Strength Improvement Of Composites Research Articles

Preparation and properties of copper matrix composites synergistically strengthened by Al2O3 and CPD

The development of copper-based composite materials is increasingly requiring both high electrical conductivity and better mechanical properties. In this paper, a novel copper-based composite was prepared by combining carbonized polymer dot (CPD) with flake copper powder (BMCu) and Al2O3 with molecular-level copper powder (MLCu). The composite obtained good mechanical properties with the yield strength of 157.00 MPa and the tensile strength of 366.14 MPa, which are increased by 17.4% and 25.1% compared with those of pure copper matrix (133.76 MPa and 292.72 MPa). The hardness of the composite is 124.7 HV, 27.4% higher than that of pure copper (97.9 HV), and the conductivity is 93.15% IACS. Besides, the strengthening mechanism of tensile property is also discussed, and the improvement of composite strength is mainly due to the dislocation strengthening. This study provides a new idea for the preparation of copper-based composite materials with high electrical conductivity and mechanical properties.

Effect of SiC particulates as secondary reinforcement on mechanical characteristics of epoxy composites with treated Luffa Cylindrica fibres

Abstract Epoxy composites with natural fibres reinforcement are of considerable research interest as they find some important applications replacing metals. Luffa Cylindrica fibres enhance the strength and strength is further improved on treating the fibres. A strength of 6.7 MPa is noticed for optimal treatment of 6 h with 10% NaOH. Inducing Silicon Carbide particulates also results in strength improvement of composites. Addition of 1.5 wt% to 7 wt% SiC has evidenced strength improvement in tension, flexure and impact. As a secondary reinforcement, 3.5 wt% of SiC is found to be appropriate from view point of strengths in impact, tension and flexure of Epoxy composites with double layer of optimally treated Luffa Cylindrica fibres.

Chocolate Milk versus carbohydrate supplements in adolescent athletes: a field based study

PurposeThe purpose of this study is to translate laboratory-based research on beverage-based supplements to a naturalistic, field setting in adolescent athletes. To this end, we tested the effects of two commercially-available drinks on strength in a field-based setting with both male and female high school athletes completing a summer training program.MethodsOne hundred and three high school athletes completed the study (M age = 15.3, SD = 1.2; 70.9% male; 37.9% Afr. Amer.). Measures included a composite strength score (bench press + squat). Participants completed 1 week of pre- and post-testing, and 4 days per week of strength and conditioning training for 5 weeks. Participants were randomly-assigned to receive either CM or CHO immediately post-exercise.ResultsA 2 (group) × 2 (time) repeated measures ANOVA showed there was a significant main effect on time for increase in the composite strength score (p = .002, ŋp2 = .18). There was a significant interaction of composite strength score between groups, (p = .04, ŋp2 = .08). The CM group (12.3% increase) had significantly greater improvements in composite strength from pre- to post-test than CHO (2.7% increase). There were no differences in these results based on demographic variables.ConclusionThis is the first study comparing the impact of CM and CHO on athletic outcomes in an adolescent population in a field-based environment. CM had a more positive effect on strength development and should be considered an appropriate post-exercise recovery supplement for adolescents. Future research will benefit from longer study durations with larger numbers of participants.

Mechanical properties of iron matrix composites reinforced by copper-coated hybrid ceramic particles

Abstract

Micromechanical deformations in PP/lignocellulosic filler composites: Effect of matrix properties

Polypropylene composites were prepared from three different PP matrices, a homopolymer, a random and a heterophase copolymer, and corn cob to study the effect of matrix characteristics on deformation and failure. The components were homogenized in an internal mixer and compression molded to 1 mm thick plates. Mechanical properties were characterized by tensile testing, while micromechanical deformations by acoustic emission measurements and fractography. The results proved that the dominating micromechanical deformation process may change with matrix properties. Yield stress determined from the stress vs. strain traces may cover widely differing processes. Debonding is the dominating process when the adhesion of the components is poor, while matrix yielding and/or filler fracture dominate when adhesion is improved by the introduction of a functionalized polymer. The dominating deformation mechanism is determined by component properties and adhesion. Interfacial adhesion, matrix yield stress and the inherent strength of the reinforcement can be limiting factors in the improvement of composite strength. The properties of polymer composites reinforced with lignocellulosic fillers are determined by micromechanical deformation processes, but they are independent of the mechanism of these processes.

Evaluation of the Mechanical Properties of Injection Moulded Hemp Fibre Reinforced Polypropylene Composites

In recent years, industrial hemp fibre reinforced thermoplastic composites have attracted substantial interest as potential structural materials. These composites have been subject to intense study for use in lightweight, recyclable and low cost applications. The aim of this research was to improve and evaluate the composite tensile strength and fibre/matrix interfacial adhesion by means of fibre treatment and addition of a coupling agent. Hemp fibre was digested in a small pressure vessel with a solution of 5wt% NaOH / 2wt% Na2SO3. Single fibre tensile tests were performed on treated and untreated fibres, and it was found that the alkali treatment resulted in an increase in fibre strength and an improvement in fibre separation. Composites containing either treated or untreated fibre, polypropylene and a maleic anhydride modified polypropylene (MAPP) coupling agent were then compounded in a twin-screw extruder and injection moulded into tensile test specimens. Tensile tests revealed that significant improvements in composite strength were made by using treated fibre and MAPP. The effect of MAPP on the interface of treated hemp fibre/polypropylene composites was assessed by means of the single fibre fragmentation test, and the interfacial shear strength was determined thereafter.

Wood flour filled polypropylene composites: Interfacial adhesion and micromechanical deformations

AbstractPolypropylene/wood flour composites were prepared in a wide composition range from 0 to 80 wt% filler content. The adhesion of the components was modified by two maleic anhydride functionalized polypropylenes (MAPP) with different maleic anhydride content and molecular weight. The components were homogenized in an internal mixer and then compression molded to 4 mm thick plates. Tensile properties were measured and micromechanical deformation processes were followed by acoustic emission as well as volume strain measurements. The detailed analysis of the results identified four micromechanical deformation processes in the matrix and the composites, respectively. The matrix polymer deforms mainly by shear yielding, which basically does not emit sound. The presence of wood flour initiates particle related processes in the composites. Debonding dominates in the absence of coupling agent. Pull‐out of fibers may follow the debonding of large particles at an intermediate stress level. The introduction of functionalized polymer increases interfacial adhesion considerably and completely changes the deformation mechanism; the fracture of wood particles becomes the dominating process in this case. Further improvement of composite strength is possible only by the increase of the inherent strength of the wood. POLYM. ENG. SCI., 47:1246–1255, 2007. © 2007 Society of Plastics Engineers

Wood flour filled PP composites: Compatibilization and adhesion

PP/wood flour composites were prepared in a wide range of compositions in an internal mixer at 180 °C, 50 rpm and 15 min. Interfacial adhesion was modified by the introduction of two maleinated polypropylenes (MAPP) with different molecular weights and functionality. Wood content was changed between 0 and 70 wt%, while MAPP/wood ratio between 0 and 0.25. Compression molded plates of 1 mm thickness were prepared for testing. Structure was characterized by X-ray diffraction and DSC measurements. Interfacial adhesion was estimated quantitatively with model calculations. The results showed that the morphology of the components and that of the composites does not change as a result of compounding and the wood flour used in these experiments does not nucleate PP. The most important structural phenomena determining properties are the orientation of the anisotropic wood flour particles and their aggregation. Both structural phenomena depend on processing conditions and on the dimensions of the product. Much larger improvement could be achieved by the addition of a functionalized polymer in thicker samples than in thin specimens. MAPP has a maximum efficiency at around 0.05–0.10 MAPP/wood ratio in the composites of this study due to the limited surface available for coupling. MAPP with larger molecular weight and smaller functionality proved to be more advantageous in the improvement of composite strength, because it can form larger number of entanglements per molecule than the small molecular weight compound. On the other hand, the smaller molecular weight coupling agent decreases viscosity and improves processability considerably, thus optimization of composition is essential to achieve maximum performance.

Performance of pineapple leaf fiber–natural rubber composites: The effect of fiber surface treatments

AbstractComposites of natural rubber (NR) and short pineapple leaf fiber (PALF) were prepared on a laboratory two‐roll mill. The influences of untreated fiber content and orientation on the processing and mechanical properties of the composites were investigated. The dependence of extent of orientation on fiber concentration was also established. Sodium hydroxide (NaOH) solutions (1, 3, 5, and 7% w/v) and benzoyl peroxide (BPO) (1, 3, and 5 wt % of fiber) were used to treat the surfaces of PALFs. FTIR and scanning electron microscope (SEM) observations were made of the treatments in terms of chemical composition and surface structure. The tensile strength and elongation at break of the composites were later studied. The fiber–matrix adhesion was also investigated using SEM technique. It was found that all surface modifications enhanced adhesion and tensile properties. The treatments with 5% NaOH and 1% BPO provided the best improvement of composite strength (28 and 57% respectively) when compared with that of untreated fiber. The PALF‐NR composites also exhibited better resistance to aging than its gum vulcanizate, especially when combined with the treated fibers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1974–1984, 2006

Pre-treatment of CaCO3 nanofiller by irradiation in the presence of vinyl monomers for the preparation of poly(vinyl acetate) composites

AbstractPoly(vinyl acetate) (PVAc) composites were prepared by different approaches, namely (i) by mechanical mixing of untreated CaCO3 and PVAc, (ii) by mechanical mixing of CaCO3 pre-treated by irradiation polymerization in the presence of vinyl acetate, and (iii) by in situ emulsion polymerization of VAc in the presence of untreated CaCO3 nanofiller. The effects of nanoparticle pre-treatment and different approaches of preparation were correlated with changes in morphology and mechanical properties of PVAc composites using scanning electron microscopy and tensile tests. Untreated CaCO3 nanoparticles in the composite prepared by mechanical mixing provided strong interactions with the PVAc matrix. On the other hand, CaCO3 pre-treated nanoparticles decreased the interfacial interactions. For composites prepared by in situ polymerization a better dispersion of encapsulated nanoparticles was achieved and, as a result, a significant improvement of composite strength was observed. Interfacial interactions in nanocomposites can be changed by filler pre-treatment or by a suitable way of nanocomposite preparation.

Structure and mechanical properties of unidirectionally solidified Fe-Cr-C and Fe-Cr-X-C alloys

In this work four different microstructures were obtained by unidirectional solidification of Fe-Cr-C eutectic alloys. Conditions for zone coupled growth were determined in alloys containing approximately 30 wt pct chromium. Furthermore, mechanical testing indicated that the maximum strength was exhibited by Fe-30Cr-C alloys with cerium or titanium additions. These alloys had the largest volume fraction of eutectic fibers and their ultimate tensile strength was of the order of 3250 MPa. Correlations between the rate of crystal growth(u) and fiber spacing (λ) or tensile strength(Rm) were found and an expression of the typeRm = Aλ-b2 was obtained whereb 2 varied between 0.283 and 0.685. Finally, manganese or chromium (35 wt pct Cr) additions did not lead to appreciable improvements in composite strength for this alloy system.