Sharp local structure, like the leading edge of hypersonic aircraft, confronts a severe aerodynamic heating environment at a Mach number greater than 5. To eliminate the danger of a material failure, a semi-active the...Sharp local structure, like the leading edge of hypersonic aircraft, confronts a severe aerodynamic heating environment at a Mach number greater than 5. To eliminate the danger of a material failure, a semi-active thermal protection system is proposed by integrating a metallic heat pipe into the structure of the leading edge. An analytical heat-balance model is established from traditional aerodynamic theories, and then thermal and mechanical characteristics of the structure are studied at Mach number 6–8 for three refractory alloys, Inconel 625, C-103, and T-111. The feasibility of this simple analytical method as an initial design tool for hypersonic aircraft is assessed through numerical simulations using a finite element method. The results indicate that both the isothermal and the maximum temperatures fall but the von Mises stress increases with a longer design length of the leading edge. These two temperatures and the stress rise remarkably at a higher Mach number. Under all investigated hypersonic conditions, with a 3 mm leading edge radius and a0.15 m design length, the maximum stress exceeds the yield strength of Inconel 625 at Mach numbers greater than 6, which means a material failure. Moreover, both C-103 and T-111 meet all requirements at Mach number 6–8.展开更多
文摘为准确测量超薄壁回转件旋压后的外径尺寸,提出了一种基于重构横截面轮廓曲线的等效外径在机测量方法。该方法利用周向均布的3套线激光位移传感器与旋轮架的轴向移动模块,获得回转件任意轴向位置横截面的外轮廓数据;通过对3套传感器所获截面数据的坐标变换及数据匹配,实现截面完整轮廓数据的精确拼接,并以离散数据点的保形曲线重构方法重构截面外轮廓曲线,利用同一闭合曲线各变形状态的长度不变性,得到了截面等效外径;分别以芯轴及薄壁回转件开展了外径检测实验。实验结果表明:所提方法可准确测量超薄壁回转件外径,其精度为0.019 mm.
文摘通过随机误差影响分析索长误差和外联节点坐标误差对索力的影响特性,确定合理的误差控制指标.对比了定值分布、均匀分布和正态分布3种索长误差分布模型,分析了环索和径向索的长度误差对索力的影响,探讨了不同索长误差控制标准.计算结果表明,环索力受径向索长误差影响较小,径向索和环向索的索力受环索索长误差影响基本一致.索长误差限值越小,外联节点的安装误差限值越大.各榀外联节点的安装误差限值不同,高处限值比低处小.为满足索力误差不超出±10%的要求,案例工程控制指标为:拉索制作长度误差应不超出索长的±0.01%,低处和高处外联节点沿径向索方向的坐标误差应分别不超出±83和±67 mm.
基金financially supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(No.51121004)the Fundamental Research Funds for the Central Universities(No.HIT.BRETIV.201315)
文摘Sharp local structure, like the leading edge of hypersonic aircraft, confronts a severe aerodynamic heating environment at a Mach number greater than 5. To eliminate the danger of a material failure, a semi-active thermal protection system is proposed by integrating a metallic heat pipe into the structure of the leading edge. An analytical heat-balance model is established from traditional aerodynamic theories, and then thermal and mechanical characteristics of the structure are studied at Mach number 6–8 for three refractory alloys, Inconel 625, C-103, and T-111. The feasibility of this simple analytical method as an initial design tool for hypersonic aircraft is assessed through numerical simulations using a finite element method. The results indicate that both the isothermal and the maximum temperatures fall but the von Mises stress increases with a longer design length of the leading edge. These two temperatures and the stress rise remarkably at a higher Mach number. Under all investigated hypersonic conditions, with a 3 mm leading edge radius and a0.15 m design length, the maximum stress exceeds the yield strength of Inconel 625 at Mach numbers greater than 6, which means a material failure. Moreover, both C-103 and T-111 meet all requirements at Mach number 6–8.
