Residual Stress Data Research Articles

Machining deformation prediction of large fan blades based on loading uneven residual stress

Fan blade is an important component of turbofan engine. It is a kind of curved thin-walled structural parts, which tends to have a certain amount of deformation after machining process. In order to predict the deformation of fan blade after machining process, the commercial simulation software Abaqus?? is used to analyze the deformation of fan blade with titanium alloy through considering the effect of residual stress. The residual stresses on the surface and subsurface of the blade after milling and shot peening processes were measured and analyzed by experimental testing. Based on the measured residual stress data, the three-dimensional model of fan blade is segmented by the operation of extracting geometric features. Then, the residual stress values are discretized according to separation layers, and the discrete results are applied to the thin-walled blade by dividing layers and dividing regions. Finally, a finite element analysis (FEA) model for the deformation prediction of blade through considering the effect of residual stress is established. The simulation deformation is compared with the measured deformation, and the feasibility of the FEA model is verified. The study provides an effective analysis method for the deformation prediction of fan blade after milling and shot peening processes.

Measurement and prediction of residual stresses in welded girders

Residual stresses can have a significant impact on the stability of structural members. In the case of I-section beam elements, such stresses can impact lateral–torsional buckling (LTB) capacity, particularly in the inelastic range. I-sections are typically fabricated by either rolling as a single shape or welding three plates together; residual stress distributions can differ considerably between the two section types. It is therefore possible for a built-up welded girder to have a different LTB capacity than that of a rolled one of identical cross-section. Concerns have been raised that such a difference may render North American steel design standards unconservative for welded girders. Because of the lack of recent physical LTB tests on welded girders, finite element modelling was used as a tool in making this assessment, and the assumed residual stress distributions were based on data from 1970 to 1980 that may not account for advancements in welding technologies and processes since the publication of these data. The paucity of recent residual stress data, however, prevents a direct assessment of these assumed distributions. In this study, residual stress measurements were carried out on a series of four welded steel test girders using the sectioning method. A comparison of the measured distributions with four existing models finds these models to be inaccurate in important ways; an updated model is therefore required for use in numerical simulations of LTB behaviour of welded girders used in industry today.

Achievements in Micromagnetic Techniques of Steel Plastic Stage Evaluation

Abstract The investigation of plastic deformation and residual stress by non-destructive methods is a subject of large relevance for the industry. In this article, the difference between plastic and elastic deformation is discussed, as well as their effects on magnetic measurements, as hysteresis curve and Magnetic Barkhausen Noise. The residual stress data can be obtained with magnetic measurements and also by the hole drilling method and x-ray diffraction measurements. The residual stress level obtained by these three different methods is different, because these three techniques evaluate the sample in different depths. Effects of crystallographic texture on residual stress are also discussed. The magnetoelastic term should be included in micromagnetic methods for residual stress evaluation. It is discussed how the micromagnetic energy Hamiltonian should be expressed in order to evaluate elastic deformation. Plastic deformation can be accounted in micromagnetic models as a term that increases the coercive field in soft magnetic materials as the steels are.

Effects of residual stresses and shape deformities on failure of rollover protective structures

Rollover Protective Structures (ROPS) are manufactured typically from components that require forming such as pipe bending process. The manufacturing process creates residual stresses and shape deformities in the pipe structure. These parameters in turn may affect the strength of the pipe to bear the load during rollover. Conventional modeling does not capture the effects of residual stresses and shape irregularities in the pipe resulting from forming. A detailed analysis is therefore required to determine the significance of the manufacturing process on the strength of ROPS. Finite Element Method (FEM) is employed to simulate the bending process. Residual stress and deformation data from bending process analysis are used to further investigate failure of the structure under different loading conditions. The maximum load the structure can withstand, before it loses its stiffness, under a specific displacement is referred to here as failure load. Results revealed that there is a significant difference in the failure loads due to presence of bending process induced residual stresses and due to shape deformities. The model with the residual stresses and shape deformities has higher failure loads as compared to the conventional model. It also has been noted that residual stress is the main contributing factor to this increase in failure load. Parametric study was performed to investigate the effect of pipe wall thickness and radius of the formed bend on the failure loads.

Integrated finite element & optimization model for laser shock pressure impulse shape determination

Laser shock peening (LSP) is a method of work hardening used to improve fatigue life. Finite element (FE) modeling of LSP lacks confidence, primarily due to the unknown shape of the acting pressure impulse in both time and space. This work developed and tested an integrated FEM/optimization model to determine a ‘best fit’ pressure impulse shape based on easy to measure surface displacement and residual stress data from a single LSP burst. Isight optimization software was used in conjunction with Abaqus FEM, MATLAB, and Excel to utilize the Hooke-Jeeves optimization algorithm for data-matching. Favorable algorithm parameters were determined for a discretized optimization space then applied to the continuous optimization space to match FEM generated target data. Residual stress results matched to within 4.5% maximum difference, and surface displacement results matched to within 2.5% maximum difference. This modeling tool shows great potential for use in matching test data from LSP treated specimens, resulting in improved FEM confidence for engineering design application.

Novel applications of centreless X-ray diffractometers for non-destructive pole figure measurements

Centreless X ray diffractometers are specially designed for non-destructive residual stress measurements. The similarity between the X-ray diffraction-based stress and texture measurement methods led us to introduce a new method on non-destructive (sample cutting-free) stress measurement devices to studies on crystallographic texture. The method that determines texture characteristics from residual stress data has recently been introduced. Afterwards, a method with which pole figures (fully equivalent to conventionally measured pole figures) at high Bragg-angles can be constructed with centreless diffractometers were developed. The paper gives an illustration of the new methods’ utilization on the field of archaeometry. In that area, only non-destructive testing modes are permitted. In the case of archaeological finds, knowing the crystallographic texture assists to reconstruct the ancient process technology (hammering, rolling, annealing) that was applied during the manufacturing. The new methods are suitable to be used on valuable and unique objects both in the automotive industry, archaeometry and in the space applications.

Modeling the Evolution of Residual Stresses in Thermally Sprayed YSZ Coating on Stainless Steel Substrate

This study is based on Eulerian method to model residual stresses for yttrium-stabilized zirconia coating applied to stainless steel substrate. A commercially available finite element software ABAQUS/Explicit is used to conduct this study. Single and multiple-particle impact analyses were carried out, and the residual stress data have been reported. The analysis is performed for two different values of thermal contact resistance and the through-thickness residual stress profiles obtained within the coating for single particle are tensile, while the substrate has a mixture of tensile and compressive residual stresses. For multiple impact model, the residual stress data have been presented for substrate with and without cooling. The residual stresses within the coating without substrate cooling are mostly tensile while the substrate is compressive. The residual stresses within the coating with substrate cooling are mostly tensile with compressive stresses on the top of the coating, while the substrate consists of compressive stresses. The obtained residual stresses are compared with experimental and analytical data.

Micro-slotting technique for reliable measurement of sub-surface residual stress in Ti-6Al-4V

Micro-slotting, a relaxation residual stress measurement technique, has recently been shown to be an effective method for measuring local residual stresses in a variety of materials. The micro-slotting method relies on a scanning electron microscope–focused ion beam system for milling and imaging, digital image correlation software to track displacements due to residual stress relaxation after milling, and finite element analysis for displacement–stress correlation and calculation of the original stress state in the imaged region. The high spatial resolution of the micro-slotting method makes it a promising technique for obtaining near-surface residual stress data in Ti-6Al-4V components for input into fatigue life models and crack growth simulations. However, use of the micro-slotting method on this alloy has yet to be evaluated against more established measurement techniques. In this study, spatially resolved sub-surface residual stress measurements were obtained on shot peened and low-stress surface-machined Ti-6Al-4V planar coupons using the micro-slotting method and were compared to measurements obtained using the conventional X-ray diffraction depth profiling technique. The sub-surface measurements were in good agreement for the shot peened sample. Observed differences in the measured near-surface residual stresses on the surface-machined sample were attributed to the larger measurement volume of the X-ray diffraction method, suggesting that the micron-sized measurement volume of the micro-slotting method may be more suitable for capturing shallow stress profiles and steep stress gradients. Prior to performing the micro-slotting measurements, finite element modeled displacements were used to verify the measurement procedure and to address uncertainties in the milled slot geometries. The results of this study demonstrated the validity of the micro-slotting procedure and established the technique as a reliable method for measuring sub-surface residual stresses in Ti-6Al-4V.

Measurement of the residual stresses in a PWR Control Rod Drive Mechanism nozzle

Residual stress in the welds that attach Control Rod Drive Mechanism nozzles into the upper head of a PWR reactor vessel can influence the vessel’s structural integrity and initiate Primary Water Stress Corrosion Cracking. PWSCC at Alloy 600 CRDM nozzles has caused primary coolant leakage in operating PWRs. We have used Deep Hole Drilling to characterise residual stresses in a PWR vessel head. Measurements of the internal cladding and nozzle attachment weld showed that although modest tensile stresses occur in the cladding, the attachment weld contains tensile residual stresses of yield magnitude. Despite the large dispersion of residual stress data for nozzle attachments of this type, all available data suggest that assuming a residual stress profile bounded by the weld material’s yield stress would be conservative for assessment purposes.

Evaluation of residual stress development in FRP-metal hybrids using fiber Bragg grating sensors

This paper presents experimental measurement methods for the determination and evaluation of process related thermal residual stresses in fiber metal laminates. A cure monitoring system with fiber Bragg grating (FBG) sensors is used to measure the in-plane strains during processing of carbon fiber reinforced plastic (CFRP)-steel laminates. The simultaneous measurement captures the thermal expansion during the heating stages, the cure shrinkage, and the cooling thermal shrinkage. The results enable the characterization of the co-cure bonding process and the stress transfer between the metal and FRP-layers during the creation process. The residual strains, which are used for calculation of the residual stresses, are recorded at room temperature after manufacturing. In addition, an advanced method using FBG-sensors and the deflection of asymmetric hybrid specimens is developed to validate the gained residual stress data. Asymmetrical specimens are created by removing selected layers after cure. Quantitative evaluation is achieved by determination of their curvature and measuring the strain changes with the embedded FBG-sensors. For validation, the methods were successfully demonstrated on two different curing cycles with different resulting residual stress levels. The simultaneous strain measurement enables the investigation of stress development and delivers more in-depth process knowledge for further optimization of the manufacturing process.

Addendum to “Cyclic plasticity and microstructure of as-built SLM Ti-6Al-4V: The effect of build orientation” [Mater. Sci. Eng. A 701 (2017) 85–100

In the present study, different residual stress and strain data measured from various techniques are analyzed using a Bayesian statistical approach and finally interpolated utilizing modified Shepard method. This research is carried out to compare the capability, simplicity and accuracy of Bayesian approach with different probability density functions. Three different probability density functions: Gaussian, Cauchy and Sivia's distribution are studied and compared here. Finally the modified Shepard method is utilized with new interpolant and weight functions, to interpolate the scattered measured data. The proposed framework is then applied to two sets of measured residual data obtained from various experimental techniques.

Residual Stress Depth Distributions for Atmospheric Plasma Sprayed MnCo<sub>1.9</sub>Fe<sub>0.1</sub>O<sub>4</sub> Spinel Layers on Crofer Steel Substrate

In solid oxide fuel cells (SOFC) for operating temperatures of 800 °C or below, the use of ferritic stainless steel can lead to degradation in cell performance due to chromium migration into the cells at the cathode side [1]. Application of a coating on the ferritic stainless steel interconnect is one option to prevent Cr outward migration through the coating. MnCo1.9Fe0.1O4 (in the following designated as MCF) spinels act as a diffusion barrier and retain high conductivity during operation [2]. Knowledge about the residual stress depth distribution throughout the complete APS coating system is important and can help to optimize the coating process. This implicitly requires reliable residual stress analysis in the coating, the interface region and in the substrate.For residual stress analysis on these specific layered systems diffraction based analysis methods (XRD) using laboratory X-ray sources can only by applied at the very surface. For larger depths sublayer removal is necessary to gain reliable residual stress data. The established method for sublayer removal is electrochemical etching, which fails, since the spinel layer is inert. However, a mechanical layer removal will affect the local residual stress distribution.As an alternative, mechanical residual stress analyses techniques can be applied. Recently, we established an approach to analyse residual stress depth distributions in thick film systems by means of the incremental hole drilling method [5, 6]. In this project, we refined our approach for the application on MCF coatings with a layer thickness between 60 – 125 μm.

Residual stress in ion-exchanged silicate glass: An analytical solution

The ion-exchanged residual stress profile influences both the strength and the wear-resistance of glass hence its description is of great importance. Currently, residual stress profiles of silicate glasses can only be estimated by numerical time-integration based on the known ionic concentration profile and the expected stress relaxation behavior of the glass. In this work, we derived and validated the constant coefficients analytical solution describing the residual stress profile in single-step ion-exchanged glasses. The proposed solution is based on Sane and Cooper's model and assumed that both the generalized Maxwell stress relaxation function applied and that a constant ionic inter-diffusion coefficient could accurately describe the behavior of the system. Furthermore, an analytical approximation for composition-dependent stress relaxation behavior of the glass was proposed. Examples of how the newly developed analytical description of the stress profile could be fitted through regression analysis to available residual stress data were also presented.

Residual stress prediction for turning of Ti-6Al-4V considering the microstructure evolution

An analytical model for residual stress prediction considering the effects of material dynamic recrystallization under process-induced mechanical and thermal stresses is proposed. The effect of microstructure evolution on residual stress generation during the turning process is considered. The Johnson–Mehl–Avrami–Kolmogorov model is used to calculate grain size evolution due to thermal mechanical effects in the machining process. A modified Johnson–Cook flow stress model is developed by introducing a material grain growth–induced softening term. The classic Oxley’s cutting mechanics theories are implemented for machining forces calculation. A hybrid algorithm accounting for thermal, mechanical, and microstructure evolution effects is used to predict the residual stress profile on a machined workpiece surface. The proposed method is implemented for the orthogonal turning of Ti-6Al-4V material. Comparison is conducted between the model prediction and the literature measurement residual stress data. The general trend of the machining-induced residual stress on the machining surface is accurately captured by the proposed model. Also, the parametric study is conducted to investigate the effect of rake angle and depth of cut on the residual stress profile.

Prediction of residual stresses in girth welded pipes using an artificial neural network approach

Management of operating nuclear power plants greatly relies on structural integrity assessments for safety critical pressure vessels and piping components. In the present work, residual stress profiles of girth welded austenitic stainless steel pipes are characterised using an artificial neural network approach. The network has been trained using residual stress data acquired from experimental measurements found in literature. The neural network predictions are validated using experimental measurements undertaken using neutron diffraction and the contour method. The approach can be used to predict through-wall distribution of residual stresses over a wide range of pipe geometries and welding parameters thereby finding potential applications in structural integrity assessment of austenitic stainless steel girth welds.

An experimental investigation emphasizing surface characteristics of electro-discharge-machined Inconel 601

The paper reports an experimental investigation on electro-discharge machining (EDM) of Inconel 601 using copper electrode tool. Based on L27 orthogonal array (OA), experiments have been conducted by varying five controllable process parameters [viz. peak current (I p), pulse-on time (T on), gap voltage (V g), duty factor (\(\tau\)) and flushing pressure (F p)] within the selected experimental domain. The following responses in relation of surface topography of the machined endproduct, i.e., surface crack density (SCD) and white layer thickness (WLT), have been investigated for each of the experimental runs. Utility theory in conjugation with Taguchi’s optimization philosophy has been proposed herein to select the most favourable process environment (optimal parameters setting) to ensure optimal (minimal) SCD and WLT, simultaneously. Apart from parametric optimization, SEM micro-graphs revealing surface morphology in terms of cracks, crater, pock mark, globule of debris, and deposition mark of the EDMed Inconel 601 have been analysed in detail and correlated with chemical composition, residual stress and micro-hardness data. Different types of cracks have been identified as well. Effects of significant process parameters on surface crack density and white layer thickness have been graphically represented.

Effect of Deep Cold Rolling on Residual Stress Distributions Between the Treated and Untreated Regions on Ti–6Al–4V Alloy

The residual stress distributions caused by the deep cold rolling (DCR) process, with a focus on the distributions at the boundary of the treatment zone, are examined in this study. A three-dimensional finite-element (FE) model, validated with experimental residual stress data, is used to study the effect of the process. The residual stress distribution in the crosswise direction (perpendicular to rolling direction) shows a region of tensile residual stress at the start and end of the track that may be a cause for concern. The reason for this region of tensile stress is likely to be due to the reduced treatment of the start and end zones due to the step over and the tool path taken. Other factors that cause a difference between the steady state and the transient zone of the burnished area are also investigated. It is shown that the net material movement causes larger plastic deformation in the boundary zone between the burnished and unburnished region of DCR.

A Combined Experimental and Modelling Approach to Elastic–Plastic Crack Driving Force Calculation in the Presence of Residual Stresses

Since all residual stress measurement methods have inherent limitations, it is normally impractical to completely characterise a three-dimensional residual stress field by experimental means. This lack of complete information makes it difficult to incorporate measured residual stress data into the analysis of elastic–plastic fracture without resorting to simplified methods such as the Failure Assessment Diagram (FAD) approach. We propose a technique in which the complete residual stress field is reconstructed from measurements and used in finite element analysis of the fracture process. Residual elastic strains and stresses in three-point bend fracture specimens were measured using neutron diffraction and an iterative method was used to generate a self-consistent estimate of the complete residual stress field. This enabled calculation of the J contour integral for a specimen acted on by both residual stress and an externally-applied load, allowing the interaction between residual and applied stress to be observed in detail.

Assessment of Stresses in Float and Tempered Glass Using Eigenstrains

Residual stress data determined using the contour method has been used to determine the misfit-strains (i.e., eigenstrains) existent in float glass. Although the uncertainty associated with the results of the contour method analysis may be high the results agree with the residual stress profiles measured using scattered-light-polariscope experiments. The relationship between the eigenstrains and the thickness of glass has been investigated and the results have been validated using scattered-light-polariscopic experiments. The paper shows that the eigenstrain distribution depends on the differential cooling takes place during the manufacturing process. Once the underlying eigenstrain distribution in a given float glass product has been determined this can be used to devise the eigenstrain distribution in tempered glass. It is also shown that eigenstrain analysis can be implemented in finite element models to predict structural response of glass structures thereby to ensure efficient, safe and reliable designs.

Numerical Simulation of Tube-Plate Welding Structure with T-Shaped Sections

At present, the finite element method (FEM) is used to predict the residual stress distribution of the welding structure. A long computational time is required for the multi-pass welding structure with complex shapes. Therefore, it is necessary to develop time-effective finite element model and computational approaches. In this study, the suitable finite element model is developed to perform the thermal and mechanical analyses for obtaining residual stress data of the tube-plate welding structure with T-shaped sections. The results of the finite element analyses show that the residual stress distribution and radial, hoop and axial direction stress distribution of the welding structure.