Applied Mechanics and Materials Vols. 651-653

Abstract: The application performances of TA2 titanium\S44660 super ferrite stainless steel\B30 cupronickel, which are widely used in power plant, were researched using electrochemical test and mechanical test. The results show that corrosion resistance of B30 is significantly lower than TA2 and S44660. Besides, corrosion resistance of S44660 is superior to TA2. Yield strength and tensile strength of S44660 is higher than TA2 and B30. When considering thickness of cooling tubes, flow rate of cooling water and clean coefficient, the thermal conductivity of three materials have little differences. The shock resistance of S44660 is better than TA2 and B30. S44660 contains a small amount of Ni, which improves greatly the anti-cracking ability of the base metal and welding bead.

Abstract: Original defects in the envelope material easily torn damage under overpressure, when the stratospheric airship in use. This paper based on linear elastic theory studied the tear strength of envelope material containing initial center crack and proposed theoretical model for this problem. Choose Vectran fiber as a reinforcing layer of stratospheric airship envelope material, Combined with digital speckle method measuring tear strength of envelope materials containing different initial center crack length. Comparative analysis found that the theoretical model applicable to estimate the tear strength of envelope material, that center initial crack width ratio is less than 50%.It estimation error within 5% .It satisfies the requirement of engineering application accuracy.

Abstract: The interface microstructure and shear strength weakening of eutectic SnAgCu (SAC)/FeNi-Cu connection after current stressing for 0~12 h were investigated to discuss the stability of the FeNi layer as UBM film layer for Sn base solder. The experiments showed that the FeNi layer separated to two layers with different Fe/Ni ratio rather than intermetallic compound (IMC) thickness variation between the cathode and anode. The IMCs became rougher with a bulk amount of (Cu,Ni)₆Sn₅ emerging in the regains near to interfaces. The shear failure mode exhibited a ductile manner companied by a fracture surface rougher and even grain boundary weakening with the current exposure time increasing.

Abstract: In this paper, the comparisons of the polishing performance between prehardened P20 and S45C steels under the different hardness were carried out by using surface grinding, manual polishing and PVA grinding wheel polishing tests. The results show that the surface roughness of the two kind steels decrease with the increase of hardness and the roughness of S45C is lower than that of P20 during the surface grinding test. After polishing process, the surface roughness of the two kind steels decrease with the increase of hardness as well. However, the surface roughness of S45C is higher than that of P20 after both manual polishing and PVA grinding wheel polishing tests.

Abstract: In this paper, the effects of contents of Fe and P on the microstructures and properties of Cu-Cr-Zr resistance spot welding electrode alloys have been studied by means of electrical conductivity and hardness measurements and optical microscopy. By the addition of 2.5%Fe and 0.03P%, after being aged for 6h, the Cu-Cr-Zr-Fe-P alloy has the highest hardness of 125HV. At this time, the electrical conductivity of alloy is 60%IACS. The addition of 0.1%Zn contributes very little to hardness and electrical changes.

Abstract: Based on macro morphology, metallographic microstructure, field emission scanning electron microscope observations and microhardness testing, failure analysis of the GCr15 steel balls in the ball screw pair was dealt with in this paper. The experimental results showed that small scratches and pits were evenly distributed on the surface of the A steel ball which showed features of wear failure. Characteristics of the B steel ball surface morphology were contacted to fatigue failure. Microstructure observation on the cross-section of the B steel ball showed that martensite and carbides were uneven distributed which were caused by the uneven elements distribution in the raw materials. It was the main cause of this abnormal failure. Therefore, the quality of the raw materials needed to be strictly controlled and the reasonable heat treatment process should be adopted to ensure the quality of the steel balls.

Abstract: Failure analysis on the GCr15 bearing steel and the 20CrMo carburized steel nuts was performed after two sets of fatigue tests of GD8020×1100 ball screw pair. By means of scanning electron microscopy observation, energy dispersive analysis and microhardness testing, it is found that there is an obvious indentation, slight pitting and microcracks on the raceway of the GCr15 bearing steel nut and shows the characteristics of contact fatigue failure. The nonuniformity of microstructure and the lower carbon and chromium content in the indentation, leading to local lower hardness, account for the nut failure. While the raceway of the 20CrMo carburized steel nut is more rough with scratches caused by the damaged steel balls so as to show the characteristics of wear failure. Therefore there are different failure ways for the different nuts made by different steels and heat treatments under the same fatigue testing condition.

Abstract: This paper, using the finite element software ABAQUS, establishes the model of laser shock peening (LSP) of TC4 titanium alloy, and analyzes the influence of different parameters on the residual stress of TC4 titanium alloy and plastic deformation. The results show that LSP can make the surface of TC4 titanium alloy have large compressive stress and plastic deformation, hardness and prolong the fatigue life of materials. Laser energy and the impact frequency are the main factor of surface residual stress effects. The multi-point LSP can perform processing enhanced in surface area, and form residual compressive stress on the surface of the material and in a certain depth.

Abstract: Fe-Cr-Ni preform reinforcing aluminum composite was produced by squeeze casting. And then, T6 heat treatment was conducted to enhance the composite’s performance. After which, isothermal compression tests in temperature range of 298 - 473 K at an strain rate range from 0.001 to 10 s^-1 were carried out on Gleeble 3500 thermo-mechanical simulation machine. It is found that, for a specific strain rate, the flow stress decreases markedly with temperature increases. And for a fixed temperature, the flow stress generally increases as the strain rate increases. Based on the experimental true stress-true strain data, the Arrhenius type model was established.