X-ray Diffraction Residual Stress Measurements Research Articles

Influence of residual stresses on the evolution of micro-structure during the partial reduction of NiAl 2O 4

Metal-ceramic microstructures were formed in situ by the partial reduction (i.e. the reduction of only one of the metallic elements) of the spinel compound NiAl 2O 4. Depending on reduction conditions, these microstructures consist of Ni particles embedded in an α-Al 2O 3 or a multiphase matrix called ‘defect spinel’. The volume shrinkage that accompanies the reaction generates residual stresses which profoundly affect the microstructure evolution. Conversely, formation of metastable, intermediate phases, generation of porosity and cracking are all observed and may act to relax the residual stresses. Electron microscopy observations as well as both neutron and X-ray diffraction residual stress measurements are used to study the influence of residual stresses on the microstructure evolution during the reduction process.

Possible Standard Specimens for Neutron Diffraction Residual Stress Measurements

ABSTRACTIncreasingly, sub-surface residual stress measurements by means of neutron diffraction are being conducted at various laboratories around the world. Unlike X-ray diffraction residual stress measurement setups, neutron instruments in use worldwide vary widely in design, neutron flux, and level of dedication towards residual stress measurements. Although confidence in the neutron technique has increased within the materials science and engineering communities, no demonstration of standardization or consistency between laboratories has been made. One of the steps in the direction of such standardization is the development of standard specimens, that have well characterized residual stress states and which could be examined worldwide.In this paper we will examine two options for a neutron stress standard specimen. 1) A steel ring-plug specimen with very well defined diametrical interference. 2) A spot weld in a High Strength Low Alloy steel disk. The results of neutron residual stress measurements on these specimens will be discussed and conclusions as to their usefulness as neutron stress standards will be presented.

Residual stress measurement and microstructural characterization of Gr/Al composites

The residual stresses in a unidirectionally reinforced P100 Gr/6061 Al metal matrix composite with different thermal histories have been measured using X-ray diffraction (XRD) methods. The study reveals that the maximum residual stresses of the Gr/A1 composite measured by the XRD method are strongly dependent on the yield strength of the aluminium matrix which depends on the thermal history of the sample. The yield strength deduced from the XRD residual stress measurement was used as input data in a finite element analysis program described elsewhere for predicting the residual stresses in the composite. Agreement was found between the measured residual stresses and the finite element analysis over a range of thermal histories. To better understand the thermal-mechanical behavior of the composites, the microstructural features of the composite were characterized by means of electron microscopy and differential scanning calorimetry (DSC).

Experimental Methods for Determination of Precision and Estimation of Accuracy in XRD Residual Stress Measurement

AbstractIt is important to establish precision and accuracy of an X-ray diffraction (XRD) residual stress measurement procedure in order to compare capabilities of instrumentation and techniques, as well as to provide confidence limits for experimental data. There is no broadly acceptable method for establishment of precision and accuracy. This paper describes a proposed approach and one which is used at The Pennsylvania State University.One impediment to the measurement of precision and accuracy is that no standard specimen with a known residual stress level is available. Proposed standard specimens have been abandoned for various reasons, including the concern for stability of the original stress condition and the existence of stress gradients, i.e., stress inhomogeneity, in the specimens. However, there is one type of specimen which has been accepted by ASTM as an alignment and zero residual stress confirmation standard. That type of specimen is a powdered sample of metal or ceramic which provides XRD peaks in the vicinity of the Bragg angle in which residual stress measurements are to be performed.Some researchers tend to report detector counting statistics as the uncertainty of stress measurement but such statistical scatter accounts for only one part of uncertainty in precision and accuracy. The total uncertainty is best determined directly through repeated residual stress measurements performed by removal and readdressing the test specimen or through a repetition of measurements under predictably changing conditions. This paper describes results from the use of powder specimens to establish the repeatability of measurements with a portable instrument after removal and readdressing of the specimens. Also, results showing the uncertainty of the measured stress change in specimens subjected to known loads are discussed.

Qualification of Induction Heating Stress Improvement for Mitigation of Stress Corrosion Cracking

This paper describes the efforts toward qualification of induction heating stress improvement (IHSI) for mitigation of intergranular stress corrosion cracking (IGSCC) in Boiling Water Reactor (BWR) piping. The IHSI process, which is applied to piping after it is fully erected, produces compressive residual stresses on the pipe inside surface in the vicinity of the weld heat affected zone (HAZ). The creation of these compressive stresses has been confirmed by surface and through-wall strain gage and X-ray diffraction residual stress measurements on 4, 10, and 16-in. dia Schedule 80 welded and IHSI treated pipes. Confirmation of increased resistance to IGSCC due to the IHSI process has been accomplished by full-sized 4-in-dia pipe tests in General Electric’s Pipe Test Laboratory. The pipe test utilized an environment of oxygenated high-purity water at 288°C (550°F). Axial loads were applied which exceeded the material 288°C yield strength.

A Method of Determining the Elastic Properties of Alloys in Selected Crystallographic Directions for X-ray Diffraction Residual Stress Measurement

A technique and apparatus are described for obtaining the elastic constant E/(1 + v) in selected crystaliographic directions for the purpose of calibrating x-ray diffraction residual stress measurement methods. The preparation of a simple rectangular beam specimen with two active electrical resistance strain gages applied to the test surface is described. Samples are clamped in a diffractometer fixture designed to minimize displacement errors, and loaded in four-point bending to several stress levels below the proportional limit. A method is described for calculating E/(l + v) and an estimate of the experimental error.Values of E/(l + v) obtained for several alloy-(hkl) combinations are presented. The results indicate that several alloys of current commercial interest exhibit significant elastic anisotropy.

A Comparison of X-Ray Diffraction Residual Stress Measurement Methods on Machined Surfaces

The two-angle and Sin2ψ methods of x-ray diffraction, residual stress measurement have been shown to yield anomalous results When applied to samples which have been plastically deformed uniaxially in tension or by rolling. These anomalous stresses, which are not true mechanical macrostresses, have been shown to arise from a nonlinear dependence,of d, the interplanar spacing employed for stress measurement, upon Sin2 ψ. A new method of x-ray diffraction stress measurement has been developed by Marion and Cohen which aLlows the separation of the Linear and nonlinear components of the dependence of d upon Sin2 ψ.The two-angle and the Marion-Cohen x-ray diffraction methods are applied to the measurement of residual stresses in the machined and shot peened surfaces of steel and aluminum samples. The results indicate that machining deformation results in a nearly linear dependence of d upon Sin2ψ , and onLy a slight deformation texture. The two x-ray methods yield stress values in ground, turned, and shot peened steel and aluminum samples which agree within the estimated experimental error. Previous results are sighted showing agreement between the two-angle method and a mechanical stress measurement technique. The results indicate that, at least in steels, the multiaxial plastic deformation produced by machining does not significantly effect the accuracy of the two-angle x-ray diffraction stress mea surement method.