Mechanical Performance Of Composites Research Articles

Enhanced mechanical properties of short carbon fiber reinforced polyethersulfone composites by graphene oxide coating

Polyethersulphone (PES) is an important special engineering plastic. In order to broaden its applications in automobile and sports fields etc., its mechanical properties have to be enhanced. This paper reports the effectively enhanced tensile and flexural properties of injection molded graphene oxide (GO)-coated short carbon fiber reinforced PES composites by GO coating. The GO content varies in a range of 0.0–1.0 wt%. First, the GO is employed as surface sizing agent to treat short carbon fibers (SCFs) by a facile physical absorption method. The GO-coated SCF/PES composites are extruded into pellets and then injection molded into tensile and flexural samples. It is shown that the GO coating on SCF surface leads to an obviously enhanced SCF/PES interfacial adhesion. As a result, both the tensile and flexural strengths are effectively enhanced by the GO coating on the SCF surfaces. The tensile and flexural moduli are also increased by the GO coating due to the excellent elastic modulus of GO. The optimal GO content is found to be 0.5 wt% for effectively improving the overall composite mechanical performance.

Residual thermal stresses in carbon/carbon–Zr–Ti–C composites and their effects on the fracture behavior of composites with different preforms

Carbon/carbon(C/C)–Zr–Ti–C composites were fabricated using chemical vapor infiltration and liquid metal infiltration processes. The residual thermal stress (RTS) distribution in the C/C–Zr–Ti–C composites was analyzed by Raman spectroscopy and finite element (FE) calculation. The mechanical behaviors of C/C–Zr–Ti–C composites with three types of carbon fiber preforms were tested. The results showed that there was very high compressive RTS in the fibers and high tensile RTS in the pyrocarbon (PyC) in the marginal region near the carbide. However, in the central region away from the carbide, relatively low compressive stress and tensile RTS were found in the fibers and PyC, respectively. The FE analysis showed that the introduction of carbide into the C/C composites caused a significant increase of the RTS in the PyC near the carbide, indicating that the carbide could change the RTS distribution in C/C composites. Moreover, the distribution of the RTS and its release combined with the carbide distribution and fiber architecture led to variations in the mechanical performance of composites with different preforms.

Mechanical and thermal investigation of thermoplastic nanocomposite films fabricated using micro- and nano-sized fillers from recycled cotton T-shirts

The thermal and mechanical performance of composites with nano-sized cotton fillers embedded in low-density polyethylene (LDPE) is investigated. Microfibrillated cotton was prepared by microgrinding mechanical treatment of pulverized cotton (pCot) derived from waste T-shirts, resulting in nano-sized fibrils of the cellulose that retain high crystallinity. Film composites of LDPE with pCot before and after microgrinding were fabricated through melt extrusion and the effect of filler size on mechanical, thermal and morphological properties of the composite was investigated. Compounding microfibrillated cotton with LDPE resulted in well-dispersed nanocomposites with no discoloration after 10 min of melt extrusion at 170 °C. At concentrations up to 10 % by weight, the composites showed increased modulus, increased tensile strength and a slight decrease in elongation to break. Further improvement in the dispersion and mechanical properties of the cotton-based fillers was realized by the use of LDPE powder instead of polymer pellets fed to the extruder. This research demonstrates the processing and applicability of the use of recycled cotton-based nano-sized fillers in melt-processing.

Polymer powder processing of cryomilled polycaprolactone for solvent-free generation of homogeneous bioactive tissue engineering scaffolds.

Synthetic polymers used in tissue engineering require functionalization with bioactive molecules to elicit specific physiological reactions. These additives must be homogeneously dispersed in order to achieve enhanced composite mechanical performance and uniform cellular response. This work demonstrates the use of a solvent-free powder processing technique to form osteoinductive scaffolds from cryomilled polycaprolactone (PCL) and tricalcium phosphate (TCP). Cryomilling is performed to achieve micrometer-sized distribution of PCL and reduce melt viscosity, thus improving TCP distribution and improving structural integrity. A breakthrough is achieved in the successful fabrication of 70 weight percentage of TCP into a continuous film structure. Following compaction and melting, PCL/TCP composite scaffolds are found to display uniform distribution of TCP throughout the PCL matrix regardless of composition. Homogeneous spatial distribution is also achieved in fabricated 3D scaffolds. When seeded onto powder-processed PCL/TCP films, mesenchymal stem cells are found to undergo robust and uniform osteogenic differentiation, indicating the potential application of this approach to biofunctionalize scaffolds for tissue engineering applications.

Mechanical properties of cermet composites with various geometrical tortuosity of metal phase: Fractal characterization

Although the mechanical properties of cermet composites have been investigated extensively, how to quantitatively determine the relationship between the performances and the geometrical structures of the reinforcement phase is still one of the top challenging problems yet to be solved. To determine the influence of the geometrical structure of the reinforcement phase on the mechanical performances of composites, Cu2O/Cu cermets were prepared with spherical or branch like Cu by the hot-pressing technology. Box-counting fractal dimension increasing rate with increasing filling content of reinforcement phase was first applied to quantitatively reflect the relationship between the geometrical structures of metal phase and the mechanical properties of composites. A simple model was developed by combining fractal theory and power law, in which the critical exponents were determined via experimental results. This study not only provides a pathway to understand the mechanisms of the geometrical structure of the reinforcement phase to the mechanical properties of composites, but also sheds light on the geometrical tortuosity characterization by using fractal approach in cermet composites.

Triticale straw and its thermoplastic biocomposites

AbstractThe potential of triticale straw for the production of green composites based on polypropylene (PP) was evaluated. The composites were prepared by melt compounding of PP and chopped triticale straw (so-called triticale particles) using different formulations and triticale concentrations. The morphology and crystallization of the PP triticale composites were characterized by means of various techniques, including optical microscopy (OM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The composite mechanical performance was also evaluated. The results obtained demonstrate that, by simply adding triticale particles into PP, they play the role of a conventional filler that increases the modulus while reduces the strength. However, the developed formulation with the combination of coupling agent and reactive additive provides superior strength and modulus for the composites; thus, it can upgrade the triticale particles from filler to reinforcement category.

Non-isothermal forming of glass fiber/polypropylene commingled yarn fabric composites

The commingled glass fiber/polypropylene (GF/PP) composites were fabricated using a double-belt press and the influence of temperature and velocity on the consolidation quality and mechanical performance of the composites were investigated. The contents and distribution of the voids in the composites were changed with varying the level of the processing parameters, and the composite tensile and flexural properties were dramatically decreased when the void contents were beyond 3.6%. Reducing the viscosity of the matrix or increasing the uniformity of fibers in the commingled yarns was important to improve the consolidation quality. But the production efficiency was not improved as hoped by increasing the velocity at higher temperatures because of the weakened interfacial bonding. The crystal form and crystallinity degree had no obvious changes under different processing conditions, but the composite mechanical performance was enhanced when the degree of order in the crystal structures was decreased, which might be caused by more effective stress transferring or less initial cracks.

Natural composites: cellulose fibres and the related performance of composites

Bio-based materials are becoming of increasing interest as potential structural materials for the future. A useful concept in this context is the fibre reinforcement of materials by stiff and strong fibres. The bio-based resources can contribute with cellulose fibres and biopolymers. This offers the potential for stiff and strong biocomposite materials, but these have some limitations and obstacles to full performance. The focus will be on the ultra-structure, and the strength and stiffness of cellulose fibres, on the (unavoidable) defects causing large reductions in strength and moderate reductions in stiffness, on the packing ability of cellulose fibres and the related maximum fibre volume fraction in composites, on the moisture sorption of cellulose fibres and the related mass increase and (large) hygral strains induced, and on the mechanical performance of composites.

From Ordered to Disordered: The Effect ofMicrostructure on Composite Mechanical Performance

From Ordered to Disordered: The Effect ofMicrostructure on Composite Mechanical Performance

Effects of fibre-surface morphology on the mechanical properties of Porifera-inspired rubber-matrix composites

In this paper, mineralised organic fibre morphologies, inspired by the structures of Porifera (sponges) are correlated to the mechanical performance of fibre reinforced rubbers. The mineralised structures are rich in calcium carbonate and silica. These compounds nucleate and precipitate on the fibre surfaces yielding different morphologies as a function of mineral ion concentrations. Smaller mineralised precipitates manifestly improve the mechanical performance of composites while thicker precipitates enveloping the fibres give rise to inferior properties. Mechanisms and evidenced reasoning for these differences are reported herein.

Interplay of colloidal stability of cellulose nanocrystals and their dispersibility in cellulose acetate butyrate matrix

Cellulose nanocrystals (CNC) prepared from eucalyptus cellulose CNCs were modified by the reaction with methyl adipoyl chloride, CNCm, or with a mixture of acetic and sulfuric acid, CNCa. The CNC were either dispersed at 0.1 wt% in the pure solvents ethyl acetate (EA), tetrahydrofuran (THF) and dimethylformamide (DMF) or in cellulose acetate butyrate (CAB) solutions prepared in these solvents at 0.9 wt%. The colloidal behavior of these dispersions was systematically investigated using a phase separation analyzer LUMiReader®. The mechanical properties and morphological features of the films resulting from the mixtures of CAB and CNC were determined by dynamic mechanical analysis, optical microscopy and atomic force microscopy, respectively. Regardless the functional group attached to the surface of CNC, the best colloidal stability was observed for dispersions prepared in CAB/DMF solution. Higher degree of substitution of modified CNCs favored the colloidal stability in EA and THF. Composite films prepared from CAB/DMF solutions were more homogeneous and presented better mechanical performance than those prepared in CAB/EA or CAB/THF. The mechanical performance of composites and neat CAB prepared from DMF was CAB/CNCs > CAB/CNCm > CAB/CNCa > CAB, indicating that the modification weakens the percolation process, which is mediated by H bonding.

Direct measurements of non-ionic attraction and nanoscaled lubrication in biomimetic composites from nanofibrillated cellulose and modified carboxymethylated cellulose

There is a growing interest to design biomimetic self-assembled composite films from renewable resources aimed at a combination of high toughness, strength and stiffness. However, the relationship between interfacial interactions of the components and the mechanical performance of the composite is still poorly understood. In this work we present evidence of the link between mechanical performance of carbohydrate-based composites with nanolubrication and with direct surface forces between the hard and soft domain in the system. Our approach was to use nanofibrillated cellulose (NFC) as the major reinforcing domain and to modify it by adsorption of a small amount of soft polyethylene glycol grafted carboxymethyl cellulose (CMC-g-PEG). The effect of the soft polymer on direct normal and friction forces in air between cellulose surfaces was evaluated using colloidal probe microscopy. The fibrillar structure of the NFC thin film affected the frictional behaviour; when decreasing load, the friction between pure cellulose surfaces increased, suggesting partial pull-out of fibrils, a phenomenon not observed for non-fibrillar cellulose substrates. Adsorption of CMC-g-PEG on both surfaces decreased the friction considerably but adhesion was still high. The symmetric system, having both cellulose substrates covered with the polymer, was compared to asymmetric systems where only one surface was covered with the polymer. Furthermore, a free standing composite film was prepared by non-ionic self-assembly of NFC and CMC-g-PEG with 99 : 1 weight-ratio; the mechanical properties of the macroscopic films were related to the nanoscaled interactions between the components. The composition studied showed excellent mechanical properties which do not follow the simple rule of mixture. Thus, a synergy in the direct surface forces and mechanical properties was found. This approach offers a robust path to aid in the efficient design of next generation biomimetic composites.

Experiment Study on Static Mechanical Behavior of Plain Steel Plate-Light Weight Concrete Hollow Composite Decks

Steel plate-light weight concrete hollow composite deck was a type of novel composite deck which composed of steel plate, perforbond ribs connectors (PBL connectors) and light weight concrete and steel pipe. In order to understand the hollow composite decks mechanical performance, Static experiments of five specimens of this hollow composite slabs were conducted, among which two specimens were composed with longitudinal steel pipes and three specimens were composed with transversal steel pipe, with the aim to study the difference of the mechanical behaviors of the composite decks at the two orthogonal directions. Based on the experiment results, the effects of the direction of steel pips and the nominal shear-span of the slabs on the composite decks mechanical performance were especially studied. During the experiment process, the failure modes, strains of concrete and steel plate, cracking type, slippage of interface and the bearing capacity of the decks were studied in detail. From the experimental study, it could be found that there were no slippage between the steel plate and concrete were measured at the composite bridge decks, and the composite bridge decks showed high flexural rigidity, good ductility as well as better bearing capacity with the strength of bottom steel plate and top concrete both fully utilized. Therefore, it could be concluded that this type of composite bridge decks have good advantages at mechanical behaviors.

An investigation of glass–fiber reinforced polyamide 66 during conditioning in various automotive fluids

AbstractInjection molded glass–fiber reinforced polyamide 66 composites and unreinforced polymer samples have been characterized during conditioning up to 900 h in water, ethylene glycol, and water–glycol mixture at 50 and 70°C. All materials showed significant fluid and temperature‐dependent weight and volume increase. Glass reinforcement significantly reduced the polymer fluid uptake. The absorption of the antifreeze mixture initially follows a simple rule of mixtures of the absorption of the two individual components. However, after absorption of ∼5% a significantly higher than predicted level of antifreeze absorption was observed. This coincided with a significant increase in the volumetric swelling coefficient. Dynamic mechanical analysis and unnotched impact testing indicated significant changes in composite mechanical performance dependent on conditioning fluid and temperature. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Improved interfacial bonding of PVC/wood-flour composites by lignin amine modification

Soda lignin was divided into two fractions with different molecular weights by methanol extraction. Lignin amine was synthesized from the low-molecular-weight lignin fraction via Mannich reaction and was used for interfacial modification of poly-(vinylchloride) (PVC)/wood-flour composites. The PVC/wood-flour composites were prepared from surface-treated wood flour and PVC by melt compounding. The lignin amine treatment provided almost equivalent improvement in mechanical performances of composites as aminosilane treatment does. The tensile and impact strengths of composites prepared from 30phr of wood flour treated with 2wt% lignin amine were increased by 21.0% and 43.9%, respectively, compared to those prepared from untreated wood flour. Furthermore, lignin amine treatment could also significantly reduce the water absorption of composites. A significant increase in storage modulus (E’) was observed upon incorporation of wood flour with lignin amine treatment. The improved dispersion of wood flour in polymer matrix was observed by SEM images when the wood flour was treated by lignin amine. The experimental data indicate that the polymer-wood interfacial combination is strengthened.

The hornification of vegetable fibers to improve the durability of cement mortar composites

Abstract The use of vegetable fibers to reinforce a cement-based matrix has its weakest point in terms of durability. The alkalinity of the matrix and the volumetric instability of the fibers are the main causes of the loss of resistance of vegetable fiber-reinforced cement mortar composites. The aim of this study was to determine the effects of the previous hornification of the vegetable fibers on the mechanical performance and durability of softwood kraft pulp and cotton linters cement mortar composites. For this purpose, composites containing 4 wt.% of the hornificated fibers and the untreated ones were prepared with both fiber types. The mechanical performance of these composites was tested after 28 days of cure treatment and after aging with four wet–dry cycles. Results indicated that the previous treatment of fibers had beneficial effects on the mechanical performance and durability of the resulting cementitious composites.

Computationally optimized formulation for the simulation of composite materials and delamination failures

The numerical simulation of complex failure modes of composite materials, such as delamination, can be computationally very demanding, as it requires special elements and/or numerical strategies to characterize damage onset and propagation. This work presents several formulations developed to optimize the computational performance of an explicit finite element code designed specifically for the simulation of large scale composite structures. The composite mechanical performance is obtained with the matrix-reinforced mixing theory, a simplified version of the serial/parallel mixing theory that does not require an iterative procedure or the calculation of the tangent stiffness matrix. The number of elements required to perform the simulation is reduced by stacking several layers inside a single finite element. This work also proposes a modification of the isotropic damage law, capable of taking into account the residual strength provided by friction in type II fracture modes. The ability of these formulations to successfully predict the mechanical performance of composite materials is assessed with the ply drop-off test. In this test a laminate with a change of thickness in its mid-span is loaded until it breaks due to a delamination process. The formulation proposed obtains a very accurate prediction of the experimental response of the test, as it provides a very good characterization of the initial laminate stiffness, the delamination onset, and its propagation along the specimen.

Mechanical performance of oil palm empty fruit bunches/jute fibres reinforced epoxy hybrid composites

Oil palm empty fruit bunches (EFB)/jute fibre reinforced epoxy hybrid composites with different sequence of fibre mat arrangement such as EFB/jute/EFB and jute/EFB/jute were fabricated by hand lay-up method. The effect of layering patterns on the mechanical performance of the composites was studied. The hybrid composites are intended for engineering applications as an alternative to synthetic fibre composites. Mechanical performance of hybrid composites were evaluated and compared with the pure EFB, pure jute composites and neat epoxy using flexural and impact testing. The flexural properties of hybrid composite is higher than that of pure EFB composite with respect to the weight fraction of fibre, where as the impact strength of pure EFB composite is much higher than those of hybrid composites. The flexural results were interpreted using sandwich theory. The fracture surface morphology of the impact testing samples of the hybrid composites was performed by scanning electron microscopy (SEM).

Shape and size effects of ceria nanoparticles on the impact strength of ceria/epoxy resin composites

Ceria nanoparticles with various shapes (rods, cubes, and plates) and sizes were controllably synthesized and then introduced into epoxy resin. Subsequently, we investigated correlations between the shape and size of ceria nanostructures and the mechanical performance of composites. The samples were characterized by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. Compared with commercial ceria filled composites, the composites made with morphology-controlled ceria nanostructures show a higher impact strength. It is found that epoxy resins made with high-aspect-ratio ceria nanorods show the highest impact strength, up to 17.27 kJ/m 2, which is about four times that of the neat epoxy resin.

Computational Analysis of the Structural Integrity of Self-Healing Composites

This paper presents a computational and experimental investigation of the influence of self-healing micro-vessels on the structural properties of laminated composites. Embedded self-healing system is rapidly emerging as an important technology for improving the damage resistance of laminated composites. Introduction of hollow fibres or hollow spheres can, however, potentially weaken the structure and lead to excessive reduction in mechanical performance of composites. In this research, computational simulation is carried out to investigate the effect of embedded microvascular vessels on the mechanical properties of self-healing composite, focusing on the stress concentrations around self-healing vessels and delamination cracking.