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Three-phase particulate composites offer greater design flexibility in the selection of phase materials and have more design variables than their two-phase counterparts, thus providing larger space for tailoring effective properties to meet intricate engineering requirements. Predicting effective elastic properties is essential for composite design. However, experimental methods are both expensive and time intensive, whereas the scope of analytical micromechanics models is limited by their inherent assumptions. The newly developed microstructure-free finite element modeling (MF-FEM) approach has been demonstrated to be accurate and reliable for two-phase particulate composites. In this study, we investigate whether the MF-FEM approach can be applied to three-phase particulate composites and, if applicable, under which conditions. The study commences with a convergence analysis to establish the threshold ratio between the element size and the RVE (representative volume element) dimension. We then validate the MF-FEM approach using experimental data on three-phase composites from the existing literature. Subsequently, the MF-FEM method serves as a benchmark to assess the accuracy of both traditional and novel analytical micromechanics models, in predicting the effective elasticity of two distinct types of three-phase particulate composites, characterized by their small and large phase contrasts, respectively. We found that the threshold element-to-RVE ratio (1/150) for three-phase composites is considerably smaller than the ratio (1/50) for two-phase composites. The validation underscores that MF-FEM predictions align closely with experimental data. The analytical micromechanics models demonstrate varying degrees of accuracy depending on the phase volume fractions and the contrast in phase properties. The study indicates that the analytical micromechanics models may not be dependable for predicting effective properties of three-phase particulate composites, particularly those with a large contrast in phase properties. Even though more time-intensive, the MF-FEM proves to be a more reliable approach than the analytical models.

To make more accurate predictions of the effective thermal conductivity (ETC) of the composites, a systematic method for predicting the effective thermal conductivity of metal matrix particle composites with arbitrarily shaped particles was proposed, and the geometry of random particles with controlled shape characteristics is reconstructed. In addition, the geometric vertices of the reconstructed particles are used to characterize the morphology of inclusions with complex profile in two-dimensional isotropic elasticity, and its explicit expression for the Eshelby tensor are explored. Moreover, the material mismatch between the particles and the matrix phase is simulate using a continuously distributed source field based on the Eshelby's equivalent inclusion method. The relationship between micro-structure and effective performance is established. Finally, the effective thermal conductivity of CuCr alloys was predicted using the ETC prediction model. Through the comparison of the numerical simulations, experiments, and calculations, the results show that the ETC model has reliable predictive capability.

Physical and mechanical properties of continuous carbon or glass fiber reinforced endodontic posts are relevant to increase the retention and resistance of the tooth-restoration system. Hollow posts have been recently designed for delivering the luting cement through the post hole, thus enhancing the post-dentin interface by reducing the risk of air bubbles formation. Methods: Three type of endodontic posts, a carbon fiber hollow post, a glass fiber hollow post and a compact glass fiber post were investigated. Mechanical properties of these posts were assessed through bending tests. Teeth were subjected to fatigue cycling and the strength of restored teeth was detected through static tests. Failure modes were investigated through optical and scanning electron microscopy. Results show that composite posts increase the mechanical stability by more than 100% compared to premolars restored with particulate composite. Carbon fiber posts retain the highest strength (1467 N ± 304 N) among the investigated post and core restoration, but an unfavorable type of fracture has been observed, preventing the tooth re-treatment. Instead, more compliant posts (i.e., glass fiber reinforced composite, providing a strength of 1336 N ± 221 N), show a favorable mode of fracture that allows the re-treatment of teeth in the case that failure occurs. Glass fiber hollow posts show a good trade-off between strength and a favorable type of fracture.

High performance lightweight structures made of metal matrix composites (MMCs) are in demand for application in variety of industries such as aircraft, spacecraft, automobile, marine, sports equipment, etc. However, uniform distribution of the reinforcement phase to improve the mechanical properties and quality of MMCs has been the challenge for the manufacturing industries. Hence, researchers are focusing on the development of traditional low-cost method of producing metal matrix composites. In the view of above facts, an attempt is made to study the processing and characterization of Si-Al alloy reinforced with zirconium dioxide particulate composites in this paper. Hence, this paper concentrates on experimentally identifying the effect of stir cast and spray forming processing techniques followed by hot pressing on micro hardness, compressive strength, and tensile strength using Taguchi’s design of experiments for aluminum silicon matrix alloy reinforced with zirconium dioxide particulates. From the extensive experimentation on aluminum and silicon reinforced with the ZrO2 powder particulates, it was observed that there was an improvement in selected mechanical properties as the percentage of ZrO2 increased with 13 wt.% of silicon under spray forming processing technique compared to stir cast composites. This may be due to uniform distribution homogenous dispersion, larger work hardening rate, and structure of dislocation tangles around the ZrO2 particulates that occurred during spray forming processing technique. Further, results obtained from the interaction plot, contour plot, main effects plot, and analysis of variance (ANOVA) proved to be successful for identifying the optimum processing parameters for Si-Al alloy reinforced with zirconium dioxide particulate composites. Further, this paper also discusses wear study using pin on disc wear testing apparatus on spray forming processed aluminum and silicon (13.0 wt.%) alloy reinforced with the ZrO2 powder particulates based on Taguchi’s design of experiments followed by second order model generation for wear using response surface methodology. Finally, electrode wear study of spray forming processed aluminum and silicon alloy reinforced with the ZrO2 powder particulates using electric discharge machining by varying peak current (A), pulse on time (μs), and pulse off time (μs) using brass, copper, and graphite as electrode material based on L27orthogonal array. The understanding gained from the design of experiments in this paper can be used to develop future guidelines for processing and characterization of Si-Al alloy reinforced with zirconium dioxide particulate composites.

Energy harvesting from mechanical vibration of buildings is usually realized by the use of devices, in which the main element is a prismatic beam with a rectangular cross-section. The beam has been the subject of scientific research; it is usually constructed with a carrying substrate that does not have piezoelectric characteristics and from piezoelectric material. In contrast, this investigation sought to create a beam structure with a piezoelectric composite only. The entire beam structure was made of a prototype piezoelectric particulate composite. Based on courses of voltage obtained in laboratory experiments and known geometry of the specimens, a series of finite element method (FEM) simulations was performed, aiming to estimate the piezoelectric coefficient d31 value at which the mentioned voltage could be achieved. In each specimen, sedimentation caused the formation of two distinct layers: top and bottom. The experiments revealed that the presented prototype piezoelectric particulate composite converts mechanical stress to electric energy in bending mode, which is used in energy harvesting from mechanical vibration. It is self-supporting and thus a carrying substrate is not required in the harvester structure.

Micromechanics models of composite materials are preferred in the analysis and design of composites for their high computational efficiency. However, the accuracy of the micromechanics models varies widely, depending on the volume fraction of inclusions and the contrast of phase properties, which have not been thoroughly studied, primarily due to the lack of complete and representative experimental data. The recently developed microstructure-free finite element modeling (MF-FEM) is based on the fact that, for a particulate-reinforced composite, if the characteristic size of the inclusions is much smaller than the composite representative volume element (RVE), the elastic properties of the RVE are independent of inclusion shape and size. MF-FEM has a number of advantages over the conventional microstructure-based finite element modeling. MF-FEM predictions have good to excellent agreement with the reported experiment results. In this study, predictions produced by MF-FEM are used in replace of experimental data to compare the accuracy of selected micromechanics models of particulate composites. The results indicate that, only if both the contrasts in phase Young’s moduli and phase Poisson’s ratios are small, the micromechanics models are able to produce accurate predictions. In other cases, they are more or less inaccurate. This study may serve as a guide for the appropriate use of the micromechanics models.

The microstructure-based finite element modeling (MB-FEM) of material representative volume element (RVE) is a widely used tool in the characterization and design of various composites. However, the MB-FEM has a number of deficiencies, e.g., time-consuming in the generation of a workable geometric model, challenge in achieving high volume-fractions of inclusions, and poor quality of finite element mesh. In this paper, we first demonstrate that for particulate composites the particle inclusions have homogeneous distribution and random orientation, and if the ratio of particle characteristic length to RVE size is adequately small, elastic properties characterized from the RVE are independent of particle shape and size. Based on this fact, we propose a microstructure-free finite element modeling (MF-FEM) approach to eliminate the deficiencies of the MB-FEM. The MF-FEM first generates a uniform mesh of brick elements for the RVE, and then a number of the elements, with their total volume determined by the desired volume fraction of inclusions, is randomly selected and assigned with the material properties of the inclusions; the rest of the elements are set to have the material properties of the matrix. Numerical comparison showed that the MF-FEM has a similar accuracy as the MB-FEM in the predicted properties. The MF-FEM was validated against experimental data reported in the literature and compared with the widely used micromechanical models. The results show that for a composite with small contrast of phase properties, the MF-FEM has excellent agreement with both the experimental data and the micromechanical models. However, for a composite that has large contrast of phase properties and high volume-fraction of inclusions, there exist significant differences between the MF-FEM and the micromechanical models. The proposed MF-FEM may become a more effective tool than the MB-FEM for material engineers to design novel composites.

Micro crystalline cellulose is mostly used to improve thermo-mechanical properties of composites. This study aims to evaluate the creep behaviour of micro-cellulose epoxy-based composites, and the effect of silanization treatment on the reinforcements. A new viscoelastic model, based on the generalized logistic function was successfully tested. The results were directly associated with the material’s structure–property relationships. Rigid particles restricted the molecular chain’s motion, mainly on the amorphous segments. This difference achieved the needing of more energy, to achieve creep deformation. Then, MCC improved the structural integrity, when incorporated into an epoxy matrix. On one hand, the incorporation of silanized-MCC increased the mechanical behavior of the composite, due to the stiffer structure. Furthermore, the chemical modification provided an increment in the glassy plateau, associated with higher thermal energy required to initiate strain of the amorphous polymeric chains. This behaviour resulted in an abrupt decrease of load-bearing capability for the composites. Finally, the proposed model is suitable to be employed in creep curves, aiming to easily interpret the structure–property relationships of this test. Graphical abstract

Polymer-piezoceramic composites have drawn a lot of attention for sensor and energy harvesting applications. Poling such materials can be difficult due to the electric field getting mostly distributed over the low dielectric constant matrix. During this process, the electrical matrix conductivity plays a vital role. This work shows how two different polymer materials, loaded with various piezoelectric ceramic fillers, have very different poling efficiencies simply due to their intrinsic matrix conductivity. It is shown how temperature increases the matrix conductivity, and hence, increases the piezoelectric charge constant of the composites. By choosing the proper matrix material under the proper conditions, piezoelectric composites can be poled at electric fields as low as 2 kV mm−1, which is identical to that of bulk ceramic fillers. In addition, the matrix conductivity can be altered by aging the composites in a high humidity atmosphere, which can increase the piezoelectric charge constant in similar fashion. This is a simple method to increase the matrix conductivity, and hence the piezoelectric charge constant, without the need to add any conductive fillers into the composites, which increase complexity, and leads to an increased dielectric losses.

Since the inelastic strain development plays an important role in the low-cycle fatigue (LCF) of High-Performance Polymers (HPPs), the goal of the research was to study the effect of an amorphous polymer matrix type on the resistance to cyclic loading for both polyimide (PI)- and polyetherimide (PEI)-based composites, identically loaded with short carbon fibers (SCFs) of various lengths, in the LCF mode. The fracture of the PI and PEI, as well as their particulate composites loaded with SCFs at an aspect ratio (AR) of 10, occurred with a significant role played by cyclic creep processes. Unlike PEI, PI was less prone to the development of creep processes, probably because of the greater rigidity of the polymer molecules. This increased the stage duration of the accumulation of scattered damage in the PI-based composites loaded with SCFs at AR = 20 and AR = 200, causing their greater cyclic durability. In the case of SCFs 2000 µm long, the length of the SCFs was comparable to the specimen thickness, causing the formation of a spatial framework of unattached SCFs at AR = 200. The higher rigidity of the PI polymer matrix provided more effective resistance to the accumulation of scattered damage with the simultaneously higher fatigue creep resistance. Under such conditions, the adhesion factor exerted a lesser effect. As shown, the fatigue life of the composites was determined both by the chemical structure of the polymer matrix and the offset yield stresses. The essential role of the cyclic damage accumulation in both neat PI and PEI, as well as their composites reinforced with SCFs, was confirmed by the results of XRD spectra analysis. The research holds the potential to solve problems related to the fatigue life monitoring of particulate polymer composites.