Showing papers in "Journal of Strain Analysis for Engineering Design in 2011"
TL;DR: In this paper, a far-field high-energy diffraction microscopy technique is presented in the context of high energy synchrotron x-ray diffraction, where the volume-averaged lattice orientations, lattice strain tensors, and center-of-mass (COM) coordinates are determined to a high degree of precision.
Abstract: The far-field high-energy diffraction microscopy technique is presented in the context of high-energy synchrotron x-ray diffraction. For each grain in an illuminated polycrystalline volume, the volume-averaged lattice orientations, lattice strain tensors, and centre-of-mass (COM) coordinates may be determined to a high degree of precision: better than 0.05°, 1 × 10−4, and 0.1 pixel, respectively. Because the full lattice strain tensors are available, corresponding mean stress tensors may be calculated unambiguously using single-crystal elastic moduli. A novel formulation for orientation indexing and cell refinement is introduced and demonstrated using two examples: first, sequential indexing and lattice refinement of a single-crystal ruby standard with known COM coordinates; and second, indexing and refinement of simulated diffraction data from an aggregate of 819 individual grains using several sample rotation ranges and including the influence of experimental uncertainties. The speed of acquisition and ...
210 citations
TL;DR: In this article, the authors investigated the application of the TDCB geometry and three common fracture geometry (the compact tension (CT), single edge notch bend (SENB), and single-edge notch tension (SENT) geometries) to the measurement of healing efficiency.
Abstract: The successful invention of self-healing polymer composites a decade ago necessitated a methodology to quantify the ability of the material to heal and recover structural properties following damage. Healing efficiency was defined as the ratio of healed to virgin fracture toughness, η = KIChealed/KICvirgin. Early work took advantage of the crack length independence offered by a tapered double-cantilever beam (TDCB) fracture geometry to simplify calculation of healing efficiency to the ratio of healed to virgin critical loads, η = PChealed/PCvirgin. The current work investigates the application of the TDCB geometry and three common geometries utilized in the broader fracture literature (the compact tension (CT), single-edge notch bend (SENB), and single-edge notch tension (SENT) geometries) to the measurement of healing efficiency. While the TDCB geometry simplifies the calculation of healing efficiency because the crack lengths do not need to be accounted for, it is shown that if the virgin and healed cra...
82 citations
TL;DR: This review thematically classifies all the developments in digital photoelasticity and highlights the relative merits and drawbacks of the various techniques to allow an end-user to make an informed choice on the type of technique to be used in a particular situation.
Abstract: Digital photoelasticity has rapidly progressed in the last few years and has matured into an industry-friendly technique. This review thematically classifies all the developments in digital photoelasticity and highlights the relative merits and drawbacks of the various techniques. The overall objective is to provide enough information and guidance to allow an end-user to make an informed choice on the type of technique to be used in a particular situation.
78 citations
TL;DR: In this paper, a digital image correlation method is proposed to detect and quantify automatically microcracks on the surface of a specimen during a fatigue test, which allows for a fast scanning of the entire surface with all possible (pixel-wise) locations of microcrack centres and the detection of cracks having a sub-pixel opening.
Abstract: A digital image correlation method is proposed to detect and quantify automatically microcracks on the surface of a specimen during a fatigue test. The proposed procedure allows for a fast scanning of the entire surface with all possible (pixel-wise) locations of microcrack centres and the detection of cracks having a sub-pixel opening. An experimental test case is presented as an illustration of the method and a comparison with a replica technique is performed.
61 citations
TL;DR: It is concluded that deoxygenation and therapeutic treatment have a significant impact on the stiffness and this analysis presents a new approach to addressing medical disorders.
Abstract: Translation of cellular mechanics findings is crucial in many diseases, including Alzheimer’s disease, Parkinson’s disease, type II diabetes, malaria, sickle cell disease, and cancer. Atomic force ...
58 citations
TL;DR: Eitner et al. as discussed by the authors showed that the gap between sola... gap between image correlation and solar cells can be closed using the digital image correlation technique (DIC).
Abstract: Recent experimental results based on the digital image correlation technique (U. Eitner, M. Kontges, R. Brendel, Solar Energy Mater. Solar Cells, 2010, 94, 1346–1351) show that the gap between sola...
53 citations
TL;DR: In this article, three-dimensional (3D) images of nodular graphite cast-iron samples obtained with synchrotron tomography are analyzed by resorting to digital volume correlation, using the material microstructure to measure displacement fields within a sample submitted to mechanical loading.
Abstract: Three-dimensional (3D) images of nodular graphite cast-iron samples obtained with synchrotron tomography are analysed by resorting to digital volume correlation. This technique uses the material microstructure to measure displacement fields within a sample submitted to mechanical loading. Compared to classical two-dimensional (2D) digital image correlation, the reconstructed volumes used by DVC tend to increase the uncertainty in the correlation calculations, yet elastic strains of the order of 10-3 can be measured. Displacement fields around the front of a fatigue crack have also been measured by an extended version of DVC, and are used to extract stress intensity factors (in modes I, II, and III) along the crack front. The values are in good agreement with finite element calculations when the experimentally measured displacements prescribed on the sample boundaries are considered as input in the numerical simulations.
52 citations
TL;DR: In this paper, the authors quantify the inherent uncertainty in a strain-measuring system using resistance strain gauges, which has been used for the measurement of strain for more than 50 years.
Abstract: Resistance strain gauges have been used for the measurement of strain for more than 50 years; however, research to quantify the inherent uncertainty in a strain-measuring system has been scarce hit...
40 citations
TL;DR: In this paper, a new two-detector set-up for simultaneous in-and out-of-plane diffraction analysis at the energy-dispersive materials science beamline EDDI at BESSY II is introduced by using the examples of real-space residual stress and texture depth.
Abstract: Responding to a growing interest from the materials science community for residual stress, texture, and microstructure analysis, strong efforts are made to enhance existing and develop novel methods that allow for fast in-situ studies at elevated temperature, measurements under external load, or residual strain, and stress scanning with high spatial resolution. In the paper, energy-dispersive diffraction using high-energy white synchrotron radiation is shown to provide some distinct advantages concerning residual stress and texture analysis, which mainly arise from the fact that the energy-dispersive diffraction mode allows for the measurement of complete diffraction patterns under fixed but arbitrary scattering angles, 2θ. A new two-detector set-up for simultaneous in- and out-of-plane diffraction analysis, which has been put into operation recently at the energy-dispersive materials science beamline EDDI at BESSY II, is introduced by using the examples of real-space residual stress and texture depth pro...
38 citations
TL;DR: A review of the methodology behind these techniques and recent experimental research on three-dimensional (3D) strain mapping can be found in this paper, where potential future research directions are also outlined.
Abstract: Recent advances in X-ray microtomography have created the opportunity to image the interior of materials. Microstructural images that are similar to or about an order of magnitude higher in resolution than those currently obtained with light microscopy can now be obtained in three-dimensions using synchrotron radiation. Local strain mapping is readily enabled by processing these high-resolution tomographic images using either the microstructural tracking technique or the digital volume correlation technique. This article is a review of the methodology behind these techniques and discusses recent experimental research on three-dimensional (3D) strain mapping. Potential future research directions are also outlined.
35 citations
TL;DR: In this paper, a detailed finite element model for a bolted joint was developed using solid elements, and the aim was to simulate the physics of the impact event as accurately as possible without any concern about computational cost.
Abstract: Mechanical components are commonly fastened together using bolts. In many applications, they are subjected to impact loads during their service life. Their response and failure behaviour under these conditions needs to be known for their safe use. The objective of this study was to develop computationally efficient and accurate finite element models for bolted joints under impact loading. First, a three-dimensional detailed finite element model for a bolted joint was developed using solid elements. With this full modelling, the aim was to simulate the physics of the impact event as accurately as possible without any concern about computational cost. In the design of mechanical structures containing numerous fastening elements, use of detailed models is not practicable, because the computational cost of the analysis dramatically increases with the increased number of complex interacting parts. Instead, simplified models that only account for dominating effects should be utilized so that the analysis time c...
TL;DR: In this paper, closed-form expressions of the stress fields in notched rounded bars subjected to torsion are obtained, where the notch axis is inclined with respect to the rounded bar axis.
Abstract: Closed-form expressions of the stress fields in notched rounded bars subjected to torsion are obtained. The notch profile is mathematically described according to Neuber’s conformal mapping z = (u + iv)q, which gives parabolic and hyperbolic profiles depending on q. The notch axis is inclined with respect to the rounded bar axis. This condition results in two eigenvalue functions: the former is associated with the antisymmetric stress field and gives a stress distribution of asymptotic nature when the notch radius is equal to zero. Conversely, the latter is associated with the symmetric stress field and results in a non-singular stress distribution. This specific condition has been noted in the literature only rarely, where only the antisymmetric part of the stress field is discussed in detail. Theoretical results are compared with numerical data as determined from two models weakened by a parabolic notch and a hyperbolic notch, both notches having the local axis inclined to 45° with respect to the bar lo...
TL;DR: In this paper, a lattice strain uncertainty expression was developed to quantify the contribution of the instrument and the material under investigation to the uncertainty of the lattice deformation prediction, which is based on the Bragg angle and the intensity of diffracted peaks.
Abstract: Crystallographic lattice strains - measured using diffraction techniques - are the same magnitude as typical macroscopic elastic strains. From a research perspective, the main interest is in measuring changes in lattice strains induced during in-situ loading: either from one macroscopic stress level to another or from one cycle to the next. The hope is to link these measurements to deformation-induced changes in the internal structure of crystals, possibly related to inelastic deformation and damage. These measurements are relatively new - little experimental intuition exists and it is difficult to discern whether observed differences are due to actual micromechanical evolution or to random experimental fluctuations. If the measurements are linked to material evolution on the size scale of the individual crystal, they have the potential to change the ideas about grain scale deformation partitioning processes and can be used to validate crystal-based simulation frameworks. Therefore, understanding the uncertainty associated with the lattice strain experiments is a crucial step in their continued development. If the measured lattice strains are of the same order as the random fluctuations that are part of the measurement process, documenting the strains can create more confusion than understanding. Often lattice strain error is quoted as {+-}1 xmore » 10{sup -4}. This simple value fails to account for the range of factors that contribute to the experimental uncertainty - which, if not properly accounted for, may lead to a false confidence in the measurements. The focus of this paper is the development of a lattice strain uncertainty expression that delineates the contributing factors into terms that vary independently: (i) the contribution from the instrument and (ii) the contribution from the material under investigation. These aspects of uncertainty are described, and it is then possible to employ a calibrant powder method (diffraction from an unstrained material with high-precision lattice constants) to quantify the instrument portion of the lattice strain uncertainty. In these experiments, the instrument contribution to the uncertainty has been found to be a function of the Bragg angle and the intensity of the diffracted peaks. To develop a model for the instrument portion of the lattice strain uncertainty two datasets obtained using a MAR345 online image plate at the Cornell High Energy Synchrotron Source and a GE 41RT amorphous silicon detector at the Advanced Photon Source have been examined.« less
TL;DR: In this article, a novel methodology simultaneously combining thermoelastic stress analysis (TSA) and digital image correlation (DIC) with a single infrared camera is presented, which improves the resolution and accuracy of TSA results by correcting for sample motion and distortion during loading.
Abstract: A novel methodology simultaneously combining thermoelastic stress analysis (TSA) and digital image correlation (DIC) with a single infrared camera is presented. DIC is an optical method to determine deformation by image tracking with strains determined via differentiation. TSA is a non-contact measurement technique that provides the full-field stress directly using measured temperature changes. The combination of the two techniques improves the resolution and accuracy of TSA results by correcting for sample motion and distortion during loading. Illustrative examples, including an aluminium alloy plate with an edge crack and a nylon plate with a hole under tension, demonstrate the combined method which simultaneously measures stress and displacement.
TL;DR: In this article, the elastic stress concentrations developed from the keyless frictionless static press-fit of a shaft into a hub are addressed, and two configurations are examined, namely (a) an infinitely long solid...
Abstract: The elastic stress concentrations developed from the keyless frictionless static press-fit of a shaft into a hub are addressed. Two configurations are examined, namely (a) an infinitely long solid ...
TL;DR: In this article, the authors present the results of uniaxial and notched bar creep tests on P92 parent material (PM) and P92 weld metal (WM) at 675°C.
Abstract: In order to predict the service life of components that operate at high temperatures, such as steam carrying pipes in conventional power plants, the material creep behaviour needs to be determined. There are little creep data available on grade P92 (9Cr2W) steel (a potential successor to P91) as it is a relatively new material; therefore a testing programme has been undertaken. This paper presents the results of uniaxial and notched bar creep tests on P92 parent material (PM) and P92 weld metal (WM) at 675 °C. The PM had higher failure times and lower minimum creep strain rates for tests in the same stress range (80–100 MPa) as the WM, but the PM and WM values tend to converge at high stress, with a significant difference between the failure times as applied stress decreases. The notch strengthening effect was found to decrease as the applied stress decreased. Processing of the test data including the calculation of the minimum creep strain rates has been performed to determine the material constants requ...
TL;DR: In this article, a new methodology for modeling the fracture process zone in cracked wooden structures has been proposed, which can be used to model the crack tip damage zone in a cracked wooden structure.
Abstract: In this paper, a new methodology for modelling the fracture process zone in cracked wooden structures has been proposed. Implementing this method for modelling the crack tip damage zone could help ...
TL;DR: In this paper, the results of experimental and analytical studies on the response of steel and aluminium square plates with different thicknesses subjected to blast loading have been presented, based on the bla...
Abstract: This article presents the results of experimental and analytical studies on the response of steel and aluminium square plates with different thicknesses subjected to blast loading. Based on the bla...
TL;DR: In this article, the effect of autofrettage on the shakedown behavior of cylinders subjected to a constant internal pressure and cyclic thermal loading was investigated theoretically and validated by the finite element method (FEM).
Abstract: Autofrettage and shakedown analysis of power law strain-hardening cylinders subjected to thermo-mechanical loads were performed in the present study. The closed form solution of the limit thermal load of autofrettage and the optimum autofrettage pressure under plane strain and open-ended conditions are investigated theoretically and validated by the finite element method (FEM). In addition, the effect of autofrettage on the shakedown behaviour of thick cylinders subjected to a constant internal pressure and cyclic thermal loading is discussed. Results reveal that the limit thermal load depends on the thickness ratio and operating pressure and the optimum autofrettage pressure relies on the thickness ratio, operating pressure, strain-hardening exponent, as well as the thermal load. The proposed solution of the optimum autofrettage pressure agrees very well with the FEM result. The theoretical solution of the optimum autofrettage pressure decreases in plane strain and can be used to estimate the case of ope...
TL;DR: In this article, some linear-elastic equations for evaluation of the critical value of the J-integral in plates with U-notches under mode I loading are presented.
Abstract: In this paper, some practical linear-elastic equations for evaluation of the critical value of the J-integral in plates with U-notches under mode I loading are presented and applied to brittle and ...
TL;DR: In this paper, the results of analytical and experimental studies on the response of steel and aluminium circular plates in two different media of air and water have been presented, and the results obtained are compared with existing empirical relations, a theoretical procedure, and a modified relation offered by Wierzbicki and Symonds.
Abstract: The dynamic plastic response of structures under blast loading and underwater explosion has found important applications in the design of energy-absorbing and collision protection devices. This paper presents the results of analytical and experimental studies on the response of steel and aluminium circular plates in two different media of air and water. Results of experimental observation of fully clamped plates have been presented. The results obtained are compared with existing empirical relations, a theoretical procedure, and a modified relation offered by Wierzbicki and Symonds. Comparing the experimental and theoretical results, it was observed that considering strain rate effect in the theoretical procedure is essential in obtaining a more accurate prediction of the deflection of the plate. The reasonable agreement between experimental results and relations proves the validity of the proposed predictions, especially when strain rate effect is considered. Since, in the case of air-blast-loaded plates...
TL;DR: In this paper, the authors used a three-dimensional double ellipsoid (Goldak) heat source to model the heat flow during welding of tungsten inert gas welding.
Abstract: Finite element (FE) simulation of welding processes enables the prediction of component distortions which significantly reduces the need for physical trials. This facilitates reduction in lead time and costs associated with process planning. In this paper, FE modelling of tungsten inert gas welding is performed using SYSWELD for a butt joint between 2 mm thick stainless steel 304 (SS304) sheets. A three-dimensional double ellipsoid (Goldak) heat source is used to model the heat flow during welding. The heat source definition as validated against an experimentally obtained grain structure (macrograph) and thermal history. The isotropic hardening material behaviour model is used in the mechanical analysis and the annealing is considered at 1300 °C. FE-predicted distortion for an unclamped situation is compared with an experimental trial. The FE-predicted fusion zone, thermal histories, and residual distortion are found to be in reasonably good agreement with experimental results. The validated FE methodolog...
TL;DR: The classical Cauchy integral equation formulation used to solve contact problems capable of representation within a half-plane formulation for elastically similar materials, is developed so that t... as discussed by the authors,.
Abstract: The classical Cauchy integral equation formulation used to solve contact problems capable of representation within a half-plane formulation for elastically similar materials, is developed so that t...
TL;DR: Stress and strain analyses of helical compression springs have long been an important factor in machine design and designs routinely incorporate helical springs, either tensile or compressive, to improve performance as discussed by the authors.
Abstract: Stress and strain analyses of helical compression springs have long been an important factor in machine design Designs routinely incorporate helical springs, either tensile or compressive, to tran
TL;DR: In this paper, the residual stress field in welded compact tension specimens is characterized using traditional destructive relaxation-based methods, as well as non-destructive diffraction-based techniques.
Abstract: Compact tension specimens are widely used for fatigue crack growth characterization. It is well known that when using this type of specimen for welded samples, residual stresses affect the crack growth behaviour, in particular, reducing the crack growth rate when the initial notch is parallel to the weldment. Several approaches have been used to characterize the residual stress field in welded compact tension specimens, including traditional destructive relaxation-based methods, as well as non-destructive diffraction-based techniques. The problem with the approaches presented so far is that the former do not provide through-the-thickness results, whereas the latter, although capable of providing through-the-thickness measurements, are only available in very few facilities worldwide. The interest in thick welded samples, where substantial through-the-thickness variations of residual stress fields are to be expected, leads to the need for a full-field characterization. In the present work, the residual stre...
TL;DR: In this article, a combined dimensional analysis and optimization approach is developed for the determination of the elastic-plastic mechanical properties of power law materials, without the need for iterative finite element (FE) analysis.
Abstract: Loading–unloading curves obtained from indentation experiments can be used to extract elastic-plastic mechanical properties using the finite element (FE) method. However, extensive computation times are required in such an approach due to the fact that the optimization procedure is based on iterative FE computations. In this study, a combined dimensional analysis and optimization approach is developed for the determination of the elastic-plastic mechanical properties of power law materials, without the need for iterative FE analysis. A parametric study using FE analysis is first conducted to construct the appropriate dimensional functions. The optimization algorithm with either a single indenter or dual indenters is then used to obtain the material properties from the given loading–unloading curves. Different sets of materials properties are used and the accuracy and validity of the predicted mechanical properties using the single indenter or dual indenters are assessed.
TL;DR: In this paper, a scale-independent theory of deformation and fracture applicable to practical engineering problems is discussed, which does not rely on empirical concepts or phenomenology, and thereby is fundamentally scale independent.
Abstract: As a scale-independent theory of deformation and fracture applicable to practical engineering problems, the field theoretical approach employed by physical mesomechanics is discussed in this paper. Being based on a fundamental physical principle known as gauge invariance, this approach does not rely on empirical concepts or phenomenology, and thereby is fundamentally scale independent. The derivation of physical-mesomechanical field equations is examined on a step-by-step basis, and the physical meaning of each step is clarified. Along the same line of argument, plastic deformation and transition to fracture is interpreted as an energy-dissipative process. Previously derived plastic deformation and fracture criteria are validated via detailed theoretical consideration and comparison with supporting experimental data.
TL;DR: Using a complete set of displacement potential functions, the exact solution of three-dimensional elasticity equations of a simply supported rectangular plates with constant thickness consisting of a transversely isotropic linearly elastic material subjected to an arbitrary static load is presented in this article.
Abstract: Using a complete set of displacement potential functions, the exact solution of three-dimensional elasticity equations of a simply supported rectangular plates with constant thickness consisting of a transversely isotropic linearly elastic material subjected to an arbitrary static load is presented. The governing partial differential equations for the potential functions are solved through the use of the Fourier method, which results in exponential and trigonometric expression along the plate thickness and the other two lengths respectively. The displacements, stresses, and internal forces are determined through the potential functions at any point of the body. To prove the validity of this approach, the analytical solutions developed in this paper are degenerated for the simpler case of plates containing isotropic material and compared with the existing solution. In addition, the numerical results obtained from this study are compared with those reported in other researches for the isotropic material, wh...
TL;DR: In this paper, the transition from ductile-to-brittle (DTB) response in polymers can be triggered by many factors such as temperature, strain rate, and environmental effects.
Abstract: The transition from ductile-to-brittle (DTB) response in polymers can be triggered by many factors such as temperature, strain rate, and environmental effects. The focus of this paper is on investi...
TL;DR: In this paper, various design charts of ample validity and prompt access are presented, which permit the contact stresses within the lug of a pinned connection to be forecast in the presence of an initial clearance between the pin periphery and the lug bore.
Abstract: Various design charts of ample validity and prompt access are presented, which permit the contact stresses within the lug of a pinned connection to be forecast in the presence of an initial clearance between the pin periphery and the lug bore. To cover the range of the practically encountered geometries and loadings, round-ended lugs of various widths and with a variously tapered shank are considered, and several inclinations of the applied load are addressed. The charts are compiled with the aid of finite elements. The employment of the recently proposed load factor Φ allows the combined effects on the peak contact stresses of the load intensity and of the initial clearance to be predicted.