Showing papers in "Journal of Strain Analysis for Engineering Design in 2013"
TL;DR: In this paper, a priori information on the mechanical behavior of the studied material is used to evaluate the gain to be expected from such a mechanical assistance, namely, the measured displacement not only satis es as best as possible the gray level conservation, but also mechanical admissibility.
Abstract: By construction digital image correlation is an ill-posed problem. To circumvent this di culty, the regularization is often performed implicitly through the kinematic basis chosen to express the sought displacement fields. Conversely, a priori information on the mechanical behavior of the studied material is often available. It is proposed to evaluate the gain to be expected from such a mechanical assistance, namely, the measured displacement not only satis es as best as possible the gray level conservation, but also mechanical admissibility.
125 citations
TL;DR: A new procedure is proposed, based on image decomposition, for reducing the dimensionality of strain field data from models and experiments and then comparing the resultant feature vectors via a simple linear correlation in which validation is deemed to be achieved when the coordinate pairs from the two feature vectors lie within a scatter band defined by the minimum measurement uncertainty.
Abstract: The need to provide strong evidence of the validity of predictions from computational solid mechanics models used in engineering design decisions is discussed. A new procedure is proposed, based on image decomposition, for reducing the dimensionality of strain field data from models and experiments and then comparing the resultant feature vectors via a simple linear correlation in which validation is deemed to be achieved when the coordinate pairs from the two feature vectors lie within a scatter band defined by the minimum measurement uncertainty. The procedure is illustrated by some simple examples that allow the advantages and drawbacks of the approach to be highlighted. It is anticipated that the procedure could become part of a corporate plan or regulatory process for verification and validation of computational solid mechanics models.
51 citations
TL;DR: In this article, a computational modeling method of the multiaxial stress-strain notch analysis has been developed to compute elasto-plastic notch-tip stress responses using linear elastic finite element results of notched components.
Abstract: In this article, a computational modeling method of the multiaxial stress–strain notch analysis has been developed to compute elasto-plastic notch-tip stress–strain responses using linear elastic finite element results of notched components. Application and validation of the multiaxial stress–strain notch analysis model were presented by comparing computed results of the model to the experimental data of SAE 1070 steel notched shaft subjected to several nonproportional load paths. Based on the comparison between the experimental and computed strain histories, the elasto-plastic stress–strain model predicted notch strains with reasonable accuracy using linear elastic finite element stress histories. The elasto-plastic stress–strain notch analysis model provides an efficient and simple analysis method preferable to expensive experimental component tests and more complex and time-consuming incremental nonlinear finite element analysis. The elasto-plastic stress–strain model can thus be employed to perform fa...
46 citations
TL;DR: In this article, the authors used the forming limit diagram for sheet metal forming to define the limit of deformation of materials without necking or fracture, and contributed in constructio...
Abstract: Forming limit diagram is extensively used in the analysis of sheet metal forming to define the limit of deformation of materials without necking or fracture. This article contributes in constructio...
44 citations
TL;DR: In this paper, the effect of copper tube casing on the effective strain and microhardness distribution of equal channel angular pressing processed Al-7075 alloy was investigated, where the material was pressed up to four passes by routes A and BC.
Abstract: Equal channel angular pressing is an effective fabrication process for obtaining ultrafine-grained materials. In the current research, the effect of copper tube casing on the effective strain and microhardness distribution of equal channel angular pressing processed Al-7075 alloy was investigated. The material was pressed up to four passes by routes A and BC .T o expose the effect of copper tube casing on homogeneity of equal channel angular pressed specimens, the finite element analysis and Vickers microhardness test were performed on the cross section of the specimens. The finite element and experimental results revealed a significant improvement in homogeneity of the specimens covered with copper tube casing as compared with specimens without cover tube. Increasing the copper tube thickness leads to further improvement in homogeneity of the equal channel angular pressed specimens. Furthermore, by covering the specimens with copper tube casing, the microhardness and strength of the equal channel angular pressed specimens increase slightly.
35 citations
TL;DR: In this paper, a set of practical equations by which one could evaluate mixed-mode I/III stress intensity factors by conducting a simple mode I single-edge notch notch was presented.
Abstract: The main objective of this study is to produce a set of practical equations, by which one could evaluate mixed-mode I/III stress intensity factors by conducting a simple mode I single-edge notch be...
31 citations
TL;DR: A complete methodology is described, consisting of surface parameterisation for the mapping of three-dimensional surfaces to two-dimensional planar domains, Gram–Schmidt orthogonalised for the construction of Orthogonal kernel functions on arbitrary domains and reconstruction of localised image features, such as regions of high strain gradient, by a windowing technique.
Abstract: Recent advances in measurement techniques such as digital image correlation, automated photoelasticity, electronic speckle pattern interferometry and thermoelastic stress analysis allow full-field maps (images) of displacement or strain to be obtained easily. This generally results in the acquisition of large volumes of highly redundant data. Fortunately, image decomposition offers feasible techniques for data condensation while retaining essential information. This permits data processing such as the validation of computational models, modal testing or structural damage assessment efficiently and in a straightforward way. The selection, or construction, of decomposition bases (kernel) functions is essential to data reduction and has been shown to produce features, or attributes, of the full-field image that are effective in reproducing the measured information, succinct in condensation and robust to measurement noise. Among the most popular kernel functions are the orthogonal Fourier series, wavelets and...
29 citations
TL;DR: In this paper, a phenomenological model was developed for prediction of the entire forming limit diagram from simple tensile material properties, based on the necking and ductile damage theories.
Abstract: The purpose of this study is to develop a phenomenological model for prediction of the entire forming limit diagram from simple tensile material properties. The phenomenological model is based on the necking and ductile damage theories. In the proposed model, void nucleation is described as a function of the equivalent plastic strain, and void growth is a function of the stress triaxiality. The forming limit curves calculated from the proposed phenomenological model matched reasonably well in the region of uniaxial tension to balance biaxial tension with the experimental forming limit curves generated on C-Mn 440 steel, interstitial-free 340 steel, and interstitial-free steel sheets.
24 citations
TL;DR: In this paper, the theoretical basis and practical aspects of each of the small specimen creep testing methods are compared in order to clearly understand which of the methods is the best for any specific application.
Abstract: Interest in and the application of small specimen creep test techniques are increasing. This is because it is only possible to obtain small samples of material in some situations, for example, the scoop samples that are removed from in-service components, the heat-affected zones that are created when welds are used to join components and the desire to produce only small amounts of material in alloy development programmes. It is therefore important to review and compare the theoretical basis and practical aspects of each of the small specimen creep testing methods, in order to clearly understand which of the methods is the best for any specific application. This article provides the theoretical basis for each commonly used test method.
23 citations
TL;DR: In this article, the small ring creep test method was used to generate uniaxial secondary creep strain rate data from small samples of material, based on the reference stress method.
Abstract: The small ring creep test method can be used to generate uniaxial secondary creep strain rate data from small samples of material. The technique used is based on the reference stress method; it ena...
18 citations
TL;DR: In this article, the state of stress in bolts and nuts with International Organization for Standardization metric thread design is examined and optimized, and the optimization results show that designing a nut, which results in a more evenly distribution of load along the engaged thread, has a limited influence on the maximum stress due to the stress concentration at the first thread root.
Abstract: The state of stress in bolts and nuts with International Organization for Standardization metric thread design is examined and optimized. The assumed failure mode is fatigue, so the applied preload and the load amplitude together with the stress concentrations define the connection strength. Maximum stress in the bolt is found at the fillet under the head, at the thread start, or at the thread root. To minimize the stress concentration, shape optimization is applied. Nut shape optimization also has a positive effect on the maximum stress.The optimization results show that designing a nut, which results in a more evenly distribution of load along the engaged thread, has a limited influence on the maximum stress due to the stress concentration at the first thread root. To further reduce the maximum stress, the transition from bolt shank to the thread must be optimized. Stress reduction of up to 34% is found, still with the standard International Organization for Standardization thread. The design changes su...
TL;DR: The foundation of this integration is proposed to be data-rich strain fields measured and compared quantitatively, with each other and with data from simulations, at temporal intervals during the life of a component.
Abstract: Experimental strain analysis, structural health monitoring and non-destructive testing and evaluation are regarded as separate disciplines that, in general, are deployed independently at different phases in the life cycle of an engineering component, i.e. in the design process, in service and after an event or service period, respectively. It is proposed that the integrated use of these three disciplines is advantageous and beneficial in terms of reduced capital and operational costs for critical and safety-relevant components, as well as, in validating simulations, in both quantifying and reducing risk of unexpected failure, and in estimating remanent life. We propose the foundation of this integration to be data-rich strain fields measured and compared quantitatively, with each other and with data from simulations, at temporal intervals during the life of a component.
TL;DR: In this article, the authors presented the notch stress intensity factors of a wide range of finite-width flat plates with periodic edge notches, varying from shallow to very shallow. But the authors focused on a broad series of notch configurations.
Abstract: This article presents the notch stress intensity factors of a wide range of finite-width flat plates with periodic edge notches. A broad series of notch configurations, varying from shallow to very...
TL;DR: In this paper, eight different equal channel angular pressing configurations including the punch shape, sample preform and die geometry have been analyzed using finite element method to achieve materials with the high effective strain magnitude, better strain distribution uniformity and less required pressing force.
Abstract: Equal channel angular pressing is one of the attractive methods of severe plastic deformation techniques to fabricate ultrafine grained materials. In this study, eight different equal channel angular pressing configurations including the punch shape, sample preform and die geometry have been analyzed using finite element method to achieve materials with the high effective strain magnitude, better strain distribution uniformity and less required pressing force. The results show that the combination of punch shape and back slant specimen is the most efficient modification as compared to the conventional equal channel angular pressing process. Furthermore, investigations on various die channel and sample slant angles indicate that the configuration of punch shape and back slant sample with the die channel angle of 75° and sample slant angle of 30° is the optimum condition. Finally, experimental work has been performed to validate the results.
TL;DR: In this article, the applicability of Neuber's rule to a specific situation requires consideration of the material model utilized, in addition to the notch geometry and loading conditions, and it can be approximately extended to any stress-strain law and to tensile and bending loads replacing shear stress with equivalent von Mises stress and strain.
Abstract: Neuber’s rule has become a popular analytical tool for evaluating notch root stress and strain for fatigue life estimation. The original study was based on the geometry of prismatic bodies with hyperbolic notches under pure out-of-plane shear with a nonlinear material model. From this study, the author observed that “The geometric mean of stress and strain concentration factors is equal to theoretical elastic stress concentration factor, Kt.” Although this conclusion was based on a “special deformation law,” Neuber suggested that it can be approximately extended to any stress–strain law and to tensile and bending loads replacing shear stress and strain with equivalent von Mises stress and strain and Neuber’s rule evolved. Extensive research has been conducted to evaluate and generalize Neuber’s rule for fatigue analysis. However, the applicability of Neuber’s rule to a specific situation requires consideration of the material model utilized, in addition to the notch geometry and loading conditions. This a...
TL;DR: In this paper, the influence of external weld flash on the formability of friction stir welding sheets through in-plane plane-strain formability tests was analyzed and the load-extension behavior and forming limit strains were measured.
Abstract: The main aim of the present work is to analyze the influence of external weld flash on the formability of friction stir welding sheets through in-plane plane-strain formability tests. The load-extension behavior and forming limit strains are measured to quantify the formability. The influence of friction stir welding parameters on the height of weld flash was also studied. The base materials used for welding trials are AA6061T6 and AA5052H32 alloy sheets of 2.1-mm thickness. It is observed that the influence of external weld flash on the maximum load and total extension for all the friction stir welding conditions is negligible. The effect of weld flash on the limiting major strain is also insignificant. But the presence of weld flash has changed the limiting minor strain, more toward plane-strain condition, indicating the change in strain-path toward plane-strain. This is due to the strain taken by weld flash, along with the major strain, minor strain, and thickness strain in the friction stir welding sheet plane because of constancy of volume. The formation of weld flash and its height are affected synergistically by the axial force and temperature development during friction stir welding. The higher the axial force and temperature, the higher the flash height.
TL;DR: In this paper, an extended Rusinek-Klepaczko constitutive equation was used to predict the mechanical response of 6082-T6 aluminum under the Taylor impact test conditions.
Abstract: The application of an extended Rusinek–Klepaczko constitutive equation to predict the mechanical response of 6082-T6 aluminum under the Taylor impact test conditions was presented in this article. ...
TL;DR: In this article, the verification and validation methodology for the vibration study of automotive structures, in particular natural frequencies and frequency response functions, is investigated, and four spot weld models are critically investigated for this study, namely two point-to-point and two surface to surface approaches.
Abstract: The purpose of this article is to investigate the so-called verification and validation methodology for the vibration study of automotive structures, in particular natural frequencies and frequency response functions. In computational mechanics, the main objective of verification and validation leading to numerical and experimental works is to assess and improve the predictive capability of finite element models. Three main applications are presented throughout the article. The first application deals with spot weld modelling techniques. Four spot weld models are critically investigated for this study, namely two point-to-point and two surface-to-surface approaches. Two examples are treated: an assembly of two plates with three spot welds and a cradle. The second application deals with modelling galvanized structures. The study is focussed on automotive engine cradles. Experimental comparison between welded and galvanized assemblies highlights the mechanical effects due to galvanization. Finite element mo...
TL;DR: In this paper, the influence of strain measurement errors is evaluated with respect to different measurement procedures, such as integral and power series, and two kinds of algorithms, namely, integral-and power-series, are evaluated.
Abstract: Among the many available methods for measuring residual stresses, the hole-drilling method is surely one of the most popular methods. It is a semidestructive method consisting in drilling a very small hole into the specimen. This produces residual stress relaxation around the hole that causes strains also to change. Strain on the surface can be measured by strain gages or by optical techniques like electronic speckle pattern interferometry. Holes can be drilled at different depths, so that a stress profile can be determined using the stress–strain relationships. However, due to the mathematics of the problem, small measurement errors on the strain can imply big errors in the calculated stress. Accuracy of the final results is strongly dependent on the measurement procedure and on the algorithms adopted to calculate stresses. In this study, the influence of strain measurement errors is evaluated with respect to different measurement procedures. Two kinds of algorithms, namely, integral and power series, ar...
TL;DR: In this article, the Chaboche unified visco-plasticity model is used to approximate material constant values in a cyclic loading model and a procedure that evaluates objective functions derived from the multiple experimental data types simultaneously (i.e. in the same optimisation iteration) was found to give the most consistently high quality fitting.
Abstract: Determining representative material constant sets for models that can accurately predict the complex plasticity and creep behaviour of components undergoing cyclic loading is of great interest to many industries. The Chaboche unified visco-plasticity model is an example of a model that, with the correct modifications, shows much promise for this particular application. Methods to approximate material constant values in the Chaboche model have been well established; however, the need for optimisation of these parameters is vital due to assumptions made in the initial estimation process. Optimisation of a material constant set is conducted by fitting the predicted response to the experimental results of cyclic tests. It is expected that any experimental data set (found using the same values of test parameters such as temperature; the dependency of which is not accounted for in the original Chaboche model) should yield a single set of optimised material parameters for a given material. In practice, this may not be the case. Experimental test programs usually include multiple loading waveforms; therefore, it is often possible to optimise for separate, different sets of material constants for the same material operating under comparable conditions. Several optimisation strategies that utilise multiple sets of experimental data to form the objective functions in optimisation programs have been applied and critiqued. A procedure that evaluates objective functions derived from the multiple experimental data types simultaneously (i.e. in the same optimisation iteration) was found to give the most consistently high-quality fitting. In the present work, this is demonstrated using cyclic experimental data for a P91 steel at 600 °C. Similar strategies may be applied to many constitutive laws that require some form of optimisation to determine material constant values.
TL;DR: In this paper, the contact between a cylindrical punch and a half plane was modeled as an elastic half plane and the contact semi-width, a, was assumed to be small relative to the radius, R, of the indenter.
Abstract: This article details the equations describing the contact between a cylindrical punch and a half plane when the punch is initially pressed against the medium with a constant normal force, N, followed by the simultaneous application of a tangential force, Q, and a bulk stress parallel to the surface, σ, with a ratio among loads such that it produces reverse slip at the edge of the contact Both bodies were assumed to be elastic and made of the same material Additionally, the contact semi-width, a, was assumed to be small relative to the radius, R, of the indenter, and as a result, the two bodies behaved as half planes Elastic plane strain conditions have been considered The equations describing surface stress are graphically illustrated for easy interpretation
TL;DR: In this article, the effect of geometrical parameters on angular distortions in butt-welded plates has been investigated numerically and experimentally, and several cases with different plate lengths, widths and thicknesses have been studied.
Abstract: Welding-induced distortions are one of the major problems frequently encountered in industry. Different geometrical and welding process parameters are believed to influence distortions. One of the most common types of distortions frequently observed in butt-welded plates is angular distortion. In this study, the effect of geometrical parameters on angular distortions in butt-welded plates has been investigated numerically and experimentally. A comprehensive study has been performed, and several cases with different plate lengths, widths and thicknesses have been studied. Distortions have been predicted by three-dimensional thermo-elastic-plastic finite element simulation. The finite element results have been verified by a series of experimental measurements for temperatures and angular distortions. The results of this study revealed that plate thickness, length and width influence the magnitude and mode of distortions greatly. The results revealed that decreasing the plate thickness or increasing the weld...
TL;DR: In this paper, the full-field deformations of Al/SiC multilayered graded material under three-point-bending loading were investigated experimentally, and the fracture of the material was investigated.
Abstract: Deformation and fracture of Al/SiC multilayered graded material under three-point-bending loading is investigated experimentally. First, the full-field deformations of Al/SiC multilayered graded ma...
TL;DR: In this article, the authors integrate full-field optical measurement methodologies with state-of-the-art computational simulation techniques for nonlinear transient dynamic events for a car bonnet frame.
Abstract: Innovative designs of transport vehicles need to be validated in order to demonstrate reliability and provide confidence. It is normal practice to study the mechanical response of the structural elements by comparing numerical results obtained from finite element simulation models with results obtained from experiment. In this frame, the use of whole-field optical techniques has been proven successful in the validation of deformation, strain, or vibration modes. The strength of full-field optical techniques is that the entire displacement field can be acquired. The objective of this article is to integrate full-field optical measurement methodologies with state-of-the-art computational simulation techniques for nonlinear transient dynamic events. In this frame, composite car bonnet frame structures of dimensions about 1.8 m × 0.8 m are considered. They have been tested in low-velocity mass-drop impact loading with impact energies ranging from 20 to 200 J. In parallel, simulation models of the car bonnet f...
TL;DR: In this article, the static tensile and the dynamic compressive behaviors of the armor structural materials were investigated. But the static and dynamic tensile properties of the materials were not considered.
Abstract: High strain rate–dependent deformation behaviors are important in design and optimization of armor structural materials. Herein, the static tensile and the dynamic compressive behaviors of the prac...
TL;DR: Based on the adaptive genetic algorithm, the ultrasonic speckle measurement technique has higher efficiency and less measurement errors than the existing ultrasonic specckle correlation method as mentioned in this paper, which can be applied to measure displacements and strains on the surface which is perpendicular to the propagation direction of ultrasound.
Abstract: By comparing the unloaded and loaded ultrasonic speckle fields with cross-correlation, ultrasonic speckle technique can be applied to measure displacements and strains on the surface which is perpendicular to the propagation direction of ultrasound. Based on the adaptive genetic algorithm, the ultrasonic speckle measurement technique has higher efficiency and less measurement errors than the existing ultrasonic speckle correlation method. By adjusting genetic parameters through the adaptive mechanism, the adaptive genetic algorithm searches for the maximum value among the whole distribution of correlation coefficients efficiently. In this study on displacement measurements of an inner surface of an underwater object, the results obtained with different algorithms, including the adaptive genetic, coarse-fine interpolation and hill-climbing searching algorithms, were compared with each other. It was clear that the adaptive genetic algorithm outperformed other methods in computational time and accuracy. Cons...
TL;DR: In this paper, the influence of welding parameters, including welding speed and wire feeding rate, on the residual stress distribution and mechanical properties of the hybrid weld was experimentally studied, and the obtained results show that there exist high compressive transverse and longitudinal residual stresses along the centerline of the weld.
Abstract: Hybrid laser/gas metal arc welding was applied to join the thick high-strength steel in square butt joints with narrow gaps. An X-ray diffraction technique was used to measure the surface residual stress distribution of high-strength steel by a hybrid laser/gas metal arc welding in a butt joint configuration. The influence of welding parameters, including welding speed and wire feeding rate, on the residual stress distribution and mechanical properties of the hybrid weld was experimentally studied. The obtained results show that there exist high compressive transverse and longitudinal residual stresses along the centerline of the weld. However, high tensile transverse and longitudinal stresses are located in the nearby heat-affected zone. An increase in the welding speed definitely decreases the residual stress concentration. A good weld quality of high-strength steel butt welds without cracking or defects can be achieved by a hybrid laser/gas metal arc welding technique.
TL;DR: In this paper, an analytical methodology is developed to study dynamic elasto-viscoplastic behavior of moderately thick circular plates subjected to high-intensity impulsive loads, comprehensively.
Abstract: An analytical methodology is developed to study dynamic elasto-viscoplastic behaviour of moderately thick circular plates subjected to high-intensity impulsive loads, comprehensively. First, incremental kinematic formulations are derived based on the first-order shear deformation theory to take into account viscous damping and rotary inertia. Geometrical and material non-linearities are applied by the complete von Karman system and a mixed strain hardening law coupled with a physically based viscoplastic model, respectively. A semi-implicit scheme of return-mapping is employed by the cutting-plane algorithm to obtain effective plastic strains apart from satisfying the consistency condition. The subsequent part is devoted to the transformation of this boundary value problem into an initial value problem, to evaluate displacement fields. Spatial and temporal discretizations are carried out by the Chebyshev pseudo-spectral collocation method and Houbolt time-marching scheme, respectively. This transformation...
TL;DR: In this paper, the authors presented a relatively simple analytical model aimed at simulating high-speed penetration into composite materials targets, and provided a qualitative explanation of the sudden drop of energy absorbed by the target with impact velocities slightly higher than the ballistic limit.
Abstract: This article presents a relatively simple analytical model aimed at simulating high-speed penetration into composite materials targets. The model is based on a set of basic hypotheses common to other previous analytical models developed in our department and elsewhere. However, this new model is of a more refined nature acquisition that allows for reliable results without requiring the use of parametric data needed in previous models. For the first time, the model provides a qualitative explanation of the sudden drop of energy absorbed by the target with impact velocities slightly higher than the ballistic limit. A qualitative explanation, experimentally observed, of the shape of woven fabric laminates after impact is also noted. The model predictions of both ballistic limit and residual velocity after perforation reasonably agree with experimental results, in spite of the use of static data of the target material. Thus, this model may serve as a useful tool for a primary stage of composite armour design,...
TL;DR: In this paper, the effect of strain paths and residual delta ferrite on failure characteristics of austenitic stainless steels cold-rolled to 20% reduction was assessed and post-mortem scanning electron microscopy was used to study fracture surface and cross-sectional views of the failed specimens.
Abstract: This study was carried out to assess the effect of strain paths and residual delta ferrite on failure characteristics of austenitic stainless steels cold rolled to 20% reduction. Optical metallography was carried out to determine grain size and quantify residual delta ferrite. Mechanical tensile tests to failure along three orthogonal directions were carried out on annealed and 20% cold rolled samples to study the effects of strain paths on mechanical properties of the material. Post-mortem scanning electron microscopy was used to study fracture surface and cross-sectional views of the failed specimens. The yield strength of material cold rolled to 20% reduction increased relative to annealed material along the rolling and transverse directions by twice as much along the normal direction. The increase in the yield strength occurred at the expense of ductility which decreased by about half in all directions. It also emerged that material loaded along rolling and transverse directions showed a gradual failu...