The double exposure method (DEM) is proposed herein as a new X-ray stress measurement method for coarse grain materials. A diffraction angle can be obtained from an incident and a spotty diffracted beam. Each X-ray beam is measured by an area detector on a linear motion stage on the 2 θ-arm in the DEM. To examine the validity of the DEM, the residual stress of the plastically bent specimen was measured. In addition, the residual stress distribution of the indentation specimen was measured. The result by the DEM was similar to the result simulated by the finite element method. As a result, the DEM is useful for the X-ray stress measurement method for coarse grain material.
This study examines the effect of welding conditions on the applicability of X-ray stress measurement at weld metal with coarsened grains. Testing material was low carbon austenitic stainless steel and 15 welded specimens were prepared through tungsten inert gas (TIG) welding under various welding conditions, in which five kinds of welding currents and three kinds of welding speeds were assigned in all combinations. In the X-ray stress measurement, 2θ-sin2ψ method was applied and then the effectiveness of enlarging a diameter of collimator and applying additional planer oscillation for weld metal with coarsened grains was evaluated. Meanwhile, the effect of welding conditions on crystal grain coarsening at weld metal was examined based on welding thermal conduction theory with a moving point heat source. The results showed that the mean crystal grain size at weld metal correlated linearly with the parameter derived from the welding thermal conduction theory. Based on relation between X-ray irradiation area and the mean crystal grain size, the effect of the welding conditions on the applicability of X-ray stress measurement with or without enlarging a diameter of collimator and applying additional planer oscillation was systematically evaluated.
An advanced welding thermal elastic-plastic analysis, which has recently been developed by authors to improve both accuracy and reliability of welding simulation techniques, was applied to validate the measurement of transient thermal stress at steel welds by synchrotron X-ray diffraction techniques. The calculated weld penetration, temperature profiles, the transient thermal stress and distribution of residual stress at welds were compared with those measured. The results showed that there were, on the whole, comparatively good agreement between the calculations and experimental values. However, an obvious discrepancy between the calculations and experimental values can be seen in the variation behavior of stress during cooling process after welding only at weld metal (WM) and heat-affected zone (HAZ). It was thought to be due to phase transformation induced by welding. This discrepancy provides one of prospects for the future that X-ray elastic constants vary according to microstructure evolution is essential to accurately estimate the transient thermal stress and residual stress at steel welds with phase transformation. It is then expected that dependence of X-ray elastic constants on the microstructure with phase transformation is clarified more clearly.
Most cold forming processes are effective methods for improving the fatigue strength of large forged steel structures. However, these methods give rise to compressive residual stresses on the surface, while causing tensile residual stresses around the cold-formed parts. The inherent strain method using FEM is one of the most effective measures for predicting the internal residual stress distribution for large forged structures, because of the depth of the residual stresses. It was found that the conditions of the inherent strain area and the order of the inherent strain distribution functions, are very important for the accuracy of the predictions, when the efficient approach that combines the inherent strain method using FEM, X-ray stress measurement, and a new measurement procedure, was applied to the fillet portion of the axisymmetric shaft with flange after the cold forming process. In the cold-formed parts, the inherent strains are induced by plastic deformation, and there is a relationship between the half value breadth of X-ray diffraction profile and the plastic strains. By noting these points, this report confirms the relationship between the half value breadth of X-ray diffraction profile and the equivalent inherent strain. Moreover, we propose that it is important to set the conditions of the inherent strain area and the order of the inherent strain distribution functions while considering the half value breadth of the X-ray diffraction profile.
This paper presents an evaluation method for thermal ageing of surface-modified layer by X-ray diffraction techniques. Test specimens with surface-modified layer were prepared through shot peening with two different processing degrees. Thermal ageing test was then carried out using these specimens. Lab X-ray in-situ measurement was applied to obtain dynamic behavior of compressive residual stress and full width at half maximum (FWHM) within surface-modified layer during thermal ageing test. After the tests, X-ray diffraction line profile analysis was also applied to characterize thermal ageing-induced evolution of microstructure, such as crystalline size and micro strain (plastic strain due to dislocation), within surface-modified layer. As the results, relaxation of compressive residual stress due to thermal ageing was correlated highly with reduction of micro strain. The quantitative relation between them was successfully established based on inherent strain theory. Thus, the evaluation method with X-ray diffraction techniques are expected to be useful for quantifying the stress relaxation and microstructure evolution within surface-modified layer during thermal ageing.
To improve reliability and manufacture yield of gas turbine blade for thermal power plant, the method of measuring crystal orientation of Ni-base superalloy turbine blade by non-destruction using laboratory X-ray was developed. Crystal orientation measurement function was added to existing X-ray residual stress measurement equipment, which is diffraction method measuring crystal orientation defined from diffraction data of particular lattice plane by characteristic X-ray. The measurement accuracy of this equipment is very high equal to Laue method or EBSD which are general technique, and a surface smooth finishing process is not necessary. Furthermore, calculation method of inclination angle of crystal growth direction from blade height direction was established in measurement from the side face of blade with this equipment. Crystal orientation of mass-produced turbine blade became able to be measured experimentally and effectively by this technique.
In order to discuss the quality assurance of additively manufactured lattice structure made by aluminum alloy (AlSi10Mg) using 3D printing technology or selective laser sintering technique, compression test, micro-CT imaging and finite element analysis were carried out. The specimens were manufactured by 2 printing service companies with different expertise, which led to the choice of different process parameters such as the building direction, support structure, powder bed temperature and laser scanning speed. The largely scattered compressive peak loads were in good linear positive correlation with the weight, which is the easiest and convenient index for the quality assurance. On the other hand, the apparent density was almost the same. The reason why the weight of the products was largely scattered was investigated by micro-CT image analysis and finite element analysis. Also by comparison with the CAD data, the influence of manufacturer-dependent process parameters on the strength was discussed.
The one-dimensional longitudinal wave propagation in the layering direction in an alternating multilayered structure with nonlinear spring-type interfaces is analyzed theoretically to study the second-harmonic generation behavior due to the presence of closed defects at interlayer interfaces. The structure consists of alternating linear elastic layers and is surrounded by two linear elastic semi-infinite media. The layers as well as semi-infinite media are bonded to each other by nonlinear spring-type interfaces possessing identical linear interfacial stiffness and different quadratic nonlinearity to model closed defects such as delaminations and cracks. On the assumption of weak nonlinearity, the second-harmonic amplitudes of the reflected and transmitted waves when a monochromatic longitudinal wave impinges perpendicularly on the structure are derived by combining a perturbation approach with the transfer-matrix method. It is found that the wave propagation characteristics are governed by five non-dimensional parameters: the non-dimensional frequency, the number of interfaces (layers), the acoustic impedance ratio between neighboring media, the stiffness ratio between the interface and the layer, and the ratio of times of flight between neighboring layers. The second-harmonic amplitudes due to a single nonlinear interface are shown to be influenced remarkably by the fundamental frequency as well as the position of nonlinear interface in the multilayered structure. These features are successfully explained by using the pass and stop band characteristics of the layered structure and the spatial distributions of the fundamental and the second-harmonic displacements inside the structure.
In a mountain tunnel, predicting geological conditions ahead of the tunnel face is quite important in order to carry out the tunnel construction safely and economically. In the logging survey performed while drilling, which is one of the forward investigations of the tunnel face, drilling data such as percussive pressure, rotational pressure, feed pressure, damping pressure, and speed of the hydraulic drill are measured, and the ground state of the drilling position is predicted. Among them, the damping pressure, which damps the repulsive force from the ground due to the impact of the hydraulic drill, provides information on the geological properties of the hole drilling position. To evaluate geological properties such as compressive strength using drilling data, drilling was performed on specimens that simulated grounds with different compressive strengths, and drilling data was measured. As a result, it was found that pulsation, which is the fluctuation of pressure, was generated at damping pressure owing to the impact of the hydraulic drill. The ratio of the pulsation amplitude to the percussive pressure is a stronger correlation with the compressive strength of simulated specimens than does the specific energy.