变形率对抗拉强度的影响及材料优选方案分析

耐拉力是用裸端子实施电气连接时的重要技术要求,变形率是影响耐拉力的重要因素,不但不同牌号的铜材在压接过程中有不同的适宜变形率范围,而且相同的裸端子用不同压接工具压接时必然出现不同的变形率,在研究裸端子耐拉力时可以用等截面纯铜导线的拉断力作为研究依据。

复合绝缘子应用于碳纤维复合芯导线增容工程的试验研究

碳纤维复合芯导线具有耐高温、载流量大等优点,其短时容许温度甚至可超过200℃,若使用复合绝缘子,其高温传递到复合绝缘子高压端部时,会影响芯棒、硅橡胶材料和金属附件连接区的压接强度性能,严重时可引起掉串事故。为此,从理论计算、试验验证、运行特性分析、模拟试验等4个方面,分析了在高温运行条件下,复合绝缘子高压端部的温度场分布情况和影响复合绝缘子运行性能的关键因素,并根据辽宁地区220kV辽元#1线在ACCC-713碳纤维合金导线下实际运行2a的复合绝缘子的电气、机械性能分析,及在实验室条件下,不同试验温度下复合绝缘子的机械性能变化结果,提出了实际应用时应注意的问题和建议。研究表明,随着绝缘子钢脚温度的上升,绝缘子强度逐渐下降,在180°C条件下可降低至初始强度的50%。

Effect of grain size of primary α phase on bonding interface characteristic and mechanical property of press bonded Ti-6Al-4V alloy

The effect of grain size of primary α phase on the bonding interface characteristic and shear strength of bond was investigated in the press bonding of Ti-6Al-4V alloy. The quantitative results show that the average size of voids increases from 0.8 to 2.6 μm and the bonding ratio decreases from 90.9% to 77.8% with an increase in grain size of primary α phase from 8.2 to 16.4 μm. The shape of voids changes from the tiny round to the irregular strip. The highest shear strength of bond can be obtained in the Ti-6Al-4V alloy with a grain size of 8.2 μm. This is contributed to the higher ability of plastic flow and more short-paths for diffusion in the alloy with smaller grain size of primary α phase, which promote the void closure process and the formation of α/β grains across bonding interface.

Bonding mechanism of X10CrNi18-8 with Ni/Al_2O_3 composite ceramic by pressureless infiltration

Abstract： An alloy steel/alumina composite was successfully fabricated by pressureless infiltration of X10CrNil8-8 steel melt on 30% （mass fraction） Ni-containing alumina based composite ceramic （Ni/Al2O3） at 1 600 ℃. The infiltration quality and interfacial bonding behavior were investigated by SEM, EDS, XRD and tensile tests. The results show that there is an obvious interfacial reaction layer between the alloying steel and the Ni/Al2O3 composite ceramic. The interfacial reactive products are （FexAly）3O4 intermetallic phase and （AlxCry）2O3 solid solution. The interracial bonding strength is as high as about 67.5 MPa. The bonding mechanism of X10CrNi 18-8 steel with the composite ceramic is that Ni inside the ceramic bodies dissolves into the alloy melt and transforms into liquid channels, consequently inducing the steel melt infiltrating and filling in the pores and the liquid channels. Moreover, the metallurgical bonding and interfacial reactive bonding also play a key role on the stability of the bonding interface.

Correlation between microstructural features and tensile strength for friction welded joints of AA-7005 aluminum alloy

Similar friction welded joints of AA-7005 aluminum rods were fabricated using different combinations of process parameters such as friction pressure(1.0, 1.5 and 2.0 MPa) and friction time(10, 15 and 20 s). Interfacial microstructure and formation of intermetallic compounds at the joint interface were evaluated via scanning electron microscopy(SEM) equipped with energy dispersive spectrum(EDS), and optical microscopy(OM). Microstructural observations reveal the formation of intermetallic phases during the welding process which cannot be extruded from the interface. Theses phases influence the tensile strength of the resultant joints. From the tensile characteristics viewpoint, the greatest tensile strength value of 365 MPa is obtained at 1.5 MPa and 15 s. Finally, the role of microstructural features on tensile strength of resultant joints is discussed.

Correlations between direct and indirect strength test methods

The difficulties associated with performing direct compression strength tests on rocks lead to the development of indirect test methods for the rock strength assessment. Indirect test methods are simple, more economical, less time-consuming, and easily adaptable to the field. The main aim of this study was to derive correlations between direct and indirect test methods for basalt and rhyolite rock types from Carlin trend deposits in Nevada. In the destructive methods, point load index, block punch index, and splitting tensile strength tests are performed. In the non-destructive methods, Schmidt hammer and ultrasonic pulse velocity tests are performed. Correlations between the direct and indirect compression strength tests are developed using linear and nonlinear regression analysis methods. The results show that the splitting tensile strength has the best correlation with the uniaxial compression strength.Furthermore, the Poisson's ratio has no correlation with any of the direct and indirect test results.

Influence of Waste Tire Chips on Strength Characteristics of Soils

An experimental study was conducted to investigate the effect of waste tire chips on the strength characteristics of two soils. A cohesive clayey silt soil and a cohesionless free sand soil were used. A program of standard Proctor tests, unconfined compression tests and California bearing ratio tests was carried out on specimens of the cohesive soft-tire mixtures, by varying tire chips content from 5% to 20% by weight of the soil. Vibratory compaction tests and direct shear tests were conducted on the cohesioliless soft-tire mixtures by adding tire chips varying from 10% to 50% by weight. The results showed that 13% and 30% chip contents, respectively by weight, were optimum for composite strength of the two reinforced soil mixtttres.