Filler Volume Content Research Articles

Interfacial Interaction and Fatigue Behavior of Asphalt Mastics

Rheological characteristics of five road bitumens with different group composition and penetration at 25оС from 60 to 115х0.1 mm and asphalt binders based on them with volume content of filler (mineral powder of MP1 grade) – 0.275 (mass ratio bitumen: filler – 1:1) have been determined in the range from 30 to -10оС on dynamic shear rheometer. The influence of temperature and frequency on the parameter of interfacial interaction K-B-G* and thickness of adsorbed layer of original and thermal oxidative aging samples of asphalt mastic has been investigated. It is shown that in all samples K-B-G* decreases with decreasing temperature and increasing test frequency. A decrease in K-B-G* and adsorbed layer thickness in mastics after aging was observed in the case of bitumen with Gestel colloidal index CI=0.46–0.53, defined as CI=(S+A)(/R+Ar), and was stability of K-B-G* and adsorbed layer thickness in the case of bitumen with CI=0.61. No relationship was found between group chemical composition of bitumen and adsorbed layer thickness in original mastics. In aged mastic the greater thickness of adsorbed layer has samples based on bitumen with higher content of asphaltenes. The peculiarities of fatigue behavior of bitumen and mastic in the linear amplitude sweep test were investigated. The correlation between the thickness of the adsorbed layer and the angle of slope of the curves of dependence of the maximum shear stress (τmax) on the complex modulus (G*) was noted for aged samples.

Modeling thermal conductivity of polymer/carbon fiber composites prepared by SCFNA method

AbstractThe spatial confining forced network assembly (SCFNA) has proven to be a promising method for greatly improving the thermal conductivity (TC) of polymer composites via transforming self‐assembled networks into force‐assembled networks in polymer matrices. Most of the models currently in use were derived to predict the TC of polymer composites with self‐assembled networks; however, these are not suitable for predicting the TC of polymer composites with force‐assembled networks. To address this issue, a TC prediction model for polymer/carbon fiber (CF) composites obtained using the SCFNA method was developed. First, a literature TC prediction model, built by abstracting a representative volume element (RVE) from a CF self‐assembled network, was utilized to determine the key parameters related to the CF distance. Thereafter, a modified RVE model was constructed based on the morphological characteristics of the force‐assembled network of CFs. In conjunction with the thermal resistance method, the TC values of the polymer composites were calculated and successfully validated using experimental data obtained by the SCFNA method. In this model, the compression ratio (ε) and a fitting coefficient f were applied to describe the relationship between self‐assembled and force‐assembled networks, and furthermore, the actual filler content in the force‐assembled network was calculated. It was found that as the ε value and filler content increased, f accordingly decreased; however, the calculated actual filler volume content in the force‐assembled network increased. These results possibly reflect the evolution of the CF microstructure obtained by the SCFNA method.Highlights Filler gaps in self‐assembled networks were studied using a literature model. The relationship between self‐assembled and force‐assembled networks was established. A thermal conductivity model of the force‐assembled network was established. The actual filler volume content in the force‐assembled network was calculated.

Modeling of Creep Behavior of Particulate Composites with Focus on Interfacial Adhesion Effect.

Evaluation of creep compliance of particulate composites using empirical models always provides parameters depending on initial stress and material composition. The effort spent to connect model parameters with physical properties has not resulted in success yet. Further, during the creep, delamination between matrix and filler may occur depending on time and initial stress, reducing an interface adhesion and load transfer to filler particles. In this paper, the creep compliance curves of glass beads reinforced poly(butylene terephthalate) composites were fitted with Burgers and Findley models providing different sets of time-dependent model parameters for each initial stress. Despite the finding that the Findley model performs well in a primary creep, the Burgers model is more suitable if secondary creep comes into play; they allow only for a qualitative prediction of creep behavior because the interface adhesion and its time dependency is an implicit, hidden parameter. As Young's modulus is a parameter of these models (and the majority of other creep models), it was selected to be introduced as a filler content-dependent parameter with the help of the cube in cube elementary volume approach of Paul. The analysis led to the time-dependent creep compliance that depends only on the time-dependent creep of the matrix and the normalized particle distance (or the filler volume content), and it allowed accounting for the adhesion effect. Comparison with the experimental data confirmed that the elementary volume-based creep compliance function can be used to predict the realistic creep behavior of particulate composites.

Introduction of an adhesion factor to cube in cube models and its effect on calculated moduli of particulate composites

The cube in cube approach was used by Paul and Ishai-Cohen to model and derive formulas for filler content dependent Young’s moduli of particle filled composites assuming perfect filler matrix adhesion. Their formulas were chosen because of their simplicity, and recalculated using an elementary volume approach which transforms spherical inclusions to cubic inclusions. The EV approach led to expression of the composites moduli that allows introducing an adhesion factor kadh ranging from 0 and 1 to take into account reduced filler matrix adhesion. This adhesion factor scales the edge length of the cubic inclusions, thus reducing the stress transfer area between matrix and filler. Fitting the experimental data with the modified Paul model provides reasonable kadh for PA66, PBT, PP, PE-LD and BR which are in line with their surface energies. Further analysis showed that stiffening only occurs if kadh exceeds sqrt{{E}_{mathrm{M}}/{E}_{mathrm{F}}} and depends on the ratio of matrix modulus and filler modulus. The modified model allows for a quick calculation of any particle filled composites for known matrix modulus EM, filler modulus EF, filler volume content vF and adhesion factor kadh. Thus, finite element analysis (FEA) simulations of any particle filled polymer parts as well as materials selection are significantly eased. FEA of cubic and hexagonal EV arrangements show that stress distributions within the EV exhibit more shear stresses if one deviates from the cubic arrangement. At high filler contents the assumption that the property of the EV is representative for the whole composite, holds only for filler volume contents up to 15 or 20% (corresponding to 30 to 40 weight %). Thus, for vast majority of commercially available particulate composites, the modified model can be applied. Furthermore, this indicates that the cube in cube approach reaches two limits: (i) the occurrence of increasing shear stresses at filler contents above 20% due to deviations of EV arrangements or spatial filler distribution from cubic arrangements (singular), and (ii) increasing interaction between particles with the formation of particle network within the matrix violating the EV assumption of their homogeneous dispersion.

Влияние структуры древесно-цементного материала на прочностные и деформационные свойства

It is established that with an increase in the length of the filler particles, the axial compression strength of the wood-concrete material (arbolite) increases, and the volume shrinkage decreases. An increase in the linear shrinkage of the arbolite across the prism parallel to the direction of the pressing force and a decrease in the linear shrinkage across the prism perpendicular to the direction of the pressing force with an increase in the length of the filler particles is determined. An increase in the specific pressure of pressing arbolite with an increase in the length of the filler particles was revealed. Studies have shown that the dependence of the strength of arbolite is inversely proportional to the content of water-soluble wood substances in the organic aggregate of which it is made, its shrinkage, the specific surface area of the aggregate, water consumption and the volume content of wood filler in arbolite. Theoretically necessary for a chemical compound, the water-concrete ratio In/C is 0,4, however, from the condition of the workability of arbolite, the ratio In/C is recommended to be equal to 0,7...0,8.

Закономірності впливу високомодульних наповнювачів на розподіл полів напружень в поверхневих шарах деталей машин, виготовлених з полімерних композитних матеріалів

In this paper, based on computer simulation of contact interaction of conjugations of samples (parts) loaded with friction, the main changes in the distribution of stress fields in the contact regions of homogeneous and heterogeneous (composite) polymeric materials are revealed. Stress fields were investigated under both static and dynamic load conditions. The focus was on identifying areas with maximum tangential stresses , their configuration and depth. The theory of N.P. Suh, which concerns the origin of destructive processes in the materials of samples and parts, is initiated by the presence of zones of maximum tangential stresses at a certain depth of the surface layer. In the homogeneous polymeric material, four stress regions are detected: in the contact region ; the contact area ; in the field of aggregate contacts ; in the area between the aggregate contacts . It is shown that in the relative motion of the conjugations of the samples (parts) the depth of the local areas and , where reaches the highest value and these areas remain in place, and areas and are mixed in operation closer to the surface. The change of configurations of these areas in the process of relative motion of conjugations of samples (details) is also revealed. In the heterogeneous (composite) polymeric material with high-modulus fillers, three local areas were identified: in the filler ; between the fillers ; under the filler . It is determined that the contact load in the polymer composite material is transmitted through high-modulus fillers and is determined by their geometry and relative position. Significant danger is posed by cases when areas and are located at the same level from the surface of the sample (part), which can cause chipping of the filler. It is shown that the most effective is the operation of the part when the area is located deeper than . A criterion corresponding to the optimal volume content of high modulus filler, which is equal to the ratio of the average distance between centers of adjacent filler particles and their size. Relevant estimates of this criterion are given.

Stiffening Effect of Fillers Based on Rheology and Micromechanics Models

The aggregate in an asphalt mixture is coated with mastic consisting of bitumen (dilute phase) and filler (particulates phase). The interaction of bitumen and filler and packing of filler plays an important role in the properties of mastics. The micromechanics models from composite rheology can be used to predict the stiffening effect of a suspension. In this research, the stiffening effect of fillers was investigated based on the rheology of mastic. The frequency sweep tests in a dynamic shear rheometer at different temperatures were performed within a linear viscoelastic range to construct the master curves. The volume fractions were expressed as compositional volumes of filler in mastic. The particle shape and surface texture are determined through microscopy. We used six micromechanics-based models to predict the stiffening potential of fillers in mastics. The models include Maron–Pierce, Lewis Nielsen, Mooney, Krieger–Dougherty, Chong, Robinson, and Hashin Models. The results show that the same volume content of filler has a different effective volume. The fillers increase the stiffening effect of the composite, especially at high temperatures. The behaviour of fillers with similar effective volume and packing is identical. The filler type affects the stiffening of mastics. Micromechanics modelling results show that most models show an accurate stiffening effect at lower concentrations with the exception of the Chong Model. The Maron–Pierce Model under-estimates the stiffening potential for granite mastic at higher concentrations beyond the 30% filler content fraction. The value of maximum packing fraction (ϕm) and Einstien coefficient (KE) in the Mooney model are significantly different from other models for limestone and granite, respectively. The line of equality graph shows good agreement of measured and predicted stiffness. It is difficult to precisely model the mastic data with any single model due to the presence of complex stiffening effects beyond volume filling.

Optimization of the particle size and structure parameters to receive dispersed filled polymer composites with maximum strength characteristics

For the first time, the generalized (Θ) and normalized (amid/d, Θ/B, and Θ/Sf) parameters were used to describe the dispersed structures and strength properties of DFPCM for different contents of a dispersed filler with different specific surface area (Sss) and particle diameter (d). This made it possible to determine the optimal parameters of the filler, its content and the type of dispersed structure with maximum strength. The optimal parameters of investigated system (FA + SiО2) were: amid/d ≈ 0.25–0.3; Θ ≈ 0.5–0.55 b.v.; Θ/В ≈ 2.0–2.5 и Θ/Sf ≈ 0.8–1.0. They are achieved by using silica-fi ller with specific surface area Sss = 1 m2/g and particle diameter d ~ 2.25 μm, the volume content of filler was ~20–25 volume % (0.2–0.25 b.v.). The optimal structure for disperse-filled polymer composite material is middle-filled system (before yield strength). It was determined, that the optimal particle size depends on interaction between growing crack and dispersed inclusions while composite is destructed as well the length of the phase boundary (normalized parameter Θ/Sf). To sum up, it is necessary to use only generalized and normalized parameters (аmid/d, Θ, Θ/В and Θ/Sf) to determine the optimal of dispersed fillers and the structure of DFPCM with maximum strength.

Experimental and computational modeling of thermal conductivity of cementitious syntactic foams filled with hollow glass microspheres

Insulating cementitious syntactic foams (CSFs) reinforced hollow glass microspheres (HGMs) have been paid much attention for the growing requirement of energy savings. In this paper, the CSF plates with different volume contents of HGMs are manufactured by a novel three-step manufacturing process and then they are tested by transient plane source (TPS) method to investigate their heat insulation performance. The filler volume content is in the range of 0–56 vol%. The experimental results reveal that the effective value of thermal conductivity of the foam decreases roughly linearly with increasing the HGM volume content. The addition of 56 vol% HGMs brings over 47% decrease of the thermal conductivity of the foam, in contrast to the pure cement material. In addition, the heat transfer mechanisms in the CSFs are further investigated by the developed computational model with randomly dispersed HGMs to approximate the real arrangement of microspheres in the foam. The experimental data are in good agreement with the numerical estimations. Moreover, the resulting numerical predictions demonstrate that the effective thermal conductivity coefficient of the foam increases as the constituent thermal conductivity increases. However, compared to the core and solid wall material, the matrix material gives significant influence to the foam. Finally, a two-phase composite model with equivalent solid spherical inclusion is presented based on Eshelby’s equivalent inclusion theory to indirectly determine the thermal conductivity of pure HGM, which are important for guiding the predesign of syntactic foams with desired low thermal conductivity.

Influence of hydrolysis degradation of silane coupling agents on mechanical performance of CAD/CAM resin composites: In silico multi-scale analysis.

The aim of this study was to build an in silico computer-aided design and computer-aided manufacturing (CAD/CAM) resin-composite-block (RCB) model with different silane coupling ratios and to evaluate the physical and mechanical properties of the models, including the elastic modulus, Poisson's ratio, compressive strength, and maximum principal strain. Nanoscale CAD/CAM RCB models were designed by using CAD software that consisted of twelve spherical silica nanofiller particles and a resin matrix. Seven nanoscale models with different silane coupling ratios were prepared with the same filler volume contents. Homogenization analysis was conducted by using voxel-base finite-element analysis software to predict the elastic moduli and Poisson's ratio of the macro CAD/CAM RCB. Localization analysis was used to analyze the maximum principal strain distribution in the hydrolysis layer. In silico multi-scale analysis demonstrated that the compressive strength of the CAD/CAM RCB was reduced with a decrease in the silane coupling ratios of the fillers.

The effect of UV irradiation on the dielectric properties of bionanocomposites with fillers of biological origin and metal nanoparticles

In this paper, information is given about the investigation of the dielectric properties of bionanocomposites modified with fish bones (FBs) and scales and metal nanoparticles (Al, Fe) with 50–80 nm dimension before and after ultraviolet (UV) irradiation, depending on the temperature, the irradiation time and the volume content of fillers. The investigations of dielectric permittivity and dielectric loss were carried out in the temperature range 300–390 K, the time of irradiation with UV rays were 50, 100, 70 and 150 h, and the filler contents were 3, 5, 7, 10, 15 vol.% and nanoparticles 1 vol.% Al (Fe). It was found that the dielectric constant of UV-irradiated biocomposites with FB additives increases and the dielectric loss decreases. An increase in dielectric constant is also observed with an increase in the volume content of a biological origin filler. Note that the effect of UV irradiation causes the appearance of a new region of dielectric loss in the temperature-dependent tan[Formula: see text] of the polyethylene. However, in modified samples after irradiation, under the same conditions, the change in dielectric properties is much less pronounced than in the initial ones, i.e. the dielectric constant increases monotonically, and the value of tan[Formula: see text] in the maximum of the new loss region is much smaller. Moreover, the effect of the additive is manifested in slowing down the process of LDPE oxidation in the irradiation zone, since the main losses of the polyethylene are primarily caused by the relaxation of the carbonyl groups. Thus, the observed dependences of [Formula: see text] and tan[Formula: see text] on the time of exposure to UV rays are explained by a change in the physical structure of the polymer matrix and the boundary layer of the components composition under the action of charges formed during irradiation.

ТЕОРЕТИЧНІ ПЕРЕДУМОВИ ЕКСПЛУАТАЦІЇ КОНСТРУКЦІЙ З МЕТАЛ-СКЛЯНИМИ ЗАХИСНИМИ ПОКРИТТЯМИ В УМОВАХ СУДНОВИХ ВІБРАЦІЙ

The article is devoted to looking for a solution for the scientific and technical issue of reducing vibrations on vessels. It is considered to be achieved with the application of the vibration-absorbing composite coatings. The purpose of the work is to theoretically substantiate the possibility of operation of structures with metal-glass coatings taking into consideration the vibration environment of a vessel. The formulation of the research includes the discovery of the solution for the micromechanics issue set up on the model of a two-layer plate St3 ‒ metal-glass coatings, taking into account their structural features, and experimental tensile tests. The influence of the polydisperse structure of coatings on the mechanisms of absorption of elastic-plastic waves of dynamic oscillations has been analyzed with the help of the analytical description of microdisplacement deformations. The influence of morphology and volume content of glass fillers, specifically hollow glass microspheres, powders of sodium silicate and lead-containing glass on the vibration coefficient, strength limit and yield strength has been investigated. Calculations have shown the feasibility of using metal-glass coatings in conditions of vessel vibration, which is due to the absorption of energy by glass inclusions of spherical and angular shape. It has been experimentally proven that coated plates are slightly inferior in tensile strength to samples with St3; the destruction of coatings occurs between glass inclusions. The obtained results have scientific and practical significance for the design of ship structures using composite materials and coatings.

Copper plated graphite, carbon nanotubes and polyaniline effect on the properties of electroconductive polyethylene compositions

There have been presented electrophysical (electrical volume resistivity), mechanical (tensile strength and elongation at break) and rheological (melt flow index) features of polyethylene compositions filled by copper plated graphite, multiwall carbon nanotubes and polyaniline in this article. An increase in the volume content of electroconductive fillers in the polyethylene matrix results in a monotonically falling curves with a well-defined threshold of leakage. The decrease in tensile strength by ∼ 4 times and relative elongation by ∼ 7 times have been observed in the polyethylene composite films having copper plated graphite and polyaniline up to 30 % vol. The tensile strength for conductive polyethylene compositions filled by multiwall carbon nanotubes slightly increases by ∼ 1.1 times, but relative elongation decreases dramatically by ∼ 5 times. The melt flow index decreases with the increase of concentration by exponential law for the compositions filled by multiwall carbon nanotubes and polyaniline by ∼ 1.4 times and increases for copper plated graphite filled compositions by ∼ 2 times due lubricating effect. There has been developed technological process of production for electroconductive polymer composite materials based on polyethylene by pressing method.

Nozzle flow behavior of aluminum/polycarbonate composites in the material extrusion printing process

ABSTRACTThis article investigates the effects of nozzle diameter, resin viscosity, and filler size and volume content on the melt flow properties and clogging of composites in the material extrusion additive manufacturing process. The flow behavior was systematically characterized by a custom nozzle flow test (NOFT) device, thermogravimetric analysis (TGA) and scanning electron microscope (SEM). Results indicated that the viscosity of the material, the particle size, and the diameter of the nozzle were important factors for clogging. TGA results showed deviations from the designed filler volume fraction, which could be due to the buildup of filler material in the nozzle and subsequent partial clogging. SEM observations showed that particle agglomeration tended to be more prevalent in strands with high filler volume content. The agglomeration could be seen near the edge of the strand. A model for the clogging formation in NOFT was summarized into four stages: particle deposition on the wall of the nozzle, creation of dendrites, particle agglomeration, and particle clogging, which explained the clogging mechanism in the NOFT. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47252.

INFLUENCE OF ALBASIA WOOD ON MECHANICAL PROPERTIES AND MORPHOLOGY OF EPOXY COMPOSITES

This research aims to investigate the effects of albasia wood filler as alternative reinforcement for extravagant and non-renewable filler being used in epoxy composites. The filler size used was 30 mesh and various filler volume fractions were 10, 20, 30 and 40 percent. Composites were manufactured using hand lay-up method. Properties such as tensile strength, elongation, modulus elasticity and strain energy absorption were determined based on ASTM standard. The results show that filler volume content significantly affects the tensile properties and impact strength of albasia wood-epoxy composites. The optimum tensile properties are achieved when 10 percent filler is added into epoxy matrix. The impact test also shows the same results. Further addition of filler decreases the mechanical properties of composites due to the existence of weak interfacial interaction between the albasia wood filler and polymer matrix for higher filler volume concentration beyond 10 vol. %. The scanning electron micrograph reveals that there are voids and pull-out mechanism on tensile fracture surface which are the cause of the composites failure.

Thermal, dielectric, and mechanical properties of h‐BN‐filled PTFE composites

ABSTRACTIn order to obtain materials for improved printed circuit boards (PCBs) with high thermal conductivity and low dielectric losses, hexagonal boron nitride (h‐BN) was incorporated into a polytetrafluoroethylene (PTFE) matrix. The filler loading in the composite was varied up to a filler volume content of 50%. Thermal conductivity and coefficient of thermal expansion (CTE) were investigated with respect to filler orientation. Further dielectric and mechanical properties were investigated. The incorporation of h‐BN improved the heat transport significantly, while the loss factor decreased. Fillers with a higher aspect ratio have a greater effect on increasing thermal conductivity. For a filler volume loading of 30%, the in‐plane thermal conductivity was up to 14 times higher than the thermal conductivity of the matrix, while the loss factor decreased slightly. The permittivity increased with the increasing filler volume content, while the CTE also decreased. Though the filler affects the mechanical properties negatively, 40% of the tensile strength could be maintained if a filler volume content of 30% is not exceeded. Such compositions may be used as raw materials for future printed circuit boards. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46859.

Post-curing in dental resin-based composites

ObjectiveTo determine the post-curing in six commercial contemporary resin-based composites (RBCs) using axial shrinkage, the degree of conversion, and Vickers hardness. MethodsFive Bulk Fill and one conventional RBCs from three companies were selected with a wide range of filler volume content. The axial shrinkage of samples that were 1.00mm thick by 9–10mm diameter was measured using a modified bonded disk method over a time between 15h and 19h at temperatures of 26°C and 34°C (mouth temperature). The degree of conversion (DC) was collected continuously for 10min using mid-infrared spectroscopy in the attenuated total reflectance geometry. Vickers hardness was measured at 1h post-irradiation using a load of 300gf. For all three tests, the samples were irradiated at five exposure times, 20, 5, 3, 1.5 and 1s with a light curing unit radiant exitance of 1.1W/cm2. Three samples (n=3) were used for each experimental condition. ResultsAfter light exposure, the axial shrinkage and degree of conversion exhibited a functional time dependence that was proportional to the logarithm of time. This suggests an out-of-equilibrium polymer composite glass that is transitioning to thermal equilibrium. At a sufficiently long time and among the RBCs investigated, the shrinkage related physical aging rate was found to vary between 1.34 and 2.00μm/log(t). The rate was a function of the filler content. Furthermore, 15h after light exposure, the post-curing shrinkage was estimated to be an additional 22.5% relative to the shrinkage at 100s for one RBC at T=34°C. The hardness in the photo-cured RBC was varied by using different light exposure times. The first two experimental techniques show that the higher the initial DC 10min after light exposure, the smaller is the post-curing shrinkage related and DC related physical aging rates. A direct correlation was observed between the shrinkage related and the DC related physical aging rates. SignificancePost-curing shrinkage should be evaluated for longer than 1h. The post-curing shrinkage 15h after light exposure in dental RBCs can be appreciable. The long-term development of built-in stress within the tooth wall structure may shorten the restoration’s lifespan.

Thermal Conductivity and Impact Properties of Iron Ore Tailings Filled Epoxy Composites

Iron ore tailings which is the waste material derived from the beneficiation of iron ore was dispersed in epoxy as micro scale particle fillers. The effect of particle size and particle loading on the thermal conductivity and impact properties of the composites were then investigated experimentally. It was discovered that the impact resistance increased with increasing volume content of iron ore tailings from 20 vol.% with a maximum toughness of 0.098 kJm-2 recorded for composite with 300 µm at 30 vol.%. Thermal conductivity of epoxy improved with decreasing particle size while 150 µm inclusion lead to improved thermal conductivity with increased volume content of filler.

Multi-scale analysis of the effect of nano-filler particle diameter on the physical properties of CAD/CAM composite resin blocks

The objective of this study was to assess the effect of silica nano-filler particle diameters in a computer-aided design/manufacturing (CAD/CAM) composite resin (CR) block on physical properties at the multi-scale in silico. CAD/CAM CR blocks were modeled, consisting of silica nano-filler particles (20, 40, 60, 80, and 100 nm) and matrix (Bis-GMA/TEGDMA), with filler volume contents of 55.161%. Calculation of Young’s moduli and Poisson’s ratios for the block at macro-scale were analyzed by homogenization. Macro-scale CAD/CAM CR blocks (3 × 3 × 3 mm) were modeled and compressive strengths were defined when the fracture loads exceeded 6075 N. MPS values of the nano-scale models were compared by localization analysis. As the filler size decreased, Young’s moduli and compressive strength increased, while Poisson’s ratios and MPS decreased. All parameters were significantly correlated with the diameters of the filler particles (Pearson’s correlation test, r = −0.949, 0.943, −0.951, 0.976, p < 0.05). The in silico multi-scale model established in this study demonstrates that the Young’s moduli, Poisson’s ratios, and compressive strengths of CAD/CAM CR blocks can be enhanced by loading silica nanofiller particles of smaller diameter. CAD/CAM CR blocks by using smaller silica nano-filler particles have a potential to increase fracture resistance.

Shrinkage stress kinetics of Bulk Fill resin-based composites at tooth temperature and long time

ObjectiveTo determine the shrinkage stress kinetics at up to 12h after light exposure and at tooth temperature during placement of selected Bulk Fill resin-based composites (RBCs). MethodsFive representative Bulk Fill RBCs from four companies were chosen with a wide range of viscosity and filler volume content. The shrinkage stress kinetics at T=33°C was measured continuously over a period of 12h using a modified tensometer with the ability to measure the cantilever beam deflection to better than 40nm accuracy at a sampling rate of up to 200 samples/s, and thermally stable resulting in a measurement accuracy better than 0.05MPa at 12h. The tensometer compliance was 0.105μm/N. A custom made heater was used to control the RBC sample temperature at T=33°C with a temperature gradient across the sample of less than 1°C. The samples were irradiated for 20s with irradiance of 1.1W/cm2 and total energy density of 22J/cm2. Three samples (n=3) were used for each RBCs. ResultsThe shrinkage stress at 12h for the five Bulk Fill RBCs ranged from 2.21 to 3.05MPa, maximum stress rate ((dS/dt)M) varied from 0.18 to 0.41MPa/s, time at which the maximum stress rate occurred (tMax) were between 1.42 to 3.24s and effective gel time (tgel) varied from 50 to 770ms. Correlations were observed between (dS/dt)M and tMax (r=−0.946), tMax and filler volume fraction (r=−0.999), and between the shrinkage stress at 12h and tgel (r=0.994). However, no correlation was observed between the stress at 12h and filler volume fraction. SignificanceThe shrinkage stress for four of the five Bulk Fill RBCs were not significantly different (p<0.05) at 6h and beyond after photo-curing and that fully developed stress induced by photo-cured RBCs may only be reached at times longer than 12h.