E-glass Fiber-reinforced Composites Research Articles

Multi-objective optimization of glass/carbon hybrid composites for small wind turbine blades using extreme mixture design response surface methodology

Small wind turbines (SWTs) are a prominent renewable energy technology for decentralized power generation. Blade material and its profile are vital parameters for the aerodynamic performance of SWTs. Traditionally E-glass fiber-reinforced composites (FRCs) are the widely accepted material for developing SWT blades. However, its application is limited by moderate tensile and fatigue properties. Alternatively, other FRC materials such as carbon, basalt and natural fiber composites are proposed as future materials for SWT blades. However, individual materials are observed to satisfy the requirements partially. Therefore, the hybridization of these materials, particularly Glass/Carbon composites is foreseen as a prospective solution for developing cost-competitive and high-strength SWT blades. There are various studies performed to obtain optimized glass/carbon hybrid composites. However, overall material properties required for SWT blades such as low cost, lightweight, moderate flexural strength and higher tensile and fatigue strengths have not been considered simultaneously during the optimization process. This work presents multi-objective optimization of Glass/Carbon hybrid composites using extreme mixture design response surface methodology (RSM) for SWT applications. The weight percentages of glass and carbon fibers are optimized to achieve desired material properties for SWT blades. The experiments are planned using extreme mixture design RSM and the regression models for desired material properties are developed with a 95% confidence level. RSM-based desirability function is employed to perform multi-objective optimization. Maximum composite desirability of 93.5% is achieved with optimal proportions of 37.9% and 27.1% for glass and carbon fibers respectively. An adequate tensile, flexural and fatigue strengths of 486.02, 435.41 and 316.27 MPa respectively are obtained for optimized glass/carbon hybrid composite at an optimum cost of 2228.76 Rs Kg−1 and density of 3.39 g cm−3. The regression models and optimization results are validated through a confirmation experiment with an error of less than 6.1%.

Experimental Evaluation and Neural Network Prediction of Fatigue Life of E-Glass Fiber Reinforced Hybrid Composite Material

The present study focuses on investigating the impact of hybrid composite content and loading parameters on the fatigue life of E-glass fiber-reinforced composite. A mathematical model of the fatigue life was developed based on experimentation and expressed as a function of the composite content (Epoxy content (80%, 60%) wt., Novolac content (20%, 40%) wt., E-Fiber Glass content (10%, 20%, and 30%) wt.), and different loads using Adaptive Neural Fuzzy Inference Systems (ANFIS). In order to validate the ANFIS model, 30 fatigue cycle experiments were conducted. Using the experimental data sets, the ANFIS was trained with a momentum algorithm and an average absolute percentage error of 6.045% was obtained and compared to the output of the conventional Artificial Neural Network (ANN) Model. The testing accuracy was then verified with 6 extra experimental data sets and the average predicting error was 5.18%. the predicted ANFIS output data were then used to discuss the effect of the composite content and loading parameters on the fatigue life. The number and shapes of cracks observed on the failed specimens were analyzed under an optical microscope. The analysis revealed that the loading impact showed the highest influence on fatigue life for all types of enforcement and the sequence of strength was E- glass fiber, epoxy, and Novolac contents, respectively.

Biocompatibility and mechanical properties of an experimental E-glass fiber-reinforced composite for dentistry

ObjectivesTo evaluate the biocompatibility and mechanical properties of experimental bis-phenol-A and bis-GMA free E-glass fiber-reinforced composites (FRCs) prepared with hexanediol dimethacrylate (HDDMA) based resin. MethodsTwo ratios of HDDMA/TEGDMA resin were evaluated: exp-1 (70/30 wt.%) and exp-2 (50/50 wt.%) with two bis-GMA resin control groups (bis-GMA/MMA and bis-GMA/TEGDMA resins, both 70/30 wt.%). E-glass fibers were embedded into the resins to prepare FRCs specimens. Biocompatibility was assessed for cytoviability and biofilm formation with Streptococcus mutans, Streptococcus sanguinis, Enterococcus faecalis, and Candida albicans. Mechanical properties were evaluated for flexural strength and hardness (24 h, water storage 1 and 28 days), water sorption (1, 7, 14, and 28 days), contact angle, and surface roughness. The data were analyzed statistically by one-way and two-way ANOVA (p < 0.05). ResultsCytoviability of the experimental groups was significantly higher than the control groups (p < 0.05). The exp-1 cytoviability (98.2 ± 1.3%) met the ISO 10993-5 standard requirement for noncytotoxic materials. The adherence of bacteria to the experimental FRCs was visibly less than the controls, while Candida albicans adhered visibly more to the experimental groups than the controls (p < 0.05). Flexural strength showed slightly higher values for controls than for the experimental groups. The exp-1 hardness value was significantly higher in the control groups for all storage conditions (p < 0.05). The water sorption of the experimental groups was significantly higher than the controls. The surface roughness indicated no significant difference (p = 0.87). The exp-1 showed a higher contact angle with the control groups. ConclusionThe experimental HDDMA/TEGDMA-based FRCs might be potential alternatives for bis-GMA-based FRCs. Clinical significanceThe HDDMA/TEGDMA E-glass FRCs might provide biocompatible restorations.

Interface failure and delamination resistance of fiber-reinforced geopolymer composite by simulation and experimental method

Fiber-reinforced geopolymer matrix composites (FRGC) have the potential areas of application to bridge the gap between the performances of polymer matrix and ceramic matrix composites. One of the major drawbacks of the geopolymer matrix is the extreme brittleness and weak interlaminar strength. To improve the interlaminar strength of composites, reinforcement of fibers such as carbon and E-glass are considered as fillers in the matrix. The study aimed to evaluate the inner strength and delamination behavior of carbon and E-glass fiber-reinforced composite. The inner structure of the delaminated area of the impacted composite is examined based on the microstructural images and internal areas. The study is being evaluated by simulation method and experimental observation was correlated. The effect of fiber reinforcement was evaluated using three-point flexural methods to obtain strength and modulus of rupture. Results indicate that the interlaminar strength of carbon fiber reinforced geopolymer composite is stronger than E-glass fiber-reinforced composite. The fibers are more intact in carbon fiber reinforced geopolymer composite with better delamination resistance and less impact area. However interlaminar strength of E-glass fiber reinforced is weak, leads to less delamination resistance, with more slippery behavior and more damage area.

Thermoelastic and vibration response analysis of shape memory alloy reinforced active bimorph composites

In this paper, thermoelastic and free vibration responses of hybrid Shape Memory Alloy (SMA) and E-glass fiber-reinforced composites are investigated using finite element analysis. We consider four composites for analysis and comparison of performances, (1) single layer SMA fiber-reinforced hybrid composite (unimorph SMAHC), (2) a two-layer (cross-ply) SMA fiber-reinforced hybrid composite (bimorph SMAHC), (3) single layer SMA fiber-reinforced with a honeycomb core, and (4) single layer SMA fiber-reinforced with reentrant-honeycomb or auxetic core. We analyze the bending response of all the aforementioned composite structures, focusing on the bimorph anticlastic and synclastic bending with negative and positive Gaussian curvatures, respectively. The uniqueness of this work is utilizing the shape memory effect of the SMA fibers to achieve active shape control of low-stiffness and lightweight auxetic composite structures. We investigated the free vibration response and analyzed the effect of the fiber volume fraction and the fiber orientation angle on the natural frequency of the system. Further, the role of the reentrant angle and stiffness of honeycomb struts on the overall effective mechanical properties of the ply is also studied. Results confirm the non-linearity of the parametric combination and the importance of optimization of these parameters for improved Gaussian curvature. The findings are envisaged to be useful for the design of lightweight rigidizable space structures and tensairity structures.

Load bearing capacity and Weibull characteristics of inlay-retained resin-bonded fixed dental prosthesis made of all-ceramic, fiber-reinforced composite and metal-ceramic after cyclic loading

PurposeThe objectives of this study were to evaluate the load bearing capacity of RBFDPs made of different materials after cyclic loading, and classify the failure types after loading. Materials and methodsSound human mandibular first premolars and first molar pairs (N = 60 per tooth type, n = 10 per group) were randomly divided into six experimental groups to receive one of the following inlay-retained RBFDP types: RC: Resin composite only, DFRC: Direct E-glass fiber-reinforced composite (FRC), IFRC: Indirect E-glass FRC, LS: Lithium disilicate glass-ceramic, ZR: Yttria-stabilized tetragonal zirconia, MC: Metal-ceramic. Box preparations were made in abutment teeth using diamond burs followed by standardized ultrasonic burs. The teeth were conditioned employing an etch-and-rinse adhesive system and the indirect RBFDPs were cemented adhesively. The specimens were subjected to cyclic loading for x1.200.000 in distilled water alternating between 5 and 55 °C (Zurich Chewing Simulator). They were then loaded to failure from the occlusal surface in the Universal Testing Machine (cross-head speed: 1 mm/min). Failure types were classified as repairable or irreparable depending on the location and size. Data were analyzed using Welch and Tamhane's T2 post-hoc tests (α = 0.05). Weibull modulus for each group was calculated based on parametric distribution analysis of censored data for maximum fracture load. ResultsMean load bearing capacity (N) of Groups LS (1274 ± 270), ZR (1567 ± 363) and MC (1544 ± 787) were significantly higher than those of other groups (p < 0.05). RC, DFRC, IFRC (601 ± 130 - 819 ± 270) and MC did not show significant difference (p > 0.05). Weibull modulus (m) was the highest in Group LS (m = 5.3) followed by Group RC (m = 5.1). Other groups presented Weibull moduli ranging between 1.4 and 3.3. Only in Group ZR, 2 early debonding occurred during cyclic loading. While in this group predominantly irreparable failures (debonding with without tooth fracture) were observed (8 out of 10), all other groups presented mainly single or a combination of repairable failures (chipping in the veneering material). DFRC, IDRC and MC did not show any debonding from the abutment teeth. ConclusionConsidering load bearing capacity, repairable failure types and Weibull moduli, lithium disilicate seem to be more durable than those of other material options for posterior inlay-retained RBFDPs. Due to early debondings and catastrophic irreparable failure types, zirconia RBFDPs should be indicated with caution in the posterior region.

Pengaruh Lama Perendaman E-Glass Fiber Reinforced Composite dalam Obat Kumur Terhadap Kekuatan Fleksural

Fiber reinforced composite (FRC) is a material consisting of a composite resin (matrix), fiber (reinforced) and silanes (to improve the adhesion strength). FRC can be used as a crown framework. More people used mouthwash for oral hygient. The objective of this study was to know the effect of the duration of E-glass FRC immersion into the mouthwash against the flexural strength. The research materials were E-glass (Fiber Splint Polydentia Multi-Layer, Switzerland), composite resin (Master Flow Biodynamic, Brazil), silane (Monobond Ivoclar Vivadent) and mouthwash (Listerine® Multi Protect). Twelve the beam-shaped specimens (25x2x2) mm The specimens were divided into 3 groups: K1 control group (was not immersed) K2 and K3 treatment groups (was immersed for 24 and 48 hours). The flexural strength value was measured using a universal testing machine (Pearson, Texas). The data were analyzed using one-way ANOVA followed-up by LSD. The results showed decrease of the average flexural strengths of mouthwash K1, K2 and K3. The one-way ANOVA test results showed that there was a significant P&gt;0.05 in the duration of E-glass FRC immersion into the mouthwash against the flexural strength. The LSD test results showed significant differences between all treatment groups. The conclusion of this study is that the duration of E-glass FRC immersion into mouthwash will lower the strength of flexural E-glass FRC.

Preparation and characterization of high radio-opaque E-glass fiber-reinforced composite with iodine containing methacrylate monomer

ObjectiveThe purpose of this study was to prepare radio-opaque E-glass fiber-reinforced composite (EFRC) with synthesized iodine containing methacrylate monomer. MethodsThe synthesized iodine containing methacrylate monomer 2-hydroxy-3- methacryloyloxypropyl(2,3,5- triiodobenzoate) (HMTIB) was mixed with Bis-GMA and MMA in different mass ratio to prepare resin impregnating solution (RIS), and RIS without HMTIB was used as control. CQ and DMAEMA were added as photoinitiation system. E-glass fiber was thoroughly wetted by resin impregnating solution to prepare radio-opaque EFRC. Degree of double bond conversion (DC) was investigated by FT-IR analysis. Fiber volume fraction was analyzed by combustion and gravimetric analyzes. The Flexural strength (FS) and modulus (FM) of EFRC were measured using a three-point bending set up. Water sorption (WS) and solubility (SL) were measured until the mass variation of EFRC in distilled water kept stable. Radiographs were taken to determine the radiopacity of EFRC. ResultsThe FT-IR and 1H NMR spectra of HMTIB revealed that it was the same as designed. ANOVA analysis revealed that increasing HMTIB concentration in RIS would decrease DC and increase fiber volume fraction. When compared with control EFRC, all of HMTIB containing EFRCs had higher or comparable FS and FM, no matter before or after water immersion. WS of EFRC decreased with increasing HMTIB concentration, while SL was nearly kept the same. Radiopacity of EFRC increased with increasing HMTIB concentration. SignificanceThe synthesized monomer HMTIB could be used to prepare EFRC with high radiopacity. Moreover, HMTIB containing EFRC would also have high mechanical properties and low WS.

The effect of silanated and impregnated fiber on the tensile strength of E-glass fiber reinforced composite retainer

Background : Fiber reinforced composite (FRC) is can be used in dentistry as an orthodontic retainer. FRC still has a limitations because of to a weak bonding between fibers and matrix. Purpose : This research was aimed to evaluate the effect of silane as coupling agent and fiber impregnation on the tensile strength of E-glass FRC. Methods : The samples of this research were classified into two groups each of which consisted of three subgroups, namely the impregnated fiber group (original, 1x addition of silane, 2x addition of silane) and the non-impregnated fiber group (original, 1x addition of silane, 2x addition of silane). The tensile strength was measured by a universal testing machine. The averages of the tensile strength in all groups then were compared by using Kruskal Wallis and Mann Whitney post hoc tests. Results : The averages of the tensile strength (MPa) in the impregnated fiber group can be known as follow; original impregnated fiber (26.60±0.51), 1x addition of silane (43.38±4.42), and 2x addition of silane (36.22±7.23). The averages of tensile strength (MPa) in the non-impregnated fiber group can also be known as follow; original non-impregnated fiber (29.38±1.08), 1x addition of silane (29.38±1.08), 2x addition of silane (12.48±2.37). Kruskal Wallis test showed that there was a significant difference between the impregnated fiber group and the non-impregnated fiber group (p<0.05). Based on the results of post hoc test, it is also known that the addition of silane in the impregnated fiber group had a significant effect on the increasing of the tensile strength of E-glass FRC (p<0.05), while the addition of silane in the non-impregnated fiber group had a significant effect on the decreasing of the tensile strength of E-glass FRC. Conclusion: It can be concluded that the addition of silane in the non-silanated fiber group can increase the tensile strength of E-glass FRC, but the addition of silane in the silanated fiber group can decrease the tensile strength of E-glass FRC. It is also known that the impregnation of fiber can increase the tensile strength of E-glass FRC.

Candida albicans adhesion on reinforced polymethylmethacrylate denture resin: effect of fibre architecture and exposure to saliva

Fiber-reinforced composites (FRC) are used to reinforce the prosthetic and restorative appliances. This may result in the exposure of the FRCs which may affect the adherence of microorganisms. This study evaluated the adhesion of Candida albicans to a denture base resin (N = 48), reinforced with E-glass FRCs with different architectures [unidirectional (n = 16) and woven (n = 16)], when exposed to either saliva or distilled water. Specimens without FRC reinforcement served as control (n = 16). After fiber surfaces were exposed, half of the specimens (n = 8/per group) were treated with saliva, the other half was stored in distilled water prior to C. albicans adhesion. The adhered microorganisms were counted under an optical microscope and the data were analyzed. When exposed to distilled water or saliva, specimens with unidirectional (5403.4 cells/cm(2) and 5013.4 cells/cm(2) , respectively) (p = 0.202), woven fibers (4053.5 cells/cm(2) and 3726.6 cells/cm(2) , respectively) (p = 0.283) and specimens without fibers (2250 cells/cm(2) and 2006.8 cells/cm(2) , respectively) (p = 0.423) showed C. albicans adhesion, being not significant. In general, all the specimens exposed to saliva showed 3582.2 cells/cm(2) C. albicans adhesion, while specimens exposed to distilled water showed 3902 cells/cm(2) C. albicans adhesion, yet being not significant (p = 0.436). Regarding fiber type, C. albicans adhesion was significantly affected by the exposed FRC architecture with more favorable results for woven fibers (p < 0.001). Polymethylmethacrylate without FRCs collected less C. albicans. The presence of saliva seems to reduce the adhesion.

Experimental Investigation of the Effect of Strain Rate on the Compression Behavior of 3D E-Glass Fiber-Reinforced Composites

The MTS810 and SHPB are used to experimentally study the quasi-static and dynamic mechanical properties of three-dimensional E-glass fiber-reinforced composite. Stress-strain curves along the plane and thickness direction are obtained under varying strain rates, ranging from 10-3 to 103s-1. Experimental results show that strain rate has a significant effect on the material response. It is found that the compressive strength and the modulus increase with increasing strain rate, the failure strain, however, decreases slightly. But, the effect of strain rate in-plane and through thickness directions is different. A higher strain rate sensitive modulus and failure is found in the thickness direction, while a higher strain rate sensitive failure strength is found in the in-plane direction.

The Effect of Resin Matrix Composition on Mechanical Properties of E-glass Fiber-Reinforced Composite for Dental Use

The effects of resin matrix composition including bis-phenol-A-diglycidyl dimethacrylate (bis-GMA)-methyl methacrylate (MMA) based or urethane dimethacrylate (UEDMA)-triethylene glycol dimethacrylate (TEGDMA) based composition and storage conditions on the mechanical properties of E-glass fiber-reinforced composites (FRCs) were studied. Three experimental groups ('Exper 1', 'Exper 2', 'Exper 3') with differing UEDMA to TEGDMA ratio in the matrix together with a control group ('Control') based on bis-GMA–MMA resin matrix were prepared by light-curing. The storage conditions for each group were dry storage at room temperature for 24 h and 30- and 60-day immersion in deionized (DI) water at 37°C, which further divided each group into three subgroups. For all the four composition groups, mechanical properties including hardness, flexural strength and modulus in both three-point and four-point bendings were tested (n = 6), together with water sorption and solubility study (n = 6) and fracture site scanning with a scanning electron microscope (SEM). The experimental specimens were relatively strong and stiff in three-point bending compared to previous research. The same specimens in three-point bending had a lower flexural modulus and fractured at higher flexural stress than in four-point bending. According to the SEM images after fracture, some resin matrix was still bound to the fiber surface, showing cohesive–interfacial fracture type and relatively stable matrix–fiber adhesion. According to comprehensive analysis, the control group showed superior mechanical performance in most of the tests.

The Bond Strength of Particulate‐Filler Composite to Differently Oriented Fiber‐Reinforced Composite Substrate

The primary failure mode of fiber-reinforced composite (FRC) materials used intraorally is delamination or debonding of particulate filler composite (PFC), the esthetic veneer, from the underlying FRC framework. The objective of the current study was to evaluate the effect of unidirectional fiber orientation and load direction on the shear bond strength of PFC to FRC. Unidirectional E-glass FRC was used as an adhesion substrate for the PFC. E-glass FRCs were oriented in three ways--Group A: in the plane perpendicular to the bonding surface; Group B: along the bonding surface longitudinal to the load; and Group C: along the bonding surface, transverse to the load. The FRC substrates were ground flat with 1200 grit. The PFC adherend was bonded to FRC using an intermediate resin. Twelve specimens for each group were water stored (37 degrees C) for 3 days before a shear bond strength test was conducted. A one-way analysis of variance showed that the direction of the applied load to the fiber direction had a significant effect on the bond strength values (p < 0.001). A Weibull analysis produced values (characteristic strength and Weibull modulus) of Group A (46.5 MPa, 12.1), Group B (40.6 MPa, 4.6), and Group C (27.6 MPa, 3.5). The highest shear bond strength values and Weibull modulus were obtained when the fibers were oriented perpendicular to the bonding surface, exposing the fiber ends to the PFC. Interface strategies between hybrid composite layers may be developed to exploit anisotropic behavior in the adherence between FRC and PFC.

Effect of water storage on the impact strength of three glass fiber-reinforced composites

The effect of water sorption on the impact strengths of two pre-impregnated fiber-reinforced composites (FRCs) and one impregnated FRC were studied. All FRCs were available clinically. Eight 1.0 mm x 2.0 mm x 25.0mm bar-shaped specimens of each material were prepared according to manufacturers' instructions. The impact strength of each specimen was tested (adoption from ISO 179-1 Plastics-Determination of Charpy impact properties) after the specimens were immersed in 23.0+/-1 degrees C distilled water for seven, 60 and 180 days. The data were analyzed using the Weibull method. Scanning electron micrographs were taken to examine the mode of failure. Weibull analysis of the B10 strength of the FRCs showed that the difference in impact strength for each FRC due to the duration of water immersion was not significant (P>0.05). The impact strength of pre-impregnated E-glass FRC (Vectris) (75 kJ/m(2)) was not significantly different from the pre-impregnated S-glass FRC (FiberKor) (66 kJ/m(2)) (P>0.05). The impregnated FRC possessed impact strength (42 kJ/m(2)) that was not significantly different from the pre-impregnated S-glass FRC but was significantly lower than the pre-impregnated E-glass FRC. x100 SEMs of the three types of FRC specimens revealed fiber failure to be the predominant mode of failure. Water immersion up to 180 days duration did not significantly affect the impact strength of three FRCs. The impact strength of the impregnated FRC was not significantly different from the pre-impregnated S-glass FRC but was significantly lower than the pre-impregnated E-glass FRC.

Fatigue resistance and stiffness of glass fiber-reinforced urethane dimethacrylate composite

Statement of problem Retentive properties of cast metal clasps decrease over time because of metal fatigue. Novel fiber-reinforced composite materials are purported to have increased fatigue resistance compared with metals and may offer a solution to the problem of metal fatigue. Purpose The aim of this study was to investigate the fatigue resistance and stiffness of E-glass fiber-reinforced composite. Material and methods Twelve cylindrical fiber-reinforced composite test cylinders (2 mm in diameter and 60 mm in length) were made from light-polymerized urethane dimethacrylate monomer with unidirectional, single-stranded, polymer preimpregnated E-glass fiber reinforcement. Six cylinders were stored in dry conditions and 6 in distilled water for 30 days before testing. Fatigue resistance was measured by a constant-deflection fatigue test with 1 mm of deflection across a specimen span of 11 mm for a maximum of 150,000 loading cycles. The resistance of the cylinder against deflection was measured (N) and the mean values of the force were compared by 1-way analysis of variance (α=.05). The flexural modulus (GPa) was calculated for the dry and water-stored cylinders for the first loading cycle. Scanning electron microscopy was used to assess the distribution of the fibers, and the volume percent of fibers and polymer were assessed by combustion analysis. Results The test cylinders did not fracture due to fatigue following 150,000 loading cycles. Flexural modulus at the first loading cycle was 18.9 (± 2.9) GPa and 17.5 (± 1.7) GPa for the dry and water-stored cylinders, respectively. The mean force required to cause the first 1-mm deflection was 33.5 (± 5.2) N and 37.7 (± 3.6) N for the dry and water stored cylinders, respectively; however, the differences were not significant. After 150,000 cycles the mean force to cause 1-mm deflection was significantly reduced to 23.4 (± 8.5) N and 13.1 (± 3.5) N, respectively ( P<.0001). Scanning electron microscopy highlighted fiber- and polymer-rich areas within the specimens and indicated that individual fibers were well impregnated with resin. The combustion analysis studies identified the fiber content to be 35.9 vol%. Conclusion The results of this study suggest that the fatigue resistance of the fiber-reinforced material examined was increased; however, the reduction in flexural modulus of fiber-reinforced composites may restrict their use where high rigidity is required, such as in removable partial denture clasps.

The Effect of Fiber Position and Polymerization Condition on the Flexural Properties of Fiber-Reinforced Composite

The aim of this study was to investigate the influence of the position of the fiber rich layer on the flexural properties of fiber-reinforced composite (FRC) construction. In addition, the total residual monomer content of FRC was quantitatively determined to find out the difference of the effectiveness of two types of light-curing units using liquid chromatography (HPLC). Unidirectional continuous E-glass FRC and hybrid particulate filler composite resins were used in the fabrication of test specimens. Four different positions of the FRC layer were used: compression, neutral, tension, and vertical side position. A three-point bending test (ISO 10477) was performed to measure the flexural properties of the specimens. Position of the FRC layer had a significant effect on the flexural strength (p<0.001, ANOVA). Also, the type of light-curing device had an effect on flexural strength (p<0.001). Specimens with FRC positioned on the compression side showed flexural strength of approximately 250 MPa, whereas FRC positioned on the tension side showed strength ranging from 500 to 600 MPa. Mean flexural modulus with FRC placed horizontally ranged between 9-12 GPa; no significant difference was found between these groups. However when fiber reinforcement was positioned vertically, the flexural modulus raised up to 16 GPa. Specimens with 24 vol% glass fibers contained 52% less residual monomer than specimens without glass fibers. The monomer content was lower in specimens polymerized with the curing device with higher polymerization temperature. In order to optimize flexural strength of low fiber volume fraction, the fibers should be placed at the tension side of the specimen.

Flexural properties of fiber reinforced root canal posts

Objectives. Fiber-reinforced composite (FRC) root canal posts have been introduced to be used instead of metal alloys and ceramics. The aim of this study was to investigate the flexural properties of different types of FRC posts and compare those values with a novel FRC material for dental applications. Methods. Seventeen different FRC posts of various brands (Snowpost, Carbopost, Parapost, C-post, Glassix, Carbonite) and diameters, (1.0–2.1 mm) and a continuous unidirectional E-glass FRC polymerized by light activation to a cylindrical form (everStick, diameter 1.5 mm) as a control material were tested. The posts ( n=5) were stored at room's humidity or thermocycled (12.000×, 5 °C/55 °C) and stored in water for 2 weeks before testing. A three-point bending test (span=10 mm) was used to measure the flexural strength and modulus of FRC post specimens. Results. Analysis of ANOVA revealed that thermocycling, brand of material and diameter of specimen had a significant effect ( p<0.001) on the fracture load and flexural strength. The highest flexural strength was obtained with the control material (everStick, 1144.9±99.9 MPa). There was a linear relationship between fracture load and diameter of posts for both glass fiber and carbon fiber posts. Thermocycling decreased the flexural modulus of the tested specimens by approximately 10%. Strength and fracture load decreased approximately 18% as a result of thermocycling. Significance. Considerable variation can be found in the calculated strength values of the studied post brands. Commercial prefabricated FRC posts showed lower flexural properties than an individually polymerised FRC material.

A COMPARATIVE STUDY OF THE PREPARATION AND CHARACTERIZATION OF AROMATIC AND ALIPHATIC BISMALEIMIDES TO PRODUCE MODIFIED SILICONIZED EPOXY INTERCROSSLINKED MATRICES FOR ENGINEERING APPLICATIONS

A novel hybrid intercrosslinked network of hydroxyl-terminated polydimethylsiloxane modified epoxy and bismaleimides [N,N′-bismaleimido-4,4′-diphenylmethane and 1,6-bis(maleimido)hexane] matrix systems were developed. Epoxy resin was modified with 5, 10, and 15% (wt%) of hydroxyl-terminated polydimethylsiloxane using γ-aminopropyltriethoxysilane as crosslinking agent and dibutyltindilaurate as catalyst. The reaction between hydroxyl-terminated polydimethylsiloxane and epoxy resin was confirmed by IR spectral studies. The siliconized epoxy systems were further modified with 5, 10, and 15% (wt%) of both aromatic and aliphatic bismaleimides separately. The castings and E-glass fiber-reinforced composites prepared were characterized for their mechanical properties. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) of the matrix samples were also performed to determine the glass transition temperature (T g) and thermal degradation temperature of the hybrid intercrosslinked systems. Data obtained from mechanical studies and thermal characterization indicate that the introduction of siloxane into epoxy resin improves the toughness and thermal stability, with reduction in strength and modulus values. The incorporation of aromatic bismaleimide into epoxy resin improved both tensile strength and thermal properties, whereas it was observed that the incorporation up to 5% of aliphatic bismaleimide into epoxy resin decreased the stress–strain value and above 5% increased the strength properties. However, the introduction of both aromatic and aliphatic bismaleimides (aromatic and aliphatic) into siliconized epoxy resin influenced both mechanical and thermal properties according to the percentage content.