Advanced Materials Research Vols. 26-28

Abstract: This paper presents the results of experimental and analytical investigations on the behavior of GFRP pipes used in the water supply pipeline systems. The pipes consist of two filament wound outer GFRP tubes and polymer mortar between the tubes. Parallel plate loading tests were conducted and the test results were compared with predicted results. The load-deflection prediction was conducted by the FE analysis and the conventional strength of materials approach. It was shown that the results obtained by the experiment and analysis were agreed well.

Abstract: Researches until now about recycled aggregate have mainly focused on illuminating physical properties and mechanical behaviors of recycled aggregate by experimenting on small batches of mixing. Unfortunately this kind of mixing does not necessarily fit the reality where a large amount of ready-mixed concrete is often made. Therefore, this study carried out an experiment by having a ready-mixed concrete manufacturing company mix a large amount of recycled aggregate that satisfies quality standard set by the MCT of Korea, then verifying the behaviors of recycled aggregate concrete. The target concrete compressive strength was selected as 24MPa had a slump flow for 120±25mm and air content of 5.0±1.5%, that is used most in site. The main experiment variable of this study is to replacement ratio of recycled aggregate(RA). The 27 test specimens were designed with recycled aggregate replacement ratio that had range of coarse recycled aggregate(CRA), 0, 10, 20, 30, 40, and 50%. The result shows that replacing the natural aggregate with the recycled one up to the ratio of 30% satisfies the quality standard for mixing concrete properly.

Abstract: A regression model was constructed to elucidate the effects of various additives on the UV- stability of glass fiber reinforced epoxy (GRE) pipes by applying a four-factor central composite design (CCD) statistical approach. Four factors investigated were amount of UVabsorber, antioxidant, carbon black, and flame retardant. The ANOVA showed that most mechanical properties except for the hardness were a strong function of the amount of UV-absorber, carbon black, and flame retardant, while quite independent of the antioxidant content within the studied range (0-10%w/w). The amount of UV-absorber and other additives seemed to exhibit significant interaction effect on mechanical properties. The photodegradation of the GRE pipes was performed by an outdoor exposure and under simulated condition in Q-UV Lamp. The GRE pipes containing 2% UV-absorber, 1% antioxidant, 3% carbon black, and 10% flame retardant revealed better mechanical properties compared to the others.

Abstract: Powder injection molding (PIM) process was applied to Fe-based metamorphic alloy powders, and microstructure, hardness, and wear resistance of the PIM products were analyzed and compared with those of conventional PIM stainless steel products. When Fe-based metamorphic powders were injection-molded and then sintered at 1200 oC, completely densified products with almost no pores were obtained. They contained 34 vol.% of (Cr,Fe)2B borides dispersed in the austenitic matrix without amorphous phases. Since these (Cr,Fe)2B borides were very hard and thermally stable, hardness, and wear resistance of the PIM products of Fe-based metamorphic powders were twice as high as those of conventional PIM stainless steel products. Such property improvement suggested new applicability of the PIM products of Fe-based metamorphic powders to structures and parts requiring excellent mechanical properties.

Abstract: It is well known that the utilization of superplastic characteristics in manufacturing process makes many of aerospace components lighter and stiffer. The weight saving is vitally important especially for aerospace application and even more weight saving is possible when the superplastic forming is carried out with diffusion bonding. In this study, the lightweight sandwich structure was fabricated with superplastic forming(SPF) process from diffusion bonded(DB) Ti-6Al-4V sheets. The solid state diffusion bonding process was conducted in non-vacuum environment under a pressure of 4MPa for 60 minutes at 875°C and the superplastic forming process was followed for another 40 minutes. Good solid state bonding interface have been observed in microstructure observation and the sandwich structure was successfully manufactured. It is important to note that the forming conditions of present study are more practical for application than the previously published conditions, which require vacuum environment, higher temperature and/or pressure.

Abstract: In this study, the effect of various binders’ compositions on the feedstock of pre-alloyed tungsten heavy alloys (WHAs) powders has been investigated. Four kinds of wax-based binders were prepared from paraffin wax (PW), high-density polyethylene (HDPE), polypropylene (PP) and stearic acid (SA), and the characteristic of each feedstock was investigated at various temperatures and shear rates. It was found that all the feedstocks exhibited pseudoplastic flow behavior. Feedstock having multi-polymer components showed better rheological properties than those having mono-polymer because of good wettability between powder and binder, and less sensitivity to temperature and shear rates. This could be due to the molecular weight and length of molecular chain of PP and HDPE.

Abstract: In this paper the effect of isothermal forging process parameters on the microstructure and the mechanical properties of TA15 titanium alloy was researched. The results of the tests indicate that, in the range of temperature of 850 °C~980 °C and deformation degree of 20%~60%, with the increase of temperature or deformation, as the reinforcement of deformation recrystallization, the primary α-phase tends to the spherical shape and secondary α-phase transforms from the acicular shape to fine and spherical shape with disperse distribution, which enhance the tensile properties at room and high temperature. With the increment of forging times, the spheroidization of primary α-phase aggrandizes and secondary α-phase transforms from spherical and acicular shape to wide strip shape, which decrease the tensile properties at room and high temperature. The preferable isothermal forging process parameters are temperature of 980 °C, deformation degree of 60%, and few forging times.

Abstract: An asymmetrical rolling of AZ31 alloy sheets was carried out at 473 K with a high reduction ratio of 70% in thickness prior to tensile-tests. For the as-rolled sheet, tensile tests were performed in a temperature range of 473 ~ 673 K at a constant strain rate of 1 × 10-3 s-1. Tensile elongation increases with increasing reduction ratio in the as-rolled sheets. A large elongation of above 530% was obtained in the specimen deformed at 673 K for the sheet fabricated by 70% thickness reduction. Although the extent of grain growth was remarkable in a high temperature range, the tensile elongation increases with increasing the tensile temperature.

Abstract: In order to improve the quality of tin-phosphor bronze strips, the horizontal electromagnetic continuous casting technology, i.e. imposing alternating electromagnetic field to the horizontal continuous casting process of tin-phosphor bronze strips was developed. The effect of electromagnetic field on the quality of tin-phosphor bronze strips was studied with electron probe microanalysis (EPMA) and optical microscope. The results showed that when the alternating electromagnetic field with 50 Hz frequency and 18 A current was imposed, the crystal grain of the tin-phosphor bronze strips was obviously refined and the segregation and shrinkage cavity were greatly reduced. The quality of tin-phosphor bronze strips was remarkably improved, so the annealing time was shortened from 7 hours to 5 hours, and the service life of graphite mold was extended from 168 hours to 334 hours.

Abstract: Ultrafine-grained (UFG) CP Ti were successfully prepared by Equal Channel Angular Extrusion (ECAE) at 390°C~400°C, small than 0.5 um in size. The compressive tests for coarse grain (CG) and UFG Ti were carried out at room temperature (RT) and 77K. UFG Ti showed excellent ductility and higher strength than CG Ti at RT and 77 K. The strain hardening of UFG Ti was improved at 77 K. The compressive ultimate strengths of CG Ti and UFG Ti were both enhanced as the strain rate increased, but CG Ti showed more obvious temperature and strain rate dependence of flow stress, comparing with UFG Ti. When the strain rate increased to 1×10-1/s, the compressive ultimate strength of UFG Ti was kept almost constant, while the ultimate strength of CG Ti increased to the strength level of UFG Ti.