Showing papers on "Flexural strength published in 2011"

Mechanical characterisation of basalt fibre reinforced plastic

Abstract: New perspectives have arisen on basalt fibre applications due to the potential low cost of this material together with its good mechanical performance, in particular at high temperature. The idea to fill these fibres into a polymer matrix is relatively recent and could offer very interesting perspectives that have not yet been sufficiently investigated. In this work, with the principal aim of evaluating the possibility to replace glass fibres in most of their applications, mechanical tests were carried out on comparable E-glass and basalt fibre reinforced plastic laminates. The latter were cut by square plates fabricated through vacuum bag technology. The results obtained on the two laminates were compared showing a high performance of the basalt material in terms of young modulus, compressive and bending strength, impact force and energy. These good properties suggest possible applications of basalt fibres in fields where glass composites are nowadays largely applied. The short-beam strength tests confirmed what above said by denoting an interfacial adhesion similar to that between E-glass and epoxy matrix.

Utilization of silica fume in concrete: Review of hardened properties

Abstract: Several types of industrial byproducts are generated. With increased environmental awareness and its potential hazardous effects, utilization of industrial byproducts has become an attractive alternative to disposal. One such by-product is silica fume (SF), which is a byproduct of the smelting process in the silicon and ferrosilicon industry. Silica fume is very effective in the design and development of high strength high performance concrete. This paper covers the physical, chemical properties of silica fume, and its reaction mechanism. It deals with the effect of silica fume on the workability, porosity, compressive strength, splitting tensile strength, flexural strength, creep and shrinkage of concrete.

Effect of alkali treatment on interfacial and mechanical properties of coir fiber reinforced poly(butylene succinate) biodegradable composites

Abstract: The poly(butylene succinate) (PBS) biodegradable composites reinforced with coir fibers were developed. The effect of alkali treatment on the surface morphology and mechanical properties of coir fibers, interfacial shear strength (IFSS) and mechanical properties of coir fiber/PBS composites was studied. The effect of fiber mass content varying from 10% to 30% on the mechanical properties of coir fiber/PBS composites was also investigated. The coir fibers which are soaked in 5% sodium hydroxide solution at room temperature (RT) for 72 h showed the highest IFSS with 55.6% higher than untreated coir fibers. The mechanical properties of alkali-treated coir fiber/PBS composites are significantly higher than those of untreated fibers. The best mechanical properties of alkali-treated coir fiber/PBS composite were achieved at fiber mass content of 25% in this study, which showed an increase of tensile strength by 54.5%, tensile modulus by 141.9%, flexural strength by 45.7% and flexural modulus by 97.4% compared to those of pure PBS resin. The fiber surface morphologies and fractured surface of the composites exhibited an improvement of interfacial fiber–matrix adhesion in the composites reinforced with alkali-treated coir fibers.

Mechanical Properties of Fly-Ash-Based Geopolymer Concrete

Abstract: The mechanical properties of fly-ash-based geopolymer concrete (GPC) were studied. Experimentally measured values of the static elastic modulus, Poisson’s ratio, compressive strength, and flexural strength of GPC specimens made from 25 fly ash (FA) stockpiles from different sources were recorded and analyzed. The results were studied using regression analysis to identify tendencies and correlations within the mechanical properties of GPC. It was found that the mechanical behavior of GPC is similar to that of ordinary portland cement (OPC) concrete, suggesting that equations, akin to those given by ACI 318-08, could be applied for GPC to determine its flexural strength and static elastic modulus. The validity of an equation to determine the density of GPC as a function of FA fineness was also put forward.

Carbon Nanotubes and Carbon Nanofibers for Enhancing the Mechanical Properties of Nanocomposite Cementitious Materials

Abstract: Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are quickly becoming two of the most promising nanomaterials because of their unique mechanical properties. The size and aspect ratio of CNFs and CNTs mean that they can be distributed on a much finer scale than commonly used microreinforcing fibers. As a result, microcracks are interrupted much more quickly during propagation in a nano- reinforced matrix, producing much smaller crack widths at the point of first contact between the moving crack front and the reinforcement. In this study, untreated CNTs and CNFs are added to cement matrix composites in concentrations of 0.1 and 0.2% by weight of cement. The nanofilaments are dispersed by using an ultrasonic mixer and then cast into molds. Each specimen is tested in a custom-made three-point flexural test fixture to record its mechanical properties; namely, the Young's modulus, flexural strength, ultimate strain capacity, and fracture toughness, at 7, 14, and 28 days. A scanning electron microscope (SEM) is used to discern the difference between crack bridging and fiber pullout. Test results show that the strength, ductility, and fracture toughness can be improved with the addition of low concentrations of either CNTs or CNFs. DOI: 10.1061/(ASCE)MT.1943-5533.0000266. © 2011 American Society of Civil Engineers.

Effects of layer thickness and binder saturation level parameters on 3D printing process

Abstract: Various parameters, such as binder properties, printing layer thickness, powder size, and binder saturation level, have effects on the strength and surface finish of the three-dimensional printing (3D printing) process. The objective of this research is to study the effects of two parameters of layer thickness and binder saturation level on mechanical strength, integrity, surface quality, and dimensional accuracy in the 3D printing process. Various specimens include tensile and flexural test specimens and individual network structure specimens are made by the 3D printing process under different layer thicknesses and binder saturation by use of ZCorp.'s ZP102 powder and Zb56 binder. Two printing layer thicknesses, 0.1 and 0.087 mm, are evaluated at 90% and 125% binder saturation levels. Experimental findings show that under the same layer thickness, increment of binder saturation level from 90% to 125% would result in an increase of tensile and flexural strengths of the specimens and decrease of dimensional accuracy and surface uniformity of specimens. On the other hand, under the same binder saturation conditions, increase in layer thickness from 0.087 to 0.1 mm would decrease tensile strength and increase flexural strength. Also, it gives better uniformity on the surface.

Flexural Strengthening of RC Beams with Cement-Based Composites

Abstract: In this paper, the effectiveness of fiber-reinforced cementitious matrix (FRCM) materials for the strengthening of reinforced concrete (RC) beams is experimentally investigated. Bending tests on RC beams strengthened with different FRCM materials, made out of (1) carbon fiber nets; and (2) poliparafenilenbenzobisoxazole (PBO) fiber nets embedded in cement-based matrix, are performed. For case (2), different net shapes, cementitious matrices, and a number of net layers were considered. Depending on the type of fibers and matrix, different flexural debonding failure modes are identified. The fiber strain at debonding is evaluated by comparing the experimental results with those obtained with two different theoretical models. The results obtained in this study confirm the effectiveness of FRCM materials for the strengthening of RC structures and encourage further experimental and theoretical work on the topic. A better understanding of the debonding phenomenon is crucial for an optimal design of the strength...

Morphological aspects and mechanical properties of single bamboo fibers and flexural characterization of bamboo/epoxy composites

Abstract: A novel mechanical extraction process was developed to obtain long bamboo fibers to be used as reinforcement in structural composites. A single-fiber tensile test at four different span lengths for...

Woven hybrid composites: Tensile and flexural properties of oil palm-woven jute fibres based epoxy composites

Abstract: In this research, tensile and flexural performance of tri layer oil palm empty fruit bunches (EFB)/woven jute (Jw) fibre reinforced epoxy hybrid composites subjected to layering pattern has been experimentally investigated. Sandwich composites were fabricated by hand lay-up technique in a mould and cured with 105 °C temperatures for 1 h by using hot press. Pure EFB and woven jute composites were also fabricate for comparison purpose. Results showed that tensile and flexural properties of pure EFB composite can be improved by hybridization with woven jute fibre as extreme woven jute fibre mat. It was found that tensile and flexural properties of hybrid composite is higher than that of EFB composite but less than woven jute composite. Statistical analysis of composites done by ANOVA-one way, it showed significant differences between the results obtained. The fracture surface morphology of the tensile samples of the hybrid composites was performed by using scanning electron microscopy.

Enhanced properties of lignin-based biodegradable polymer composites using injection moulding process

Abstract: Composites from polybutylene succinate (PBS) and lignin-based natural material were fabricated using a melt mixing process. The effects of lignin material and polymeric methylene diphenyl diisocyanate (PMDI) compatibilizer on the properties of composites were investigated. Incorporation of 65% lignin material into PBS was achieved with an improvement in the tensile and flexural properties of composites. Incorporation of 1% PMDI in 50% lignin filled composites enhanced the tensile, flexural and impact strength simultaneously. Heat deflection temperature (HDT) of the virgin plastic also increased with lignin and PMDI incorporation. Improved interfacial adhesion was observed from SEM micrographs of the compatibilized composites.

Mechanism of reinforcement in a nanoclay/polymer composite

Abstract: Using organomodified montmorillonite (MMT) (commonly called “Nanoclay”) to reinforce polymer-based composites have raised much attention to academic and industrial sectors due to the addition of small amount of nanoclay could substantially enhance the mechanical properties of pristine polymers. However, most of the works done previously have neglected to comprehensively study the basic reinforcing mechanism of the composites, particular the interaction between nanoclay and surrounding matrix even though high tensile strength and modulus were obtained. In this paper, uniformly-dispersed nanoclay/epoxy composite samples, based on our tailor-made experiment setup were fabricated. A tensile property test was conducted to examine the mechanical properties of the samples with different nanoclay content. It was found that the Young’s modulus and tensile strength of a composite with 5 wt.% of nanoclay increased up to 34% and 25% respectively, as compared with a pristine sample. Images obtained from scanning electron microscopy (SEM) and results extracted from transmission electron microscope (TEM) proved that interlocking and bridging effects did exist in the composites. Nanoclay clusters with the diameter of 10 nm could enhance the mechanical interlocking inside the composites and thus, breaking up the crack propagation. The formation of boundaries between the nanoclay clusters and epoxy can refine the matrix grains and further improve the flexural strength of the composites.

Property enhancement of a carbon fiber/epoxy composite by using carbon nanotubes

Abstract: We investigated the effect of carbon nanotube (CNT) modifications on the flexural and wear behaviors of multiscale carbon/CNT/epoxy composites in this study. Carbon/epoxy woven composites and two types of multiscale carbon/CNT/epoxy composites were fabricated by incorporating woven-type carbon fibers into epoxy matrices modified with 2 wt% acid-treated and silane-treated multi-walled carbon nanotubes (MWCNTs). Three-point bending and ball-on-disk wear tests were performed on the three composites. The results showed that the flexural moduli and strengths of carbon/CNT/epoxy composites were greater than those of carbon/epoxy composites, regardless of CNT modification. Specifically, the flexural modulus and strength of the silane-treated specimens were 10% and 15% greater, respectively, than those of the acid-treated samples. The results also showed that the wear properties of carbon/epoxy composites are improved by the addition of CNTs. In addition, the wear properties of silane-treated samples were superior to those of acid-treated samples. Scanning electron microscopic examination of fractured and worn surfaces showed that the improvement in the flexural and wear properties of the silane-treated carbon/CNT/epoxy composites was attributed to the improved dispersion of CNTs in the epoxy and the better interfacial characteristics caused by the silanization of the CNTs.