Key Engineering Materials Vols. 353-358

Abstract: The optimized conditions of pressureless sintering were investigated in order to obtain the bending strength and the elastic wave signal of Al2O3 composite ceramics for textiles machinery. As sintering conditions, a temperature range from 1400°C to 1700°C and time from 30 minutes to 150 minutes were applied. Three-point bending tests were conducted on the sintered materials to obtain the strength property. From the test results, the optimum sintering condition was 1600°C, 100 minutes. Al2O3 composite ceramics showed that the elastic wave signal characteristics had a regular correlativity between the optimum sintering temperature and time as well as the maximum bending strength.

Abstract: The strengthening effects of the Cu-80 wt.% W (CuW80) alloy and the copper parts in Cu-80wt.% W /Cu (CuW80/Cu) solid contact alloy, which was sintered and infiltrated prepared by powder metallurgy, were investigated. The effects of different compressive deformation on microstructure and properties of the CuW80 were studied. Furthermore, the influences of HextrusionH on copper parts, the carrier material of the solid contact alloy CuW80/Cu were also investigated. The results show that the tungsten and copper phases are closely bonded by physical bond in the form of pseudo-alloy and the copper phase is homogeneously dispersed within the tungsten framework. The hardness of the CuW80 increases with increasing compressive deformation. Especially, the hardness of the copper parts in CuW80/Cu increases remarkably after extrusion and the maximum value can reach 200%. The hardness increases from the inner to the surface and is proportional to the distance departing from the interface of the CuW80 and Cu. TEM observation shows that the dislocation tangles exist, even inside the dislocation cell, in copper grains after extrusion.

Abstract: This paper examined the microstructure and tensile properties of an Al8Si0.35Mg cast alloy during several prolonged aging treatments. The results show that there is a improvement in ductility for solution treated Al8Si0.35Mg samples aging at 150 °C more than about 20 h to 48 h or ageing at 200 °C more than about 10 h to 20 h, but no significant reductions in UTS are observed. There is a substantial improvement in ductility at long aging times at the cost of UTS decreases. The morphology changes and distribution characteristics of precipitates and its effect on tensile properties in prolonged aging conditions have been analyzed.

Abstract: The present work was performed on Al11Si3Cu0.35Mg samples cast in a permanent mold preheated to 200 °C. The tensile properties for varies solution treated samples aged at 200 °C for 6 h were examined in order to study the influence of solution temperature on the alloy properties. The dissolution of copper-containing phases and the incipient melting were analyzed for cast samples solution treated in the temperature range 500~520 °C for 8 h followed by quenching in water. The influence of the incipient melting on mechanical properties has been discussed.

Abstract: The mathematical model of the braced stress-strain in the vacuum glazing was established with the crunode method by elastic mechanics. The braced stress-strain field of vacuum glazing was received, and the stress-strain distribution was analyzed at the same time. Electric test method was used to validate the stress distribution. The experimental results are shown that the maximal stress of vacuum glazing occurs in the second braced pillar of the four-square side. The maximal stress value by elastic mechanics is 11.057MPa, while the measured value by electric test method is 11.765MPa, and its tolerance is only 6.02%. The positive stress in the cross section of the braced pillar is 179MPa, the longitudinal strains of steel and glazing braced pillar are 0.2686μm and 0.7414μm, respectively. The tolerance of braced pillar height and the glazing level degree are controlled to guarantee force equality, which increases strength, dependability, and service life of vacuum glazing.

Abstract: The TiB/Ti metal matrix composites (MMCs) with different volume fractions of in situ TiB reinforcements were spark plasma sintered at 1000 °C with a pressure of 20 MPa for 5 minutes in vacuum. The in situ synthesized TiB is whisker shape with a hexagonal transverse section and distributes uniformly and randomly in the Ti matrix. The Young’s modulus of TiB was back-calculated from the elastic properties of the composites using the Halpin-Tsai model. The Young’s moduli of all the composites were found to increase with the increase of TiB volume fraction. The calculated value of TiB Young’s modulus is about 489±83GPa. Values of Young’s moduli of TiB whisker obtained according to different methods were compared and discussed.

Abstract: Based on the experimental and theoretic studies of the frictional materials in literatures, a generalized non-linear strength theory is presented. The generalized strength theory has the same mathematical form as classical Drucker-Prager strength (D-P) criteria. It describes strength characteristics of various materials using a unified formula, and it includes or approximates numerously present strength criterions. The shape of generalized Drucker-Prager (GDP) criteria is convexly smooth curve between the classical D-P criteria (upper bound) and the external contour line of Mohr-Coulomb (M-C) criteria (lower bound) on the deviator-plane, and a straight line on the meridian-plane. Through variation of parameters in the criteria, a series of criterions ranging between these two bounds may be introduced by the unified strength criteria, and the different strength properties of various materials were denoted.

Abstract: A key problem in engineering application of “design by analysis” approach is how to decompose a total stress field obtained by the finite element analysis into different stress categories defined in the ASME Code III and VIII-2. In this paper, we suggested an approach to separate primary stress with the principle of superposition, in which the structure does not need to be cut into primary structure but analyzed as a whole only with decomposed load. Taking pressurized cylindrical vessel with plate head as example, the approach is demonstrated and discussed in detail. The allowable load determined by the supposed method is a little conservative than that determined by limited load analysis.

Abstract: With the analysis of thickness distributions of elbow by the equal-strength criterion and plastic deformation by pushing bending process, an ideal thickness distribution is proposed with the consideration of elbow processing characteristics to improve its ratcheting resistance. Ratcheting of elbows under internal pressure and reversed in-plane bending is analyzed with Chaboche model by finite element method, which shows that elbows with the proposed thickness distribution have great resistance to ratcheting compared with equal thickness elbows.

Abstract: Based on the structure of the rock mass surrounding a highway tunnel under construction, a new methodology for defining the strength of jointed rock mass is proposed. The laboratory experiments and numerical simulations of rock samples, including both intact rock and rock with a single typical joint, are carried out to ensure that the mechanical parameters of the rock and the joint can be obtained. In addition, the strength of the rock mass surrounding the tunnel, without resorting to the difficult task of sampling and testing of large-scale rock mass, is evaluated by using the proposed method. It is shown that the strength reduction of rock mass is governed by the geometric configurations as well as the mechanical properties of the joints, and that the presence of joints results in the non-linearity of the pre-peak region.