Applied Mechanics and Materials Vols. 268-270

Abstract: According to the characteristics of NM360, a contrast experiment for drilling performance in YG8 cemented carbide twist drill, high-speed steel twist drill and factories used in coating the ordinary high-speed steel twist drill has been done. Using microscope to observe the damage of drills, we found that form this experiment some causation in tool invalidation that tool breakage is main factor for the high-speed steel drill bits, brittle fracture is main factor for carbide drill bits. Brittle carbide cutting tools, feed speed too much impact load is too large, causing the blade fracture. As the tool edge wedge angle is too small, poor edge strength, easy chipping, edge wedge angle can not be too small.

Abstract: The results of an experimental investigation on the shear strength of structural joints are presented and discussed. Joint typologies generally employed in structural frames of industrial warehouses and intermediate floors are taken into consideration. Specimens were supplied by an industrial shelving manufacturer, in two different configurations: the first one characterized by steel pressed geometrical connectors and the second one consisting in bolted fittings to angular welded supporting plates. A specific testing device has been designed in order to transfer axial loading into shear loading applied to a couple of joints in a symmetrical testing configuration. Quasi-static loads were applied with increasingly intensity steps, until the yielding of the material or the overall structure collapse were reached. Failure modes of the tested joints are analyzed and discussed.

Abstract: Abstract. This work studied the feasibility of dissimilar welding between AISI 304 stainless steel and AISI 1020 carbon steel plates with the thickness of 15 mm. The processes applied in this work were gas tungsten arc welding (GTAW) and shield metal arc welding (SMAW). Microstructure of weld metal produced by GTAW consists of delta ferrite network in austenite matrix, while the dendrite of delta ferrite finely distributed in austenite matrix was found in the weld produced by SMAW. Hardness values of weld metals produced using these two techniques were superior to those of stainless steel and carbon steel base metals respectively. Weld metals produced by these two processes were qualified under tension and bending. This was justified by the result that the failed part after transverse tensile test was on carbon steel, and no crack was found in weld metal after U-shape bending. Impact test exhibited higher toughness of weld metal produced by GTAW than that produced by SMAW. This might be from microstructure of the former weld as network of delta ferrite in austenite matrix which might help absorb impact energy. Pitting corrosion potential of weld metal produced by GTAW was higher than that produced by SMAW and stainless steel base metal respectively. In the aspect of mechanical and corrosion properties of the weld, GTAW was considered as a promising process that could be used for dissimilar welding between these two metals.

Abstract: Ultrafine-grain or even nano-grain microstructure can be made by equal channel angular pressing (ECAP), mainly resulting from shear strain. The authors experimentally investigated 00Cr18Ni12 austenitic stainless steel and its mechanical properties during and after ECAP. The results showed that because of larger shear stress, many slipping bands occured inside grains, with the increase of pressing pass, the slipping bands may interact with each other to separate slipping bands into sub-grains, finally, the sub-grains transformed into new grains with large angular boundaries. The grain size was about 200nm after the 7th pass. After the 1st and 2nd pass, the tensile strength was higher 93% and 144% than that without ECAP, the yield strength was 5.3 and 6.6 times of that without ECAP respectively.

Abstract: In hot metal forming processes, the material is subjected to the thermo-mechanical processing. A fully three dimensional thermo-mechanically coupled FEM-simulation of an eleven pass hot rough rolling process of H-beam has been performed. Microstructure evolution equations available in literatures were incorporated into the commercial FE solver ABAQUS/Explicit, through user defined subroutine VUMAT, to simulate the microstructure evolution. Since it’s impractical to obtain the austenite grain size distribution in the beam blank during industrial hot rolling, the calculated rolling loads are compared with the mills loads instead of grain size comparison between the predicted average value and the real ones.

Abstract: Novel multicomponent amorphous alloys have been manufactured by the method of equiatomic substitution for the Y element in Y56Al24Co20 amorphous alloy. Y56-xMxAl24Co20(M=Ce, Pr or Nd; x= 5, 10, 15 and 20at.%) alloys with a diameter of 2 mm have been prepared by suction casting. The glass-forming ability(GFA) was characterized by differential scanning calorimetry(DSC). The supercooled liquid region ∆Tx(=Tx-Tg ) and parameter γ (=Tx/(Tg+Tl)) increase with the increasing of the addition element content. The effects of equiatomic element on ∆Tx of Y56Al24Co20 alloy arise from the increasing of the electronegativity difference Δx, the atomic size parameter δ and the valence electron difference Δn. The results suggest that the GFA of some alloys might be improved by the addition of other equiatomic elements substitution for the alloy constituent elements.

Abstract: The elastic-plasticity of the titanium alloy material has certain effect on the stability of the milling system. When the material is incompressible, the curve and the simple tensile curve are the same, and the material’s curve and the one-way shear’s curve are also the same. This may be called single curve theory. This paper is, under simple loading conditions, gets the data in the titanium alloy’s tensile experiment and torsion experiment. It studies the constitutive relation in the state of the multidimensional stress and the strain, by the material data obtained in the simple tensile experiment and torsion experiment according to the single curve theory. In the simple loading condition, it obtains the data of the titanium alloy’s tensile experiment and torsion experiment, and then gets the titanium alloy’s incremental constitutive relation, and by integration, it gets the constitutive relation of the titanium alloy’s total strain theory.

Abstract: The effect of ageing temperature on damping capacity of the Cu-20.4Al-8.7Mn alloy at room temperature was investigated by internal friction measurements. The results indicated that damping capacity of the alloy exhibits a non-monotonous changing trend with ageing temperature. Ageing at lower temperature of less than 150oC, damping capacity rapidly increses even up to maximum of 0.01 with the increasing ageing temperature, the reason of which should relate with the increased amount of twin boundaries and phase interfaces between martensites due to the thinning and splitting of martensitic plates, whereas when the ageing temperature exceeds 150oC, the damping capacity trends to steeply decrease as the ageing temperature increases until close to a constant in last corresponding to the ageing at higher temperature due to the occurrence and complete finish of transformation of martensites to austenites.

Abstract: Microstructure of as-cast AZ91D alloy doped with 0.7wt% silicon was investigated, the damping capacity of the alloy was measured by cantilever beam technique, and the damping mechanism was also analyzed. The results show that after addition 0.7%Si into AZ91D alloy, the dendritic grains are refined, and Chinese script Mg2Si phase forms in the interdendritic areas. The damping capacities of the alloy are improved by Si addition, and increase with increasing of strain amplitude. The damping behavior of the alloy is mainly resulted from dislocation movement, and can be explained by the theory of Granato and Lücke.

Abstract: The pore distribution of low silica sinter ore samples with different alkalinity was measured by pressure mercury, and the fractal characteristic of pore distribution was calculated with multifractal theory, then metallurgical properties were also obtained, finally, their connection among them was discussed. The results showed that the pore distribution has experienced a process from non-uniform to uniform with increasing alkalinity. When the alkalinity was 2.0, the spectral width Δα was minimum, multifractal structure was more uniform, fractal characteristics was better, in the meantime, the pore distribution was more uniform, and the pores were larger, which improved metallurgical properties. The results also showed that when the alkalinity was 2.0, its metallurgical properties was optimal.