Elastic Modulus Of Composites Research Articles

Tests and numerical simulation of rectangular RACFST stub columns under concentric compression

Tests and numerical simulation of rectangular recycled aggregate concrete filled steel tube (RACFST) stub columns under concentric compression are carried out. Eighteen specimens, including 12 RACFST specimens and 6 concrete filled steel tube (CFST) specimens as reference, with varied width-to-thickness ratio (B/t), depth-to-width ratio (β) and recycled coarse aggregate replacement ratio (r) are tested. The test results show that rectangular RACFST stub column specimens have similar failure pattern as their counterparts. However, the bearing capacity and the composite elastic modulus of RACFST specimens are lower than those of CFST ones while they both decrease with higher r. Moreover, the specimens with larger B/t and β possess a smaller ductility index. Numerical simulation of rectangular RACFST stub columns under concentric compression is executed using a finite element analysis (FEA) model developed based on the ABAQUS software, and the predicted results are verified by the experimental observations. The mechanism of concentrically loaded rectangular RACFST stub columns is further revealed by the FEA model. Finally, simplified formulae for the bearing capacity of rectangular RACFST stub columns are proposed, with the comparison between simplified and experimental results showing that the simplified model is a good predictor.

Prediction of the modulus of elasticity of building materials based on wood-polymer composites

The modulus of elasticity of mixtures of two polymers in glassy or crystalline states is predicted. In addition, the elastic modulus of composites containing a mixture of organic polymers and a mineral filler is predicted. The preparation of wood-polymer composites increases the elastic modulus from 2400 to 4660 MPa under tensile conditions. The introduction of a mineral filler in the form of CaCO3 leads to an increase in the E modulus to 3230 MPa with a CaCO3 content relative to the wood filler of 42%. The prediction of the elastic modulus for composites containing moso bamboo as a wood filler shows that with this content of wood filler, the modulus of elasticity can increase to 4400 MPa.

Compressive behaviors of ultra-low-weight foamed cement-based composite reinforced by polypropylene short fibers

With advantages in sustainability, low thermal conductivity, and self-weight, the foamed cement-based composites have captured tremendous attention in various low strength structural and nonstructural applications. This paper aimed to investigate the effects of the short polypropylene fibers on the quasi-static compression performance of the ultra-low-weight foamed cement-based composites. The results show that the elasticity modulus, peak strength, and ultimate linear strength of the fiber-reinforced composites are increased by 208%, 42%, and 71%, respectively. The plateau stress and the densification strain energy of fiber-reinforced composites are improved by up to 49% and 47%. Simultaneously, the failure mode of the fibrous sample is altered from a brittle behavior to plastic behavior. The significance of this work shows that short synthetic fibers can improve the compressive capacity considerably, turning out to be an effective strategy for obtaining higher mechanical strengths associated with ultra-low-weight typical cement-based elements. According to the experiment results, a constructive damage model is carried out to describe the compressive properties of short PP fiber-reinforced composites. Thus, such theoretical curves can describe the compression behavior successfully and can be potentially applied in practical project and numerical simulation. This work can also be useful toward the foundation of optimal design for toughening behavior in fiber-reinforced lightweight cement elements.

Forecasting the Elasticity Modulus of Composites Based on Polymer Blends

Forecasting the Elasticity Modulus of Composites Based on Polymer Blends

Prediction of elastic modulus of polymer composites using Hashin–Shtrikman bound, mean field homogenization and finite element technique

Polymer matrix composites are developed by reinforcing biodegradable rubber seed shell, cashew nut shell and walnut shell powder in epoxy resin. Theoretically, elastic modulus is calculated using Hashin–Shtrikman bounds using variational principles. Investigation of the elastic modulus of the composites is extended by varying filler weight up to 25% in Digimat 2017-MF which applies Mori–Tanaka mean field homogenization and ANSYS 15.0 Workbench which uses a three-dimensional model of representative volume element having spherical shaped filler particles to calculate elastic modulus. Elastic modulus is the measurement of resistance of the material under tensile load. The corresponding stress–strain relationship predicts the stiffness of the material. The results are confirmed with experimentation approach for 5% wt filler content. Elastic modulus obtained from these approaches show a maximum error of 7% with experiment results. Investigation further reveals that elastic modulus of composites increases with increase in weight fraction of fillers. However, above 15% wt of filler content, no significant increase in the elastic modulus of the composites is observed.

Investigation of the mechanical performance of fiber-modified ceramic composites using finite element method

Ceramic materials are widely used in impact safekeeping systems. Ceramic is a heterogeneous material; its characteristics depend considerably both on specifications of its ingredients and the material structure completely. The finite element method (FEM) can be a useful tool for strength computation of these materials. In this paper, the mechanical properties of the ceramic composites are investigated, and the mechanical performance modeling of fiber-fortified ceramic matrix composites (CMC) is expressed by the instance of aluminum oxide fibers in a matrix composite based on alumina. The starting point of the modeling is an infrastructure (primary cell) that contains a micromechanical size, the statistical analysis characteristics of the matrix, fiber-matrix interface, fiber, and their reciprocal influences. The numeral assessment of the model is done using the FEM. The numerical results of composite elastic modulus were computed based on the amount of the added fibers and the porosity was evaluated for empirical data of samples with a similar composition. Various scanning electron microscope (SEM) images were used for each sample to specify the porosity. Also, the unit cell method presumed that the porous ceramic substance is manufactured from an array of fundamental units, each with the same composition, material characteristic, and cell geometry. The results showed that when the material consists of different pores and fibers, the amount of Young’s modulus reduces with the increment of porosity. The linear correlation model of elasticity versus porosity value from experimental data was derived by MATLAB curve fitting. The experimental data from the mechanical test and numerical values were in good agreement.

Physico-Mechanical Characterization of Composite Materials Based on Date Palm Tree Fibers

ABSTRACT The aim of this research is to characterize physico-mechanically fibers extracted from different parts of a palm; This characterization shows that the physico-mechanical properties of this kind of fibers are different from one to another depending on the part from which the tested fiber was extracted. Furthermore, we performed the physico-mechanical characterization of a composite material based on these fibers and matrix Epoxy. Tensile strength tests carried out for composites with different fiber percentages (4, 7, 10 and 15%) reveal that there is an improvement in the mechanical properties of the virgin resin proportional to the fiber mass ratio up to 10%; while a degradation of these properties is observed for a fiber mass ratio of 15%. The rate of 10% corresponds to the highest value of composite modulus of elasticity with an increase of 73% compared to the virgin resin. The results of mechanical and thermo-gravimetric analysis obtained are used to valorize these fibers for possible industrial applications such as thermal insulation.

In vitro evaluation of multi-walled carbon nanotube reinforced nanofibers composites for dental application

The goal of this study was to evaluate the mechanical properties of an experimental composite resin filled with nylon-6 nanofibers (N6), nylon-6 nanofibers with multi-walled carbon nanotubes (N6-MWCN) or with pre-polymerized resin at different concentrations. The fillers/particles were obtained from nanofibers produced by electrospinning technique or from pre-polymerized composite resin. The fillers were distributed in the composite resin in four different mass fractions (2.5, 5.0, 10.0, and 20.0%), totaling 12 groups. The volumetric polymerization shrinkage (VPS), composite film thickness (CRFT), flexural strength (FS) and elastic (E) modulus of the composite resins were calculated. The data were evaluated using two-way ANOVA and Tukey test (p < .05). The interaction concentration*filler material was statistically significant for the VPS (p = .0008) and for FS (p = .0001). The smallest VPS was observed in 20% concentration without a difference to 10% for N6-MWCN particles. For FS, N6-MWCN in 2.5 and 5.0% presented the highest values (116.4 ± 9.32; 118.5 ± 7.72). Both factors (p = .0001) were significant for CRFT. Higher concentration (20%) showed a higher film thickness. E modulus was similar for all conditions, with p = .0590 for filler material and p = .3987 for concentration. The most indicated composite reinforcement in order to achieve suitable flexural strength with decreased polymerization shrinkage is the use of pre-polymerized composite-based material at a concentration of 20%. N6-MWCNT particles in 2.5 or 5% concentrations should be incorporated to produce a composite resin presenting adequate strength associated with reduced film thickness.

Novel prediction models for composite elastic modulus of circular recycled aggregate concrete-filled steel tubes

Incorporating recycled aggregate concrete (RAC) into steel tubes provides a value-added and promising solution that can reduce environmental impact of waste concrete and meanwhile increase mechanical performances and durability of RAC material. Composite elastic modulus (CEM) is one of the most essential structural properties in the design and evaluation of recycled aggregate concrete-filled steel tubes (RACFST); however, it is found that available design provisions developed for conventional concrete members fail to predict the CEM of RACFST with good accuracy.This paper proposes a set of novel models to address this both research and engineering gap. A reliable experimental database is first established containing test results of circular RACFST beam and column specimens under axial and/or flexural loading. Based on this work, a mathematical approach, i.e., the grey correlation analysis, is used to evaluate the sensitivity influence of key parameters on the CEM of circular RACFST. It is demonstrated that the replacement ratio of recycled concrete aggregate (RCA) is less decisive on CEM than some other parameters such as the steel tube yield strength and the diameter-to-thickness ratio, but the RCA replacement ratio is still significant and should be considered for better representing the elastic stiffness of circular RACFST. Derivations based on elasticity theory are then presented to obtain an elastic stress-strain relationship and hence the expression of CEM of concentrically-loaded circular RACFST. A comparison between the theoretical results and the experimental ones is made to validate the proposed model. For easy use in routine design, two empirical models in compliance with design codes based on the superposition principle are also provided to estimate respectively the composite elastic compressive stiffness and flexural stiffness of circular RACFST. A good agreement between the predictions using the empirical models and the test data is exhibited.

Thermoresponsive Stiffening with Microgel Particles in a Semiflexible Fibrin Network

We report temperature-responsive soft composites of semiflexible biopolymer networks (fibrin) containing dispersed microgel colloidal particles of poly(N-isopropylacrylamide) (pNIPAM) that undergo a thermodynamically driven de-swelling transition above a Lower Critical Solution Temperature (LCST). Unlike standard polymer-particle composites, decreasing the inclusion volume of the particles (by increasing temperature)is concomitant with a striking increase of the overall elastic stiffness of the composite. We observe such a behavior over a wide composition space. The composite elastic shear modulus reversibly stiffens by up to 10-fold over a small change in temperature from 25-35{\deg}C. In isolation, the fibrin network and microgel suspension both soften with increased temperature, making the stiffening of the composites particularly significant. We hypothesize that stiffening is caused by contracting microgel particles adsorbing on the fibrin filaments and modifying the structure of the semiflexible network. We develop two phenomenological models that quantify this hypothesis in physically distinct manners, and the derived predictions are qualitatively consistent with our experimental data

Mechanical behavior of CuZr dual-phase nanocrystal-metallic glass composites

Molecular dynamics (MD) simulations are conducted to investigate the influence of various critical structural aspects such as crystallographic direction, spatial distribution and size/volume fraction of nanoscale crystalline secondary phase on the mechanical behavior of dual-phase nanocrystal-metallic glass composites (NCMGCs). The results of MD simulations show that the ‘softer’ amorphous matrix and amorphous-crystal interfaces serve as the nucleation sites of the shear transformation zones, and eventually developing into mature shear bands (SBs). We find that the different crystallographic directions of the nanocrystals have great influence on elastic modulus of composites. Moreover, the spatial distribution of nanocrystals plays an important role in SBs propagation direction. In particular, by increasing the volume fraction of the crystalline phase, plastic co-deformation of the SBs and stacking faults is achieved for the NCMGCs with nanocrystals of [1 1 0] and [1 1 1] directions. Moreover, the presence of stacking faults releases most of the stress of nanocrystals and retards the formation of a mature SB. By systematically varying the characteristics of the B2 CuZr nanoscale crystalline phase one can design composites with improved mechanical properties.

Tribological behavior of polymer composites containing microcapsules and fibrous fillers: Finite element analysis and experimental verification

In allusion to the repeatability and complexity of tribological experiments, numerical simulations were carried out successfully to study the effect of microcapsules (MCs) and carbon fibers (CFs) contents on the longitudinal frictional temperature and Von Mises stress transfers of composites. Novel MC‐(fibrous filler) finite element (FE) models for polyvinylidene fluoride (PVDF) composites were established by observing morphologies of truncation surface, thermogravimetric analyzer (TGA) test and mathematical calculation. The thermal‐stress coupled analysis revealed the influence of oily microcapsules (OMCs) and CFs on thermal conductivity, thermal expansion, and elastic modulus of composites had further transformed the tribological properties of polymer composites. Moreover, tribological tests were carried out scientifically to verify the high accuracy of the simulated results with the error &lt;8%. Both the experiment and simulation results indicated that 20 wt% OMCs/8 wt% CFs/PVDF composites possessed the optimal tribological properties. These demonstrate the novel FE models can predict the tribological properties of polymer composites containing MCs and fibrous fillers legitimately. POLYM. COMPOS., 40:3453–3463, 2019. © 2019 Society of Plastics Engineers

Guaruman: a Natural Amazonian Fiber with Potential for Polymer Composite Reinforcement

The Amazonian region of South America is known for its diversified number of plants from which food, medicine, wood and fibers have, since long time, been produced by local natives. A typical example is the guarumã (“guaruman”as suggested English spelling) scientifically identified as Ischinosiphon koem, an abundant plant found in the low lands alongside rivers of the state of Para in Brazil. Fibers extracted from the stem of the guaruman are used in ropes and baskets owing to their strength. In the present work, the possibility of applying guaruman fibers as reinforcement of polymer matrix composites is, for the first time, investigated. Amounts up to 30 vol% of continuous and aligned fibers were incorporates into epoxy matrix composites. Density measurements disclosed the guaruman to be one of the lightest natural fibers. Tensile tests indicate that the guaruman fiber addition was able to improve the composite elastic modulus. However, no significant change was found in the ultimate strength, total strain and resilience. On the other hand, a cost-effective analysis revealed a substantial reduction of ~29% in the epoxy composite price due to the incorporation of fibers. Preliminary ballistic evaluation disclosed a potential for application of guaruman epoxy composites in multilayered armor.

Study on Composite Elastic Modulus of Elevated Temperature Diffusion Self-lubricating Material

Based on the pore structural characteristics of elevated temperature diffusion self-lubricating material, its two-phases composite model was established, and the composite elastic modulus of the materials was predicted by Mori-Tanaka method, as well as the results were compared with test data of Yaman in order to verify the validity of the proposed model. Moreover, the effects of lubricating oil characteristics on the composite elastic modulus of the materials were explored by taking the 4129 type of aerospace lubricating oil as an example. The research shows that the results calculated by the model agree well with the test data of Yaman, and the average error is less than 5%, which proves that the model can predict the composite elastic modulus of elevated temperature diffusion self-lubricating materials accurately. In addition, the composite elastic modulus of the materials decreases linearly with the increase of porosity, which indicates that the increase of lubricant content will cause a decline in the overall strength of the materials. Under the condition of oil lubrication, the composite elastic modulus of the materials decreases with the increase of temperature and velocity, and increases with the increase of the load.

Effect of the Al–CNT interlayer on the tensile elastic modulus of Al matrix composites with random dispersion of CNTs

This work studies the effect of Al4C3 layer formation in the carbon nanotube (CNT)–Al interface on the tensile elastic modulus of the resulting composite material, focusing on the thickness of this layer. 3-D models combining discrete element model and finite element analysis (FEA) were used in order to simulate the behavior of composites with different volume fractions of CNTs randomly dispersed into the Al matrix. Layers of 1, 5, 10 and 15 nm were modeled, affecting the CNTs according to the expected interfacial reaction. Estimations were compared to those obtained in a previous work using unit cell models for an ordered composite. Results showed that the presence of this interface increases total reinforcement volume fraction. Besides, elastic modulus of the composites increased with CNT volume fraction, while the increase in the interface thickness also provoked an increment in the Young’s modulus, attributed to the combined reinforcement effect of CNT and Al4C3. Estimations for the 3-D models were between maxima and minima values predicted by longitudinal and transversal moduli for ordered composites. Results also showed the importance of the use of more realistic FEA models for improving the predicting ability of this method for predicting the mechanical behavior of composites.

The effect of double grafted interface layer on the properties of carbon fiber reinforced polyamide 66 composites

Given the advantages of polyethyleneimine (PEI) for interface modification of carbon fiber reinforced polyamide 66 composite (CF/PA66), an effective method was developed to fabricate CNT@PEI-CF. The XPS results confirmed CNT@PEI-CF was covered with a double grafted layer. Interface stability investigated showed thermal stability (under injection molding temperature, about 270 °C) and structural stability of CNT@PEI-CF/PA66 interface were both improved, but PA66 crystallization behavior affected by CNT@PEI-CF was identical with that of pure PA66. The contact angle tests exhibited that its compatibility with PA66 was also enhanced. Its interfacial shear strength, composite tensile strength and elastic modulus increased by 64.74%, 27.58% and 22.68% compared with that of untreated-CFs and composite, respectively. These best mechanical properties were ascribed to the formation of “fish-scale” layers on pull-out fibers resulted from CNT@PEI-CF modification. It could be concluded that CNT@PEI-CF would not only enhance its composite mechanical properties, but also exhibit much fiber pull-out and avoid the catastrophic failure for CNT@PEI-CF/PA66 composites. This CF surface modification study would be beneficial to expand application of thermoplastic composite with reusability.

Effect of Cu6Sn5 nanoparticle on thermal behavior, mechanical properties and interfacial reaction of Sn3.0Ag0.5Cu solder alloys

This work studied the additions of nano-Cu6Sn5 intermetallic particles into a lead-free Sn3.0Ag0.5Cu (SAC305) solder alloy with content ranging from 0.05 to 2 wt%. The thermal behavior, mechanical properties and interfacial reaction of Cu6Sn5 nanoparticle containing SAC305 solder alloys were evaluated. The Cu6Sn5 nanoparticles successfully synthesized by using chemical precipitation method were re-melted in SAC305 solder and the X-ray diffraction analysis exhibited more obvious Cu6Sn5 diffraction peak with nanoparticles addition. The thermal behavior was revealed that the Cu6Sn5 nanoparticles addition has not visibly changed the solidus temperature but significantly reduced the onset temperature of composite solder alloy during cooling, which resulted in a higher undercooling. In addition, a slight decline of melting point was found and it dropped to 222.7 °C with 0.1 wt% Cu6Sn5 nanoparticles addition. The nanoindentation results showed that nanoparticles addition could distinctly improve the mechanical performances of composite solder alloy, including hardness and elastic modulus, which were optimal for SAC305–0.1Cu6Sn5 solder alloy. Furthermore, nanoparticles addition could effectively suppressed the growth of interfacial IMCs layers and IMCs grains formed between Cu substrate and composite solders during aging. The inhibiting effect was the most obvious when the content of Cu6Sn5 nanoparticles was 0.1 wt% and the restraining mechanism was also explained.

Nanoindentation study on mechanical properties and curing depth of dental resin nanocomposites

Mechanical properties and curing depth of bisphenol‐α‐glycidyl methacrylate/triethylene glycol dimethacrylate‐based dental composites were systematically investigated by site‐specific nanoindentation tests. Effects of filler (20‐nm silica nanoparticle) content on the nanohardness and elastic modulus of the composites were studied in comparison with micromechanics theoretical models. Results showed that the incorporation of the silica nanoparticles at low contents (up to 5.66 vol%) significantly increases the hardness and elastic modulus of the dental composites by up to 65% and 30%, respectively. It was found that the Counto model gave good predictions for the composite modulus as a function of filler content. For the specific composites studied here, the depth of cure increases approximately linearly with the filler content, which may be ascribed to the stronger reinforcement effect of the silica nanoparticles on the dental composites at a higher particle content. These results combined demonstrate the effectiveness of silica nanoparticles as the reinforcement for dental restorative materials even at small volume fractions. POLYM. COMPOS., 40:1473–1480, 2019. © 2018 Society of Plastics Engineers

Predicting tensile behaviors of short flax fiber-reinforced polymer–matrix composites using a modified shear-lag model

Natural fiber-reinforced composites are increasingly being used in the industry. The fiber–matrix interfacial properties of the composites are influenced by many factors, including chemical treatment of the natural fiber, type of polymer matrix, composites fabrication method, and process and the service environment of the composites. In this paper, a modified shear-lag model based on a cohesive fiber/matrix interface is proposed and applied to the analysis of the stress–transfer characteristics and the tensile properties of unidirectional short flax fiber-reinforced composites. The model takes into account of the interfacial shear stiffness, bonding strength between fiber end face and matrix, fiber aspect ratio and fiber volume fraction. 3D finite element models of the composites using a cohesive zone method are used to verify the accuracy of the modified shear-lag model. The fiber tensile strength and the composite tensile elastic modulus are significantly influenced by the interfacial shear stiffness, fiber aspect ratio, and fiber volume fraction. The bonding strength between the fiber end face and the matrix only has an effect when the interfacial shear stiffness is low. The predicted results from the modified shear-lag model show good agreement with the finite element analysis and experimental results in the literature. The modified cohesive shear-lag model provides a simple and effective method for analyzing fiber axial stress, shear stress in the fiber/matrix interface, and tensile elastic modulus of the final composite.

Antibacterial dental adhesive containing nanoantibacterial inorganic fillers

This investigation aimed to develop a novel antibacterial dental adhesive containing nanoantibacterial inorganic fillers and measure the dentin bonding strength, mechanical properties, and antibacterial property of the novel adhesive in vitro. Novel nanoantibacterial inorganic fillers containing quaternary ammonium salt with long chain alkyl were synthesized on the basis of previous research. These novel nanoantibacterial inorganic fillers were added into the dental adhesive to prepare novel nanoantibacterial dental resin composite at mass fractions of 0%, 2.5%, 5.0%, 7.5%, and 10%; 0% was used as control. Dentin shear bonding test was used to evaluate the bonding strength. Flexural test was utilized to measure the novel resin composite flexural strength and elastic modulus. A dental plaque microcosm biofilm model with human saliva as inoculum was formed. Colony forming unit, lactic acid production, and live/dead assay of the biofilm on novel dental adhesive were calculated to assess the effect of novel dental adhesive on human dental plaque microcosm biofilm. The dentin shear bond strength, flexural strength, and elastic modulus were 28.9 MPa, 86.6 MPa, and 4.2 GPa, respectively, when the nanoantibacterial inorganic filler mass fraction in the dental adhesive reached approximately 5.0%. Consequently, the dentin shear bond strength and mechanical properties significantly increased. Addition of 2.5% nanoantibacterial inorganic fillers into the dental adhesive exerted no adverse effect on the mechanical properties significantly (P>0.05). Dental adhesive containing 5% or more nanoantibacterial inorganic fillers inhibited the metabolic activity of the dental plaque microcosm biofilm significantly, thereby displaying a strong antibacterial potency (P<0.05). This novel antibacterial dental adhesive, which contained 5.0% nanoantibacterial inorganic filler, exhibited promising bonding strength, mechanical property, and antibacterial ability. Hence, this adhesive can be potentially used in caries inhibition in dental application.