Meso-scale Finite Element Analysis Research Articles

Size effect of compressive performance of concrete under elevated temperatures: Tests and meso-scale analysis

This study investigates the size effect of concrete under ambient and elevated temperatures through tests and numerical simulations. Compressive performance of prismatic and cylindrical concrete specimens with varying dimensions were tested at temperatures ranging from ambient temperature to 600°C. Meso-scale finite element analysis (FEA), assuming that the mechanical properties of matrix and interfacial transition zones (ITZ) followed Weibull distribution, was employed to simulate the tested specimens and to conduct parametric analysis on specimens with larger or smaller sizes and under temperatures up to 800°C. Both experimental and numerical results showed that the cracks on the specimen surface became finer and denser as an increase of specimen sizes under elevated temperatures. A noticeable decrease in concrete compressive strength with increasing specimen dimensions was observed below 600°C, but peak strain and elastic modulus did not exhibit significant size effect. Size effect on strength diminished at temperatures exceeding 800°C. Classic Size Effect Laws (SEL), such as Weibull's and Bažant's SEL, were applicable to characterize the size effect on strength of specimens within common lab test dimensions under elevated temperatures. Based on the results from experiments, FEA and Bažant's SEL, a stress-strain model under elevated temperatures considering size effect was proposed. The predicted results from this model showed good agreement with test results.

Effect of steel fibre with different orientations on mechanical properties of 3D-printed steel-fibre reinforced concrete: Mesoscale finite element analysis

It is widely recognized that steel fibres exhibit directional distribution during the preparation of 3D-printed steel fibre reinforced concrete (SFRC). The degree of fibre orientation varies due to several factors, such as nozzle size and layer height. This variation in fibre orientation range may result in different mechanical performance exhibited by 3D-printed SFRC at hardened state. To explore the relationship between steel fibre orientation and the mechanical properties of 3D-printed SFRC at hardened state, this study firstly establishes three-dimensional mesoscale finite element models based on the distribution of fibres in 3D-printed SFRC. The steel fibre and matrix work together through a mechanism for fluid-structure interaction between models. Then, compares the simulation results with experimental data to verify the accuracy of the models. After that, different steel fibre distribution orientations were set, and parametric analysis was conducted for the compressive and tensile loading conditions to explore the effects of fibre orientation on the damage mode and strength of 3D-printed SFRC. The results indicate that 3D-printed SFRC exhibits different damage modes with varying steel fibre orientation ranges. Additionally, the strength of 3D-printed SFRC varies in steel fibre orientation range and exhibits anisotropic characteristics. This study provides a theoretical basis for improving and controlling the performance of 3D-printed SFRC in future engineering applications.

Numerical analysis of large masonry structures: bridging meso and macro scales via artificial neural networks

This paper presents a methodology for analysis of large-scale masonry structures. The approach involves development of a series of artificial neural networks which enable the identification of main variables employed in the macroscopic formulation that incorporates an inelastic constitutive law with embedded discontinuity. The data required for training of neural networks is generated using ‘virtual experiments’, whereby the ‘equivalent’ anisotropic response of masonry is obtained through a mesoscale finite element analysis of masonry wallets. The paper outlines the procedure for identification of approximation coefficients describing the orientation-dependency of strength, and other relevant parameters. A numerical example is provided involving analysis of a large masonry wall with multiple openings. The results of macroscale approach are compared with those based on a detailed mesoscale model for the same geometry and boundary conditions.

Bead geometry–induced stress concentration factors in material extrusion polymer additive manufacturing

PurposeMaterial extrusion additive manufacturing processes inevitably produce bead-shaped surface patterns on the walls of parts, which create stress concentrations under load. This study aims to investigate the influence of such stress concentrations on the strength along the build direction (“Z-strength”).Design/methodology/approachThis work consists of two main parts – an experimental demonstration to show the significance of stress concentrations on the Z-strength, followed by numerical modeling to evaluate the theoretical stress concentration factors (kt) for such shapes. Meso-scale finite element analysis (FEA) was performed to evaluate kt at the roots of the intersecting bead shapes. The critical bead shape parameters influencing kt were identified, and parametric FEA studies were performed on different bead shapes by varying the normalized parameters.FindingsThe experimental results showed that up to a 40% reduction in the effective Z-strength could be attributed only to the presence of surface bead shapes. Bead overhang and root radius were identified as critical shape parameters influencing kt. The results of the parametric FEA studies were used to generate a single empirical equation to determine kt for any bead shape.Originality/valuePredictive models for Z-strength often focus on crystallization kinetics and polymer chain interdiffusion to predict interlayer adhesion strength. The authors propose that the results of such studies must be combined with surface bead-shape induced stress concentration factors to obtain the combined, “effective” Z-strength.

Numerical modeling on off-axial fatigue behavior and failure characterization of 3D braided composites

Fatigue is an important factor leading to the structural failure of 3D braided composites during the service. In this paper, a meso-scale finite element analysis (FEA) model based on continuum damage mechanics (CDM) is developed to study the fatigue damage behavior and predict the fatigue life of 3D braided composites subjected to off-axial tension loadings. Stress analysis, failure criteria and material properties degradation scheme in the meso-scale model are implemented by a user-material subroutine UMAT based on ABAQUS/Standard solver. The damage initiation and propagation of 3D braided composites under diverse off-axial fatigue loadings are simulated and analyzed in detail and the corresponding off-axial fatigue lives are obtained from the predicted S- N curves. The proposed FE modeling provides a suitable reference for the numerical research on the off-axial fatigue problems in other textile composites.

Mesoscale Simulation-Based Parametric Study of Damage Potential in Brain Tissue Using Hyperelastic and Internal State Variable Models.

Two-dimensional mesoscale finite element analysis (FEA) of a multilayered brain tissue was performed to calculate the damage-related average stress triaxiality and local maximum von Mises strain in the brain. The FEA was integrated with rate-dependent hyperelastic and internal state variable (ISV) models, respectively, describing the behaviors of wet and dry brain tissues. Using the finite element results, a statistical method of design of experiments (DOE) was utilized to independently screen the relative influences of seven parameters related to brain morphology (sulcal width/depth, gray matter (GM) thickness, cerebrospinal fluid (CSF) thickness and brain lobe) and loading/environment conditions (strain rate and humidity) with respect to the potential damage growth/coalescence in the brain tissue. The results of the parametric study illustrated that the GM thickness and humidity were the two most crucial parameters affecting average stress triaxiality. For the local maximum von Mises strain at the depth of brain sulci, the brain lobe/region was the most influential factor. The conclusion of this investigation gives insight for the future development and refinement of a macroscale brain damage model incorporating information from lower length scale.

Prediction of tensile failure of stochastic tow-based discontinuous composites via mesoscale finite element analysis

Stochastic tow-based discontinuous composite (STBDC) laminates are made from compression-molded tows of carbon fiber reinforced polymer (CFRP). STBDCs are a material system that can be manufactured in complex three-dimensional geometries which provides an alternative to metallic components for primary and secondary structures. The effective elastic properties of STBDCs are often approximated as quasi-isotropic; however, this approximation does not adequately represent the material properties. A random sequential addition representative volume element (RVE) generation algorithm has been developed that considers the mesostructural morphology of STBDCs using a non-conforming voxel-based mesh framework. Using the framework, a full factorial design of experiments is performed on unnotched tension coupons. Simulations are performed using the Abaqus/Explicit solver. Results are compared to reported values found in the available literature, demonstrating good correlation compared effective stiffnesses and unnotched tensile failure strengths.

Mesoscale finite element analysis for uniaxial compressive failure and size effect of concrete at cryogenic temperature

Mesoscale finite element analysis for uniaxial compressive failure and size effect of concrete at cryogenic temperature

Reconstruction of meso-structure and numerical simulations of the mechanical behavior of three-dimensional four-directional braided ceramic matrix composites

Textile-reinforced ceramic matrix composites are key structural materials for aerospace applications. In this paper, the influence of meso-structure and damage mechanisms on mechanical behavior of three-dimensional (3D) four-directional braided SiC/SiC composites is systematically investigated by using numerical simulations. First, periodic preform geometry model, also known as representative volume element (RVE), is reconstructed by using micro-computational tomography (μ-CT). Then, two damage mechanics models are employed to establish non-linear behavior of tows and matrix. Moreover, cohesive model is introduced to represent tow/tow and tow/matrix delamination behavior. It is noteworthy that homogenized tow model is derived from micromechanical model on fiber scale. Finally, macro stress-strain and failure behaviors of 3D braided SiC/SiC composites are simulated by meso-scale finite element analysis. Numerically simulated tensile modulus and strength of 3D braided SiC/SiC composites are compared with experimental results, exhibiting good consistency. Numerical simulations revealed failure mechanism and confirmed that, in addition to globally evolved damage process under tensile load, meso-scale preform caused stress concentration and subsequent local rupture behavior. Current research shows that reconstructed textile model realistically describes tensile mechanical behavior and damage evolution of 3D braided SiC/SiC composites.

Experimental and numerical study on stiffness and damage of glass/epoxy biaxial weft-knitted reinforced composites

This paper deals with investigating the tensile characteristics of biaxial weft-knitted reinforced composites in terms of stiffness, strength and failure mechanism. The biaxial weft-knitted fabric was produced on an electronic flat knitting machine by E-glass yarns and then was impregnated with epoxy resin. Using an accurate geometrical model, the composite unit cell was designed in Abaqus software’s environment. Tensile tests were simulated in different directions on the created unit cell and the stiffness was calculated. By applying the proper failure theories, the composite strength was predicted and then critical regions of the unit cell were determined. In the next step, a micromechanical approach was also applied to estimate the same tensile features. Failure theories were also applied to predict the strength and most susceptible areas for failure phenomenon in the composite unit cell. The tensile properties of the produced composites were measured and compared with outputs of the finite element and micromechanical approaches. The results showed that the meso-scale finite element analysis approach can well predict the composite strength. In contrast, the meso-scale analytical equation model was not able to predict it acceptably because this model ignores the strain concentration. Both meso-scale finite element analysis and meso-scale analytical equation approaches predicted the similar locations for the composite failure in wale and course directions.

Surface topography evolution of woven thermoplastic composites under deformation

The evolution of architectural distortion of woven composites can significantly influence the deformation behaviour but is challenging to measure experimentally. In this paper, two techniques are proposed to examine the out-of-plane topography of composites under deformation measured using stereo Digital Image Correlation (DIC). The primary method relies on fitting a surface to the data to compensate for global sample distortion and reveal local topography while the supplementary method uses local curvatures calculated for each data point on the surface. These methods have been applied to thermoplastic composites with different weave architectures, matrix and fibre materials. Topography results show good agreement in magnitude and form with mesoscale Finite Element Analysis (FEA). The methods improve existing experimental techniques to examine local effects with multiple applications regarding deformation, defect detection and failure analysis of composites.

Mesoscale finite element analysis of cracked composite laminates under out-of-plane loads using 3D periodic boundary conditions

The behavior of composite materials under out-of-plane loads is strongly affected by the presence of transverse ply cracks. The cracks perturb the distribution of stresses leading to large out-of-plane shear stiffness reductions. It is crucial to include these effects in the damage material models to improve their accuracy. Therefore, the stress transfer and stiffness reduction in cracked laminates have been studied with a mesoscale finite element model (FEM) under general in-plane, out-of-plane normal and shear loads. A symmetric laminate containing ply cracks in a single orientation has been considered under the hypothesis of periodicity using a novel relaxed three-dimensional formulation of Periodic Boundary Conditions (PBCs). The local stresses have been verified versus different analytical and numerical methods. In addition, the degraded effective thermo-elastic constants involving out-of-plane properties have been calculated as a function of crack density. Both uniform and non-uniform distributions of cracks have been considered for different lay-ups including angle-ply and unbalanced laminates. The effect of contact between the crack surfaces has been studied for specific loading conditions. It is shown that a single formulation based on three-dimensional periodic boundary conditions is sufficient to determine the interfacial stresses and the complete thermo-elastic constants under in-plane and out-of-plane loads accurately.

Meso-scale finite element analysis on creep behaviour of asphalt mixture considering interface effect

This paper investigated the creep behaviour of asphalt mixtures using a randomly generated meso-scale finite element model that takes into account the effect of asphalt-aggregate interface. Simulation analysis on the three-point bending creep tests of asphalt mixture were performed and validated. Furthermore, parameters studies were conducted to evaluate the effect of gradation and angularity of coarse aggregate, air void content, and asphalt-aggregate interface strength. The results indicated that mesostructural parameters and interface properties have an important effect on the creep behaviour of asphalt mixture. The creep performance of medium-sized asphalt mixture is better than that of fine-sized asphalt mixtures. The larger the angularity index of coarse aggregate is, the better ability asphalt mixture has to resist deformation. As to the suspended dense structure asphalt mixtures, with the increase of void ratio, the creep deformation increase gradually, and the excessive void ratio would lead to the fracture of the interface. Asphalt-aggregate interface with higher interface strength would result in better resistance to of the mixture to permanent deformation.

Meso-Scale Finite Element Simulations of 3D Braided Textile Composites: Effects of Force Loading Modes

Meso-scale finite element method (FEM) is considered as the most effective and economical numerical method to investigate the mechanical behavior of braided textile composites. Applying the periodic boundary conditions on the unit-cell model is a critical step for yielding accurate mechanical response. However, the force loading mode has not been employed in the available meso-scale finite element analysis (FEA) works. In the present work, a meso-scale FEA is conducted to predict the mechanical properties and simulate the progressive damage of 3D braided composites under external loadings. For the same unit-cell model with displacement and force loading modes, the stress distribution, predicted stiffness and strength properties and damage evolution process subjected to typical loading conditions are then analyzed and compared. The obtained numerical results show that the predicted elastic properties are exactly the same, and the strength and damage evolution process are very close under these two loading modes, which validates the feasibility and effectiveness of the force loading mode. This comparison study provides a suitable reference for selecting the loading modes in the unit-cell based mechanical behavior analysis of other textile composites.

Meso-Scale Finite Element Analysis of Mechanical Behavior of 3D Braided Composites Subjected to Biaxial Tension Loadings

In many engineering applications, 3D braided composites are designed for primary loading-bearing structures, and they are frequently subjected to multi-axial loading conditions during service. In this paper, a unit-cell based finite element model is developed for assessment of mechanical behavior of 3D braided composites under different biaxial tension loadings. To predict the damage initiation and evolution of braiding yarns and matrix in the unit-cell, we thus propose an anisotropic damage model based on Murakami damage theory in conjunction with Hashin failure criteria and maximum stress criteria. To attain exact stress ratio, force loading mode of periodic boundary conditions which never been attempted before is first executed to the unit-cell model to apply the biaxial tension loadings. The biaxial mechanical behaviors, such as the stress distribution, tensile modulus and tensile strength are analyzed and discussed. The damage development of 3D braided composites under typical biaxial tension loadings is simulated and the damage mechanisms are revealed in the simulation process. The present study generally provides a new reference to the meso-scale finite element analysis (FEA) of multi-axial mechanical behavior of other textile composites.

Comparison of periodic mesh and free mesh on the mechanical properties prediction of 3D braided composites

Periodic unit-cells are the premises for applying the periodic boundary conditions in the meso-scale finite element analysis of textile composites. However, due to the extremely complicated microstructure, there is a conflict between high-quality quick mesh generation and efficient application of periodic boundary conditions. A freely generated mesh of the unit-cell combined with more general periodic boundary conditions is assumed to be a more practical approach. In this paper, the general periodic boundary conditions are imposed by establishing linear constraint equations between master surface nodes and slave surface nodes of the unit-cell on ABAQUS software platform. For the same unit-cell model of 3D braided composites with periodic mesh and free mesh, the deformation, stress distribution and the predicted stiffness and strength properties under typical loadings are compared. The numerical results obtained by means of free mesh unit-cell agree well with those using periodic mesh proving the effectiveness and practicability of the new approach. It can be remarked that the general periodic boundary conditions are suitable for the free mesh generation of unit-cells for a complicated microstructure reducing the difficulty of meshing and improving the quality of mesh generation.

Hierarchical multiscale modeling of Polyvinyl Alcohol/Montmorillonite nanocomposites

Abstract The mechanical responses of low volume fraction Polyvinyl Alcohol (PVA)/Montmorillonite (MMT) nanocomposites were modeled using a hierarchical multiscale modeling method. Nanoscale Molecular Dynamics (MD) and mesoscale Finite Element Analysis (FEA) were used to bridge information regarding deformation mechanics within Polymer/Clay Nanocomposites (PCNs). MD computations of PVA/MMT interfaces were employed to calibrate a Traction-Separation (T-S) relation, which was then upscaled into a cohesive zone model (CZM) to model interfaces between PVA and MMT in a mesomechanical finite element framework. Virtual Composite Structure Generation (VCSG) was used to generate a quasi-realistic Representative Volume Element (RVE), and explicit FEA was performed on the RVE to demonstrate delamination in the PCNs. The FEA featured an elasto-viscoelastic-viscoplastic Internal State Variable (ISV) model for the polymer host (PVA) and a CZM for the interfaces between MMT and PVA. The hierarchical length scale bridging methodology employed here for a polymer based composite has applications for many other material systems.

A mesomechanics parametric finite element study of damage growth and coalescence in polymers using an Elastoviscoelastic-Viscoplastic internal state variable model

A split-level factorial design of experiments (DOE) parametric study using a two-dimensional mesoscale Finite Element Analysis (FEA) was executed to elicit the most essential aspects pertaining to void/crack growth and void/crack coalescence in polymers above the glass transition temperature. The FEA was coupled to a physically based, strain rate and temperature dependent, elastoviscoelastic-viscoplastic internal state variable polymer model that was calibrated to physical experiments. The DOE method examined the relative influences of seven independent parameters related to mechanics (stress state, strain rate, and temperature) and materials science (polymer blend, number of initial defects, defect type, and initial microporosity—also called the subscale free volume) with respect to both void/crack growth and void/crack coalescence in polymers. The results of the DOE algorithm clearly illustrated that the stress state and applied strain rate were the most critical factors affecting void/crack growth. For void/crack coalescence, the stress state and number of defects were the crucial parameters. The conclusions of this study gives insight for the development of a macroscale damage model for polymers.

Carbon composites based on multi-axial multi-ply stitched preforms. Part 7: Mechanical properties and damage observations in composites with sheared reinforcement

Abstract Biaxial multi-ply carbon fabrics (+45°/−45° and 0°/90°) were sheared up to 30°, 45° and 50° using a shearing frame. The carbon/epoxy composite plates were made using resin transfer moulding. Tensile properties were measured in two principal directions and compared with results computed with the classical laminate theory and meso-scale finite element analysis. Damage initiation in laminates due to tensile loading was investigated using acoustic emission and X-ray radiography. Shearing changes the fibre orientation and hence the behaviour of the composites, leading to the shear angle dependence of damage initiation. Thermal cracks in composites with unsheared reinforcements, induced by post-curing, are not present in the composites with sheared reinforcement. The analysis of the experimental observations of the damage initiation and development is supported by finite element analysis.