Can Ban, Na Na Pu, Yi Fei Zhang and Ma Wentao
This article aims to develop an accurate and efficient meshfree Galerkin method based on the strain smoothing technique for linear elastic continuous and fracture problems.
Abstract
Purpose
This article aims to develop an accurate and efficient meshfree Galerkin method based on the strain smoothing technique for linear elastic continuous and fracture problems.
Design/methodology/approach
This paper proposed a generalized linear smoothed meshfree method (LSMM), in which the compatible strain is reconstructed by the linear smoothed strains. Based on the idea of the weighted residual method and employing three linearly independent weight functions, the linear smoothed strains can be created easily in a smoothing domain. Using various types of basic functions, LSMM can solve the linear elastic continuous and fracture problems in a unified way.
Findings
On the one hand, the LSMM inherits the properties of high efficiency and stability from the stabilized conforming nodal integration (SCNI). On the other hand, the LSMM is more accurate than the SCNI, because it can produce continuous strains instead of the piece-wise strains obtained by SCNI. Those excellent performances ensure that the LSMM has the capability to precisely track the crack propagation problems. Several numerical examples are investigated to verify the accurate, convergence rate and robustness of the present LSMM.
Originality/value
This study provides an accurate and efficient meshfree method for simulating crack growth.
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Adel Chine, Amine Ammar and J.R. Clermont
The purpose of this paper is to compute flow effects of the transition from adherence-to-slip in two-dimensional flows, for a polymer melt obeying a memory-integral viscoelastic…
Abstract
Purpose
The purpose of this paper is to compute flow effects of the transition from adherence-to-slip in two-dimensional flows, for a polymer melt obeying a memory-integral viscoelastic equation, in isothermal and non-isothermal cases.
Design/methodology/approach
Temperature dependence is expressed by Arrhenius and William-Landel-Ferry models. A coupling approach is defined. For the dynamic equations, the Stream-Tube Method (STM) is used with finite differences in a mapped rectangular domain of the real domain, where streamlines are parallel and straight. STM avoids particle-tracking problems and allows simple formulae to evaluate stresses resulting from the constitutive equation. For the temperature field, a finite-element method is carried out to solve the energy equation in the real domain.
Findings
The approach avoids numerical problems arising with classical formulations and proves to be robust and efficient. Large elasticity levels are attained without convergence and refinement difficulties that may arise close to the “stick-slip” transition section. The method highlights the role of temperature conditions and reveals interesting differences for the ducts considered.
Practical implications
The results of the study are of interest for polymer processing where slip at the wall can be encountered, in relation with the physical properties of the materials.
Originality/value
The paper presents a simple approach that limits considerably numerical problems coming from stick-slip boundary conditions and avoids particle-tracking. Results are obtained at flow rates encountered in industrial conditions.
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M. Grujicic, R. Yavari, J.S. Snipes, S. Ramaswami and R.S. Barsoum
The purpose of this paper is to address the problems of interaction of tensile stress-waves with polyurea/fused-silica and fused-silica/polyurea interfaces, and the potential for…
Abstract
Purpose
The purpose of this paper is to address the problems of interaction of tensile stress-waves with polyurea/fused-silica and fused-silica/polyurea interfaces, and the potential for the accompanying interfacial decohesion.
Design/methodology/approach
The problems are investigated using all-atom non-equilibrium molecular-dynamics methods and tools. Before these methods/tools are employed, previously determined material constitutive relations for polyurea and fused-silica are used, within an acoustic-impedance-matching procedure, to predict the outcome of the interactions of stress-waves with the material-interfaces in question. These predictions pertain solely to the stress-wave/interface interaction aspects resulting in the formation of transmitted and reflected stress- or release-waves, but do not contain any information regarding potential interfacial decohesion. Direct molecular-level simulations confirmed some of these predictions, but also provided direct evidence of the nature and the extent of interfacial decohesion. To properly model the initial state of interfacial cohesion and its degradation during stress-wave-loading, reactive forcefield potentials are utilized.
Findings
Direct molecular-level simulations of the polyurea/fused-silica interfacial regions prior to loading revealed local changes in the bonding structure, suggesting the formation of an interphase. This interphase was subsequently found to greatly affect the polyurea/fused-silica decohesion strength.
Originality/value
To the authors’ knowledge, the present work is the first public-domain report of the use of the non-equilibrium molecular dynamics and reactive force-field potentials to study the problem of interfacial decohesion caused by the interaction of tensile waves with material interfaces.
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Mica Grujicic, Ramin Yavari, Jennifer Snipes, S. Ramaswami and Roshdy Barsoum
The purpose of this paper is to study the mechanical response of polyurea, soda-lime glass (glass, for short), polyurea/glass/polyurea and glass/polyurea/glass sandwich structures…
Abstract
Purpose
The purpose of this paper is to study the mechanical response of polyurea, soda-lime glass (glass, for short), polyurea/glass/polyurea and glass/polyurea/glass sandwich structures under dynamic-loading conditions involving propagation of planar longitudinal shockwaves.
Design/methodology/approach
The problem of shockwave generation, propagation and interaction with material boundaries is investigated using non-equilibrium molecular dynamics. The results obtained are used to construct basic shock Hugoniot relationships associated with the propagation of shockwaves through a homogeneous material (polyurea or glass, in the present case). The fidelity of these relations is established by comparing them with their experimental counterparts, and the observed differences are rationalized in terms of the microstructural changes experienced by the shockwave-swept material. The relationships are subsequently used to predict the outcome of the interactions of shockwaves with polyurea/glass or glass/polyurea material boundaries. Molecular-level simulations are next used to directly analyze the same shockwave/material-boundary interactions.
Findings
The molecular-level simulations suggested, and the subsequent detailed microstructural analyses confirmed, the formation of topologically altered interfacial regions, i.e. polyurea/glass and glass/polyurea interphases.
Originality/value
To the authors’ knowledge, the present work is a first attempt to analyze, using molecular-level simulation methods, the interaction of shockwaves with material boundaries.
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Mica Grujicic, S. Ramaswami and Jennifer Snipes
In the recent work, a new blast-wave impact-mitigation concept involving the use of a protective structure consisting of bimolecular reactants (polyvinyl pyridine+cyclohexyl…
Abstract
Purpose
In the recent work, a new blast-wave impact-mitigation concept involving the use of a protective structure consisting of bimolecular reactants (polyvinyl pyridine+cyclohexyl chloride), capable of undergoing a chemical reaction (to form polyvinyl pyridinium ionic salt) under shockwave loading conditions, was investigated using all-atom reactive equilibrium and non-equilibrium molecular-dynamics analyses. The purpose of this paper is to reveal the beneficial shockwave dispersion/attenuation effects offered by the chemical reaction, direct simulations of a fully supported single planar shockwave propagating through the reactive mixture were carried out, and the structure of the shock front examined as a function of the extent of the chemical reaction (i.e. as a function of the strength of the incident shockwave). The results obtained clearly revealed that chemical reactions give rise to considerable broadening of the shockwave front. In the present work, the effect of chemical reactions and the structure of the shockwaves are investigated at the continuum level.
Design/methodology/approach
Specifically, the problem of the (conserved) linear-momentum accompanying the interaction of an incident shockwave with the protective-structure/protected-structure material interface has been investigated, within the steady-wave/structured-shock computational framework, in order to demonstrate and quantify an increase in the time period over which the momentum is transferred and a reduction in the peak loading experienced by the protected structure, both brought about by the occurrence of the chemical reaction (within the protective structure).
Findings
The results obtained clearly revealed the beneficial shock-mitigation effects offered by a protective structure capable of undergoing a chemical reaction under shock-loading conditions.
Originality/value
To the authors’ knowledge, the present manuscript is the first report dealing with a continuum-level analysis of the blast-mitigation potential of chemical reactions.
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L. Ravi Kumar, P.K. Datta and D.L. Prabhakara
To predict the critical flutter load and frequencies of doubly curved panels using first‐order shear deformation theory considering the effects of shear deformation and rotary…
Abstract
Purpose
To predict the critical flutter load and frequencies of doubly curved panels using first‐order shear deformation theory considering the effects of shear deformation and rotary inertia.Design/methodology/approach – A finite element analysis procedure is based on the extension of dynamic, shear deformable theory initially according to Sanders' theory, which can be reduced to Love's and Donnell's theories by means of tracers.Findings – Flutter is observed to be more common than divergence under follower loading; the magnitude of the flutter load is gradually decreasing with the increasing cut‐out size; load bandwidth and type of load conditions have significant influence on flutter and divergence characteristics of both isotropic and laminated curved panels; damping is perceived to have significant effect on flutter behaviour; the effect of direction control parameter with damping significantly affects the critical load.Practical implications – The practical behaviour of follower forces involving: aerodynamic drag; engine thrust; cantilever pipe conveying fluid; gas turbine rotor; automatic control system application; and automobile disk brakes can be monitored more successfully.Originality/value – Will assist students of elastic systems, both conservative and non‐conservative.
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It has been usual to prefer an enrichment pattern independent of the mesh when applying singular functions in the Generalized/eXtended finite element method (G/XFEM). This choice…
Abstract
Purpose
It has been usual to prefer an enrichment pattern independent of the mesh when applying singular functions in the Generalized/eXtended finite element method (G/XFEM). This choice, when modeling crack tip singularities through extrinsic enrichment, has been understood as the only way to surpass the typical poor convergence rate obtained with the finite element method (FEM), on uniform or quasi-uniform meshes conforming to the crack. Then, the purpose of this study is to revisit the topological enrichment strategy in the light of a higher-order continuity obtained with a smooth partition of unity (PoU). Aiming to verify the smoothness' impacts on the blending phenomenon, a series of numerical experiments is conceived to compare the two GFEM versions: the conventional one, based on piecewise continuous PoU's, and another which considers PoU's with high-regularity.
Design/methodology/approach
The stress approximations right at the crack tip vicinity are qualified by focusing on crack severity parameters. For this purpose, the material forces method originated from the configurational mechanics is employed. Some attempts to improve solution using different polynomial enrichment schemes, besides the singular one, are discussed aiming to verify the transition/blending effects. A classical two-dimensional problem of the linear elastic fracture mechanics (LEFM) is solved, considering the pure mode I and the mixed-mode loadings.
Findings
The results reveal that, in the presence of smooth PoU's, the topological enrichment can still be considered as a suitable strategy for extrinsic enrichment. First, because such an enrichment pattern still can treat the crack independently of the mesh and deliver some advantage in terms of convergence rates, under certain conditions, when compared to the conventional FEM. Second, because the topological pattern demands fewer degrees of freedom and impacts conditioning less than the geometrical strategy.
Originality/value
Several outputs are presented, considering estimations for the
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J.P.M. Gonçalves, M.F.S.F. de Moura, P.M.S.T. de Castro and A.T. Marques
An interface finite element for three‐dimensional problems based on the penalty method is presented. The proposed element can model joints/interfaces between solid finite elements…
Abstract
An interface finite element for three‐dimensional problems based on the penalty method is presented. The proposed element can model joints/interfaces between solid finite elements and also includes the propagation of damage in pure mode I, pure mode II and mixed mode considering a softening relationship between the stresses and relative displacements. Two different contact conditions are considered: point‐to‐point constraint for closed points (not satisfying the failure criterion) and point‐to‐surface constraint for opened points. The performance of the element is tested under mode I, mode II and mixed mode loading conditions.
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Leslie Banks‐Sills, Natalie Konovalov and Adi Fliesher
Fracture tests carried out on bimaterial Brazilian disk specimens have been reported elsewhere. Two material pairs are tested in which each of the constituents is linearly…
Abstract
Purpose
Fracture tests carried out on bimaterial Brazilian disk specimens have been reported elsewhere. Two material pairs are tested in which each of the constituents is linearly elastic, isotropic, and homogeneous. For this material type, the crack fields decouple into in‐plane and out‐of‐plane deformation. Hence, a two‐dimensional approach is taken to analyse the tests. The purpose of this paper is to examine the necessity of using a three‐dimensional approach to predict interface fracture when in‐plane loading is applied.
Design/methodology/approach
To this end, the specimens are analysed by means of two‐ and three‐dimensional finite elements. The interaction energy or M‐integral is used to calculate the stress intensity factors.
Findings
The paper shows that the Mode III stress intensity factor KIII is not negligible near the specimen outer surfaces. Nevertheless, a two‐dimensional analysis will be seen to be sufficient to analyse these tests. This has implications for the practical engineer.
Originality/value
The paper offers a comparison between two‐ and three‐dimensional fracture criteria for a crack along the interface between two homogeneous, isotropic, linear elastic materials when in‐plane loading is applied to the body, and assesses the importance of the out‐of‐plane deformation.
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Mohammad Bardi, Andrea Burbank, Wayne Choi, Lawrence Chow, Wesley Jang, Dawn Roccamatisi, Tonia Timberley-Berg, Mandeep Sanghera, Margaret Zhang and Andrew J. Macnab
– The purpose of this paper is to describe activities used to initiate health promotion in the school setting.
Abstract
Purpose
The purpose of this paper is to describe activities used to initiate health promotion in the school setting.
Design/methodology/approach
Description of successful pilot Health Promoting School (HPS) initiatives in Canada and Uganda and the validated measures central to each program. Evaluation methodologies: quantitative data from the tools used complimented by descriptive/qualitative methods.
Findings
Previously validated tools/methodologies used include: The World Health Organization (WHO) growth charts for comparison of children ' s height, weight, head circumference, and BMI against multi-ethnic standards; a 24-h dietary recall instrument to assess dietary diversity as a proxy measure of nutritional adequacy; urine analysis to evaluate baseline renal function and the effect of supplemental hydration; “photo-voice” to aid discussion of personal and community issues of concern; “role play” to promote dialogue and promote social competence; and fitness training. Each activity can combine the “curriculum content” and “healthy practices” components central to HPS concepts. All activities engaged more than 95 percent of pupils enrolled, generated positive responses, and had the potential to impact behaviors and promote health.
Practical implications
All the activities are inexpensive and straightforward to initiate, offer schools interested in health-promotion-driven education a broad range of potential “entry points” that can be matched to the interests/challenges of individual communities, and use validated methodologies aiding objective evaluation.
Originality/value
These activities foster a community empowerment (“bottom up”) approach, but are also relevant for policy makers exploring HPS to address disease prevention through lifestyle change (“top down” approach). Engagement of communities and ultimately their “ownership” of the HPS initiative have been achieved with these entry point activities.