Abstract: Laboratory X-ray diffraction is commonly used for surface residual stresses determination. Nevertheless, the in-depth residual stress gradient also needs to be known. Chemical or electro-polishing method is generally used for material removal. However, material removal may seek a new equilibrium and stress field may change in such a way that experimental residual stress values must be corrected. Different methods exist to account for the residual stress relaxation associated with the material removal operation and will be discussed in this paper.
Abstract: All aspects of instrument control, data acquisition, simulation and analysis are expected to merge in the future. For instance real time data analysis will feed back influencing the instrument control in order to optimize the measurement time and simulations themselves will control the instrument. This presentation will discuss how the all-important pre-planning of a measurement can be optimized and used to define the whole measurement, efficiently and effectively using the neutron beamtime.
Abstract: In the past decade energy-dispersive (ED) synchrotron diffraction has evolved into a powerful tool for materials analysis. Recording complete diffraction patterns in rather few different measuring directions allows for depth-resolved analysis not only of the near-surface residual stress state, but also of composition and even texture gradients. However, since the number of synchrotron beamlines dedicated to ED-diffraction is restricted to very few instruments, alternatives have to be found which allow for ED residual stress analysis even under low flux laboratory conditions. In this project we start to establish the scientific basis for a measuring and evaluation method to make the transfer of the ED method to the laboratory dimensions possible, which is adapted to the conditions of much lower photon flux and larger beam divergences of laboratory X-ray sources. In this paper, we present the concept of an ED-diffractometer which is equipped with two detectors to enable simultaneous data acquisition for two orientations of the diffraction vector with respect to the sample reference system. The first constructive and experimental steps are presented and furthermore the possibilities and limitations of the new laboratory method and the advantages of the ED diffraction method to realize short measurement times in order to realize a high resolution of information depth are discussed.
Abstract: A simulation of realistic samples within a neutron scattering or imaging experiment has been created in order to support the accuracy, feasibility and analysis of residual stress measurements as well as the development of novel experimental methods and instrument components. Covering the influences of individual neutron instrument parameters, the simulation also assists in optimizing the experimental configuration towards precise measurements and effective usage of neutron beamtime.
Abstract: MYTHEN is a single-photon-counting strip detector. Its main features are high spatial resolution, zero noise, fluorescence suppression, fast readout, high dynamic range, radiation-hard and maintenance-free design. Perspectives of such a detector in residual stress measurements involve: (i) Measurements of absorbing/thick materials (ii) Well resolved peaks (iii) excellent signal-to-noise ratio (iv) Analysis of alloys (v) Fast data collection (vi) Accurate low content retained austenite measurements (vii) in situ measurements and mapping (viii) infinite life cycle. Technical details and application in synchrotron and laboratory diffractometers will be presented.
Abstract: Two-dimensional X-ray diffraction pattern can be described by the diffraction intensity distribution in both 2θ and γ directions. The 2D pattern can be reduced to two kinds of profiles: 2θ-profile and γ-profile. The 2θ-profile can be evaluated for phase identification, crystal structure refinement and many applications with many existing algorithms and software. The γ-profile contains information on texture, stress, and crystal grain size. This article introduces the concept and fundamental algorithms for stress, texture and crystal size analysis by γ-profile analysis.
Abstract: It is shown that the knowledge of standard deviations (Δσij ) of the components of a stress tensor (σij) is not sufficient to calculate also standard deviations of quantities derived from the stress tensor, as principal stresses (σI, σII, σIII), von Mises stress, Tresca stress, and the components of the deviatoric stress tensor σ'ij. For such a calculation one needs all information about the measurement and the method for the calculation of σij. This information is: the accuracy of each measured lattice plane distance and the x-ray elastic factors Fij(φ,ψ,hkl) of each measured point. Equations are given for the calculation of the standard deviations of all the mentioned quantities. For special cases of measurement strategy the wanted calculations become easier. This is also given.
Abstract: The GFAC (French Association for residual stress analysis) has been working for several years on external reference samples in relation with the EN 15305-2009 standard. The purpose of this campaign is to provide an external reference sample to each laboratory involved in the round-robin to allow a good calibration, a good quality control of their X-ray diffraction system and an easiest way to compare results between laboratories. All the procedures to qualify external reference materials will be described in the paper.
Abstract: In recent years, the demand for high spatial resolution in X-ray residual stress analysis has drastically increased. The locations of interest are frequently small foot radii of teeth of gears. Also the inner surface of holes or hollow cylinders in general with small diameter must be investigated after opening the cylindrical cavities. In resolving such measuring problems, significant progress has been made in reproducibly manufacturing and applying glass capillary X-ray optics. With focusing elliptical polycapillaries and conventional laboratory X-ray sources, spot sizes of few 10 μm can be realized at sufficiently intensities for residual stress analyses. However, glass capillary optics require refined alignment strategies which are completely different from those for conventional beam shaping optics. Moreover, the small spot sizes cannot be aligned and positioned on the sample surface by eye. Microscopy fixtures are required. Finally, measurements in small radii result in high precision requirements for the diffractometers as well as for the sample positioning in axes and directions which are significantly less relevant when measuring on plane surfaces. The specific requirements resulting from residual stress analyses with high spatial resolution using glass capillaries and small spot sizes at curved surfaces are described and discussed.
Abstract: Residual stress measurement techniques can be categorized as either relaxation or diffraction methods. Practitioners often advocate a particular category and sometimes a specific technique (hole drilling, contour, XRD, neutron, etc) based on their experience or capability rather than using the best technique for the particular application. This paper considers some of the implications from applying this “drunkard’s search” or “streetlight” approach by examining examples where the critical stress could be hidden from both relaxation and diffraction measurements. A better approach to planning residual stress measurements would begin with a detailed consideration of why the stresses should be measured and how the results will be used. Only then can the most appropriate measurement plan be developed. Since a single measurement technique cannot reveal the full state of stress, especially in challenging parts, the use of multiple measurement types often provides the most useful information to customers.