Mechanical properties of titanium foam for biomedical applications

Understanding the mechanical behaviour of pure titanium (Ti) foam is crucial for the design and development of Ti foam-based load-bearing implants. In this work, pure titanium foam is fabricated by a powder metallurgical process using the space-holder technique with a spacer size of 500 to 800 µm. Experimental data from static compression testing on the Ti foam are presented. The application of theoretical formulae to predict Young's modulus and yield strength of titanium foams is also discussed. A foam with 63% porosity, 87 ± 5 MPa yield strength, and 6.5 ± 1.3 GPa Young's modulus is found to be appropriate for a number of dental and orthopaedic applications.

Improvement in mechanical properties of aluminum polypropylene composite fiber

Aluminum particles (Al) were added to polypropylene (PP) in the presence of poly ethylene glycol (PEG) and polypropylene-graft-maleic anhydride to produce composites. The composites were then melt-spun into a mono filament and tested for tensile properties, diameter evenness and morphology. Melt rheological properties of Al/PP composites were studied in linear viscoelastic response regions. It was observed that level of dispersion of aluminum particles within a polypropylene composite fiber could be improved by incorporating polyethylene glycol. The improvement of dispersion led to an improvement in the fibers mechanical properties through a reduction of the coefficient of variation of fiber diameter.

The effect of solvent uptake on the relaxation behaviour, morphology and mechanical properties of a poly(ether ether ketone)/poly(etherimide) blend

The effects of solvent uptake on the relaxation behaviour, morphology and mechanical properties of poly(ether ether ketone) (PEEK), poly(etherimide) (PEI) and a 50/50 PEEK/PEI blend have been investigated. Amorphous films were immersed in acetone at 25°C, 35°C and 45°C until equilibrium uptake was achieved. The films were then examined by wide angle X-ray scattering (WAXS), differential scanning calorimetry (d.s.c.), dynamic mechanical relaxation spectroscopy and mechanical testing. WAXS and d.s.c. revealed that the degree of solvent induced crystallinity in PEEK is constant with immersion temperature, whereas the degree of induced crystallinity in the 50/50 blend is strongly temperature dependent. The dynamic mechanical studies confirmed that a significant decrease in glass transition temperature results from the plasticizing effect of the solvent and that solvent and thermally crystallized samples have different relaxation characteristics. Mechanical property tests showed that the yield stress and tensile strength of the blend are dominated by PEEK and the degree of crystallinity, while the modulus is more sensitive to the extent of plasticization.

Mechanical properties of polyether-plasticiser-salt systems as polymer electrolytes

The mechanical properties of urethane crosslinked poly(ethylene oxide-co-propylene oxide) glyceryl ether-plasticiser (tetraethylene glycol dimethyl ether, or methylformamide)-salt (LiClO₄)-based polymer electrolytes have been studied. It was found that, with increasing concentration of salt, the elastic modulus and tensile strength of the materials unexpectedly decrease. This is interpreted in terms of a predominance of intramolecular coordination of the Li⁺ ions by the polymer.

Interfacial energy states of moisture-exposed cracks in mica

Results of crack growth observations on mica in water-containing environments are described. The study focuses on equilibrium crack states for reversed loading cycles, i.e., for initial propagation through virgin solid and subsequent retraction-repropagation through healed or misoriented-healed interfaces. Departures from these equilibrium states are manifest as steady-state forward or backward crack velocities at specific applied loads. The equilibria are thereby interpreted as quiescent, threshold configurations G = W_E, with G the Griffith mechanical-energy-release rate and W_E the Dupré work of adhesion, on crack velocity (v-G) diagrams. Generally, W_E is found to decrease with concentration of water, in accordance with a Gibbs formalism. Hysteresis is observed in the forward-backward-forward crack propagation cycle, signifying a reduction in the adhesion energy on exposure of the open interface to environmental species prior to healing. This hysteresis is especially marked for those interfaces that are misoriented before healing, indicating that the structure of the underlying solid substrate as well as of the intervening fluid is an important consideration in the interface energetics. The equilibrium states for different environments can be represented on a simple energy-level diagram, as differences between thermodynamic end-point states: initial, closed-interface states refer to crystallographic bonding configurations ahead of the crack-tip adhesion zone; final, open interface states refer to configurations behind the crack-tip zone. The significance of this diagram in relation to the fundamental atomic structure of interfaces in fracture and other adhesion geometries, including implications concerning kinetics, is discussed.

Microstructural characterization and mechanical properties of Mg-Zr-Ca alloys prepared by hot-extrusion for biomedical applications

This paper investigated the microstructural characterization and mechanical properties of Mg-Zr-Ca alloys prepared by hot-extrusion for potential use in biomedical applications. Mg-Zr-Ca alloys were fabricated by commercial pure Mg (99.9%), Ca (99.9%), and master Mg-33% Zr alloy (mass%). The microstructural characterization of the hot-extruded Mg-Zr-Ca alloys was examined by X-ray diffraction analysis and optical microscopy, and the mechanical properties were determined from tensile tests. The experimental results indicate that the hot-extruded Mg-Zr-Ca alloys with 1 mass% Ca are composed of one single phase and those alloys with 2 mass% Ca consist of both Mg2Ca and α phase. The hot-extruded Mg-Zr-Ca alloys exhibit equiaxed granular microstructures and the hot-extrusion process can effectively increase both the tensile strength and ductility of Mg-Zr-Ca alloys. The hot-extruded Mg-1Zr-1Ca alloy (mass%) exhibits the highest strength and best ductility among all the alloys, and has much higher strength than the human bone, suggesting that it has a great potential to be a good candidate for biomedical application.

Effect of baking process on microstructures and mechanical properties of low silicon TRIP steel sheet with niobium

After 2% predeformation, the baking treatment with different schedule was carried out for low silicon TRIP steel sheet with niobium. The effects of baking temperature and time on microstructures and mechanical properties were investigated. The results showed that with increasing the baking temperature and time, the volume fraction of retained austenite decreases, and the volume fraction of tempered martensite increases; as baking temperature ranges from 80°C to 170°C, the bake-hardening (BH) value increases obviously, while from 170°C to 230°C, the variation of BH value is very slight; as baking time ranges from 2 min to 20 min, the BH value increases significantly, while the BH value decreases when baking time exceeds 20 min. So that when the baking temperature is 170°C and the baking time is 20 min, the low silicon TRIP steel sheet exhibits good bake-hardening behavior, and the highest BH value is above 70 MPa.

Oxygen plasma treatment of sisal fibers and polypropylene: Effects on mechanical properties of composites

Polypropylene powder and sisal fibers were oxygen plasma treated, and the mechanical properties of their composites were tested. Two main effects were investigated: the incorporation of oxygen polar groups in the polypropylene surface and the surface degradation and chain scission of both polypropylene and sisal fibers. Prior to these treatments, three reactor configurations were tested to investigate the best condition for both effects to occur in PP film. Results showed that polypropylene-cellulose adhesion forces are about an order of magnitude higher for PP film treatments at 13.56 MHz than at 40 kHz owing to much higher chain scission at lower frequencies, although it probably also occurs at high frequency and high power. Polypropylene powder treated with oxygen plasma in optimum conditions for polar group incorporation did not result in improvement in any composite mechanical property, probably owing to the polymer melting. Sisal fibers and PP powder treated In conditions of surface degradation did not improve flexural or tensile properties but resulted in higher impact resistance, comparable to the improvement obtained with the addition of compatibilizer.

Sinterização de uma mistura de cavaco de aço inoxidável com pó do mesmo material. Uma nova tecnologia para a reciclagem de metais?

The reuse of materials has as its main objective to minimize environmental impacts and to rationalize the use of energy chains. In the present work, samples of scraps of 316 stainless steel mixed with powder of the same material were sintered. For this case, the percentage of scrap was varied from zero to 25% in weight, with 5% increases. After compacting, under a pressure of 600MPa, the samples were sintered simultaneously at a temperature of 1473 K. The mechanical behavior of the final product was evaluated through Assays of Transversal Rupture recommended and normalized by the MPIF - Metal Powder Industries Federation. Using Conventional Quantitative Metallography, the analyses of the sintered samples demonstrated regions of intense diffusion, therefore, regions of sufficiently intense sintering. The mechanical resistance of the samples was compared with the mechanical resistance of the sintered stainless steel with no scrap. The results were greater than expected, demonstrating the viability of this new procedure.

Developing descriptors to predict mechanical properties of nanotubes

Descriptors and quantitative structure property relationships (QSPR) were investigated for mechanical property prediction of carbon nanotubes (CNTs). 78 molecular dynamics (MD) simulations were carried out, and 20 descriptors were calculated to build quantitative structure property relationships (QSPRs) for Young's modulus and Poisson's ratio in two separate analyses: vacancy only and vacancy plus methyl functionalization. In the first analysis, C N2/CT (number of non-sp2 hybridized carbons per the total carbons) and chiral angle were identified as critical descriptors for both Young's modulus and Poisson's ratio. Further analysis and literature findings indicate the effect of chiral angle is negligible at larger CNT radii for both properties. Raman spectroscopy can be used to measure CN2/C T, providing a direct link between experimental and computational results. Poisson's ratio approaches two different limiting values as CNT radii increases: 0.23-0.25 for chiral and armchair CNTs and 0.10 for zigzag CNTs (surface defects <3%). In the second analysis, the critical descriptors were CN2/CT, chiral angle, and MN/CT (number of methyl groups per total carbons). These results imply new types of defects can be represented as a new descriptor in QSPR models. Finally, results are qualified and quantified against experimental data. © 2013 American Chemical Society.

Evaluation of mechanical and thermal properties after chemical degradation of PVC and HDPE geomembranes

Chemical compatibility between geomembranes and site-specific waste liquids should be assessed since the waste liquids are highly complex mixtures. This paper presents some considerations about the chemical compatibility of geomembranes and some results of mechanical tests in HDPE and PVC geomembranes that were exposed to leachate and chemical residue (niobium). PVC and HDPE geomembranes of two thicknesses were tested: 1.0, 2.0 mm (PVC) and 0.8, 2.5 mm (HDPE). The results obtained show that after exposure the PVC geomembranes (1.0, 2.0 mm) were more rigid and stiffer than fresh samples. The HDPE geomembranes, on the other hand, when exposed to leachate and niobium residue presented increases in deformation. Melt flow index (MFI) tests were also carried out to verify the oxidation. © 2013 ejge.

Simple green approach to reinforce natural rubber with bacterial cellulose nanofibers

Natural rubber (NR) is a renewable polymer with a wide range of applications, which is constantly tailored, further increasing its utilizations. The tensile strength is one of its most important properties susceptible of being enhanced by the simple incorporation of nanofibers. The preparation and characterization of natural-rubber based nanocomposites reinforced with bacterial cellulose (BC) and bacterial cellulose coated with polystyrene (BCPS), yielded high performance materials. The nanocomposites were prepared by a simple and green process, and characterized by tensile tests, dynamical mechanical analysis (DMA), scanning electron microscopy (SEM), and swelling experiments. The effect of the nanofiber content on morphology, static, and dynamic mechanical properties was also investigated. The results showed an increase in the mechanical properties, such as Young's modulus and tensile strength, even with modest nanofiber loadings. © 2013 American Chemical Society.

Aspects of Mechanical Behavior and Modeling of a Tropical Unsaturated Soil

The research studies the applicability of two elastoplastic models for the collapse prediction of the lateritic soil profile from Southeastern Brazil. These tropical soils have peculiar geotechnical behavior, due to their mineralogical composition and porous structure coming from intense process of formation. Two elastoplastic models were analyzed: the Barcelona Basic Model (BBM) and another one based on BBM, however developed for tropical soils. Oedometric tests with suction control were performed at three distinct depths of the soil profile. The BBM was not suitable for the upper layer of the soil profile, because BBM considers the compressible behavior of the soil in function of the reduction of the elastoplastic compressibility index with the increase of the matric suction. The model developed for tropical soils showed better suited to the compressible behavior of the soil profile, resulting in good prediction of the collapse potential, mainly by accepting increasing values of the elastoplastic compressibility index of the soil profile with the matric suction rise. © 2013 Springer Science+Business Media Dordrecht.