Advanced Materials Research Vol. 811

Abstract: Electron beam melting (EBM) is a direct metal additive manufacturing technique in which a 4 kW electron beam is utilized to manufacture the parts in a layer by layer fashion. This paper represents an investigation into the quasi-static compressive deformation behavior of EBM made specimens. The mechanical testing was carried out at strain rate of 10^-3 s^-1 by a numerically controlled hydraulic MTS machine on both as-built and machined samples manufactured by this high-tech process. The Vickers micro-hardness of the samples has been measured before and after the compression test. The microstructure of the compressed sample was characterized. The particle size distribution, morphology, and chemical composition of the Ti6Al4V, which is one of the most common materials for biomedical implants because of its high strength to weight ratio, corrosion resistance, and its biocompatibility features, have been investigated. The fracture surface has been characterized by scanning electron microscope.

Abstract: The sustainable development of engineering, mechanical instrument requires higher speed and higher power. It cause a physical damage is excessive damage for underwater rotating system as cavitations and erosion, but also electrochemical corrosion by chloride ion and flow of current in marine environment. In this study, we assessed electrochemical corrosion characteristics of aluminum-bronze that are the material for the underwater rotating system used in the ocean industry and studied the complex behavior of electrochemical corrosion and cavitation corrosion through the hybrid test that also included cavitation corrosion environment. After the cavitation hybrid tests, surface of specimens are observed to measurement damage degree using 3D optical microscope and compared the average of damage depth by immersion time. The observation of the surface micro-structure suggested that the corrosion took place initially in β phase that has poor corrosion resistance in spite of high hardness.

Abstract: In this work, the properties of frictional materials for motorcycle clutch with fly ash replacements of some original substances were studied aiming to reduce the raw materials cost. The fly ash was obtained from the domestic BLCP power plant in Rayong, Thailand. Two replacement schemes were studied;1) all of the original ingredients comprising the clutch was replaced with 15-35 %wt. fly ash and 2) only the original ingredients with similar physical and chemical properties were replaced with 40-55 %wt. fly ash. The mechanical properties, the friction coefficient and the wear performance were then studied. In addition, micro-structural characterizations of the contact surface and the wear debris were carried out. It was found that the fly ash replacement to a certain level increased the hardness resulting in a decrease in the surface wear. The specimens with fly ash replacement were found to have smoother surface leading to a lower static friction coefficient. The dynamic friction coefficient was altered according to the wear debris characteristics. The prototypes with the optimum amount of fly ash, i.e. giving minimum cost with superior or similar properties to the original product, for each scheme was produced and tested on a dynamometer. The prototypes for the 1^st and 2^nd schemes were found to offer the reduction in the wear rates of approx. 22 to 56% with a reduction in the cost of raw materials of approx. 15 and 23%, respectively. Severe damage of the prototypes was observed slightly sooner than that found for the original product.

Abstract: In this paper, three kinds of Cr-based hard coatings have been studied for its structural, mechanical and tribological properties at room temperature. By the technology of closed field unbalanced magnetron sputter ion plating (CFUMSIP), CrN CrAlN and CrTiAlN hard coatings were deposited onto DC53 cold die steel and silicon (100) substrate. The coatings were characterized by means of field emission scanning electron microscopy (FESEM), X-ray diffractometer (XRD), microhardness tester, optical microscope and ball-on-disc tribometer, in order to check their structural, as well as to determine the mechanical and tribological properties. The experimental results showed that the CrTiAlN coating performed better than the CrN coating and the CrAlN coating in terms of mechanical and tribological properties. The wear resistances of CrN, CrAlN and CrTiAlN coatings have been significantly improved compared with DC53 steel substrate.

Abstract: In order to analyze the stress relaxation behavior under repeated loadings for 1Cr-0.5Mo-0.25V steel, a stress relaxation model based on creep equations has been developed. The model was implemented into the ANSYS finite element program in terms of user define material model. The calculated results were compared to the observed results of uniaxial reloading stress relaxation testing, which were performed by the National Research Institute for Metals of Japan (NRIM) for 1Cr-0.5Mo-0.25V stainless steel bolting material at 500°C. It was shown that the proposed model could be applied for the present data. The calculated residual stresses versus time curves were in good agreement with the observed for initial stress level of 297.1MPa at 500°C and for specific reloading time intervals of 24, 72, 240, and 720 hours.

Abstract: Creep is one of important properties of polymer matrix composites (PMC).It can be analysis by finite element method (FEM).But creep will be affected by a lot of factors and the creep material parameters are very difficult to be obtained. Shift factors method is one simple method which can be used to obtain the creep properties by fewer tests. Here the basic method analysis of the creep of PMC by FEM was studied. Focus on the analysis of how the material parameters of finite element creep analysis needed to get through the shift factors method. Finally the actual PMC pipe structure is calculated by this method.The error of FEM result and theory result around 2%, the results show that this method has certain rationality and reliability.

Abstract: The purpose of this research is to study the characteristic of stainless steel particles under the sliding motion. The effects of effective stress and relative velocity on the characteristic of stainless steel wear particles were studied. The is aiming to monitor possible failure mode in various machine elements, especially in the case of a closed system or contamination sensitive processes such as the hard disk drive manufacturing process, etc. The research results showed that the particles smaller than 1 micron generated from material surface asperities. Moreover, the stress magnitude and velocity have the influence on the size and shape of the stainless steel particles, respectively. The increase in stress and speed will result in a larger particle size and more slender shape, respectively. It can be seen that the size and the shape of wear particles vary according to the sliding conditions. Therefore, the results could be used to identify the process in which the contaminated particles were generated for sliding motion.

Abstract: The Flexible Intermediate Bulk Container (FIBC) is a flexible transportation packaging container that is weaved by polyolefin plastic ribbon-like filament, which is widely used in the storage and transportation of granular and powder materials. When the FIBC was affected by environment factors synthetically under using, such as light, heat and air etc, it would come into degradation and its mechanical properties reduced. In this study, the basic mechanical properties of polypropylene FIBC base material were tested by tensile experiment and the reason of main base material mechanical properties difference between theoretical value and experimental value was analyzed. Based on the FIBC different using environments, the natural exposure experiment and high/low temperature experiments were carried out, we took tensile strength holding ratio and elongation holding ratio as evaluating indicator and analyzed law of influence of the different experiment condition on base material mechanical properties, which provided valuable reference for FIBC designing and manufacturing. Along with the experiment time increased, the color of base material changed from milk white to yellow slowly, the tensile strength and elongation reduced, the influencing grade was as follow: natural exposure>high temperature>low temperature. The results of natural exposure experiment showed that there was difference of anti-aging performance among the FIBC base material, the mechanical properties of woof fabric and belt reduced evidently, while others reduced slowly. For high (45°C)/low (-25°C) temperature experiments, the reduction of FIBC base materials mechanical properties were not obvious and woof fabric reduced a little faster comparatively.

Abstract: In order to study the hot workability of TC21 titanium alloy, isothermal hot compression tests were conducted in the temperatures range of 1123~1203K and strain rates range of 0.01~10s-1. The influence of strain was incorporated in hyperbolic sine constitutive equation by considering the effect of strain on material constants. Correlation coefficient (R) and average absolute relative error (AARE) were introduced to verify the validity of the developed hyperbolic sine constitutive equation. The values of R and AARE were determined to be 0.9891 and 7.753% respectively, which indicated that the developed hyperbolic sine constitutive equation considering strain compensation could precisely predict the flow behavior of TC21 titanium alloy throughout the entire range of temperatures and strain rates.

Abstract: In this paper we consider the geometrical structure of carbon nanotubes with artificially inplanebond alternation. The quinoid and the Kekule structures of carbon nanotubes with two differentbond lengths are fully described for various symmetries, including chiral and achiral carbon nanotubes.Consideration of the geometrical structure or the atomic structure is the first step for studies of carbonnanotubes with dimerization structures.