Abstract: The effect of heat treatment on microstructure and hardness of internal crack healing in a low carbon steel was studied. The internal cracks were produced into the samples by a drilling and compression method. The microstructure of crack healing zone was examined using optical microscopy (OM) and scanning electron microscopy (SEM). The hardness of crack healing zone was measured using a Vickers micro-hardness testing machine (FM-800). The results show that healing temperature plays a more significant role in internal crack healing than holding time. Compared as-quenched samples with as-normalized samples under the same healing parameters, it is found that cooling speed is also an important factor for internal crack healing. The migration and enrichment of iron atoms provide material source for recrystallization and grain growth of crack healing zone. The existence of micro-voids leads to the hardness of the ferrite in the crack healing zone lower than that in the matrix.
Abstract: The article contains a block diagram of the mechanical activation process of multicomponent shape memory materials, taking into account the variety of influencing factors. We proposed to evaluate the reactivity of the deposited material by using the energy criterion (energy intensity), determined by additivity concept as an amount of the basic material energy and energy accumulated during mechanical activation. The energy intensity of the basic material depends on the chemical and phase composition and is determined by the thermodynamic characteristics and is based on diagrams of the systems. The energy accumulated during the MA, is determined on the basis of X-ray structural analysis. We have shown experimentally that increase in fineness of grind leads to growth in the number of active centers. This enables nanopatterning of surface layers in high-velocity oxygen-fuel spraying (HVOF). Increasing the time of MA (1.5 h) promotes a more homogeneous structure during HVOF. The study results allow developing practical recommendations for effective implementation of multi-component SME materials with HVOF.
Abstract: The current research status of reheat crack in welded joint of low alloy heat-resistant steels are outlined. Some new phenomena discovered in engineering in recent years are summarized, and related problems that remain to be studied are also presented. Reheat crack in welded joint is occurred frequently during postweld heat treatment (PWHT) or in service at elevated temperature. Mainly four mechanisms leading to reheat crack, respectively, impurity segregation grain boundary weakening, precipitation hardening, creep rupture and no-precipitation zone weakening have been generally accepted now. Several essential factors consist of parent material chemical composition, microstructure and thickness of welded joint, filler material, preheat and postheat procedures, welding energy input, PWHT parameter, and stress and strain and so on. Theoretical calculation methods, criterion of RoA (Reduction of Area) and several experimental methods are put forward to evaluate reheat crack susceptibility. Based on new issues emerged in engineering, problems of concerning reheat crack are necessary to be researched, which include at least mechanism and influence factors of new multi-element composite strengthening heat-resistant steels, the mitigation measures for increasing wall thickness weldment, the root cause analysis and prevention methods of conventional low alloy heat-resistant steels for long term service.
Abstract: The Inconel 600 alloy relies on high temperature strength and aggressive environment resistance for main pipes and heat exchangers for power plant. Through high energy laser beam surface treatment, upgrade oxidation performance and design based accident prevention, the durable Inconel 600 alloy is realized. At the same time, the chemical diffusion and high energy beam welding are used for wearness enhancement and chemical oxidation. It is suggested that, the laser surface treatment and hydrogen effect are accurately selected for abrasive wear resistance and high temperature oxidation, repectively. As a result, the lifespan of Inconel 600 alloy increases, the pitting concentration and cracks formation are prevented effectively.
Abstract: In this work, water vapor permeability of linear low density polyethylene (LLDPE)/ethylene vinyl acetate copolymer (EVA) film is improved by incorporation of zeolite A as filler (0-25%wt) for prolonging shelf-life of fresh produces. All films were characterized by SEM, DSC, tensile testing, contact angle measurement and tested for water vapor permeability (WVP). The shelf-life of Bird’s eye chili in the film samples was also tested at 10°C for 21 days. It was found that zeolite A particles were virtually dispersed in EVA phase. Accordingly, crystallinity and tensile properties of LLDPE/EVA/Zeolite A films is independent to zeolite loading. Despite, when zeolite loading was increased, the dispersion became low. The film’s wetting behavior was enhanced by increasing zeolite content in the LLDPE/EVA/Zeolite A films. The observed increase in the film’s polarity significantly enhances the WVP. Therefore, less water condensed can be found inside the package made with LL80E20Ze25 film, as compared to LLDPE or LLDPE/EVA film. The LL80E20Ze25 also possesses comparable tensile properties to the commercial LLDPE film and hence can used as packaging for extending the shelf-life of fresh produces.
Abstract: In this paper carboxylated carbon nanotubes/polypyrrole composite (CNTs/PPy) was synthesized in different surfactants aqueous under sonication. Carboxylated CNTs was synthesized in hydrogen nitrate by ultrasonic method and coated by PPy. The synthesized CNTs/PPy in different surfactants was evaluated by Fourier transform infrared spectrometer (FT-IR) and transmission electron microscope. The FT-IR patterns illustrate that CNTs were successfully doped by PPy. The morphology of CNTs/PPy synthesized showed on the transmission electron microscope images. The composite materials sythesized without surfactant are easy reunited. It is also found the surface of CNTs/PPy synthesized in cetyl trimethyl ammonium bromide (CTAB) is smoother than that in other surfactants. The coating effect is better with thicker coating layer. The higher magnification of HRTEM images show the PPy was deposited directly on the surface of carbon nanotubes. The final products are the ordered coaxial composite with well-defined core-shell structure.
Abstract: The present study investigates the dielectric constant, loss factor and dissipation factor of pineapple leaf fiber reinforced epoxy composites as in function of fiber loading, fiber surface modification and frequency. The dielectric properties of the composites were measured using HP 16451 as the dielectric test fixture and was carried out on pineapple leaf fiber reinforced epoxy composites with varying fiber loading (5wt%, 10wt%, 15wt%, and 20wt%) and fiber subjected to sodium hydroxide treatment. It was observed that the dielectric properties of these composites were influenced by fiber loading and sodium hydroxide treatment. The dielectric constant increases with increase of fiber concentration and decrease with the increase of frequency in the case of all composites. It was also observed that the increase of dielectric constant with fiber loading was more significant at low frequency. Due to a reduction in the hydrophilic nature of pineapple leaf fiber brought about by sodium hydroxide treatment the dielectric properties of the composites was less than that of the untreated ones.
Abstract: This research focuses on the sound absorption coefficient of three different natural fibers reinforced epoxy composites. The natural fibers used are coconut coir, kenaf, and sugarcane bagasse. All of these fibers were mixed with epoxy resin and hardener with a ratio of 4:1. The mixtures were then poured into a circular mold and compressed by using compression molding technique. It was left for curing for 24 hours at standard room temperature. The results were obtained using the two-microphone transfer functions impedance tube method according to ASTM E1050-12. It is found that as the fiber loading increased, the sound absorption coefficient of the composites increased. 20wt% Coconut coir epoxy composites and 20wt% kenaf fiber epoxy composites have the highest sound absorption coefficient with almost similar sound absorption of 0.078 at 5000Hz. While, 20wt% sugarcane bagasse epoxy composites have sound absorption of 0.075 at 5000Hz.
Abstract: The effects of the montmorillonite clay surface modified with 0.5-5 wt% aminopropyltriethoxysilane and 15-35 wt% octadecylamine (Clay-ASO) and polyethylene-g-maleic anhydride (PE-g-MA) on morphology and mechanical properties of poly (lactic acid) (PLA)/acrylonitrile-butadiene rubber copolymer (NBR) blends were investigated and compared. The PLA/NBR blends and composites were prepared by melt mixing in an internal mixer and molded by compression molding. The ratio of PLA and NBR was 80/20 by weight and the Clay-ASO and PE-g-MA contents were 3, 5 and 7 phr. The morphology analysis showed that the addition of Clay-ASO and PE-g-MA at high content could improve the miscibility of PLA and NBR to be homogeneous blends due to the voids in the polymer matrix were decreased. The tensile properties showed Young’s modulus of the PLA/NBR/Clay-ASO composites was more than that of the PLA/NBR blends and Young’s modulus of composites increased with increasing Clay-ASO content, while the tensile strength and strain at break decreased with increasing Clay-ASO content. The incorporation of PE-g-MA 3 phr could improve the tensile strength, stress at break and strain at break of PLA/NBR blends.