Flexural Strength Of Composites Research Articles

Effect of Ingredients on Flexural Strength of Friction Composite

In the present work, a friction composite material which will be used for material of train brake shoe was investigated to study the effect of ingredients on flexural strength. The Taguchi method is used to measure relative effect of ingredients on flexural strength of composite. Taguchi L8 orthogonal array which consists of 7 factors with 2 levels each is applied to perform experiment. Ingredients of friction composite were considered as factors or parameters and % volume for each factor was varied at 2 levels. Phenolic resin and barite (BaSO4) were not included as factor. Phenolic resin was always kept constant at 30 % volume and % volume of barite (BaSO4) was varied to compensate the changing of other ingredients amount. The results show that glass fiber and cast iron chip have significant effect on increasing of flexural strength of brake shoe composite. Conversely, NBR has significant effect on decreasing of flexural strength of brake shoe material. Cashew dust, Cu short wire, fly ash and graphite have insignificant effect on flexural strength. Cu short wire cant play a role as reinforcement fiber in brake shoe composite because there is weak bonding between Cu short wire and matrix.

Comparative Analysis of Rigid PVC Foam Reinforced with Class C and Class F Fly Ash

Fly ash particles are usually spherical and based on their chemical composition; they are categorized into two classes: C and F. This study compares the microstructural, mechanical and thermal properties of extruded rigid PVC foam composites reinforced with class C and class F fly ash. The mechanical properties: such as tensile and flexural strength of composites containing class C fly ash were superior to the composites containing class F fly ash particles. Composites containing 6 phr class C fly ash showed a 24% improvement in the tensile strength in comparison to a mere 0.5% increase in composites reinforced with class F fly ash. Similarly, the addition of 6 phr of class F fly ash to the PVC foam matrix resulted in a 5.74% decrease in the flexural strength, while incorporating the same amount of class C fly ash led to a 95% increase in flexural strength. The impact strength of the composites decreased as the amount of either type of fly ash increased in the composites indicating that fly ash particles improve the rigidity of the PVC foam composites. No significant changes were observed in the thermal properties of the composites containing either type of fly ash particles. However, the thermo-mechanical properties measured by DMA indicated a steep increase in the viscoelastic properties of composites reinforced with class C flyash. The microstructural properties studied by Scanning Electron Microscopy (SEM) confirmed that fly ash particles were mechanically interlocked in the PVC matrix with good interfacial interaction with the matrix. However, particle agglomeration and debonding was observed in composites reinforced with higher amounts of fly ash.

Mechanical and dielectric properties of 2.5D SiCf/SiC–Al2O3 composites prepared via precursor infiltration and pyrolysis

2.5D KD-1 SiC fabrics were employed to fabricate SiCf/SiC composites by a modified polymer infiltration and pyrolysis (PIP) process, using Al2O3 as inert filler. The effects of Al2O3 content on the microstructure, mechanical and dielectric properties of SiCf/SiC–Al2O3 composites were investigated. The results reveal that the infiltration efficiency is remarkably improved by incorporating the Al2O3 filler into the PIP process. The Al2O3 filler can effectively compensate for volume shrinkage to form dense matrix and act as strengthening phase to deflect microcracks, thus a maximum flexural strength of 186MPa is obtained when the Al2O3 content is 10wt%, which is 75% higher than that of composites without filler (106MPa). Both ε' and ε″ of complex permittivity for the composites decrease as Al2O3 content increases from 0 to 20wt%. With the incorporation of PyC interphase, the flexural strength of composites with 10wt% Al2O3 filler is improved from 186 to 234MPa, and its complex permittivity increases from 20.5-i15.5 to 43-i37.

Effects of the Preparation Parameters on the Properties of Graphite/Carbon Fiber/Copper/Phenolic Resin Composites

The polymer composites consist of phenolic resin, natural graphite, carbon fiber and copper powder, are fabricated by hot compression moulding or compression moulding followed by post-curing. The density, electrical conductivity and flexural strength of composites are analyzed to determine the influences of post-curing temperature and preparing method on the physical, electrical and mechanical properties of composites. It is found that the density, electrical conductivity and flexural strength of composites increase with increasing post-curing temperature for composites prepared by compression moulding followed by post-curing. The flexural strength is more strongly dependent on post-curing temperature. At 170 °C, the density, electrical conductivity and flexural strength of composites were 1.85 g/cm3, 2.94 × 103S/m and 40 MPa respectively. The cross-linking skeleton structure well established in the composites could be the main reason for the largely increasing of flexural strength as post-curing temperature increases. The results also show that the properties of composites prepared by hot compression moulding are higher than those of composites prepared by compression moulding followed by post-curing.

The Study of Volume Electrical Resistivity and Mechanical Property of CBT/Carbon Black/Aluminum Composites

Cyclic Butylene Terephthalate (CBT)/carbon black (CB)/aluminum composites were prepared by melting blend method and their conductivity and mechanical property were studied by Milliohmmeter and material testing machine. The results showed that at below 1.6 wt% of flake aluminum（Al）, volume electrical resistivity and flexural strength of composites increased with Al content increases and reached the maximum value at 1.6 wt% of Al. Composites containing 18.4 wt% of CB and 1.6 wt% of aluminum exhibited excellent comprehensive performance (electrical resistivity, 20.3 Ω.cm; flexural strength, 40.0 MPa).

Experimental Research on Mechanical Properties of Cement Based Composites PVA Fiber Reinforced

Airport pavement surface mechanical characteristics and PVA fiber content, through experiments on PVA fiber reinforced cement matrix composites flexural strength, compressive strength and other mechanical properties are analyzed experimentally.

Flexural and tensile strengths of unidirectional hybrid epoxy composites reinforced by S-2 glass and T700S carbon fibres

A study on the flexural strength of hybrid epoxy composites reinforced by S-2 glass and T700S carbon fibres in an intra-ply configuration is presented in this paper. The flexural strength was obtained from the three point bend test in accordance with ASTM: D790-10 at various span-to-depth ratios. Nonlinear large displacement finite element analysis (FEA) and the classic lamination theory (CLT) were employed to model the flexural behaviour of the hybrid composites. The models were validated using the experiment specimens from a previous study. With the aid of the developed models, the effects of fibre volume fractions, hybrid ratio and span-to-depth ratio were studied. It is shown that the flexural strength increases with span-to-depth ratio and converges when the span-to-depth ratio is greater than 32. Hybridisation can be used to improve the flexural strength. The hybridisation phenomena are dependent on the strength ratios of carbon/epoxy and glass/epoxy laminas. The overall maximum flexural hybrid effect is achieved when the hybrid ratio is 0.25 ([02G/06C]) when both Vfc and Vfg are 70%. The strength increases are 16.6% and 42.58% when compared with those of the full carbon and glass configurations, respectively. The overall maximum tensile hybrid effect is achieved when the hybrid ratio is 0.125 ([0G/07C]) when Vfc is 30% and Vfg is 50%.

Effects of the Mould Pressure and Mould Pressing Time on the Properties of Graphite/Phenolic Resin Composites

Polymer matrix composites made from phenolic resin are filled with natural graphite powders. They are fabricated by compression molding technique. The density, electrical conductivity and flexural strength of composite are analyzed to determine the influences of mould pressure and mould pressing time on the physical, electrical and mechanical properties of composite. It is found that the density, electrical conductivity and flexural strength of composites increased with increasing mould pressure. Under pressure of 40 MPa for 60 min, the density, electrical conductivity and flexural strength of composites were 1.85 g/cm3, 4.35  103 S/cm and 70 MPa, respectively. The decreased gaps could be the main reason for the increasing of density, electrical conductivity and flexural strength as mould pressure increases. The results also show that the density of composites increased with increasing mould pressing time.

The effect of neutron irradiation on the mechanical properties of C/SiC composites

The effects of neutron irradiation to 3.5 and 9.5dpa at 730°C on a 2D plain woven carbon fiber reinforced polymer derived SiC matrix composite are presented. For both fluences, the irradiation caused in-plane contraction and trans-plane expansion. Irradiation also caused substantial reduction in composite flexural strength (−54%) and increase in flexural tangent modulus (+85%). The extents of dimensional/mechanical property changes were greater for the higher fluence irradiated samples. Those changes suggest the instability of the polymer derived SiC matrix following irradiation. The nature of the mechanical property changes suggest increased clamping stress between the fiber and the matrix. The composite property changes are explained in terms of irradiation effects on composite constituents and are compared with carbon fiber reinforced carbon matrix composite as a reference material.

Cytocompatibility and Mechanical Properties of Short Phosphate Glass Fibre Reinforced Polylactic Acid (PLA) Composites: Effect of Coupling Agent Mediated Interface.

In this study three chemical agents Amino-propyl-triethoxy-silane (APS), sorbitol ended PLA oligomer (SPLA) and Hexamethylene diisocyanate (HDI) were identified to be used as coupling agents to react with the phosphate glass fibre (PGF) reinforcement and the polylactic acid (PLA) polymer matrix of the composite. Composites were prepared with short chopped strand fibres (l = 20 mm, ϕ = 20 µm) in a random arrangement within PLA matrix. Improved, initial composite flexural strength (~20 MPa) was observed for APS treated fibres, which was suggested to be due to enhanced bonding between the fibres and polymer matrix. Both APS and HDI treated fibres were suggested to be covalently linked with the PLA matrix. The hydrophobicity induced by these coupling agents (HDI, APS) helped to resist hydrolysis of the interface and thus retained their mechanical properties for an extended period of time as compared to non-treated control. Approximately 70% of initial strength and 65% of initial modulus was retained by HDI treated fibre composites in contrast to the control, where only ~50% of strength and modulus was retained after 28 days of immersion in PBS at 37 °C. All coupling agent treated and control composites demonstrated good cytocompatibility which was comparable to the tissue culture polystyrene (TCP) control, supporting the use of these materials as coupling agent’s within medical implant devices.

Novel dental restorative materials having low polymerization shrinkage stress via stress relaxation by addition-fragmentation chain transfer

ObjectivesTo produce a reduced stress dental restorative material while simultaneously maintaining excellent mechanical properties, we have incorporated an allyl sulfide functional group into norbornene–methacrylate comonomer resins. We hypothesize that the addition-fragmentation chain transfer (AFCT) enabled by the presence of the allyl sulfide relieves stress in these methacrylate-based systems while retaining excellent mechanical properties owing to the high glass transition temperature of norbornene-containing resins. MethodsAn allyl sulfide-containing dinorbornene was stoichiometrically formulated with a ring-containing allyl sulfide-possessing methacrylate. To evaluate the stress relaxation effect as a function of the allyl sulfide concentration, a propyl sulfide-based dinorbornene, not capable of addition-fragmentation, was also formulated with the methacrylate monomer. Shrinkage stress, the glass transition temperature and the elastic modulus were all measured. The composite flexural strength and modulus were also measured. ANOVA (CI 95%) was conducted to determine differences between the means. ResultsIncreasing the allyl sulfide content in the resin dramatically reduces the final stress in the norbornene–methacrylate systems. Both norbornene–methacrylate resins demonstrated almost zero stress (more than 96% stress reduction) compared with the conventional BisGMA/TEGDMA 70/30wt% control. Mechanical properties of the allyl sulfide-based dental composites were improved to the point of being statistically indistinguishable from the control BisGMA–TEGDMA by changing the molar ratio between the methacrylate and norbornene functionalities. SignificanceThe allyl sulfide-containing norbornene–methacrylate networks possessed super-ambient Tg, and demonstrated significantly lower shrinkage stress when compared with the control (BisGMA/TEGDMA 70–30wt%). Although additional development remains, these low stress materials exhibit excellent mechanical properties which are appropriate for use as dental restorative materials.

Polyoxymethylene composites with natural and cellulose fibres: Toughness and heat deflection temperature

Abstract Cellulose and abaca fibre reinforced polyoxymethylene (POM) composites were fabricated using an extrusion coating (double screw) compounding followed by injection moulding. The long cellulose or abaca fibres were dried online with an infrared dryer and impregnated fibre in matrix material by using a special extrusion die. The fibre loading in composites was 30 wt.%. The tensile properties, flexural properties, Charpy impact strength, falling weight impact strength, heat deflection temperature and dynamic mechanical properties were investigated for those composites. The fibre pull-outs, fibre matrix adhesion and cracks in composites were investigated by using scanning electron microscopy. It was observed that the tensile strength of composites was found to reduce by 18% for abaca fibre and increase by 90% for cellulose fibre in comparison to control POM. The flexural strength of composites was found to increase by 39% for abaca fibre and by 144% for cellulose fibre. Due to addition of abaca or cellulose fibre both modulus properties were found to increase 2-fold. The notched Charpy impact strength of cellulose fibre composites was 6-fold higher than that of control POM. The maximum impact resistance force was shorted out for cellulose fibre composites. The heat deflection temperature of abaca and cellulose fibre composites was observed to be 50 °C and 63 °C higher than for control POM respectively.

Mechanical and physical properties of core–shell structured wood plastic composites: Effect of shells with hybrid mineral and wood fillers

The effects of shells filled with silane treated precipitated calcium carbonate (TPCC) and wood fiber (WF) on properties of core–shell structured wood plastic composites (WPCs) were studied with two different core systems. In a weak core system made with recycled polypropylene (PP)/high density polyethylene (HDPE), coextruded WPCs with reinforced virgin HDPE shells showed significantly improved flexural strengths compared with their core-only controls. In a strong core system made of virgin HDPE, the composite flexural strengths were lowered in relation to their core-only controls. Impact strengths for both systems were noticeably improved with added shells. Specially, the impact strengths of the weak core coextruded WPCs showed up to 150% increases in relation to their core-only controls. Impact fracture types varied largely with core quality and filler composition in the shell. Water absorption of coextruded WPCs with high TPCC contents in the shell was lower than that of core-only controls and coextruded WPCs with high wood contents in the shell layer. The use of high percentage of plastic in the shell layer led to the increases of overall composite’s coefficient of thermal expansion (CTE). However, increased filler loadings in the shell helped reduce the CTE values, especially, for the weak core system.

Nondestructive investigation of density defect in C/SiCs and its effect on the mechanical properties

Density defect in a 3D needled C/SiC composite was successfully prepared by chemical vapor infiltration. Infrared thermal wave imaging, X-ray radiographic methods were used to examine the sensibility to the density defect in the C/SiC composite. Mechanical properties of the C/SiC composite containing the density defects were investigated by the three-point bending tests. Results show that both thermography and radiography methods can detect the density defect of the C/SiC composites, and the former is more effective than the latter especially with respect to detecting the superficial gas pores and delamination. There exists a critical defect ration Rd of 30% (i.e., ration of defect volume to the whole specimen volume) about the effect of the density defect on the flexural strength of composites. With the increase of the defect length, the material strength decreased when the density defect ration Rd<30%, and then the material strength slightly recovered when the Rd>30%.

Study on the Bio-Composite from Sisal Fiber Reinforced Cellulose Acetate

In this paper, sisal fibers (SF) reinforced cellulose acetate composites were prepared using twin-screw extrusion followed by hot-press moulding technology. Both the mechanical properties and the biodegradable rate of the composite were investigated in terms of effect of initial length and mass content percentage of sisal fiber on. The results showed that the fibers tended to be shorter and thinner during the processing of twin-screw blending and the tensile and flexure strength of composites were enhanced, with the content or initial length of sisal fibers increasing. Furthermore, the biodegradation rate of the composite was forward at first, and gradually became slow in later period and then leveled off finally. In addition, Micro-morphologies of the fracture surface of the composite were visualized by scanning electron microscopy (SEM) to analyze the effect of initial length and content of sisal fibers on interfacial adhesion and the distribution of sisal fibers in the composites.

Influence of Surface Finish on Flexural Strength and Microhardness of Indirect Resin Composites and the Effect of Thermal Cycling

This study investigated the effect of surface finish and thermal cycling procedures on flexural strength and surface microhardness of three indirect resin composites, Artglass®, Signum®, and Solidex®. The specimens were prepared in sufficient number and size according to flexural and microhardness test requirements (n = 10). Scanning electron microscopy-energy dispersive x-ray (SEM-EDX) analysis was also used for studying the morphology, dispersion, and elemental compositions of fillers. The EDX results showed that Artglass contained 1.57% aluminium oxide (Al2O3), 53.29% silicon dioxide (SiO2), and 2.62% barium oxide (BaO); Signum had 55.69% silicon dioxide (SiO2) and Solidex had 44.99% silicon dioxide (SiO2) of total mass. Artglass appeared to display the best flexural strength values under all the test conditions employed (range: 116.8 ± 32.18 to 147.8 ± 47.97 MPa), and it was followed by Signum (range: 93.7 ± 22.84 to 118.0 ± 33.45 MPa). Thermal cycling did not seem to have affected the flexural strength of Artglass and Signum (p > 0.05); however, it led to a significant decrease, from (110.5 ± 20.69 MPa) to 74.0 ± 13.30 MPa (p < 0.001), in the strength of polished Solidex specimens. While surface microhardness of the three materials increased by polishing (Artglass: 55.7 ± 2.64/74.1 ± 8.63 Vickers Hardness Numbers (VHN); Signum: 44.8 ± 3.12/60.7 ± 4.50 VHN; Solidex: 44.0 ± 2.31/53.4 ± 3.58 VHN for unpolished/polished specimens), thermal cycling had a deleterious effect on this property (p < 0.001).

Mechanical properties and oxidation resistance of SiCf/CVI-SiC composites with PIP-SiC interphase

SiC coatings were successfully synthesized on SiC fibers by precursor infiltration and pyrolysis (PIP) method using polycarbosilane (PCS) as precursor. The morphology of as-fabricated coatings was observed by SEM, and its structure was characterized by XRD and Raman spectrum. The SiC fiber reinforced chemical vapor infiltration SiC (SiCf/CVI-SiC) composites with PIP-SiC coatings as interphase were fabricated. And, the effects of PIP-SiC interphase on mechanical properties of composites were investigated. The experimental results point out that the coating is smooth and there is little bridging between fibers. The coating is amorphous with SiC and carbon micro crystals. The flexural strength of composites with and without PIP-SiC interphase is 220 and 100MPa, respectively. And the composites with PIP-SiC interphase obviously exhibit a toughened fracture behavior. The oxidation resistance of composites with PIP-SiC interphase is much better than that of composites with pyrolytic carbon (PyC) interphase.

Effect of sintering temperature and siliconcarbide fraction on density, mechanical properties and fracture mode of alumina–silicon carbide micro/nanocomposites

In this study Al2O3–SiC micro/nanocomposites have been fabricated by mixing alumina nanopowders and silicon carbide micro/nanopowders, followed by hot pressing at 1550, 1600, 1650 and 1700°C. The density, mechanical properties and fracture mode of Al2O3–SiC composites containing different volume fractions (2.5%, 5%, 7.5%, 10% and 15%) of micro/nanoscale SiC particles were investigated and compared with those of alumina. The relative density of composites could reach values very close to theoretical density, especially after sintering at 1700°C. However, relative density declined by increasing the SiC fraction at the same sintering temperature. The flexural strength of composites was best for sintering temperature of 1700°C and showed a maximum of 545MPa for Alumina–10%SiC sintered at 1700°C. Hardness showed a remarkable increase by adding SiC and reached a pick of 22.6GPa for Alumina–15%SiC. Fracture toughness and fracture mode of alumina and composites with 5%, 10% and 15% SiC sintered at 1700°C were also investigated. Composites were tougher than alumina and the scanning electron microscopy observations showed that fracture mode changes from intergranular for alumina to transgranular for composites. Finally X-ray diffraction analysis could not detect any chemical reactions between Al2O3 and SiC particles.

Mechanical and Electrical Properties of Graphite/Carbon Fiber/Phenolic Resin Composite

Composites made of phenolic resin filled with natural graphite platelets and carbon fibers are fabricated by mechanical mixing, followed by compression molding. The flexural strength and electrical conductivity of composite are analyzed to determine the influence of phenolic resin and carbon fiber on mechanical and electrical properties. It is found that there is a marked dependence of the electrical conductivity and flexural strength on phenolic resin content. The electrical conductivity decreases and flexural strength increases with the increasing of phenolic resin loading. The presence of carbon fiber helps improve the flexural strength of composite such that 4 wt% CF increases the flexural strength of composite about 90%. However, an excess amount of carbon fiber reduces the flexural strength due to poor dispersion of carbon fiber in composite. The result also shows that the addition of carbon fiber exhibits a slight effect on the electrical conductivity of composite at low carbon fiber loadings.

Electrical and Flexural Properties of Copper and Graphite Filled Phenolic Resin Composites

Composites made of phenolic resin filled with graphite platelets and copper particles (copper powder, copper fiber or both mixture), are fabricated by mechanical mixing. The electrical conductivity of composite composed of 30 wt% resin, 50 wt% graphite and 20 wt% copper powder is up to 600S/cm. The efficiency of copper powder is compared with copper fiber. The results show that copper powder is more effective than copper fiber in improving electrical conductivity. The particle shape is also a principal factor in influencing flexural strength. In this study, the flexural strength of composites tends to increase with decreasing the ratio of copper fiber/copper powder because the dendritic structure of copper powder enhances the probability of graphite platelets embedded in the dendritic arms, which in fact help to distribute the external load from matrix to copper powders.