Multiphase Composites Research Articles

Microvesicle-Embedded Solid-liquid Composite Coating for the Tribological Behavior Regulation and Long-Acting Lubrication.

Friction interfaces in liquid-embedded composite lubrication coatings commonly comprise a combination of discontinuous fluid films and rough solid contact surfaces, which together ensure easy shearing and a prolonged wear life. However, achieving high efficacy in mixed lubrication poses a challenge due to the conflicting nature of enhanced migration freedom for the liquid lubricant and increased mechanical strength of the solid matrix. Recent efforts have focused on incorporating reinforcing fillers to develop multicomponent, multiphase composites that can address this paradox. Here, we describe a modified attapulgite (APT) with strong biphasic wettability via the oil decompressive osmosis treatment on APT nanocontainers grafted with long nonpolar alkyl chains. This modified APT enables control over the size, distribution, and mobility of lubricant droplets by constructing a Pickering emulsion and toughens the solid-phase matrix through dispersion strengthening. Additionally, the introduction of APT induces the formation of a solid tribofilm during friction, which possesses a higher oil adsorption capacity, as verified through first-principles calculations based on density functional theory (DFT). Consequently, the fluid films can be replenished by the fracture of nanocontainers and adsorption from the bulk phase; further comprehensive and effective regulation of the friction interface leads to low friction and wear.

Valence state of V combined with D-tartaric acid and heat treatment affect sodium storage performance of NASICON-type multiphase composite

The polyanionic compound Na3V2(PO4)3 (NVP) and Na3V2(PO4)2F3 (NVPF) are promising cathode materials for sodium-ion batteries, but their poor electronic conductivity affects the electrochemical performance and the output energy density. The easy interconversion between V4+ and V5+ in the solution appears due to the weak bonds of D-tartaric acid, which lowers the energy barrier for further transition to V3+ and results in an excess V3+ in the product. A small amount of NVPF/C is converted to NVP/C due to the volatility of fluorine after heat treatment. D-tartaric acid as a carbon source forms a 3D network structure after calcination, thresholds the growth of NVP or NVPF and hinders the volume expansion during sodium storage. The initial discharge specific capacity of NVPF/C-650 is 85 mAh g−1 at 5C, and remains 59.2 mAh g−1 after 1000 cycles, which is related to the low charge transfer resistance, rapid Na+ ion diffusion and the pseudocapacitance effect. The binding of V and the carbon source in the solution affects the content of V3+/V4+ content, and the annealing temperature affects the formation and composition of the conducting carbon, both of which influence the electrochemical performance. This result provides a concept for possible screening of the carbon source for sodium storage materials with excellent performance.

Polyolefin Blends with Selectively Crosslinked Disperse Phase Based on Silane-Modified Polyethylene.

Polypropylene-based multiphase compositions with a disperse elastomer phase provide superior impact strength. Making this property indifferent to processing steps requires stabilization of the morphology of these materials. Various approaches have been tested over time, each of which shows limitations in terms of performance or applicability. Using polyethylene (PE) homo- and copolymers capable of silane-based crosslinking as modifiers was explored in the present study, which allows decoupling of the mixing and crosslinking processes. Commercial silane-copolymerized low-density PE (LD-PEX) from a high-pressure process and silane-grafted high-density PE (HD-PEX) were studied as impact modifiers for different types of PP copolymers, including non-modified reference PE grades, LDPE and HDPE. Blends based on ethylene-propylene random copolymers (PPR) and based on impact- (PPI) and random-impact (PPRI) copolymers show improvements of the stiffness-impact balance; however, to different degrees. While the absolute softest and most ductile compositions are achieved with the already soft PPRI copolymer base, the strongest relative effects are found for the PPR based blends. Modifiers with lower density are clearly superior in the toughening effect, with the LD-PEX including acrylate as second comonomer sticking out due to its glass transition around -40 °C. The impact strength improvement found in most compositions (except at very high content) results, however, not from the expected phase stabilization. For comparable systems, particle sizes are normally higher with crosslinking, probably because the process already starts during mixing. Thermoplastic processability could be retained in all cases, but the drop in melt flow rate limits the practical applicability of such systems.

Prediction and evolution of core-shell morphology and their effect on mechanical properties of PP blends

The prediction of phase morphology is highly valuable in designing and regulating the properties of multiphase composites, particularly polymer blends. In this study, we prepared two types of ternary blends, PP/HDPE/EPR and PP/HDPE/EPDM composites and compared and analyzed the predicted and observed phase morphology of blends with different elastomers. Using Palierne and Bousmina equations, we calculated the interfacial tensions between two components in PP blends and then predicted the relationship between the spreading coefficient, interfacial tension, and phase morphology according to the spreading coefficient theory. Based on our findings, it was observed that the core-shell structure of EPR and EPDM rubber phase encapsulated HDPE core tends to form in PP ternary blends, which aligns with our experimental results. Additionally, SEM morphology observation results revealed a less number of dispersed phases in PP/HDPE/EPR composites with the same composition ratio. It was observed that the shell had a greater thickness due to the difficulty in dispersing EPR with higher viscosity. Mechanical tests indicated that composites with thin-shell and small-core dispersed phases had better toughness. These composites also displayed less yield strength loss under the same impact conditions compared to those with single rubber phases.

A novel method to determine the multi-phase ejection parameters of high-density battery thermal runaway

The growing demands on high-performance energy systems for emerging technologies drive the advancement of high-density batteries. However, the issue of thermal runaway (TR), particularly in high-density battery, remains a major challenge worldwide. One of the primary hazards associated with TR is the emission of combustible ejections. Therefore, elucidating the TR ejection parameters holds significant meaning. In this study, we propose a novel method to determine the ejection parameters. Based on the principles of momentum conservation, the proposed method is applicable to high-density battery types. For the 52 A h ternary battery, our results indicate the following: 1) the ejection velocity reaches a peak of 210 m/s, a maximum mass loss rate of 0.041 kg/s and a maximum total pressure of 112.325 kPa; 2) the temperature of the particles is 200 °C higher than that of the gas. Furthermore, we have derived empirical formulas that encompass the ejection dynamics, thereby facilitating the modeling of TR degassing and ventilation within a battery pack. This approach overcomes the challenges associated with measuring the ejection parameters in high-density battery TR, such as the extreme temperature, flammability, and multiphase composition. Consequently, this method exhibits great potential to bolster the fire safety and structural design of battery packs.

A novel microstructure-informed machine learning framework for mechanical property evaluation of SiCf/Ti composites

In this work, a novel microstructure-informed machine learning (MIML) framework is proposed for the longitudinal ultimate tensile strength (UTS) evaluation and the construction of microstructure-property linkages of titanium matrix composites (TMCs). The main components of the MIML framework include (i) high-fidelity simulation and dataset generation using finite element method (FEM), (ii) the quantitative characterization of microstructures obtained by 2-point cross-correlation analysis and principal component analysis, (iii) the extraction of structure-property linkages based on support vector regression model and (iv) the validation of MIML by experimental data. The fiber breakage observed by advanced microstructure characterization is considered as the dominant failure mode during mechanical tests of TMCs, which is embedded in the FEM simulations. The MIML approach reaches capable accuracy in UTS prediction of TMCs using FEM-generated datasets and trained MIML is validated by experimental data. In addition, the permutation importance-based method is utilized to accurately identify the key feature parameters related to UTS. The first two principal components of microstructural reduced-order representation are recognized as highly relevant features for UTS. The well-trained MIML model is a promising tool in the evaluation of the mechanical property, and further provides a technical chain for the establishment of microstructure-property linkages of multi-phase composites.

Fabrication, microstructure and mechanical properties of multi-phase tantalum carbide based (TaCz-Ta5Si3) ceramics

Three multi-phase tantalum carbide composites (TaCz-Ta5Si3) were fabricated by Spark plasma Sintering (SPS) using Ta, TaC and SiC powders. SiC was added to control the C:Ta ratio (z = 0.6, 0.74, 1.0), regulating the phase composition and grain morphology while also serving as a deoxidizer. Composite TaC0.6-Ta5Si3 had Ta2C as the major phase and contained Ta4C3−x, TaC and Ta5Si3. It exhibited an excellent combination of high flexure strength (714 ± 21 MPa) and toughness (13.9 ± 0.2 MPa·m1/2), despite a low Ta4C3−x fraction, a phase known to have very high toughness. The outstanding performance was attributed to the elongated Ta2C grain morphology, highly laminated intra-granular Ta4C3−x laths, and the refined Ta2C grain size. Composite TaC0.74-Ta5Si3, characterised by equiaxed grain morphology, exhibited good flexure strength (571 ± 36 Mpa) and toughness (7.6 ± 1.1 MPa·m1/2) due to the presence of Ta4C3−x laths in the c-TaC. Lastly, composite TaC1.0-Ta5Si3, composed of c-TaC and Ta5Si3, exhibited moderate strength (545 ± 25 MPa) and toughness (5.3 ± 0.1 MPa·m1/2).

Mechanical property enhancement of graphene-kenaf-epoxy multiphase composites for automotive applications

Kenaf composites have a high strength-to-weight ratio, but weak fiber–matrix interface bonding limits their automotive use. To address this, a novel technique was developed to fabricate multiphase composites using graphene nanoplatelets (GNPs), kenaf fibers, and an epoxy matrix. The composites were made using vacuum infusion molding, with the GNPs exfoliated using a bath sonicator for uniform dispersion. The composites modified with 0.2 wt% GNP showed the most significant improvement in mechanical properties. Specifically, these composites exhibited a 30.5% increase in tensile strength, a 61.5% increase in tensile modulus, a 17.6% increase in flexural strength, a 22.7% increase in flexural modulus, a 35.1% increase in interlaminar shear strength, and a 17.1% increase in fracture toughness. Additionally, the water absorption resistance of the multiphase composites improved by up to 7%. These improvements were attributed to the uniform dispersion of GNPs and improved interlocking with the fiber surface. The developed composite has the potential for interior parts (such as dashboards, interior walls, and luggage compartments) in the automotive vehicle.

Evaluation of the damping characteristics of a hybrid piezo-shunt nanocomposite using a two-step homogenization approach

Composite materials containing piezoelectric particles have attracted remarkable attention because of their distinctive electromechanical conversion characteristics. These supreme properties lead to their applications in various fields, such as vibration damping of structures. The damping parameter of dynamic systems is crucial, especially when they undergo resonance phenomena. Multi-phase polymer matrix composites consisting of piezoelectric particles are innovative material systems that have been recently introduced to convert the mechanical vibrations into electrical energy, and subsequently dissipate into heat through an internal electrical circuit. The present study aims to analytically investigate the viscoelastic characteristics of a shunted three-phase composite composed of a polymer matrix, electrically conductive nanoparticles and piezoelectric particles. The effective viscoelastic characteristics of a shunted composite are calculated using one- and two-step homogenization procedures and by considering the viscoelastic characteristics of constituent materials. The influence of several key parameters, namely, the non-dimensional frequency, the volume fraction of electrically conductive nanoparticles and piezoelectric particles, and the shape of the inclusions, on viscoelastic characteristics, such as phase angles, the storage modulus and loss modulus, are examined. The viscoelastic characteristics are considerably affected by these parameters, and the perceived behavior is justified by the governing equations. The assessment of results confirms that the damping characteristics can be improved by careful selection of a volume fraction of constituent materials and control of the excitation frequency of the smart composite, while avoiding additional costs and likely inconveniences in the fabrication process.

Controllable Fabrication of Sn/Sb Nanodomains Improved Sb2SnO5 Anodes for Sodium Ion Batteries

AbstractEmbedding the metal phase and modifying the microstructure is an important way to improve the storage capability of Sb2SnO5 (SSO) anodes. Pertaining to sodium‐ion batteries (SIBs), we design and fabricate Sb and Sn embedding porous carbon wires (PCWs) with SSO encapsulated (SSO@Sn/Sb‐PCWs) composite as a high capability anode in this study. Not only accelerate the Na+ ions diffusion, but also augment the stress resistance and the electrochemical reaction reversibility for the multiphase composite. Furthermore, the porous structure finely increases the ions diffusion kinetics, preventing the aggregation of Sn, Sb, and SSO particles, which achieves high reversible capacity while eliminating structure damage. As a consequence, the fabricated SSO@Sn/Sb‐PCWs electrode exhibited exceptional cycling stability, maintaining a high reversible capacity of 448 mAh g−1 after 150 charge/discharge cycles, and good rate capability with current density up to 5.0 A g−1. This new composite material studied in current work could shed light for the creation of sodium ion batteries with high specific energies in the near future.

Novel Cr–Mn–Fe–Co–Ni oxide composites fabricated by in situ spark plasma sintering for high-temperature applications

Spinel composite is being considered for electrode materials in molten salt electrolysis, aiming to improve high-temperature stability and conductivity. Multi-phase composites with the general formula of (Fe1-3x-y Niy Cox Crx Mnx)3 O4 (x = 0.03, 0.06, 0.09, y = [1-2x]/3) were prepared via in situ SPS method. The composites were confirmed to consist of spinel and rock-salt phases through XRD and SEM analysis. Compared to the Ni–Fe–O system, the doping of Cr, Mn and Co improved the phase stability of the spinel during SPS, but hindered the shrinkage process. These composite exhibited low thermal diffusivity (1.236–2.481 m2/s, room temperature) and low coefficient of thermal expansion (9.8 - 14.4 × 10−6 K−1, 400–800 °C). Moreover, the composite with x = 0.06 and y = 0.29 exhibit 94.4 % lower permittivity, 7 times higher dielectric loss (at 40 Hz) and 26.6 % lower high-temperature conductivity (at 800 °C) than that of Ni–Fe–O system. This work demonstrates the enhanced thermal and electrical properties of spinel-based composites, which can provide inspiration to researchers and promote the development of high-temperature electrodes.

Multiphase hybrid model and thermal insulation simulation of elytra-mimetic ceramic fiber aerogel

In our previous work, the coaxial electrostatic spinning method was applied to construct nanofiber/SiBCN ceramic aerogel with an elytra-mimetic structure. The material presented excellent mechanical, insulation, oxidation resistance, and other properties. Based on preliminary experiments and literature reports, the integrated heat transfer behavior of nanofiber/SiBCN composite ceramic aerogels in high-temperature environments was affected by several factors, such as coaxial fiber size properties, fiber particle content, interactions, and spatial distribution. Moreover, the above factors overlapped and interacted with each other, and it was hard to generalize a clear law of action through traditional experiments and characterization. Therefore, the paper constructed a representative volume unit (RVE) model based on the complex spatial distribution characteristics of composite aerogels, using fractal theory, Rosseland equation theory, and multiphase model theory. This paper investigated the fiber and particle content, the size characteristics of the coaxial fibers, and the overall heat transfer process in high-temperature environments using the finite element method. The finite element simulated the effective thermal conductivity of multiphase aerogel composites under multiple parameters, such as fiber occupancy, fiber core-shell diameter ratio, temperature, and heat transfer mode. We obtained the property parameters of the complex composition of the material through fractal theory. The model was combined with finite elements to study the fiber particle content, the size characteristics of coaxial fibers, and the integrated heat transfer process in high-temperature environments. The fibers improved the absorption and reflection of thermal radiation with increasing fiber mass fraction, leading to improved ability of ceramic fiber aerogel to extinguish light. The fibers had a larger area to absorb and reflect thermal radiation. Based on the excellent extinction ability of SiC fibers, the composite ceramic aerogel had improved thermal performance at a specifically fiber-to-shell diameter ratio through a comprehensive multifactor simulation analysis.

Trap engineering in LiInSi2O6:Cr,Pr by excess cristobalite silica for X-ray activated near-infrared persistent luminescence imaging in vivo

Chromium-doped persistent luminescence nanoparticles (PLNPs) have promising biomedical applications in X-ray charged near-infrared (NIR) luminous imaging. The persistent luminescence (PersL) property was usually adjusted by co-doping with other ions. Impurity phases were thought to be adverse to the PersL. In this study, a composite material, LiInSi2O6:Cr,Pr·2SiO2 (LICP-S), was synthesized with a PersL peak at 800 nm after being charged by 1 Gy X-ray while LiInSi2O6:Cr (LIC) and LiInSi2O6:Cr,Pr (LICP) possessed no or very weak PersL. Distinctively, excess metastable cristobalite silica was found essential for the much more intense PersL of LICP-S than LICP and LIC. Thermostimulated luminescence spectra studies indicated that cristobalite adjusted the Pr-related traps from deep traps to shallow ones, which facilitated the room temperature PersL. The low dose X-ray charged PersL of LICP-S was applied to demonstrate the luminous labeling of a medical silicone prosthesis that was supposed to be imbedded in body for years via X-ray activated PersL imaging in vitro and in vivo. This work not only provides a kind of PLNPs with 800 nm emission suitable for low dose X-ray activation, but also an unusual strategy for trap engineering in PersL materials by designing multi-phase composites.

Analysis of ex-vessel debris bed formation of multi-material and multiphase composition based on coupled system of MELCOR2 and THERMOS–JBREAK/MSPREAD

THERMOS is being developed to analyze the multidimensional process by which molten debris released from the lower head of the reactor pressure vessel forms a non-uniform debris bed. THERMOS consists of four modules, JBREAK, DPCOOL, MSPREAD and REMELT. To evaluate a wide range of ex-vessel debris bed formation, the authors have developed the coupled system composed of the integrated severe accident (SA) analysis code MELCOR2, THERMOS-JBREAK and THERMOS-MSPREAD. JBREAK simulates the molten jet release and impingement on the cavity floor using the separated flow model consisting of the molten jet and particle debris. MSPREAD simulates the melt spread as the multi-layered structure composed of the partially solidified molten debris, the upper and lower crusts growing on both sides using the shallow water equation.The conversion algorithm of the multi-material and multiphase composition of the released molten jet calculated by MELCOR2, which is based on lumped parameters, to the composition suitable for THERMOS, which is based on distributed parameters, is recognized to be critical to the success of this system and has been implemented as the Python script MELTHER. This conversion also includes the contribution of suspended particles embedded in the molten jet to the viscosity of partially solidified molten debris. As the JBREAK–MSPREAD interface, the method of overlapping the mesh systems of the two codes was implemented to solve the multidimensional flow equations in the near impinging region. Filtration of the molten debris inside the particle layer at the jet-impinging point was modeled using the particle debris deposition and molten debris filtration models.This coupled system was applied to a station blackout scenario in a typical BWR3 Mark-I plant, where approximately 14 tons of mixed molten and particle debris were released from the lower head and impinged on the pedestal floor. The calculation space was set to handle molten jet falling, impingement on the floor, and spreading from the pedestal to the outside dry well region. Complex anisotropic melt spreading was analyzed on the dry pedestal floor with two sumps covered with thin lids and a low weir at the bottom of the slit made in the cylindrical wall separating the pedestal floor and outer dry well regions.A series of sensitivity analyses were performed varying a combination of the initial suspended particle fraction and melt filtration inside the particle layer. Deceleration of the molten debris flow is significant due to the melt-particle bed frictional force and therefore the timing of molten debris running over the sump lids is faster when there is no particle layer. In this case, a large circulating flow is generated on the pedestal floor, and this flow promotes cooling and increases the viscosity. Influences of the initial suspended particle fraction on the melt viscosity become more pronounced in the peripheral region, and spreading behaviors are more susceptible to protrusions on the pedestal floor.

A continuum mixture model for transient heat conduction in multi-phase composites

The difference between transient thermal responses of each constituent in composites is one of the important factors to cause significant nonuniform deformation, high stress gradient and failure of composites. While direct numerical simulations for transient heat conduction in multi-phase composites are highly costly and even formidable, classical homogenization methods are focused on predicting the effective conductivities and the macroscopic thermal responses of a whole representative volume element, leaving the prediction of this difference at the macroscopic level to be a challenging issue during structural analysis of composite materials. In order to solve this issue, we propose a continuum mixture model for the transient heat conduction in multi-phase composites through dynamic homogenization methods. The derived governing equations retain the identity of each constituent behaviour and relate them to the overall response of each constituent. All the coefficients in the equations can be directly determined by the constituent phases and geometric parameters through explicit relations. The precision of the model is verified by comparison with direct numerical simulations. The results indicate that the model not only captures the disparate thermal responses of each constituent at the macroscopic level, but also accurately predicates the macro-average responses. The methodology can be generalized to other non-equilibrium thermodynamic phenomena such as diffusion and other kinds of conduction in multi-phase systems.

Interlocking Evaluation of Mesoscopic Skeleton with the Compaction Degree of Hot-Mix Asphalt.

Asphalt mixtures are multi-phase composites composed of aggregates, bitumen, mineral powders, and voids, and various structures are intertwined during the compaction process. Most of the traditional research focuses on the macro-scale domain, and it is difficult to obtain the internal structure of asphalt mixture in different compaction processes. With the continuous development of digital image technology, the influence of the meso-structure of the asphalt mixture on the compaction quality of the asphalt mixture has become a new means to evaluate the performance of the asphalt mixture. In this paper, different numbers of compactions are selected to represent different stages in the compaction process, the digital images of specimens in different compaction stages are obtained by industrial CT scanning technology. Then, the images are processed and reconstructed in three dimensions using improved image segmentation methods, and the position characteristics and geometric information of coarse aggregate are obtained by combining the Oriented Bounding Box (OBB). The meso-response characteristics of the skeleton structure of the asphalt mixture during compaction were studied. The influence of the internal structure of the mixture on the compaction quality of the mixture was obtained, which is of great significance for the study of improving the durability of the pavement. The results show that the "effective coordination number" (the number of aggregate particles that can transmit force in the skeleton structure) is greatly related to the aggregate size. With the compaction process, the centroid of coarse aggregate in the upper layer of the specimen reflects the overall downward movement trend. The inclination angle of the aggregate spindle tends to be in the range of 80°~100°; the anisotropic amplitude of the xy plane increases, and the direction of the aggregate spindle becomes more and more consistent. With the increase in the number of rotational compactions, these four parameters showed obvious rules, indicating that this meso-characteristic index could well characterize the compaction quality of the asphalt mixture in the compaction process.

The emergent behavior of three-dimensional and three-phase thermal network model for the heterogeneous materials

The study of the heat transfer properties of heterogeneous materials has been a world-wide research focus, for example in sectors related to thermal management in aerospace, architecture, and geology. In this paper, the emergent behavior and thermal conduction characteristics of three-dimensional and three-phase heterogeneous materials thermal networks are studied using the finite element method. The results show that the existence of percolation paths of each phase has a strong impact on the effective properties of the network when the contrast in thermal conductivities of each phase is high, and percolation also affects the effective thermal conductivity of the whole thermal network system. However, when the contrast in thermal conductivity between the two phases is low, the thermal networks exhibit a more consistent and “emergent” behavior, and the effective thermal conductivity of thermal networks at the same volume fraction changes to a lower extent from network to network. This paper also demonstrates that a logarithmic mixing rule can predict the effective thermal conductivity in the low contrast emergent region in three-dimensional networks, and the modeling method provides new approaches for the design of multi-phase composites and prediction of their thermal conduction properties.

Influence of the composite interface on the mechanical properties of semi-flexible pavement materials

Semi-flexible pavement (SFP) materials, composed of porous asphalt mixture (PAM) and cement-based grouting material, are multiphase composites commonly used in roadway construction. However, damage frequently occurs at the composite interface of two-phase materials, and most SFP research has focused on the design of grouting material, with insufficient attention given to the composite interface. This paper aims to investigate the effect of bonding properties between organic PAM and inorganic grout on the mechanical properties of SFP. To investigate the different bonding properties of the SFP asphalt-grout interface, a simple method was employed, in which PAM specimens were immersed in a silane coupling agent solution to form a layer of coupling agent on the PAM surface. A series of SFP specimens were created using PAM with a porosity of 28–30%, and different strength grouting materials (40 MPa, 60 MPa, 70 MPa), and three laboratory tests were conducted to evaluate their mechanical properties. The results demonstrated that the interfacial bonding strength between asphalt and grouting material significantly influences the low-temperature splitting tensile strength, uniaxial penetration strength and uniaxial compression strength of SFP. Compared to specimens formed from high-strength grouting materials, SFP specimens immersed in a silane coupling agent solution exhibited superior low-temperature splitting tensile strength (2.06 MPa > 1.97 MPa, 2.63 MPa > 2.34 MPa) and shear strength (7.28 MPa > 6.46 MPa, 7.97 MPa > 7.26 MPa). As a result, this study highlights the importance of considering the bonding properties of the asphalt-grout interface in the design and preparation of SFP. The results of this study can be useful for enhancing the performance and durability of SFP materials in a more economically efficient way.

Increase of specific interfacial coherence in nanocrystalline ceramic-metal composites

A new strategy to establish a large number of interfacial coherence in nanocrystalline multi-phase composites was proposed. The route consisting of amorphization, crystallization and in-situ reaction was demonstrated using WC-Co composites as a typical example. Characteristics of crystal nucleation, growth crystallography, and phase transformation were studied in detail on the atomic scale for the ceramic grains. Mechanisms for the formation of specific interfacial coherence in the prepared nanocrystalline ceramic-metal composites were disclosed. Assisted by the interfacial coherence, the continuity of local deformation is maintained from metal to ceramic phase, resulting in a uniform strain extension instead of stress concentration at the interfaces. The present nanocrystalline composite achieved outstanding mechanical properties with simultaneously high hardness and fracture toughness. The findings in this work provide new insights to tailor grain structure and interface relationship in cermet composites for superior comprehensive mechanical performance.

The Parametric High-Fidelity-Generalized-Method-of-Cells with phase-field damage micromechanical model for heterogeneous composites

A new coupled micromechanical-damage formulation is presented by directly integrating the phase-field (PF) modeling approach for fracture and damage with the Parametric High-Fidelity-Generalized-Method-of-Cells (PHFGMC) micromechanical model. The combined PHFGMC-PF approach is proposed for progressive damage analysis of multi-phase heterogeneous composites with evolving microstructure subject to general multi-axial remote loading. New variational equations are introduced to couple the macro/micro deformation and PF variables of the discrete finite volumes (subcells). An iterative computational formulation is also presented for the numerical solution of the overall nonlinear equations. The proposed approach can accommodate various phase-field damage models and fracture energy approximations. Two PF damage laws, available in the literature, are implemented. The proposed PHFGMC-PF model verification is first accomplished by solving the single-edge crack problem under tension and shear and comparing the results to a finite element PF (FE-PF) analysis. Results of the presented case studies demonstrate a comparable ability of the PHFGMC-PF to solve similar FE-PF non-periodic problems. Applications are presented for progressive damage of carbon-fiber-reinforced (CRP) composites. The PHFGMC-PF in-situ elastic and fracture properties are calibrated for the carbon-reinforced polymer IM7/977-3 composite material system at the fiber–interface–matrix constituents. The micromechanics-PF model can capture the composite overall nonlinear mechanical and damage responses compared to experimental data.