Advanced Materials Research Vols. 399-401

Abstract: α-Glucosidases play critical role both in primary metabolism and in glycoconjugate biosynthesis and processing. In this paper, the reasonable three-dimensional molecular model of AglA was generated by homology modeling. This modeled protein is divided into five major structural domains, and the catalytic domain is classical (β/α) 8 barrel with the active site pocket positioned at its C-terminal side. With analyses of conserved residues and overlay of homology structures, the residues Tyr 662, Tyr527, Glu521, His238 and Tyr235 was predicted as the main substrate binding sites, and residues Asp490, Glu493 and Asp660 were deduced to be the acid/base catalytic residues.

Abstract: In an effort to improve the reliability and reduce the operating costs of helicopter structure, an increasing emphasis is being placed on the damage tolerant approach for life management of helicopter structure. Corrosion damage of helicopter dynamic components and life reliability prediction approach has been systematically analyzed. Based on the conclusion of fatigue life under normal environment, the model for life reliability analysis of helicopter dynamic components has been established. A hybrid approach based on a mixture of the traditional safe-life and damage tolerance techniques can be used as an optimal strategy for ensuring helicopter structural integrity; the life of a helicopter main rotor blade under corrosion environment has been obtained according to flaw-tolerance method. According to probabilistic fracture mechanics theory, the analytical model of structures with initial corner cracks has been established. Thus the service life and inspection intervals according to the request of reliability can be determined; it is very valuable in engineering for life prediction and monitoring of helicopter dynamic components under corrosion environment.

Abstract: Fractals and catastrophe analysis are applied to analyze photos of the law of crack of three sets of fatigue samples under different stress cycles. The results indicate that the law of crack has fractal characteristics. For undestroyed samples, the law of crack appears and develops, and the fractal dimension tends to be constant eventually. For destroyed samples, fractal dimension development is divided into four stages, that is, increasing gradually, increasing stably, decreasing stably and decreasing rapidly to the approximate value of one. When rupture occurs, the catastrophe point is the corresponding number of stress cycle.

Abstract: After the CS-444 infrared ray carbon sulfur analyzer reducing and stabilizing the blank value, we use it for the initial measurement and second measurement, and the third measurement if necessary, we can get the blank value of the sulfur. The results show that the precision and accuracy are better.

Abstract: Experimental study on surface stress measurement of laser cladding Fe-based alloy coating based on Rayleigh wave acoustoelastic theory was introduced. Two Rayleigh wave transducers with 5MHz frequency, the distance between which was fixed, were employed to measure the difference in time of flight along the surface of laser cladding Fe-based alloy coating. Rayleigh wave signal responding to different tensile stress was collected and the difference in time of flight between unstressed and each stressed Rayleigh wave signal was calculated with normalized cross correlation function. Results show that the propagation velocity of Rayleigh wave linearly increases with tensile stress increasing, and the maximum difference in time of flight is obtained at tensile stress level of 492MPa, while the relation between tensile stress and the difference in time of flight is obscure with tensile stress further increasing. Furthermore, the thickness of laser cladding Fe-based alloy coating and the deformation of coating surface may result in errors in experiment. Finally the surface stress of laser cladding Fe-based alloy coating is evaluated by Rayleigh wave acoustoelastic technique and the experimental result is well compared with the theoretical value.

Abstract: The tribological behaviour of beryllium copper alloy QBe2 against 30CrMnSiA steel under sliding condition were tested at the M2000A model wear tester. It studied the hardness, surface roughness, load and prior corrosion of QBe2 specimens under the dry or grease lubricated conditions. The volume wear and friction coefficient were relatively better when the hardness of QBe2 was lager under the grease lubricated sliding friction. The volume wear was the smallest when surface roughness was 0.8μm, and its tribological properties were the best under the grease lubricated sliding friction. Meanwhile the values of wear loss, wear rate and average friction coefficient under the grease lubricated friction were one level smaller than that under the dry friction. The volume wear and friction coefficient decreased with the loads declined under the grease lubrication condition. Prior corrosion process made the lubricant effect worse, which obviously reduced the wear-resisting property of QBe2 and enlarged its wear rate and friction coefficient.

Abstract: Based on GM yield criterion, the analytical solutions for shape and size of mode I crack tip plastic zone and the burst pressure for X70 pipeline steel are derived. Comparing the solutions with those based on Mises and Trasca criteria shows that under plain strain condition the area of plastic zone on GM is between Tresca and Mises solutions, and very close to Mises one. Among the areas Tresca’s is the largest and Mises is the smallest and all three zones are dumbbell shaped. However, for pipeline burst pressure based on Tresca criterion is the smallest and that on Twin shear stress criterion (TSS) is the largest, those on GM and Mises are also very close to each other and lie between Tresca and TSS results.

Abstract: Metallographic analysis, hardness testing and diffusion kinetics analysis were used to investigate the influences of temperature and time on morphology of eutectic Si and properties of A357 alloy under the solution heat treatment, and optimal solution parameters were determined. The results indicate that solution heat temperature strongly influences the morphology of eutectic Si and mechanical properties of the A357 casting alloys. Spheroidization degree of eutectic Si decreases and the mechanical properties of A357 alloy with the increasing of solution temperature. According to the experiment results, optimal solution parameters of A357 alloy were determined as 550°C×6h.

Abstract: By the investigation of the 400°C low cycle fatigue behavior of 4 kinds of notched cylindrical specimens made 2.25Cr-1Mo stee1. The high temperature low cycle fatigue life was evaluated by the criterons of equivalent range. The results show that equivalent criterion for evaluating high temperature low cycle fatigue life has its experimental and theoretical foundation, but further investigation is still needed．

Abstract: The lattice constants, total energies and densities of states of Ti, Zr and Hf in ⅣB group with different crystalline structures have been calculated, and the results have been compared with the results of the projector augmented wave (PAW) method in first-principles, CALPHAD and experiments. It is found that the results of lattice stability in this paper agree completely with those of the PAW method in first-principles and agree well with those of CALPHAD. Further analyses of lattice stability from electronic structures show that the crystalline Ti,Zr and Hf with hcp structures have the obvious character of stable phases, but fcc and bcc structures have the character of metastable and unstable phases, agreeing with the results of total energy calculations. It is found from the analyses of atomic populations that the transiton numbers of electrons from the s state to the p and d states for the hcp, fcc and bcc crystals decrease with the increase in elemental period, and the transiton number of electrons from the s state to the p state decrease dramatically, but the transiton from the s state to the d state increase dramatically, leading to much more number of electrons in the d state than that in the s or p state, stronger cohesion or higher cohesive energy between atoms in heavy metals and accordingly the stabler lattice in these heavier metals.