陶瓷基复合材料疲劳寿命预测方法

为了建立CMC疲劳寿命预测方法,推广CMC在航空发动机中的应用,根据BHE剪滞模型理论,分析了随着疲劳峰值应力的大小不同,CMC可能出现的4种疲劳迟滞行为,推导了每种迟滞行为下的循环应力-应变公式,模拟了给定应力条件下的疲劳迟滞回线,通过与试验数据对比,证明了迟滞回线模拟的准确性,进一步分析了界面剪应力随疲劳循环数的退化关系。结合界面剪应力退化模型与纤维强度退化模型,设计了纤维应力计算和疲劳寿命计算流程。针对2维编织CMC,根据单胞有限元计算结果提取了纤维束应力,并对CMC进行了疲劳寿命计算,推导了CMC疲劳寿命S-N曲线,其结果与试验数据基本吻合。针对2维编织CMC的疲劳寿命预测方法,可用于编织结构的CMC涡轮导叶疲劳寿命分析。     

由裂纹嘴位移确定双悬臂梁试样应力强度因子的权函数解法

双悬臂梁(DCB)试样在材料的损伤容限性能评价,特别是应力腐蚀开裂门槛值(K_ISCC)测定中有重要应用。由于该试样几何的特殊性,一般采用与试样端部(裂纹嘴)有一定距离的特定位置裂纹面位移加载方式,然而该加载点的位移测量不但费时而且精度低,位移测量最方便和准确的位置是在DCB试样的裂纹嘴。通过对一种参考载荷条件的有限元计算,应用边缘裂纹的经典权函数解法,推导出DCB试样的权函数解析解,并与复变函数泰勒级数展开的权函数解法作了比较验证。在此基础上根据特定加载点的位移反算出相应位置均布应力加载下的应力强度因子,进而建立DCB试样在特定位置的裂纹面位移加载条件下的应力强度因子与裂纹嘴位移之间的关系式,为采用这种试样的材料损伤容限性能评价,特别是K_ISCC的高精度自动化测定奠定了基础。     

孔冷挤压有限元仿真中的铰削分界面位置确定方法

开展孔冷挤压过程有限元仿真计算是残余应力分布获取和疲劳寿命预测的前提。在有限元建模阶段，设置铰削层单元与基体材料单元之间的分界面，是模拟铰制终孔工艺过程的关键。通过弹塑性力学分析，建立了挤压强化过程芯棒、衬套和被挤压强化连接孔的应力分析方法；基于分析中得到的不同位置处微单元的径向位移量，建立了铰削分界面相对位置计算模型。并开展了关键参数的敏感性分析，定量研究了关键参数变化对残余应力分布和径向位移量的影响程度。本工作为孔冷挤压强化有限元模型建立中，铰削层单元与基体材料单元分界面相对位置确定，提供了便捷可靠的方法。     

Multi-scale thermodynamic analysis method for 2D SiC/SiC composite turbine guide vanes

Ceramic Matrix Composite (CMC) turbine guide vanes possess multi-scale stress and strain with inhomogeneity at the microscopic scale. Given that the macroscopic distribution cannot reflect the microscopic stress fluctuation, the macroscopic method fails to meet the requirements of stress and strain analysis of CMC turbine guide vanes. Furthermore, the complete thermodynamic properties of 2D woven SiC/SiC-CMC cannot be obtained through experimentation. Accordingly, a method to calculate the thermodynamic properties of CMC and analyze multi-scale stress and strain of the turbine guide vanes should be established. In this study, the multi-scale thermodynamic analysis is investigated. The thermodynamic properties of Chemical Vapor Infiltration (CVI) processed SiC/SiC-CMC are predicted by a Representative Volume Element (RVE) model with porosity, leading to the result that the relative error between the calculated in-plane tensile modulus and the experimental value is 4.2%. The macroscopic response of a guide vane under given conditions is predicted. The relative error between the predicted strain on the trailing edge and the experimental value is 9.7%. The calculation of the stress distribution of micro-scale RVE shows that the maximum value of microscopic stress, which is located in the interlayer matrix, is more than 1.5 times that of macroscopic stress in the same direction and the microscopic stress distribution of the interlayer matrix is related to the pore distribution of the composite.     

旋翼桨叶动力分析及内力计算中有限元法的改进

提高用有限元法进行桨叶动力分析、特别是动内力计算的精度是本文工作的主要目的。本文建立了变剖面旋转梁协调单元族;提出利用单元动刚度矩阵直接由节点位移计算桨叶内力（简称为计算内力的“动刚度法”）。作为例子,用所导出的不同精度的有限单元和建议的内力计算方法计算了具有不连续结构特性的变剖面桨叶弯曲振动固有频率、振型和模态内力。计算结果表明,工作可以达到预期的目的。     

Modified micro-mechanics based multiscale model for progressive failure prediction of 2D twill woven composites

To consider fiber random distribution at the microscale for the multiscale model based on the micro-mechanics failure (MMF) theory, clustering method is used for the extraction of amplification factors. As the clustering method is a kind of unsupervised machine learning method, the elements with similar mechanical behavior under external loading can be included in a cluster automatically at the microscale. With this modification, the fiber random distribution model can be used for multiscale damage analysis in the framework of MMF theory. To validate the modified multiscale analysis method, progressive damage analysis of a kind of 2D twill woven composites is conducted based on different microscale models. The stress values for microscale models with fiber hexagonal and random distribution patterns are compared first. Much higher stress concentration is generated in the fiber random distribution model due to the smaller inter-fiber distance especially under longitudinal shear loading. The obtained cluster distribution results exhibit the characters of the stress distribution in the two microscale models. Thereafter, tensile and compressive responses of the 2D twill woven composite are predicted with the modified multiscale analysis method and accuracy of the method is verified through comparison with published experimental results. From the simulation results, it can be found that the matrix damage initiation from the model based on the fiber random distribution model is premature compared with that from the model based on the fiber hexagonal distribution model. Besides, under tensile loading, the damage all initiates from the fill tows and propagates to the wrap tows. However, under compressive loading, the matrix damage initiates from the wrap tows in the model based on the fiber random distribution model.     

Microstructure-based Simulation of Plastic Deformation Behavior of SiC Particle Reinforced Al Matrix Composites

This article, in order to unearth the deformation mechanism of particle reinforced metal matrix composites, establishes a finite element model (FEM) based on the actual microstructures. It finds out and analyzes the distribution of von Mises effective stress, strain and the maximum principal stress in the matrix and particles. Moreover, the overall stress and strain in the matrix and composites are calculated. By comparison, a tiny discrepancy exists between the experimental results and the simulation with respect to flow stresses. The effects of deformation parameters, such as temperature and strain rate, on the strengthening mechanism are explored and proved to be weak.     

Modeling bending behavior of shape memory alloy wire-reinforced composites: Semi-analytical model and finite element analysis

In this study, we propose a novel and simple exact semi-analytical model for superelastic Shape Memory Alloy (SMA) wire reinforced composites subjected to bending loads. In order to study the mechanical response of the composite during loading/unloading, a Representative Volume Element (RVE) is extracted to examine the bending response of the composite. Analytical moment–curvature, and shear force-shear strain relations are derived based on a 3-Dimensional (3D) thermomechanical SMA model and Timoshenko beam theory. The composite Simpson’s rule is adopted to numerically solve the exact analytical moment–curvature and shear force-shear strain relationships. Results including the moment–curvature response, axial stress distribution along the vertical and longitudinal directions, martensite volume fraction, and the tip deflection are reported and validated against 3D finite element simulations. The influence of temperature, martensite volume fraction distribution, and matrix stiffness on the mechanical performance of the composite is also investigated. In particular, the composite is found to behave superelastically under certain conditions of temperature, SMA volume fraction, and elastic stiffness of the matrix. Such behavior is advantageous in applications requiring large recoverable strains or high energy dissipation density.     

一种平纹编织复合材料的三维通用单胞模型

为了解决采用通用单胞(GMC)方法开展编织复合材料多尺度模拟的技术难题，发展了一种三维通用单胞模型，可用于二维平纹编织复合材料的多尺度模拟。概述了三维通用单胞方法的基本理论和求解流程；基于对二维平纹编织复合材料细观结构特征分析，建立了其三维通用单胞模型，并通过与传统有限元单胞模型的宏细观力学响应分析计算结果对比，验证了所建模型的正确性。采用基于通用单胞模型的有限元多尺度模拟方法，开展了二维平纹编织复合材料平板试件的模态分析。与试验结果对比表明，采用所建立的通用单胞模型预测得到的前五阶固有频率绝大部分的精度较传统有限元方法有了明显提升。该方法的优势在于可以基于通用单胞模型开展多尺度模拟，进而研究宏细观力学响应的相互关联。      

全复合材料主承力梁结构研制与分析验证

根据结构特点和受力特性,研制了一种全复合材料主承力梁结构。给出了主梁的铺层设计,详述了其成形工艺。基于MSC.Patran/Nastran建立了主梁有限元分析模型,采用线性求解器对多级载荷作用下的主梁进行了静强度分析,给出了结构应变与位移结果。同时设计了强度试验方案,对主梁结构进行了静强度试验验证,采集了应变与位移信息,确定了结构的响应。结果表明,全复合材料主承力梁结构满足强度设计要求,为复合材料应用于主承力结构提供了依据。     

一种考虑截面任意变形模式梁的有限元模型

提出了一种考虑截面完整变形的截面插值梁模型,并用于机翼结构的建模与分析。首先引入截面插值函数——拉格朗日函数描述截面形状,以位移向量为未知变量描述截面位移,在此基础上依据插值理论构造梁单元位移场。不同于传统梁单元通过假定的中性轴的挠度和转角来确定梁截面各点位移,该梁模型摒弃了中性轴假设与平截面假设,通过截面插值函数得到梁截面面内、面外变形;然后通过有限元理论推导了梁单元刚度矩阵与质量矩阵;最后利用截面插值梁单元对机翼各部件进行有限元建模,并展开典型工况下的静力学分析以及动力学分析,与Nastran实体单元计算结果进行了对比分析,验证了该梁模型的有效性,为机翼的结构设计和强度分析提供了一种新的简化建模方法。     

考虑横法向热应变的Reddy型功能梯度梁理论

Reddy型高阶理论已被广泛用于功能梯度材料(FGM)结构分析,然而此理论忽略了横法向应变,难于准确分析功能梯度梁的热力行为。为提高Reddy理论分析热力响应的精度,提出了一种考虑横法向热应变的三参数Reddy型高阶功能梯度梁理论。此模型考虑了横法向热应变,但不增加额外位移变量。应用构建的模型分析了功能梯度梁的热力响应,并研究了不同体积分数对面内应力和位移的影响。数值结果表明,所提出的模型能准确分析功能梯度梁的热力响应,而忽略横法向应变的模型计算结果精度较低。     

Multiscale modeling of mechanical behavior and failure mechanism of 3D angle-interlock woven aluminum composites subjected to warp/weft directional tension loading

The mechanical behavior and progressive damage mechanism of novel aluminum matrix composites reinforced with 3D angle-interlock woven carbon fibers were investigated using a multiscale modeling approach. The mechanical properties and failure of yarns were evaluated using a microscale model under different loading scenarios. On this basis, a mesoscale model was developed to analyze the tensile behavior and failure mechanism of the composites. The interfacial decohesion, matrix damage, and failure of fibers and yarns were incorporated into the microscopic and mesoscopic models. The stress–strain curves and fracture modes from simulation show good agreement with the experimental curves and fracture morphology. Local interface and matrix damage initiate first under warp directional tension. Thereafter, interfacial failure, weft yarn cracking, and matrix failure occur successively. Axial fracture of warp yarn, which displays a quasi-ductile fracture characteristic, dominates the ultimate composites failure. Under weft directional tension, interfacial failure and warp yarn rupture occur at the early and middle stages. Matrix failure and weft yarn fracture emerge simultaneously at the final stage, leading to the cata-strophic failure of composites. The weft directional strength and fracture strain are lower than the warp directional ones because of the lower weft density and the more serious brittle fracture of weft yarns.     

含裂纹梁的动力特性

 本文研究了含裂纹梁的动力特性。首先,由应力强度因子积分得到含裂纹单元体的刚阵,继而提出了一种有限元方法。将该方法应用于单边裂纹悬臂梁,计算出不同裂纹长度与位置时梁的固有频率,结果与实验值吻合良好。最后,给出了一种确定裂纹位置的简捷方法。     

飞机结构的损坏过程承载能力、破坏部位有限元分析

本文提出一个适合于飞机结构非线性分析的有限元素组合算法。考虑到元素材料屈服和/或失稳后出现的非线性问题导出了有限元计算格式。本方法已经实际用于描述××型直升机结构静力试验从开始加载到局部损伤或失稳、扩展直至破坏的全过程受力状态;用于确定该机结构的最大承载能力和破坏部位,并取得了非常好的结果。文中介绍了数值算例及其与试验结果的对此。     

三维机织复合材料的一个细观力学模型

根据三维机织复合材料中细观几何和变形的周期性,提出了一种反映细观周期约束条件的组合梁单元模型,该模型既考虑了纤维束的偏轴拉压效应,又考虑了纤维束的弯／剪耦合效应和纤维束之间的相互作用,可以描述纤维束和基体中的细观应力分布。针对一种典型的三维机织复合材料,研究了根据编织参数确定材料细观结构的方法,在此基础上选取材料中最小周期的一段纤维束作为分析胞元,用上述模型分析了面内拉伸荷载下胞元中各相材料的细观应力,进而得到材料平均的宏观模量。材料试验和二维细观有限元分析证明了本模型的可靠性。研究表明,三维机织复合材料中,纤维束拉、弯耦合效应引起的细观应力在应力分析中不可忽略。     

Analysis of an arbitrarily loaded shell of revolution based on the finite element method in a mixed formulation

The volume finite element in the form of hexahedron with nodal unknowns as components of the displacement vector and stress tensor has been developed to analyze the shells of revolution. The displacement vector components for the inner point of the finite element and the components of its stress tensor are expressed through the nodal unknowns using the method of vector and tensor fields interpolation by the trilinear shape functions; that provides taking into account the finite element displacement as a whole solid. The variational principle in a mixed formulation is applied to form the matrix of hexahedron deformation. The efficiency of the proposed method for approximating the values being sought as vector and tensor fields in comparison with the traditional method for approximating the values being sought as scalar fields is confirmed by a numerical example.     

修正的有效系数法

 提出了一种修正的有效系数法。该方法无需将真实载荷谱从绝对值最大的载荷处截断,即可进行构件危险部位的局部应力应变响应模拟,从而得到构件危险部位真实的局部应力应变响应和真实的局部应力 (或局部应变 )谱。用该方法分析了一个缺口试件在随机谱载下的裂纹形成寿命,结果比常规的有效系数和雨流法更接近试验结果。说明该方法比常规的有效系数法更加合理,也更具实用性。     

转、静子轴向间距对转子叶片振动应力的影响

采用数值模拟方法,分析了转、静子轴向间距对转子叶片振动应力的影响.利用CFD程序对进口静叶尾迹作用下的压气机转子叶片排非定常流动进行了数值模拟,并采用所编写的程序将气动载荷转化为有限元模型上的动态压力载荷,进行了结构瞬态响应分析.结果表明:在所考查的轴向间距下,随轴向间距的增大,转子叶片振动应力呈减小趋势,这主要是由于造成压力载荷波动的尾迹强度沿流向是减弱的.      

滚弯成形解析建模与数值分析

建立了考虑材料塑性强化的滚弯成形力学分析解析模型,推导出了应力应变、残余应力以及回弹半径计算公式.基于非线性有限元软件,对滚弯成形进行了动态模拟,对应力应变状态、塑性应变分布、残余应力以及回弹等进行了分析计算,结果表明:板料滚弯成形初始效应明显,下压点附近曲率不均匀;采用足够的滚弯时间后,中间段的曲率均匀度很好;成形半径与上辊下压量呈近似幂函数关系;多道次滚弯可以减小两端的曲率波动和最大应力应变.最后通过与滚弯成形试验数据的对比,分析和验证了解析模型与数值模型的适用性和精度.