Particle-filled Composites Research Articles

Multi-scale modeling of damage evolution for particle-filled polymer composites

In this study, a multi-scale modeling framework that spans from molecular chains to macroscopic structure was proposed for a typical particle-filled polymer composite (HTPB propellants). The cohesive zone model (CZM) is utilized in the RVE model of HTPB propellants to capture the debonding phenomena at the AP/HTPB interface. For the HTPB matrix, a free energy function based on the Gaussian chain network is employed. To depict the chain scission behavior, the phase fracture (PF) method along with gradient-damage theory is introduced. Subsequently, microscale fracture behavior under uniaxial tensile load was investigated based on the constructed RVE model, and a phenomenological macroscopic damage model was developed correspondingly. In this developed model, two damage factors related to the debonding of AP/HTPB interface and the growth of voids in matrix are introduced respectively. Thus, it can not only predict the macroscopic stress–strain response, but also can give the microscopic damage evolution information. Overall, this multi-scale modeling framework can offer us a deeper insight into the microstructural changes and the resulting macroscopic mechanical behavior of HTPB propellants.

The effect of nanocellulose and silica filler on the mechanical properties of natural fiber polymer matrix composites

Natural fiber-reinforced polymer matrix composites recently got great attention in biomedical applications due to their inherent characteristics such as biocompatibility, lightweight, and biodegradability. However, natural fiber composites suffer from poor mechanical properties and weak interfacial adhesion. It is well documented that the addition of nanofiller has improved the mechanical properties of different synthetic fibers such as glass and carbon composites. The main objective of this paper is to study nanofillers' effect on the mechanical properties of unidirectional false banana fibers reinforced polymer composites. The filler materials, crystalline nanocellulose fibrils, and crystalline nanosilica particles were extracted from sugarcane bagasse and its byproducts. The composite samples were fabricated by adding the nanofillers in unidirectional natural fibers arranged in four fiber orientations (0°, 0o/90o ±45o, and quasi-isotropic), and their tensile, flexural, compression strength, thermal stability, and void content were measured following ASTM standards. The results revealed that adding nanofillers increased the tensile, flexural, and compressive strengths by 16 % (98.83 Mpa), 11 % (161.60 Mpa), and 23 % (114.62 Mpa), respectively. Similarly, at 0° orientation, the addition of nanoparticles enhances the tensile, bending, and compressive modulus by 30 % (15.43 Gpa), 12 % (13.52 Gpa), and 60 % (42.6 Gpa), respectively. On the other hand, the void content was reduced with the addition of nanofillers. The results also revealed that composites with crystalline nanosilica particle fillers had superior thermal stability compared to crystalline nanocellulose fibril fillers. The overall results of this research give the confidence that nano particle-filled natural fiber composites can be used for bio-based engineering applications, such as prosthetic sockets.

An investigation of the electrical dynamics in electroactive polymer transducers with resistive electrodes

To pursue a variable-capacitance working principle, transducers based on soft electroactive polymers (EAPs) need deformable electrodes that match the compliance and stretchability of the EAP polymeric substrates. A variety of manufacturing procedures are available to create conductive materials that can achieve this, including solutions that can provide remarkably low resistivity. However, the simplest and most feasible options often involve the use of particle-filled (e.g. carbon-filled) polymer composites, which, while easy to produce, tend to exhibit relatively high resistivity. This high level of resistivity, combined with the inherent capacitance of EAP transducers, introduces dynamic effects in the devices electrical activation, which may affect performance. This paper investigates the impact of electrode resistivity on the electrical dynamics of EAP devices, combining continuum models and experimental validations. We use a continuum generalisation of known resistive-capacitive (RC) transmission line models to accurately predict voltage gradients on the surfaces of electrostatic transducers subject to rapidly varying voltages. We then present an experimental validation by measuring the spatial voltage distributions over carbon-based polymeric electrodes of dielectric elastomer (DE) transducers, and find a good agreement with our model predictions. We use our validated model to provide general estimates of the typical charging time and limit working frequency ranges of DE devices as a function of their dimensional scale and electrode sheet resistance. Our model provides useful indications for designing compliant electrodes in EAP transducers given target performance, or to understand the working limits of devices with given geometry and dielectric-electrode properties.

Contribution to manufacturing control of particle-filled composites by RTM process

Contribution to manufacturing control of particle-filled composites by RTM process

Storage Life of Particle-Filled Polymer Composites Considering Aging Effects.

This study investigates the storage life of particle-filled polymer composites (PFPCs) under the influence of aging effects. High-temperature accelerated aging tests were conducted at 60 °C, 70 °C, and 80 °C for various days to analyze the impact of aging time and temperature on the mechanical behavior of the materials. A predictive model for crosslink density was established using the Arrhenius equation, and the relationship between crosslink density and relaxation modulus was determined based on polymer physics theory. On this basis, a viscoelastic constitutive model that incorporates aging effects was developed. Structural analyses of a PFPC column with a length of 2.3 m and outer diameter of 1.8 m were performed using the UMAT subroutine in ABAQUS. Subsequently, a safety margin assessment method based on dewetting strain was employed to predict the storage life of the PFPC column. The results indicate that the aging viscoelastic constitutive model effectively characterizes the hardening effects caused by aging in the composites during storage. The storage life for the PFPC column considering aging effects decreases from 22 years to 19 years compared to models that ignore such effects. This approach provides a reference for estimating the storage life of PFPC columns considering aging effects.

Mechanical behavior of glass fiber-reinforced hollow glass particles filled epoxy composites under thermal loading

The use of hollow glass particle-filled fiber-reinforced composites for aircraft applications requires proper understanding of their behavior under in-service temperature conditions in order to exploit their usage in the exterior parts of aircraft and other space vehicles. In this study, the glass fiber reinforced composites containing 0–30 vol% of glass microspheres were subjected to testing for monotonic tensile and flexural loading from room temperature to the test temperature (40°C – 120°C). The evolution of microscopic damage under different temperatures was elucidated by digital image correlation (DIC) strain fields. The strain fields revealed a transition from homogeneous to non-homogeneous pattern as the temperature increases due to softening of the matrix. As the glass microsphere contents in the matrix increased, the tensile and flexural properties of the composites decreased, and their reduction was highest for the specimen containing a 30 vol% microsphere by volume. The tensile properties are slightly decreased by increasing the temperature. The tensile specimens tested at room temperature exhibited limited delamination and fiber pullout, while extensive delamination and fiber splitting occurred in the specimens tested at 120°C. The flexural results of the glass fiber reinforced composite specimens exposed at 120°C demonstrated a considerable decrease in flexural strength compared with room temperature for 0 vol%, 10 vol%, 20 vol% and 30 vol% glass microsphere volume fraction. Finally, the Weibull parametric investigation was performed to model the degradation of modulus for various GMS contents with temperature variations.

Effect of temperature on the mechanical behavior of glass fiber reinforced with hollow glass particle-filled epoxy composites

The design of marine ships and aircraft components with hollow glass particle-filled fiber-reinforced composites demands an understanding of their performance under outdoor conditions. The continuous glass fiber-reinforced epoxy matrix filled with hollow glass particles in the range of 0–0.3 vol fraction was prepared by the compression molding machine. The influence of temperature exposure on the mechanical behavior of glass fiber-reinforced hollow glass particle composites was studied by conducting tensile and flexural tests. The temperature exposure varying from room temperature up to 60 °C was used to investigate the effect of service temperature on the hollow glass particle-filled fiber composite specimens. Differential scanning calorimetry (DSC) analysis was conducted to study the glass transition behavior of the composites. The incorporation of microspheres in the glass fiber composites gradually reduced the tensile and flexural strength, while their specific values increased as increasing the microspheres. The hollow glass particle-filled fiber composites tested at 60 °C exhibited a decrease in tensile and flexural strength compared with room temperature. As the température of the test spécimens was nearer to the glass transition value, the polymer chain was softened, leading to a reduction in strength. In contrast, the modulus values remain unaffected by increasing the temperature to 60 °C.

Influence of quartz and marble on the performance of particulate-filled rigid polyurethane foams

This work was carried out to investigate the roles of quartz and marble on the performance of polyurethane particulate-filled composites. Prior to the mixing, the quartz and marble were pulverized and sieved to obtain an average particle size of less than 90 µm. Polyurethane (PU) was produced from isocyanate and polyol by a two-step method in which marble and quartz particles were incorporated in predetermined proportions. Three different weight ratios were utilized to investigate the physical, chemical, and mechanical behavior of the pristine rigid polyurethane foam (RPUF) and the marble and quartz-filled RPUF using analytical equipment such as FTIR, XRF, and SEM. The mechanical properties were performed according to the ASTM standards, where the compressive and flexural strengths were investigated using the universal testing machine. Overall, the RPUF shows the hydroxyl bands, while the principal elements of fillers are Calcium and Silicon. It was discovered from the results that adding these fillers improved the mechanical properties of the filled samples, where the compressive strength was enhanced.

Prediction of Aging Performance of Particle-Filled Polymer Composites Based on RVE Model.

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.

Tribological Performance of Automobile Brake Pads by Using Metal Matrix Composites

In today's ambitious world, there's a growing demand for high-performance components that are strong yet lightweight, durable, and energy-efficient, especially in industries such as automotive, aerospace, military, and sports. Aluminum, known for its low weight and excellent dimensional stability, is a popular choice. It is often reinforced with materials like SiC (silicon carbide) and Ni-Gr (nickel-graphite) to enhance wear and temperature resistance, making it suitable for various automotive applications, including cylinder fins, heat sinks, and piston materials. Additionally, common filler materials like silicon nitride (Si3N4), boron carbide (B4C), boron nitride (BN), aluminum oxide (Al2O3), aluminum nitride (AlN), titanium carbide (TiC), and titanium oxide (TiO2) tend to exhibit better compatibility with aluminum when it is in alloy form. Composites, especially metal matrix composites made of aluminum, offer superior mechanical properties compared to traditional metals. These composites are characterized by high specific strength, low weight, hardness, and wear resistance. Unlike unreinforced alloys, metal matrix composites possess exceptional tribological properties, allowing them to effectively compete with conventional materials in various tribological applications. These aluminum particle-filled metal matrix composites are actively pursued across sectors, including aerospace and automotive, due to their improved physical and tribo-mechanical properties.

A comprehensive study on enhancing effective thermal conductivity of polymer composites with randomly distributed triple fillers

This paper describes a comprehensive study on the effective thermal conductivity (ETC) of triple-filled polymer composites. A very complicated behavior was revealed under various effective factors, such as thermal conductivity (TC), volume fraction (VF), particle distribution, particle size, and filler arrangement. Consequently, some prediction models, which were well validated with numerical results, are first developed. Additionally, the ETC of polymer composite dramatically and non-linearly depends on TC ratios, VF ratios, particle distribution, filler arrangement, and particle size of the triple filler. The mountain shape of the ETC forms and depends on a variety of effective factors. The maximum ETC exists at the given optimum TC ratios ranging from approximately 0.1 to 100. It was also found that the ETC increases with the increase of the VF ratio for a threshold TC ratio; however, this trend changes when TC ratios go beyond the threshold values. Particularly, the ETC of the particle-filled polymer composite also depends on the filler arrangement, even though particles are straightly arranged along the direction of thermal flow. This effect becomes more significant when the difference in VF and TC between particles is larger. The results obtained are very useful in enhancing and maximizing the ETC of polymer composites with triple fillers and even multiple fillers in general.

Data-Driven Framework toward Accurate Prediction of Interfacial Thermal Resistance in Particulate-Filled Composites.

The interfacial thermal resistance (ITR) inside the particulate-filled polymer composite is a bottleneck for improving the thermal conductivity (TC) of the material. Getting full knowledge of the ITR is crucial to the material design as well as to a faithful prediction of TC of the composite. However, a method fully taking into account the local circumstances inside the composite is yet to be developed to precisely characterize the ITR. Here, we propose a comprehensive framework combining high-throughput numerical simulations, machine learning and optimization algorithms, and experiments, which is demonstrated to be robust for the accurate determination of ITRs inside the particulate-filled composites. The strategy extracts as much information as possible about the structure and heat transfer characteristics of the composite based on simple experiments, which lays the foundation for the method to be effective. We show that the polymer-filler ITRs and the effective filler-filler contact ITRs predicted with the method faithfully represent the true characteristics inside the composite materials; they also provide the exact effective parameters, which cannot be obtained from experiments, for accurate numerical prediction of TCs of composite materials with high efficiency. As a result, the framework not only provides a robust tool for accurate characterization of ITRs inside composites but also paves the way for virtual high-throughput formula screening of thermally conductive composite materials that could be used in industrial product design.

Comparison of a Nanofiber-Reinforced Composite with Different Types of Composite Resins.

The aim of this study was a comprehensive evaluation and comparison of the physical and mechanical properties of a newly developed nano-sized hydroxyapatite fiber-reinforced composite with other fiber-reinforced and particle-filled composites. Commercially available eight composite resins (3 fiber-reinforced and 5 particle-filled) were used: Fiber-reinforced composites: (1) NovaPro Fill (Nanova): newly developed nano-sized hydroxyapatite fiber-reinforced composite (nHAFC-NF); (2) Alert (Pentron): micrometer-scale glass fiber-reinforced composite (µmGFC-AL); (3) Ever X Posterior (GC Corp): millimeter-scale glass fiber-reinforced composite (mmGFC-EX); Particle-filled composites: (4) SDR Plus (Dentsply) low-viscosity bulk-fill (LVBF-SDR); (5) Estelite Bulk Fill (Tokuyama Corp.) low-viscosity bulk-fill (LVBF-EBF); (6) Filtek Bulk Fill Flow (3M ESPE) low-viscosity bulk-fill (LVBF-FBFF); (7) Filtek Bulk Fill (3M ESPE) high-viscosity bulk-fill (HVBF-FBF); and (8) Filtek Z250 (3M ESPE): microhybrid composite (µH-FZ). For Vickers microhardness, cylindrical-shaped specimens (diameter: 4 mm, height: 2 mm) were fabricated (n = 10). For the three-point bending test, bar-shaped (2 × 2 × 25 mm) specimens were fabricated (n = 10). Flexural strength and modulus elasticity were calculated. AcuVol, a video image device, was used for volumetric polymerization shrinkage (VPS) evaluations (n = 6). The polymerization degree of conversion (DC) was measured on the top and bottom surfaces with Fourier Transform Near-Infrared Spectroscopy (FTIR; n = 5). The data were statistically analyzed using one-way ANOVA, Tukey HSD, Welsch ANOVA, and Games-Howell tests (p < 0.05). Pearson coefficient correlation was used to determine the linear correlation. Group µH-FZ displayed the highest microhardness, flexural strength, and modulus elasticity, while Group HVBF-FBF exhibited significantly lower VPS than other composites. When comparing the fiber-reinforced composites, Group mmGFC-EX showed significantly higher microhardness, flexural strength, modulus elasticity, and lower VPS than Group nHAFC-NF but similar DC. A strong correlation was determined between microhardness, VPS and inorganic filler by wt% and vol% (r = 0.572-0.877). Fiber type and length could affect the physical and mechanical properties of fibers containing composite resins.

The effect of spherical filled particles on the energy storage density of composite materials

As one of the popular directions of new energy storage technology, dielectric energy storage technology has a wide application demand and market prospect in the modern new energy field. The research and manufacturing of composite materials is a core technology for the development of energy storage. In particle-filled composites, different filler particles can change a range of electromagnetic parameters of the composite, which can have an impact on the energy storage density of the composite. This paper presents an analytical study on the effect of spherical filled particles in composites on energy storage density. It turns out that when the volume ratio of filled particles is certain, as the permittivity of the filled particles increases, the energy storage density of the composite increases. When increased to a certain range, a limit value is reached. Therefore, under the condition of a certain volume ratio, it is not always possible to optimize the electrical energy storage density by changing the dielectric constant of spherically filled particles only.

Determination of effective properties of porous piezoelectric composite with partially randomly metalized pore boundaries using finite element method

In this study, we investigate the effective characteristics of a porous piezocomposite with randomly distributed pores of arbitrary size and with partly metalized pore boundaries. Using the ANSYS APDL finite element software, we created a novel random representative volume element (RVE), applied the finite element approach to solve boundary value problems of homogenization, and calculated equivalent properties using the Hill–Mandel principle. The results demonstrate that when large random RVE and an appropriate finite element mesh are used, the porous piezocomposite with randomly metalized porosity borders will have the same crystal symmetry as the piezoceramic matrix. Therefore, when there is a significant material contrast between the various phases, a large random RVE is preferred in the modeling of particulate-filled composites. Furthermore, when the areas of metalized surfaces increase, the performance of the investigated composite in transverse sensing and actuation applications improves.

Multi-Scale Model for the Aging Performance of Particle-Filled Polymer Composites.

In this study, we developed a novel multi-scale model to predict the aging performance of particle-filled polymer composites (PFPCs) under thermo-oxidative aging conditions. To investigate the aging behavior, high-temperature accelerated aging tests were conducted in combination with macroscopic and microscopic characterization. At the microscopic level, the crosslinking density of the polymer matrix is calculated using the closed-loop chain reaction of polymer oxidation. In addition, the theory of polymer physics was used to determine the relationship between crosslinking density and elastic modulus. Relationships between elastic modulus and dewetting strain were analyzed at the macroscopic level. Based on the observations and analyses, a multi-scale model was developed to predict the aging performance of PFPCs. The predicted results show good agreement with the test results, which verifies the reliability of the model.

Evaluation of fracture behavior in short fiber–reinforced direct and indirect overlay restorations

ObjectivesThe aim was to assess how incorporating a short-fiber composite (SFC) core would affect the fracture behavior of direct and indirect overlays. Furthermore, to examine the relationship between the thickness ratio of SFC core to particulate-filled composite (PFC) veneering and the fracture-behavior of bilayered-structured restorations.Materials and methodsA total of 120 molars were used to create MOD cavities, with palatal cusps removed. Four different groups of direct overlays were then made (n = 15/group), all of which featured a SFC core (everX Flow) with varying thicknesses (0, 1, 4, and 5 mm), as well as a surface layer of PFC (G-aenial Posterior), with the overall thickness of the bilayered-structured restoration set at 5 mm. Additionally, four groups of CAD/CAM restorations were created (Cerasmart 270 and Initial LiSi Block), with or without 2 mm of SFC core reinforcement. Following the fabrication of these restorations, cyclic fatigue aging was carried out for a total of 500,000 cycles, with an applied maximum load (Fmax) of 150 N. Subsequently, each restoration underwent quasi-static loading until fracture. The fracture mode was subsequently evaluated using optical microscopy and SEM.ResultsThere were no statistically significant differences (p > 0.05) observed in the fracture resistance of indirect overlays reinforced with a 2-mm SFC core compared to those made solely from restorative materials. Direct overlays constructed using plain SFC or with a 4-mm layer thickness of SFC core exhibited significantly higher fracture resistance values (2674 ± 465 and 2537 ± 561 N) (p < 0.05) when compared to all other groups tested, according to the statistical analysis ANOVA.ConclusionsThe most effective method for restoring large MOD cavities was found to be direct restoration using SFC either alone or as a bulk core in combination with PFC composite.Clinical relevanceThe use of SFC as bulk reinforcing base will significantly improve the loading performance of directly layered restorations.

Efficient numerical and ANN models for optimization of filler gradation of particulate-filled composites

Based on hard-sphere-like truncated Lennard-Jones interactions, a box compression simulation method, which belongs to molecular statics, was proposed to calculate the random close packing density of spherical particles. This method accurately provides the gradation corresponding to the maximum random close packing density with higher efficiency than the discrete element method (DEM). We trained an artificial neural network (ANN) model based on the data generated using this method to predict the packing densities of ternary and quaternary packing systems and discussed the applicability of this model in design of particulate-filled composites for electronic packaging. We found that the negative correlation between viscosity and random close packing density only applies to fillers of sizes greater than several microns. When the average filler size is reduced to submicron level, the specific surface area becomes the dominant factor in determining the upper limit of filler loading and viscosity of composites.

An investigation of the bonding properties of Cu particle-filled solderable isotropic polymer composites (Cu-SIPCs)

An investigation of the bonding properties of Cu particle-filled solderable isotropic polymer composites (Cu-SIPCs)

Towards a numerical modeling of the coupling between RTM process and induced mechanical properties for rigid particle-filled composites

Towards a numerical modeling of the coupling between RTM process and induced mechanical properties for rigid particle-filled composites