Three-point Flexural Strength Research Articles

Recyclability and reutilization of carbon fiber fabric/epoxy composites

Solid carbon fiber/epoxy laminates manufactured by liquid resin infusion of twill fabric reinforcement are recycled in a bath of boiling sulfuric acid to separate the fibers from the matrix. The recycled reinforcement consists of long fibers arranged in a random, entangled mat. Using the same epoxy matrix and infusion materials and process, the recycled fibers are reutilized to manufacture solid laminates. The physical properties of the recycled laminates are evaluated by means of pulse-echo ultrasound, visual microscopy, and fiber volume content. The average fiber volume content of the recycled laminates is 33%, compared to the 62% of the twill laminates. The mechanical properties of the recycled composite include tension modulus and strength, compression modulus and strength, three-point bend flexure strength, and short beam shear strength. The properties are compared against the values of the twill reinforcement with quasi-isotropic stacking sequence. Results show that the recycled material offers promising elastic properties and strength values, similar to those of advanced carbon fiber sheet molding compounds, and therefore can be used as structural material.

Fabrication and characterisation of bulk Al2O3/Mo nanocomposite by mechanical milling and sintering

In this study, fabrication and mechanical properties of alumina based ceramic matrix nanocomposite reinforced with 15 and 26·6 vol.-%Mo particles were investigated. Alumina–molybdenum nanocomposite powders were prepared by ball milling of Al and MoO3 in an SPEX8000 type ball mill. The powder particles were consolidated by cold uniaxial pressing followed by sintering in vacuum atmosphere at 1300 and 1400°C. The structural evaluation of as milled and sintered samples was studied by X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. Sintered samples were examined by hardness measurements and three-point flexural strength. Results show a significant improvement in flexural strength of Al2O3–Mo nanocomposites in comparison to monolithic alumina and increases by Mo content. During sintering, grain growth and α-Al2O3 to γ-Al2O3 transformation occurred. In addition, an increase in temperature of sintering resulted in higher density and hardness of consolidated nanocomposites.

Engineering characteristics of the compressed-stabilized earth brick

Utilization of lime and rice husk ash for soil stabilization produced considerable strength gain and other geotechnical properties of the stabilized soils. Its application could be also superior for construction materials as compressed-stabilized earth (CSE) or unfired-brick. This paper presents the investigation result of the application of lime and rice husk for unfired brick or compressed stabilized earth. The compressive and three-point flexural strength tests including compressive strength after water submersion were carried out in this present study. The investigation results show that compressive and flexural strength of clay brick are improved by adding of lime and RHA. The best quantity of lime and RHA in this study, is obtained by ratio 1:1 of lime and RHA. The addition of sand in stabilized clay resulted in more improvement in the water retention ability.

In situ platelet-toughened TiB 2–SiC composites prepared by reactive pulsed electric current sintering

Partially textured TiB2–SiC composites were prepared by reactive pulsed electric current sintering of attrition-milled TiH2–B–SiC–B4C powder mixtures. Plate-like TiB2 grains, formed in situ with their elongated direction perpendicular to the pressing direction, improved both the strength and fracture toughness of the composites. The TiB2 composites with 20–30 vol.% SiC combined a three-point flexural strength of 625–695 MPa with a Vickers hardness of 21.1–23.5 GPa and a fracture toughness of 5.7–7.3 MPa m1/2.

Mechanical properties of novel calcium phosphate–mullite biocomposites

Herein, the results of systematic mechanical property measurements of pressureless sintered calcium phosphate (CaP)-mullite composites are discussed. Our experimental results demonstrated how the mullite addition (upto 30 wt%) influenced hardness, elastic modulus, strength and toughness properties of the composites. In assessing each of these fundamental material properties, either a range of load or a number of complimentary techniques were used to obtain reliable measure of mechanical properties. Importantly, the results of single edge V notch beam measurements revealed that a reliable toughness value of ~1.5 MPa m(0.5) could be obtained in composites containing 20 or 30 wt% mullite. Our results clearly illustrated that a combination of elastic modulus (~80 GPa), compressive strength of more than 350 MPa, three-point flexural strength of 70-80 MPa, hardness of 4-5 GPa were achievable with the investigated composites. Such a combination of material properties, in addition to modest toughness property appeared to indicate that CaP-mullite composites could be used as a biomaterial for hard tissue replacement.

A New Self Healing Method in Composite Laminates Using the Hollow Glass Fiber

The purpose of the present study is to obtain the least strength reduction and uttermost healing efficiency in a typical [(90/0)/(90/0)Hollow/90/(0/90) Hollow/90/(0/90) Hollow/(0/90)] self-healing laminate. It has been done using a hollow glass fiber (HGF) with a given diameter and an individual method to distribute the HGF in the host laminate. The results of three-point bend flexural strength testing indicated that for the investigated distribution, the inclusion of HGF imparts little reduction in undamaged strength (4%) which is due to the non-integrity of self-healing laminate related to the host laminate. After healing it was found that the laminate had a residual strength of 97% compared to the undamaged control and 100% compared to an undamaged self healing laminate.

Investigation into the Mechanical Properties of Nanometric Zirconia Dental Ceramics

This study was focused on the testing and assessment of the mechanical properties of nanometric zirconia dental ceramics. The density and the apparent porosity of specimens were tested with the Archimedes drainage method. The length variation of the specimens before and after sintering was measured with a vernier caliper, and the linear contraction was tested. An X-ray diffractometer was used for the specimen phase analysis. SEM was used to observe the section micrograph of the specimens. A universal mechanical testing machine was used to test the three-point flexural strength and the fracture toughness. A microhardness tester was used to test the Vickers hardness of the test specimens. Results indicates that the flexural strength of the test specimens ≥ 890MPa, the fracture toughness ≥6Mpa.m1/2, the Vickers hardness ≥ 1240MPa, the linear contraction ≥ 21%, and the apparent porosity ≥ 0.32%. Fully satisfying the requirements in oral medicine, the ceramic is an ideal material for biological joints and dental prosthesis.

Consolidation and mechanical properties of reactive nanocomposite powders

Reactive nanocomposite powders with bulk compositions of 8Al·MoO 3, 12Al·MoO 3, and 8Al·3CuO were prepared by arrested reactive milling (ARM) and consolidated into cylindrical and rectangular pellets using a uniaxial die. Pellets were pressed at room temperature without any binder. Reference pellets were prepared from conventional Al powder and from Al-metal oxide powder blends with bulk compositions identical to those of the nanocomposite powders. Materials could be consolidated to densities greater than 90% of the theoretical maximum density while maintaining their high reactivity. Tensile strength and flexural strength of the consolidated materials were measured using diametrical compression and three-point flexural strength tests, respectively. Higher strengths were observed for higher relative densities, and the strength of the composite materials was comparable to that of consolidated aluminum powders. Yield strength of the reactive nanocomposite powders was determined from compaction load vs. die displacement curves using the Heckel equation. It was greater for the nanocomposite powders as compared to the powder blends or pure aluminum. Organic, or low melting point metal binders were added to selected samples to improve strength. Respective pellets were pressed at temperatures above the melting point of the metal binder. The highest density (~ 2.9 g/cm 3) and tensile strength (~ 17.5 MPa) was observed with indium as binder. All consolidated samples were found to be highly reactive, and the effect of partial reaction during consolidation remained below the limit quantifiable by differential scanning calorimetry.

Caracterização in vitro de um Novo Sistema de Resina Composta de Laboratório

Aim : this study aimed to determine some of the properties of a laboratory composite indicated for metallic and non-metallic crowns, anterior and posterior bridges, inlays, onlays and laminate veneers. Methology: the properties evaluated were surface roughness, flexural strength, shear bond strength to three metal alloys and the microleakage at the composite/metal interface. All specimens were subjected to cycles of polymerization, according the manufacturer instructions. Ten round specimens (4x3 mm) were prepared for hardness (VHN) and surface roughness tests (Ra). The three-point flexural strength was measured on rectangular shaped specimens (10x5x2 mm), at 1 mm/min speed. The experiments involving dental alloys (bond strength and microleakage) were submitted to statistical analysis (p Results : there were no statistically significant diferences between the bond strength means. As for the marginal leakage, the CoCr group differed of the Au and NiCr groups in specimens without mechanical retention and subjected to thermocycling. Conclusion : according to our results and the literature search, the Resilab system showed satisfactory performance regarding the properties evaluated. The bond strength was not dependable on the metal alloy used.

Effect of Heat-Pressing on the Microstructure and Properties of a Novel Lithium Disilicate Glass-Ceramic

The purpose of this study was to investigate the effects of heat pressing on the microstructure and properties of a novel lithium disilicate glass-ceramic located in Li2O-SiO2-K2O-Al2O3-ZrO2-P2O5 system. Before and after respective heat pressing, the crystalline phase composition and microstructures were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Three-point flexural strength of glass-ceramic specimens was measured following the instruction of ISO 6872. The results showed that the bonding strength of the heat-pressed specimens was higher than that of the heat- treated controls. XRD examination showed the main crystallization in specimens after heat pressing was lithium disilicate as controls. SEM examination indicated crysta1s were aligned along the direction of pressing, and while in control groups crystals randomly interlocked. Dental heat pressing procedure leads to an anisotropic structure in lithium disilicate glass-ceramic, which is a useful method to improve the mechanical property. With the results under the present conditions, the novel lithium disilicate glass-ceramic may be considered as a promising candidate material for dental all-ceramic application.

Intragranular Porous Aluminum Titanate Ceramics with Low Thermal Expansion and High Strength Simultaneously

Intragranular porous aluminum titanate ceramics were prepared by using graphite powder as pore-forming agent and magnesium-doped aluminum titanate powder as starting material. FESEM was employed to observe the microstructure. In order to investigate the expansion behavior and mechanical property, the dilatometric curve and three-point flexural strength of the prepared aluminum titanate ceramics were measured respectively. The results demonstrate that because of the formation of the intragranular pores, the aluminum titanate ceramics are of low thermal expansion and high strength simultaneously.

High-strength nanograined and translucent hydroxyapatite monoliths via continuous hydrothermal synthesis and optimized spark plasma sintering

The synthesis of high-strength, completely dense nanograined hydroxyapatite (bioceramic) monoliths is a challenge as high temperatures or long sintering times are often required. In this study, nanorods of hydroxyapatite (HA) and calcium-deficient HA (made using a novel continuous hydrothermal flow synthesis method) were consolidated using spark plasma sintering (SPS) up to full theoretical density in ∼5 min at temperatures up to 1000 °C. After significant optimization of the SPS heating and loading cycles, fully dense HA discs were obtained which were translucent, suggesting very high densities. Significantly high three-point flexural strength values for such materials (up to 158 MPa) were measured. Freeze-fracturing of disks followed by scanning electron microscopy investigation revealed selected samples possessed sub-200 nm sized grains and no visible pores, suggesting they were fully dense.

Achieving uniform microstructure and superior mechanical properties in ultrafine grained TiB 2–TiSi 2 composites using innovative multi stage spark plasma sintering

We report here the development of ultrafine grained TiB 2–TiSi 2 composites, adopting multi stage Spark Plasma Sintering (SPS) route. As opposed to the commonly used Single Stage SPS (SSS), the samples are held for a desired timescale at intermediate temperatures, before reaching the final sintering temperatures (1400 °C, 1450 °C and 1500 °C). In our innovative sintering schedule, the powder compacts are held for a comparatively lesser period at intermediate stages, in order to maintain a net holding time of 10 min altogether at different holding stages during Two Stage Sintering (TSS) and Multi Stage SPS (MSS). TSS and MSS allowed the achievement of relatively higher sinter densities with respect to SSS, when the final sintering temperature remains same. The development of finer microstructural scale, with the presence of tabular TiB 2 grains (1–1.5 μm) and TiSi 2 grains (200–300 nm) is exhibited by the ceramics sintered via TSS/MSS, with respect to those developed via SSS. MSS resulted in sintering reactions between the TiB 2 and TiSi 2 components, leading to the formation of reaction layer of Ti 5Si 3 of 50–100 nm thickness. However, such sintering reactions were relatively suppressed in the case of SSS. Finer scale microstructure allowed much higher hardness (∼27–31 GPa) to be achieved on sintering via MSS. Also, more uniform microstructural development in the case of MSS led to an improvement in three-point flexural strength (∼500 MPa), compared to composites developed via conventional hot pressing or SSS route using SPS.

Flexural properties of repaired heat‐polymerising acrylic resin after wetting with monomer and acetone

Repair strength can be improved by treating fractured surfaces of a denture. This study investigated flexural properties of heat-polymerised acrylic resin specimens repaired with auto-polymerising and visible light curing (VLC) resins after the repair surfaces were wetted with monomers or acetone. Fifty-four specimens (65 x 10 x 2.5 mm) were prepared and 48 of them were sectioned to simulate denture fracture. Butt-joint designed repair surfaces were wetted with heat-, auto-polymerising monomers and acetone for 180 s and repaired with auto-polymerising and VLC resins. After repairs, specimens were subjected to three-point bending test and flexural strength, strain, fracture load, modulus of elasticity and deflection values were recorded. Data were analysed with Student t and LSD tests (p < or = 0.05). Overall flexural strength, strain, fracture load and deflection values of specimens repaired with VLC resin were significantly higher than the specimens repaired with auto-polymerising resin for all types of wetting agent (p < 0.05). Within the wetting agents, heat- and auto-polymerising monomers produced the best mechanical properties, while wetting with acetone did not provide superior effect over both monomers. In clinical use, wetting the repair surfaces may result in stronger repairs. The use of bonding agent in VLC resin repairs in combination with wetting agent results in improved flexural properties.

Recycling of fly ash for preparing porous mullite membrane supports with titania addition

In order to effectively utilize industrial waste fly ash, porous mullite ceramic membrane supports were prepared from fly ash and calcined bauxite with chemically pure titania as sintering additive. The effects of TiO 2 on the sintering behaviors and main properties of porous mullite were studied in detail. Due to the addition of titania, the sintering of the flyash-based mullite was inhibited at low temperatures, but effectively improved at high temperatures, the latter is suitable for preparing porous mullite membrane supports by incomplete sintering. Titania entered into liquid glassy phase with low high-temperature viscosity during sintering, resulting in the improvement of sintering activity, as well as the lowering of secondary mullitization temperature (where 2.0% titania). Between 1300 and 1500 °C, with increasing titania content, the samples exhibit increased trends in both linear shrinkage percent and bulk density, but a slightly decreased trend in open porosity, at all sintering temperatures. At 1300–1500 °C, the samples sintered at 1450 °C for 2 h exhibit the lowest shrinkage and bulk density, as well as the highest open porosities in the investigated titania content range of 0–6.0 wt.%. Also, with increasing titania content, the pore size decreases slightly but the three-point flexural strength increases gradually at 1450 °C.

High sintering activity Cu–Gd co-doped CeO 2 electrolyte for solid oxide fuel cells

Nano-sized Ce 0.79Gd 0.2Cu 0.01O 2− δ electrolyte powder was synthesized by the polyvinyl alcohol assisted combustion method, and then characterized by crystalline structure, powder morphology, sintering micro-structure and electrical properties. The results demonstrate that the as-synthesized Ce 0.79Gd 0.2Cu 0.01O 2− δ was well crystalline with cubic fluorite structure, and exhibited a porous foamy morphology composed of gas cavities and fine crystals ranging from 30 to 50 nm. After sintering at 1100 °C, the as-prepared pellets exhibited a dense and moderate-grained micro-structure with 95.54% relative density, suggesting that the synthesized Ce 0.79Gd 0.2Cu 0.01O 2− δ powder had high sintering activity. The powders made by this method are expected to offer potential application in intermediate-to-low temperature solid-oxide fuel cells, due to its very low densification sintering temperature (1100 °C), as well as high conductivity of 0.026 S cm −1 at 600 °C and good mechanical performance with three-point flexural strength value of 148.15 ± 2.42 MPa.

Fabrication and Characteristic Evaluation for Clay Tile Composites Reinforced with Flaky Nickel-Chromium Alloy Particles

The flake-forming behavior of Ni-Cr alloy powders during a wet ball milling process and the effect of volume percent of flaky Ni-Cr alloy particles on three-point flexural strength and fracture toughness of clay tile composites reinforced with flaky Ni-Cr alloy particles have been investigated. The flexural strength and fracture toughness of composites can be simultaneously improved by increasing the volume percent of flaky Ni-Cr alloy particles. The SEM observations indicates that the improvement in fracture toughness may be attributed to plastic deformation of flaky Ni-Cr alloy particles at crack tip. Fabricating composites reinforced with flaky Ni-Cr alloy particles is an effective toughening technique capable of simultaneously improving the strength and toughness of brittle materials by utilizing plastic deformation of ductile phase. The volume resistance of the clay tile/30%flaky Ni-Cr alloy particle composites is 7.5×10-2 Ω·cm, which is larger than that of Ni-Cr (JIS NCH-1) (1.1×10-4 Ω·cm). The resistance temperature coefficient of the composite is almost the same as that of Ni-Cr (JIS NCH-1). The composite is therefore promising candidate as resistance materials.

Effect of sintering temperature on three-point flexural strength of different zirconia materials

Effect of sintering temperature on three-point flexural strength of different zirconia materials

Microstructure, mechanical, and in vitro properties of mica glass-ceramics with varying fluorine content

The design and development of glass ceramic materials provide us the unique opportunity to study the microstructure development with changes in either base glass composition or heat treatment conditions as well as to understand processing-microstructure-property (mechanical/biological) relationship. In the present work, it is demonstrated how various crystal morphology can develop when F(-) content in base glass (K(2)O-B(2)O(3)-Al(2)O(3)-SiO(2)-MgO-F) is varied in the range of 1.08-3.85% and when all are heat treated at varying temperatures of 1000-1120 degrees C. For some selected heat treatment temperature, the heat treatment time is also varied over 4-24 h. It was established that with increase in fluoride content in the glass composition, the crystal volume fraction of the glass-ceramic decreases. Using 1.08% fluoride, more than 80% crystal volume fraction could be achieved in the K(2)O-B(2)O(3)-Al(2)O(3)-SiO(2)-MgO-F system. It was observed that with lower fluoride content glass-ceramic, if heated at 1040 degrees C for 12 h, an oriented microstructure with 'envelop like' crystals can develop. For glass ceramics with higher fluorine content (2.83% or 3.85%), hexagonal-shaped crystals are formed. Importantly, high hardness of around 8 GPa has been measured in glass ceramics with maximum amount of crystals. The three-point flexural strength and elastic modulus of the glass-ceramic (heat treated at 1040 degrees C for 24 h) was 80 MPa and 69 GPa of the sample containing 3.85% fluorine, whereas, similar properties obtained for the sample containing 1.08% F(-) was 94 MPa and 57 GPa, respectively. Further, in vitro dissolution study of the all three glass-ceramic composition in artificial saliva (AS) revealed that leached fluoride ion concentration was 0.44 ppm, when the samples were immersed in AS for 8 weeks. This was much lower than the WHO recommended safety limits of 1.5 ppm. Among all the investigated glass-ceramic samples, the glass ceramic with 3.85% F(-) content in base glass (heat treated at 1040 degrees C for 12 h), exhibits the adherence of Ca-P layer, which consists of spherical particles of 2-3 mum. Other ions, such as Mg(+2) and K(+1) ion concentrations in the solution were found to be 8 and 315 ppm after 8 weeks of leaching, respectively. The leaching of all metal ions is recorded to decrease with time, probably due to time-dependent kinetic modification of sample surface. Summarizing, the present study illustrates that it is possible to obtain a good combination of crystallization, mechanical and in vitro dissolution properties with the careful selection of base glass composition and heat treatment conditions.

Mechanical Properties of Cost-Effective Polypropylene Composites Filled with Red-Mud Particles

In recent years, the use of filler materials, such as red mud, in composites has increased. In this study, the use of industrial waste red mud as a filler material in an isotactic polypropylene (iPP) polymer–matrix composite (PMC) was investigated. A variety of mechanical tests were performed on the unreinforced polymer and on composites with 10, 20, 30, 40 and 50 wt.% red mud. Tensile strength, three-point flexural strength and hardness tests have been carried out, and the relationships between the red-mud content and properties were examined. Scanning electron microscopy (SEM) was applied to the fractured surfaces after three-point flexural tests. The results showed that, while the values of tensile and flexural strength were decreased, the hardness was increased with increasing red-mud content.