热处理工艺对复合熔体处理A356合金组织和性能的影响

利用熔体超声处理、Sr/Ce复合变质及热处理相结合的方法提高铝合金的强韧性,通过金相组织分析及力学性能测试研究了固溶处理对A356合金组织和性能的影响。研究结果表明,熔体处理有利于改善α-Al枝晶和共晶硅相,铸态合金的抗拉强度和伸长率分别达到215 MPa和9.5%;T6热处理后,共晶硅的形态由纤维状转变成独立分布的颗粒状,而除了伸长率之外,合金的力学性能都显著提高;随着固溶时间的延长,共晶硅的等效直径呈现先减小后增大的趋势,而长径比逐渐减小,合金的拉伸性能和硬度均呈现先增大后减小的趋势;当固溶时间为4 h时,合金的综合力学性能达到最佳,其抗拉强度、屈服强度、伸长率和显微硬度分别达到300、240 MPa、8.0%和110HV。     

圆片刀超声切削Nomex蜂窝芯的切削力和表面质量研究

为了研究圆片刀加工参数对切削力和表面质量的影响,首先对圆片刀超声切削和普通切削的切削力进行了理论分析,在此基础上开展了圆片刀超声切削Nomex蜂窝芯试验,获得了进给速度、刀具转速和超声振幅对切削力的影响规律.进一步以蜂窝芯孔壁撕裂数量和长度作为加工表面质量的表征参数,定量研究了加工参数对于蜂窝芯表面质量的影响.试验结果...     

Chatter stability and precision during high-speed ultrasonic vibration cutting of a thin-walled titanium cylinder

Titanium alloys are widely used in the aviation and aerospace industries due to their unique mechanical and physical properties. Specifically, thin-walled titanium (Ti) cylinders have received increasing attention for their applications as rocket engine casings, aircraft landing gear, and aero-engine hollow shaft due to their observed improvement in the thrust-to-weight ratio. However, the conventional cutting (CC) process is not appropriate for thin-walled Ti cylinders due to its low thermal conductivity, high strength, and low stiffness. Instead, high-speed ultrasonic vibration cutting (HUVC) assisted processing has recently proved highly effective for Ti-alloy machining. In this study, HUVC technology is employed to perform external turning of a thin-walled Ti cylinder, which represents a new application of HUVC. First, the kinematics, tool path, and dynamic cutting thickness of HUVC are evaluated. Second, the phenomenon of mode-coupling chatter is analyzed to determine the effects and mechanism of HUVC by establishing a critical cutting thickness model. HUVC can increase the critical cutting thickness and effectively reduce the average cutting force, thus reducing the energy intake of the system. Finally, comparison experiments are conducted between HUVC and CC processes. The results indicate that the diameter error rate is 10% or less for HUVC and 51% for the CC method due to a 40% reduction in the cutting force. In addition, higher machining precision and better surface roughness are achieved during thin-walled Ti cylinder manufacturing using HUVC.     

面向超声波机床加工芳纶纸蜂窝芯的新型固持方法

根据超声波机床加工蜂窝芯的基本原理及切削方式,在双面胶带固持技术的基础上,提出了一种高效、经济的芳纶纸蜂窝固持方法,极大地提高了固持效率,降低了成本。建立了机床功率、真空压力、切削参数以及刀具参数与最小薄膜面积之间的解析表达式,根据机床参数求解可选用新型固持方案的最小薄膜面积。     

大型复材构件自动检测设备中超长梁的结构设计优化及其变形控制

CUS-6000大型超声自动扫描成像检测设备是中航工业北京航空制造工程研究所针对大型复合材料构件的高效自动化检测,研制的20通道大型超声自动化检测设备.在设备的研制过程中,采用有限元方法,广泛计算了多种结构方案和工况条件,提取扫描头部位的变形值,通过数值插值的方法得到各种变形参数随扫描头移动的关系曲线,计算结果对横梁反...     

A multiple-rendezvous,sample-return mission to two near-Earth asteroids

We propose a dual-rendezvous mission, targeting near-Earth asteroids, including sample-return. The mission, Asteroid Sampling Mission (ASM), consists of two parts: (i) flyby and remote sensing of a Q-type asteroid, and (ii) sampling of a V-type asteroid. The targeted undifferentiated Q-type are found mainly in the near-Earth space, and to this date have not been the target of a space mission. We have chosen, for our sampling target, an asteroid from the basaltic class (V-type), as asteroids in this class exhibit spectral signatures that resemble those of the well-studied Howardite–Eucrite–Diogenite (HED) meteorite suite. With this mission, we expect to answer specific questions about the links between differentiated meteorites and asteroids, as well as gain further insight into the broader issues of early Solar System (SS) evolution and the formation of terrestrial planets. To achieve the mission, we designed a spacecraft with a dry mass of less than 3 tonnes that uses electric propulsion with a solar-electric power supply of 15 kW at 1 Astronomical Unit (AU). The mission includes a series of remote sensing instruments, envisages landing of the whole spacecraft on the sampling target, and employs an innovative sampling mechanism. Launch is foreseen to occur in 2018, as the designed timetable, and the mission would last about 10 years, bringing back a 150 g subsurface sample within a small re-entry capsule. This paper is a work presented at the 2008 Summer School Alpbach,“Sample return from the Moon, asteroids and comets” organized by the Aeronautics and Space Agency of the Austrian Research Promotion Agency. It is co-sponsored by ESA and the national space authorities of its Member and Co-operating States, with the support of the International Space Science Institute and Austrospace.     

大厚度复合材料制件(内埋金属)的超声检测分析

采用超声波无损检测及金相试验方法研究了内埋金属件的大厚度复合材料实心部位的微观结构,发现采取0o纤维在金属件周围进行缠绕铺层时容易引起超声波的衰减,分析了超声波衰减的机理,首先预浸料中夹杂微小气泡引起孔隙率较低,形成了复合材料内部的疏松缺陷;其次由固化过程时内应力引起的微裂纹,导致超声波信号发生衰减;另外,纤维屈曲或局部树脂分布不均匀对超声波也有一定影响。     

超声波智能料位遥测系统

介绍了无线遥控式超声波智能料位测量系统的工作原理。该系统具有测量精度高，速度快，重复误差小的特点，并有数据运算与记忆功能。     

超声波流量计的全数字式准确计时方法

本文详细讨论了超声波流量计的测量与计时原理,采用两组高频脉冲序列计数以提高计时电路的分辨率,并通过电路实验测定了两组脉冲频率分别为2.1MHz和1.93MHz时,计时电路分辨率的大小。实验结果与理论计算完全相符。最后提出了一种新型的功能性强的超声波流量计实施方案。