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The need of efficient modelling of textile materials at meso-scale increased considerably in the last decade. Several approaches have been proposed which present different kinds of drawbacks, the most important being their high computation time. The present paper aims to present a new tool for modelling textile materials using the yarn as constitutive element. Because fibre tows length is much higher than their transverse dimensions, beam elements seem to be the most convenient structural finite element tool. Unfortunately, classical beam theories assume that the cross section acts as a rigid which cannot describe the transverse compression and shape change of the yarn. In this paper, we present a new 3D beam element with the aim to achieve the results with section changes while breaking from classical beam hypothesis. Firstly, we start from 2D beam element with thickness change by adding a transverse strain component, which is inspired by previous works on the shell elements. Secondly, the formulation is extended to 3D beam elements, two transverse normal strain components are added with coupling so that full 3D constitutive law can be used. Finally, some numerical examples are presented using the new 3D beam elements which show that the results are exactly the same as those given by 3D elements in ABAQUS/Standard. [ABSTRACT FROM AUTHOR]

Abstract: The subject of this paper is the plate composed of two identical layers connected to each other in a discontinuous way, i.e. via discontinuous elements (connectors). This paper presents a model that describes the mechanical behavior of this plate by a system of exact, analytical (explicit) equations. The discrete distribution of discontinuous connectors is replaced by a fictitious continuous medium (interlayer). Accordingly, the plate is modeled as an equivalent three-layered plate: Two outer layers and a connecting inner interlayer. In order to obtain a fast and easy to use tool, something that is necessary for an analytical model to be chosen over finite elements and empirical formulas, modeling process is developed within the framework of two-dimensional elasticity. In so doing, the model also represents a means for attaining full comprehension of the mechanical phenomena that are involved, something that neither three-dimensional elasticity nor finite elements and empirical formulas can attain. The transition from three to two-dimensional behavior is obtained by relating the normal stress in the direction transverse to the plate to the distortion in the interlayer. The two-dimensional behavior is governed using kinematic and force assumptions that do not impose appreciable constraints on the stress–strain state and structural behavior. Starting from these assumptions, the paper develops the relationships between displacements and interface stresses, for both continuous and discontinuous connection. The latter relationships, which are used in this model, and the former relationships, which were used in a previously presented model, are discussed and compared to each other. The subsequent sections of the paper describe the model and present some real case applications of discontinuously-connected layered plate. [Copyright &y& Elsevier]

Shape-memory polymers (SMPs) represent a class of smart materials able to store a temporary shape and to recover the original shape upon an external stimulus, such as temperature. The present paper proposes a three-dimensional finite-strain phenomenological model for thermo-responsive SMPs, which distinguishes between two material phases presenting different properties and is based on a rule of mixtures. The proposed model is motivated by the earlier work of Reese et al. (2010) and it considers several significant material features that had not been addressed in previous phenomenological approaches. Specifically, the model reproduces both heating-stretching-cooling and cold drawing shape-fixing procedures and it takes into account the non-ideal behavior of realistic SMPs (i.e. imperfect shape-fixing and incomplete shape-recovery). Several numerical tests are reported to assess model performances, from simple uniaxial and biaxial tests to complex simulations of biomedical devices. Comparisons with experimental data taken from the literature are also provided to validate the model. The proposed improvements increase the model applicability over a wide range of polymer types and operating conditions. [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses transversely-cracked slender beams on elastic foundations. The bending problem of a cracked beam resting on Winkler’s soil is addressed by means of the finite element method. This paper thus covers the derivation of a new finite element, where the soil is modelled by classical Winkler’s soil model, and the cracked beam is represented by the simplified computational model, as widely-used for various analyses of transversely-cracked slender beams. The newly presented finite element has three nodes – one at each end of the finite element, and an additional internal node at the location of the crack. The stiffness matrix for the transversely-cracked slender beam, the corresponding load-vector for the linear continuous transverse load, as well as the derivation of transverse displacements’ interpolation functions are presented, and all expressions are derived at in closed symbolic forms. The presented approach is ideal for the effortless modelling of cracked beams in conditions where neither information about the crack’s growth nor the stresses at the crack’s tip is required. A numerical example covering several load situations is briefly presented to support the discussed approach. The results obtained with the presented approach are further compared with the values from a large 2D finite elements model, where a detailed description of the crack was accomplished. It is evident that the drastic difference in the computational effort is not reflected in any significant difference in the results between the models. [Copyright &y& Elsevier]

Abstract: Shotcrete is one of the main support elements for tunnels constructed according to the principles of the New Austrian Tunnelling Method (NATM). In this paper, a sophisticated constitutive model for the complex mechanical and time-dependent behaviour of shotcrete is presented, which is formulated within the framework of elasto-plasticity. Two independent yield surfaces govern the material behaviour in compression and tension under multi-axial loading conditions, which is further controlled by non-linear plastic strain hardening and softening rules following uniaxial stress–strain curves. The main novelty of the model is the introduction of normalised hardening and softening parameters which enable a more realistic simulation of the shotcrete loading history. In addition, cracking of the shotcrete is treated within the smeared crack concept by applying a fracture energy approach as a regularisation technique, which eliminates the dependency of the results on the size of the elements in a finite element mesh. Furthermore, the model takes into account the gradual change of the main material properties of the shotcrete due to cement hydration during the first 28days after spraying. Other important time effects such as creep, shrinkage and hydration temperature induced deformations at early ages are considered in the current model formulation. This paper aims to describe in detail the developed structure of the constitutive model and model calibration. [Copyright &y& Elsevier]

Abstract: This paper presents a three-dimensional elastic viscoplastic constitutive model that is able to reproduce the time dependent behaviour of soils with isotach viscosity. This constitutive law is based on the overstress theory and incorporates some important features, namely: (i) a non-linear creep law with a limit for the amount of creep deformation under isotropic stress conditions; (ii) a flexible loading surface that is capable of reproducing a wide range of shapes in p′− J stress space and incorporates the Matsuoka–Nakai failure criterion in the deviatoric stress space and (iii) assumes that the viscoplastic scalar multiplier is constant on a given loading surface to ensure that critical state conditions are reached. A full description of the model, its governing equations and implementation in a finite element program are presented. The model is then used to simulate the results of laboratory tests, highlighting the model’s abilities and shortcomings in reproducing the time dependent behaviour of soft clays. Furthermore, the paper investigates the importance of accounting for creep non-linearity and the consequences of isotach viscosity on the critical state line. [Copyright &y& Elsevier]

Abstract: The yield vertex non-coaxial model is different from classical elastoplastic models, in that there is an additional plastic strain rate tangential to yield surfaces, as well as the plastic strain rate normal to yield surfaces, when orientations of principal stress change. This feature raises concerns on its finite element implementations. In nonlinear finite element numerical iterations, a large tangential plastic strain rate is likely to make the trial total strain rate direct inside a yield surface, which entails convergence difficulty. Some modifications are introduced on the non-coaxial model itself to make numerical convergence easier in the work published in Yang and Yu (2010) . This paper is an extension of the previous work. Instead of modifying the non-coaxial model itself, this paper concerns the use of finite element explicit procedure, which is suitable for highly discontinuous problems. The simulations of shallow foundation load-settlement responses indicate that the finite element explicit procedure, assisted with a robust and explicit automatic substepping integration scheme of the non-coaxial model, does not encounter numerical difficulty. In addition, the overall trends of implicit and explicit simulations are similar. [Copyright &y& Elsevier]

Abstract: This paper first presents a critical review and assessment of the ability of the existing Drucker–Prager (D–P) type concrete plasticity models to predict the behavior of confined concrete using both experimental observations and numerical results. This assessment shows that for a D–P plasticity model to succeed in predicting the behavior of FRP-confined and other passively-confined concrete, it needs to be modified to possess the following three features: (a) a yield criterion including the third deviatoric stress invariant; (b) a hardening/softening rule which is dependent on the confining pressure; and (c) a flow rule which is dependent not only on the confining pressure but also on the rate of confinement increment. None of the existing D–P type models includes all three features, so they cannot be expected to lead to accurate predictions for both actively-confined and passively-confined (e.g. FRP-confined) concrete. A modified D–P type model, which includes all three features mentioned above, is then presented in this paper. The capability of the proposed model in providing close predictions of the behavior of both actively-confined and FRP-confined concrete is next demonstrated through comparisons between numerical predictions obtained using this modified D–P type model and available test results. Finally, the limitations of the proposed plasticity model are discussed. These limitations are addressed in the companion paper through the development of a plastic-damage model. [Copyright &y& Elsevier]

Abstract: This paper presents a numerical multiscale modelling strategy for simulating fracturing in materials where the fine-scale heterogeneities are fully resolved, with a particular focus on concrete. The fine-scale is modelled using a hybrid-Trefftz stress formulation for modelling propagating cohesive cracks. The very large system of algebraic equations that emerges from detailed resolution of the fine-scale structure requires an efficient iterative solver with a preconditioner that is appropriate for fracturing heterogeneous materials. This paper proposes a two-grid strategy for construction of the preconditioner that utilizes scale transition techniques derived for computational homogenization and represents an adaptation of the work of Miehe and Bayreuther and its extension to fracturing heterogeneous materials. For the coarse scale, this paper investigates both classical -continuous displacement-based finite elements as well as -continuous elements. The preconditioned GMRES Krylov iterative solver with dynamic convergence tolerance is integrated with a constrained Newton method with local arc-length control and line searches. The convergence properties and performance of the parallel implementation of the proposed solution strategy is illustrated on two numerical examples. [Copyright &y& Elsevier]

Abstract: A Tailor-Welded Blank (TWB) consists of steels of different thicknesses, strength types welded together to produce a single blank prior to the forming process. TWBs offer several notable benefits including decreased part weight, reduced manufacturing costs, increased environmental friendliness, and improved dimensional consistency. In order to take advantage of these benefits, however, designers need to overcome the formability of TWBs and be able to accurately predict unique characteristics related to TWB forming early in the design process. In this paper, a numerical model to predict the forming height dome and a specific forming curve of TWBs is presented. Finite element analyses of standard TWB forming tests (Nakazima) were performed in Arcelor Mittal Auto Application Research Center to determine the interaction between the weaker and the stronger materials. One of the most important aspects in the instability analysis is the problem of the measurement of the critical strain at necking. A new method is presented in this paper based on the analysis of the major strain rate using the discrete Gaussian convolution. A comparison of numerical and experimental results highlights a good agreement. The numerical approach offers a considerable gain to obtain specific FLC for all configurations. [Copyright &y& Elsevier]

Abstract: This paper deals with the development of a new second gradient model, its numerical implementation and its validation. In order to remedy to the spurious mesh dependency of the post localized computation enhanced models incorporating some internal length are necessary. These models are very time consuming. In this paper we present a simplified theory within the framework of constrained micromorphic models involving only the micro volumetric strain. Provided the use of an additional penalty term in the numerical treatment, this model is quite efficient to regularize problems modelling behaviors exhibiting plastic volumetric strain such as the ones of geomaterials. More over this model is notably less time consuming than the more general ones. [Copyright &y& Elsevier]

As an alternative to externally bonded FRP reinforcement, near-surface mounted (NSM) FRP reinforcement can be used to effectively improve the flexural performance of RC beams. In such FRP-strengthened RC beams, end cover separation failure is one of the common failure modes. This failure mode involves the detachment of the NSM FRP reinforcement together with the concrete cover along the level of the tension steel reinforcement. This paper presents a new strength model for end cover separation failure in RC beams strengthened in flexure with NSM FRP strips (i.e. rectangular FRP bars with a sectional height-to-thickness ratio not less than 5), which was formulated on the basis of extensive numerical results from a parametric study undertaken using an efficient finite element approach. The proposed strength model consists of an approximate equation for the debonding strain of the FRP reinforcement at the critical cracked section and a conventional section analysis to relate this debonding strain to the moment acting on the same section (i.e. the debonding strain). Once the debonding strain is known, the load level at end cover separation of an FRP-strengthened RC beam can be easily determined for a given load distribution. Predictions from the proposed strength model are compared with those of two existing strength models of the same type and available test results, which shows that the proposed strength model is in close agreement with test results and is far more accurate than the existing strength models. [ABSTRACT FROM AUTHOR]

Meso-level finite element analysis (FEA) is a popular way to study the influences of meso-level structure of concrete (namely the aggregate, the mortar and the Interfacial Transitional Zone (ITZ) structures) on the macro-level properties. However, it’s been a huge challenge to mesh the ITZ structure in concrete because of the unique layer structure of ITZ, which is 10–50 µm thick and rather small compared to the normal sizes of coarse aggregates. If ITZ were meshed by hexahedral elements or tetrahedral elements which were 10–50 μm in all three dimensions, millions of ITZ elements would be generated and it’s impossible to perform FEA on such a huge concrete model. In the current meso-level FEA in the literature, ITZ is either represented by zero-thick interface elements or over-thick elements, either of which is far from the real dimension of ITZ, leading to big discrepancies between the numerical results and experimental results. In this paper a method to generate ITZ meshes called aggregate-expansion method (AEM) is proposed to generate wedge elements around 50 µm thick to represent ITZ’s layer structure. The total number of generated ITZ meshes is limited and acceptable in meso-level FEA for concrete. A digital concrete specimen is generated from CT images with ITZ meshes generated by AEM and effects of ITZ on the compressive stress/strain/displacement distributions of concrete were studied. The characteristics of stress–strain response of the digital concrete specimen under tension were also studied and compared with experimental data. [ABSTRACT FROM AUTHOR]

Abstract: In the last decades, a number of hydro-mechanical elastoplastic constitutive models for unsaturated soils have been proposed. Those models couple the hydraulic and mechanical behaviour of unsaturated soils, and take into account the effects of the degree of saturation on the stress–strain behaviour and the effects of deformation on the soil–water characteristic response with a simple reversible part for the hysteresis. In addition, the influence of the suction on the stress–strain behaviour is considered. However, until now, few models predict the stress–strain and soil–water characteristic responses of unsaturated soils in a fully three-dimensional Finite Element code. This paper presents the predictions of an unsaturated soil model in a Three-dimensional Framework, and develops a study on the effect of partial saturation on the stability of shallow foundation resting on unsaturated silty soil. Qualitative predictions of the constitutive model show that incorporating a special formulation for the effective stress into an elastoplastic coupled hydro-mechanical model opens a full range of possibilities in modelling unsaturated soil behaviour. [Copyright &y& Elsevier]

Abstract: This paper presents a material model suitable for simulating the behavior of dry fabrics subjected to ballistic impact. The developed material model is implemented in a commercial explicit finite element (FE) software LS-DYNA through a user defined material subroutine (UMAT). The constitutive model is developed using data from uniaxial quasi-static and high strain rate tension tests, picture frame tests and friction tests. Different finite element modeling schemes using shell finite elements are used to study efficiency and accuracy issues. First, single FE layer (SL) and multiple FE layers (ML) were used to simulate the ballistic tests conducted at NASA Glenn Research Center (NASA-GRC). Second, in the multiple layer configuration, a new modeling approach called Spiral Modeling Scheme (SMS) was tried and compared to the existing Concentric Modeling Scheme (CMS). Regression analyses were used to fill missing experimental data – the shear properties of the fabric, damping coefficient and the parameters used in Cowper-Symonds (CS) model which account for strain rate effect on material properties, in order to achieve close match between FE simulations and experimental data. The difference in absorbed energy by the fabric after impact, displacement of fabric near point of impact, and extent of damage were used as metrics for evaluating the material model. In addition, the ballistic limits of the multi-layer fabrics for various configurations were also determined. [Copyright &y& Elsevier]

Abstract: Radially polarized piezoelectric fibers are now considered to be used in smart composites. The piezoelectric layers in these fibers are generally anisotropic in the transverse direction and therefore difficult to analyze when dynamic loads are involved. The present paper presents a theoretical study of the dynamic behavior of radially polarized cylindrical piezoelectric layers between isotropic elastic media. A new interphase model is developed to provide simple yet accurate evaluation of the dynamic response of such anisotropic elastic layers. Unlike the traditional interface-spring model, the current interphase model satisfies the equations of motion of the layers and can provide reliable prediction of the stress and displacement. A comparison between the developed model, the interface-spring model and the finite element analysis is conducted. The results clearly show the advantages of the current model over the traditional interface-spring model in simulating anisotropic layers. Numerical examples based on this interphase model for different interphase thicknesses, loading frequencies and material combinations are presented to evaluate the dynamic behavior of multilayered elastic media. [Copyright &y& Elsevier]

Abstract: This paper deals with a comparative study of several laminated plate theories with respect to their capability to capture the steep transverse stress gradients occurring in vicinity of free edges. The considered laminated plate theories pertain to the family of Equivalent Single Layer (ESL) as well as Layer-Wise (LW) descriptions. Reference is made to the classical displacement-based approach as well as to a partially mixed variational formulation, which allows to introduce independent assumptions for the transverse stresses and the displacements. Finite element solutions are obtained for free-edge effects that arise in several representative laminates subjected to uniaxial tension. An equivalent stress measure is proposed for assessing the three-dimensional (3D) stress fields predicted by the various theories. It is shown that refined LW models can provide quasi-3D results that compare well with full 3D FEM computations, whereas ESL models fail to capture the free-edge effects. Present results indicate that free-edge effects induced by a ±45° interface are most critical for the accuracy of laminated plate models. [Copyright &y& Elsevier]

Abstract: In this paper, a new set of models in the framework of Carrera’s Unified Formulation (CUF) is presented for the static analysis of sandwich plates. Concerning the study of multilayered structures, it is important to fulfill the interlaminar continuity conditions for the transverse stresses. For this aim, the CUF has been conceived by allowing to handle in a unified manner many theories that can differ by the order of expansion and the variables description in the thickness direction. This last can be Equivalent-Single-Layer (ESL), if the variables are assumed for the whole laminate, or Layer-Wise (LW), if the variables are described independently for each layer. The models considered in this work are derived from the Reissner Mixed Variational Theorem (RMVT) in order to model a priori the transverse shear and normal stresses. If sandwich plates with composite faces are considered, the transverse stresses are described as LW while the displacements are assumed ESL in the faces and LW at sandwich level (faces+core). This procedure permits to save degrees of freedom, preserving the same accuracy of a full layer-wise description. The new formulation is implemented in the framework of finite element analysis. Comparisons are made with 3D results. [Copyright &y& Elsevier]

Abstract: This paper presents the constitutive aspects and a finite element application for an energetic damage criterion within Cristescu’s viscoplastic constitutive law. The numerical model is implemented in finite element code LCPC-CESAR [1] by the author. The numerical solution is used to perform an analysis of the evolution of the damage zones around a circular lined cavity in a viscoplastic material subjected to a far field stress. Two important factors regarding the opening stability, namely the lining mounting time and the tunnel face influence, are analyzed. The initial stress of rock mass varies with the depth at which the tunnel is excavated and this fact determines a bigger displacement of the tunnel bottom than the tunnel ceiling. The time emphasizes this asymmetry. The results obtained are in completely accordance with the practical observations. [Copyright &y& Elsevier]

Abstract: This paper reports on the formulation and implementation of the displacement and stress models of the hybrid-Trefftz finite elements for elastostatic problems defined on saturated porous media. The supporting mathematical model is the (u–w) formulation of the Biot theory of porous media. The hybrid-Trefftz models are derived from the corresponding (pure) hybrid models by selecting the domain trial functions from the free-field solutions of the governing Navier equation. The resulting elements are highly robust and convergent, as they embody the physical characteristics of the modelled problem. Moreover, all coefficients present in the solving system are defined by boundary integral expressions. [Copyright &y& Elsevier]

Abstract: The Third-order Plate Theory proposed by Reddy for modeling laminated composite plates has earned wide acceptance in the engineering community. It involves the same five generalized displacement components as the first-order models (e.g. Mindlin’s) and, at the same time, its higher-order expansion across the thickness enables it to provide more accurate displacements and layer-wise stress estimates. However, its FEM implementation is somewhat hindered by the need to employ a continuous basis for the transverse displacement . In this paper, an instance of the Generalized Finite Element Method, GFEM, which allows an arbitrary continuity, is used to solve arbitrary anisotropic laminated composite plate bending problems. The resultant basis functions naturally exhibit inter-element continuity and can be easily enriched to generate arbitrary p-enriched basis functions. These characteristics result in excellent abilities in terms of approximating the layer stresses. In particular, the high degree of the basis, combined with its continuity, enables the transverse shear stresses to be integrated from the local equilibrium equations, and also post-processed in a scaling operation explored by the authors to provide additional accuracy of the estimates across the thickness. Additionally, all of the estimated strain and stress fields are naturally continuous, without the need for any heuristic averaging or smoothing operation. The procedure is robust enough to allow for Partition of Unity (PoU) construction free of geometrical restrictions on the elements and it is suitable for mixed formulations, using continuous functions only for those variables which require such continuity, in order to reduce the computational cost. The method is implemented with three-node triangular elements, and its performance is illustrated through comparisons with analytic solutions, with special emphasis on the computation of the transverse stress field for thick laminates. [Copyright &y& Elsevier]

Abstract: High performance fiber reinforced cement-based composites (HPFRCCs) are distinguished from regular cement materials by their strain hardening behavior under uniaxial tension as well as significantly enhanced durability, damage tolerance, and shear resistance. This paper presents a three-dimensional constitutive model for the nonlinear finite element analysis of HPFRCC structures. The proposed material model is an orthotropic hypoplastic model. Based on the smeared rotating crack approach, the directions of orthotropy are assumed to coincide with the principal strain directions. The constitutive model is capable of accounting for the general nonlinear behavior of HPFRCC, including the effects of multiple narrow cracking, crack localization, and compression crushing. The performance of the proposed model is demonstrated using data from experimental tests carried out on a punching shear slab and a two-span continuous beam. Comparisons between numerical solutions and experimental results suggest that the developed material model is able to represent the observed experimental behavior with reasonable accuracy. [Copyright &y& Elsevier]

Abstract: This paper introduces a finite strain extension of a non-linear visco-plastic material model, previously proposed by the authors, and its application to the finite element simulation of incremental cold forming processes of thermoplastics, demonstrated on PVC. Preserving the original structure of the model, its finite strain extension does not rely on any presumed kinematic split, either multiplicative or additive, among elastic and inelastic parts. It uses a systematic replacement of the strain and stress tensors and their rates by their respective spatial counterparts. A deviatoric Oldroyd rate is introduced to preserve the objectivity as well as the deviatoricity of the integration of the rate forms of deviatoric tensors. To cope with the incremental loading paths within the process, where through-thickness variations of the variables gain importance, the material model is posed in 3D formulation. The developed model is implemented as an /UMAT subroutine and used in the simulations following parameter identification studies. The numerical results are compared with analogous experimental ones to evaluate the performance of the material model where PVC sheets of three different thicknesses are formed incrementally with path controlled tool force monitoring. The investigations have the following consequences: the deformation-limited homogeneous stress–strain portion at uni-axial tensile tests, which is generally used in parameter identification of the constitutive model, is not able to reflect the post necking regime and its extrapolation ends up with a stiffer response with much less retained strains. Once a semi-inverse parameter identification is followed by taking into account the overall experimental outputs, one ends up with a considerable improvement in the tool force, geometry and the wall thickness predictions. Nevertheless, these improvements are inversely proportional with the sheet thickness where the local indentation effects (strains and stresses) become larger. [Copyright &y& Elsevier]

Abstract: In this paper, employing the logarithmic (or Hencky) strain as a more physical measure of strain, the time-dependent response of compressible viscoelastic materials is investigated. In this regard, we present a phenomenological finite strain viscoelastic constitutive model, developed within the framework of irreversible thermodynamics with internal variables. The formulation is based on the multiplicative decomposition of the deformation gradient into elastic and viscoelastic parts, together with the use of the isotropic property of the Helmholtz strain energy function. Making use of a logarithmic mapping, we present an appropriate form of the proposed constitutive equations in the time-discrete frame. Numerical examples are presented to show features of the new proposed model. In these examples, behavior of a bushing system under radial, torsional and combined radial–torsional loadings is studied. A very good agreement is observed between the predicted results and experimental data reported in the literature. [Copyright &y& Elsevier]

Abstract: This paper presents the possibility of applying the finite element method for the analysis of stress level in hard dental tissues, restored with class I dental filling and exposed to thermal and mechanical load. The studies were made on a geometrical model imitating the real geometry of a premolar tooth obtained using the X-ray microtomography technique and CAD software. The distributions of reduced stress defined in accordance with the Huber–Mises–Hencky (H–M–H) hypothesis in hard dental tissues were analyzed, and assessment of the degree of strength of the adhesive layer at the border of the composite restoration and biological tissue was attempted. The application of numerical simulations (Abaqus) enables real assessment of the tooth tissue strength, which allows assessing the risk of unsuccessful dental treatment, and helps prepare rational methods of preventing tooth damage resulting from load. Maximum reduced stresses were located in areas of the external load attachment and exceeded 668.8MPa with the force loading and 34MPa and 58.4MPa with temperature loading of 55°C and 5°C respectively. Superposition of loadings has produced maximum stresses of 669.4MPa in the case of 5°C. [Copyright &y& Elsevier]

Abstract: This paper discusses the results of one finite element modeling strategy to assess the behavior of pipelines buried in rainy forest regions, which are prone to failures by axial stresses from land movement. Two failures had already been investigated; conclusions of Root Cause Analyses agree with numerical predictions. The model allows quantifying soil displacements that load the system, a parameter that could not be estimated by geotechnical specialists. The model also confirmed other facts suggested by different failure analysis with no trivial theoretical demonstration, such as the notable effect of pipe diameter. The model is based on a three-dimensional simulation of the zone under analysis, which can be up to 1 km long. The finite element method is used for the resolution of partial derivative differential equations and incorporates complex nonlinear physical–mathematical models. A typical geometry considers a 20m wide and up to 20m deep right of way, supported in the solid rock layer. Two sufficiently documented events were used to verify if the tool really reproduces the stress state in the pipe due to soil movements. The model is properly adjusted using field instrument data and test results from the region under study, which include geotechnical measurements and pipe strains via vibrating wire strain gauges. The tool is meant to assist the Line Operators on the Integrity Management Policy. [Copyright &y& Elsevier]

Abstract: This paper presents and discusses a hybrid-mixed stress finite element model based on the use of polynomial wavelets for the physically non-linear analysis of concrete structures. The effective stress and the displacement fields in the domain of each element and the displacements on the static boundary are independently approximated. As none of the fundamental equations is locally enforced a priori, the hybrid-mixed stress formulation enables the use of a wide range of functions. In the numerical model reported here, all approximations are defined using complete sets of polynomial wavelets. These bases present some important features. In one hand, the functions are orthogonal, which is an important issue when implementing hybrid-mixed stress elements as it ensures high levels of sparsity. On the other hand, the polynomial wavelet basis is defined through linear combinations of Legendre polynomials. This fact enables the use of closed-form solutions for the computation of the integrations involved in the definition of all linear structural operators. A simple isotropic damage model is adopted and a non-local integral formulation where the strain energy release rate is taken as the non-local variable is considered. The numerical model is both incremental and iterative and is solved with a modified Newton–Raphson method that uses the secant matrix. Classical benchmark tests are chosen to illustrate the use of the model under discussion and to assess its numerical performance. [Copyright &y& Elsevier]

Abstract: This paper reports an analytical exploration into excess pore pressures generated during offshore spudcan installations. The analysis was conducted using ABAQUS/Explicit for three effective-stress constitutive models coded using the user-defined material subroutine VUMAT. The results demonstrate the feasibility of conducting effective-stress finite element analysis of undrained spudcan penetration using Eulerian approach. They also show that the computed penetration resistance and pore pressure response depend significantly on the undrained shear strength computed by the different models. [Copyright &y& Elsevier]

Abstract: The hybrid-Trefftz displacement and stress elements for poroelasticity are applied here to the spectral analysis of bounded saturated porous media. The displacement model is derived from the direct approximation of the displacement and fluid seepage fields in the domain of the element and of the tractions and pore pressures in the solid and fluid phases, respectively, on the Dirichlet boundary of the element. Conversely, the stress model is obtained by the direct approximation of the total stress and pore pressure fields in the domain, while independent approximations of the displacement and fluid seepage fields are enacted on the Neumann boundaries. As typical of the Trefftz methods, for both models, the domain approximation bases are constrained to satisfy locally all field equations. The central objective of the paper is to present a consistent set of tests designed to evaluate the ability of the proposed models to accurately predict the response of saturated porous media subjected to harmonic excitation and to assess the corresponding convergence patterns. Emphasis is placed on some key advantages of the presented formulation, namely the insensitivity of the results to gross mesh distortion, to near-incompressibility of the medium and to the wavelength content of the propagating wave, which enables the use of frequency-independent finite element meshes. [Copyright &y& Elsevier]

Abstract: This paper presents a safety evaluation of steel-plate girder bridges subjected to Military Load Classification (MLC). Three-dimensional finite element models are developed to predict the bridge response, including three different span lengths (L =12m, 24m, and 36m) that represent short- and medium-span bridges. A total of 36 load cases are considered to examine the flexural behavior of the bridges. Evaluation methodologies used here are a critical weight approach and load rating based on the allowable stress rating (ASR), load factor rating (LFR), and load and resistance factor rating (LRFR) methods. The gross weight of the MLC truck is a dominant parameter for the safety of the bridges, rather than longitudinal axle spacing. Load-sharing effects between the girders improve the behavior of the bridge superstructures. Existing empirical formulas developed for nonstandard civilian trucks (e.g., Formula B) exhibit noticeable errors for MLC applications with an average error ranging on the order of 6.7–17.9. The LFR (operating) and the LRFR methods show acceptable rating factors. A safety index of 2.5 is recommended for the evaluation of bridges subjected to MLC trucks. A simplified formula is proposed to promptly assess the critical weight of MLC trucks for short- and medium-span bridges. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to develop a probabilistic model for a stiffened panel subjected to correlated growth of cracks in the stiffener and plate elements. The geometry functions of the correlated cracks in the plate and in the stiffener are defined based on the stress intensity factors calculated by finite element analysis. A validation of the stress intensity factor and the geometry function calculation has been performed for an isolated crack in a plate with a central/edge through thickness crack. The Paris–Erdogan law is used to predict the crack propagation. Monte Carlo simulation is employed to define the statistical descriptors of the crack growth in the stiffened panel under different correlation functions and a probabilistic model of crack size as a function of time are presented adopting a truncated normal distribution to describe the probability density function of the crack size in the plate and in the stiffener. A procedure for the development of a probabilistic crack growth model for a stiffened panel has been proposed, allowing for the existence of multiple cracks both in the stiffeners and in the plate and accounting for the correlation between them. The developed probabilistic model may be used for fatigue crack growth analysis and is suitable for reliability assessment of a stiffened panel subjected to correlated crack growth. [Copyright &y& Elsevier]

Abstract: The analysis of parallel cracks in an elastic orthotropic material, representing a fibre reinforced elastic composite is important from practical point of view. Such a case takes place in many engineering problems, particularly in operation of aircrafts, where local parallel cracks in structural parts of airplane can appear. The most important is to investigate if the cracks are stable or become suddenly unstable under certain level of loading. The paper presents analytical, numerical and experimental studies of the parallel cracks propagation and interaction. Two cases of cracks configuration were considered: two equal cracks and two un-equal cracks. The mathematical model was elaborated for two parallel cracks with different lengths in Mode I of fracture. Following Muskhelishvili formalism the stress and displacement fields were determined in the vicinity of the crack tips and using Griffith–Irwin theory the interaction between cracks was studied. The numerical calculations done within Finite Element Analysis (FEA) allows for estimations of the G I and G II for different directions of cracks propagation. The important for kinks initiation is the value of G II, but the growth of the cracks depends mainly on G I in considered two cases of cracks arrangement. The tests were performed for the orthotropic polymer matrix composite material used for production of helicopter parts. The two cases of cracks configuration were experimentally examined, i.e. the equal and un-equal cracks. In order to assess the displacement and strain fields in the tested materials, the 3-D digital image correlation system ARAMIS was used. The system allows for displacement and strain measurement in all three directions, on the whole measured area of a specimen, particularly near edges of cracks. Comparison to analytical analysis and numerical calculations confirms correctness of the proposed models. [Copyright &y& Elsevier]

Abstract: In this paper a bond–slip relationship for long anchored bar has been proposed for modeling the structural behavior of r.c. elements and joints, able to take into account the interaction phenomena between ribbed bars and concrete also in condition of highly-stressed reinforcement. In such conditions some factors play a key role in modifying maximum tangential stress which can be transferred, for example the variation of the section area of the bar due to the Poisson’s effect, as well as the modification of the geometry of the ribs due to yielding. The proposed formulation has been developed by considering mean parameters, in order to obtain a tool usable also with general-purpose finite element codes. A first series of validation tests have been carried out by means of FE simulations of experimental pull-out tests on long anchored bars. Then the proposed formulation has been applied to simulate the well-known experimental tests carried out by Leonhardt and Walter on beams and finally to reproduce the cyclic response of a beam-column joint highly affected by the bond conditions of the longitudinal reinforcement. [Copyright &y& Elsevier]

Abstract: This paper details the numerical implementation of a constitutive model for unidirectional (UD) polymer-matrix fibre-reinforced composites, which is able to accurately represent the full non-linear mechanical response. Features such as hydrostatic pressure sensitivity, the effect of multiaxial loading and the dependence of the yield stress on the applied pressure are often neglected in constitutive modelling, but are included in this model. The constitutive model includes a novel yield function, non-associative flow rule and a non-linear kinematic hardening rule. It is combined with suitable failure criteria and associated damage model. The complete model is implemented in an explicit finite element code. Experimental test data is used to show that the model is able to predict the non-linear response of both unidirectional and multidirectional composite laminates. The model is shown to accurately predict the constitutive response under complex multiaxial loading and unloading, including significant hydrostatic pressure. Predictions are also shown to compare favourably for the evolution of matrix cracking after initial matrix cracking is detected by the failure criteria. [Copyright &y& Elsevier]

Abstract: There has been much work over the past two decades to aid the design and assessment engineer in the selection of a suitable material model of creep for high temperature applications. The model needs to be simple to implement as well as being able to describe material response over long times. Familiar creep models, as implemented in the majority of nonlinear finite element analysis systems, are still widely used although not always accurate in modeling creep behavior at the end of the secondary phase. The Characteristic Strain Model (CSM) has been shown to be able to effectively model creep behavior at long times; it is simple to implement and requires a minimum of creep data. This paper examines the ability of the CSM to model the recognized behavior of the steady state creep of simple structures under multi-axial stress. [Copyright &y& Elsevier]

Abstract: This paper presents recent developments of a simplified finite element method called the inverse approach (IA) for the estimation of large elastoplastic strains and thickness distribution in tube hydroforming. The basic formulation of the IA, proposed by , has been modified and adapted for the modeling of three-dimensional tube hydroforming problems in which the initial geometry is a circular tube expanded by internal pressure and submitted to axial feed at the tube ends. The application of the IA is illustrated through the analyses of numerical applications concerning the hydroforming of axisymmetric bulge, made from aluminum alloy 6061-T6 tubing, the hydroforming of square section hollow component and the hydroforming of a free Tee extrusion from welded low carbon steel LCS-1008 tubing. Verifications of the obtained results have been carried out using experimental results together with the classical explicit dynamic incremental approach using ABAQUS® commercial code to show the effectiveness of our approach. [Copyright &y& Elsevier]

Abstract: This paper provides experimental validation of the approach for simulating ductile failure using finite element methods, recently proposed by the authors. The proposed method is based on a phenomenological stress-modified fracture strain model. Incremental damage is defined by the ratio of the plastic strain increment to the fracture strain, and total damage is calculated using linear summation. When the accumulated damage becomes unity, all stress components at the finite element gauss point are reduced to a small value to simulate progressive failure. The proposed method is validated against four experimental data sets of cracked specimens made of three different materials. Despite the simplicity of the proposed method, the simulated results agree well with experimental data for all cases considered, providing sufficient confidence in the use of the proposed method to simulate ductile failure. [Copyright &y& Elsevier]

Abstract: We describe a significant extension of the finite element method (FEM) that allows finite element analysis (FEA) to be performed in situ, on a native geometric representation of a solid domain. The proposed method, called Scan&Solve, is a particular implementation of the solution structure method (SSM) that builds on the classical ideas of Kantorovich and Rvachev. It can be applied to any geometric model and used within any geometric modeling system that supports two fundamental queries: point membership testing and distance to boundary computation. The advantages of this approach include unmatched flexibility in handling geometric errors, small features, complex boundary conditions, and interfaces, while maintaining most of the benefits of classical FEA. This paper describes the technical background behind the proposed method, compares it to classical FEA formulation, details its implementation, and demonstrates its advantages. [Copyright &y& Elsevier]

Abstract: In the present paper, an estimation is made to investigate the transient phenomena in magneto-thermoelastic model in the context of the theory of generalized thermoelasticity LS model with variable thermal conductivity. FEM is proposed to analyze the problem and obtain the numerical solutions for the displacement, temperature, and radial and hoop stresses. The boundary conditions for the mechanical and Maxwell’s stresses at the internal and outer surfaces is considered. An application of an infinitely long annular cylinder is investigated for the inner surface is traction free and subjected to thermal shock, while the outer surface is traction free and thermally isolated. Finally, the displacement, incremental temperature, the stress components are obtained and then presented graphically. [Copyright &y& Elsevier]

Abstract: The paper presents a procedure for the formulation of constitutive equations for rate-independent pseudoelastic SMA material models. The procedure applies a rheological scheme representing mechanical properties of the material. An additive decomposition of strains into two parts is proposed. The first part describes strains of a perfectly elastic body while the second part may be represented by a combination of a rigid perfectly elastic body and a rigid perfectly plastic body. It is demonstrated that the key problem of formulation of constitutive relationships is to derive the 1st order differential equation with respect to the tensor describing the second part of the strain field. This equation may be obtained in explicit form starting from the variational inequalities defining non-elastic parts of rheological model. The uniqueness of the obtained differential equation has been proved. A numerical implementation of the constitutive relationships of SMA material was done through the user subroutine module VUMAT within the FE commercial code ABAQUS/Explicit. As an example we analyzed the problem of vibration of a simple 3D structure made of SMA. [Copyright &y& Elsevier]

Abstract: The paper considers two techniques to model the Cone Penetration Test (CPT) end resistance, qc in a dense sand deposit using commercial finite element programmes. In the first approach, Plaxis was used to perform spherical cavity expansion analyses at multiple depths. Two soil models, namely; the Mohr–Coulomb (MC) and Hardening Soil (HS) models were utilized. When calibrated using simple laboratory element tests, the HS model was found to provide good estimates of qc . However, at shallow depths, where the over-consolidation ratio of the sand was highest, the relatively large horizontal stresses developed prevented the full development of the failure zone resulting in under-estimation of the qc value. The second approach involved direct simulation of cone penetration using a large-strain analysis implemented in Abaqus/Explicit. The Arbitrary Lagrangian Eulerian (ALE) technique was used to prevent excessive mesh deformation. Although the Druker–Prager soil model used was not as sophisticated as the HS model, excellent agreement was achieved between the predicted and measured qc profiles. [Copyright &y& Elsevier]

Abstract: The paper presents several cost-effective modeling strategies that can be used by structural engineers in practice to determine the stresses in the spliced members. The computational efficiency and the modeling effort required for the several modeling options are also discussed. The deformation mechanisms and load transfer for several types of connections are illustrated. Optimization techniques are also presented to economize the computer time for connections with large number of bolts. Results are presented to compare the accuracy of several modeling strategies commonly used in practice. It is shown that for eccentric connections, the flexural bending largely affect the maximum tensile and compressive stresses within the joint. The difference may reach up to 54%. Finally, Experimental comparisons are made with the numerical procedures for typical connection model. [Copyright &y& Elsevier]

Abstract: Analytical backward Euler stress integration is presented for a volumetrically non-associated pressure-sensitive yield criterion based on a modified Reuleaux triangle. This advances previous work on associated Reuleaux plasticity using energy-mapped stress space. The analytical solution is 2–4 times faster than a standard numerical backward Euler algorithm. The merit in transforming to (and operating in) this space is that the stress return is truly the closest point on the surface to the elastic trial state. The paper includes a tension cut-off (formed by a second cone) and describes the steps necessary to allow the model’s incorporation within a finite deformation framework. Finite-element results show a 59% runtime saving for a modified Reuleaux model over a Willam–Warnke cone giving comparable accuracy in a thick-walled cylinder expansion problem. The consistent tangent provides asymptotically quadratic convergence in the Newton–Raphson scheme under both (i) small strain, infinitesimal deformation and (ii) large strain, finite deformation finite-element simulations. It is shown that the introduction of non-associated flow changes the plastic deformation field and reduces the heave predicted in a plane strain rigid strip-footing problem. The proposed model offers a significant improvement over the Drucker–Prager and Mohr–Coulomb formulations by better reproducing the material dependence on the Lode angle and intermediate principal stress, at little extra computational effort. [Copyright &y& Elsevier]

Abstract: Pin-loaded connections are widely used in the industry. Connecting rods of reciprocating engines in automotive applications or pin-loaded lugs of landing gears and airframe structures can be cited as examples. These systems are subject to thermomechanical cyclic loadings and fatigue mechanisms are often observed. The calculation of stresses in the lug is crucial in view of a fatigue lifetime analysis. Analytical modelling may be very helpful in the early design stage, by allowing fast parametric studies and the identification of the most influent parameters on the response in stresses. In this paper, we propose analytical models for bush fitting and pin-loading conditions, leading to the complete calculation of the stress distribution in the lug. In each case, the analytical solutions are compared with finite element simulations. In the last part, we perform a sensitivity analysis as an application of the presented analytical tools. [ABSTRACT FROM AUTHOR]

Abstract: In this paper creep crack growth behaviour of P92 welds at 923K are presented. Creep crack growth behaviour for P92 welds are discussed with C * parameter. Creep crack growth behaviour of P92 welds has been compared with that of P91 welds with C * parameter. NSW and NSW–MOD model were compared with the experimental creep crack growth data. Plane strain NSW model significantly overestimates the crack growth rate, and plane stress NSW model underestimates it. Whilst, NSW–MOD model for plane stress and plane strain conditions gives lower and upper bound of the experimental data, respectively. FE analysis of creep crack growth has been conducted. Constrain effect for welded joints has been examined with C * line integrals of C(T) specimens. As a result, constant C * value using the material data of welded joint gives 10 times lower than that of only HAZ property. Whilst, the predicted CCG rates for welded joint are 10 times higher than those for only HAZ properties. Compared with predicted CCG rate from FE analysis and the experimental CCG rate, it can be suggested that creep crack growth tests for lower load level or for large specimen should be conducted, otherwise the experimental data should give unconservative estimation for components operated in long years. [ABSTRACT FROM AUTHOR]

Abstract: A new finite element model based on the coupled displacement field and the tapering functions of the beam is formulated for transverse vibrations of rotating Timoshenko beams of equal strength. In the coupled displacement field, the polynomial coefficients of transverse displacement and cross-sectional rotation are coupled through consideration of the differential equations of equilibrium. The tapering functions of breadth and depth of the beam are obtained from the principle of equal strength in the longitudinal direction of the beam. After finding the displacement functions using the tapering functions, the stiffness and mass matrices are expressed by using the strain and kinetic energy equations. A semi-symbolic computer program in Mathematica is developed and subsequently used to evaluate the new model. The results of the illustrative example regarding the problem indicated in the title of this paper are obtained and compared with the results found from the models created in ABAQUS. Very good agreement is found between the results of new model and the other results. [ABSTRACT FROM AUTHOR]

Abstract: Finite element modeling of the impact of flexible woven fabrics using a yarn level architecture allows the capturing of complex projectile-fabric and yarn–yarn level interactions, however it requires very large computational resources. This paper presents a multiscale modeling technique to simulate the impact of flexible woven fabrics. This technique involves modeling the fabric using a yarn level architecture around the impact region and a homogenized or membrane type architecture at far field regions. The level of modeling resolution decreases with distance away from the impact zone. This results in a finite element model with much lower computational requirements. The yarns are modeled using both solid and shell finite elements. Impedances are matched across all interfaces created between the various regions of the model to prevent artificial reflections of the longitudinal strain waves. A systematic approach is presented to determine geometric and material parameters of the homogenized zone. The multiscale model is extensively validated against baseline models. The limitations of using shell elements to model the yarn level architecture underneath the projectile are addressed. [Copyright &y& Elsevier]

Abstract: The mechanism underlying plasticity-induced shielding of a crack tip under fatigue loading has been already experimentally investigated by means of photoelasticity using a recently-developed mathematical model which considers stress field near the crack tip and along the flanks. Stress intensification factors have also been defined to describe shielding effects on the applied elastic field. In this paper a new application of this model is developed through a numerical simulation of the experimental tests, which were previously performed. The study is aimed to analyze the shielding effect related to constant amplitude cycling loading and a single overload peak, considering numerical simulation. By means of the models developed by XFEM technique, the plastic region is reproduced finding a good agreement with the experimental data, and a systematic procedure is proposed to evaluate the stress intensity factors. A good correspondence is found by comparing the numerical with the experimental parameters, obtained from the mathematical model. [Copyright &y& Elsevier]

Abstract: Laboratory and field experiments have shown that secondary fracture treatment along a different direction to the primary hydraulic fracture can increase the recovery of gas from tight sands. Success of a restimulation treatment (secondary fracture treatment) is, however, highly dependent on transient stress distribution around the well. In this paper a numerical poroelastic reservoir model is used to provide a more realistic picture of stress field around a stimulated well during post-fracture production. Initiation of a re-oriented hydraulic fracture and its interaction with the primary hydraulic fracture are also studied using a wellbore re-pressurization model that includes a poroelastic formation, a wellbore and a pair of finite conductive hydraulic fractures. Numerical results have shown that during post-fracture production the directions of maximum and minimum horizontal stresses are reversed within a large area around the wellbore and the hydraulic fractures. We have also shown that relatively small areas exist at the wellbore wall where the original directions of horizontal principal stresses remain unchanged. It is shown that the presence of these small areas could act against initiation of a secondary hydraulic fracture along the most desired directions in terms of recovery enhancement. This study also shows that oriented perforations prior to refracture treatment help initiate secondary fractures in a preferred direction before the primary hydraulic fractures start propagation during re-pressurisation of the wellbore. [Copyright &y& Elsevier]