Showing papers in "Journal of Strain Analysis for Engineering Design in 2016"
TL;DR: In this article, the evolution of microstructure strain partitioning during quasi-in situ tensile loading of grade 2205 duplex stainless steel was investigated, and the digital image correlation revealed the developme...
Abstract: The evolution of microstructure strain partitioning during quasi in situ tensile loading of grade 2205 duplex stainless steel has been investigated. Digital image correlation revealed the developme...
41 citations
TL;DR: In this article, the Bolt Tension Monitor (BSTM) is described and tested using fiber Bragg-grating sensor(s) embedded in a bolt shaft for preload and retained clamping force measurements.
Abstract: Bolted/mechanical fastening is one of the oldest and most widely used joining techniques. While it has many advantages such as ease of assembly and repair, it also has some important limitations. One such concern is bolt clamping load control and monitoring during and after joint assembly. Conventionally used torque wrenches can provide only an approximation of the clamping load and cannot be used for load monitoring. Clamping force transducers are bulky, expensive, and cannot usually be incorporated into the bolted joint for continuous load monitoring in the field. In this work, a novel implementation of a transducer device, called here for convenience the “bolt tension monitor,” is described and tested. It utilizes removable and reusable fiber Bragg-grating sensor(s) embedded in a bolt shaft for preload and retained clamping force measurements. While the inherent small size of the fiber Bragg-grating provides precise monitoring without significant effect on the intrinsic properties of the bolt, the embe...
40 citations
TL;DR: In this article, a method of predicting the failure of a thermal barrier coating system due to interfacial cracks and cracks within bulk coatings is described, which is modelled by applying cohesive interfaces where the thermally grown oxide is bonded to the ceramic thermal barrier.
Abstract: The present paper describes a method of predicting the failure of a thermal barrier coating system due to interfacial cracks and cracks within bulk coatings. The interfacial crack is modelled by applying cohesive interfaces where the thermally grown oxide is bonded to the ceramic thermal barrier coating. Initiation and propagation of arbitrary cracks within coatings are modelled using the extended finite element method. Two sets of parametric studies were carried out, concentrating on the effect of thickness of the oxide layer and that of initial cracks within the ceramic coating on the growth of coating cracks and the subsequent failures. These studies have shown that a thicker oxide layer creates higher tensile residual stresses during cooling from high temperature, leading to longer coating cracks. Initial cracks parallel to the oxide interface accelerate coating spallation and simulation of this process is presented in this paper. By contrast, segmented cracks prevent growth of parallel cracks which can lead to spallation.
35 citations
TL;DR: In this paper, the identification of the parameters of several constitutive laws is performed with the integrated digital image correlation (IDIC) technique in a biaxial experiment for a cruciform specimen made of stainless steel.
Abstract: The identification of the parameters of several constitutive laws is performed with the integrated digital image correlation (IDIC) technique in a biaxial experiment for a cruciform specimen made of stainless steel. The sought material parameters are assessed with the contribution of both reaction forces (from load sensors) and displacement fields (measured via digital image correlation). For each constitutive law a global residual quantifying the model error is assessed.
34 citations
TL;DR: In this paper, the generalized continuum theory of couple-stress elasticity was used to derive general solutions for two-dimensional plane strain contact problems within the framework of the generalized continuous theory of elasticity.
Abstract: In this study, we derive general solutions for two-dimensional plane strain contact problems within the framework of the generalized continuum theory of couple-stress elasticity. This theory introd...
31 citations
TL;DR: The main limitation of digital image correlation is the remarkable noise affecting the image correlation-computed strain distributions as mentioned in this paper, and neither manufacturers of DICs nor their users are aware of this limitation.
Abstract: The main limitation of digital image correlation is the remarkable noise affecting the digital image correlation–computed strain distributions. Neither manufacturers of digital image correlation sy...
29 citations
TL;DR: The hole drilling method is a well-known technique for the determination of non-uniform residual stress profiles by measuring relaxation distortions caused by the presence of the hole as discussed by the authors, which is known as hole-drilling.
Abstract: The hole drilling method is a well-known technique for the determination of non-uniform residual stress profiles by measuring relaxation distortions caused by the presence of the hole. The integral...
25 citations
TL;DR: In this paper, a prospective method for structural health monitoring of engineering materials and structures is based on embedded strain sensors in the form of electrically conductive carbon rovings, which are used to measure the structural health of composite materials.
Abstract: A prospective method for structural health monitoring of engineering materials and structures is based on embedded strain sensors in the form of electrically conductive carbon rovings. This article...
23 citations
TL;DR: In this paper, an experimental study of the residual stresses present in the thermally autofrettaged thick-walled cylinders is carried out, where the idea of thermal autorefrettage has been conceived.
Abstract: In this work, an experimental study of the residual stresses present in the thermally autofrettaged thick-walled cylinders is carried out. The idea of thermal autofrettage has been conceived recent...
22 citations
TL;DR: In this paper, the influence of the type of geometry used to model a cylindrical contact has on fretting fatigue life prediction, and the effect that the assumed fatigue crack sh...
Abstract: This work analyses the influence that the type of geometry used to model a cylindrical contact has on fretting fatigue life predictions. It also studies the effect that the assumed fatigue crack sh...
18 citations
TL;DR: The offset between the hole and the center of the strain-gage rosette is unavoidable, although usually small, in the hole-drilling technique for residual stress evaluation as discussed by the authors, but it is not a significant offset in the case of a single hole.
Abstract: The offset between the hole and the centre of the strain-gage rosette is unavoidable, although usually small, in the hole-drilling technique for residual stress evaluation. In this article, we revi...
TL;DR: In this article, a one-dimensional harmonic finite element is proposed for the transient elasto-plastic analysis of axisymmetric structures loaded by non-axisymetric thermal and mechanical loads.
Abstract: This work presents a one-dimensional harmonic finite element for the transient elasto-plastic analysis of axisymmetric structures loaded by non-axisymmetric thermal and mechanical loads. The one-dimensional element exploits a semi-analytical approach, based on Fourier series decomposition of the applied loads. The initial stress method is used for the non-linear solution of elasto-plastic analysis. As a case study, the proposed one-dimensional harmonic element is applied for modelling a two-dimensional circle under thermal and mechanical loadings rotating over its surface, which is used as an approximation of a work roll in hot strip rolling. With the one-dimensional harmonic element, the cyclic thermo-mechanical behaviour of the work roll can be simulated by considering localized plasticity caused by thermo-mechanical loads representative of strip and back-up roll. Compared to two-dimensional models already used in the literature, the one-dimensional element allows a significant reduction in the computat...
TL;DR: The objective of the reported study was to assess the effectiveness and usefulness of a recently published approach that provides an efficient method for comparing data fields from the simulations and experiments, and which incorporates the uncertainty arising in the experimental data in the assessment of the model validity.
Abstract: The terminology of validation of computational models and the framework within which it should be performed has been well-defined in a series of standards documents developed in the United States. ...
TL;DR: In this article, both acoustic emission and evolution of composite laminates were investigated for delamination damage and evolution, and a detailed characterization of delamination deformation and evolution was provided.
Abstract: Accurate characterization of delamination damage and evolution plays a significant role in studying the failure behaviors of composite laminates. In the present research, both acoustic emission and...
TL;DR: The AA-6061 (T6) aluminum alloy sheet is used extensively for structural applications in various automotive and aerospace industries due to its excellent mechanical and physical properties as discussed by the authors, and it is used in many automotive applications.
Abstract: AA-6061 (T6) aluminum alloy sheet is used extensively for structural applications in various automotive and aerospace industries due to its excellent mechanical and physical properties. Due to lowe...
TL;DR: The formability of automotive materials such as aluminum alloys, magnesium alloys and steels is influenced by forming temperatures while adjusting the temperature level of die, punch, and powder as discussed by the authors.
Abstract: The press formability of the automotive materials such as aluminum alloys, magnesium alloys and steels is influenced by forming temperatures While adjusting the temperature level of die, punch and
TL;DR: In this paper, a shrink fit sample is manufactured with a Ti-8Al-1Mo-1V alloy and a set of strain and orientation pole figures are measured at various locations across the disk using synchrotron high-energy X-ray diffraction.
Abstract: A shrink-fit sample is manufactured with a Ti-8Al-1Mo-1V alloy to introduce a multiaxial residual stress field in the disk of the sample. A set of strain and orientation pole figures are measured at various locations across the disk using synchrotron high-energy X-ray diffraction. Two approaches—the traditional sin2Ψ method and the bi-scale optimization method—are taken to determine the stresses in the disk based on the measured strain and orientation pole figures, to explore the range of solutions that are possible for the stress field within the disk. While the stress components computed using the sin2Ψ method and the bi-scale optimization method have similar trends, their magnitudes are significantly different. It is suspected that the local texture variation in the material is the cause of this discrepancy.
TL;DR: In this paper, an asymptotic matching is performed between an available analytical expression of the contact pressure that neglects the finiteness of the seal dimensions and a fracture mechanics solution describing a periodically laterally cracked strip of finite width.
Abstract: The contact pressure is considered for an elastomeric rectangular seal with rounded edges. An asymptotic matching is performed between an available analytical expression of the contact pressure that neglects the finiteness of the seal dimensions and a fracture mechanics solution describing a periodically laterally cracked strip of finite width. This matching provides a corrected formula for the peak contact pressure that accounts for the finiteness of the seal dimensions. The analytical expression for the peak contact pressure is validated versus finite element predictions for a large family of seal geometries and, in particular, for a seal reference shape extracted from the pertinent literature. An appraisal of the finite deformation effect has been carried out numerically.
TL;DR: In this paper, a profound understanding of plastic anisotropy of sheet metal is crucial in controlling complex sheet-metal structures, and finite element model updating is a powerful technique to inversely identify material behaviour.
Abstract: Finite element model updating is a powerful technique to inversely identify material behaviour. A profound understanding of plastic anisotropy of sheet metal is crucial in controlling complex sheet...
TL;DR: In this article, the authors show that the normal contact problem between two elastic bodies in the half-space approximation can always be transformed to an equivalent problem of the indentation of a profile into an elastic Winkler foundation.
Abstract: In this article, we show that the normal contact problem between two elastic bodies in the half-space approximation can always be transformed to an equivalent problem of the indentation of a profile into an elastic Winkler foundation. Once determined, the equivalent profile can also be used for tangential contact problems and arbitrary superimposed normal and tangential loading histories as well as for treating of contact problems with linearly viscoelastic bodies. In the case of axis-symmetric shapes, the equivalent profile is given by the method of dimensionality reduction integral transformation. For all other shapes, the profile is deduced from the solution of the elastic contact normal problem, which can be obtained numerically or experimentally.
TL;DR: In this article, it was shown that roughness induced adhesion enhancement is very high and depends uniquely on a Johnson parameter for adhesion of a sinusoidal contact, which leads to unbounded enhancement for conditions of large roughness for which the Johnson parameter is low.
Abstract: While adhesion reduction due to roughness is not surprising, roughness induced adhesion remained a puzzle until recently. Guduru and coworkers have shown a very convincing mechanism to explain both the increase of strength and of toughness in a sphere with a concentric single scale of waviness. Kesari and coworkers later showed some very elegant convenient asymptotic expansions of Guduru’s solution. This enhancement is very high and indeed, using Kesari’s solution, it is here shown to depend uniquely on a Johnson parameter for adhesion of a sinusoidal contact. However, counterintuitively, it leads to unbounded enhancement for conditions of large roughness for which the Johnson parameter is very low. Guduru postulated that this enhancement should occur after sufficiently large pressure has been applied to any spherical contact. Also, although the enhancement is limited to the Johnson, Kendall and Roberts (JKR) regime of large soft materials with high adhesion, the DMT limit for the smooth sphere is found o...
TL;DR: In this article, the authors solved two three-dimensional contact problems for a linearly viscoelastic foundation in sliding contact with a separate indenter and a periodic wavy surface taking into account adhesion.
Abstract: Solutions of two three-dimensional contact problems for a linearly viscoelastic foundation in sliding contact with a separate indenter and a periodic wavy surface taking into account adhesion are p...
TL;DR: In this article, the authors defined a feasible method for assessing the heterogeneity of the surface residual stress state based on the theoretical relationship between the deviation of the residual macrostress and the intensity of the microstress.
Abstract: The residual stress analysis is a well-established method for predicting fatigue failures of mechanical components. Within industrial constraints, the X-ray diffraction is a technique usually applied to measuring a small spot of the workpiece surface. This punctual and averaged outcome does not allow the proper representation of the residual stress. The objective of this study is to define a feasible method for assessing the heterogeneity of the surface residual stress state. The proposal is based on the theoretical relationship between the deviation of the residual macrostress and the intensity of the microstress. Steel shot peened gears were produced and their microstresses were assessed by means of the diffraction profiles broadening. The reference database was composed of topography measurements, metallographic analyses and residual macrostress maps. The stress heterogeneity was reasonably correlated to the intensity of the Gauss integral breadth. Applied to ground parts, the correlation’s parameter f...
TL;DR: In this article, the one-dimensional impact problem in the case of Fung's quasi-linear viscoelastic model is studied for the relaxation function of the standard solid model (or Zener model).
Abstract: The one-dimensional impact problem in the case of Fung’s quasi-linear viscoelastic model is studied for the relaxation function of the standard solid model (or Zener model). Additionally, quasi-lin...
TL;DR: In this article, a singular integral equation was derived for the problem of thin elastic films bonded on an elastic orthotropic substrate under thermal load, where the effect of the anisotropic behavior of the elastic substrate was taken into account.
Abstract: The problem of thin elastic films bonded on an elastic orthotropic substrate under thermal load is investigated in this work. Differently from past studies on the same topic, the effects induced by anisotropic behavior of the elastic substrate will be taken into account. Particular attention will also be paid to the determination of the displacement and stress fields induced by thermal loading. In particular, it is assumed that the thin films are deposed on the substrate at high temperature, and then the mismatch occurring during the cooling process, due to the difference between the thermal expansion coefficients of the two materials, is responsible for the permanent deformation assumed by the system. This phenomenon can be exploited for realizing a crystalline undulator. To this aim, the permanent deformation must be optimized in order to encourage the channeling phenomenon. By imposing equilibrium conditions and perfect adhesion between the film and the substrate, a singular integral equation is derive...
TL;DR: In this article, the authors investigated the possibility of failure by crack-opening mode III (out-of-plane shearing) in sheet-bulk metal forming processes and showed that incremental ploughing of thin sheets with a roll-tipped tool under large indentation depths gives rise to transverse cracks that are triggered at the upper groove surface and propagate downward across thickness along an inclined direction to the sheet surface.
Abstract: This article investigates the possibility of failure by crack-opening mode III (out-of-plane shearing) in sheet–bulk metal forming processes. The investigation makes use of experimentally and theoretically determined fracture-forming limits of aluminium AA1050-H111 sheets with 1 mm thickness, experimental tests in incremental ploughing with a roll-tipped tool and numerical simulation using a commercial finite element programme. Results show that incremental ploughing of thin sheets with a roll-tipped tool under large indentation depths gives rise to transverse cracks that are triggered at the upper groove surface and propagate downward across thickness along an inclined direction to the sheet surface. In contrast to sheet–metal forming processes that only fail by fracture in crack-opening modes I and II, sheet–bulk metal forming processes present the unique ability of failing in all three possible crack-opening modes, namely, in mode III that is typical of bulk metal–forming processes.
TL;DR: In this article, the authors review the representation of fretting fatigue crack nucleation sites by simple asymptotic forms and show that the multipliers on these fields produce very satisfactory quantifiers of the tendency of any contact (but particularly incomplete ones) to nucleate a crack.
Abstract: We review the representation of fretting fatigue crack nucleation sites by simple asymptotic forms and show that the multipliers on these fields produce very satisfactory quantifiers of the tendency of any contact (but particularly incomplete ones) to nucleate a crack. A procedure is suggested to adopt simplified contact geometries, easily tested under carefully controlled conditions in a laboratory, to assess the likelihood of the avoidance of all failure or to estimate the time needed for crack initiation. The results found are true material properties which may then easily be used to solve a wide range of practical problems.
TL;DR: In this article, the isotropic and kinematic hardening parameters of printed circuit boards under cyclic thermal loads were determined by using finite element analysis software Abaqus.
Abstract: In printed circuit boards, thin copper layers are used as current paths. During the thermal loading of printed circuit boards, stresses arise due to the different coefficients of thermal expansion of the used materials. To be able to model the mechanical behavior of printed circuit boards under cyclic thermal loads, cyclic mechanical tests of thin copper foils under changing tensile and compression loads at different temperatures were conducted. From these experiments, the isotropic and kinematic hardening parameters were determined serving as material input data for a nonlinear isotropic/kinematic hardening model in the finite element analysis-software Abaqus. The kinematic hardening parameters were fitted in an optimization process. The isotropic hardening variables were determined based on the stress versus plastic strain relationship that was constructed incrementally from the available individual cycles. The so-obtained curve was found to be not unique, but to depend on the loading situation. Hence, ...
TL;DR: In this paper, a framework for the development of accurate yet computationally efficient numerical models is proposed within the context of computational model validation, which relies on the implementation of a recently derived multiscale finite element formulation, able to alternate between scales of different complexity.
Abstract: A framework for the development of accurate yet computationally efficient numerical models is proposed in this work, within the context of computational model validation. The accelerated computation achieved herein relies on the implementation of a recently derived multiscale finite element formulation, able to alternate between scales of different complexity. In such a scheme, the micro-scale is modelled using a hysteretic finite elements formulation. In the micro-level, nonlinearity is captured via a set of additional hysteretic degrees of freedom compactly described by an appropriate hysteric law, which gravely simplifies the dynamic analysis task. The computational efficiency of the scheme is rooted in the interaction between the micro- and a macro-mesh level, defined through suitable interpolation fields that map the finer mesh displacement field to the coarser mesh displacement field. Furthermore, damage related phenomena that are manifested at the micro-level are accounted for, using a set of additional evolution equations corresponding to the stiffness degradation and strength deterioration of the underlying material. The developed modelling approach is utilized for the purpose of model validation; firstly, in the context of reliability analysis; and secondly, within an inverse problem formulation where the identification of constitutive parameters via availability of acceleration response data is sought.
TL;DR: In this paper, the results of finite element (FE) analyses of Small Punch Creep Testing (SPCT) of a P91 steel at 600°C using two different approaches to model the friction between the specimen and the punch are compared with those obtained by a more modern formulation, which takes into account the effects of local loading conditions, i.e., the contact pressure, between the contacting bodies (the small disc specimen and a punch) on the coefficient of friction.
Abstract: This paper shows the results of finite element (FE) analyses of Small Punch Creep Testing (SPCT) of a P91 steel at 600°C using two different approaches to model the friction between the specimen and the punch. The numerical results obtained by using the “classical” Coulomb friction model (i.e. constant friction coefficient) have been compared with those obtained by a more modern formulation, which takes into account the effects of local loading conditions, i.e. the contact pressure, between the contacting bodies (the small disc specimen and the punch) on the coefficient of friction. The aim of the work is to investigate the effects of the friction formulation used for the calculations on the numerical results representing the output of the test, i.e. the variation of the punch displacement versus time and the time to rupture. The calculations, carried out for various load levels, showed that the friction coefficient is not constant at all positions on the contacting surface between the punch and the specimen during the deformation process. The maximum value for the coefficient of friction is reached at the contact edge, which is a very important region in the specimen, because this is the position at which most of the creep deformation occurs. As expected, the displacement versus time curve (that is usually the only output obtained from experimental SPCTs) is affected by friction formulation which is used, as this directly influences the stress and strain fields in the specimen.