Compressive Strength Of Composites Research Articles

Compressive behavior of steel spiral confined engineered cementitious composites in circular columns

Extensive research has been conducted on the uniaxial tensile and compressive behavior of engineered cementitious composites. Despite the high tensile ductility and high toughness of engineered cementitious composites, transverse steel reinforcement is still necessary for high-performance structural members made of engineered cementitious composites. However, very limited research has been concerned with the compressive behavior of steel-confined engineered cementitious composites. This article presents the results of axial compression tests on a series of circular engineered cementitious composite columns confined with steel spirals. The test variables included the engineered cementitious composite compressive strength, the spiral pitch, and the spiral yield stress. The test results show that steel-confined engineered cementitious composites in the test columns exhibited a very ductile behavior; the steel spiral confinement contributed effectively to the enhancement of both strength and ductility of engineered cementitious composites. The test results were then interpreted by comparing them with the predictions from some existing models. It was found that the existing models previously developed for confined concrete failed to predict the compressive strength of steel-confined engineered cementitious composites with sufficient accuracy. New fitting equations for the compressive properties of steel-confined engineered cementitious composites were then obtained on the basis of the test results of this study as well as those from an existing study.

Computational Micromechanics for the Optimization of Compression Strength of Unidirectional Carbon Fiber Composites for Use in Wind Turbine Blades

As wind turbine blades grow longer, new design parameters gain additional importance such as blade weight, tip deflection and material cost. These parameters require designers to relook at carbon fiber as a potential design solution. However, the composite materials in wind turbine blades are subjected to significant compressive loading, and the compressive strength of carbon fiber reinforced polymer (CFRP) composites is much lower than its tensile strength. This reduction in compression strength is due to a change in failure mode from that seen in tensile loading. The aim of this study is to investigate three factors that affect the compressive failure response of CFRP composites. These factors include fiber defect severity, volume fraction, and multiaxial loading.Compressive strength was shown to have decaying sensitivity with increasing fiber misalignment. Decreasing the volume fraction not only decreased the compressive strength but also increased the compressive failure strain. In addition, adding in-plane shear loads proved detrimental to the compressive load-carrying capacity of a composite structure. This research showed minimizing fiber misalignment in manufacturing processes is only beneficial for high tolerance processes. Decreasing volume fraction could be beneficial for highly flexible structures. Finally, the results demonstrated the need to minimize multiaxial loading for optimal composite compressive response.

Evaluation of commercial biochar in South Korea for environmental application and carbon sequestration

AbstractThe performance of commercial wood chip (WC) and biosolid (BS) biochars available in bulk from carbonization processes in South Korea was examined via determination of sorption capacity from batch experiments and evaluation of carbon sequestration using biochar–mortar composites according to construction and environmental properties. Compared with rice straw (RS) biochar synthesized in a laboratory, the sorption capacities of WC and BC biochars are determined by the types of contaminants, the properties of the biochar, and sorption mechanisms. BS and WC biochars are competitive as sorbents for nitro explosives and chlorinated phenols. Characterization of biochar–mortar composites showed that 3–5 wt% biochar inclusion did not significantly change the composites' engineering properties, including flowability, compressive strength, and thermal conductivity. As the biochar content increased in the biochar–mortar composites, the benzene and toluene concentrations in air were accordingly reduced, suggesting that biochar inclusion may be favorable to remove volatile toxic contaminants that cause sick building syndrome. The toxicity characteristics leaching procedure (TCLP) and Micotox® bioassay tests showed that biochar–mortar composites were not toxic. These results suggest that BS and WC biochars in South Korea are competitive as sorbents for some organic contaminants and that biochar–mortar composites may be environmentally friendly carbon‐sequestering construction materials.

Evaluation of the Mechanical Properties of Carbon Nanotube (CNT) Reinforced Aluminum (6061) Composites Using Closed Die Forging

In this study, the closed die forging of aluminium based compoistes reinfoced with CNTs (1vol% and 3vol%) were investigated. Initially, the composites were fabricated using high energy ball milling followed by compaction and sintering. The microstructural results showed that finer grain size and homogeneous dispersion of CNTs were obtained. Composites with up to 97% densification were produced when fine open porosities were removed by closed die forging. The results imply that the hardness and compressive strength of composites with 3vol.% of CNTs has improved without any deterioration. In addition, workability behaviors of composites were investigated by cold upsetting test. For that pore reopening test was performed to confirm the closure of micro-pores after the closed die forged, and to further analyze the densification of the composites. Typical cases, as the pores were not re-opened even after increasing the strain, additional forming is possible up to large deformations.

Mechanical Behavior and Fractography of Al2218 Nano B4C Metal Composites

In the present examination, the mechanical properties of Al2218-nano B4C composites displayed. The composites containing 4 to 8 wt. % of nano boron carbide in ventures of 4 wt.% were readied utilizing liquid metallurgy method through stir casting. For every composite, fortification particles were preheated to a temperature of 400˚C and afterward added in ventures of two into the vortex of liquid Al2218 compound to improve the wettability and dispersion. Microstructural examination was carried out by SEM and elemental investigation was finished by EDS. XRD Analysis used to recognize the B4C phases in the Al grid. Density, tensile, compression and hardness tests were done to distinguish various properties of composites. The aftereffects of this investigation uncovered that as the weight % level of nano B4C particles were expanded, there was noteworthy increment in hardness, UTS, yield and compression strength of Al2218 amalgam composites. Further, there was slight drop in the density and malleability of the Al2218 amalgam composites when contrasted with the base. Tensile fractured surfaces analysis was conducted by using SEM.

Microstructural, tribological and compression behaviour of Copper matrix reinforced with Graphite-SiC hybrid composites

Metal Matrix Composites (MMCs) are generating a wide and varied range of interest in the recently developed materials because of their high applicability in the industries. Copper matrix composites have rich properties like high thermal conductivity, high temperature resistance, high corrosion resistance and high weldability which makes them promising and demanding material for heat exchangers, electrical components and automoblies. Graphite and Silicon Carbide are the most economical reinforcements to improve the wear characteristics of pure copper. Present study concentrates on preparation of Copper-Graphite-Silicon Carbide hybrid metal matrix composite by stir casting technique. XRD analysis of composites show that there is no intermediate reaction occuring between copper and reinforcement particles. Micrographs of composites revealed the uniform distribution of reinforcement particles in copper matrix. A good interfacial bonding between Copper and Graphite-Silicon Carbide particles is found. Hardness of composites is tested by Vickers hardness tester and it is found that hardness of composites decreases with increase in graphite content. Wear tests were performed on Pin-on-Disc test rig. It is found that wear rate is decreasing with increase in reinforcement content. The maximum wear resistance is found at 8 wt% reinforcement content. Compressive strength of composites is tested using Universal testing machine and showed a decrease in value with increase in graphite content. It is spontaneously expected that present composite will be highly beneficial in structural and mechanical applications.

Mechanical, microstructural properties and wear characteristics of hybrid aluminium matrix nano composites (HAMNCs) – review

This review article is on hybrid nano composite material and its mechanical, microstructural and tribological behavior of aluminum alloy. The aluminum alloys are commonly used as substitute materials for aerospace, automobile and structural applications because of its high strength to weight ratio and high wear resistance. The fabrication of hybrid aluminum nano composites were developed by applying stir casting techniques. The combination of proper reinforcement on Hybrid aluminum nano composite materials plays an vital role in enhancing its mechanical, microstructural and tribological properties. The results were obtained by the past literature survey reveals that the mechanical properties were improved by increasing the percentage of nanoparticles in base alloy such properties are ultimate tensile strength, compression strength, impact strength, hardness and fracture toughness of hybrid nano composites. The analysis on microstructural properties of hybrid nano composite shows that the homogeneous dispersion of reinforcements are uniformly distributed in a base alloy and provides a strong bonding between the reinforcements and base alloy. The tribological properties of the hybrid nano composite results show that the wear resistance and coefficient friction improved compared with a base alloy.

Physical, mechanical and thermal properties of lightweight insulating mortar with recycled Etna volcanic aggregates

The study concerns the reuse of pyroclastic products generated by volcano Etna eruptions for the production of lightweight insulating mortar. Fourteen mixtures, grouped into three families, with three types of natural binder were designed. The first family (CEM) contains Portland cement and calcium hydroxide, the second Natural Hydraulic Lime (NHL), the third (POZZ) combines pozzolanic sand and calcium hydroxide, to form a cementitious compound. The effect of the presence of an Air Entraining Agent (AEA), added in three different ratio with respect to the dry mixture (0.02%, 0.05% 0.1%) to increase the porosity, was investigated. In the mixtures containing the 0.1% of AEA, a breathable resin in the ratio 0.1% of the binder was added, to compensate for the degradation of the mechanical strength due to the AEA. On the basis of the mechanical and physical properties of the composites (flexural and compressive strength, density, porosity, water absorption) and of the thermal conductivity, always within the range of 0.154–0.266 W/mK, the mixtures suitable for lightweight and thermal mortar are identified. The correlation between density and porosity and between thermal conductivity and pososity is discussed. A numerical simulation, based on a numerical homogenization technique at the mesoscale, is used to show how the thermal properties of the constituents of the mixture influence the equivalent thermal conductivity of the composite.

Graphene/barium titanate/polymethyl methacrylate bio-piezoelectric composites for biomedical application

The introduction of BaTiO3 (BT) particles into biomaterials, such as polymethyl methacrylate (PMMA) bone cement, is among the effective ways to improve their osteoinductivity. However, excessive addition leads to mechanical degradation. An important problem to solve is the manner by which piezoelectric properties matching human bones can be obtained under the premise of sufficient mechanical properties. The piezoelectric effect is obtained by adding BT particles into PMMA bone cement. The piezoelectric coefficient close to the human bone is obtained at a relatively low BT addition amount by adding graphene on this basis. High mechanical properties can also be obtained. Graphene increases the piezoelectric coefficient by increasing the conductivity, dielectric constant, and effective polarization voltage of graphene (G)/BT(BaTiO3)/PMMA bio-piezoelectric composites. The compression strength of the aforementioned composites increases from 83.5 MPa to 89.5 MPa after the addition of 0.5 vol% graphene, and the requirements of bone implant materials were met. G/BT/PMMA bio-piezoelectric composites have no cytotoxicity, and graphene can also promote cell adhesion and proliferation on the composite's surface. The polarized bio-piezoelectric composites can improve cell morphology and promote cell proliferation. The number of cells increases with increasing piezoelectric coefficient. The composite has potential application prospects in various fields, such as oral cavity and bone implant.

Investigation on mechanical properties of hybrid graphene and beryl reinforced aluminum 7075 composites

The emerging technologies and trends of present generation requires downsizing the unwieldy structures to light weight structures on one hand and integration of varied properties on other hand to meet the application demands. In the present investigation an attempt is made to familiarize and best possibilities of reinforcing agent in aluminum 7075 matrix with naturally occurring beryl (Be) and graphene (Gr) to develop a new hybrid composite material. A stir casting process was used to fabricate with fixed volume fraction of 6wt% weight beryl and various volume fractions of 0.5wt%, 1wt%, 1.5wt% and 2wt% of graphene. The properties such as tensile strength, compression strength, and hardness of hybrid composites were examined. The crystallite size and morphology of the graphene and beryl particles were analyzed with X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. It was observed that ultimate tensile strength and compression strength of the hybrid composite increased with increasing reinforcement volume fraction as compared to specimen without reinforcement additions.

Regulating Cu(II)-benzimidazole coordination structure in rigid-rod aramid fiber and its composites enhancement effects

Coordination crosslinking, as the kind of strongest supramolecular interaction, has been widely introduced into flexible polymer chains, including rubbers and aerogels, while that in rigid-rod polymer is much rare, due to the difficulty in rigid-rod macromolecules' configuration change. Moreover, the exact coordination structure inside those polymers is not clear. Herein, this coordination interaction was incorporated into a traditional rigid-rod polymer, aramid fiber, by Cu2+-benzimidazole coordination reaction, through the careful control of the dynamic reaction conditions, and the structural/performance relationships of fiber and its composites are detailed studied. It is seen that two different coordination structures, S-coordination style (Cu2+ coordination with single benzimidazole unit) and M-coordination style (Cu2+ coordination with multiple benzimidazole units from different macromolecular chains), could be both obtained inside fiber, using different solvents as the reaction medium. Moreover, using reaction kinetics equilibrium, we presented a mathematical method to investigate those two coordination structures in detail, including their average coordination numbers of Cu2+ and reaction equilibrium constant (K). Further, the experimental results show that the fiber with average coordination number of 2 exhibits a comprehensive improved performance in heat/solvent resistance, fluorescence emission as well as fiber's transverse properties, with the corresponding increase of 54.2% and 47.1% for its composites interfacial properties and compressive strength, compared with untreated fiber.

Injectable Porous Bioresorbable Composite Containing Fluvastatin for Bone Augmentation.

The purpose of this study was to evaluate the effects of an injectable composite made up of calcium sulfate (CAS), fluvastatin (FS), and atelocollagen on bone augmentation in rats. Porous structures and compressive strength of composites were evaluated. The cumulative release kinetics of FS were determined in vitro by a spectrophotometer. To observe bone regeneration in vivo, five different materials (normal saline; atelocollagen gel only; composite of CAS and atelocollagen; composite containing 0.5% FS; and composite containing 1.0% FS) were injected in extraction sockets and in the crania of rats. Microcomputed tomography and histological evaluation were performed after 2, 4, and 8 weeks of healing time. The composites had high porosity (greater than 55%). FS kept a slow and stable release for >30 days. In vivo results demonstrated that more new bone was formed in the FS groups compared with the other groups, and both bone mass and bone density had prominent increase in maxillae and crania. Resorption of the composite was also observed for cranial tissues. In conclusion, this composite can be applied percutaneously, without any incision. It has excellent properties with replaceability into bone and anabolic effects for bone formation, as well as a drug delivery system for bone formation.

Effect of CNT on microstructure, dry sliding wear and compressive mechanical properties of AZ61 magnesium alloy

Carbon nanotubes (CNTs) reinforced AZ61 magnesium alloy was successfully fabricated through stir casting method with the concentration of (0, 0.1, 0.5, 1) wt.% CNTs followed by age heat treatments. The influence of the CNTs concentration on compressive mechanical properties, dry sliding wear behavior and microstructure of synthesized composites have been investigated using compression test, hardness, block on wear apparatus, scanning electron microscope and X-ray diffraction (XRD) respectively. The comparative study of as-cast and aged CNTs/AZ61 composites have been analyzed. The experimental results reveal that the addition of CNTs content in AZ61 magnesium alloy causes the decrease in mass wear loss and coefficient of friction, improves grain refinement and compressive strength. Three dominant wear mechanism (i.e. abrasion, oxidation, and delamination) have been observed. The compression strength of composites increases with the increase in CNTs contents for both aged and as-cast composite. The addition of CNTs contents has very small effects on fracture strain of as-cast composites and aging has remarkable effects to increase fracture strain which increases up to 0.5wt%CNTs/AZ61 and then decrease for 1wt%CNTs/AZ61. Evaluation of microstructure revealed that CNTs have grain refining eligibility and cause the diffusion of secondary phases to improve the strength. The diffusion of phases in aged CNTs/AZ61 composites causes the formation of shallow cavities at grain boundaries.Results analysis indicated that aged-CNTs/AZ61 composites exhibit enhanced wear and mechanical properties with load-bearing capacity, grain refinement and modification at grain boundaries than as-cast composites.

Hydroxyapatite-Collagen Composite Made from Coral and Chicken Claws for Bone Implant Application

Synthesis of porous hydroxyapatite-collagen composites for bone implant applications has been carried out. Hydroxyapatite synthesized from coral by the precipitation method, while Collagen synthesized from chicken claws. Collagen formation was carried out by freeze-dry technique with variations in freezing time of 2, 4 and 6 hours at -80 ° C. The next process was by drying in a lyophilizer. Characterization of samples was carried out using Fourier Transform Infra Red (FTIR), Scanning Electron Microscopy (SEM), compressive strength test and cytotoxicity test with Microtetrazolium (MTT) assay. FTIR results proved that collagen uptake and hydroxyapatite combine chemically. This is indicated by the absorption of functional groups that did not coincide between collagen and hydroxyapatite functional groups with composites. SEM observations showed that the largest pore size was obtained at freezing for 2 hours which was 774 μm and the smallest in freezing for 6 hours was 640 μm. This pore size was an important parameter of the bone implant because it played a role in the osteoinductive process. The composite compressive strength test results for freezing 2 hours, 4 hours and 6 hours respectively was 737 KPa, 842 KPa and 707.7 KPa. The results of the cytotoxicity test with MTT showed the percentage of cell viability above 100%. This means that the Hydroxyapatite-collagen composite is non-toxic. So, the sample formed has qualified as a bone implant candidate.

Constructing a weaving structure for aramid fiber by carbon nanotube-based network to simultaneously improve composites interfacial properties and compressive properties

Compared with carbon fiber, aramid fiber exhibits weak performance in its transverse direction, and it is the bottleneck problem for its further application. To address the problem, a new weaving strategy is proposed by incorporating carbon nanotube (CNT)-based network inside bulk fiber to bundle the extended macromolecules together. Firstly, this unique three dimensional CNT-based network (CNT-NT) was synthesized and incorporated into bulk fiber by solution blending. Then, the influences of CNT-NT on fibers' axial and transverse performance are evaluated. The results of macromolecules' axial orientation suggest that the macromolecules could easily penetrate into this three dimensional network (CNT-NT), forming a weaving structure, and this further hinders the movement of macromolecules and decrease its orientation in axial direction. More importantly, fiber transverse performance is greatly improved by this weaving structure, mainly due to (1) the improvement of skin/core connection and (2) the restraining of nanofibrils' relative sliding. It is found that the composites interfacial failure mode changes from fiber's skin/core destruction to fiber/resin debonding, and the composite interfacial properties and fiber’ compressive strength are correspondingly increased by 131% and 82%. Unlike traditional “increasing the macromolecules interaction” strategy, it is believed this new weaving strategy integrates the advantage of easy production, cost-effective as well as simultaneously improving fiber's composite interfacial properties and compressive strength, and can be employed as valuable guidance for the design and manufacture of other high performance organic fibers.

Improving compressive strength of high modulus carbon-fiber reinforced polymeric composites through fiber hybridization

There has been a strong demand in using high-modulus (HM) carbon-fiber composites potentially enabling lightweight aircraft structures with significant weight savings. However, extremely low fiber-direction compressive strength has been a well-recognized weakness of the HM composites, prohibiting their implementation in aircraft platforms. Hybridizing fibers with varying moduli provides an innovative means for improving the fiber-direction compressive strength of composites. This has been implemented by comingling intermediate-modulus (IM) and high-modulus (HM) carbon fibers in HM carbon fiber-reinforced polymer (CFRP) toughened with nano-silica. Comingling IM and HM fibers at the filament level in addition to the matrix nano-sized structural reinforcement throughout the composite, increases shear modulus to axial modulus ratio of the composite material, thus improving microstructural stability likely governing the fiber-direction compressive strength behavior. The basis for this new material design stems from the fact that fiber-direction compressive strength increases with the shear modulus to axial modulus ratio of composites across different fiber and resin combinations. The results demonstrate that the new hybrid HM composite fiber-direction compressive strength achieves that of IM legacy composites but with more than 30% higher axial modulus.

A porous collagen-carboxymethyl cellulose/hydroxyapatite composite for bone tissue engineering by bi-molecular template method

Inspired by the mechanism of bone formation, a porous collagen-carboxymethyl cellulose/hydroxyapatite (Col-CMC/HA) composite was designed and fabricated using a biomimetic template of Col and CMC protein-polysaccharide bi-molecules. The morphology, composition and physical properties of Col-CMC/HA composites were characterized systematically. It was found that the nano-HA homogenously distributed on the surface of Col-CMC bi-templates while the composite presented 3D porous structure with pore size from 100 μm to 300 μm. The porosities of composites were located at the range of 71%–85%. Besides, the compressive strength of composites was highly depended on the ratio of Col to CMC in the organic template. The optimized composite in respect to physical properties showed a compressive strength as high as 7.06 MPa, quite close to that of natural bone. The high relative growth rate of wild-type mouse embryonic fibroblasts cells was found for the composite, indicating a good biocompatibility. The organic-inorganic composite also behaved good in collagenase resistance and could be biodegraded in 8 weeks, with about 50% of initial weight left at the ratio of Col to CMC of 1:9. The results demonstrated that the Col-CMC/HA composite by bi-molecular template method was a rational and safe method to prepare biomaterials with tunable properties.

Effect of MWCNT Content on the Structure and Properties of Spark Plasma-Sintered Iron-MWCNT Composites Synthesized by High-Energy Ball Milling

The effect of multiwall carbon nanotube (MWCNT) content on the physical and mechanical properties of Fe-MWCNT composites has been studied. High-energy ball milling (HEBM) is employed to produce the composite powder; following this, spark plasma sintering (SPS) process has been adopted for powder consolidation. The composite powder and the sintered products were subjected to structural characterization by XRD. Microstructural studies were carried out by optical, field-emission scanning and high-resolution transmission electron microscopy. While Fourier transform infrared spectroscopic study of composites was done to understand the bonding characteristics, Raman spectroscopy was employed to assess the structural damage of MWCNT after HEBM. The effects of processing on the behavior of C-C, C-O and Fe-O bonds are studied by x-ray photoelectron spectroscopy. Microhardness and compressive strength of composites are also determined. Finally, magnetic and electrical properties of the composites were characterized. It was observed that optimized ball milling conditions help to preserve the structural identity of MWCNT. Consolidation by SPS insured good interfacial bonding. The microhardness and compression strength are significantly improved in MWCNT-reinforced iron matrix composite. MWCNT has appreciably improved the electrical conductivity of the composites. Tethering of MWCNT by iron oxide has led to appreciable improvement in saturation magnetization till 3 wt.% MWCNT.

Preparation and properties of graphene/carbon nanotube hybrid reinforced mortar composites

The successful application of multi-wall carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) in mortar composites depends on their dispersion properties. In this study, MWCNTs and GNPs were modified by the surfactant polycarboxylate ether (PC). One-dimensional MWCNTs and two-dimensional GNPs led to the MWCNTs forming a bridge between adjacent GNP sheets, effectively avoiding restacking of GNPs and agglomeration of MWCNTs, which resulted in greater dispersion. An excellent synergetic effect was generated between MWCNTs and GNPs, enhancing various physical and chemical properties. Hybrid GNP/MWCNT structures improved the mechanical properties of mortar composites (compressive strength and tensile strength) and volume stability (drying shrinkage). Scanning electron microscope images clearly showed that hybrid GNPs/MWCNTs were compatible for use in mortar composites. The hybrid weight ratio of GN11-PC (GNPs:MWCNTs = 1 : 1) led to optimal compressive strength, greater than that obtained upon addition of GNPs or MWCNTs individually. The compressive strength of the mortar composites containing 0·05 wt% GN11-PC (by weight of cement) aged for 28 d increased by 61% in comparison with the blank sample, and the tensile strength increased by 47·1%, while shrinkage decreased by 6·9%.

Fabrication and characterization of an engineered cementitious composite with enhanced fire resistance performance

This study evaluated the fire resistance of a lightweight engineered cementitious composite under elevated temperature up to 900 °C. To achieve lightweight, waste recycled hollow glass microspheres, which comprise 45% of waste glass were obtained as an ultra-high-performance lightweight filler. And carbon nanofibre was added to maintain the mechanical properties of engineered cementitious composite while reducing the weight. This study aims to thoroughly understand the effect of hollow glass microsphere, carbon nanofibre, and their combination to the fire resistance of engineered cementitious composite. Three different types of hollow glass microspheres and four different types of carbon nanofibers were conducted in this research. The results showed that engineered cementitious composite contains both hollow glass microsphere and carbon nanofibre presented high fire resistance, which is able to remain 50% of original strength when exposed to high temperature at 900 °C. The compressive strength of composite was found to be slightly influenced with using hollow glass microsphere, although the total densities were reduced. Carbon nanofibre contribute to the composite’s strength of both normal and lightweight engineered cementitious composite and it is able to enhance mechanical performance when the samples are under elevated temperatures. Microscopy study found that carbon nanofibre contribute to the composite rehydration at high temperature. The work provides a promising way to develop lightweight engineered cementitious composite with high mechanical performance and fire resistance, and proved the possibility of partially replacing cementitious material with hollow glass microsphere.