A setup to characterize the tensile mechanical properties of poly(L-lactic acid) materials applied in bioresorbable polymer stents

A method for testing mechanical properties of miniature poly(L-lactic acid)(PLLA) specimens is instrumented and set up in this research. This method is specially designed to measure mechanical properties, including elasticity modulus, yield strength and breaking elongation, of miniature PLLA specimens in three different shapes at various tensile speeds and temperatures. Moreover, the measurement results are significantly dependent on the tensile speeds and temperatures. This phenomenon further verifies the obvious existence of the viscoelasticity of PLLA. Finally, it can be concluded that, with this method, mechanical properties of PLLA can be better investigated and understood, especially for PLLA used for biodegradable polymer stents.

Effect of Microstructure on Micro-Mechanical Properties of Composite Solid Propellant

This study was aimed at determining the effect of microstructure on the macro-mechanical behavior of a composite solid propellant. The microstructure model of a composite solid propellant was generated using molecular dynamics algorithm. The correlation of how microstructural mechanical properties and the effect of initial interface defects in propellant act on the macro-mechanics were studied. Results of this study showed that the mechanical properties of propellant rely heavily on its mesoscopic structure. The grain filling volume fraction mainly influences the propellant initial modulus, the higher the volume fraction, the higher initial modulus. Additionally, it was found that the ratio of particles influences the tensile strength and breaking elongation rate of the propellant. The big particles could also improve the initial modulus of a propellant, but decrease its tensile strength and breaking elongation rate. Furthermore, the initial defects lowered the uniaxial tensile modulus, tensile strength, and the relaxation modulus of propellant, but did not affect the relaxation behavior of the propellant.

Microstructure and Mechanical Properties of AlSi12CuNi Alloy Fabricated by Laser Powder Bed Fusion Process

The microstructure and mechanical properties of the AlSi12CuNi alloy fabricated by the additive manufacturing technique, laser powder bed fusion (L-PBF), were investigated. Several laser irradiation conditions were examined to optimize the manufacturing process to obtain a high volume density of the fabricated alloy. Good fabricated samples with a relative density of 99% or higher were obtained with no cracks. The fabricated samples exhibited significantly good mechanical properties, such as ultimate tensile strength, breaking elongation, and micro-hardness, compared to the conventional die casting AlSi12CuNi alloy. Fine microstructures consisting of the α-Al phase and a nano-sized eutectic Al-Si network were observed. The dimensions of the microstructures were smaller than those of the conventional die-casting AlSi12CuNi alloy. The superior mechanical properties were attributed to the microstructure associated with the rapid solidification in the L-PBF process. Furthermore, the influence of the building direction on the mechanical properties of the fabricated samples was evaluated. The ultimate tensile strength and breaking elongation were significantly affected by the building direction; mechanical properties parallel to the roller moving direction were significantly better than those perpendicular to the roller moving direction. In conclusion, AlSi12CuNi alloys with good characteristics were successfully fabricated by the L-PBF process.

Preparation of different scale firous membranes and their filtration properties

In this work, the PAN monolayer/composite nanofibrous membranes were successfully fabricated at different processing parameters. As expected, compared with monolayer membranes, the composite membrane revealed high breaking strength, high breaking elongation, high porosity and good filtration performance. The composite method used in this article also provides new ideas for designing filter materials.

Kinetics of formation and viscoelastic and mechanical properties of optically transparent interpenetrating networks of poly(methyl methacrylate)/polyurethane

An optically transparent material with enhanced physical-mechanical properties was synthesized, which is based on the in situ formed sequential interpenetrating polymer networks of poly(methyl methacrylate)/polyurethane with an oligoester component. The kinetic features of polymerization of methyl methacrylate in these systems were studied. It was established that the polymerization rate of methyl methacrylate increases with an increase in the content of a polyurethane component, which results from an increase in the system viscosity. Irrespective of the content of polyurethane (15, 20 or 25 wt.%), optically transparent materials with a light transmission coefficient of about 90% were formed. The method of dynamic mechanical analysis showed that the modification of cross-linked poly(methyl methacrylate) with cross-linked polyurethane led to a decrease in the value of the elastic modulus; the value of the loss modulus being increased with an increase in polyurethane content. This indicated bot a decrease in fragility and the improvement in impact strength of the glass-like material. According to the study of physical-mechanical properties of the materials, the presence of polyurethane in their composition resulted in an increase in the impact strength and relative breaking elongation and in the reduction of the Young modulus. It was found that the interpenetrating polymer network containing 20% of polyurethane showed the best values of breaking strength, breaking elongation and Charpy impact.

Microstructure and Mechanical Properties of AlSi12CuNi Alloy Fabricated by Selective Laser Melting

In this study, the microstructure and mechanical properties of AlSi12CuNi alloy fabricated by Selective Laser Melting (SLM) were investigated. Wide range of laser irradiation conditions were selected to optimize the process in terms of optimum volume density. As a result, fabricated objects with a relative density of 99% or higher and no crack could be obtained. The as-fabricated alloy exhibited significantly good mechanical properties; an ultimate tensile strength, a breaking elongation, and micro-hardness in comparison with the conventional die casting AlSi12CuNi alloy. The fine microstructures composed of the α-Al phase and nano-sized eutectic Al-Si network could be observed. The dimensions of the microstructures were smaller than that of the conventional die casting AlSi12CuNi alloy. The superior mechanical properties were attributed to the microstructure associated with the rapid solidification of the SLM process. The influence of building direction of mechanical properties on fabricated objects was evaluated. The ultimate tensile strength and breaking elongation were significantly affected by the building direction, which was higher in the case of a parallel direction to the roller moving direction. AlSi12CuNi alloy with good characteristics can be successfully fabricated by the SLM process.

About the Static Mechanical Properties of Epoxy/Hemp Composites

In this paper, static mechanical characteristics for some epoxy/hemp composites are studied. By using the tensile test, the static mechanical characteristics are determined, such as: breaking strength, yield stress, Young modulus and breaking elongation. There is also determined the standard deviation. Then, by using some known theories, there is validated the static Young modulus.

Investigation of the Effects of Different Bias Angles of Stitching on Seam Performance of Wool Suits

Wool suits are always preferred due to their warmth retention in cool weather, comfort, and aesthetic features. Seams are very important for the quality of wool suits. The tensile characteristics of seamed fabric change with the change of fabric bias angle. This study aimed to investigate the effects of different seam angles with various stitch densities on the seam strength and the seam breaking extension of wool suit stitches. In this study, seam strength and seam-breaking elongation at different bias angles were investigated for the stitches of trousers and jackets of wool suits. As is known, in the production of trousers and jackets, the seams are applied not only in the direction of the weft and warp but also in the different bias angles at the crotch area and arm hole seams. Six wool fabrics with different structural properties were chosen as experimental samples. Fabrics were cut at 0°, 30°, 45°, 60°, and 90° angles and then sewn with three different stitch densities (3, 4, and 5 stitches/cm), with lockstitch stitch type for each fabric angle. Therefore, 90 differently seamed fabric samples were prepared. The results indicated that seams prepared with 0°,45° and 90° bias angles give the highest seam strength and that 30°, 45°, and 60° bias angles give the highest seam-breaking elongation values all over the samples. Seams prepared with 30° and 60° bias angles give the lowest seam strength, and 0° and 90° bias angles give the lowest seam-breaking elongation values all over the samples.

Investigation on the Synthesis Process of Bromoisobutyryl Esterified Starch and Its Sizing Properties: Viscosity Stability, Adhesion and Film Properties

To confirm the suitable synthesis process parameters of preparing bromoisobutyryl esterified starch (BBES), the influences of the synthesis process parameters—amount of 2-bromoisobutyryl bromide (BIBB), amount of catalyst (DMAP), reaction temperature and reaction time—upon the degree of substitution (DS) were investigated. Then, to produce a positive effect on the properties of graft copolymers of BBES prepared in the near future, a series of BBES samples were successfully prepared, and their sizing properties, such as apparent viscosity and viscosity stability, adhesion, and film properties, were examined. The BBES granules were characterized by Fourier transform infra-red spectroscopy and scanning electron microscopy. The adhesion was examined by determining the bonding forces of the sized polylactic acid (PLA) and polyester roving. The film properties were investigated in terms of tensile strength, breaking elongation, degree of crystallinity, and cross-section analysis. The results showed that a suitable synthesis process of BBES was: reaction time of 24 h, reaction temperature of 40 °C, and 0.23 in the molar ratio of 4-dimethylaminopyridine to 2-bromoisobutyryl bromide. The bromoisobutyryl esterification played the important roles in the properties of the starch, such as paste stabilities of above 85% for satisfying the requirement in the stability for sizing, improvement of the adhesion to polylactic acid and polyester fibers, and reduction of film brittleness. With rising DS, bonding forces of BBES to the fibers increased and then decreased. BBES (DS = 0.016) had the highest force and breaking elongation of the film. Considering the experimental results, BBES (DS = 0.016) showed potential in the PLA and polyester sizing, and will not lead to a negative influence on the properties of graft copolymers of BBES.