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This study employs a two-dimensional and incompressible flow of Herschel–Bulkley visco-plastic materials in order to investigate the hydrodynamic forces that are acting on a barrier that is located close to the inlet of a channel. As the benchmark configuration, the flow domain that has been selected is a channel that still contains the impediment. The two important parameters of the Herschel–Bulkley Model (HBM) are the yield stress τ y and power law index n. Obtaining special situations within the HBM, such as Newtonian, power-law, and Bingham fluids, can be accomplished by assigning certain values to these parameters at the appropriate times. Utilizing a numerical strategy grounded in the Finite Element Method (FEM), we tackle the nonlinearity of the governing equations as well as the viscosity models. As a result of this nonlinearity, FEM becomes an essential tool. The generation of a refined hybrid mesh is done in order to guarantee accuracy in the computations. The stable finite element pair ( ℙ 2 ∕ ℙ 1 ) has been selected for discretization purposes. The discretized nonlinear system is linearized with Newton's method and subsequently, a direct linear solver PARDISO has been employed in the inner iterations. The pressure, velocity, and viscosity profiles are plotted for various values of n and Bingham number (Bn). In addition, the velocity behavior is observed along the y-direction in a channel through line graphs. Code validation is done as a special case Bn = 0 and a good agreement is found with the results available in the literature. Finally, a correlation analysis has been performed for the drag coefficient C d and lift coefficient C l . [ABSTRACT FROM AUTHOR]

This study investigated how printing conditions influence the fracture behaviour of 3D-printed acrylonitrile butadiene styrene (ABS) under tensile loading. Dog-bone-shaped ABS specimens were produced using the fusion filament fabrication technique, with varying printing angles. Tensile tests were conducted on pre-notched specimens with consistent pre-notch lengths but different orientations. Optical and scanning electron microscopies were employed to analyse crack propagation in the pre-notched specimens. In order to support experimental evidence, finite element computation was implemented to study the damage induced by the microstructural rearrangement of the filaments when subject to tensile loading. The findings revealed the simple linear correlation between the failure properties including elongation at break and maximum stress in relation to the printing angle for different pre-notch lengths. A more progressive damage was found to support the ultimate performance of the studied material. This experiment evidence was used to build a damage model of 3D-printed ABS that accounts for the onset, growth, and damage saturation. This damage modelling is able to capture the failure properties as a function of the printing angle using a sigmoid-like damage function and a modulation of the stiffness within the raster. The numerical results demonstrated that damage pattern develops as a result of the filament arrangement and weak adhesion between adjacent filaments and explains the diffuse damage kinetics observed experimentally. This study concludes with a topological law relating the notch size and orientation to the rupture properties of 3D-printed ABS. This study supports the idea of tailoring the microstructural arrangement to control and mitigate the mechanical instabilities that lead to the failure of 3D-printed polymers. [ABSTRACT FROM AUTHOR]

A second‐order asymptotic analysis method is developed for the Steklov eigenvalue problem in periodically perforated domain. By the two‐scale expansions of the eigenfunctions and eigenvalues, the first‐ and second‐order cell functions defined on the representative cell are obtained successively, the homogenized elliptic eigenvalue problem is formulated, and effective coefficients are derived. The first‐ and second‐order correctors of the eigenvalues are expressed in terms of the integrations of the cell functions and homogenized eigenfunctions. The error estimations of the expansions of eigenvalues are established, and the corresponding finite element algorithm is proposed. Numerical examples are carried out, and both qualitative and quantitative comparisons with the solutions by classical finite element computations are performed. It is demonstrated that this asymptotic model is effective to capture the local details of the eigenfunctions by considering the second‐order expansion terms, and the algorithm presented in this work is efficient to obtain the accurate spectral properties of the porous material at lower cost. [ABSTRACT FROM AUTHOR]

The annulus fibrosus of the intervertebral disc exhibits an unusual transversal behavior for which a constitutive representation that considers as well regional effect, chemical sensitivity and time-dependency has not yet been developed, and it is hence the aim of the present contribution. A physically-based model is proposed by introducing a free energy function that takes into account the actual disc annulus structure in relation with the surrounding biochemical environment. The response is assumed to be dominated by the viscoelastic contribution of the extracellular matrix, the elastic contribution of the oriented collagen fibers and the osmo-induced volumetric contribution of the internal fluid content variation. The regional dependence of the disc annulus response due to variation in fibers content/orientation allows a micromechanical treatment of the soft tissue. A finite element model of the annulus specimen is designed while taking into consideration the 'interlamellar' ground substance zone between lamellae of the layered soft tissue. The kinetics is designed using full-field strain measurements performed on specimens extracted from two disc annulus regions and tested under different osmotic conditions. The time-dependency of the tissue response is reported on stress-free volumetric changes, on hysteretic stress and transversal strains during quasi-static stretching at different strain-rates and on their temporal changes during an interrupted stretching. Considering the effective contributions of the internal fluid transfer and the extracellular matrix viscosity, the microstructure-based chemo-mechanical model is found able to successfully reproduce the significant features of the macro-response and the unusual transversal behavior including the strong regional dependency from inner to outer parts of the disc: Poisson's ratio lesser than 0 (auxetic) in lamellae plane, higher than 0.5 in fibers plane, and their temporal changes towards usual values (between 0 and 0.5) at chemo-mechanical equilibrium. The underlying time-dependent mechanisms occurring in the tissue are analyzed via the local numerical fields and important insights about the effective role of the interlamellar zone are revealed for the different disc localizations. The structural complexity of the annulus fibrosus has only been appreciated through recent experimental contributions and a constitutive representation that considers as well regional effect, chemical sensitivity and time-dependency of the unusual transversal behavior has not yet been developed. Here, a microstructure-based chemo-viscoelastic model is developed to highlight the interlamellar-induced time-dependent response by means of a two-scale strategy. The model provides important insights about the origin of the time-dependent phenomena in disc annulus along with regional dependency, essential for understanding disc functionality. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In this paper, a bioheat model of temperature distribution in the human eye is studied, the mathematical formulation of this model is described using adequate mathematical tools. The existence and the uniqueness of the solution of this problem is proven and four algorithms based on finite element method approximation and domain decomposition methods are presented in details. The validation of all algorithm is done using a numerical application for an example where the analytical solution is known. The properties and parameters reported in the open literature for the human eye are used to approximate numerically the temperature for bioheat model by finite element approximation and nonoverlapping domain decomposition method. The obtained results that are verified using the experimental results recorded in the literature revealed a better accuracy by the use of algorithm proposed. [ABSTRACT FROM AUTHOR]

With their gradual and continuous properties, functionally graded polymers (FGP) have high potentials to reproduce the regional variation in microstructure/property of the natural intervertebral disc and, therefore, the functional anatomy and biomechanics of the soft tissue. This paper evaluates by finite element analysis the biomechanical response and stress distribution of a novel disc prosthesis using FGP. The kinetics of the FGP parameters is designed using experimental data issued from linear ethylene copolymers over a wide crystallinity range. The radial variation in crystallinity index within the disc prosthesis varies gradually and continuously following a special function in the aim to tailor and optimize the FGP parameters. The experimental data of a healthy human cervical spine segment are used to predict the optimal model of the FGP disc prosthesis loaded under different physiological loading conditions, i.e. rotation, lateral bending and flexion/extension. The results suggest that the FGP parameters can be tailored to control the stiffening, the non-linear behavior, the inelastic effects and the stress distribution in the aim to propose the optimal prosthesis model giving the great opportunity of patient-specific FGP prostheses via 3D printing technologies. [ABSTRACT FROM AUTHOR]

The aim of this work is to deliver a precise statement about the mechanical effect of microstructural defects induced by stereolithography. Design of cellular structures based on a photosensitive resin with varied porosity content is performed up to 60%. The compressive behaviour of these structures is captured and microstructural defects are analysed using X-ray micro-tomography. Finite element computation is considered to predict the compressive behaviour of both 3D microstructures and CAD (Computer-Aided Design) models up to the densification stage. X-ray micro-tomography analyses reveals that two main defects are generated by the process, namely residual support material and excess of resin trapped inside the porous network. Significance of the defects is proved to be related to the design of cellular structures with porosity levels in the range 10–30%. In addition, both experimental and numerical results show no evidence of anisotropic effect related to additive layering of resin. Finally, the suggested damage – densification constitutive law captures the main characteristics of the compressive response of studied cellular structures. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, we suggest a simple scheme to derive interfacial behavior using combination of nanoindentation and finite element computation. The starting point is the experimental generation of a rectangular grid composed of 32 indentations to measure the exact variation of stiffness across the interface of a bio-based composite. A finite element simulation of nanoindentation is implemented based on elasto-plastic material model. An optimization strategy is used to identify the behavior of all phases by matching predicted results to observed mechanical response. Results show that extent of interphase layer has a typical dimension of 8.0 ± 4.9 µm. The optimization strategy based on simplex proves to be efficient to derive the elasto-plastic behavior of the blend across the interface with a residual value of less than 30 µN. The identification procedure demonstrates that the extent of the interfacial region depends on the measured physical quantity. The contrast across the interface for both Young's and the tangent moduli appear to be more effective than the contrast given by the yield stress. Identified Young's moduli for zein, starch, and interfacial zone are 4.78 ± 0.27, 4.13 ± 0.19, and 3.91 ± 0.17 GPa. Plasticity parameter represented by tangent modulus varies in the same order as 1238 ± 120, 847 ± 108, and 976 ± 94 MPa, respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44891. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new instrumented spherical indentation test (ISIT) methodology to determine fracture toughness of high strength steels. • Tensile properties estimation by an improved representative stress–strain method with Meyer power-law correction. • A new dimensionless function was developed to determine critical indentation depth. • Estimated tensile properties and fracture toughness by ISIT agree well with experimental results. A new instrumented spherical indentation test (ISIT) methodology is proposed to determine fracture toughness of metallic materials that their strain hardening can be adequately described by a power-law function. Firstly, tensile properties, including Young's modulus (E), yield stress (σ y) and strain hardening exponent (n) are determined by an improved representative stress–strain method with the Meyer power-law correction. Secondly, by performing dimensional analysis and finite element computation, a new dimensionless function of critical indentation contact pressure (P m cr) versus tensile properties is developed. To generalize the above dimensionless function to a broad scale of metallic materials, 100 different combinations of tensile properties have been implemented in the finite element computation of spherical indentation tests. Consequently, P m cr of various tested metallic materials can be calculated conveniently by substituting the corresponding tensile properties into the dimensionless function. The critical indentation depth (h c cr) of metallic materials can then be determined by identifying P m cr on the curve of mean contact pressure versus indentation depth. Finally, fracture toughness is calculated by the concept of indentation energy to fracture at h c cr. To demonstrate the repeatability of the above methodology, it has been applied to predict fracture toughness of three different high strength steels by two research groups, independently. The best measurement capacity of the present approach could be optimized in a relative small error, as ±6 % in tensile properties and ±10 % in fracture toughness, that is close to the conventional standard testing results upon multiple samples of the same group. [ABSTRACT FROM AUTHOR]

The aim of this study is to understand the microstructural changes occurring during severe compression of a biopolymeric foam. In-situ airy microstructure evolution is monitored as function of loading using X-ray micro-tomography. Cell shrinkage and cell wall thickening are quantified using image analysis. Cell connectivity, morphology and size distributions are related to structural anisotropy generated by loading. Finite element computation is attempted to derive the mechanical model representing the compressive response up to densification. Three models are tested, namely unit cell with elasto-plastic constitutive law, Ogden hyperelasticity and an effective elasto-plastic model. The effective elasto-plastic model is the most realistic model to capture compressive behaviour of the studied foam under all drying situations. Thanks to a densification stiffening term added to account for an evolving cell contact, the effective model shows superior capabilities to capture severe compression of the bio-based foam under all drying conditions. [ABSTRACT FROM AUTHOR]

A new second-order two-scale (SOTS) asymptotic analysis method is presented for the heat conduction problems concerning composite materials with periodic configuration under the coordinate transformation. The heat conduction problems are solved on the transformed regular domain with quasi-periodic structure in the general curvilinear coordinate system. By the asymptotic expansion, the cell problems, effective material coefficients and homogenized heat conduction problems are obtained successively. The main characteristic of the approximate model is that each cell problem defined on the microscopic cell domain is associated with the macroscopic coordinate. The error estimation of the asymptotic analysis method is established on some regularity hypothesis. Some common coordinate transformations are discussed and the reduced SOTS solutions are presented. Especially by considering the general one-dimensional problem, the explicit expressions of the SOTS solutions are derived and stronger error estimation is presented. Finally, the corresponding finite element algorithms are presented and numerical results are analyzed. The numerical errors presented agree well with the theoretical prediction, which demonstrate the effectiveness of the second-order asymptotic analysis method. By the coordinate transformation, the asymptotic analysis method can be extended to more general domain with periodic microscopic structures. [ABSTRACT FROM AUTHOR]

Date palm residues capabilities in civil engineering are evaluated by combining numerical and experimental approaches. Date palm spikelet originated from Elghers variety is added to mortar as a raw material or after chemical modification. Evaluation of reinforcement effect is performed using mechanical testing. Finite element modelling is considered to predict the interfacial behaviour and mechanical performance under various structural and mechanical hypotheses. Experimental results show limited effect of untreated spikelet on mortar performance for volume reinforcement of 1%. Larger contents result in severe degradation of mechanical performance compared to reference mortar. The addition of carbon nanotubes improves slightly the performance. Chemical treatment using both NaOH and CaO results in reinforced effect of spikelet. Numerical predictions show limited load transfer across the matrix/untreated spikelet interface and large interface stiffness for those formulations including small spikelet, CNT and chemical treatment. [ABSTRACT FROM AUTHOR]

Over the past few decades, the measurement and analysis of thermal undulations has provided a route to estimate the mechanical properties of membranes. Theoretically, fluctuating elastic membranes have been studied mostly by Fourier analysis coupled with perturbation theory (to capture anharmonic effects), or by computer simulations of triangulated surfaces. These techniques as well as molecular dynamic simulations have also been used to study the thermal fluctuations of graphene. Here, we present a semi-analytic approach in which we view graphene as a triangulated membrane, but compute the statistical mechanical quantities using Gaussian integrals. The nonlinear coupling of inplane strains with out-of-plane deflections is captured using a penalty energy. We recover well-known results for the scaling of the fluctuations with membrane size, but we show that the fluctuation profile strongly depends on boundary conditions and type of loading applied on the membrane. Our method quantitatively predicts the dependence of the thermal expansion coefficient of graphene on temperature and shows that it agrees with several experiments. We also make falsifiable predictions for the dependence of thermal expansion coefficient and the heat capacity of graphene on applied loads and temperature. [ABSTRACT FROM AUTHOR]

The combination of experimental and numerical approaches is attempted to shed more light on 3D microstructural imperfections and mechanical performance of 3D printed acrylonitrile butadiene styrene parts. The starting point is the virtual building of airy structures using a reverse engineering approach. This approach combines microstructure generator, finite element model, and optimization strategy to propose virtual airy structures satisfying structural and mechanical criteria up to a desired porosity content of 60%. Optimal structures are printed using fused deposition modeling and X-ray microtomography is used to assess all microstructural defects. Compression testing is performed for load levels above 50% of reduction in sample height. The main outcome of this work is the demonstration of small amount of process induced porosity inducing high pore connectivity. The interdependence of process induced and desired porosity reveals genuine microstructural effects that are only characteristics of 3D printed materials. [ABSTRACT FROM AUTHOR]

A large debate animates the community about the mechanical performance of complex parts obtained by injection moulding (IM) of short glass fibre reinforced polymer (SGFRP) composites. Difficulties to measure exact fibre length and orientation distributions in complex geometries are limiting in terms of basic understanding of damage mechanisms in industrial parts and fatigue design improvement. In this work, we are interested to shed more light on the mechanical performance of short glass fibre reinforced polyamide composites in correlation to local microstructural heterogeneities which are caused by inserts used during IM. For such purpose, we combine X-ray microtomography (μ-CT) and finite element computation to determine the elastic modulus in various positions in an open hole plate configuration with a dissymmetric fibre distribution. Our predictions show that effective properties do not vary significantly around the hole in all space directions. However, stress profiles (through the thickness) far enough from the hole reveal a five-layer quasi symmetric structure evolving to three-layer near the cylindrical insert. We believe that such alteration is responsible for the observed failure of the composite at precisely the positions of highly affected fibre distribution. [ABSTRACT FROM AUTHOR]

We propose to shed more light on deformation and structural changes of bread crumb submitted to severe compression. The analysis of such behaviour refers to an adequate approximation of human mastication of airy and spongy products. X-ray microtomography is coupled to mechanical testing of soft bread characterised by a fine cellular architecture. Structural attributes, namely, relative density, cell size and cell wall thickness distributions are determined using image analysis and related to the load level. Kinetics of pore shrinkage is also studied depending on its shape and size. Finite element model is developed to assess mechanical anisotropy induced by deformed airy structure. Results show that the pore content decreases from 72% to 24% after more than 89% of reduction in height. An irregular trend of pore shrinkage is also revealed which depends on deformation stages. Finite element results show a heterogeneous stress distribution but only a minor mechanical anisotropy is revealed as a result of the deformed airy structure. [ABSTRACT FROM AUTHOR]

The anisotropic gold nanotriangles (AuNTs) were synthesized by a fast seedless growth process. The high-yield monodispersed AuNT colloids were obtained through a purification process based on depletion-induced interactions. AuNTs were modulated with a localized surface plasmon resonance (LSPR) peak of 638 nm wavelength coherent with the Raman excitation light. However, from finite element computation results, the AuNT clusters showed better performance for the 785 nm laser source due to a red shift in their LSPR properties, hence it was selected for the surface-enhanced Raman scattering (SERS) immunoassay. A self-assembly strategy using a thiol group and ON-OFF strategy in the heat map was performed to ensure the stability of SERS immunoassay platform. The sandwich SERS immunoassay biosensor platform for adiponectin detection demonstrated a wide assay range (10–15–10–6 g/mL), good reliability (R2 = 0.994, clinically relevant range), femto-scale limit of detection (3.0 × 10–16 g/mL), and excellent selectivity without interference from other biomarkers. This showed the possibility of effectively detecting adiponectin levels in the biofluids of pregnant women. Therefore, our technology is the first to quantitatively detect adiponectin based on SERS technology for early detection of gestational diabetes mellitus and has the potential to be used as a clinical biosensor capable of diagnosing various obstetric diseases during early pregnancy. • The SERS immunoassay biosensor was first proposed for early detection of GDM. • High-yield AuNTs were synthesized by one-pot seedless and depletion-induced interaction methods. • Thiol-based self-assembly and ON-OFF strategies were performed to ensure the stability of SERS biosensor. • The SERS immunoassay biosensor showed femto-scale LOD, good reliability, and excellent selectivity. [ABSTRACT FROM AUTHOR]

Electrophoresis is the motion of charged particles relative to the surrounding liquid under the influence of an external electric field. This electrochemical transport process is used in many scientific and technological areas to separate chemical species. Modeling and simulation of electrophoretic transport enables a better understanding of the physicochemical processes developed during the electrophoretic separations and the optimization of various parameters of the electrophoresis devices and their performance. Electrophoretic transport is a multiphysics and multiscale problem. Mass transport, fluid mechanics, electric problems, and their interactions have to be solved in domains with length scales ranging from nanometers to centimeters. We use a finite element method for the computations. Without proper numerical stabilization, computation of coupled fluid mechanics, electrophoretic transport, and electric problems would suffer from spurious oscillations that are related to the high values of the local Péclet and Reynolds numbers and the nonzero divergence of the migration field. To overcome these computational challenges, we propose a stabilized finite element method based on the Streamline-Upwind/Petrov-Galerkin (SUPG) formulation and discontinuity-capturing techniques. To demonstrate the effectiveness of the stabilized formulation, we present test computations with 1D, 2D, and 3D electrophoretic transport problems of technological interest. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate that the result of a fragmentation process during a compressive loading of brittle cereal products can be approached using a mechanical damage model. We investigate experimentally the mechanical behaviour of one selected transformed cereals from the market. Our experiments allow us to determine the force–displacement response as well as the fragment size distribution. We develop then a mechanical model to capture the fragmentation process. For that purpose, we determine the 3D cellular structure of the studied product using X-ray tomography. The role of the porous structure is accounted by converting the solid into a heterogeneous structure described by a collection of elasticity moduli. We implement the damage criterion based on a critical stress at which stiffness is reduced locally as to represent cell wall rupture events. Our numerical results show that fragmentation is associated to the development of low stress regions. All needed mechanical parameters to match the experimental response are determined. [Copyright &y& Elsevier]

In several applications, the geometry of induction motor (IM) lamination is not optimized for achieving optimal performance of a given power rating, but to achieve "adequate" performance for various power ratings. This is, for example, to limit the cost of the lamination stamp or to adopt commercial lamination. In this paper a suitable procedure proper for this cases is used to design a set of IMs. The procedure considers a normalized motor, independent of the motor length and number of winding turns. It is based on a combined finite element and analytical analysis of the motor yielding a rapid and accurate performance prediction at the same time. In the paper, experimental tests on some IM prototypes confirm the accuracy of the predictions achieved by the proposed analysis. [ABSTRACT FROM AUTHOR]

In this study, we show the extent of interfacial behaviour in the mechanical performance of thermoplastic polyurethane elastomer (TPU)/acrylonitrile butadiene styrene (ABS) composite material manufactured using droplet-based additive manufacturing. Both the interface orientation and the interface strength are varied during the processing. Prior to tensile experiments, X-ray micro-tomography imaging is undertaken to obtain the microstructural arrangement of polymer droplets in the part. Tensile loading is performed simultaneously with digital image acquisition to reveal the extent of strain localization using a digital image correlation approach. The experiments are performed up to the failure of the specimens. Finite element computation based on 3D imaging of the ABS/TPU composite is considered to predict the role of the interface as well as the defect influence on the tensile performance. The experimental results show a major connectivity of the process-generated porosity and a distinct morphology of the ABS/TPU interface. The predictions demonstrate that, despite the limited amount of porosity, their connectivity plays a significant role in triggering damage initiation and growth up to the failure of the composite material. [ABSTRACT FROM AUTHOR]

A finite-element (FE)-based phase variable model of single-phase transformers is developed for fast and accurate dynamic simulation purposes. In the developed model, the winding flux linkages, ψ1 and ψ2 are used as the phase variables. Their values are obtained from a series of nonlinear FE computation over the full operating range of the transformer. An equivalent magnetizing current, iem is defined. The variation of flux linkages ψ1 and ψ2 with the defined iem and the primary current i1 or the secondary current i2 are used to describe the magnetization nonlinearity of the core. Our study shows that the utilization of iem enables the FE-based phase variable model has the same accuracy as the full FE model without the necessity of excessive number of FE computations. The validity of the developed FE-based circuit model is verified through comparing with the full FE model and demonstrated by simulating the inrush current and the magnetizing currents at various saturation levels. [ABSTRACT FROM AUTHOR]