Search

We describe an algorithm for generating fiber-filled volume elements for use in computational homogenization schemes which accounts for a coupling of the fiber-length and the fiber-orientation. For prescribed fiber-length distribution and fiber-orientation tensor of second order, a maximum-entropy estimate is used to produce a fiber-length-orientation distribution which mimics real injection molded specimens, where longer fibers show a stronger alignment than shorter fibers. We derive the length-orientation closure from scratch, discuss its integration into the sequential addition and migration algorithm for generating fiber-filled microstructures for industrial volume fractions and investigate the resulting effective elastic properties. We demonstrate that accounting for the length-orientation coupling permits to match the measured Young's moduli in principal fiber direction and transverse to it more accurately than for closure approximations ignoring the length-orientation coupling. [ABSTRACT FROM AUTHOR]

This work presents a new two‐level representative volume element model for generating random fiber distributions in continuous fiber composite materials. A representative volume element (RVE) model with random geometric boundaries is generated, and the adaptive connections between neighboring RVEs are realized to eliminate unreasonable connections that may occur at the boundaries of RVEs. Subsequently, a novel adaptive generation and construction algorithm for larger RVE (LRVE) is proposed to consider more micro‐scale geometric and material uncertainties. A computational framework is established to implement the adaptive construction of LRVE and determine the statistical uncertainties of continuous fiber composite materials. The uncertain statistical results of the proposed algorithm are compared with those of the random sequential expansion algorithm and the complete spatial random pattern, showing good agreements among them. Finally, the uncertainty of macro‐scale linear elastic anisotropic material parameters is evaluated by using the integrated software framework. The maximum relative error of the predicted macro‐scale elastic properties is only 8.70%, which outperforms other numerical analysis results in literatures. The proposed algorithm is helpful for further research on multi‐scale linear elastic uncertainty analysis and reliability design of continuous fiber composite materials. [ABSTRACT FROM AUTHOR]

The properties of unidirectional (UD) composites has been investigated by analyzing their elastic and strength characteristics under shear loading. The UD fiber‐reinforced polymer (FRP) composites usually consist of fibers randomly dispersed throughout the cross‐section in the transverse direction which is generally not accounted for. A micromechanical model based on finite element analysis (FEA) approach is utilized here to examine these properties. The study begins by identifying micro scale unit cells or repetitive unit cells (RUCs) at the micro scale, as well as representative volume elements (RVEs). The distribution of fiber volume fraction (Vf) varies among various micro scale unit cells positioned in the transverse cross‐section. The elastic properties and strength are estimated by considering the properties of the matrix and fibers, and the configuration of micro scale unit cells, which feature a fiber arrangement which is categorized as hexagonal and varying Vf at different locations (from 0.35 to 0.75). However, the overall Vf for the UD composite remains constant at 0.65. Studies are also carried out with the random distribution of fibers at micro scale unit cells. The findings reveal that the random distribution of fibers significantly impacts the shear behavior of the composite. This investigation provides valuable insights into how the mechanical properties of the UD composite are subjective by the distribution of fiber, thereby contributing to the design and development of this light weight high‐performance material. Highlights: Elastic and strength analysis of UD composites is presented.Emphasis is on fiber dispersion in transverse plane.Microscale unit cells, RUCs and RVE are identified.Studies are carried out based on micromechanical model.Influence of fiber distribution on shear behavior is investigated. [ABSTRACT FROM AUTHOR]

Estimating the elastic characteristics of natural fiber‐reinforced polymer composites such as luffa fiber reinforced with epoxy is challenging. The structure of luffa cylindrica is complex, like a three‐dimensional natural fibrous mat, netting‐like structure. The multiscale modeling of such structures is the challenge to be addressed. The prime objective of this work is to determine the specific elastic properties of luffa–cenosphere‐reinforced epoxy (LCE) composite, considering the effect of filler volume fractions. Furthermore, multiscale modeling techniques, such as representative volume elements (RVEs) of finite element techniques with chopped, unidirectional, plain, and twill weaving fiber arrangements, were employed. The longitudinal modulus, transverse modulus, shear modulus, and Poisson's ratio were predicted through these modeling approaches. However, experimental and analytical methodologies, including the rule of mixture and Halpin–Tsai, were considered to validate the finite element analysis results. The elastic characteristics of LCE composite were therefore shown to be enhanced by increasing filler volume fraction. However, the cenosphere's 20% volume fraction has the highest elastic properties as determined by analytical, experimental, and computational models. Analytical and finite element simulation results were compared with the experimental results, and based on the findings, the most suitable (unidirectional, chopped, plain, and twill weaving) RVE was identified for finite element modeling of LCE composite for the evaluation of elastic properties. Results from practical approaches and the RVE twill weaving model showed good agreement, with less than 1% error, compared to the other analytical and finite element methods. Highlights: NFCs are gaining ground in polymer composites.Overcoming challenges in modeling of luffa fiber inside epoxy matrix.The study uses multiscale modeling with diverse fiber arrangements.Experimental and analytical methods used to confirm FEA results.Increased cenosphere volume fraction boosts LCE composite properties. [ABSTRACT FROM AUTHOR]

Purpose: During the forming process, aluminum alloy sheets develop various types of textures and are subjected to cyclic loading as structural components, resulting in fatigue damage. This study aims to develop polycrystalline models with different orientation distributions and incorporate suitable fatigue indicator parameters to investigate the effect of orientation distribution on the mechanical properties of Al-7.02Mg-1.78Zn alloys under cyclic loading. Design/methodology/approach: In this study, a two-dimensional polycrystalline model with 150 equiaxed grains was constructed based on optical microscope images. Subsequently, six different orientation distributions were assigned to this model. The fatigue indicator parameter of strain energy dissipation is utilized to analyze the stress response and fatigue crack driving force in polycrystalline models with different orientation distributions subjected to cyclic loading. Findings: The study found that orientation distribution significantly influences fatigue crack initiation. Orientation distributions with a larger average Schmid factor exhibit reduced stress response and lower fatigue indicator parameters. Locations with a larger average Schmid factor experience greater plastic deformation and present a higher risk for fatigue crack initiation. RVE with a single orientation undergoes more rotation to reach cyclic steady state under cyclic loading due to the ease of deformation transfer. Originality/value: Currently, there are no reports in the literature on the calculation of fatigue crack initiation for Al-Mg-Zn alloys using the crystal plasticity finite element method. This study presents a novel strategy for simulating the response of Al-7.02Mg-1.78Zn materials with different orientation distributions under symmetric strain cyclic loading, providing valuable references for future research. [ABSTRACT FROM AUTHOR]

A combined experiment and multiscale modeling approach was presented to correlate the mechanical properties of a roll-bonded AA1050/AA3004 bimetal clad sheet and constituents. The mechanical responses of the 2-ply AA1050/AA3004 and constituents were measured under various loading conditions. For the measurements, each constituent was separated from the clad sheet using electrical discharge machining and uniaxial tensile tests. Continuum-scale yield functions such as isotropic von Mises and anisotropic/non-quadratic Yld2000-2d were developed for the two constituents and the bimetal clad sheet. A grain-scale crystal plasticity finite element (CPFE) simulations were also performed incorporated with newly developed representative volume element considering measured microstructural attributes. These CPFE predictions were used to identify the anisotropy coefficients for Yld2000-2d. Using the identified yield functions, finite element modeling was followed in which the mechanical properties of each constituent sheet were addressed separately. This is a new approach developed in the current work and it enables a fundamental correlation between multilayered material and its constituents. The mechanical properties of the bimetal clad sheet under the uniaxial tensions were predicted using those of the constituents and compared with calculations based on known rule of mixture (ROM) approach. The two approaches well reproduced stress–strain curves and r–value evolutions. The two FE modeling approaches were also applied to an independent test (i.e., the limiting dome height). The predictions were in good agreement with the experimental data. Finally, the mechanical properties of the bimetal clad sheet and constituents were correlated, and proper modeling scheme for multilayered materials is proposed.

Although the effects of additive manufacturing process parameters on the mechanical properties of 3D printed parts have been numerically investigated in the literature, less attention has been paid on the size effects of voids between deposited filaments. This study fills this gap by developing a methodology based on a combined finite element (FE) and design of experiment (DoE) technique. The development of FE methodology is based on micro-mechanical analysis of representative volume element (RVE) of 3D printed parts to predict the effective orthotropic properties. To account for the size effects of inter-bead voids, the RVE includes contribution of the multiple parameters of layer heights, layer widths and overlapping regions. To study the main and interaction effects of the above input parameters on the stiffness properties of 3D printed parts, a structured approach based on full factorial design is used. Although the size effects of voids on the constituents of elastic moduli of RVE were investigated, the main focus in the present work is to develop a regression model to predict the stiffness properties. The FE stress analysis of the RVE conducted in this study provides an insight about the potential failure modes such as delamination and filament debonding that may occur in load bearing 3D printed parts. For a case study, the results of FE-based homogenization technique in terms of stiffness properties are validated against the experimental data via three-point bending and Iosipescu shear tests which were conducted in conjunction with digital image correlation technique. The combined numerical and statistical approach proposed in this study provides a swift iterative design of 3D printed parts prior to the time-consuming computation modelling, contributing to reduce the number of tests and manufacturing costs. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of metamaterials typically depends on their microstructural configuration and composition, in addition to their relative density. The design of these materials requires extensive experiments or complex finite element models which tend to be numerically demanding. In order to understand, control and optimise the macroscopic mechanical behaviour, in this paper numerical homogenisation is applied to a simple square unit cell with a single inclusion using a combination of elastic and viscoelastic responses on the micro level. Through a systematic analysis of unit cell behaviour with increasingly complex microstructural configurations, it is shown how certain macroscale constitutive laws can be obtained in a controlled and controllable manner. [ABSTRACT FROM AUTHOR]

This study is to investigate the effects of random interfacial debonded on the elastic constants of carbon fiber reinforced composites. The results reveal that the interfacial debonded fraction (IDF) significantly effects the elastic constants, and the randomness of interfacial debonded position significantly effects the stress distribution, but different interfacial debonded positions at the same IDF have a negligible effect on the elastic constants. The increase of IDF leads to a gradual increase in the disruption of tandem integrity between fibers and matrix, limiting the capability of the interface to transfer loads more significantly. [ABSTRACT FROM AUTHOR]

In the article, we propose a new method to generate representative volume element (RVE) of random spatial distributions with cylindrical fibers and spherical particles based on the Improved Artificial Bee Colony (IABC) algorithm. In this employed bee phase of IABC, the proposed algorithm adopts a new search strategy, which improves the computational efficiency. To analyze the differences between the fiber distribution generated by this algorithm and the actual fiber distribution, we conducted statistical analysis on the distribution of the generated RVE. The statistical analysis results of the nearest neighbor distance (NND), Second-order intensity function, and pair correlation function were in good agreement with the experiment and complete spatial randomness (CSR) patterns. In addition, the predicted elastic properties were compared with experimental measurements and theoretical prediction methods. The results demonstrate the accuracy and efficiency of the proposed algorithm. This algorithm can quickly generate the RVE of cylindrical fibers and spherical particles with volume fractions of 80% and 62%, and the calculation time for generating the RVE of cylindrical fibers is about 17s. [ABSTRACT FROM AUTHOR]

To investigate the enhancement mechanism and effect of laser treatment on the performance of an interface between a carbon-fiber-reinforced polymer and magnesium (CFRP/Mg), finite element simulations and experiments were conducted to demonstrate the macroscopic and microscopic failure processes of the laser-treated interface. Based on the high controllability of the groove parameters in laser machining, the quantitative relationship between the texture parameters and the shear properties of the CFRP/Mg interface was analyzed. In addition, shear tests and simulations of the laser-treated interfaces with different groove parameters were performed. Increasing the groove depth and decreasing the groove spacing effectively improved the shear strength of the CFRP/Mg interface. In addition, the reliability of the interface cohesion parameters obtained using the representative volume element model was verified by experiments and simulations, which is important for the application of laser technology to composite laminates. [ABSTRACT FROM AUTHOR]

We present an extension of a multiscale micromorphic theory to three-dimensional problems for porous materials, where a clear scale separation is not given. Following the multiscale micromorphic framework of Biswas and Poh (J Mech Phys Solids 102:187–208, 2017), macroscopic governing equations of a micromorphic continuum are derived from a classical continuum on the microscale by means of a kinematic field decomposition. The macro–microenergy equivalence is guaranteed via the Hill–Mandel condition. For linear elasticity problems, generalized elasticity tensors are determined via several RVE computations once and for all, avoiding concurrent RVE computations for an online structural analysis. A three-dimensional implementation is revealed in detail. A comparative study with direct numerical simulations and first-order multiscale computations shows that the computational multiscale micromorphic method has sufficient accuracy and computational efficiency, thus providing a powerful tool for design and practical engineering applications of porous materials. [ABSTRACT FROM AUTHOR]

The skin is the largest organ in the human body and serves various functions, including mechanical protection and mechanosensation. Yet, even though skin's biomechanics are attributed to two main layers—epidermis and dermis—computational models have often treated this tissue as a thin homogeneous material or, when considering multiple layers, have ignored the most prominent heterogeneities of skin seen at the mesoscale. Here, we create finite element models of representative volume elements (RVEs) of skin, including the three-dimensional variation of the interface between the epidermis and dermis as well as considering the presence of hair follicles. The sinusoidal interface, which approximates the anatomical features known as Rete ridges, does not affect the homogenized mechanical response of the RVE but contributes to stress concentration, particularly at the valleys of the Rete ridges. The stress profile is three-dimensional due to the skin's anisotropy, leading to high-stress bands connecting the valleys of the Rete ridges through one type of saddle point. The peaks of the Rete ridges and the other class of saddle points of the sinusoidal surface form a second set of low-stress bands under equi-biaxial loading. Another prominent feature of the heterogeneous stress pattern is a switch in the stress jump across the interface, which becomes lower with respect to the flat interface at increasing deformations. These features are seen in both tension and shear loading. The RVE with the hair follicle showed strains concentrating at the epidermis adjacent to the hair follicle, the epithelial tissue surrounding the hair right below the epidermis, and the bulb or base region of the hair follicle. The regions of strain concentration near the hair follicle in equi-biaxial and shear loading align with the presence of distinct mechanoreceptors in the skin, except for the bulb or base region. This study highlights the importance of skin heterogeneities, particularly its potential mechanophysiological role in the sense of touch and the prevention of skin delamination. [ABSTRACT FROM AUTHOR]

In this paper, we present an enhanced version of the two-scale numerical homogenization with application to asphalt concrete modeling in the elastic range. We modified the method of effective material parameters tensor assessment for analysis based on the representative volume element (RVE). As the method was tested on asphalt concrete, we also present two possible approaches to geometrical modeling of its internal microstructure. Selected numerical tests were performed to verify the proposed approach. The main novelties of this study, i.e. higher order approximation at the macroscale and modification of boundary conditions at the level of RVE analysis, improved the efficiency of our methodology by error reduction. Practically, we obtained a reduction of NDOF up to 3 orders of magnitude (comparing to full-scale and homogenized analysis) that was accompanied with the introduced error of order of several percent (measured in L2 norm). [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The influence of prior austenite grain (PAG) orientation on the deformation behavior of a low-carbon martensitic steel is investigated using crystal plasticity (CP) modeling with hierarchical representative volume elements (RVEs). The Kurdjumov-Sachs (K-S) relationship is refined for accurate PAG reconstruction in martensitic steel. A robust calibration strategy for CP parameters based on nanoindentation tests is developed by integrating analytical calculations with inverse methods. Virtual polycrystalline aggregates are subsequently generated by manipulating initial PAG orientations. The simulations reveal that assigning cube texture to PAGs enhances strain hardening of martensite under plane strain tension. Moreover, the RVEs with brass and copper orientated PAGs exhibit similar deformation behavior, and a more homogeneous strain distribution is realized in the RVE with PAG cube orientation. The influence of PAG orientation on stress and strain fields is correlated with lattice rotation behavior during deformation. Notably, different strain paths elicit distinct lattice rotation trajectories, wherein uniaxial tension and plane strain tension favor grains reorientation toward hard γ-fiber, whilst equi-biaxial tension drives the crystal matrix to concentrate on 〈001〉 and 〈011〉 directions. These findings provide insights into the intricate relationship between microstructural orientation and deformation behavior in martensitic steels, which is crucial for performance optimization.

Part II of the paper presents comprehensive investigations aimed at demonstrating the validation and effectiveness of the proposed integrated model for simulating Coble creep deformation and void nucleation/growth in polycrystalline solids for material design. Quantitative comparisons between the model’s predictions of void area fraction in a 2D cross-section and experimental results using Alloy 201, a commercially pure nickel, demonstrated a high degree of agreement. Furthermore, the numerical simulation results align with theoretical equations, affirming the model’s validity and its capacity to represent complex phenomena accurately. Although traditional laboratory testing for pure Coble creep is challenging due to constraints such as time and equipment limitations, the proposed model offers a distinct advantage, allowing numerical simulation of Coble creep in materials with arbitrary polycrystalline morphologies under various environmental conditions. Leveraging this capability, the study conducted comprehensive numerical simulations to quantitatively explore the effects of environmental and polycrystalline morphology factors on Coble creep deformation and void nucleation/growth in polycrystalline solids. These aspects, which have not been comprehensively addressed in existing studies, were thoroughly investigated. The findings presented here establish a novel foundation for designing heat-resistant materials applicable across diverse equipment scenarios.

This study proposes an integrated model for simulating Coble creep deformation and void nucleation/growth in a 3D polycrystalline solid. Part I of the paper provides a theoretical framework for the proposed model. A representative volume element approach is employed to predict the effects of 3D polycrystalline morphology. The model comprises two distinct but interconnected stages: deformation and void nucleation/growth. The deformation stage of the proposed model comprises two sub-models: grain boundary (GB) migration and GB diffusion. The void nucleation/growth stage is composed of three consecutive calculations: void nucleation, void growth, and postprocessing. The process simulated in the void nucleation/growth stage is driven by relative GB velocity of the respective GBFs and diffusional fluxes between adjacent GBFs, which are provided from the deformation stage. The void nucleation rate is quantified using the relative GB velocity, and the initial void size is determined based on the stability condition for void existence derived from Helmholtz free energy. The void growth rate is evaluated by the atomic diffusion on the GBF and the surface of each void.

Carbon fiber reinforced polymers are widely used to manufacture aerospace deployable structures. These structures are folded in launch configuration and then deployed in space for operational activities. Since the stowage of deployable structures in folded configuration occurs for long time, the understanding of the viscoelastic properties of the material is essential to predict the structural behavior during both the deployment phase and the operational life. In this work, numerical relaxation analysis is performed on the representative volume element (RVE) of a carbon fiber reinforced polymer using a homogenization approach at the microscale. This aims to predict the effects of matrix viscoelasticity on the structural performance of a deployable structure. [ABSTRACT FROM AUTHOR]

AbstractPiezoelectric bimorph cantilevered beams are frequently employed in energy harvesting applications. The use of macro-fiber composites, which combine piezoelectric fibers with rectangular cross-sections and interdigitated electrodes, has significantly enhanced their performance by enabling operation in the 33-mode of piezoelectricity, thereby increasing conversion efficiency. In this article, the Timoshenko beam theory is applied to overcome the limitations of the Euler-Bernoulli theory in modeling transverse vibrations of harvesters with low slenderness ratios (length to thickness ratios). The mixture rule formulation is applied to determine the equivalent properties of the macro-fiber composite (MFC) structure. The electromechanical properties of a representative volume element (RVE) bounded by two successive interdigitated electrodes are coupled to the overall electro-elastic dynamic model of the structure using the Timoshenko theory. Frequency response functions for the power and tip vibration displacement of the MFC bimorph beam are determined from the model. Experimental data from the literature are used to validate the improved results predicted by the model developed in this article. A comparative analysis between the electromechanical responses predicted using a model based on Timoshenko and a model based on Euler-Bernoulli theory is conducted showing agreement, for harvesters with large slenderness ratios and discrepancies of up to 30% for low slenderness ratios. It has also been shown that the model based on Euler-Bernoulli theory overestimates both the mechanical and the electrical responses for low slenderness ratios as the shear and rotary inertia effects are not negligible in this case. [ABSTRACT FROM AUTHOR]

The present article investigates the failure mechanism of the composite laminates with respect to a coupled thermo-mechanical effect. To this end, a novel coupled thermo-mechanical modeling scheme is presented. To accurately capture the nonlinear deformation at macro- and micro-scale affected by the temperature field, the finite volume method is employed to compute the thermal stress, which is introduced into the representative volume element to evaluate the whole microscopic stress field and the macroscopic mechanical behaviors on basis of the finite volume direct averaging micromechanics. In addition, a visco-plastic constitutive model with full consideration of the temperature effect is implanted into the presented multi-scale model to investigate their nonlinear responses. The thermo-mechanical coupling test scheme is subtly designed, and the experimental data shows a high consistency with the theoretical results. On this basis, the microscopic morphology of the fracture surface is further characterized. It is revealed that an elevate temperature improve the matrix toughness to some extent. [ABSTRACT FROM AUTHOR]

Hydrogen grain boundary (GB) trapping is widely accepted as the main cause for hydrogen induced intergranular failure. Several studies were conducted to unveil the role of GBs on hydrogen transport; however, a clear understanding is yet to be attained. This is due to the limitations of the state-of-the-art experimental procedures for such highly kinetic processes. In this study, we aim at providing a deeper understanding of hydrogen-GB interactions using full-field representative volume element (RVE). The phase-field method is chosen for generating RVEs, since it is an appropriate numerical tool to represent GBs. A novel fully-kinetic formulation for hydrogen diffusion and GB trapping is presented, which is compatible with the phase-field based RVEs. GB diffusivity (D gb) and trap-binding energy (E gb) were used as parameters to understand the interactions between diffusion and GB trapping. Uptake and permeation simulations were performed with constant and gradient occupancy boundary conditions respectively. In both cases, increasing E gb , increased the hydrogen GB occupancy. The permeation simulations showed that the hydrogen flux along the GBs increased with increasing both, D gb and, surprisingly, E gb. Since trapping increases the hydrogen occupancy along GBs, it also increases the occupancy gradients, resulting in a higher flux. This led to the conclusion that, in the case of an external occupancy gradient, GB trapping and diffusion cooperate, rather than compete, to increase the hydrogen flux. On the other hand, the decisive factor for the retention of hydrogen at the GBs in permeation simulations was D gb rather than E gb. [Display omitted] • A new full-field model for H diffusion and GB trapping is presented. • The model shows the kinetic interactions of GB diffusivity and trapping. • The build-up of H due to trapping increases the permeation flux. • GB diffusion and trapping constructively interact, increasing H flux. [ABSTRACT FROM AUTHOR]

Summary: A multiscale model for saturated porous media is proposed, based on the concept of representative volume element (RVE). The physics between macro and micro‐scales is linked in terms of virtual power measures given by the general theory of poromechanics. Then, applying the so‐called Principle of Multiscale Virtual Power, together with suitable admissible constraints on micro‐scale displacement and pore pressure fields, a well‐established variational framework is obtained. This setting allows deriving the weak form of micro‐scale balance equations as well as the homogenization rules for the macro‐scale stress‐like variables and body forces. Whenever the micro‐scale mechanical constitutive functionals admit, as input arguments, the full‐order expansion of the micro‐scale pore pressure field, a size effect is inherited on the macro‐scale material response. The current literature attributes this issue to the so‐called "dynamical" or "second‐order" term of the homogenized flux velocity. It has been commonly suggested that the influence of this term is negligible by assuming infinitely small micro‐scale dimensions. However, such an idea compromises the fundamental notion of the existence of RVE for highly heterogeneous media. In this work, we show that the micro‐scale size dependence can be consistently eliminated by a simple constitutive‐like assumption. Accordingly, slight and selective redefinitions in the input arguments of micro‐scale material laws are proposed, leading to a constitutive formulation that allows the combination of micro‐scale variables with different orders of expansion. Just at this specific (constitutive) level, a reduced‐order expansion is selectively adopted for the micro‐scale pore pressure field. Thus, the RVE notion is restored while still retaining the major effects of the "dynamical" component of the homogenized flux velocity. The proposed formulation is implemented within a finite element squared (FE2$$ {}^2 $$) environment. Some numerical experiments are presented showing the viability of the methodology, including comparisons against analytical, mono‐scale and DNS solutions. [ABSTRACT FROM AUTHOR]

Tidal turbine infrastructure is currently in the large-scale prototype and short-term demonstration phase. However, the immediate requirement is to develop materials, processes and long-term life predictive facilities for tidal turbine plant that has decades of operational lifetime requirements. Computational modelling is a key tool to interpret the experimental data, understand the relevant mechanisms and provide a predictive capability for the performance of aged components for industries. The goal of this paper is a prediction of the long-term life of marine-based glass/epoxy and carbon/epoxy composite laminates aged in artificial seawater with 3.5% salinity based on Arrhenius degradation theory and tensile strength retention over 180 days ageing at room temperature and 60°C. Three different analytical models (linear and exponential) were implemented to calculate time shift factors and corresponding life in a real marine environment. Additionally, multi-scale modelling has been implemented via a representative volume element approach for square and hexagonal cells, and two-step homogenization of textile composites in accordance with nanoindentation testing for matrix/resin cells and fibre constraint cells after 90 days of immersion in saltwater. In general, the multi-scale modelling in ABAQUS and TexGen4SC was able to approximate (with about 10% difference) the mechanical properties of dry and aged composite laminates. [ABSTRACT FROM AUTHOR]

Development of load-bearing fiber reinforced plastic (hereinafter referred to as FRP) composite structures in civil engineering, exploited under high temperatures, such as industrial chimneys and gas ducts, requires the knowledge of their long-term behavior under constant and cyclic mechanical and temperature loads. Such conditions mean that the viscoelasticity of FRP should be considered along with the thermal aging effect. This research is devoted to the effects of thermal aging on the viscoelastic behavior of polymers. Two sets of experiments were conducted: creep tensile tests and cyclic heating in a constrained state. The Kelvin–Voigt viscoelasticity model was used to determine the rheological parameters of binder from experimental creep curves. Cyclic heating was used to compare the behavior of normal and thermally aged binders and to evaluate the possibility of temperature stress accumulation. Fourier-transform infrared spectroscopy was used for polymer's structural changes investigation. Both tests showed that non-aged glassed polymer (hereinafter referred to as GP) was prone to viscoelastic behavior, while the thermally aged GP lost viscosity and worked almost perfectly elastic. It was assumed that long heat treatment had caused changes in the inner structure of the GP, reducing the number of weak bonds and increasing the number of elastic ones. Therefore, the results show that the designing of FRP structures, exploited under thermomechanical load, requires using the elastic model while taking into account the properties of FRP after long-term heat treatment. [ABSTRACT FROM AUTHOR]

This article characterized the mechanical performance and failure mode of single‐lap joints (SLJs) of carbon fiber reinforced boron‐modified phenolic resin plastic (CF/BPR) and TC4 titanium alloy by quasi‐static tensile tests at four temperatures (25, 100, 175, and 250°C). The experimental results indicated that the shear strength of SLJs is 10.8 MPa at 25°C, which experiences monotonic drop to 80%, 42.6%, and 18.5% with temperature increase from 100 to 175°C, and to 250°C, respectively. Additionally, there was a transformation in the failure mode from composite material failure to cohesive failure in the adhesive along with the temperature increase. The intralaminar elasticities of CF/BPR were predicted using representative volume element (RVE), and the mechanical properties of three types of bondlines (i.e., the interlamination, interface of CF/BPR and the epoxy adhesive layer) were determined by both experiment and predictive methods. A finite element model taking into account the intralaminar damage of CF/BPR and the cohesive behavior of three bondlines was established. The simulated results showed good consistency with the experimental data for failure prediction, and the mechanical performance and damage propagation of SLJs at different temperatures were discussed. This research provides reference for the design and manufacture of high‐temperature bonded structures. Highlights: RVE and degradation factor methods evaluate the elasticity of composite material.Four types of damage behaviors are considered in the established FE model.The SLJs exhibit single or multiple failure modes at different temperatures.The mechanical properties of SLJs severely degraded with increasing temperature. [ABSTRACT FROM AUTHOR]

We study the large-scale behavior of a small-strain lattice model for a network composed of elastoplastic springs with random material properties. We formulate the model as an evolutionary rate independent system. In an earlier work we derived a homogenized continuum model, which has the form of linearized elastoplasticity, as an evolutionary T-limit as the lattice parameter tends to zero. In the present paper we introduce a periodic representative volume element (RVE) approximation for the homogenized system. As a main result we prove convergence of the RVE approximation as the size of the RVE tends to infinity. We also show that the hysteretic stress-strain relation of the effective system can be described with the help of a generalized Prandtl--Ishlinskii operator, and we prove convergence of a periodic RVE approximation for that operator. We combine the RVE approximation with a numerical scheme for rate-independent systems and obtain a computational scheme that we use to numerically investigate the homogenized system in the specific case when the original network is given by a two-dimensional lattice model. We simulate the response of the system to cyclic and uniaxial, monotonic loading, and numerically investigate the convergence rate of the periodic RVE approximation. In particular, our simulations show that the RVE error decays with the same rate as the RVE error in the static case of linear elasticity. [ABSTRACT FROM AUTHOR]

Improving the ductile deformation behavior of Mg-SiC nanocomposites without compromising strength is critical to enhancing their mechanical properties. Mg-SiC nanocomposites are produced through mechanical milling, cold isostatic pressing, sintering, and hot extrusion processes. This study investigates the uniaxial stress–strain response and deformation behavior of the Mg-SiC nanocomposite compared to pure Mg samples with and without the milling process. The deformation behavior was investigated by two-dimensional (2D) digital image correlation (DIC) at two macroscopic and microscopic scales, employing light micrographs and in situ loading samples, respectively, in the scanning electron microscope. Compared to the pure Mg samples, the mechanical test results demonstrated a significant improvement in strength (80 MPa) and fracture strain (23.5%) of the Mg-SiC nanocomposite. The three-dimensional (3D) representative volume element (RVE) model revealed the particle dispersion effect on the mechanical properties of the nanocomposite. The RVE results demonstrate ductile deformation behavior in the sample with homogenous dispersion of SiC particles compared with the heterogeneous dispersion of SiC particles in Mg-SiC nanocomposite. The results demonstrated a good agreement between DIC and RVE predictions for Mg-SiC nanocomposites across macro- and microscales. [ABSTRACT FROM AUTHOR]

The objective of this study is to improve the mechanical properties of self-healing carbon fiber reinforced polymer (CFRP) with microcapsules (MCs) incorporating healing agents, in order to achieve superior mechanical properties and healing efficiency. The approach to improve the mechanical properties is to hybridize spread carbon fiber (SCF) and woven carbon fiber (WCF) as reinforcements. The interlaminar shear strength and the healing efficiency of the self-healing SCF/WCF hybrid laminates were evaluated by short beam shear tests, and then compared with those of self-healing SCF/EP laminates and self-healing WCF/EP laminates. Moreover, the finite element analysis (FEA) using a representative volume element (RVE) model of the SCF/WCF hybrid laminates containing MCs was performed to evaluate the elastic properties and the internal stress and reveal the relation between them and microstructure. Furthermore, we performed the FEA of short beam shear test using the elastic properties predicted from the RVE models and verified the validation of the RVE model by comparing the analytical results with the experimental results. The experimental results showed that the hybridization of SCF and WCF can be effective for improving mechanical properties of self-healing CFRP laminates compared to those of self-healing SCF/EP laminates. However, the self-healing SCF/WCF hybrid laminates did not present sufficient healing efficiency due to the large transverse cracks in the WCF layers. Therefore, in order to improve healing efficiency, it is necessary to suppress the large crack propagation in the WCF layer. The analytical results indicated that the stress concentration occurred in the WCF layer and could be mitigated by increasing the thickness of the SCF layer. The experimental results and analytical results were in good agreement. Therefore, the RVE model used in this study effectively predicted the properties of the self-healing CFRP laminates and provided microstructure design guidelines for achieving superior mechanical properties and healing efficiency.

Despite recent advancements in using machine learning (ML) techniques to establish the microstructure-property linkage for composites’ representative volume elements (RVEs), challenges persist in effectively characterising the effect of microstructural randomness on material properties. This complexity arises from the difficulty of expressing randomness as definitive variables and its intertwined relations with other factors, such as material constituents. Such complexities result in limitations in generalising ML models across different material constituents. Conventional solutions to these challenges usually necessitate large datasets, which require considerable computational resources, for an accurate and generalisable ML models to be trained. This paper presents an innovative approach to tackling these challenges by integrating a high-accuracy convolutional neural network (CNN) with a novel microstructure-factored constitutive model (MCM). The MCM, rooted from classic empirical constitutive modelling, effectively segregates the microstructural and constituting material effects, extending the generalisability and thus significantly enhancing the efficacy of the CNN. This new approach enabled a CNN trained on the transverse stress-strain curves of one set of material constituents (CF/PEEK at 270 °C) to be generalised for the rapid prediction of various sets of material constituents at different temperatures, unseen by the CNN during training, with an average mean absolute percentage error around 3 %.

In this study, the aging performance of particle-filled polymer composites (PFPCs) under thermo-oxidative conditions was investigated on multiple scales. High-temperature-accelerated tests were conducted to analyze the effects of aging time and temperature. A representative volume element (RVE) model was established for the PFPCs using a random particle-filling algorithm. A predictive model for the crosslink density was conducted based on the closed-loop chain reaction of polymer oxidation. According to the theory of polymer physics, the relation between the crosslink density and matrix modulus was determined. The particle/matrix interface in the RVE model was represented by the cohesive zone model (CZM). The parameters of the CZM were determined by the inversion techniques. Then, a comprehensive multiscale RVE model was constructed, which was applied to predict the modulus and dewetting strain of the aged PFPCs. The predicted results show good agreement with the test results, which verifies the reliability of our model. [ABSTRACT FROM AUTHOR]

Three‐harness twill woven composite (THT‐WC) is an advanced carbon fiber reinforced composite that compromises the mechanical behaviors in both longitudinal and latitudinal directions. To explore the further practical application, the structural characteristics and static mechanical behavior of the material were investigated in this article. X‐ray computerized tomography was adopted to obtain the mesostructure details and to capture the key characteristics. With the help of mesoscale information, the 2D and 3D geometric models were established in the form of representative volume elements (RVEs). Combined with voxel mesh generation technology, a finite element model was proposed based on a 3D geometric model where macroscopic mechanical properties of materials along different yarn directions were gained. To verify the simulated geometry and predicted mechanical properties, mesoscale geometric comparison and specimen tensile tests were performed. The results show that the geometric model established in this article can reasonably reflect the periodicity fluctuation of binder warp yarns and the randomness fluctuation of weft yarns. Compared with the experimental results, the relative error of stiffness in the weft direction of the RVE is 4.25%, and that in the warp direction is 5.33%. Highlights: The mechanical properties of THT‐WC were investigated experimentally.Meso‐scale reconstruction of THT‐WC was presented.A model to predict the mechanical properties of THT‐WC is established. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is an additive manufacturing technique commonly used in the rapid prototyping of components. The complexity of the SLM microstructure poses a unique challenge to deriving effective mechanical properties at different length scales. Representative volume elements (RVEs) are often used to homogenize the material properties of composites. Instead of RVEs, we use statistical volume elements (SVEs) to homogenize the elastic and fracture properties of the material. This relates the inherent variation of a material's microstructure to the variation in its mechanical properties at different observation scales. The convergence to the RVE limit is examined from two perspectives: the stability of the mean value as the SVE size increases for the mean-based approach, and the tendency of the normalized variation in homogenized properties to zero as the SVE size increases for the variation-based approach. Fracture properties tend to make the RVE limit slower than do elastic properties from both perspectives. There are also differences between vertical (normal to printing plane) and horizontal (in-plane) properties. While the elastic properties tend to make the RVE limit faster for the horizontal direction, i.e., having a smaller variation and more stable mean value, the fracture properties exhibit the opposite effect. We attributed these differences to the geometry of the melt pools. [ABSTRACT FROM AUTHOR]

Abstract This paper proposes a novel concept and methodology to study longitudinal wave propagation in entangled metallic wire material (EMWM), a porous structural network consisting of spatial helix wires. The numerical model of EMWM is constructed using representative volume elements (RVE) obtained through X-ray tomography and skeletonization of a standard specimen. By increasing the approximate periodic boundary, the improved wave and finite ele-ment method (WFE) is employed to model EMWM as approximately periodic structures, allowing for numerical simulations of wave propagation characteristics. Frequency bands and resonance modes of EMWM are calculated to analyze the characteristics of one-dimensional wave propagation. The numerical results show that EMWM exhibits unique frequency band characteristics compared to typical periodic porous materials. In the frequency range of 15 to n n 35 kHz, the first pass band corresponds to the tensile-compressive motion of the entire specimen, while the higher pass bands correspond to localized vibrations within the spatial wires. Additionally, the frequency bands can be adjusted across a wide range based on the relative density of EMWM specimens. The improved WFE method and obtained numerical data can facilitate the application of EMWM on high frequency vibration isolation. [ABSTRACT FROM AUTHOR]

This paper investigates the 20 wt.% SiCp/A356 composites used for brake discs through finite element simulation. A Representative Volume Element (RVE) model considers microstructure morphology, particle geometry, content, and the elastic-plastic damage behavior of the matrix. Tensile deformation and damage failure of the RVE at 200°C is simulated. The advisable interfacial strength is determined by combining simulation and experiment. Parametric modeling of SiC particle characteristics (size, shape, distribution) explores their influence on tensile mechanical properties and damage behavior at 200°C. Refining SiC particles (10~25 μm) improves ultimate strength but reduces ductility. Recommended fabrication: SiC particles with 13 μm nominal size, with main distribution between 10 μm and 16 μm, enhancing ultimate strength while maintaining ductility. Increasing the minimum angle of particle sharp corner (>45°) improves both ultimate strength and ductility, ensuring mechanical stability and reducing brittle fracture risk. SiC particle agglomeration accelerates damage initiation, crack propagation, and reduces elastic modulus. Suggested quality control standard: 25% particle agglomeration within a 140 μm × 140 μm field of view. These findings provide insights into optimizing mechanical properties and damage behavior of SiCp/A356 composites for brake discs. [ABSTRACT FROM AUTHOR]

The present work is an investigation on the elastic properties of Luffa as well as Palm natural fiber composites (NFC) in high density polyethylene (HDPE) and polypropylene (PP) matrixes, taking into consideration the effect of the variation of the volume fractions (Vf) of fibers. Moreover, representative volume element (RVE) models with unidirectional and chopped random fiber orientations were utilized for predicting longitudinal, transverse, and shear moduli as well as Poisson's ratio. Furthermore, rule of mixture (ROM), Halpin-Tsai, Chamis, and Nielsen analytical approaches were used for comparing and validating the finite element analysis (FEA) results. RVE Chopped showed highest accuracy in predicting the elastic properties of luffa and palm-reinforced thermoplastics. RVE unidirectional model findings revealed a significant agreement with analytical results. [ABSTRACT FROM AUTHOR]

Advanced high-strength steel (AHSS) is of great technological interest in automotive lightweight applications. The dual-phase (DP) steel with a higher volume fraction of martensite has been rarely studied. In this work, the micromechanical deformation incompatibility of DP1180 steel was analyzed by a microstructure-based representative volume element (RVE) model. Via the electron-backscattered diffraction (EBSD) and the open-source software DREAM.3D, the statistically real microstructure-based RVE model was established. The flow curve of ferrite was obtained by the dislocation-based method. And the flow curve of martensite was obtained by the isostrain method (ISM) and the non-isostrain method (NISM). The simulation results showed good coincidence with the experiments. Furthermore, the ISM and the NISM were well clarified and improved. The microscale stress and strain in ferrite and martensite are approximately normal distributions due to the deformation incompatibility. The simulations verified that martensite carries much higher stress than ferrite. The mean value of strain in martensite is smaller than that in ferrite. And the strain variances of ferrite and martensite are similar. A larger variation range of stress triaxiality in ferrite indicates that the ferrite has gone through a more complex stress state. While the martensite has been approaching from the tension–compression state to the uniaxial-tension state. Consequently, the strain localization and damage initiation are predicted to be preferentially through ferrite compared to martensite, which is in good agreement with the results of the in situ tensile test. This paper provides a detailed analysis of the deformation incompatibility of the DP steel, especially in which the volume fraction of martensite is larger than that of ferrite. And it has theoretical significance for accurately predicting the micromechanical deformation behavior of multi-phase materials. [ABSTRACT FROM AUTHOR]