胶接是复合材料结构连接的主要方式之一,而胶接面的表面处理对胶接性能有显著的影响.本文采用紫外激光对氰酸酯树脂基复合材料的胶接面进行处理,研究了激光参数对表面形貌、胶接性能等的影响规律.数值模拟结果显示激光热影响区很小,且根据纤维与树脂的温度响应及各自的气化温度可知激光处理以表面树脂消融为主.表面形貌观察发现:激光处理时会因为氰酸酯树脂的不完全热解而形成炭黑.准静态单搭接胶接拉伸剪切试验结果表明合适的激光参数能够提升胶接强度,并且离散系数较小;但不合适的激光处理参数反而会降低胶接强度.激光处理后最大剪切强度为22.575 MPa,相比于不处理提升27.1％,对应离散系数为2.7％.

将SMA片状驱动器粘贴于复合材料结构表面制成的可变形结构有诸多优势,但也存在如何确保胶接质量和设计许用可回复应变等问题.本文首先采用合适的红外激光参数对SMA片进行了表面处理,然后通过引入预应变制得SMA片状驱动器,进而将之粘贴于复合材料板梁的上表面制得了可变形复合梁,并对不同预应变情况下的变形性能进行了试验研究.经与仅做丙酮擦拭表面处理复合梁的驱动变形性能对比,结果表明:合适的激光表面处理可以使复合梁在胶层不失效的前提下获得更大的变形能力.但随着预应变的增大,在驱动过程中复合梁的胶层仍会发生大面积的内聚破坏.

双一流大学办航空航天学院、培养航空宇航学科人才,有双重使命:一是要培养能够站在世界航空宇航科学前沿,引领航空宇航科技发展方向的拔尖创新型飞行器研制、维护、运营与管理人才,谓为能"顶天"的人才;二是要培养更多的能够满足我国航空航天事业发展战略需求的人才,即能"立地"的人才.要实现这一目标,需在培养方案制定、师资队伍建设、教育教学理念、课程教学实践、校企合作办学、学科平台建设、国际合作交流、教学科研评价等诸多方面共向发力,要深化对航空宇航科学与技术本质的理解和人才培养规律的认识,既培养学生的科学探索精神,又培养学生的工程思维,既要放眼全球,又要胸怀祖国.

基于混杂形状记忆合金(Shape Memory Alloy,简称"SMA")驱动器的自适应可变形复合材料结构正常服役的前提是界面性能良好.研究表明在光圆SMA丝上引入细压痕可显著提升界面性能.进一步研究压痕SMA丝复合材料的本构是开展混杂压痕SMA丝复合材料结构设计、应用的基础.本文通过圆柱拉拔试验,基于搭建的粘结-滑移测试系统,采集到了载荷-滑移数据,结合理论分析,建立了界面的粘结-滑移本构模型,并通过分析得出了基于区域平均准则思想的界面临界失效剪应力强度值.

为了使风筝能够更好地在青少年航空教育教学实践中得到推广,本文阐述了风筝构造、空气动力,以及受力与稳定性分析等风筝设计的相关概念与原理,介绍了美国NASA航空教育的风筝设计软件Kite Modeler,以及自己的教育教学实践情况.实践表明,风筝设计、制作、放飞是一项集简易航空器设计、手工制作、体能锻炼、休闲娱乐等为一体的实践活动,在大中小学航空教育中具有良好的现实意义.

Intelligent morphing wings have become a research hotspot due to their potential value. This paper is also an innovative basic research work to study it. The deformation performances of the GFRP(glass fiber reinforced polymer) composite beams embedded different pre-strained indented SMA wires were experimentally and numerically studied. The indentation SMA wire made by mechanical indentation method has better interface bonding strength than normal SMA wire. In this paper, the indented SMA wires acting as actuators, were embedded in a symmetrically GFRP laminated composite beam and located at the eccentric position of the laminate. The layering scheme of the laminated plate is as follows: [90°(4:1 fabric)/SMA/0°/0°/90°(4:1)]. The 0° direction is consistent with the direction of the axis of the SMA wire. The Finite element method is adopted to simulate the deformation of the beam with indented SMA wire in which the linear constitutive model of fully constrained SMA wires, together with considering their thermally-induced strain response, is used to describe the recoverable properties of SMA. The prediction from the numerical simulation agrees well with experimental measurements.

被列入一流大学建设目录的高校,其学科建设自应对标“一流”,但作为培养社会发展所需的不同领域专门人才的专业建设是否有对应的国际“一流”标杆呢？“一流学科”和“一流专业”的内涵、关系如何？结合航空专业的建设,我们该如何理解一流标杆？我们认为,我国的航空专业建设必须面向我国航空业发展的实际,扎根中国大地,致力于培养符合中国乃至全人类当前及中、远期发展要求的研究型、创新型人才,以人才质量是否能很好地支撑航空强国梦的实现作为衡量专业建设是否“一流”的根本准绳.其有别于一流学科的建设,又与一流学科的建设关系密切.

The cohesive parameters of a polyurethane (PU) adhesive are experimentally tested under different strain rate conditions. As the strain rate of this adhesive is constantly changing under the actual impact conditions, this paper proposes a method, called weighted average strain rate method, to determine the effective strain rate of the adhesive under the high strain rate condition for numerical simulation. Based on this method, the relationship between cohesive parameters and the determined effective strain rate is established and a strain rate-dependent cohesive constitutive model of the adhesive is developed and implemented into commercial finite element analysis software via a subroutine. The model is calibrated and verified against experimental data for double cantilever beam (DCB), end notched flexure (ENF) tests and thick adherend shear tests (TAST). Finally, impact tensile shear test and numerical analysis on composite single-lap joints at high loading rates are carried out to validate the reliability of the subroutine. By comparing the FEA results with experimental results, a good agreement is achieved which proves the effectiveness of the strain rate determination method and the subroutine.

The shear properties of the polyurethane adhesives at room temperature (RT) and low temperatures under different loading speeds were experimentally studied by thick adherend shear test (TAST) specimens. The shear strength of the polyurethane (PU) adhesive decreases with the temperature reducing at quasi-static conditions. The ultimate shear strain also shows a decreasing trend with the decrease of the temperature. With the loading speed increases, the shear strength of the adhesive increases significantly. When the loading speed increases to 1000 mm/s, compared with the data under quasi-static conditions, the strength of the adhesive increases by 177%. Under the impact conditions, the strength of the adhesive at low temperatures decreases a lot compared with that at RT. The mechanical behavior of the TAST specimens under impact loadings at different temperatures were reasonably predicted by the 3D finite elements method by ABAQUS. It is concluded that the shear strength of adhesive at RT under quasi-static cannot be used to design and analyze the adhesive joints at low temperatures under impact loading conditions.

The mode I fracture toughness of an adhesive at low temperatures under high loading rates are studied experimentally. Typical R-curves of the polyurethane adhesive under different loading rates (0.5 mm/min, 50 mm/min, 500 mm/min) at different temperatures (room temperature, -20 degrees C, -40 degrees C) respectively are obtained. From the experimental results, the mode I fracture toughness of this adhesive is extremely sensitive to the high loading rates and low temperatures. With the increase of the loading rate and decrease of temperature, the mode I fracture toughness of this adhesive decreases significantly. Under the loading rate of 500 mm/min at -40 degrees C, the mode I fracture toughness of adhesive is 15% of the value at room temperature (RT) under quasi-static conditions. Through the experiment, the relationship between mode I fracture toughness of this adhesive, nominal strain rate and temperature is obtained.

In order to study the vibration characteristics of flow-induced open cavity structures, the dynamic model of stiffened multi-plate is established. The first-order shear deformable plate theory and the Timoshenko beam theory are used to model the displacement fields of isotropic plates and stiffeners, respectively. A modified variational principle combined with a multi-segment partitioning procedure is employed to formulate the discretized equations of motion. The stiffeners are considered as discrete elements, and the energy contributions are included into the system energy functional by using the displacement compatibility conditions. The displacement and rotation components of each plate segment are expanded by a duplicate series of Chebyshev orthogonal polynomials of first kind. The convergence and accuracy of the present results for isotropic stiffened plates with different boundary conditions have been validated using comparisons with the published data and those obtained from the finite element analyses. Free vibration and dynamic responses of stiffened multi-plates with either longitudinal or orthogonally oriented stiffeners are discussed. The mathematical model and methodology presented in this paper may be used as an appropriate numerical tool in the analysis and design of stiffened multi-plate structures.

业内专家已深刻地意识到影响我国复合材料在高性能结构上广泛应用的最主要的原因之一是复合材料结构设计人才的匮乏,因此做好复合材料结构设计人才的培养工作已成为推动复合材料在若干重要产业领域创新应用发展的关键.本文围绕有关概念、培养方法和培养标准等给出了作者的若干思考,抛砖引玉,愿能对推动复合材料结构设计人才的培养工作有所裨益.

The vibration and stability of axially loaded sandwich cylindrical shells with the functionally graded (FG) core with and without shear stresses and rotary inertia resting Pasternak foundation are investigated. The dynamic stability is derived based on the first order shear deformation theory (FSDT) including shear stresses. The axial load and dimensionless fundamental frequency for FG sandwich shell with shear stresses and rotary inertia and resting on the Pasternak foundation. Finally, the influences of variations of FG core, elastic foundations, shear stresses and rotary inertia on the fundamental frequencies and critical axial loads are investigated.

Shape memory alloy (SMA) wire reinforced polymer-based composites have been recognized as a new type of smart materials. However, their weak interfacial bonding strength between the wire and its surrounding matrix limits its applications in many engineering industries. In this paper, a new method called “mechanical indentation” is introduced to effectively enhance the interfacial bonding strength of SMA composites. According to the results from a wire pullout test, the interfacial bonding strength of an indented SMA wire composite increased by 4.48–8.58 times as compared with a hand-sanded SMA wire composite at a room temperature condition. Two different sizes of indentations, sparse and dense indentations were studied in detail and the results indicated that the dense indented SMA wire had a better performance in terms of tensile and recovery properties, than that of the sparse indented wire. Furthermore, the interface between the dense indented wire and vinyl-ester (VE) matrix demonstrated a better restoration performance during a repeated loading-and-unloading process at room temperature condition.

The tensile properties of a polymer-based adhesive subject to different strain rates at low temperature were investigated. Experimental results showed that the strength of adhesive increased remarkably with the increase of strain rate and decrease of temperature. According to the results, the strength of adhesive at low temperature (-40 degrees C) and high strain rate increases as compared with that at room temperature and the same strain rate. The effect of strain rate and low temperature on strength of adhesive is not simply superimposed. Meanwhile the coupling effects on strain rate and low temperature to the tensile strength, failure strain, Young's modulus, and fracture energy are also discussed in this paper. A constitutive model of adhesive at high strain rate and low temperature is proposed. (C) 2015 Elsevier Ltd. All rights reserved.

要使复合材料轻质高强的优势得到充分发挥,在给定设计条件下开展复合材料结构的优化设计研究是十分必要的.以SAMPE超轻复合材料竞赛机翼为研究对象,根据给定的外形及工况,基于Hyperworks软件的OptiStruct分析和优化模块,对机翼的结构形式、铺层位置、铺层方向、铺层厚度等进行了优化设计,结合实际制造时的工艺性等,确定出了一款复合材料模型机翼的优化设计方案.基于该优化设计方案开展了模型机翼的制备与试验研究工作,并根据试验结果进行了进一步的改进,最终得到了该赛事组织以来满足承载及变形要求的最轻的一个机翼.

Multi-scale modeling method was used to study tensile properties of single-walled carbon nanotube (SWCNT) and double-walled carbon nanotube (DWCNT) reinforced polymer-based composites at room temperature (RT) and cryogenic temperature (like liquid nitrogen temperature 77 K) conditions. At RT, Young's Modulus of a SWCNT reinforced polymer composite is 1.88 times of a DWCNT reinforced polymer composite due to a weak interfacial bonding between layers of DWCNT, which is bound by the weak Van der Waal interaction. The Young's Modulus of DWCNT reinforced polymer composite is significantly improved with the decrease of temperature and the difference in Young's Modulus between SWCNT and DWCNT reinforced polymer composites has been largely reduced. The radial stress imposed on an outer surface of nanotubes due to the contraction of polymer at liquid nitrogen environment is examined to explain the stress transfer mechanism in a composite system. The extra stresses imposed on the surface of DWCNT increase bonding forces between outer and inner layers of DWCNT. This tendency agreed well with experimental results found in other literature. (C) 2016 Elsevier Ltd. All rights reserved.

The tensile properties of an epoxy-based adhesive subject to high strain rate loadings at low temperatures were studied. Tensile split Hopkinson bar incorporating with an environmental chamber was utilized to conduct tensile property tests. Mechanical Parameters, like strength, Young's Modulus, strain to failure and fracture energy at low temperatures (-20 degrees C and -40 degrees C) with different strain rates were investigated. The results show that at room temperature (RT), the strength and stiffness both increase significantly with the increase of strain rate. However, the increment of strength at low temperatures is insignificant. Interestingly, at RT and -20 degrees C, strain to failure increase with the increase of strain rates. From the stress-strain curves, strain softening phenomenon at high strain rates are observed at RT and -20 degrees C. This could be explained by the localized temperature rise in the specimens when the strain rate reaches high. At -40 degrees C, strain to failure decreases with the increase of strain rate and strain softening disappears. The larger temperature difference between the environment and the localized temperature rise in the specimens may reduce the strain softening phenomenon. Effects of high strain rate on tensile properties of epoxy adhesive at low temperatures are different from that on polyurethane based adhesive in the literature. (C) 2016 Elsevier Ltd. All rights reserved.