Showing papers in "Journal of Strain Analysis for Engineering Design in 2008"
TL;DR: The emerging message is that, although closely related to the surface-oriented method of digital image correlation, the volume method is distinct due to its predominant reliance on naturally occurring image texture for displacement tracking.
Abstract: Digital volume correlation, an experimental method for volumetric strain measurement, has experienced a growth in technique development and application since its introduction in 1999. This has largely been the result of more accessible volumetric imaging methods and greater speed and capacity of computational facilities. This paper reviews recent work using the method and presents examples from the author's laboratory. The emerging message is that, although closely related to the surface-oriented method of digital image correlation, the volume method is distinct due to its predominant reliance on naturally occurring image texture for displacement tracking. This requires careful tuning for successful application with different materials, and therefore the appropriate focus should not be on developing the ‘best’ digital volume correlation method, but on developing a set of tools that can be selected from and adjusted to specific mechanics problems.
182 citations
TL;DR: In this article, the authors constructed a closed-form analytical model that is capable of dealing with the fundamentals of single-point incremental forming and explaining the experimements of SPIF.
Abstract: In recent work, the present authors constructed a closed‐form analytical model that is capable of dealing with the fundamentals of single‐point incremental forming (SPIF) and explaining the experim...
169 citations
TL;DR: In this paper, a generalized approach for determining the stress intensity factors (SIFs) K-I and K-II for any mode mixity directly from displacement fields obtained by digital image correlation is presented using a center fatigue cracked aluminium plate as an example problem.
Abstract: A generalized approach for determining the stress intensity factors (SIFs) K-I and K-II for any mode mixity directly from displacement fields obtained by digital image correlation is presented using a centre fatigue cracked aluminium plate as an example problem. It was found that the crack-tip position could be determined on average to within 50 per cent of the displacement vector spacing (60 mu m). The approach has been shown to be fairly robust, both in terms of the stability of the SIFs thus obtained and their sensitivity (less than 0.07 MPa root m) to the above uncertainty in the crack-tip location. Differences between the nominal and experimentally determined K-I and K-II values were found to be comparable (around 1.0 MPa root m) for values of K-I ranging from 0 to 15 MPa root m and K-II from 15 to 0 MPa root m, and may have arisen because the nominal values are not representative of those acting at the real crack tip.
128 citations
TL;DR: The application and practice of DIC at high speeds, rather than the experimental results themselves, provide the main thrust of the discussion.
Abstract: Digital image correlation (DIC) is a method of using digital images to calculate two-dimensional displacement and deformation or for stereo systems three-dimensional shape, displacement, and deformation. While almost any imaging system can be used with DIC, there are some important challenges when working with the technique in high- and ultra-high-speed applications. This article discusses three of these challenges: camera sensor technology, camera frame rate, and camera motion mitigation. Potential solutions are treated via three demonstration experiments showing the successful application of high-speed DIC for dynamic events. The application and practice of DIC at high speeds, rather than the experimental results themselves, provide the main thrust of the discussion.
123 citations
TL;DR: In this paper, the finite element method has been applied to simulate residual axial and hoop stresses generated in the weld region and heat-affected zone of an axisymmetric 50-bead circumferentially butt-welded P91 steel pipe, with an outer diameter of 145 mm and wall thickness of 50 mm.
Abstract: The finite element (FE) method has been applied to simulate residual axial and hoop stresses generated in the weld region and heat-affected zone of an axisymmetric 50-bead circumferentially butt-welded P91 steel pipe, with an outer diameter of 145 mm and wall thickness of 50 mm. The FE simulation consists of a thermal analysis and a sequentially coupled structural analysis. Solid-state phase transformation (SSPT), which is characteristic of P91 steel during welding thermal cycles, has been modelled in the FE analysis by allowing for volumetric changes in steel and associated changes in yield stress due to austenitic and martensitic transformations. Phase transformation plasticity has also been taken into account. The effects of post-weld heat treatment (PWHT) have been investigated, including those of heat treatment holding time. Residual axial and hoop stresses have been depicted through the pipe wall thickness as well as along the outer surface of the pipe. The results indicate the importance of including SSPT in the simulation of residual stresses during the welding of P91 steel as well as the significance of PWHT on stress relaxation.
119 citations
TL;DR: In this paper, a loading stage was integrated into the scanning electron microscopy (SEM) imaging system and the digital image correlation (DIC) technique was applied to these images to calculate the displacement and strain field at the area of interest.
Abstract: This paper presents a study of micro-scale deformation of materials utilizing scanning electron microscopy (SEM) images and the digital image correlation (DIC) technique. A loading stage was integrated into the SEM imaging system. During the experiment, a series of SEM images of the specimen were acquired in situ. The DIC technique was then applied to these SEM images to calculate the displacement and strain field at the area of interest. Additional surface preparation may be needed in order to have an effective pattern for DIC analysis. Two applications are presented in the paper.Using small tensile specimens, the mechanical properties of electrodeposited nickel-based LIGA (an acronym from German words for lithography, electroplating, and moulding) specimens were characterized. In this case, the natural microstructural feature of the specimen surface was used directly as the pattern for DIC analysis.This method was also applied to study the strain concentration around the crack tip during the ductile fra...
95 citations
TL;DR: In this article, an experimental set-up was developed to estimate locally the terms of the energy balance associated with the high-cycle fatigue (HCF) of DP 600 steel.
Abstract: This paper presents the first results provided by an experimental set-up developed to estimate locally the terms of the energy balance associated with the high-cycle fatigue (HCF) of DP 600 steel. The experimental approach involves two quantitative imaging techniques: digital image correlation and infrared thermography. First, a variational method is used to derive stress fields from the displacement fields. Patterns of deformation energy per cycle can then be determined on the basis of stress and strain data. Second, a local form of the heat equation is used to derive separately the thermoelastic and dissipative sources accompanying HCF. Energy balances show that around 50 per cent of the deformation energy associated with the mechanical hysteresis loop is dissipated while the rest corresponds to stored energy variations.
69 citations
TL;DR: In this article, a recently developed methodology for scanning electron microscopy (SEM) image correction has been successfully adapted to correct the drift and spatial distortion of atomic force microscopy images.
Abstract: The characterization of nanomaterials and nanostructures on the nanoscale has been a tremendous challenge for many existing testing and measurement techniques. With the rapid development of microfabrication and nanofabrication technologies, appropriate and accurate tools for nanometrology and nanomechanical testing must be developed. In this study, a recently developed methodology for scanning electron microscopy (SEM) image correction has been successfully adapted to correct the drift and spatial distortion of atomic force microscopy (AFM) images. Using this approach with a standard AFM sample stage, the errors in AFM images, artificial strains for zero deformation, have been reduced to 150×10−6 ± 1300×10−6. When using a sample stage with closed-loop control, the method reduces errors to 200×10−6 ± 1000×10−6, confirming that the SEM-based approach is capable of removing much of the distortion present in typical AFM images.
52 citations
TL;DR: In this paper, the effect of optical refraction at an interface between optically dissimilar media is modelled in order to apply the principles of three-dimensional digital image correlation (DIC) to measure defo...
Abstract: The effect of optical refraction at an interface between optically dissimilar media is modelled in order to apply the principles of three-dimensional digital image correlation (DIC) to measure defo...
45 citations
TL;DR: In this article, the forming limit curve (FLC) of welded blanks for varied weld conditions was predicted by simulating the limit dome height (LDH) test using PAM-STAMP (ESI Group, PAM System International).
Abstract: This work aims at predicting the forming limit strains of welded blanks using a thickness gradient-based necking criterion. In order to reduce the complexity and synergistic effect of tailor-welded blank (TWB) parameters, the same material and thickness sheets are considered for the entire work. The forming limit curve (FLC) of welded blanks for varied weld conditions – namely, weld orientation and location – are predicted by simulating the limit dome height (LDH) test using PAM-STAMP (ESI Group, PAM System International), a finite element code. The un-welded blank and TWB FLCs thus predicted by the thickness gradient-based necking criterion are compared with the experimental FLCs obtained by LDH test. Dome height at failure and failure location data of TWBs from experiments and prediction are also compared for varied weld conditions. It is found from the analyses that limit strain predictions correlate well (less than five per cent error) with the experimental results in the drawing region of the forming...
44 citations
TL;DR: In this article, the T-stress and mixed-mode stress intensity factors have been determined experimentally using thermo-elastic stress analysis and using a finite element method, and a new technique has been proposed to identify the crack tip from thermal images.
Abstract: T-stress and mixed-mode stress intensity factors have been determined experimentally using thermoelastic stress analysis and using a finite element method. Pure mode I, strong mixed-mode I and II, and interacting cracks have been used as the case studies. A new technique has been proposed to identify the crack tip from thermoelastic images. It has also been shown that using three terms of Williams's stress field formulation to determine the T-stress, yields a more accurate solution than using only the first two terms of the expansion.
TL;DR: In this article, the behavior of high-strength steel TRIP 700, commonly applied in automotive industries, is evaluated for crash applications, namely the plastic behaviour at intermediate strain rates 50 s− 1eee3×102 s−1 and for the maximum stress level observed at emax≈103 s−
Abstract: This paper presents the behaviour of high‐strength steel TRIP 700, frequently applied in automotive industries. This material is used to design some car components owing to high stress levels induced by phase transformation. Generally, a pre‐plastic deformation is induced in the sheet steel at a low strain rate to transform austenite into martensite. The next step is to design for example a crash box, as described previously by Durrenberger et al. [1], in order to increase the level of energy absorption. The problem with testing this material is the specimen attachment during the tension test, notably at intermediate and high strain rates. A special problem appears when this material is used for crash applications, namely the plastic behaviour at intermediate strain rates 50 s−1eee3×102 s−1 and for the maximum stress level observed at emax≈103 s−1 must be defined correctly. In order to evaluate the behaviour of materials for this range of strain rates, servohydraulic machines are used. However, even if th...
TL;DR: In this article, the influence of weld conditions, namely weld region, weld orientation, and weld location, on the forming-limit strains of steel laser-welded blanks was studied experimentally.
Abstract: The main objective of the present work is to study experimentally the influence of just the weld conditions, namely the weld region, weld orientation, and weld location, on the forming-limit strains of steel laser-welded blanks. Transverse and longitudinal weld orientations are considered for this study. The weld location includes both centre and offset weld positions in the transverse weld orientation. To investigate the forming behaviour of tailor-welded blanks, limit dome height (LDH) tests are performed. Forming behaviour is quantified by the forming-limit curve (FLC). The FLCs of welded blanks are compared with that of an unwelded blank. It is found from the analyses that the weld region shows a negligible effect on the FLC when placed at the centre position irrespective of weld orientation. In the case of transverse welded blanks, when placed at offset locations (20 mm and 30 mm from geometric centre), limit strains are found to decrease when compared with that of the unwelded blank, with the 30 mm ...
TL;DR: In this article, a simple procedure is proposed to correct the measured stresses obtained from the hole-drilting technique, based on the obtained results, and the procedure is tested on several tensile specimens with pre-existing holes.
Abstract: The hole-drilling strain gauge method, described in ASTM E837, is the common method used in evaluation of residual stresses. However, yielding of the material around the hole causes errors related to disregarding the hypotheses of the basic theory of the method.In this work, several welded specimens were prepared and welding residual stresses were measured by using the standard hole-drilling technique. Next, plasticity effects on the measured results of the hole-drilling technique were investigated by using numerical modelling and experiments.In the experimental part of this work, several tensile specimens with pre-existing holes were tested, and the errors at different load levels were evaluated. In the numerical part of the work, drilling a blind hole on a preloaded infinite plate was simulated, and the plasticity errors for different materials and loading combinations were studied. Based on the obtained results, a simple procedure is proposed to correct the measured stresses obtained from the hole-dril...
TL;DR: In this article, the ratio of the ellipse half-axes was used to reduce the stress concentration factor for notches and grooves in axisymmetric tensile shafts.
Abstract: For machine elements that must also be designed with respect to fatigue, the stress concentration factor for notches and grooves is an important quantity. Traditional designs with circular shapes are not advantageous and, in the present paper, it is shown that stress concentration factors can be reduced significantly without the need for complicated shapes. To keep the shape simple, the circular shapes are modified into elliptic shapes with only one design parameter: the ratio of the ellipse half‐axes.Comparisons with classical results are performed for notches in two‐dimensional flat tensile bars and for grooves in axisymmetric tensile shafts. In general, the detailed finite element analyses agree well with these results and this gives confidence in the improved designs. Shapes are obtained with constant maximum stress along a major part of the elliptic shape, and the stress concentration factors are reduced considerably.
TL;DR: In this article, the authors interpreted the response of a woven composite component by treating the woven structure as a patchwork of unidirectional cells and considering each in isolation, and demonstrated that the response is sensitive to small variations in certain quantities and this is discussed in detail in the paper.
Abstract: The thermoelastic response from a woven composite component is complicated because of the variation in material properties across its surface. In this paper the response is interpreted by treating the woven structure as a ‘patchwork’ of unidirectional cells and considering each in isolation. To make matters as simple as possible, single-ply specimens loaded in uniaxial tension are studied. The experiments show that, even for this simple tensile case, the strain field is non-uniform and the approach fails to produce any correlation with predictions based on treating each cell in isolation. In deriving the predicted response a detailed knowledge of the material properties required for thermoelastic stress analysis (TSA) is necessary. It is demonstrated that the response is sensitive to small variations in certain quantities and this is discussed in detail in the paper. The TSA is carried out using a new system and a description of this together with the motion compensation techniques used in the analysis of the high-resolution data is provided.
TL;DR: In this paper, a new technique was developed for motion compensation in thermoelastic stress measurement by the infrared thermography, which used only infrared images, and the other technique uses visible images for motion analysis as well as infrared images for stress analysis.
Abstract: A new technique was developed for motion compensation in thermoelastic stress measurement by the infrared thermography. Two different techniques for motion compensation are proposed in this study. One technique uses only infrared images, and the other technique uses visible images for motion analysis as well as infrared images for stress analysis. The feasibility of the proposed motion compensation techniques was demonstrated by experimental studies.
TL;DR: In this paper, the authors used digital image correlation to measure the residual strains created by hole cold expansion both before and after insertion of an interference fit fastener, and found that the tensile strains at the low edge side of the coupon increased exponentially for both thick (6.35 mm) and thin (1.59 mm) coupons.
Abstract: The paper presents the results of an experimental study that used digital image correlation to measure the residual strains created by hole cold expansion both before and after insertion of an interference fit fastener. The study used 7075-T6 aluminium test coupons with multiple fastener holes to more closely simulate a real aircraft structure where multiple fastener holes are often cold expanded sequentially and where the interactions between the holes are a function of both the hole-to-free-edge distance as well as the pitch between the fastener holes. Both hole-to-free-edge distance and coupon thickness were varied to measure their effects on residual strain after hole cold expansion and after hole cold expansion and interference fit fastener insertion. The results showed that as the edge distance was decreased, the tensile strains at the low edge side of the coupon increased exponentially for both thick (6.35 mm) and thin (1.59 mm) coupons.
TL;DR: In this paper, a non-linear kinematic and isotropic hardening model of Lemaitre and Chaboche in a simplified formulation suitable for contact problems is introduced, which allows the calculation of accumulated plastic strain under the contact surface.
Abstract: A model for plasticity assessment in rolling contact is introduced, aimed at simulating the effect of the application of thousands of load cycles in a reasonable time. It is based on the non-linear kinematic and isotropic hardening model of Lemaitre and Chaboche in a simplified formulation suitable for contact problems and allows the calculation of accumulated plastic strain under the contact surface. Wear is introduced as an independent phenomenon, interacting with the plasticization process by removing material layers from the surface and modifying during the load process the stresses which each point is subjected to. The typical material responses to cyclic loading (elastic shakedown, plastic shakedown, and ratchetting) can be obtained by application of the present method; moreover, the effect of wear in stabilizing the strain field for a large number of cycles is shown. The model is validated through comparison with results obtained by other methods and by experiments.
TL;DR: In this paper, compression tests are conducted to determine the strain, strain rate, and temperature sensitivities of Van Aken plasticine at elevated temperatures, and a true stress-true strain relationship is presented in the form of the Norton-Hoff viscoplastic model.
Abstract: In this study, compression tests are conducted to determine the strain, strain rate, and temperature sensitivities of Van Aken plasticine at elevated temperatures. A true stress—true strain relationship is presented in the form of the Norton—Hoff viscoplastic model. The plasticine is most sensitive to the deformation rate and temperature. At low strains, the material hardens with increasing strain, but strain hardening is negligible above a logarithmic strain of approximately 30 per cent. The shear friction factor for a plasticine—metal interface with and without lubrication is estimated using ring compression tests. Without lubrication, the shear friction factor approaches 1.0; however, lubrication with Vaseline considerably reduces friction. In addition to the mechanical properties of the plasticine, thermal conductivity and specific heat capacity are measured. The thermal conductivity is independent of temperature, and the heat capacity varies only slightly with temperature. A discussion on plasticine ...
TL;DR: In this paper, an infrared thermographic experimental set-up has been proposed and evaluated towards the capability to measure thermoelastic-effect-induced temperature changes, where a standard infrared thermocamera with a nominal noise-equivalent temperature difference (NETD) resolution of 0.12 K has been employed to measure the temperature from unidirectional glass-reinforced plastic tensile coupons under cyclic sinusoidal loads.
Abstract: An infrared thermographic experimental set-up has been proposed and evaluated towards the capability to measure thermoelastic-effect-induced temperature changes. A standard infrared thermocamera with a nominal noise-equivalent temperature difference (NETD) resolution of 0.12 K has been employed to measure the temperature from unidirectional glass-reinforced plastic tensile coupons under cyclic sinusoidal loads. The raster scanning mode of the camera single detector produces a time delay in acquiring the signal from two succeeding pixels on the same row, and from consecutive scanned rows. By exploiting the acquired dwell times, it was possible to produce a periodic pattern on the thermal maps, caused by and correlated with the thermoelastic-effect-induced temperature changes. The acquired raw data have then been post-processed with a lock-in algorithm implemented in MATLAB® and based on a two-dimensional fast Fourier transform analysis. The filtered thermoelastic component from the lock-in analysis showed ...
TL;DR: In this article, the authors present the characteristics of residual stresses in strength mismatched dissimilar steel butt welds by carrying out three-dimensional thermal elastic-plastic FE analysis, and the effects of weld metal strength on residual stress distributions are further investigated on the basis of the FE analysis results.
Abstract: The presence of residual stresses in and around the welds can be detrimental to the performance of the welded part. Therefore, a good estimation of residual stresses in welds is needed. Simulation tools based on the finite element (FE) method are very useful to predict welding residual stresses. However, the numerical simulation of residual stresses in dissimilar steel welds is generally more challenging than that of residual stresses in similar steel welds because of the difference in the mechanical properties of the base metals to be joined and the weld metal strength mismatch which lies between two different base metals resulting from the use of weld metal fitted to either one. This paper presents the characteristics of residual stresses in strength‐mismatched dissimilar steel butt welds by carrying out three‐dimensional thermal elastic—plastic FE analysis, and the effects of weld metal strength on residual stress distributions are further investigated on the basis of the FE analysis results. Moreover,...
TL;DR: In this paper, shot peening has been recognized as a method for treating metal surfaces in order to improve their resistance to crack initiation and propagation, in view of shot-peening control.
Abstract: Shot peening has long been recognized as a method for treating metal surfaces in order to improve their resistance to crack initiation and propagation. In view of shot-peening control, it would be ...
TL;DR: In this article, the authors derived the general expressions for the displacements and stresses of the plate under static loads, which exactly satisfy the governing differential equations and the simply supported boundary conditions at four edges.
Abstract: This paper studies the stress and displacement distributions of rectangular plates with a continuously varying thickness that are simply supported at four edges. On the basis of three-dimensional elasticity theory, the general expressions for the displacements and stresses of the plate under static loads, which exactly satisfy the governing differential equations and the simply supported boundary conditions at four edges of the plate, are analytically derived. The unknown coefficients in the general expressions of the stresses are approximately determined by using the double Fourier sinusoidal series expansions to the boundary conditions on the upper and lower surfaces of the plate. The present solution gives rapid convergence and accurate results which are in good agreement with those obtained from the commercial finite element software ANSYS.
TL;DR: In this article, a branch junction without weld or reinforcement around the intersection is considered with two locations of wall thinning; one in the run pipe and the other in the branch pipe.
Abstract: This paper presents plastic limit loads of piping branch junctions with local wall thinning under in-plane bending, based on systematic three-dimensional finite element (FE) limit analyses using elastic—perfectly plastic materials. As in Part 1, an ideal branch junction without weld or reinforcement around the intersection is considered with two locations of wall thinning; one in the run pipe (opposite to the intersection), and the other in the branch pipe (next to the intersection). Based on FE results, effects of thinning geometries on plastic limit moments are quantified and simple approximations of plastic limit loads for piping branch junctions with local wall thinning under in-plane bending are proposed.
TL;DR: In this article, a computational procedure capable of predicting the quasistatic response of uncoupled, thermoviscoelastic, frictionless contact problems is presented, where the constitutive equations are transformed to be a function of reduced time as the only independent variable, maintaining the convolution integral form.
Abstract: Thermomechanical contact of viscoelastic bodies is a non-linear time- and temperature-dependent problem. Consideration of temperature as an independent variable destroys the convolution integral form of the viscoelasticity constitutive relations. This paper presents a computational procedure capable of predicting the quasistatic response of uncoupled, thermoviscoelastic, frictionless contact problems. The contact problem as a convex programming model is solved throughout an incremental procedure. The Wiechert model is adopted to simulate the linear behaviour of viscoelastic materials. The temperature dependency of viscoelasticity is accounted for by applying the time—temperature superposition principle, in which the William, Landel, and Ferry relationship is adopted to determine the shift factor. Thus, the constitutive equations are transformed to be a function of the reduced time as the only independent variable, maintaining the convolution integral form. Therefore, the complications that arise during th...
TL;DR: In this article, the authors developed a three-dimensional equation for the stress concentration factor Kt through a detailed finite element analysis for a wide range of countersunk hole configurations and plate sizes and verified the resulting equation is within 5 per cent of the finite element results for all practical cases.
Abstract: Countersunk rivets are used to join components to achieve aerodynamic or hydrodynamic surfaces. At countersunk holes, three‐dimensional stress and strain concentrations occur. Previously, the present authors developed a three‐dimensional equation for the stress concentration factor Kt through a detailed finite element analysis. This paper extends the study to include an equation for three‐dimensional strain concentration factor Kte using a similar approach. The resulting equation was verified by finite element analysis for a wide range of countersunk hole configurations and plate sizes. Results showed that the maximum strain concentration is at the countersunk edge. The developed equation is within 5 per cent of the finite element results for all practical cases. It was also found that the Kte and Kt expressions are similar and Kte≥Kt. The maximum difference between the two is 8 per cent (for = 0.3) or 2 for straight‐shank holes and about 2/2 for countersunk holes. The proposed equation is a valuable tool...
TL;DR: In this paper, the authors examined the influence of this crystallographic resistance to small crack growth in micromechanical terms and argued that the crystallographic orientation alone alone alone cannot explain the difference between small and long-crack growth thresholds found in metals.
Abstract: The growth of small fatigue cracks is strongly influenced by the microstructure of the material concerned. Particularly in the early stages, the crystallographic orientation of the grains through which the crack must propagate plays a fundamental role. Cracks are generally initiated in well-oriented grains, but afterwards they are forced to grow through less favourably oriented grains. This work examines the influence of this crystallographic resistance to small crack growth in micromechanical terms. It is argued that the crystallographic orientation alone cannot explain the difference between small- and long-crack growth thresholds found in metals. Other phenomena must be called upon to account for this difference. For instance, crack closure exerts a resistance to crack growth whose evolution with crack length is similar to that due to the crystallographic orientation. Finally, it is shown that, when microstructural and mechanical thresholds are interpreted within the context of micromechanical models, ...
TL;DR: In this paper, a finite element (FE) continuum damage mechanics methodology was developed to deal with anisotropic creep and anisotropy damage for a P91 weld metal, employing a second-order damage tensor, together with a novel rupture stress approach to define the evolution of this tensor.
Abstract: This paper describes the development of a finite element (FE) continuum damage mechanics methodology to deal with anisotropic creep and anisotropic damage for a P91 weld metal. The method employs a second-order damage tensor, together with a novel rupture stress approach to define the evolution of this tensor. The method takes advantage of the transverse isotropic nature of the weld metal, to achieve a reduction in the number of material constants required from test data (and hence tests) to define the damage evolution. Hill's anisotropy potential theory is employed to model the secondary creep. An FE implementation of the model is applied to the creep life assessment of an internally pressurized axisymmetric P91 pipe weldment. The study also considered the effect of various material mismatch ratios in the various zones of the weldment. Here material mismatch is considered to be a combination of the difference in uniaxial minimum strain rates and in the uniaxial rupture times.
TL;DR: In this article, the effect of plastic deformation in small diameter stainless steel pipework that has been subjected to multiple deformation cycles has been investigated and it is shown that strain hardening during the deformation process plays an important role in modifying the thermoelastic constant.
Abstract: Thermoelastic stress analysis (TSA) is used to assess the effect of plastic deformation in small-diameter stainless steel pipework that has been subjected to multiple deformation cycles. In theory the residual stress resulting from the plastic deformation cannot be detected as the thermoelastic response is only a function of the stress change. However, it has been shown that plastic deformation may modify the thermoelastic constant in steel and aluminium. This change can be used to estimate the level of plastic strain that a component has experienced and has potential for TSA to be used as the basis for non-contact non-destructive full-field residual stress assessment. In this paper it is shown that strain hardening during the deformation process plays an important role in modifying the thermoelastic constant. X-ray computed tomography is used on the pipework to verify the estimates of geometry change that are used in determining the applied stress and estimating the residual stress levels. It is shown that TSA is not sensitive to residual stress; however, some interesting anomalies appear in the experimental results that provide a basis for discussion and open avenues of further work. Finally the non-adiabatic thermoelastic response is used to assess whether any damage has occurred in the pipework.