To develop materials suitable for spent-nuclear-fuel containers, the effect of forced cooling on mechanical properties and fracture toughness of heavy section ductile iron was investigated. Two cubic castings with dif...To develop materials suitable for spent-nuclear-fuel containers, the effect of forced cooling on mechanical properties and fracture toughness of heavy section ductile iron was investigated. Two cubic castings with different cooling processes were prepared: casting A was prepared in a totally sand mold, and casting B was prepared in a sand mold with two chilling blocks placed on the left and right sides of the mold. Three positions in each casting with different solidification cooling rates were chosen. In-situ SEM tensile experiment was used to observe the dynamic tensile process. Fracture analysis was conducted to study the influence of vermicular and slightly irregular spheroidal graphite on the fracture behavior of heavy section ductile iron. Results show that the tensile strength, elongation, impact toughness and fracture toughness at different positions of the two castings all decrease with decreasing cooling rate. With the increase of solidification time, the fracture mechanism of conventional casting A changes from ductile fracture to brittle fracture, and that of casting B with forced cooling changes from ductile fracture to a mixture of ductile-brittle fracture.展开更多
基金financially supported by the National Natural Science Foundation of China(No.51174068 and No.51374086)
文摘To develop materials suitable for spent-nuclear-fuel containers, the effect of forced cooling on mechanical properties and fracture toughness of heavy section ductile iron was investigated. Two cubic castings with different cooling processes were prepared: casting A was prepared in a totally sand mold, and casting B was prepared in a sand mold with two chilling blocks placed on the left and right sides of the mold. Three positions in each casting with different solidification cooling rates were chosen. In-situ SEM tensile experiment was used to observe the dynamic tensile process. Fracture analysis was conducted to study the influence of vermicular and slightly irregular spheroidal graphite on the fracture behavior of heavy section ductile iron. Results show that the tensile strength, elongation, impact toughness and fracture toughness at different positions of the two castings all decrease with decreasing cooling rate. With the increase of solidification time, the fracture mechanism of conventional casting A changes from ductile fracture to brittle fracture, and that of casting B with forced cooling changes from ductile fracture to a mixture of ductile-brittle fracture.
文摘采用暂态短路电流计算方法和有限元法,分析了高压大截面电缆短路电动力的计算过程,推导出高压大截面电缆金具短路电动力的计算公式,同时考虑电缆蛇形敷设因素、导体外层介质缓冲作用及电缆位移偏转量,引入短路电动力工频分量(50 Hz)修正系数K1和两倍工频分量(100 Hz)修正系数K2对作用在电缆金具上的短路电动力进行修正。基于ANSYS建立电缆金具系统三维有限元计算模型,分别研究电缆敷设跨距和相间距对金具应力场的影响,并对双桥子-桃乡220 k V电缆段进行计算。由计算结果可知,在螺杆中点处产生的应力最大,即该位置最易变形或拉裂,对于220 k V电缆工程中"一"字形排列形式,电缆敷设跨距和相间距分别应满足l≤2.7 m,0.28 m≤a≤0.30 m。
