a flexible wavelength. The installation of a vacuum furnace has enabled the residual strain measurement of specimens at high temperature on HB4. The furnace had to fulfil three main criteria for the investigation of these specimens; high-temperature, good neutron penetration and negligible oxidation of the specimens. The ceramic specimens, which have outer and inner diameters of 50 and 40 mm, respectively, and a length of 100 mm have been measured to temperatures of up to 1450°C. Measurements were carried out in two directions on the SiC phase of several specimens, i.e. in the radial and tangential (hoop) directions. The implications of these results with respect to the structural integrity assessment of these components at high temperatures are discussed.

Abstract: This paper describes the measurement of longitudinal residual stresses within specially designed 200x180x25mm groove weld specimens. The purpose of these measurements was to compare the residual stress field arising from single and multi-pass weld beads laid down within the constraint of a groove in order to validate finite element simulations of the welding process. Measurements were made over the cross section at the mid-bead length, utilising the relatively new Contour method and neutron diffraction. Results from these measurements indicate a larger peak tensile longitudinal residual stresses within the weld region of the multi-pass weld sample. Good agreement is found between both techniques.

Abstract: Plastic anisotropy can affect the strains measured by neutron diffraction. If this is not properly accounted for significant errors can result in the calculated stresses. This paper illustrates addresses this issue using measurements of the residual strain field around a 60 mm long single weld bead deposited on the surface of a 17 mm thick stainless steel plate. Measurements were made on ENGIN-X, the engineering spectrometer at the ISIS facility of the Rutherford Appleton Laboratory (UK). Diffraction spectra from these measurements have been fitted using both single and multi-peak fitting approaches. Both residual strain and stress results have been presented for (111) and (200) single peak fits and compared to a multi-peak fit (Rietveld) analysis. Results from these analyses have revealed significant anisotropy in the response of the individual lattice planes. This effect is most severe in measurements carried out in the normal direction and is shown to be predicted using an elasto-plastic self-consistent model.

Abstract: Pearlitic steel and pure tungsten specimens were ground using a table-type grinding machine. The thin surface layers affected by the grinding process were characterized using focussed ion beam milling and microscopy. The strongly graded zone altered due to severe plastic deformation and recrystallisation was found to be less than 3m thick. The microstructure in that zone depends on the grinding parameters. Using synchrotron X-ray diffraction, the residual stresses were measured for penetration depths ranging from 0.25 m to 9 m. Based on the approach by Dölle and Hauk, the residual shear stresses were separated from the residual normal stresses. In pearlitic steel, residual shear stresses of opposite sign were observed in the two phases (ferrite and cementite) and found to be compensating each other, while shear stresses were proved to be absent in single-phase tungsten. These results underline that residual shear stresses caused by severe plastic shear deformation exist only as micro-stresses.

Abstract: The strain scanning method was applied to the evaluation of the subsurface distribution of the residual stress beneath the shot-peened surface of an austenitic stainless steel SUS304L which had coarse grains and preferred orientation. The experiment was performed at beam line BL22XU at SPring-8 using monochromatic X-rays of 70.14 keV and a Ge (111) analyzer. The sizes of both incident and receiving slits were 2 × 0.2 mm2. The specimens were annealed or shot-peened and had the dimensions of 20 × 20 × 5 mm3. The grain size was about 37 μm. In order to obtain the diffractions from an enough number of grains, various types of oscillation methods, which were translation, rotation and tilting of the specimen, were examined. The translational oscillation was found to be enough to obtain the accurate strain distribution. By combining the translational oscillation method with the correction to the surface aberration, the subsurface distribution of the residual stress of shot-peened austenitic stainless steel was successfully determined.

Abstract: Residual stress generated in Type-316 austenitic stainless steel butt-weld jointed by Inconel-182 was measured using a neutron diffraction method and compared with values calculated using FEM analysis. The measured values of Type-316 austenitic stainless steel as base material agreed well with the calculated ones. The diffraction had high intensity and a sharp profile in the base metal. However, it was difficult to measure the residual stress at the weld metal due to very weak diffraction intensities. This phenomenon was caused by the texture in the weld material generated during the weld procedure. As a result, this texture induced an inaccurate evaluation of the residual stress. Procedures for residual stress evaluation to solve this textured material problem are discussed in this paper. As a method for stress evaluation, the measured strains obtained from a different diffraction plane with strong intensity were modified with the ratio of the individual elastic constant. The values of residual stress obtained using this method were almost the same as those of the standard method using Hooke’s law. Also, these residual stress values agreed roughly with those from the FEM analysis. This evaluation method is effective for measured samples with a strong texture like Ni-based weld metal.

Abstract: The production technologies development of thermonuclear reactors is a actual problem of today. The work researches zirconium goods used in the atomic industry – thin-walled tubes for the fuel elements shells, thin-walled tubes for the channels of watery and boiling reactors, rods for lock – plugs of fuel elements; mechanical properties of zirconium and zirconium alloys, production methods and technologies as well. The power approach is used in the work. The potential energy of the elastic deformation is regarded as a part of the plastic deformation energy and a portion of the energy used for residual stresses formation. Using these methods the distributions of residual stresses are determined by the volume of a product depending on the main technological parameters of a process and mechanical properties of the material. The results have shown that hoop stresses take maximum values. The activity of residual stresses can lead to the elastic deformations and to the departure from the rated dimensions of a product, subsequently, that is inadmissible for the precision parts. These methods are used to determine the influence of residual stresses on mechanical properties, precision and operating strength of tube products made of different zirconium alloys.

Abstract: A new method is presented which allows the determination of experimental stress factors in anisotropic thin films on the basis of static diffraction measurement. The method is based on the simultaneous characterization of macroscopic stress and elastic strain in thin film using substrate curvature and sin2ψ methods, respectively. The curvature of monocrystalline substrate with known mechanical properties is determined using rocking curve measurements on substrate symmetrical reflections. The experimental stress and strain values are used to calculate stress factors for the specific film as a function sample tilt angle and reflection measured. The approach represents a relatively simple recipe to determine residual stress magnitude in thin films on the absolute scale. The procedure is demonstrated on polycrystalline Cu thin film deposited on Si(100).