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The imperative to attain net-zero emissions emphasizes energy conservation. Radiative cooling stands out as a compelling technology in this pursuit for its self-sufficiency and cost-effectiveness. However, the radiative cooling faces the challenge in varied weather, including high ultraviolet (UV), cloudy and rainy days, primarily due to instability of radiative cooling materials and mono-energy conservation mechanism. To address this issue, a durable, breathable, and weather-adaptive coating (porous PTFE coating) has been developed through assembling polyfluortetraethylene (PTFE) nanoparticles enabled by the differential interaction in a binary-solvent system. The porous PTFE coating exhibits high solar reflectivity (94%) and thermal emissivity (93%), which results from the precisely tunable assembly of PTFE nanoparticles, forming a desired porous morphology. This design serves as effective scattering, achieving a sub-ambient cooling effect of approximately 5 ℃ at midday. With an outstanding UV protection factor (UPF) of 179.15, the porous PTFE coating sustained stability after 40 days exposure to solar radiation. Leveraging the porous PTFE coating's exceptional negative triboelectric effect, an engineered high-performance droplet electricity nanogenerator (DEG) achieves a notable power density of 153.8 mW/m2, revealing significant potential for raindrop energy harvesting on rainy days. The versatile porous PTFE coating, with its exceptional weather adaptation and UV stability, holds promise for diverse applications, advancing sustainable and efficient energy solutions with reliability in varying conditions. [Display omitted] • Porous PTFE coating is developed to adapt to various weather conditions, aiding in energy conservation. • Porous structure scatters all sunlight wavelengths; PTFE particles effectively scatter UV radiation. • High reflectivity (94%) and infrared emissivity (93%) provide ~5℃ cooling under ~1000 W/m2 solar intensity. • Porous PTFE coating resists UV damage, with a UPF of 179.15, remaining stable after 40 days of solar exposure. • A DEG based porous PTFE coating captures energy from raindrops, achieving a power density of 153.8 mW/m2. [ABSTRACT FROM AUTHOR]

• An original ICVI algorithm reproducing the pyrolytic carbon deposition process is proposed. • The relationship between the process parameters and mechanical properties of unidirectional carbon/carbon composites is investigated. • The transverse modulus and tensile strength increase with an increase of the infiltration time, pressure, and temperature. • Interfacial debonding and propagation of multiple cracks result in the complete failure of unidirectional carbon/carbon composites. This paper proposes an innovative algorithm derived from the isothermal chemical infiltration process to generate quasi-real microstructures of unidirectional carbon/carbon composites. This algorithm, which can predict the relationship between the composite density and infiltration time, is termed the isothermal chemical infiltration algorithm. To further evaluate the relationship between the process parameters and the mechanical properties, a mesoscale finite element model of the unidirectional carbon/carbon composite is established based on the isothermal chemical infiltration algorithm. After validation, the developed numerical model is employed to study the effects of the infiltration time, pressure, and temperature on the effective mechanical properties. The results show that the transverse modulus and tensile strength increase with an increase in the infiltration time, pressure, and temperature, with the effect of temperature being the most significant. In parallel, it is revealed that the complete failure of unidirectional carbon/carbon composites results from interfacial debonding and propagation of multiple cracks during transverse tension. The proposed model has potential applications in the process design and optimization of high-performance carbon/carbon composites. [Display omitted] [ABSTRACT FROM AUTHOR]

Combining with the modified random sequential adsorption algorithms and the microstructure information obtained from substantial PLM images of carbon/carbon (C/C) composites, a strategy is presented for generating the representative volume elements (RVEs) with complex microstructures such as fiber and spatially randomly distributed pores. The formulation of the Minimum Distance Search Method for efficiently checking the intersection of the fibers-pores or pores-pores in the RVEs is discussed. Within the frameworks of elasticity, the effect of volume fraction and aspect ratio of pore inclusions on the effective elastic properties of C/C composites are investigated using the finite element method (FEM) and numerical homogenization method. The validation is performed by comparing the predicted effective elastic modulus against those measured by uniaxial tensile tests. FEM results show that with increase of porosity, the effective elastic properties of C/C composites decreased rapidly. Compared with the transverse elastic of unidirectional C/C composites, the downward trend of elastic properties of the felt C/C composites is more inclined. Furthermore, under a certain porosity, with increase of the aspect ratio, the effective elastic properties of C/C composites increase. [ABSTRACT FROM AUTHOR]

For investigating the effect of the irregular pores on transverse elastic properties of the unidirectional Carbon/Carbon (C/C) composites, a new strategy is proposed to generate the representative volume element (RVE) on the basis of scanning electron microscope (SEM) images, in which these pores are approximated as the polygons and the identical fibers are generated by using the RSA algorithm. A good agreement is achieved by comparing the effective elastic properties obtained from the FEM-homogenization techniques to those predicted by experimental tests and two-step Mori-Tanaka method. FEM results indicate that the convergence of the results is seen when the number of vertices of the polygon reaches 40 and the RVE edge length is eight times of the maximum pores size ( L/l max  = 8). Meanwhile, the average departure from isotropy is below 5% and the UD composites can be considered as transverse isotropic. The effective transverse elastic properties would decrease with increase of the porosity and with increase of the pores clustering η p . [ABSTRACT FROM AUTHOR]

Numerical simulation with progressive damage criterion is implemented to investigate the effect of porosity on the bending properties of 2D cross-ply carbon/carbon (C/C) composites. The mechanical properties of Pyrocarbon matrix regarding the change of porosity are calculated by using Mori-Tanaka approach. Combining with the stiffness degradation scheme, the ultimate bending strengths are calculated in Abaqus though a user-defined subroutine (USDFLD). Delamination is modelled by inserting cohesive elements between two adjacent plies. A good agreement is obtained when the FEM results are compared to three-point bending experiments. The FEM results show that the bending strength decreases greatly with the increase of porosity. When the porosity reaches up to 18%, the bending strength is decreased by 57%. The major fracture behaviors are interlamination delamination and continuous crack damage in 90° plies. With the increase of porosity, more severe interlamination delamination will be slightly aggravated. In addition, the increase of porosity will also accelerate the damage in 90° plies. [ABSTRACT FROM AUTHOR]

• Introduces an interpretable surrogate solver for computational solid mechanics. • The numerical framework, architecture, algorithms, code and associated packages of PINN are summarized. • PINN-based methods are validated for the constitutive modeling and its inverse problems. • Advances of PINN for addressing identification, prediction, and evaluation of solids' damage are presented. • Concludes the emerging opportunities and open challenges of prevailing trends for PINN. For solving the computational solid mechanics problems, despite significant advances have been achieved through the numerical discretization of partial differential equations (PDEs) and data-driven framework, it is still hard to seamlessly integrate imperfect, limited, sparse and noisy data into existing algorithms. Besides the expensive tasks and struggling completion of mesh-based and meshless-based solutions in complex computational domain, the high-dimensional solid mechanics problems governed by parameterized PDEs cannot be tackled. Furthermore, addressing inverse solid mechanics problems, especially with incomplete descriptions of physical laws, are often prohibitively expensive and require obscure formulations and elaborate codes. Since the physics-informed neural networks (PINN) was originally introduced by Raissi et al. in 2019, it has been recognized as effective surrogate solvers for PDEs while respecting any given laws, data, initial and boundary conditions of solid mechanics. PINN has emerged as a promising approach to mitigate the shortage of available training data, enhance model generalizability, and ensure the physical plausibility of results. The prior physics information can act as a regularization agent that constrains the space of admissible solutions to a manageable size, enabling it to quickly steer itself towards the right solution. To catch up with the latest developments of PINN in computational solid mechanics, this work summarizes the recent advances in the field. We first introduce the foundational concepts of PINN, including the framework, architecture, algorithms, code and associated software packages. We then discuss the applications of PINN in constitutive modeling and its inverse problem, identification, evaluation, and prediction of damage in solid materials and structures. Finally, we address the current capabilities and limitations of PINN in computational solid mechanics, and present perspectives on emerging opportunities and open challenges of the prevailing trends. [ABSTRACT FROM AUTHOR]

In this work, a simple but effective fractal model is proposed to predict the mechanical properties of complex porous composites. By extending the Mori-Tanaka and Double Inclusion models, we develop a computationally efficient algorithm based on the mean-field homogenization, to quickly determine the macroscopic elastic properties of the random porous media by the fractal theory. The random pore sizes and locations are properly characterized by a single fractal dimension, and the fractal model agrees well with the numerical results obtained by the finite element homogenization technique and the existing experimental data from literature. Moreover, the effect of pore size distribution has been investigated, indicating that the elastic properties decrease with the increase in the fractal dimension. In particular, the computation time can be reduced from 4 h for the finite element analysis to 15 s based on the fractal model. Based on the mathematically analogous governing equations, the present fractal modeling has great potential to determine the other significant physical properties such as thermal conductivity and coefficient of thermal expansion. [Display omitted] [ABSTRACT FROM AUTHOR]

This work proposes a new algorithm entitled "sequential absorption algorithm" to generate Representative Volume Elements (RVEs) of randomly distributed spherical particles reinforced composites by combining the Random Sequential Absorption (RSA) algorithm and the molecular dynamics based method. The proposed algorithm overcomes limitations of the RSA algorithm and is capable of efficiently generating the RVEs with the high Particle Volume Fractions (PVFs) (≥ 50.0 %). The proposed algorithm comprises of the modified RSA algorithm, the detection algorithms of the collisions between particles and between a particle and matrix surface(s), the post-collision particle velocity update algorithm, the particle periodic image generation algorithm and the acceleration algorithm. Particle distribution in the generated RVEs is analyzed through several statistical functions and consistent with the completely spatial random pattern. Regarding the elastic properties of composites, the critical sizes of RVEs and meshed elements are determined. The agreement of the elastic properties of composites with the different PVFs acquired using the finite element homogenization method, the experimental tests and the analytical models exhibits the validation of the proposed algorithm to generate RVEs of composites. [Display omitted] • A new sequential absorption algorithm to generate RVE of composites is proposed. • The proposed algorithm can generate RVEs with high particle volume fractions. • The proposed algorithm has good computational efficiency for small particle number. • Particle distribution in the RVEs is consistent with completely spatial random pattern. [ABSTRACT FROM AUTHOR]

In this work, an improved version of the Random Sequential Absorption (RSA) algorithm, comprising of the particle re-orientation algorithm, the particle intersection checking algorithm, the particle periodicity constraint algorithm and the acceleration algorithm, is proposed to efficiently generate Representative Volume Elements (RVEs) of spheroidal particles reinforced composites with specified particle orientations. The re-orientation of the particles is realized using the gradient descent based optimization method, and the RSA algorithm is accelerated by combining with the RVE subcell method and the bounding sphere concept. Several statistical functions are introduced to analyze the distributions of the orientation and centroids of the particles in the RVEs generated by the improved algorithm. The results show that the particle orientations of the generated RVEs match well with the specified particle orientations, and the centroids of the particles in the generated RVEs are not completely randomly distributed. Based on the generated RVEs, the elastic properties and coefficients of thermal expansion of spheroidal particles reinforced composites are predicted by using the FE homogenization method, and the predicted thermo-elastic properties of the composites agree well with those of the analytical models. The advantage of the improved algorithm lies in two aspects: (1) much better computational efficiency and (2) capability of generating the RVEs with specified particle orientations. Image 1 [ABSTRACT FROM AUTHOR]

In this paper, a new algorithm for the periodic boundary condition used for numerically predicting the coefficients of thermal expansion (CTEs) of different composite systems based on the finite element homogenization method is proposed. The results demonstrate that the proposed algorithm guarantees stress and strain continuities on the opposite surfaces of the representative volume elements (RVEs) for composites with spherical particles and plain woven fabrics but not for composites with cylindrical fibers and three-dimensional four-directional braided yarns. Meanwhile, the proposed algorithm ensures the micro–macro energy balance (Hill's lemma) and the zero macro-stress constraint of the RVEs for all composite systems. Through the comparison with experimental tests and other numerical methods, the proposed algorithm is validated to be capable of accurately predicting the CTEs of composites. • A new numerical implementation algorithm of periodic BC is proposed. • The proposed algorithm guarantees thermal flux continuity on RVE boundaries. • The proposed algorithm ensures the balance of RVE micro-/macro-strain energy. • ETCs of four composite systems are accurately predicted by the proposed algorithm. [ABSTRACT FROM AUTHOR]

This paper investigates the feasibility of using porous pyrolytic carbon (PyC) to produce low thermal expansion (CTE) carbon/carbon composites by using a multi-scale representative volume element (RVE) based on a finite element (FE) homogenisation strategy. The distribution of pores is characterized by mercury intrusion test and multi-peak Gaussian function. The RVEs of porous structures at micro- and macro-scale are generated using a modified random sequential adsorption (RSA) algorithm. The effective CTEs of porous PyC composites are obtained by implementing the periodic boundary conditions and the numerical implementation is detailed herein. The predicted effective macroscopic CTEs are validated by experimental measures. The results show that the absolute values of effective macroscopic CTEs of PyC composites nonlinearly increase with increasing pore volume fraction. For the high-texture (HT) chopped C/C composites, the effective CTEs reach a minimum at fibre yarn volume fraction of V fm ≈ 7%, whereas the effective CTEs of low-texture (LT) PyC composites increase with increase of the fibre volume fraction. In addition, the effect of aspect ratio of the fibre yarn on the effective CTEs of both HT and LT composites are not significant. [ABSTRACT FROM AUTHOR]

Highlights • Periodic BCs are used to predict the effective thermal conductivity of composites. • Numerical implementation algorithm of the periodic BCs is presented. • Thermal flux continuity of the RVE boundary is maintained by the periodic BCs. • Thermal conductivity of spherical inclusions reinforced composites is isotropic. • Thermal conductivity of short random fibers reinforced composites is isotropic. Abstract Boundary condition plays an important role in prediction of the effective thermal conductivity of composites. In this research, the periodic boundary condition and the representative volume element (RVE) based finite element (FE) homogenization method are adopted to evaluate the effective thermal conductivities of the composites reinforced by the spherical, ellipsoidal and cylindrical inclusions, and the emphases are on the numerical implementation algorithm and validation of the periodic boundary condition. The heat flux continuity of the node pairs on the opposite surfaces of the RVEs of the composites is analyzed and the effective thermal conductivity of the composites are homogenized. The results show that the heat flux continuity of the node pairs on the opposite surfaces of the RVEs of the composites can be guaranteed by the proposed numerical implementation algorithm for the periodic boundary condition, and that the predicted effective thermal conductivities of the composites agree well with those determined by the Lewis-Nielsen model and the experimental tests. Therefore, the RVE based FE homogenization method with the periodic boundary condition can accurately evaluate the effective thermal conductivity of the composites with discontinuous inclusions. [ABSTRACT FROM AUTHOR]

Abstract To evaluate the effective mechanical properties of the composites with complicated micro-structures, the RVE based FE homogenization method with the periodic boundary condition is introduced and implemented in this paper, and the emphasis is on the periodic boundary condition and its numerical implementation algorithm. The pre-processing (such as the generation of geometry model and application of periodic boundary condition), FE analysis and post-processing (such as the average of stress and strain and stress contouring of the surface nodes) concerning the evaluation of the effective mechanical properties of the composites with complicated micro-structures are conducted in the FE package ABAQUS through the Python Interface. Numerical results show that the proposed numerical implementation algorithm of the periodic boundary condition guarantees the stress and strain continuities and uniaxial deformation constraint of the RVEs for the composites with complicated micro-structures. Compared with the Halpin-Tsai model and two-step M-T/Voigt mean-field homogenization method, the RVE based FE homogenization method with the periodic boundary condition is verified to accurately predict the effective elastic properties and elasto-plastic responses of the composites with the complicated micro-structures. [ABSTRACT FROM AUTHOR]

Abstract To accurately predict the effective elasto-plastic responses of two-phase composites, an interpolative M-T/D-I mean-field homogenization model with the tangent formulation is proposed, and the numerical implementation algorithm of the proposed M-T/D-I model with the tangent formulation is presented. The comparisons between the effective elastic properties and elasto-plastic responses of two-phase composites predicted by the M-T/D-I model with the tangent formulation and the RVE based FE homogenization method show that the M-T/D-I model with the tangent formulations can accurately evaluate the effective mechanical properties of two-phase composites. The simulation results demonstrate that the elastic properties of two-phase composites predicted by the M-T/D-I model are more accurate than those predicted by the D-I and M-T models, and the effective elasto-plastic responses of two-phase composites predicted by the M-T/D-I model vary in the range of those predicted by the D-I and M-T models. It is revealed that the M-T/D-I model with the tangent formulation allows to simulate the tensile/compression and biaxial tensile/shear elasto-plastic responses of two-phase composites. Lastly, the effects of the inclusion volume fraction and elastic properties on the effective elasto-plastic responses of two-phase composites are discussed for showing the capability of the proposed interpolative M-T/D-I model with the tangent formulation. [ABSTRACT FROM AUTHOR]

2-D Cf/Mg composites consisting of AZ91D magnesium alloy and carbon non-woven fabrics are prepared by using the LSEVI process and their mechanical properties are experimentally tested. The experimental results show that the 2-D Cf/Mg composites have the better mechanical properties: elastic modulus of 71.0 GPa and ultimate tensile strength of 366.0 MPa, compared to AZ91D magnesium alloy matrix with the elastic modulus of 45.0 GPa and ultimate tensile strength of 250.0 MPa. The effective elastic properties of the 2-D Cf/Mg composites are numerically predicted by using a multi-scale homogenization method: the RVE based FE homogenization method at the macro-scale coupling the D-I mean-field homogenization model at the micro-scale. The agreement between the results of the experimental tests and the multi-scale homogenization method illustrates the validation of the multi-scale homogenization method to evaluate the effective mechanical properties of the 2-D Cf/Mg composites. For improving the computational efficiency, at the macro-scale the laminated composites theory is coupled with the RVE based FE homogenization method to predict the effective mechanical properties of the 2-D Cf/Mg composites. [ABSTRACT FROM AUTHOR]

• A novel odd harmonic method is proposed to eliminate the satellite droplet. • The odd harmonic superposition perturbation induces droplet velocity difference. • The phase angle determines the breakup location and merging characteristics. • The novel method enhances the droplet spacing while maintaining droplet size. In tin-droplet laser-produced plasma sources, uniform droplet streams with large droplet spacing are desired to minimize the interference of explosion on neighboring droplets. Such droplet streams can be generated in low wavenumber regimes. However, satellite droplets easily appear among main droplets in those regimes, resulting in plenty of undesirable debris. Herein, a novel odd harmonic superposition perturbation method is proposed to eliminate satellite droplets and enhance droplet spacing of uniform droplet streams. The superposition number (N) and the phase difference (θ) of odd harmonic perturbations are adjusted to facilitate the coalescence of satellite droplets with main droplets. First, the superposed odd-order harmonic components could induce additional disturbance growth in jet surfaces, and finally lead to the asymmetric necking on filaments formed between two adjacent main droplets, featured as various carrot-shaped configurations. This asymmetric necking will cause unbalanced surface tension forces at the two sides of filaments, resulting in a velocity difference between satellite and main droplets. Based on this principle, by setting N and k to 3 and 0.2, respectively, satellite droplets positioned above main droplets accelerate, while those below decelerate, achieving complete coalescence between main and satellite droplets. Furthermore, the phase difference is found to determine the jet breakup location and satellite droplet merging characteristics. As θ varies from 0° to 90°, the droplet size significantly decreases while the droplet spacing remains constant since the perturbation energy increases. The merge direction of satellite droplets reverses from upward to downward due to enhanced unbalanced surface tension forces and velocity differences. As θ continuously increases to 270°, the droplet size further decreases along with a slight decrease in droplet spacing. Finally, by setting N = 3 and θ = 0°, mono-disperse tin droplet streams with a mean diameter of 31.5 μm and a maximum droplet spacing-to-diameter ratio of 17.7 are successfully formed. This work presents a novel approach for eliminating satellite droplets to achieve uniform tin droplet streams with large droplet spacing without increasing the droplet diameter. [Display omitted] [ABSTRACT FROM AUTHOR]

This work proposes a novel multi-step dynamic FE compression method to generate Representative Volume Elements (RVEs) of composites containing a variety of inclusions. This method is actualized through a sequential and four-stage procedure: (1) Sparse and periodic inclusions exhibiting a predefined orientation distribution are generated by implementing a modified random sequential adsorption algorithm, (2) Sparse inclusions undergo biaxial compression into the region of the targeted RVE via a dynamic FE analysis, (3) Periodic inclusions are compressed into the region utilizing a dynamic FE analysis with periodic boundary conditions, and (4) Positions and orientations of the compressed inclusions are extracted and the RVE in computer-aided design format is then generated. The proposed method confers advantages from four distinct perspectives: (1) applicability to various inclusion geometries, including ellipses, lobules, polygons, kidneys and stars, (2) ability to generate periodic RVEs of composites with high inclusion volume fractions (up to 80.0% for circular inclusions), (3) simple and straightforward numerical implementation without explicitly considering inclusion intersection check and (4) capacity to predefine inclusion orientation distribution. Statistical analyses utilizing multiple spatial descriptors, i.e., inclusion orientation angle, local volume fraction, Voronoi cell area, nearest-neighbor distance and orientation, second order intensity function, radial distribution function and two-point probability function, confirm randomness of inclusion distribution in the generated RVEs. The elastic properties and damage behaviors of composites via the FE homogenization method are predicted based on the generated RVEs and are compared with those of available experimental data, the literature and the mean-field homogenization models to demonstrate effectiveness of the proposed multi-step dynamic FE compression method. • A novel method to generate composite RVE with high inclusion volume fraction. • The method are available for composite RVEs with diverse inclusions. • The method has better computational efficiency and simpler implementation. • The method can predefine inclusion orientation distribution. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel framework generates realistic 3D meso -scale RVEs for concrete, integrating aggregates, ITZ, mortar, and pores. • This efficient framework achieves aggregate volume fractions from 0% to 80% within 30 seconds for 1,000,000 elements. • This work reveals the relationships between mesoscale structures and compressive properties of multi-phase concretes. • Analytical models elucidate the influence of aggregate volume fraction and porosity on the mesoscopic properties of concrete. This paper presents an innovative numerical modeling framework capable of generating highly realistic 3D mesoscale multi-phase concrete models with unprecedented efficiency and accuracy. Addressing a significant wide range in aggregate volume fraction (0 to 80%) and featuring rapid model generation capabilities, our framework marks a breakthrough in reducing computational time—achieving simulations of 1 million elements within mere 30 s on readily available hardware. By analyzing randomly generated concrete samples across varying compositions, our algorithm can provide deep mesoscopic insights into their compressive properties, validated against a wide array of experimental results. Additionally, our comprehensive analytical model sheds light on the intricate roles of aggregate volume fraction and porosity, enhancing understanding of the meso -scale compressive behavior. We also make the source code available on GitHub, offering a valuable tool for the engineering and research community to optimize concrete material design and performance. [ABSTRACT FROM AUTHOR]

In this paper, the microhardness of the AZ91D matrix in C f -SiCNWs/AZ91D composites is investigated. It is found that introducing SiCNWs into composites can increase the microhardness of the AZ91D matrix close to the SiCNWs (the vertical distance does not exceed 100 μm from the SiCNWs), which is as high as 84.34 HV and is 36.78 % higher than that of the alloy far away from the SiCNWs. The SiCNWs/AZ91D zone has the highest average microhardness (103.76Hv), which is 68.28 % higher than that of the AZ91D alloy in the C f -SiCNWs/AZ91D composite. The increase in microhardness of AZ91D matrix is attributed to the synergistic effect of several reasons, including the increased dislocation density, the uneven dispersion of aluminum element caused by SiCNWs, as well as the nanocrystals of Mg 17 Al 12 precipitates. [ABSTRACT FROM AUTHOR]

A modified random fiber removal algorithm is proposed to numerically study transverse elastic properties of unidirectional carbon fiber reinforced pyrolytic carbon (C/C) composites. This method can efficiently generate the Representative Volume Element (RVE) of composites with random distribution fibers. On the basis of the numerical homogenization strategy, the effect of interphase between carbon fiber and pyrolytic carbon on the mechanical behaviors of unidirectional C/C composites are investigated. Meanwhile, periodic boundary conditions and linear elastic constitutive materials are taken into account. For validation, numerical calculations are compared with these obtained by atomic force microscopy (AFM) tests, which shows that more accurate results will be pursued when the interphases are considered. In addition, the influences of interphase parameters including the thickness, modulus, and Poisson's ratio, on the effective transverse behavior of unidirectional C/C composites are studied numerically.The results demonstrate that the effective transverse properties of unidirectional C/C composites are mainly determined by the interphase modulus and independent of the interphase Poisson's ratio. If the interphase thickness (less than 140 nm) of unidirectional C/C composites are very small, the modulus of interphase beyond 8 GPa makes little effect on the effective transverse properties. [ABSTRACT FROM AUTHOR]

In this study, a novel composite with dual interface, namely T-700 carbon fibers grafted with SiCNWs reinforced AZ91D (C f -SiCNWs/AZ91D), was designed. The microstructure of the C f -SiCNWs/AZ91D composite was fully characterized and its thermal expansion behaviors from 25 to 450 °C investigated. The results show that the C f -SiCNWs/AZ91D has dual interface of C f /AZ91D and SiCNWs/AZ91D. In the alloy matrix, the nanowires are uniformly distributed without any agglomerates and showing a good bond with the matrix. Near the interface of SiCNWs/AZ91D, considerable dislocations were observed, which can be attributed to the different thermal expansions of SiCNWs and AZ91D matrix. It was found that the thermal expansion behavior of the C f -SiCNWs/AZ91D composite was significantly influenced by its interfacial configuration, which can reduce the coefficients of thermal expansion and improve the stability of the composite. [ABSTRACT FROM AUTHOR]

Thermal conductivity (TC) is essential to characterize for thin-walled parts made of needled carbon/carbon (C/C) composites in the aviation sector. This paper thus proposes a hierarchical multiscale model to predict the TCs of needled C/C composites. This model can comprehensively consider the effects of the anisotropy of pyrolytic carbon matrices and the orientation and elongation of pores. At the microscale, representative volume element models of the needled fibers and weftless plies are established, respectively, and their TCs are estimated using the finite element homogenization method. Meanwhile, a combination of the finite element and orientation average method is developed for short-cut fiber plies. At the macroscale, a generated needled laminated model consisting of the weftless plies, short-cut fiber plies, and needled region, is established, where input properties are from homogenization results of microscale models. By comparing with experimental results, the proposed multiscale model is validated. The results show that effective TCs in the directions perpendicular and parallel to needled fibers drop by 13.18% and 13.06% respectively as the porosity increases from 6% to 14%. Additionally, it is found by microstructural parameter studies that it is possible to realize needled C/C composites with isotropic TCs. • A multiscale model of needled C/C composites is established. • The multiscale model agrees well with the Mori–Tanaka and experimental results. • Pores cause the almost same drop of thermal conductivities in X/Y and Z directions. • It provides roadmap for thermal-conductivity isotropic needled C/C composites. [ABSTRACT FROM AUTHOR]

This work proposes a novel method, entitled minimum potential method, to generate Representative Volume Elements (RVEs) of unidirectional fibers composites with high fiber volume fractions (FVFs, generally ≥ 70. 0 %). In the proposed method, a given VF of random and periodic fibers are initially created within the matrix and the fiber overlap is allowed, and then the fiber overlap is gradually removed by adjusting the fiber centroids based on the principle of the minimum overall potential. In the process of fiber overlap removal, the fiber periodicity and the fibers completely or partly contained in the matrix are preserved. The overall potential of the fibers consists of fiber overlap potential, fiber position potential and fiber periodicity potential, and is minimized using the gradient descent method. The numerical implementation of the proposed method is detailed, and the RVEs of the composites with various FVFs are generated. Through the probability distribution function of the nearest neighbor distance, the cumulative probability distribution function of the nearest neighbor orientation angle, the second-order intensity and pair correlation functions, the fiber distribution in the generated RVEs is analyzed, and the results indicate a completely random distribution of the fibers in the generated RVEs. Comparing with the available experimental test, the literature and the Double-Inclusion model, the proposed method to generate RVEs of the composites with high FVFs is validated. • A novel minimum potential method is proposed to generate RVEs of composites. • The method can generate the RVEs of composites with high fiber volume fractions. • The method owns good computational efficiency, even for high fiber volume fraction. • The numerical implementation of the method is relatively simple. [ABSTRACT FROM AUTHOR]

The elasticity of carbon/carbon (C/C) composites is strongly dependent on the properties of pyrocarbon. Carbon planes of pyrocarbon prepared by the chemical vapor infiltration (CVI) method orient along the axial direction of fibers, leading to the anisotropy of pyrocarbon. This paper proposes a novel numerical model to accurately predict the effective elastic properties of C/C composites with anisotropic pyrocarbon. At first, the pore-pyrocarbon system is homogenized as an equivalent matrix. The equivalent matrix is then partitioned using a pyrocarbon micromorphology-based modified Voronoi tessellation method. Meanwhile, the cohesive elements are introduced to capture the interphase effect on the effective elastic properties of C/C composites. Regarding the prediction of the effective elastic properties of unidirectional C/C composites and short carbon fiber reinforced pyrocarbon (C sf /C) composites, the proposed model is validated by analytical and experimental results. Additionally, the results show that increasing interphase stiffness improves the effective elastic properties of C/C composites while an increase in porosity reduces the effective elastic properties of C/C composites. [ABSTRACT FROM AUTHOR]

• An interphase model is proposed to model imperfect interface in the composites. • The FE homogenization method is employed to predict the ETCs of composites. • The ETCs of composites maintain constant with the interphase thickness variation. • The ETCs of the composites with imperfect interfaces are inclusion size dependent. • The ETCs of the composites with imperfect interfaces show an asymptotic behavior. This paper addresses the Finite Element (FE) homogenization of the Effective Thermal Conductivities (ETCs) of the Composites with Imperfect Interfaces (CIIs). To model the imperfect interfaces between the matrix and inclusions in the composites, the thin interphases between the matrix and inclusions are introduced, which are combined with the FE homogenization method to predict the ETCs of the CIIs. The Representative Volume Elements (RVEs) containing the interphases are adopted to characterize the micro-structures of the CIIs and generated by the modified Random Sequential Absorption (RSA) algorithm. Compared with the micro-mechanical models, the proposed interphase model with the FE homogenization method is validated to be able to accurately predict the ETCs of the CIIs. The simulation results demonstrate that the ETCs of the CIIs are size-dependent, and the interphase thickness in the range of 50.0–100.0 nm has few impact on the ETCs of the composites. In addition, the ETCs of the CIIs show an asymptotic behavior so that a transition zone and two plateaus zones can be identified for the curves of the ETCs of the CIIs. This work provides a new and simple approach for predicting the ETCs of the CIIs. [ABSTRACT FROM AUTHOR]