Papers by Keyword: X-Ray Stress Analysis

Abstract: In this paper the microstructural and residual-stress analysis of an induction hardened plate of medium carbon steel is described. The stress gradient was determined using laboratory X-ray diffraction (IWT, Bremen, Germany) and neutron strain scanning (ILL, Grenoble, France). Due to slight variations of chemical composition in the depth, matchstick like (cross section 2×2mm²) d₀-reference samples were prepared from a similarly treated sample. The d₀ shift induced by variation of chemical composition was measured by neutron and by X-ray diffraction along the strain free direction (sin²ψ*) and used for the evaluation of the neutron stress calculation. The d₀ distribution obtained from the neutron measurement did not appear reliable while the method using X-ray diffraction seems to be an efficient and reliable method to determine d₀ profiles in small samples. The evaluation of neutron measurements was then done using the X-ray diffraction d₀ distribution. High compressive residual stresses were measured in the hardened layer followed by high tensile residual stresses in the core. A comparison of the neutron measurements with X-ray diffraction (XRD) depth profiles obtained after successive layer removal showed that both methods give similar results. However, these investigations opened the question about the direct comparison of the residual stresses obtained by neutron and XRD. Indeed, a correction of the neutron data regarding the residual stresses in thickness direction might be necessary as these are released in the case of X-ray diffraction measurements after layer removal.

Abstract: The effects of laser surface hardening of steel samples on the microstructure and residual stresses were determined for single as well as multiple laser pulses. Samples made of steel grade AISI 4140 were hardened by means of a high-power diode laser (HPDL) system using either single or multiple laser pulses resulting in single as well as repeated austenite-martensite transformations. The hardening was carried out in a specially designed process chamber allowing laser surface treatment in inert atmosphere in order to avoid oxide scale formation. The residual stress distributions in lateral and in depth direction were analysed by means of X-ray diffraction for samples hardened by up to 27 laser pulses. Residual stress analyses were carried out by means of the sin²y - method. The results indicate the extension of the hardened zone in lateral and in depth direction with an increase in the number of applied laser pulses. This evolution is connected with significant changes in the local residual stress distributions.

Abstract: Instrumented indentation testing has been carried out on steel samples subjected to uniaxial loading. It is distinguished between purely elastic as well as elasto-plastic loading up to plastic strains of 3%. The experimental approach allows the combination of local in-situ residual stress analyses by means of X-ray diffraction and the subsequent realisation of instrumented indentation testing for the same material volumes beforehand irradiated by the X-rays. The aim of the investigations was to explore a potential correlation between the imposed macroscopic stresses and the characteristic values of instrumented indentation testing evaluated from the measured force-indentation depth curves according to the standard ISO EN 14577. The studies illustrate that results of depth sensing indentation testing have to be handled with care for prestressed material states. The effect of mechanical stresses on the results of instrumented indentation testing is not stringently limited on the hardness measures alone. Other indentation parameters like e.g. the indentation modulus EIT or the elastic part of the indentation work η IT are likewise affected by the prestresses, whereas the impact is in the order of magnitude that it has to be taken into account during interpretation of indentation readings.

Abstract: X-ray computer tomography for non-destructively measuring residual stress with depth resolution was suggested to aim at improving of traditional X-ray stress analysis in this paper. Based on higher penetrating capacity of X-ray in low atomic order materials it could non-destructively measure three-dimensional residual stresses and calculate the stress free lattice spacing, d0, by current X-ray stress analyzer with taper slits. The evaluation of reliable results were controlled by three criteria, linear correlation coefficient, R, Poisson’ ratio, ν, and the stress free lattice spacing, d0. Finally, the residual stresses in the axial direction around the weld of arc Beryllium weldment could be calculated by this method.