X-ray Diffraction Residual Stress Measurements Research Articles

Surface Integrity in Dry Milling of 304L Steel: A Parametric Study

Austenitic stainless steels represent a significant portion of the metallic components employed in the nuclear industry. In this paper, a detailed study of machining of Type 304L steel in dry milling was performed with the aim of characterising the response of the components’ surface quality and microstructure to variations of the cutting speed, depth-of-cut, and feed-per-tooth. Surface roughness parameters were optically evaluated and X-ray diffraction (XRD) residual stress measurements were employed to measure the extent of machining abuse on the surface. In addition, deformation in the sub-surface layer was examined via scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The experimental measurements of surface roughness and surface residual stresses were used to test a statistical model developed to optimise the selection of the process parameters. Preliminary results showed the effects of machining parameters to residual stresses and near-surface deformation levels in finished components. The ultimate aim of this work is to illustrate the availability of cost-effective materials and manufacturing techniques to the nuclear industry, alongside meeting the high standards of the required properties.

Effect of Peak Positioning Method on Accuracy of X-Ray Diffraction Residual Stress Measurement

In this paper, five peak positioning methods and their effects on the accuracy of X-ray diffraction (XRD) residual stress measurement are considered. Also the effects of various parameters such as absorption coefficient, Lorentzpolarization factor, background correction and Kα2 stripping are evaluated on the precision of different methods. For this aim, the residual stress of a multilayer Al/Cu cold rolled plate is measured by the XRD method. These five peak positioning methods are: maximum intensity method (Imax method), middle position of the width at half maximum intensity method (MPHM method), Gaussian peak profile function method, parabola method, and center of gravity (C.o.G) method. It is shown that not only the results of all methods are not same, but also all of them have different behaviors and responses in respect to the mentioned parameters. Among the mentioned parameters, Kα2 striping and background correction are the most effective parameters in results of all peak positioning methods. It is also shown that the C.o.G. method has the lowest standard deviation, leading to the high linearly d-spacing versus sin2ψ diagram for the residual stress measurements of the samples. Moreover, it is concluded that higher R2 value does not necessarily indicate a more accurate method.

Optimization of Shot-Peening Conditions and Wave Profiles to Improve Durability of Wave Cushion Spring

This study presents a determination procedure of optimal shot-peening process conditions, wave profiles and thickness in order to precisely control and improve durability and fatigue life of wave cushion springs assembled into automobile automatic transmission clutch. For this shot-peening process, residual stress analysis was applied under various conditions. Experimental works were conducted to evaluate proposed approach by using X-ray diffraction residual stress measurement tester. It could be expected that this study provided guideline for wave spring optimal design and improving fatigue life.

On Residual Stresses in Resistance Spot-Welded Aluminum Alloy 6061-T6: Experimental and Numerical Analysis

In this study, an electro-thermal-structural-coupled finite element (FE) model and x-ray diffraction residual stress measurements have been utilized to analyze distribution of residual stresses in ...

Fatigue behavior of X70 microalloyed steel after severe shot peening

The so called “severe plastic deformation” (SPD) processes are object of increasing interest due to their ability to obtain a nanostructured surface layer of material with supposed superior properties. Among these processes, severe shot peening (SSP) is very attractive from an industrial point of view, due to its versatility and wide applicability.In this study the X70 microalloyed steel is considered and treated by severe shot peening.Fatigue tests were performed to assess how SSP treatment affects the fatigue behavior of this steel.Roughness and X-ray diffraction residual stress measurements as well as microscopy observations have been carried out on the treated specimens. Rotating bending fatigue tests at room temperature on smooth and notched specimens were performed to evaluate the effect of the treatment on fatigue strength. Fracture surfaces have been then observed by scanning electron microscopy. The results were compared with the ones of a series of not peened specimens and another series of specimens shot peened with conventional parameters and interpreted by considering the characteristics of the nanostructured layer, the induced residual stresses and the surface work hardening. The comparison shows a very significant fatigue strength improvement for severely shot peened specimens, especially for the notched specimens.

Residual Stress Assessment in Inconel 718 Machining Through Wavelet Sensor Signal Analysis and Sensor Fusion Pattern Recognition

On-line residual stress assessment in turning of Inconel 718 was carried out through multiple sensor monitoring based on cutting force, acoustic emission and vibration signals acquisition and analysis. The detected sensor signals were processed by the wavelet packet transform technique to extract statistical features from the packet coefficients for the construction of wavelet feature vectors. The latter were used for sensor fusion pattern recognition through neural network data processing grounded on X-ray diffraction residual stress measurements on the turned part surface. The scope of the sensory data fusion approach was to achieve a robust scheme for multi-sensor monitoring decision making on machined surface integrity in terms of residual stress level acceptability.

Fatigue behavior of notched steel specimens with nanocrystallized surface obtained by severe shot peening

Among severe plastic deformation methods that result in surface nanocrystallization, shot peening has proved to be a promising technique. Application of severe air blast shot peening results in surface nanocrystallization, affects a thick layer of material with high compressive residual stresses but at the same time produces rather high surface roughness. In this study notched specimens with a stress concentration factor common in many structural components have been subjected to severe shot peening process. The mentioned treatment uses peening parameters essentially different from conventional ones. Roughness and X-ray diffraction residual stress measurements as well as microscopy observations have been carried out on the treated specimens. Room temperature rotating bending fatigue tests are performed to evaluate the effect of the treatment on specimens’ fatigue strength. Fracture surfaces have been then observed by scanning electron microscopy. The results indicate a very significant fatigue strength improvement for severely shot peened specimens in spite of their very high surface roughness.

Mapping Multiple Components of the Residual Stress Tensor in a Large P91 Steel Pipe Girth Weld Using a Single Contour Cut

The contour method is applied in an innovative manner to measure the distribution of hoop residual stress in a large martensitic-ferritic steel pipe containing a multi-pass girth weld. First, a novel one-step wire electro-discharge machining cut is conducted to divide the pipe lengthways into two halves. The deformation of the cut halves is then measured and analysed in a way that simultaneously gives maps of hoop stress across the wall thickness on both sides of the pipe and automatically accounts for through-thickness hoop bending effects and how they may vary along the pipe. Finally the contour method results are combined with X-ray diffraction residual stress measurements using the principle of superposition to determine the distribution of the axial and radial residual stresses in the pipe. It is thereby demonstrated how the distribution of three direct components of the residual stress tensor in a welded pipe can be readily determined using a “hybrid” contour measurement approach.

A Simulation of the Quenching Process for Predicting Temperature, Microstructure and Residual Stresses

A finite element model capable of predicting the temperature history, evolution of microstructure and residual stresses in the quenching process is presented. Proposed model was integrated into Msc. Marc® software via user subroutines. Verification of the model was performed by X-ray diffraction residual stress measurements on a series of steel cylinders quenched.

The Influence of Residual Stresses on the Fatigue Strength of Cold-Formed Structural Tubes

Abstract Rectangular hollow sections (RHS) are widely used in load-carrying structures due to their good load transfer behavior and aesthetic form. During fabrication of a cold-formed rectangular hollow section (CFRHS), the concave inside corner surfaces experience significant compressive plastic strains. The resulting tensile residual stresses in the corner region significantly reduce the fatigue strength in some design applications. Sections cut from CFRHSs with two different wall thicknesses were studied using distortion fatigue loading and using X-ray diffraction residual stress measurements. Residual stresses and fatigue strengths were virtually identical for the two thicknesses even though the corner radius to thickness ratio was different. Residual stresses were found to significantly influence those corners subjected to compression-compression loading. Fatigue strength of these corners was improved by a stress relief heat treatment, but the treatment had no significant effect on corners subjected to tension-tension loading.

A Method for Direct Measurement of Multiaxial Stress-Strain Curves in Sheet Metal

A method has been developed that allows measurement of stress-strain curves for sheet metal being deformed in multiaxial tension. The strain state is imposed using a modification of the Marciniak in-plane biaxial stretching test. Resulting stresses are measured using a modified X-ray diffraction (XRD) residual stress measurement system. This system is flexible enough to allow spatial mapping of in-plane stress and measurement of stresses at specific locations of interest on the sample, such as developing localizations. Results are presented correlating measurements on a thin strip of AA5182 with data from standard uniaxial tension test. Also presented are experimentally determined curves for this material in balanced biaxial tension in both the rolling and transverse directions.

RESIDUAL STRESS ESTIMATION OF BONE TISSUE USING X-RAY IMAGING TECHNIQUE

INTRODUCTION X-ray diffraction residual stress measurement method has shown that bone possesses some inherent stress as ‘residual stress’ [1]. In more advanced application of X-ray diffraction, two-dimensional detectors called imaging plate are being used to obtain the diffracted Debye rings directly. These Debye rings are distorted by stress and the degree of distortion gives the basis for strain measurement.

Characterisation of Residual Stresses in Machined Surfaces of a High Strength Nickel-Base Superalloy

The near surface residual stresses introduced by turning on a nickel-base superalloy RR1000 are studied. X-ray diffraction residual stress measurements have been made in both radial and circumferential directions as a function of depth. These show systematic changes in stress magnitude and depth profile. The extent of the plastic deformation has been determined by the variation of the diffraction peak width in the XRD measurement. Both the residual stresses and the plastic work have been found to vary sharply over the first 100 mu m. The variation in unstressed lattice spacing with depth points to a heat affected zone of 40 mu m in thickness.

Laser‐Assisted Machining of Damage‐Free Silicon Nitride Parts with Complex Geometric Features via In‐Process Control of Laser Power

A methodology to achieve optimal operating conditions for laser‐assisted machining (LAM) is developed for silicon nitride parts with complex geometric features by applying a three‐dimensional, transient thermal model and in‐process laser power control. Complex silicon nitride parts are successfully produced by the LAM operation, where the maximum and material removal temperatures are carefully designed and controlled to achieve good machining results and avoid thermal damage on the final part. On‐line temperature and laser power measurements are conducted and compared with prescribed values to show the effectiveness of the power control scheme. Scanning electron microscopy examination reveals virtually no subsurface microcrack or thermal damage on the silicon nitride parts. The X‐ray diffraction (XRD) study shows the preservation of the silicon nitride microstructure and no phase transformation of β‐Si3N4 during the LAM experiments. XRD residual stress measurements show moderate compressive residual stresses on the silicon nitride workpieces produced by the LAM operation.

Application of Low Plasticity Burnishing (LPB) to Improve the Fatigue Performance of Ti-6Al-4V Femoral Hip Stems

Abstract Low plasticity burnishing (LPB) is a surface enhancement method that produces a deep layer of compressive residual stress with minimal cold working and an improved surface finish. Extensive fatigue testing, performed on numerous metal alloys in simulated environmental conditions, demonstrates that LPB significantly improves fatigue strength of highly stressed components. LPB is a flexible process, capable of being implemented on a wide variety of CNC machine tools. A product-specific LPB process was developed and applied to the modular neck taper junction of a Ti-6Al-4V total hip prosthesis (THP). LPB produced a compressive residual stress field with an improved surface finish, which enhanced component fatigue strength and resistance to fretting damage. X-ray diffraction (XRD) residual stress measurements, made before and after LPB application, are shown. High cycle fatigue (HCF) results obtained on LPB-processed hip stems are shown along with baseline data for unprocessed hip stems. HCF tests demonstrate complete elimination of fretting fatigue failures in the LPB processed area of the taper junction and a substantial increase in overall THP fatigue strength.

Residual stress magnitudes and related properties in quenched aluminium alloys

The surface and through thickness residual stress magnitudes present in heat treated high strength aluminium alloy components are frequently reported to exceed the uniaxial yield stress of small specimens of the same alloy measured immediately after quenching. In thick section plate and forgings, it is proposed that these high residual stress magnitudes are a consequence of hardening precipitation that occurs during quenching which allows a greater elastic stress to be supported. To investigate this theory, a Jominy end quench technique is used to determine the hardness of aluminium alloys 7010, 7175 and 5083 as a function of distance from the quenched end. Cooling curves have been measured for Jominy end quench specimens using deeply buried thermocouples and are compared with finite element model predictions. Tensile properties are also determined for small specimens quenched into cold and boiling water. Vickers hardness and X-ray diffraction residual stress measurements are undertaken on specimens of varying size acting as a comparison with the Jominy results. These results in combination with optical and electron microscopy data do suggest that low temperature rather than high temperature precipitation during the quench leads to increased as quenched mechanical strengths, with the consequence that less quench sensitive alloys will support higher residual stress magnitudes as section thicknesses increase.

Effects of fretting fatigue on the residual stress of shot peened Ti–6Al–4V samples

X-ray diffraction residual stress measurement has been utilized as nondestructive tool for the characterization of fretting fatigue damage in shot peened samples of Ti–6Al–4V. Prior to fretting fatigue damage, compressive residual stresses were found to be uniform over the entire face of the sample and independent of the measurement direction. After fretting fatigue, inside and in the vicinity of the fretting damage zone large relaxation of compressive residual stress was observed. An anisotropic residual stress distribution has been observed in the fretting fatigue damaged region. Residual stress measurements in interrupted fretting fatigue experiments showed that the relaxation of residual stress increases as the number of fretting fatigue cycles increase. The results are discussed in the light of their importance in establishing X-ray diffraction residual stress measurement technique as a nondestructive tool to characterize fretting fatigue damage.

Effect of precipitation during quenching on the mechanical properties of the aluminium alloy 7010 in the W-temper

Residual stress magnitudes in quenched high-strength aluminium alloys determined by several researchers using a variety of techniques indicate values that far exceed the as measured yield strength of the material in the quenched condition. Some research has indicated that the high residual stress magnitudes in large forgings may partly occur as a result of precipitation during the quench. To investigate this theory, a novel Jominy end quench technique is used to determine the hardness of aluminium alloy 7010 as a function of cooling rate. Cooling curves have been measured for Jominy end quench type samples using deeply buried thermocouples and are compared with finite element model predictions. Tensile properties are also determined for samples quenched into boiling water and compared with samples quenched into cold water.Vickers hardness and X-ray diffraction residual stress measurements are undertaken on samples of varying size acting as a comparison with the Jominy results to indicate how both homogenous and heterogeneous precipitation lead to increased as quenched mechanical strengths.

X-Ray Diffraction Residual Stress Measurement Reliability: Stressed Reference Samples

To validate the experimental setting adjustments and to detect geometrical errors as sample misalignment (translation and rotation defects) and the missetting of the incident beam, some external stressed standard samples have been realized. A fine analysis of the raw robin-test results by a statistical analysis, taking into account the uncertainty of each measurement is then performed to understand the critical discrepancy of the results between the laboratories. It is shown that the most relevant uncertainty origin is induced by the inter-laboratory errors and an improvement of the stress value accuracy can be made by the standardization of the diffraction treatment peak procedure. This work is sponsored by Peugeot S.A., RENAULT S.A. and SNECMA.

Effect of prestraining on Barkhausen noise vs. stress relation

Mild steel specimens were uniaxially strained in tension at strain levels varying from 0.5 to 10% followed by X-ray diffraction residual stress and Barkhausen noise (BN) measurements. After this tension and compression loading was applied to the specimens. BN measurements were carried out during the whole reloading sequence. These measurements showed that prestrain increased the tensile stress value at which the BN saturated. The linear range of the stress vs. BN curve shifted towards the tensile stress range as a function of prestrain. In the linear range the stress sensitivity remained unchanged despite the prestrain. The obtained stress vs. BN relation was used in the residual stress measurements of a welded tube segment. The residual stress values measured by the BN were compared to X-ray diffraction residual stress values. When the BN values were within the linear range of the stress vs. BN curve, the BN residual stress values agreed quite well with the X-ray diffraction residual stress values.