Estimation Of Residual Stresses Research Articles

Estimation formula for residual stress from the blind-hole drilling method

In this study, the accuracy of blind-hole method on weld residual stress estimation is investigated. A modified parameter group has also proposed to improve the accuracy. The thermal-elastic-plastic finite element model is employed to build up the residual stress distribution and the blind-hole process. The MSC Marc finite element software package is used to simulate the welding process and the welding residual stress and strain distributions around the weld of two inconel 690 alloy plates filled with I-52 GTAW filler. Then the process of the traditional blind hole is simulated by employing the inactive elements. The data of the residual strain variations of strain gages located around the blind hole is introduced into the blind-hole method to estimate the original residual stress components at the hole center. The effects of drilling depth, drilling size, gage radius, gage position, and the distance on the accuracy of estimated residual stress have also been studied and discussed. Based on the residual stress components simulated from the welding process, a modified stress parameter group has also been proposed to improve the accuracy of blind-hole method. Numerical results indicate that the accuracy of estimated residual stress can be improved significantly by employing the proposed blind-hole parameters.

An approach to predict the residual stress and distortion during the selective laser melting of AlSi10Mg parts

In the selective laser melting manufacturing, an accurate estimation of residual stresses and distortion is necessary to achieve high-quality specimens. During the manufacturing, the scanned layers are subjected to rapid thermal cycles. Steep temperature gradients generate residual stresses. Residual stresses can be detrimental to the proper functioning and the structural integrity of built parts. Therefore, it becomes particularly important to build a method to control the quality of the model. In order to realize the quality control of the SLM modeling, in this study, a three-dimensional model was developed for studying thermal behavior and residual stress during selective laser melting (SLM) of AlSi10Mg. Through the simulation, a prediction method for residual stress and deformation is found. To explore the relationship of the thermal effect between adjacent scanning trajectories, the calculated residual stress distributions are compared with independent experimental results. The effects of process parameters such as the laser power, scan speed, and scan strategy on the residual stress were also investigated. The results showed that the stress of the specimen gradually increased during the SLM process, caused by a heat accumulation effect.

FE analysis of shot-peening-induced residual stresses of AISI 304 stainless steel by considering mesh density and friction coefficient

ABSTRACT In order to investigate the effect of shot peening (SP) on residual stress distribution of AISI 304 stainless steel, a 3D dynamic model for describing single and multiple shot impact phenomenon was built via ABAQUS/Explicit 6.10 by considering the mesh density of treated component as well as the friction coefficient between shot and treated component and validated via X-ray residual stress measurement. The results show that an optimal surface element size about 1/18th of the dimple diameter and reasonable friction coefficient of μ > 0.2 are the key factors for the accuracy of residual stress estimation and the computational efficiency. The error of simulated residual stresses indicates the effect of the deformation-induced martensitic transformation phenomenon should be considered in AISI 304 stainless steel SP model. The effects of shot hardness, impact angle, velocity, diameter and coverage ratio on residual stress distribution were examined and discussed via the optimised SP model.

Revealing mechanisms of residual stress development in additive manufacturing via digital image correlation

The severe thermal gradients associated with selective laser melting (SLM) additive manufacturing (AM) generate large residual stresses (RS) that geometrically distort and otherwise alter the performance of printed parts. Despite broad research interest in this field, it has remained challenging to measure warpage in general as well as RS distributions in situ, which has obfuscated the mechanisms of stress formation during the printing process. In pursuit of this goal, we have developed a non-destructive framework for RS measurement in SLM parts using three-dimensional digital image correlation (3D-DIC) to capture in situ surface distortion. A two-dimensional analytical model was developed to convert DIC surface curvature measurements to estimates of in-plane residual stresses. Experimental validation using stainless steel 316 L “inverted-cone” parts demonstrated that residual stress varied across the surface of the printed part, and strongly interacted with the component geometry. The 3D-DIC based RS measurements were validated by X-ray diffraction (XRD), with an average error of 6% between measured and analytically derived stresses. Systematic variation in RS was attributed to the sector-based laser raster strategy, which was supported by complementary finite element calculations. Calculations showed that the heterogeneous RS distribution in the parts emerged from the sequential re-heating and cooling of the new surface, and changed dynamically between layers. The unique DIC based RS methodology brings substantial benefits over alternatively proposed in situ AM RS measurements, and should facilitate enhanced process optimization and understanding leading towards AM part qualification.

Rietveld refinement and estimation of residual stress in GDC–LSCF oxygen transport membrane ceramic composites

The phase purity and crystal structure of dual-phase Ce.9Gd.1O2–δ–La.6Sr.4Co.2Fe.8O3–δ (GDC–LSCF) composites were refined using data obtained from X-ray diffraction (XRD) by employing the Rietveld method. Rietveld analysis indicated that the structures of GDC and LSCF phases are well crystallized as cubic Fm3̅m and rhombohedral R3̅c space groups, respectively. Scanning electron microscopy images showed smooth and dense structures, depicting a homogeneous crystalline structure of the samples. When the composites were cooled from their sintering temperature (1250 °C), compressive stresses were generated in the GDC and corresponding tensile stresses were generated in the LSCF due to differences in thermal expansion coefficients. The compressive residual stresses of the composites were investigated by high-angle XRD measurements using the well-known sin2ψ method. The average compressive residual stresses in GDC phase are estimated to be − 312 and − 290 MPa for 80 GDC–20 LSCF and 50 GDC–50 LSCF, respectively. The aim of this study is to provide a better understanding of the crystal structures and residual stresses in GDC–LSCF composites through XRD and the suitability of these composites for oxygen transport membranes.

Estimation of residual stresses in perovskite films for capacitor applications

The performance of perovskite films in capacitor devices is strongly determined by the level of residual stresses developed after their fabrication at high temperatures. Quantification of these stresses by X-ray diffraction is not straightforward in perovskite films due to the complexity of the crystalline structure and a lack of effective elastic diffraction constants. In this work we apply a simple and accurate method to estimate the residual stresses developed in Pb(Nb,Zr,Ti)O3 perovskite films grown by metal–organic chemical vapor deposition on the Pt electrode. The stress was directly measured in the Pt bottom electrode film before and after the deposition of the perovskite film and compared with intrinsic and thermal stresses calculations. Our results reveal in-plane tensile stresses of 676(8) MPa developed in the Pt electrode, which mainly originate from the relative thermal contraction between Pb(Nb,Zr,Ti)O3 and Pt as well as the cubic-tetragonal perovskite phase transformation after deposition. This methodology is straightforward and highlights the possibility to perform systematic studying for tailoring stress conditions and improving the performance of perovskite films for capacitor applications.

Analysis of distortion during laser metal deposition of large parts

Laser Metal Deposition (LMD) of large parts is very challenging technology for aerospace industry. Due to high productivity of several kilograms per hour and nearly unlimited part size, this technology becomes competitive to traditional production technologies of casting, welding and rolling. One of the main problem of large parts manufacturing is the high distortion. Estimation of residual stresses and distortion is necessary to obtain required dimensional accuracy and prevent fracture of additively manufactured parts. Effects of layer-by-layer evolution of stresses and strains was studied by finite-element simulation. It was shown that distortion of axially symmetrical parts can be successfully predicted by the developed simulation procedure. It was established that the effect of increasing cylinder radius is to increase residual radial displacement and curvature of the sidewall. The highest tension hoop and axial stress amounted to 1.15-1.2 times of yield stress near the substrate. If deposited material have a weak ductility (e.g. titanium alloys) there is a high probability that the fracture could occurs in the sidewall near the substrate. Several experimental trials was carried out for validation of accuracy of developed simulation procedure. Shape of build parts was analysed by 3D laser scanner.

Simulation and Calculation of Residual Stresses in Mining Machines Components

Technologies of surface plastic deformation (SPD) provide a hardening effect and create compressive residual stresses in the surface layer of mining machine parts. This leads to a significant increase in the limit of endurance and fatigue cyclic life, increases the life in fretting conditions, improves the quality of assembly joints fit, etc. Very complex are both the physical nature of the occurrence and the estimation of residual stresses, since the machining processes are related to complex nonmonotonic types of loading. The study shows the relevance of the development of computational methods for determining residual stresses in the processes of hardening treatment of critical surfaces of mining machine parts. At the same time, the design and development of experimental nondestructive express methods based on the determination of various physical parameters (acoustic, magnetic noise, coercive force, etc.) are relevant and promising. A model of the process is developed and numerical calculations of the residual stresses arising during the SPD treatment are carried out. The results of the calculations are in good agreement with the experimental data.

Residual stress estimation based on 3D DIC displacement filed measurement around drilled holes

Residual stress might influence noticeably fatigue strength and fracture behavior of materials, therefore accurate methods of its determination are desired. The most popular method up today is based on strain measurements resulted from material relaxation near the drilled hole. Tensometric rosettes of defined geometry are used for strain measurements in 3 or 6 positions around the hole. The method has some drawbacks related to its sensitivity to hole and rosette centers eccentricity, averaging strain from tensometers area, time consuming rosettes fixing procedures and calculations based on only a few strain readings. Tensometric rosettes might be replaced by non-contact optical displacement fields measurements by means of Digital Image Correlation (DIC) giving much more information (hundreds or thousands of data points) for residual stress calculations. In the paper results of experiments concerning 3D DIC measurements usage for displacement field determination near the drilled hole in preloaded steel samples which afterwards were used as input data in the iterative procedure for the analytical model parameters fitting are presented. Details of testing stand allowing precise hole drilling without need of cameras used for DIC measurements movement during the drilling process and algorithm for inverse method calculations are described. Additionally, FEM model developed for introducing correction terms for blind hole case to the analytical model existing only for through hole instance is discussed.

Application of 3D DIC Displacement Field Measurement in Residual Stress Calculations

Abstract The knowledge of residual stress distribution is of great importance from the viewpoint of both, industrial and basal research. The most commonly utilized method of residual stress determination is based on strain measurements near the drilled holes of known geometry made by means of tensometric rosettes. An alternative to tensometers way of strain measurement is Digital Image Correlation (DIC). This optical method utilizes digital images registered during observed object deformation and delivers results in the form of displacement field maps consisting of hundreds or thousands of data points. Therefore, it is possible to deliver much more data in comparison to rosettes (only 3 or 6 tensometers, usually) and use them in the inverse method numeric procedure for residual stress calculations. In the paper the experimental stand consisting of micro driller and stereo imaging system for 3D DIC measurement and its application to residual stress estimation in prestrained steel samples are presented followed by obtained results discussion.

Residual stress estimation in laminated ZrB2-SiC ultra-high temperature ceramics with strong interfaces using X-ray diffraction and indentation techniques

Abstract Laminated ZrB2–SiC ultra-high temperature ceramics (UHTCs) with different layer thickness ratios and strong interfaces were fabricated by hot-pressing. Residual stresses developed on the surfaces of laminated ZrB2-SiC ceramics were evaluated by X-ray diffraction (XRD) and indentation techniques. Results showed that the characteristic XRD peaks of the ZrB2 phase on the surface of the laminated ceramics presented a shift due to the residual surface stress existence. Both XRD and indentation tested results suggested that the surface residual stress increases with the increasing layer thickness ratio confirming the theoretical analysis and calculation reported by our previous work. The presence of a compressive residual stress in the external layer of the heterogeneous material is expected to improve the mechanical properties of laminated ZrB2-SiC ceramics.

Identification of residual stresses in multi-layered arterial wall tissues using a variational framework

In the past decades a considerable amount of literature has been published addressing the study of the mechanical behavior of arterial walls. Ex-vivo experimentation made possible the development of constitutive models and the characterization of material parameters contributing to the understanding of the mechanobiological response of vascular tissues. Moreover, the existence of residual stresses in configurations free of load was revealed, and its impact in the general stress state of the tissue was quantified. In recent years, data assimilation techniques have seen a rapid development in cardiovascular modeling field, primarily focusing on the estimation of material parameters for arterial wall segments using information provided by medical imaging as well as by in-vitro settings. However, concerning the estimation of residual stresses, this research field is in its early stages, and much work is still required for the full functional characterization of arterial tissues.In this context, a conceptual variational framework for the development of residual stress estimation tools is proposed. Particularly, a variational formulation for the characterization of residual deformations and the associated stresses in arterial walls, based on full displacement field measurements of the vessel, is presented. Considering as known data the material parameters characterizing the behavior of the tissue and a set of arterial wall configurations at equilibrium with well defined pressure loads, we propose a cost functional that measures the mechanical imbalance caused by the lack of knowledge of residual stresses. In this manner, the characterization of residual stresses becomes a problem of minimizing such cost functional. Three numerical examples are presented highlighting the potential of the proposed approach. Among these examples, the characterization of residual stresses in a cylindrical geometry representing a three-layered aorta artery is performed.

Estimation of residual stress in welding of dissimilar metals at nuclear power plants using cascaded support vector regression

Abstract Residual stress is a critical element in determining the integrity of parts and the lifetime of welded structures. It is necessary to estimate the residual stress of a welding zone because residual stress is a major reason for the generation of primary water stress corrosion cracking in nuclear power plants. That is, it is necessary to estimate the distribution of the residual stress in welding of dissimilar metals under manifold welding conditions. In this study, a cascaded support vector regression (CSVR) model was presented to estimate the residual stress of a welding zone. The CSVR model was serially and consecutively structured in terms of SVR modules. Using numerical data obtained from finite element analysis by a subtractive clustering method, learning data that explained the characteristic behavior of the residual stress of a welding zone were selected to optimize the proposed model. The results suggest that the CSVR model yielded a better estimation performance when compared with a classic SVR model.

Determination of equi-biaxial residual stress and plastic properties in structural steel using instrumented indentation

This study describes a method that allows estimation of the equi-biaxial residual stress (σR), yield strength (σy), the strain hardening exponent (n), and the ratio (α) between strain at starting-point of strain hardening (εst) and yield strain (εy) of structural steel from the load-depth curve of one sharp indentation test. In this method, the relationships between the structural steel properties, residual stress, and the characteristics of the indentation loading-unloading curves were established in the form of dimensionless functions via extensive finite element (FE) analyses. Based on the FE analysis results of the indentation process with a large number of different material properties combinations, the effects of residual stress and plastic parameters on the indentation response were investigated, and a reverse algorithm for estimating four unknown quantities (σR, σy, n, and α) of steel from an indentation test was proposed. A stress-applying apparatus that allows the introduction of a compressive or tensile stress to the sample by applying a compressive or tensile force and maintaining the stress after releasing the force was also developed in this study. Indentation and tensile tests of structural steels (SS400 and SM490) were carried out and the proposed algorithm was validated through both numerical analyses and experimental results.

Estimation of residual stresses by inverse analysis based on experimental data from sample removal for “small punch” tests

“Small Punch” (SP) tests, at present frequently employed for mechanical characterizations of structural metals, particularly for diagnosis of plant components, are here considered in view of employment also for assessments of stresses. In the procedure proposed herein the standardised sample removal from an in-service component for SP tests is exploited as external action altering the residual stress state possibly present near to the surface in the location considered. Full-field measurements of consequent displacements in the surrounding surface are employed as input for inverse analysis based on the following features: computer simulations of the sample removal as for its consequences due to relaxation of the pre-existing stress state; “non-uniformity” of residual-stress dependence on depth described as layer-dependent with uniformity in each layer of a pre-defined set of layers; “discrepancy function” minimization with employment of the elasticity parameters provided by the subsequent SP test. The advantages of the novel method consist of no-more need of traditional usual “Hole Drilling” (HD) tests or other tests for residual-stress estimation. The SP experimental procedure proposed herein for estimations of both stress state and elastic-plastic material properties would imply reductions of damages, costs and times in structural diagnoses.

Review on finite element analysis for estimation of residual stresses in welded structures

In this review various finite element analysis approaches available for estimation of residual stresses in welded structures are presented. FEA can effectively estimate residual stresses, especially the relaxation of residual stresses in weld region and region in close vicinity under repeated loading. The amount of the residual stress relaxation depends on the magnitude of applied repeated loading. Comparison revealed that rapid dumping approach have least computational time and shows qualitatively good agreement with experimental values for welding residual stresses whereas gradual weld bead deposition approach estimated more exact results as compared to experimental and various other approaches. Using substructuring approach computation is remarkably reduced without any loss to acceptable accuracy of predicted welding residual stresses. In this composition various assumptions required to carry out finite element analysis of welded structures are also explained. Conclusion indicates that it is important to include all weld sequences for accurate estimation of residual stresses in a structure but even before that it is required to analyze the weld sequences in critical area as a starting point in initial design stage.

Feasibility of Residual Stress Nondestructive Estimation Using the Nonlinear Property of Critical Refraction Longitudinal Wave

Residual stress has significant influence on the performance of mechanical components, and the nondestructive estimation of residual stress is always a difficult problem. This study applies the relative nonlinear coefficient of critical refraction longitudinal (LCR) wave to nondestructively characterize the stress state of materials; the feasibility of residual stress estimation using the nonlinear property of LCR wave is verified. The nonlinear ultrasonic measurements based on LCR wave are conducted on components with known stress state to calculate the relative nonlinear coefficient. Experimental results indicate that the relative nonlinear coefficient monotonically increases with prestress and the increment of relative nonlinear coefficient is about 80%, while the wave velocity only decreases about 0.2%. The sensitivity of the relative nonlinear coefficient for stress is much higher than wave velocity. Furthermore, the dependence between the relative nonlinear coefficient and deformation state of components is found. The stress detection resolution based on the nonlinear property of LCR wave is 10 MPa, which has higher resolution than wave velocity. These results demonstrate that the nonlinear property of LCR wave is more suitable for stress characterization than wave velocity, and this quantitative information could be used for residual stress estimation.

214 Residual Stress Estimation by Indentation

214 Residual Stress Estimation by Indentation

Evaluating the level of residual stresses in anisotropic electric steel

The level of residual stresses (RS) in anisotropic electric steel (AES) is its most important functional characteristic that is responsible for losses of electric power in magnetic circuits of transformers during their service life. Reasons are given for the emergence of RS in AES and the known estimation methods are provided, the main shortcoming of the latter being the lack of quantitative estimates of RS. A simple and practically feasible method is suggested for estimating RS based on measurement of the anisotropy of magnetic properties of AES.

An improved prediction of residual stresses and distortion in additive manufacturing

In laser assisted additive manufacturing (AM) an accurate estimation of residual stresses and distortion is necessary to achieve dimensional accuracy and prevent premature fatigue failure, delamination and buckling of components. Since many process variables affect AM, experimental measurements of residual stresses and distortion are time consuming and expensive. Numerical thermo-mechanical models can be used for their estimation, but the quality of calculations depends critically on the accurate transient temperature field which affects both the residual stresses and distortion. In this study, a well-tested, three-dimensional, transient heat transfer and fluid flow model is used to accurately calculate transient temperature field for the residual stress and distortion modeling. The calculated residual stress distributions are compared with independent experimental results. It is shown that the residual stresses can be significantly minimized by reducing the layer thickness during AM. Inconel 718 components are found to be more susceptible to delamination than Ti-6Al-4V parts because they encounter higher residual stresses compared to their yield strength.