Materials Science Forum Vols. 675-677

Abstract: Thixotropy is an important property possessed by fresh concrete of changing from gel to liquid under shearing stress and returning to the original state when at rest. The thixotropic process is usually described to be an isothermal and static (or quasi-static) gel-sol-gel transformation. Now the thixotropy of concrete subjected to explosive loads became a new subject in research of synchronous explosive lining technology, which offers an advanced trechless method for underground space construction in soil. Because the detonation of explosives is a short-duration process accompanying with high temperature and high pressure, thixotropic behavior of concrete is no longer as same as that of in general meaning. This review summarizes the recent progress in research on explosion induced thixotropy of concrete, including the thixotropic behavior, thixoforming, influence of thixotropic process on microstructure, macrostructure and mechanical performances of concrete and steel fibre reinforced concrete. Additional, some arguments and suggestions for the future research are presented.

Abstract: Raw Japanese timber bamboo was hot-pressed in order to investigate its static and dynamic mechanical properties such as flexural strength, flexural modulus, and impact strength. The purpose of this work was to examine the effect of molding pressure on the mechanical properties of hot-pressed bamboo. The hot-pressing pressures used were varied from 5 to 100 MPa and hot-pressing temperature was fixed to be 160°C. The density, flexural strength and flexural modulus remarkably increased up to 20 MPa, and then gradually increased. However Izod impact strength showed different pressure dependence. In conclusion, remarkable densification both in vascular bundles parts and parenchyma parts was achieved after hot-pressing of bamboo resulting in the increase in density and mechanical properties.

Abstract: In this paper, rare earth La modifying ZL101 alloy was studied by using of optical microscope, scanning electron microscopy, universal materials tester and small-load Brinell hardness. The influence of T6 heat treatment of the alloy’s microstructure and properties was also studied. The results show that microstructure and mechanical properties of the alloy have much obvious modification effect at modification temperature (690°C). The microstructure and mechanical properties are improved remarkably when La content is up to 0.15wt%.

Abstract: One of the vertical magnetic recordings medium materials of the hard disk drive (HDD) is a Pt-Fe thin film. The development of ultra-high density magnetic recording medium in next generation is expected the magnetic disks such as HDD with capacity enlargement of the data. In order to study effectiveness of the proposed sputtering method, we evaluated micro structure, magnetic and the mechanical properties of a Pt-Fe thin film by some sputtering process conditions. From research results, effect sputtering conditions on micro-structure and mechanical properties of Pt-Fe nano film are verified.

Abstract: The influence of the interfacial friction on the continuous rheo-forming microstructures of magnesium alloy. The effects of interfacial friction on the microstructure evolution in magnesium alloy were investigated. It was shown that strong shear stress and internal friction occur inside the melt under the interfacial friction. In roller-shoe chamber, the growth direction of dendrites growing along the normal direction of the roller near the roller-shoe is changed under shear stress and melt resistance force. when the degree between dendrite and normal direction of roller is about 45 degree, the dendrites can be stablized and grow easily along this direction. Under an appropriate pouring temperature, with the increase of pouring temperature, there is enough room for the grains near the roller-shoe to grow, the grains are not easy to collide mutually, so the dendrites form. In roller-shoe chamber, coarse dendrites near the roller become gradually refined when they grow into the mushy region. Moreover, because dynamic friction force and shear stress of roller are stronger at the exit of the chamber, dendrites fracture and fracture layer or cracks appears. The microstructures consist of mainly rosette and spherical grains on the central position.

Abstract: In order to enhance grinding efficiency of the magnetic abrasive finishing (MAF) method, we usually use the sinter method or the cementation method to mix the magnetic particles and abrasive particles together. However, the cost is high, and the variety is incomplete. Therefore, with the ferromagnetism to iron particles, the alumina particles and the lipin three kind of material simple mixture participate in the magnetic abrasive finishing which directly polishes, already obtained the good effect through the experiment. This paper analyses and explains the characteristic of the friction coefficient and the friction force on magnetic abrasive finishing according as account and experiment data.

Abstract: A total weight reduction approach has been key issue for car manufacturers to cope with more and more stringent requirements for fuel economy. This paper describes the twin-roll casting technology of magnesium alloys that contain relatively high weight ratios of aluminum, such as AZ91,AZ101 and AZ111. The magnesium alloy sheets were cast by a horizontal twin roll caster to manufacture relatively high-strength Mg alloys with high aluminum content. The influences of such process parameters as casting temperature and roll speed were ascertained. The microstructures of cast magnesium alloy sheets were observed to investigate the effects of roll-casting conditions on crystal growth in the cast products. It was found that Mg alloys with high aluminum content can be fabricated at a roll speed of 15 m/min with a horizontal-roll caster. The grain size of the manufactured wrought magnesium alloy sheet was about 10 μm due to rapid solidification in the proposed process.

Abstract: Molecular dynamics (MD) simulations with an EAM potential are carried out to study the strain rate effects on the tensile deformation of single-crystal copper films. The stress, the atomic energy, as well as the atomic configurations of the systems are presented to explore the strain rate effects on copper films. It is found that yield stress increases with loading rate. Meanwhile, deformation mechanisms with different strain rates are analyzed in the present work. At lower strain rate, slips along {111} planes are primarily responsible for the plastic deformation in nano-Cu films. As strain rate increased, the motion of dislocations becomes easier, a transition of the deformation mechanism from sequential propagation of slips along well-defined slip planes to complex cross-slip.

Abstract: The paper reported using a mathematical model that simulated the wear volume in comparison to measurement by a ball-on-disc for deposited CrN films on tool steel (JIS SKD11). Three dimensional profile instruments were used to measure the wear scar trace for variations of numerical data of two dimensional profiles. By using numerical algorithms, the wear volume measurements of wear profiles are to save considerable time and economical. A new mathematical method is issued for determining wear volumes in this study. The estimated results were precisely fitted as compared with other calculations for three dimensional estimations of wear volumes.

Abstract: Evaluation of manufacturing process in milling by direct measurement of cutting force is considered to be effective comparing to indirect measurement of electricity. This paper proposed a new evaluation method of end-mills by the direct measurement of cutting force. Cutting forces were precisely obtained by a 3-component dynamometer during end milling. Each flute cutting forces was evaluated for two types of end-mills (non wear-out, wear-out) by wave patterns of cutting force. A distinctive difference in the two types of end-mills has been clearly seen. The effectiveness of the proposed evaluation method has been clarified.