Hossein Sepiani, Maria Anna Polak and Alexander Penlidis
The purpose of this study is to present a finite element (FE) implementation of phenomenological three-dimensional viscoelastic and viscoplastic constitutive models for long term…
Abstract
Purpose
The purpose of this study is to present a finite element (FE) implementation of phenomenological three-dimensional viscoelastic and viscoplastic constitutive models for long term behaviour prediction of polymers.
Design/methodology/approach
The method is based on the small strain assumption but is extended to large deformation for materials in which the stress-strain relation is nonlinear and the concept of incompressibility is governing. An empirical approach is used for determining material parameters in the constitutive equations, based on measured material properties. The modelling process uses a spring and dash-pot and a power-law approximation function method for viscoelastic and viscoplastic nonlinear behaviour, respectively. The model improvement for long term behaviour prediction is done by modifying the material parameters in such a way that they account for the current test time. The determination of material properties is based on the non-separable type of relations for nonlinear materials in which the material properties change with stress coupled with time.
Findings
The proposed viscoelastic and viscoplastic models are implemented in a user material algorithm of the FE general-purpose program ABAQUS and the validity of the models is assessed by comparisons with experimental observations from tests on high-density polyethylene samples in one-dimensional tensile loading. Comparisons show that the proposed constitutive model can satisfactorily represent the time-dependent mechanical behaviour of polymers even for long term predictions.
Originality/value
The study provides a new approach in long term investigation of material behaviour using FE analysis.
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The paper aims to present a method of implementing layered shell finite elements for punching shear analysis of reinforced concrete slabs. The emphasis is on the influence of…
Abstract
Purpose
The paper aims to present a method of implementing layered shell finite elements for punching shear analysis of reinforced concrete slabs. The emphasis is on the influence of different material modelling parameters on the calculated results.
Design/methodology/approach
The finite element approach utilizes quadratic isoparametric C0 shell elements. The elements take into account an out‐of‐plane shear response and allow implementation of three‐dimensional constitutive models and out‐of‐plane reinforcement. Through the consideration of 3D states of strain and stress, the formulation can predict structural failures caused by either flexure or punching shear.
Findings
Comparisons are shown between analytical solutions and several test results, which show that the presented non‐linear finite element formulation works well for modelling slab behaviour.
Originality/value
The most important contribution of this work is the use of shell elements for punching and flexure analysis of reinforced concrete slabs and the discussion on the influence of material modelling on the calculated results. Shell finite elements have been extensively used in the analysis of slabs for flexure. However, the critical issue in the design of these slabs is a 3D shear effect around the column area called punching shear. 3D elements can be used for punching shear analysis of reinforced concrete slabs, but the cost of using these elements and the computational effort make them impractical for real design situations. Therefore, shell finite elements, with appropriate element and material modelling formulations that make them applicable for punching shear analysis, are employed in the presented work.
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J.A. Alvarado‐Contreras, M.A. Polak and A. Penlidis
The purpose of this paper is to formulate an algorithm for a novel damage‐coupled material law for crystalline polyethylene at finite inelastic strains followed by investigation…
Abstract
Purpose
The purpose of this paper is to formulate an algorithm for a novel damage‐coupled material law for crystalline polyethylene at finite inelastic strains followed by investigation of the influence of the aggregate representation and material parameters on the material response.
Design/methodology/approach
The constitutive equations are developed within the framework of continuum damage mechanics to describe crystal fragmentation caused by atomic debonding of the crystallographic planes. The material is assumed initially isotropic and homogeneous and is represented as an aggregate of randomly oriented crystals with an orthorhombic lattice. For the velocity gradient, an additive decomposition into symmetric and skew‐symmetric components is applied, where the skew‐symmetric part (spin) is decoupled from the lattice shear by means of a damage variable. Structural features such as lattice parameters and orientations, slip systems, and kinematic constraints are incorpo‐rated.
Findings
The proposed model is implemented to predict stress‐strain behaviour under uniaxial tension and damage accumulation and texture development at the different stages of deformation. In the numerical examples, the effects of the aggregate size, crystal orientations, and material parameters on the model estimates are analyzed.
Originality/value
The model used herein is a first attempt to analyze the influence of crystal fragmentation caused by the debonding of the crystallographic planes on the predicted mechanical behaviour and texture development of polyethylene prior to failure.
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Gives a bibliographical review of the finite element methods (FEMs) applied for the linear and nonlinear, static and dynamic analyses of basic structural elements from the…
Abstract
Gives a bibliographical review of the finite element methods (FEMs) applied for the linear and nonlinear, static and dynamic analyses of basic structural elements from the theoretical as well as practical points of view. The range of applications of FEMs in this area is wide and cannot be presented in a single paper; therefore aims to give the reader an encyclopaedic view on the subject. The bibliography at the end of the paper contains 2,025 references to papers, conference proceedings and theses/dissertations dealing with the analysis of beams, columns, rods, bars, cables, discs, blades, shafts, membranes, plates and shells that were published in 1992‐1995.
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J.A. Alvarado‐Contreras, M.A. Polak and A. Penlidis
The purpose of this paper is to provide a computational procedure for a novel damage‐coupled material law for semicrystalline polyethylene. Using a damage mechanics approach, the…
Abstract
Purpose
The purpose of this paper is to provide a computational procedure for a novel damage‐coupled material law for semicrystalline polyethylene. Using a damage mechanics approach, the model seeks to gain insight into the mechanical behaviour of polyethylene considering the microstructure and degradation processes occurring under uniaxial tension.
Design/methodology/approach
The material morphology is modelled as a collection of inclusions. Each inclusion consists of crystalline material lying in a thin lamella attached to an amorphous layer. The interface region interconnecting the two phases is the plane through which loads are carried and transferred by the tie molecules. It is assumed that the constitutive model contains complete information about the mechanical behaviour and degradation processes of each constituent. After modelling the two phases independently, the inclusion behaviour is found by applying some compatibility and equilibrium restrictions along the interface plane.
Findings
The model provides a rational representation of the damage process of the intermolecular bonds holding crystals and of the tie‐molecules connecting neighbouring crystallites. The model is also used to analyze the degree of relationship between some of the material properties and the mechanical responses.
Practical implications
In practice, the numerical model clearly helps to understand the influence of the different microstructure properties on the tensile mechanical behaviour of semicrystalline polyethylene – an issue of particular interest in improving material processability and product performance.
Originality/value
To the authors’ knowledge, a phenomenon such as microstructural degradation of polyethylene has not received much attention in the literature. The proposed model successfully captures aspects of the material behaviour considering crystal fragmentation and tie‐molecule rupture.
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Bruno S. Sergi, Elena G. Popkova, Aleksei V. Bogoviz and Tatiana N. Litvinova
I.M.V. Caminiti, A. Formisano, M.C. Lupoli and R. Martone
The purpose of this paper is to propose the optimal allocation and alignment of probes for current distribution measurement (CDM) in the case of twin cable in conduit conductor…
Abstract
Purpose
The purpose of this paper is to propose the optimal allocation and alignment of probes for current distribution measurement (CDM) in the case of twin cable in conduit conductor (CICC) cables with equal and opposite current.
Design/methodology/approach
The most effective approach to CDM in CICC cables is to perform indirect measurements starting from magnetic field map measured externally to the cable. A number of approaches have been proposed to optimize the layout of magnetic field probes external to the cable, but all dealing with single cables. In this paper, an approach to the optimized design of measurement system for twin cables will be proposed, based on the minimization of a suitable cost function.
Findings
A method for the optimal allocation of probes both in terms of rejection of the background field and of condition number of the Green matrix has been defined.
Research limitations/implications
The method is valid only in the hypothesis of linear relationship between currents and magnetic field.
Practical implications
The proposed approach allows to design more robust CDM systems, with increased noise and background field rejection capability.
Originality/value
The problem of optimal design of CDM systems has been previously tackled in literature, but typically with reference to single cables. In the paper, an approach able to explicitly deal with twin cables is proposed.
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The aim of the current study is to recommend and compare the estimates of finite element model (FEM), analytical model, and artificial neural networks (ANN) model for capturing…
Abstract
Purpose
The aim of the current study is to recommend and compare the estimates of finite element model (FEM), analytical model, and artificial neural networks (ANN) model for capturing the LCC of FCSC members. A database comprising 325 FCSC columns was constructed from previous studies to propose FEM and ANN models while the analytical model was proposed based on a database of 712 samples and encasing mechanics of steel tube and FRP wraps. The concrete damage plastic model was used for concrete along with bilinear and linear elastic models for steel tube and FRP wraps, respectively. Analytical and ANN models effectively considered the lateral encasing mechanism of FCSC columns for accurate predictions.
Design/methodology/approach
The study aimed to compare the prediction accuracy of finite element (FEM), analytical, and artificial neural network (ANN) models for the load-carrying capacity (LCC) of fiber reinforced polymer (FRP)-encased concrete-filled steel tube (CFST) compression members (FCSC). A database of 325 FCSC columns was developed for FEM and ANN models, while the analytical model was based on 712 samples, utilizing encasing mechanics of steel tube and FRP wraps. FEM used a concrete damage plastic model, bilinear steel tube, and linear elastic FRP models. Statistical accuracy was evaluated using MAE, MAPE, R², RMSE, and a 20-index across all models.
Findings
Based on the experimental database, the FEM presented the accuracies in the form of statistical parameters MAE = 223.76, MAPE = 285.32, R2 = 0.94, RMSE = 210.43 and a20-index = 0.83. The analytical model showed the statistics of MAE = 427.229, MAPE = 283.649, R2 = 0.8149, RMSE = 275.428 and a20-index = 0.73 while ANN models portrayed the predictions with MAE = 195, MAPE = 229.67, R2 = 0.981, RMSE = 174 and a20-index = 0.89 for the LCC of FCSC columns.
Originality/value
Although various investigations have already been performed on the prediction of the load-carrying capacity (LCC) of fiber reinforced polymer (FRP)-encased concrete-filled steel tube (CFST) compression members (FCSC) using small and noisy data, none of them compared the accuracy of prediction of different modeling techniques based on a refined large database.
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Mojtaba Labibzadeh, Farhad Bostan Shirin and Amin Khajehdezfuly
This study aims to investigate the effects of using circular spirals as the longitudinal reinforcing bars on the performance of the concrete beams subjected to four-point bending…
Abstract
Purpose
This study aims to investigate the effects of using circular spirals as the longitudinal reinforcing bars on the performance of the concrete beams subjected to four-point bending load.
Design/methodology/approach
The effects of using circular spirals as the longitudinal reinforcing bars on the performance of the concrete beams subjected to four-point bending load are investigated in this study. Employing circular spirals as the main longitudinal reinforcement is a novel idea presented in this paper. In this regard, a finite element model of the beam with spiral longitudinal reinforcement was developed. After model verification, several configurations of concrete beams reinforced by longitudinal spirals were simulated under the four-point loading condition.
Findings
Obtained results showed that using the longitudinal spirals in place of the conventional longitudinal reinforcing bars can improve the bearing capacity of the concrete beam, but at the same time, increases its ductility unacceptably. In other words, the spirals reduce the initial stiffness of the beam significantly. To solve the problem, the authors decided to use the longitudinal spirals as the auxiliary bars added to the main conventional longitudinal bars in the beams. New gained results were satisfactory. By adding the longitudinal spirals to the conventional bars, not only the bearing capacity of the beam increases between 24% and 63%, but also the initial stiffness and ductility of the beam raises between 11%–29% and 3%–57%, respectively, in comparison to the corresponding beam reinforced with conventional longitudinal bars.
Originality/value
Employing circular spirals as the main longitudinal reinforcement is a novel idea presented in this paper.
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Using data from a multi-method study with a national reproductive justice coalition, this chapter examines the emergence of the US reproductive justice movement. I first examine…
Abstract
Using data from a multi-method study with a national reproductive justice coalition, this chapter examines the emergence of the US reproductive justice movement. I first examine how reproductive justice emerged in relation to the mainstream women's movements. Then I demonstrate how, due to the relationship between reproductive justice and social identity, the boundaries of the reproductive frame and movements are simultaneously broader and more constrained in meaning than reproductive rights. Finally, I show how (perceived) co-optation leads to tensions between movement sectors and weakens the potential for reproductive justice to reinvigorate activism around reproductive issues. I conclude with how the success of the reproductive justice movement, including around diversity and coalition building, can inform other social movements.