Flexural Strength Of Composites Research Articles

Properties of Graphite Matrix Composite Bipolar Plate Reinforced by Short Carbon Fiber

Short carbon fiber is used to reinforce phenol formaldehyde (PF) resin/graphite composite. With carbon fiber by thick nitric acid liquid-phase oxidative surface treatment (TNALPOST) and its content 3.wt%~ 4.wt%, the composite flexural strength is increased highly and electrical conductivity is also increased on some degree. To PF resin/graphite matrix material without carbon fiber added, if PF resin content is 15.wt%, its flexural strength is 49.0MPa and electrical conductivity is 111S/cm. But with adding carbon fiber by TNALPOST and the same PF resin content , the composite flexural strength and electrical conductivity approach 68MPa、122S/cm respectively, both mechanical property and electrical property satisfy the requirement of USA Department of Energy on carbon filler/polymer composite bipolar plate. The PF resin/graphite composite without carbon fiber added presents brittle fracture mode, but with carbon fiber added, it presents ductile fracture mode. According to the fracture morphology by scanning electron microscopy, carbon fiber and matrix is on relatively weak boundary bonding state accompanied by fiber de-bounding、sliding、pulling-out and bridge-making to crack, they are main factors contributed to improving composite toughness.

The effect of partially carbonized fibers on the mechanical properties of carbon/carbon composites

The carbon/carbon (C/C) composite with satisfactory mechanical properties were obtained through introduction of partially carbonized fibers as a precursor. Applying this procedure the production cost of C/C composites may be significantly reduced. Stabilized PAN fibers were partially carbonized at temperatures ranging from 400 to 1000°C and reinforced with phenolic resin, resole type. Cured composite were carbonized up to 1000°C in an inert atmosphere. Monofilament tensile test strength, Young's modulus and tensile strength of partially carbonized fibers were determined. Mechanical properties of carbon/carbon composites (flexural strength and flexural modulus) determined by using three-point bending test. The effect of partially carbonized fibers on the mechanical properties of C/C composites was examined by scanning electron microscope (SEM) through analysis of the fracture surface. The C/C composite reinforced with partially carbonized fibers at 600°C showed quite satisfactory flexural strength. This confirms assumptions that through co-carbonization of partially carbonized fibers and resin C/C composite with suitable mechanical properties could be obtained.

Flame retardant diglycidylphenylphosphate and diglycidyl ether of bisphenol-A resins containing Borassus fruit fiber composites

Natural fiber composites containing diglycidylphenylphosphate (DGPP) resin were prepared from DGPP, diglycidyl ether of bisphenol-A (DGEBA), and Borassus fruit fiber. Morphology, thermal, and mechanical properties of blends and fiber-reinforced composites were investigated. The tensile strength, flexural strength, and tensile modulus increased up to 10% addition of DGPP and decreased with high percentage of DGPP. The flexural strength of composites was increased up to 15% addition of DGPP due to good dispersion and toughening of DGPP in DGEBA. As observed by the SEM analysis, the matrix–fiber adhesion was poor in the case of 20% DGPP containing composites and failure occurred through fiber pullout whereas for composites with 5 and 10% of DGPP, interaction of fiber and matrix was strong and failure occurred through fiber breakage rather than fiber pullout. Addition up to 15% DGPP improved desired thermal and mechanical properties of these composites.

Effect of Fiber Acid Treatment on the Dynamic Mechanical Properties of Unsaturated Polyester/Carbon Fiber Unidirectional Composites

In this study, the surface modification of carbon fiber by sulfuric acid is investigated. Atomic Force Microscopy was employed to capture the corresponding changes in the surface roughness of the carbon fiber. Moreover, using treated and untreated fibers, unsaturated polyester unidirectional composite rods were prepared and their flexural properties were determined by three-point bending and dynamic mechanical thermal analysis. The results indicated that the carbon fiber surface roughness increases in all samples. It is also found that treating the fiber decreases the magnitude of loss modulus. Besides, the flexural strength of composites made of the treated carbon fiber significantly increased.

Flexural strength and microstructure of alkali-resistant glass fibre reinforced calcium aluminate-phenol resin composite

Calcium aluminate-phenol resin composites are a new class of macro-defect-free cements that have better water resistivity compared with polyvinyl acetate high alumina cement composites. In this paper the effects of alkali-resistant (AR) glass fibre reinforcement on the flexural strength and microstructure of calcium aluminate-phenol resin composite were investigated. The results showed that the flexural strength can be increased by adding fibres, but there is an optimum condition that is influenced by various factors, including fibre length and fibre content. The flexural strength of composites without fibre was 120 MPa but with 5%wt. AR glass fibre with 6 mm length reached 165 MPa. The microstructural studies with scanning electron microscopy are also consistent with flexural strength tests; it was shown that the dispersing of fibre in a matrix was difficult when the fibre content was too high.

Natural Fibre Composites with 3D Woven Reinforcement for New Application Areas

The cross-discipline research embodied in this paper is a culmination of substantial research advancing the field of natural fibre reinforced composites. This international peer reviewed paper was selected for its pioneering approach to developing sustainable woven composite materials. Contributors in this issue were selected from high profile experts that tackle issues on ‘Materials for a Low Carbon Future’ presented at the Natural Fibres ‘09 Conference in Dec 2009 at The Institute of Materials, London. Materials that contribute to a prominent environmental agenda were presented, such as composite materials made from natural plant-based fibres as an alternative to synthetic petroleum based fibres. The author gave a keynote address at this conference. The research determines the fabrics initial mechanical properties against standard fabric benchmarks. It highlights technical trade-off’s between old materials that fail in a familiar way and new materials that combat these failure mechanisms but fall slightly short (in certain tests) on enhanced properties. The work establishes both benefits and production challenges these materials face en-route to commercialisation and wider acceptance. Published by Elsevier (USA), the Journal special issue featured International research from global experts who were working at various 'technology-readiness levels' to generate data and future products. The paper was also a key outcome of AHRC project 3D Reinforced Natural Fibre Reinforced Woven Preforms and Eco-composites’ (AH/E007953/1)). Spin-off benefits from this publication included future collaborations with the technical textile Industry in the UK and with natural fibre composite experts. PUBLISHED ABSTRACT: The cross-discipline research embodied in this paper has been generated from a technical textile design perspective, where the author, as an established technical weave designer, has developed 3D woven natural fibre preforms for composite production and subsequent testing. This research is a comparative study between commercially available 2D bi-axial woven plied composite laminate and 3D reinforced woven multiple layer composites using both flax and naturally derived viscose yarns for natural fibre composite applications. The objective is to determine the initial properties of two natural fibre 3D woven composites with relatively low fibre volume fraction and assess their performance against a standard natural fibre 2D woven fabric lay-up arrangement. In order to achieve this, the textile design and production cycle must be considered. The paper focuses on the design and assemblage of 3D woven textile preforms, discussing the complex design parameters associated with obtaining desired loom state fibre volume fractions within the 3D material. It also highlights the weave production issues that impact on the quality and integrity of 3D woven fabric architectures for flat and tailored reinforcements. Treatment experiments with 4% NaOH on flax yarns were attempted to establish if the woven fabrics would benefit from post-production treatment prior to resin processing to improve interfacial bonds between fibres and matrix. Once woven, it details the Vacuum Assisted Resin Transfer Moulding (VARTM) processing method using epoxy resin and presents initial results from mechanical test programs assessing flexural strength and damage resistance. By selecting a 2D 2/2 woven twill laminate and angle interlock (AI) 3D architecture as baseline control samples, an early assessment will establish the benefits and challenges these materials face, and their future potential. Findings from the research indicated that 2D twill flax composites achieve a higher fibre volume fraction which, in turn, leads to superior flexural properties with respect to 3D AI composites. 2D 2/2 twill viscose rayon composites flexural strength and modulus were found to be superior to 3D angle interlock structures but inferior in damage resistance. The damage characteristics from impact resistance tests show differences in damage area, impact depths and the dispersal of subsidiary cracking. Test specimens demonstrate that 3D woven viscose rayon composites displayed mostly localized damage around the location and did not allow the damage to radiate out substantially which is in contrast to the delamination damage observed in the 2D material. From this publication the author was invited to be a member of the International Organising Committee for conference “Emerging Green Technologies”, the Annual Environmental Biopolymer Society (BEPS) in USA, held in Toronto, Oct 2010 and member of the organising committee for the ECOCOMP conferences in the UK (2013). Keywords: WOVEN; PREFORM; NATURAL FIBRE COMPOSITES; VACUUM ASSISTED RESIN TRANSFER MOULDING (VARTM)Document Type: Research article DOI: 10.1166/jbmb.2010.1078

Effect of Moisture Absorption on Mechanical Properties of Chopped Natural Fiber Reinforced Epoxy Composite

This paper describes the moisture absorption behavior and its effect on mechanical properties of Lantana camara fiber reinforced epoxy composite. Composite samples reinforced with different wt% of fibers were prepared by hand lay-up technique. Increase in tensile and flexural strength was observed with increase in fiber content up to 30%. Moisture absorption tests were carried out in three different environmental conditions (steam, saline water and sub-zero temperature). The moisture diffusivity constant and equilibrium moisture uptake were calculated. Moisture absorption of the studied composites was proved to follow the kinetics of a Fickian diffusion process. Tensile and flexural strength of composite were found to decrease with moisture absorption. After the mechanical tests, fracture characteristics analysis of the tested specimens was carried out to reveal a reasonable interaction between the reinforcement and matrix.

세라믹(BNT)-폴리머(LCP) 복합체 제조 및 유전특성

In this research, the composites (100-x)LCP-xBNT (x = 0, 10, 20, 30, 40 vol.%) were fabricated with thermoplastic LCP(Liquid Crystal Polymer) and BNT(<TEX>$BaNd_2Ti_4O_{12}$</TEX>) which is a high frequency dielectric material. Their dielectric properties, mechanical strength and microstructure were investigated by Impedance analyser, Instron and SEM. In order to fabricate LCP-BNT composites, LCP resin was put into the twin screw type mixer(<TEX>$310^{\circ}C$</TEX>), melted by keeping for 10 min. After that, BNT filler was dispersed with melted LCP resin for 15 min. in the mixer. For measuring the dielectric properties and mechanical strength, Composite specimens were made by pressing composite granule (LCP-BNT) with 7 ton in the mold at <TEX>$310^{\circ}C$</TEX>. With increasing the BNT content (0~40 vol.%) of the composite, Its dielectric constant increased, dielectric loss and flexural strength decreased. The dielectric constant and flexural strength of composites with 20~30 vol.% of BNT filler are 4.1~6.0 and 35~55 MPa respectively. BNT/LCP composite is the potential substrate material for the high frequency application.

Mechanical Properties and Thermal Shock Resistance of Al2O3-TiC-Co Composites

Ductile cobalt was introduced into Al2O3-TiC (AT) composites by using a chemical deposition method to improve toughness and resistance to thermal shock. The mixture of Co-coated Al2O3 and TiC powders was hot-pressed into an Al2O3-TiC-Co (ATC) composite. The flexure strength and fracture toughness of the ATC composites have been improved considerably, compared with AT and Al2O3. The fracture surface of ATC shows a large proportion of transgranular cracks with some intergranular type, unlike the intergranular fracture modes of AT and Al2O3. The thermal shock properties of the composites were evaluated by water quenching technique and compared with the traditional AT and Al2O3. The composites containing only 3.96 vol.% cobalt exhibited higher critical temperature difference and retained flexure strength. The SEM examination of the fracture surfaces of the ATC composites after single thermal cycle showed that voids increased in number and size, and most isolated voids coalesced with increasing temperature difference, which caused the density and strength to decrease. The ATC composite is less sensitive to repeated thermal shock than the AT composite.

Effects of Glass Fiber Layering on the Flexural Strength of Microfill and Hybrid Composites

In stress-bearing cavities, low fracture resistance adversely affects the longevity of the dental resin composite restorations. The aim of this in vitro study was to investigate the effect of glass fiber layering on the flexural strength of microfill and hybrid composites. Flexural test specimens (N = 75) were prepared according to International Organization for Standardization (ISO) 4049 specifications (25 x 2 x 2 mm) by using a standard metallic mold. Materials used and groups were as follows (N = 15): group 1: hybrid composite (Clearfil APX, Kuraray Co.Ltd, Osaka, Japan); group 2: microfill composite (Clearfil ST, Kuraray Co.Ltd.); group 3: hybrid + microfill composite; group 4: woven glass fiber (EverstickNet, StickTech Ltd, Turku, Finland) + hybrid composite; group 5: woven glass fiber + microfill composite. The specimens were stored in distilled water at 37 degrees C for 7 days. Afterward, they were loaded to fracture (1 mm/min) by using a universal testing machine (AG-50 kNG Shimadzu Co., Kyoto, Japan). Flexural strengths were expressed as maximum flexural load per cross-sectional area of the specimen. The results were statistically analyzed with Kruskall-Wallis and Mann-Whitney U tests (p < 0.01). Significant increases in the flexural strength were found for both hybrid and microfill composites when fiber layering was used (group 1: 78 +/- 7 MPa; group 4: 93 +/- 4 MPa) (group 2: 42 +/- 5 MPa; group 5: 64 +/- 4 MPa) (p < 0.01). Flexural strength of fiber-reinforced hybrid composite was significantly higher than the other groups evaluated (p < 0.01). There were no significant differences in flexural strength between microfill/hybrid combination and fiber-reinforced microfill composite (p > 0.01). Glass fiber layering of microfill and hybrid composites presented higher flexural strength, and veneering of hybrid composite with microfill composite increased the resistance of the restoration.

Influence factors of C/C–SiC dual matrix composites prepared by reactive melt infiltration

The effects of the type of carbon matrix, the infiltration temperature and high temperature treatment (HTT) on the infiltration behavior of molten Si and preparation of C/C–SiC dual matrix composites have been investigated. The results showed that: Resin carbon matrix is benificial to the infiltration of molten Si than pyrolysis carbon matrix. 1650 °C is more suitable for the infiltration of molten Si in porous C/C preforms than 1550 °C. The high infiltration depth at 1650 °C is responsible for the high density of C/C–SiC composites. HTT facilitates to the infiltration of molten Si and the formation of more SiC. High density and low open porosity C/C–SiC dual matrix composites can be prepared by optimal reactive molten infiltration method. The flexural strength, elastic modul and impact toughness of C/C–SiC composites are high up to 265.4 MPa, 28.1 GPa and 28.5 kJ/m 2 respectively. Heat treatment at 2300 °C decreases the composites flexural strength, elastic modul and impact toughness, but improve the fracture behavior of C/C–SiC dual matrix composites.

Analysis of the Effects of Atmospheric Helium Plasma Treatment on the Surface Structure of Jute Fibres and Resulting Composite Properties

This work investigates the mechanisms involved in the improvement of flexural properties of a jute/polyester composite when the reinforcement material has been atmospherically plasma treated using helium gas. All composites were laid-up by hand and cured using a Quickstep™ cure cycle. Surface characterization techniques including scanning probe microscopy (SPM), and surface wettability combined with fabric tensile strength, composite flexural strength and composite Mode-I properties have been used to quantify the effects of plasma modification. Flexural strength and modulus increased with plasma treatment time, reaching a maximum at 25 passes before decreasing. SPM topographical analysis showed that roughness of the fibre decreased as the plasma treatment time increased until 25 passes after which the roughness was found to increase again. The coefficient of friction increased rapidly after only a short plasma treatment time (5 passes) whilst wettability continued to increase until 25 passes after which it remained constant. The fabric tensile strength followed the same trend as the flexural properties of the composites. Decreasing fibre surface roughness is postulated as a reason for decreasing Mode-I interlaminar fracture toughness properties of the composites.

Development of dual-curing type experimental composite resin cement for orthodontic bonding-Effect of additional amount of accelerators on the mechanical properties-

In this study, a dual-curing type composite resin cement that included a photo-initiator and two accelerators was designed. In particular, special emphasis was made on addressing questions on the effects from different amounts of additional accelerators on the flexural strength of the designed experimental composite resin cement, as well as on the tensile bond strength of the bracket bonded onto the enamel surface by the experimental composite resin cement. When 0.25 mass% of the p-tolydiethanolamine and sodium p-toluenesulfinate were added, the maximum flexural strength was obtained for the chemical-cured and dual-cured experimental composite resin cement. The dual-cured experimental composite resin cement's flexural strength value was in the mid-range of the values exhibited from the commercial resin cements. However, the dual-cured experimental composite resin cement exhibited noticeably high tensile bond strength when compared with the results obtained with the commercial resin cements.

Biological and electrical resistance of acetylated flax fibre reinforced polypropylene composites

Flax fibre reinforced polypropylene composites were fabricated using a high speed mixer followed by injection moulding. Prior to composite production, the fibre was modified by acetylation in the presence of perchloric acid. The effect of acetylation of the fibre was assessed on the basis of moisture resistance and dielectric properties of the resulting composites. It was found that the moisture absorption and swelling properties of the composites were reduced respectively to 60% and 30% due to acetylation. Two different types of biocide were mixed with untreated flax fibre, and the samples were exposed to decay fungi for up to 3 months along with control polypropylene. The composites with acetylated fibres showed good protection against fungi, and biocide had less effect on biological resistance. The dielectric properties of the flax-polypropylene composites were also estimated as a function of aging period. The composites with modified fibre showed more improvement in dielectric properties compared to the composites with untreated fibres. The mechanical properties were investigated for those composites. Tensile and flexural strengths of composites were found to be increased following acetylation due to modification, and strength properties of both untreated and acetylated flax fibre reinforced polypropylene composites decreased with respect to aging period. The Charpy impact strengths of composites were found to increase with increasing aging periods.

Enhanced Mechanical Strength of BFRP Composite Using Modified Bamboos

In the present study epoxy and polyester resins have been reinforced with physically modified (alkali treated) bamboos strip matting to develop bamboo fiber-reinforced plastic (BFRP) composites. Bamboo mats were treated with 1, 2, 5, 10, 15, 20, and 25% concentration of NaOH in distilled water for 30 min at 20°C (room temperature). The mechanical properties of the alkali treated bamboo composites (tensile strength, elastic modulus, flexural strength, flexural modulus, toughness, and impact strength) were determined. Optimum results have been obtained by bamboos treated with 5% NaOH solutions. Higher percentages of NaOH concentration result in poor mechanical properties of composites. The morphology analysis reveals that the bamboo treated with 5% NaOH exhibited better compatibility with the epoxy and polyester resins than the untreated bamboo. The improvements in tensile strength and flexural strength were higher by 55.15 and 43.92%, respectively, for composites with epoxy matrix. In the case of alkali-treated composites with polyester matrix, the tensile strength and flexural strength were higher by 69 and 59%, respectively.

Developing and characterizing new materials based on waste plastic and agro-fibre

This study optimizes flexural properties of composites made from waste materials, corn stalk, seed flax and Agave americana fibres along with waste linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) matrices. The surface morphology of fibres and composites was characterized with light and scanning electron microscopes. Thermal behaviour of the corn stalk outer rings and pith parenchyma was shown using thermogravimetric analysis. There was no significant difference between the LLDPE composites made with corn stalk outer rings versus whole stalks, possibly due to an insignificant role played by parenchymatous part of the pith. Water retted seed flax fibres in LLDPE matrix optimized the composite flexural strengths at 6–8 days of retting, above which the properties declined. Field retted seed flax varieties in LLDPE matrix showed no significant differences in their flexural strengths. With additional fibre loading, flexural strength of A. americana HDPE composites first dropped before improving after extrusion, and only improved when using the layer method.

Experimental evaluation of precast, prestressed concrete, three-wythe sandwich wall panels

This paper describes an experimental program designed to verify the behavior of 3-wythe panels under later load and at the time of prestress transfer. The general flexural behavior of the 3-wythe panels was investigated using lateral load tests. Load-deflection behavior, degree of composite action, flexural strength, and horizontal shear of the panels under the action of a uniform pressure over the panel span were evaluated in this study. Fabrication of the panels for the lateral load tests revealed that cracking at prestress transfer was a concern. Thus, additional tests were performed to evaluate stresses at prestress transfer. These tests examine the actual behavior of full-scale, 3-wythe panels under the action of prestress force. Experimental results presented in this paper are compared with FEM analysis results. Descriptions of FEM analyses and models were given in a prior paper, and complete details of the work presented in this paper were provided in 2 other earlier papers.

Synergistic effects of carbon fillers on tensile and flexural properties in liquid‐crystal polymer based resins

AbstractOne emerging market for thermally and electrically conductive resins is bipolar plates for use in fuel cells. Adding carbon fillers to thermoplastic resins increases the composite thermal and electrical conductivity. These fillers have an effect on the composite tensile and flexural properties, which are also important for bipolar plates. In this study, various amounts of three different types of carbon (carbon black, synthetic graphite particles, and carbon fibers) were added to Vectra A950RX liquid‐crystal polymer. In addition, composites containing combinations of fillers were also investigated via a factorial design. The tensile and flexural properties of the resulting composites were then measured. The objective of this study was to determine the effects and interactions of each filler with respect to the tensile and flexural properties. The addition of carbon black caused the tensile and flexural properties to decrease. Adding synthetic graphite particles caused the tensile and flexural modulus to increase. The addition of carbon fiber caused the tensile and flexural modulus and ultimate flexural strength to increase. In many cases, combining two different fillers caused a statistically significant effect on composite tensile and flexural properties at the 95% confidence level. For example, when 40 wt % synthetic graphite particles and 4 wt % carbon black were combined, the composite ultimate tensile and flexural strength increased more than what would be expected from the individual additive effect of each single filler. It is possible that linkages were formed between the carbon black and synthetic graphite particles that resulted in improved ultimate tensile and flexural strength. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The effects of acetylation on properties of flax fibre and its polypropylene composites

Flax fibre was modified with acetylation. The influence of the acetylation on the structure and properties of flax fibre were investigated as well as modified flax fibre reinforced polypropylene composites were also prepared. The catalyst was used to accelerate acetylation reaction rate. Flax fibre was characterised after modification. Surface morphology, mois- ture absorption property, components content, degree of polymerisation, crystallinity of cellulose and thermal stability of flax fibres were studied. Due to acetylation, the flax fibre surface morphology and moisture resistance properties improved remarkably. Flax fibre (modified and unmodified) reinforced polypropylene composites were fabricated with 30 wt% fibre loading. The mechanical properties were investigated for those composites. Tensile and flexural strengths of composites were found to increase with increasing degree of acetylation up to 18% and then decreased. Charpy impact strengths of composites were found to decrease with increasing degree of acetylation. Owing to addition of coupling agent (maleated polypropylene -MAH), the tensile and flexural strength properties were found to increase in between 20 to 35% depending on degree of acetylation.

Preparation of 3D-Cf/SiC composites at low temperatures

The conversion process of the polycarbosilane (PCS) into silicon carbide (SiC) was investigated by TG–DTA, IR, XRD, etc., which indicated the feasibility of transition from PCS to SiC ceramics at low temperatures under 1000 °C. The results show that the inorganic transition of PCS appears at about 750 °C, and the crystal emerges at 880 °C approximately. The carbon fiber reinforced silicon carbide composites (Cf/SiC) were hereby prepared at low temperatures as 700 °C, 800 °C, 900 °C, 1000 °C, respectively through precursor infiltration and pyrolysis (PIP). The mechanical properties of Cf/SiC composites prepared at low temperatures were almost all outstanding, with the flexural strength of 600.3 MPa for Cf/SiC composites prepared at 1000 °C, the shear strength of 64.2 MPa and the fracture toughness of 22.5 MPa m 1/2. And the flexural strength of composites at 1600 °C in vacuum was 411.2 MPa, which was prepared at 900 °C, while the flexural strength at room temperatures was 527.4 MPa.