Effect of interface debonding on matrix multicracking evolution of fiber-reinfroced ceramic-matrix composites

An analytical methodology was developed to investigate the effect of fiber/matrix interface debonding on matrix multicracking evolution of fiber-reinforced CMCs(ceramic-matrix composites). The Budiansky-Hutchinson-Evans shear-lag model was adopted to analyse the micro-stress field of the damaged composites. The critical matrix strain energy criterion, which presupposes the existence of an ultimate or critical matrix strain energy with matrix, was obtained to simulate the matrix multicracking evolution of CMCs. With the increase of the applied stress, the matrix multicracking and fiber/matrix interface debonding occurred to dissipate the additional energy entered into the composites. The fiber/matrix interface debonded length under matrix multicracking evolution was obtained by treating the interface debonding as a particular crack propagation problem. The conditions for no-debonding and debonding during the evolution of matrix multicracking were discussed in terms of two interfacial properties, i.e., the interface shear stress and interface debonded toughness. When the fiber/matrix interface was bonded, the matrix multicracking evolution was much more intense compared with the interface debonding; when the fiber/matrix interface was debonded, the matrix crack density increased with the increasing of interface shear stress and interface debonded energy. The theoretical results were compared with experimental data of unidirectional SiC/CAS(calcium alumina silicate), SiC/CAS-Ⅱ and SiC/borosilicate composites.      

基于叶端定时的转子叶片动应变重构不确定性量化

基于叶片非接触式动应变重构理论,开展动应变重构不确定性量化方法研究。基于方差合成定理建立重构叶片动应变不确定性量化分析模型;以模拟转子叶片为研究对象,开展旋转叶片叶端定时试验,利用周向傅里叶算法获取不同叶端定时传感器布局下的测点振幅,通过最大熵方法拟合振幅分布概率密度函数,确定叶端定时测振的不确定性参数;结合Kriging代理模型和试验共振频率数据对叶片有限元模型进行修正,获取关键测点位移-应变转换因子,并获取考虑共振转速以及测点位置不确定性的转换因子不确定性参数;获取重构动应变的均值、标准不确定度和包含区间,与应变片测量数据作对比。结果表明,除5号叶片A测点外,测量动应变均位于重构动应变的95%置信度下的包含区间内,且所有叶片的应变片测点动应变重构误差不超过15%。     

复合材料固化应力模型

本文建立了描述复合材料固化应力史的综合模型。在本模型中考虑了化学收缩对残余应力史的贡献,并考虑了以玻璃化转变区为应力释放区的应力松弛过程。整个模型由四部分组成:描述温度场的模型、物理力学参数的模型、描述细观纵向残余应力史的模型、描述层合固化应力史的模型。     

高应变率下的玻璃钢力学性能的实验研究

利用分离式Ｈｏｐｋｉｎｓｏｎ压杆研究了国产环氧玻璃钢和聚脂玻璃钢在平均应变率约为１０＾３ｓ＾－１下的动态力学性能，给出这两种材料在冲击压缩下的弹性模量和能量吸收率，为新型飞行保护头盔的设计提供了材料的实验依据。     

橡胶变形响应的非线性有限元分析

由于材料及几何两方面的原因，橡胶有限元分析中具有很强的非线性性质。此外，又因为问题中含有不可压约束条件，使得分析变得更加复杂，其结果，不恰当的单元列式将导致“锁闭”现象，从而得出错误的解答；使用低阶单元会造成压力的不稳定；等。本文将讨论并比较不同的能量函数及有限元列式，推导本构关系式，并建议一种新的迭代技术，已经通过一些典型例题的解析和数值解，证明了它们有优良的数值特性及逼近绝对不可压缩体的能力。     

橡胶O形圈密封结构的有限元分析

建立固体火箭发动机的橡胶O形圈的二维轴对称模型,采用非线性有限元方法计算了O形橡胶圈在库存和工作状态的变形及应力,分析了上下法兰张开间隙、初始压缩量、密封槽口及槽底倒角半径、密封槽宽、密封圈材料、O形圈截面尺寸及工作温度等典型参数对密封性能的影响:上下法兰张开间隙、密封圈的初始压缩率、密封圈材料等典型参数对最大接触压应力影响较大,而密封槽槽口和槽底处倒角对剪切应力影响明显.这些分析为密封结构的优化设计打下了基础;同时探讨O形圈应力分布规律,确定密封圈易受损和失效关键部位,初步确立了固体火箭发动机密封失效准则和失效模式.     

涡轴发动机燃气涡轮叶片动应力测试技术研究及验证

针对涡轴发动机高转速燃气涡轮叶片动应力测试中出现的应变计短路、高温导线断裂和线芯窜动问题,开展了动应力测试技术研究。提出了加宽基底喷涂固定应变计、优化高温导线布线、改进高温导线等工艺方法,并进行了试验验证。试验结果表明,共振转速试验测试值与计算值基本一致,共振转速测试结果准确有效。通过研究,获得了具有实际应用价值的涡轴发动机燃气涡轮叶片动应力测试技术,可为同类测量提供参考。     

航空发动机真实机匣的包容性试验

为了研究某发动机机匣的包容性, 在旋转试验器上进行了该机匣的包容性试验.试验考虑了相邻叶片的影响, 得到了叶片断裂甩出时的转速、断叶撞击机匣的应变响应和断叶撞击机匣过程的高速摄影照片.试验结果表明, 断叶与机匣碰撞了两次, 第2次撞击时在未断叶片作用下断叶击穿机匣, 机匣的失效模式主要是剪切破坏.采用包容曲线法对机匣的包容性进行了计算, 计算结果与试验结果吻合良好.研究结果对航空发动机机匣的包容性设计有一定的参考价值.      

70kN载荷应变天平校准系统研制进展

研制了70kN量级的应变天平校准系统,以满足2m量级高速风洞测力试验天平的静态校准需求。70kN载荷应变天平校准系统基于传统的单元校准方法,采用四自由度复位式体轴系自动校准方案,加载力源为标准砝码,采用砝码独立控制技术的自动加载装置实现天平校准载荷的自动加载。砝码产生的重力通过双十字铰链施力定位装置和刚性加载头准确地传递到天平上,无间隙复位传动机构可以保证天平的精确复位。建成后的校准系统可满足20～70kN量程范围的杆式天平和环式天平等不同类型天平的校准需求。     

Plastic deformation analysis and forming quality prediction of tube NC bending

Plane strain assumption and exponent hardening law are used to investigate the plastic deformation in tube bending. Some theoretical formulae including stress, curvature radius of neu-tral layer, angle of neutral layer deviation, bending moment, wall thickness variation and cross-section distortion, are developed to explain the phenomena in tube bending and their magnitudes are also determined. During unloading process, the springback angle is deduced using the virtual work principle, and springback radius is also given according to the length of the neutral layer which remains unchanged before and after springback. The theoretical formulae are validated by the experimental results or the validated simulation results in literature, which can be used to quickly predict the forming quality of tube numerical control (NC) bending.