The effect of thermal cycling under loading on martensitic transformation and two-way shape memory effect was investigated for Ti-49.8 at. pci Ni alloy. It is shown that Ms and Mf temperature increase with increasing ...The effect of thermal cycling under loading on martensitic transformation and two-way shape memory effect was investigated for Ti-49.8 at. pci Ni alloy. It is shown that Ms and Mf temperature increase with increasing the number of cycles, while As and Af temperature decrease during thermal cycling. The total strain et and permanent strain ep increase with increasing applied stress and number of cycles. The two-way shape memory effect can be improved by proper thermal cycling training under loading, while excessively high applied stress results in the deterioration of TWSME. The reason for the changes in martensitic transformation characteristics and two-way shape memory effect during thermal cycling under loading is discussed based on the analysis of microstructure by TEM observations.展开更多
The most significant differences between continuous welded rails (CWRs) and general split-type connectors are axial compression in the longitudinal direction, buckling stability and other issues generated under the in...The most significant differences between continuous welded rails (CWRs) and general split-type connectors are axial compression in the longitudinal direction, buckling stability and other issues generated under the influence of thermal effect. Under thermal effect, a dynamical behavior similar to that of a beam fixed on two sides occurs in the central locked area of the welded rail, as there is axial compression but no possibility of sliding. Continuous welded rails do not contract or expand, and are supported by the dynamical system made up of ballasts and rail clips. The rail-support system mentioned above has the features of non-uniform material distribution and uncertainty of construction quality. Due to these facts, the dynamics method based on the linear elastic hypothesis cannot correctly evaluate the rail’s buckling conditions. This study is aimed at applying Finite Difference Method (FDM) and Monte Carlo Random Normal Variables Method to the analysis of welded rail’s buckling behavior during the train’s acceleration and deceleration, under thermal effect and uncertain factors of ballast and rail clips. The analysis result showed that buckling occurs under the combined effect of thermal effect and the train’s deceleration force co-effect and the variance ratio of ballast and rail clips is over 0.85, or under the combined effect of thermal effect and the train’s acceleration force when the variance ratio is over 0.88.展开更多
A thermal hydraulic model based on the lumped parameter method is presented to analyze the load-carrying capacity of a slipper pair in an aviation axial-piston pump under specified operating conditions. Both theoretic...A thermal hydraulic model based on the lumped parameter method is presented to analyze the load-carrying capacity of a slipper pair in an aviation axial-piston pump under specified operating conditions. Both theoretical and experimental results are presented to demonstrate the validity of the thermal hydraulic model. The results illustrate that the squeezing force and thermal wedge bearing force are the main factors that affect the film thickness and load-carrying capacity.At high oil temperature and high load pressure, the film thickness decreases with increasing clamping force due to a combined action of the squeezing bearing force and the thermal wedge bearing force, but the load-carrying capacity will increase. An increase of the film thickness is proven to be beneficial under high shaft rotational speed but especially dangerous as it strongly increases the ripple amplitude of the film thickness, which leads to decreasing the load-carrying capacity. The structural parameters of the slipper can be optimized to achieve desired performance, such as the slipper radius ratio and orifice length diameter ratio. To satisfy the requirement of the load-carrying capacity, the slipper radius ratio should be selected from 1.4 to 1.8, and the orifice length diameter ratio should be selected from 4 to 5.展开更多
文摘The effect of thermal cycling under loading on martensitic transformation and two-way shape memory effect was investigated for Ti-49.8 at. pci Ni alloy. It is shown that Ms and Mf temperature increase with increasing the number of cycles, while As and Af temperature decrease during thermal cycling. The total strain et and permanent strain ep increase with increasing applied stress and number of cycles. The two-way shape memory effect can be improved by proper thermal cycling training under loading, while excessively high applied stress results in the deterioration of TWSME. The reason for the changes in martensitic transformation characteristics and two-way shape memory effect during thermal cycling under loading is discussed based on the analysis of microstructure by TEM observations.
基金Project supported by the National Science Council of Taiwan (No.NSC 93-2211-E-167-002), China
文摘The most significant differences between continuous welded rails (CWRs) and general split-type connectors are axial compression in the longitudinal direction, buckling stability and other issues generated under the influence of thermal effect. Under thermal effect, a dynamical behavior similar to that of a beam fixed on two sides occurs in the central locked area of the welded rail, as there is axial compression but no possibility of sliding. Continuous welded rails do not contract or expand, and are supported by the dynamical system made up of ballasts and rail clips. The rail-support system mentioned above has the features of non-uniform material distribution and uncertainty of construction quality. Due to these facts, the dynamics method based on the linear elastic hypothesis cannot correctly evaluate the rail’s buckling conditions. This study is aimed at applying Finite Difference Method (FDM) and Monte Carlo Random Normal Variables Method to the analysis of welded rail’s buckling behavior during the train’s acceleration and deceleration, under thermal effect and uncertain factors of ballast and rail clips. The analysis result showed that buckling occurs under the combined effect of thermal effect and the train’s deceleration force co-effect and the variance ratio of ballast and rail clips is over 0.85, or under the combined effect of thermal effect and the train’s acceleration force when the variance ratio is over 0.88.
基金co-supported by the National Natural Science Foundation of China (No. 51505338 and No. 51475332)the Youths Science Foundation of Zhejiang (No. LQ16E050004 and No. LQ17E050003)
文摘A thermal hydraulic model based on the lumped parameter method is presented to analyze the load-carrying capacity of a slipper pair in an aviation axial-piston pump under specified operating conditions. Both theoretical and experimental results are presented to demonstrate the validity of the thermal hydraulic model. The results illustrate that the squeezing force and thermal wedge bearing force are the main factors that affect the film thickness and load-carrying capacity.At high oil temperature and high load pressure, the film thickness decreases with increasing clamping force due to a combined action of the squeezing bearing force and the thermal wedge bearing force, but the load-carrying capacity will increase. An increase of the film thickness is proven to be beneficial under high shaft rotational speed but especially dangerous as it strongly increases the ripple amplitude of the film thickness, which leads to decreasing the load-carrying capacity. The structural parameters of the slipper can be optimized to achieve desired performance, such as the slipper radius ratio and orifice length diameter ratio. To satisfy the requirement of the load-carrying capacity, the slipper radius ratio should be selected from 1.4 to 1.8, and the orifice length diameter ratio should be selected from 4 to 5.
文摘采用数值模拟的方法研究浇注式沥青混凝土摊铺时钢桥面摊铺温度场及温度变形效应.建立钢箱梁温度场模型,对浇注式沥青混凝土摊铺过程中钢桥面温度场分布规律进行了数值模拟,拟合出最不利温度荷载公式.根据时空等效原理建立考虑施工过程的温度荷载公式,计算钢桥面板的局部温度变形,并分析其对铺装效果的影响.研究结果表明,摊铺10 min后钢板局部迅速升温至120℃,并在17 min后达到最大温度123℃,此阶段摊铺温度对钢板结构的影响较大;摊铺区域钢板会产生局部温度变形,最大竖向变形达到7.5 mm,使摊铺层局部厚度有偏差,模拟值接近1 mm.
