机匣模拟疲劳试验的相似条件研究

理论分析和试验结果表明，受内压的机匣与其相应的平板模型在开孔附近的等效应力分布非常相似；机匣模拟疲劳试验的应力相似条件下可表为，机匣与其模型在控制疲劳寿命的关键部位的等效应力水平和分布相同。     

机匣碰摩热应力梯度变化影响分析

针对航空发动机叶片-机匣碰摩故障产生局部热应力问题,考虑碰摩产生冲击热应力对机匣强度的影响,提出对叶片、机匣碰摩的局部细节进行数值分析。首先建立叶片-机匣碰摩模型,然后分别进行接触分析和热-结构耦合分析,得到接触处应力梯度变化和碰摩产生的温升。通过分析结果,判断碰摩产生冲击热应力是否达到材料屈服极限及碰摩产生热是否会引起结构破坏。研究结果表明:碰摩产生热使得接触处最大应力增加,尤其是机匣上的应力,但应力场分布梯度不变;碰摩产生冲击热应力低于材料屈服极限,但会随时间累积,其影响不可忽略。     

饱和砂土的三剪弹塑性边界面模型研究(一)——模型理论

基于边界面模型方法研究了不同密实度和含泥量的饱和砂土在静、动荷载作用下的力学和变形特性。其中,初始边界面方程是通过改进修正剑桥模型椭圆形屈服方程得到的,后继边界面方程则是在前次边界面方程的基础上采用中心点映射法获得。针对原模型破坏应力比为定值,不能反映全应力状态和黏聚力在土体受力过程中的作用这一问题,基于三剪统一强度准则,通过等量代换法、坐标平移法对破坏应力比、相变应力比进行了修正,使修正后的椭圆形边界面适用于不同密实度和含泥量的饱和砂土。在此基础上应用边界面理论,研究了饱和砂土的三剪弹塑性边界面本构模型及有限元算式。该模型能够描述密实砂土在受力时表现的剪胀特性,同时可以反映中间主应力效应、应力区间效应、拉压差效应和黏聚力对应力-应变特性的影响。     

关于弹性力学位移边条件的注记

1.众所周知,在解用位移表示的各向同性三维弹性力学方程(即所谓拉梅方程)时,如果只给应力边条件,则解存在的充分必要条件是应力边条件必须满足弹性体整体平衡条件.设弹性体上体力为(?),边界上应力为(?),即     

关于以应力表示的弹性力学边值问题

以六个应力分量表示的弹性力学边值问题由九个方程和三个边条件组成,本文探讨了它等价于六个方程和六个边界条件的可能情形和不可能情形。     

航空发动机叶片-机匣碰摩热-结构耦合仿真

针对转静子碰摩过程中的摩擦热效应现象,建立了叶片-机匣的碰摩热-结构耦合模型。采用热-结构耦合单元,对航空发动机叶片-机匣进行了碰摩热效应特性研究。考虑摩擦因数及旋转过程中的离心力作用,对瞬态-热结构耦合场进行了有限元分析,研究了结构在温度场作用下的热-结构耦合应力和温度分布。与纯机械载荷下的应力分布对比,发现了碰摩热效应在叶片与机匣上的扩散规律。研究结果表明,考虑摩擦热效应时由于热应力的作用,导致结构的总应力水平升高进而产生热变形,从而使故障进一步恶化。由此可见,碰摩热效应的影响在实际航空发动机振动分析中不能忽视。     

Airy应力函数在狭长矩形梁问题中的解

狭矩形梁上下表面作用有多项式形式的分布外力,二端边界满足Saint-Uenant边条件,考虑无体力情况,求其应力状态。文献[1]指出了Airy应力函数的一种求解方法,但没有给出梁上下两边在任意多项式分布外力下的解;文献[2]根据边界上应力函数及其导数的力学意义, ...     

弹性力学应力状态理论求解器开发及应用研究

论文基于吴家龙教授编著的《弹性力学》教材内容和课程"三难"特点,以应力状态理论部分常见题型求解任意微分斜面应力矢量、正应力、切应力、主应力和应力主方向及最大切应力为例,应用Matlab-GUI模块编制应力状态理论求解器,通过界面物理参数输入和结果显示过程,再现弹性力学求解思维,验证学生数理求解结论;把繁琐抽象的力学公式和微分斜面结果进行图形可视化,使学生的抽象思维和力学思维得到兼容;通过弹性力学应力状态理论求解器开发及应用,可为学生力学学习及力学同行教学提供借鉴。     

不同厚度及冲击角度对复合材料平板抗冲击能力的影响

为了考核叶片飞脱碎片撞击机匣的抗包容能力，采取钛合金方块作为弹体撞击复合材料平板机匣进行等效模拟。通过获取弹体不同冲击角度撞击不同厚度平板时的抗冲击临界速度，得到复合材料机匣在不同工况下的抗冲击能力极限。基于试验所获得的物理参数，进一步分析了抗冲击临界速度、应变响应、位移响应等关键物理量随平板厚度及撞击角度变化的规律。结果表明，复材平板抗冲击能力对厚度较为敏感，但呈非线性变化趋势；复材表面压应力会抑制表面裂纹的扩展，且厚度越大，这种效应越明显；机织复合材料结构抗冲击能力和裂纹扩展速度与其内部经纬纱编织角度有密切关系，且呈非单调关系。本文提出的等效考核机匣结构抗包容能力的试验方法和获得的试验数据可为真实机匣包容性试验的顺利完成提供支撑，降低适航试验取证的风险。     

纵筋加强的凸锥柱结合壳应力状态的有限元分析

本文应用SAP5程序对均匀外压下纵筋加强的凸锥拄结合壳的应力状态作有限元分析。计算结果与钢模试验值一致。它揭示了该结构的力学特性,证明采用纵筋加强能有效地降低凸锥柱结合壳在结合边附近的高应力。本研究为潜艇的结构设计提供了一种简易可行,且行之有效的加强方法。     

压气机流动稳定性自适应控制方法研究进展

压气机流动稳定性自适应控制是未来智能航空发动机的一项关键技术. 基础研究需要回答3个关切: 如何描述系统的稳定性？如何改变系统的稳定性？如何监测系统的稳定性？为此, 本团队在压气机流动稳定性通用理论、壁面阻抗边界扩稳方法和在线实时失速预警技术等3个方面开展了系统深入的研究工作. (1)所发展的叶轮机流动稳定性通用理论既能包含流动非均匀性又能考虑叶片几何, 计算高效, 预测精度高, 为压气机气动/稳定性一体化设计提供了可靠的评估工具. (2)所发展的基于壁面阻抗边界调控策略的SPS (stall precursor-suppressed)机匣处理和泡沫金属机匣处理在扩稳、降噪和保持系统气动性能方面取得实质性进展, 采用等价分布源方法建立了包含机匣处理影响的压气机失速起始预测模型, 对SPS机匣处理和泡沫金属机匣处理关键结构参数进行敏感性分析, 使其具有明确的理论设计准则. 实验结果证实, SPS机匣处理通过抑制失速先兆波的非线性演化达到扩稳的目的, 在扩稳的同时可以保持压气机的压比和效率特性; 泡沫金属机匣处理可以实现扩稳和降噪的双重效果, 也具有良好的工程应用前景. (3)所发展的基于气动声学原理的实时失速预警方法将压气机失速预警时间提高到秒量级以上, 能够在线监测系统稳定性. 综合上述理论预测方法、扩稳技术和实时失速预警技术, 发展了闭环反馈自适应控制方法, 为未来智能航空发动机提供了一种自适应扩稳控制技术.      

两种典型螺栓连接结构的刚度特性比较研究

针对法兰对接和径向套接两种典型舱段螺栓连接形式,基于有限元静刚度计算、动力学简化建模、冲击响应特性分析及结构冲击试验,系统研究了两种连接形式的轴向刚度特性及其对动力学冲击响应的影响.有限元静刚度分析揭示了法兰对接与径向套接的轴向拉压刚度分别是非对称的和对称的,而法兰对接的平均刚度更大.之后,为两种连接形式建立了统一的动力学模型,证明非对称的轴向拉压刚度导致结构在受到横向载荷作用时会产生附加的耦合轴向振动,并且利用高精度幂函数拟合刚度跳变,得到耦合轴向振动频率是弯曲振动频率的二倍的结论.最后,通过冲击动力学试验证明了法兰对接存在二倍频的耦合轴向振动,而径向套接则不存在该耦合振动.径向套接虽然一阶频率较低,但阻尼效果更好.     

Modal Analysis of Monolithic and Jointed Type Cantilever Beams with Non-Uniform Section

Modal analysis of non-uniform bolted structures are of significance in modeling many complex mechanical structures. There are vast literatures available related with the analytical as well as numerical modeling of bolted joint. However, most of the analytical model discuss about the modeling of first mode of uniform structures with single bolted joint. In this paper, we present the modeling of single as well as bolted non-uniform beams using approximate mode shapes. To develop the model, we first carry out experiments to measures the modal frequencies and shapes of the test structures. Subsequently, we also do numerical modeling of non-uniform beams in ANSYS to verify the validity of the Euler-Bernoulli beam theory in developing the analytical models. Finally, using the Euler-Bernoulli beam theory, we obtain the analytical values of frequencies using the approximate the mode shapes. The analytical results are found to be closer to the experimental results with a maximum percentage error of about 15 %. The model presented in the paper can be extended to the mechanical structures with many non-uniform sections with or without bolted joints.     

Three-dimensional investigation of thick single-lap bolted joints

Stresses in single-lap bolted joints of thick plates are complex and difficult to analyze. Previous studies involving stresses through the thickness of bolted joints have been limited to finite element method (FEM) simulations and have been implemented only for the joining of relatively thin plates. In this paper we report on several experimental and numerical analyses that were conducted to evaluate the stress distribution inside thick bolted plates along the bearing plane normal to the plate surface. Experimental analysis was conducted via embedded-polariscope photoelasticity and embedded resistance strain gages. The FEM analysis was performed with the ABAQUS commercial code using material properties and other data obtained experimentally as input. Experimental and numerical results agreed reasonably well, and are believed to depict the behavior of the joint under load well enough to assist in development of improved joint design.     

石英纤维布氰酸酯树脂基复合材料的环境试验性能研究

对石英纤维布增强氰酸酯树脂基复合材料进行了常温、低温和湿热三种环境下的拉伸、压缩、面内剪切、层间剪切和钉孔挤压等试验研究,得到了该复合材料的拉伸压缩面内剪切的强度和弹性模量以及层间剪切强度和钉孔挤压强度等力学性能参数。结果表明:石英纤维布增强氰酸酯树脂基复合材料的力学性能参数具有温度相关性。在低温环境下,力学性能参数不同程度地增强,最大增长量达40%;而在高温环境下,力学性能参数则明显下降,最高下降量达到56%。另外,由于复合材料的层间性能主要由基体决定,所以湿热环境对复合材料层间性能的影响很大,在工程实际中应特别关注。     

A method to simplify the strength design of bolted joints—Case of connecting-rod bolts

This study shows the development of the strength-design system for general bolted joints. Specifically, a simplified method of the strength design for the connectingrod bolts is proposed. The connecting-rod joint is transformed into a single-bolted-joint model by using the ring model. The axial stress on the bolt and separation behavior at the contact plane are discussed. The strength design of the connecting-rod joint can be performed by applying the unified procedure to the single-bolted-joint model. The local deformation of the connecting-rod joint and the stress on the bolt were measured and the analytical results are compared with the experimental results. Both results show fairly good agreement.     

Application of subharmonic resonance for the detection of bolted joint looseness

Bolted joint structures are prone to bolt loosening under environmental and operational vibrations, which may severely affect the structural integrity. This paper presents a bolt looseness recognition method based on the subharmonic resonance analysis. The bolted joint structure was simplified to a two-degree-of-freedom nonlinear model, and a multiple timescale method was used to explain the phenomenon of the subharmonic resonance and conditions for the generation of subharmonics. Numerical simulation predictions for the generation of the subharmonics and conditions for the subharmonics can be found with respect to the excitation frequency and the excitation amplitude. Experiments were performed on a bolt-joint aluminum beam, where the damage was simulated by loosening the bolts. Two surface-bonded piezoelectric transducers were utilized to generate continuous sinusoidal excitation and to receive corresponding sensing signals. The experimental results demonstrated that subharmonic components would appear in the response spectrum when the bolted structure was subjected to the excitation of twice its natural frequency. This subharmonic resonance method was found to be effective on bolt looseness detection.     

Monitoring of L-Shape Bolted Joint Tightness Using Thermal Contact Resistance

In this paper, we describe the possible use of hermal contact resistance measured under ambient conditions as a non-destructive feature to monitor L-shape bolted joints. We demonstrate that thermal contact resistance can be correlated to the contact pressure of L-shape bolted joints and thus can be used to infer joint tightness. Five different torque levels of bolt tightness in an L-shape bolted joint were measured for contact pressure and thermal contact resistance using Fuji Prescale® pressure-sensitive film and a test setup in ambient conditions. Using probabilistic analysis, probability density functions (PDFs) and intervals developed from the PDFs, the contact pressure and thermal contact resistance were developed and correlated. By examining the intervals of the contact pressure and thermal contact resistance at each torque level, it was concluded that thermal contact resistance measured under ambient conditions can be used to describe bolted joint tightness.     

平面编织复合材料胶螺混合连接接头拉伸性能分析

对平面编织复合材料胶螺（单排螺钉）混合连接结构拉伸性能进行了试验研究,分析了螺钉直径为4mm和6mm两种情况下连接结构的破坏形式。基于ANSYS平台建立了胶螺混合连接三维损伤扩展模型,其中融入了非线性接触问题,数值计算的结果与试验结果吻合良好。研究发现,机械连接可以通过分担部分载荷而起着加强胶接连接的作用;如果机械连接工艺稳定的话,应该有螺钉直径越大,其加强效果越明显的规律;对于胶接与多钉混合连接复合材料结构的拉伸性能分析和计算确实存在很大困难,应该谨慎使用。研究结果与分析方法可以为今后的复合材料胶螺混合连接接头的设计提供一定的依据与技术支撑。     

考虑微观粘滑的连接梁结构动力响应分析

连接的存在对结构的动力学响应有重要影响.界面的微观/宏观粘滑运动引起结构刚度和阻尼的非线性.传统的结构动力学研究中通常采用等效线性化的方式处理含连接结构的动响应分析问题.本文从连接界面微/宏观滑移运动引起结构非线性和阻尼迟滞的物理机理出发,利用一种弹簧-滑块并联系统模型模拟界面上的微/宏观粘滑行为,以该模型描述的本构关系为基础,推导了能应用于平面梁结构有限元动响应分析的非线性连接单元.利用上述模型和单元研究了含连接平面梁结构的动响应问题.设计了实验件,进行了力锤冲击实验,并将数值计算结果与实验结果进行了对比和分析.结果表明,界面微/宏观粘滑是引起干摩擦阻尼的主要原因,考虑非线性微/宏观粘滑运动对含连接结构的动响应分析至关重要.本文的模型和方法能够有效地预测含连接结构的非线性动力学响应,特别是在瞬态响应的高振幅阶段.