多墙翼面结构后屈曲强度试验和数值研究

采用静态试验和有限元分析相结合的方法研究了复合材料中厚蒙皮多墙翼面结构的后屈曲性态、强度和破坏过程。有限元分析取得的载荷-位移曲线和试验结果的一致性说明了有限元模型的正确性。在此模型基础上,采用非线性弧长法追踪外载-位移路径,研究了盒段在压缩和集中力两种不同载荷下的后屈曲行为。给出了屈曲临界载荷和屈曲变形性态,分析了后屈曲强度和破坏过程。     

复合材料胶铆混合修理的拉伸性能研究

为研究不同修理方法以及不同损伤尺寸对复合材料层合板拉伸性能的影响,针对复合材料飞机蒙皮,设计了无损板、60 mm与30 mm损伤孔径的胶接修理板和胶铆混合修理板五组试验件,并对这五组结构件进行静强度拉伸试验及失效机理分析.建立试验件的三维有限元仿真模型,分析无损板和四组修理件的破坏强度、破坏模式、应力分布、应力大小和危...     

复合材料桨叶蒙皮层间裂纹的应力强度因子求解方法研究

蒙皮分层是复合材料桨叶疲劳破坏的主要形式.文中以应力强度因子为蒙皮分层扩展参数,应用准三维方法及复合材料桨叶结构模型,推导带预扭角的直升机桨叶蒙皮的三维应力-应变关系;同时依据各向异性体界面断裂力学,分析蒙皮存在初始裂纹时裂尖的振荡性,并采用相互积分法给出应力强度因子的求解方法,最后通过数值算例论证文中的方法是可行的.     

基于三维CDM的复合材料开口层合板失效分析

建立了复合材料层合板三维连续介质损伤力学模型,并将该模型应用于复合材料开口层合板的损伤破坏分析中。与相关试验中开口层合板强度和损伤破坏情况对比分析表明:本文模型能够有效地模拟开口层合板从初始损伤到完全破坏的全过程,具有较高的计算精度和良好的数值模拟收敛性。基于该模型,详细分析了在单向拉伸载荷作用下开口层合板不同铺层的损伤破坏情况。     

筋条分层损伤复材加筋壁板的稳定性分析及修理

从工程实际问题出发,采用有限元方法,模拟典型结构/典型分层类型,对某型飞机筋条带分层损伤的复合材料加筋壁板稳定性进行计算分析,针对分层原因提出损伤控制和修理的工程可行方案。全尺寸带分层损伤结构静强度试验表明壁板稳定性决定结构整体承载能力,由于筋条分层提高壁板工作应力的同时降低了蒙皮局部支持刚度,导致初始失稳载荷及总体承载能力的下降。试验结果较好的印证了有限元分析方法的正确性。     

真空辅助湿法斜接型挖补修理后层合板拉伸性能研究

对真空辅助玻璃纤维增强复合材料斜接型挖补修理后结构进行了拉伸强度试验研究,获得了修理后结构最终破坏模式。分别建立了挖补修理结构中母板与补片三维有限元模型,采用了各向异性连续损伤力学模型模拟了母板与补片复合材料单向带失效模式,假定母板与补片通过黏性力接触,在真空辅助湿法挖补修理形成的无厚度二次固化界面处定义了接触面, 采用指数型软化cohesive模型模拟了界面接触属性。试验结果与数值模拟结果吻合较好,表明所采用的模型能很好地预测整个修理结构的拉伸性能。分析了整个拉伸过程中层合板斜接挖补修理结构的损伤破坏过程,发现了附加补片引起的应力集中是造成母板中薄弱层过早损伤的原因。讨论了不同斜接挖补角度对修理后结构强度的影响,结论可以引导工艺人员制订合理的修补方案。     

含分层复合材料层合板拉伸剩余强度研究

以T300/BMP316复合材料层合板为研究对象,开展了含预制分层层合板的静拉伸试验及静强度预测方法研究.通过试验获得含预制分层层合板的拉伸剩余强度.基于三维逐渐损伤分析方法,采用双层节点法模拟初始分层,建立了含分层复合材料层合板的静载逐渐损伤分析模型,静强度预测误差在5％以内.采用所建立的方法对分层处于不同层间位置的...     

含孔复合材料层合板的疲劳寿命研究

建立了三维有限元模型,分析了复合材料层合板的应力场。使用修正Hashin失效准则判定复合材料的失效模式,并突降失效单元的材料性能。疲劳载荷引起复合材料刚度降和强度降依靠缓降模型实现。笔者将突降模型和缓降模型植入有限元模型中,模拟了复合材料层合板在拉伸和压缩疲劳载荷下的渐进损伤过程,并计算了层合板的纵向刚度损伤和疲劳寿命。层合板的纵向刚度损伤具有三阶段特点,与试验观察是一致的。层合板疲劳寿命预测值与试验值吻合地很好。     

含离散源损伤复合材料加筋板剩余强度及其修理技术研究

飞机复合材料结构在使用过程中难免遭受离散源损伤,这种损伤会严重降低结构的承载能力。针对含穿透性切口的复合材料加筋板,采用试验和数值分析方法研究其拉伸载荷作用下的剩余强度,并根据设计应变设计了金属补片机械连接修理方案,提出了一种评估复合材料机械连接修理结构剩余强度的数值分析方法。分析方法以有限元模拟为主,用壳元模拟层压板,用梁元模拟紧固件,用多点约束模拟紧固件与孔的接触,用0°层点应力准则预估复合材料破坏载荷。通过试验验证了评估方法,得到了修理结构强度恢复率。本文的研究对于飞机复合材料结构修理技术研究有一定的借鉴意义。     

几何缺陷对复合材料加筋平板轴压屈曲影响研究

当前的设计准则要求复合材料结构在限制载荷下蒙皮不发生局部屈曲,因此对蒙皮屈曲载荷的准确预测至关重要。设计了三种构型复合材料加筋平板轴压试验件,研究蒙皮在轴压载荷下的屈曲和后屈曲;采用线性特征值有限元方法计算了蒙皮的轴压屈曲载荷;采用多阶屈曲模态线性组合的方式引入初始缺陷,应用非线性方法计算了蒙皮轴压屈曲载荷并进行了缺陷灵敏度分析。计算结果和试验结果对比表明:当前计算蒙皮屈曲的工程方法过于保守,有限元方法可以更准确的计算蒙皮的屈曲载荷;初始缺陷对复合材料平板屈曲载荷有一定影响,其影响大小与缺陷幅值息息相关,不考虑该缺陷,会得到非保守的计算结果。     

The compressive behavior of CFRP laminates with delamination of different shapes using numerical and experimental approaches

Composite laminates often produce delamination due to a series of factors during the manufacture and service process. In order to research the effect of containing oblique elliptical and circular initial delamination damage on the compressive strength of composite laminates, numerical and experimental methods are used in this paper. Finite element models (FEMs) and the progressive damage subroutine USDFLD are developed to predict the damage initiation and extension behavior of the intralaminar of the laminate. Interlaminar damage is predicted based on cohesive zone models (CZM). At the same time, four compression tests containing different initial delamination damage are performed. The results show that experimental measurements of compression tests concur with the numerical predictions and validate the FEMs. The strength and stiffness of the specimens gradually decrease with the increase of the initial delamination area. It reveals that, for the compression process, the delamination damage extends from the edge of the initial damage to the surroundings. The bearing capacity of the composite laminates is mainly determined by the material properties of the fibers and matrix, rather than the initial delamination.

     

Three-dimensional topography of the matt surface in aluminium pack rolling

A model has been presented in a companion paper (Utsunomiya et al., Int. J. Mech. Sci., in press) to predict the generation of roughness on the matt surface in pack rolling of aluminium foil. This model was based on a two-dimensional (2D) finite element analysis using an isotropic plasticity model for the material. The spread of crystallographic grain orientations was simulated by ascribing different material properties to each grain. The predictions showed good qualitative agreement with experiments. It was found that the formation of shear bands causes roughening of the matt surface. The effect of material properties was further explored in Utsunomiya et al. (Int. J. Mech. Sci., in press).In the current study the model for evolution of the matt surface roughness is extended to a three-dimensional (3D) analysis and compared with predictions using a 2D analysis, a full crystallographic 3D model and experiments. The amplitude of the predicted roughness for the 3D model is lower than for the corresponding 2D analysis. In the 3D model, grains deform more uniformly due to the homogeneous constraint from adjacent grains. The predicted roughness shows good quantitative agreement with experiments, as well as with the predictions of the crystal plasticity model. The influences of grain shape and deformation mode are investigated. It is found that peaks or valleys running perpendicular to the first principal axis of strain are generated at the matt surface, regardless of initial grain shape.     

基于弹性壳体模型的波箔型气体动压径向轴承静特性分析

采用有限单元法,对波箔型气体动压径向轴承的箔片建立了弹性壳体单元模型。该模型综合考虑了箔片膜效应与弯曲效应之间的耦合,更能真实地反映出波箔和平箔的变形。运用有限差分法及Newton-Raphson迭代法耦合求解Reynolds方程和气膜厚度方程,分析了轴承气膜厚度分布、压力分布、箔片变形量分布以及承载能力,并与实验结果进行了比较,证明了该方法的可行性和精确性。分析了转速、箔片厚度对轴承特性的影响,结果表明:转速上升,承载能力增大;箔片厚度小于0.2mm时,厚度的改变对轴承的影响较大。     

基于FEA的车轮结构形状优化设计

为了更好地指导车轮结构设计,采用UG三维造型软件建立3种常见轮辐结构的车轮模型,并采用有限元分析方法对几种车轮模型在冲击试验和弯曲试验中的应力分布及强度性能进行了分析,对冲击试验利用响应分析模块进行分析,对弯曲试验进行旋转弯矩下的分析.比较3种结构的分析结果,从应力分布及应力集中强度等方面,分析讨论了车轮轮辐结构的设计原则与方向,得出直辐条背面有掏料的车轮结构更适合承受弯曲载荷,以及曲辐条车轮结构更适合承受冲击栽荷的结论.     

Minimum Film Thickness in a Gas Foil Journal Bearing with an Unbalanced Rotor

A gas-lubricated foil journal bearing consists of a compliant metal shell structure that supports a rigid journal or rotor by means of a gas film. The response of this system to the periodic forces of an unbalanced rotor supported by a single bearing is predicted using perturbation analysis. The foil structure and the gas film are modeled with an analytically perturbed finite element approach to predict the rotor dynamic coefficients. A dynamic model of the rotor is used to predict periodic journal motion. The perturbation analysis is then used with the periodic response of the rotor to calculate periodic changes in the gas film thickness. Other quantities such as the gas film pressure and the foil deflection can also be calculated. The model includes bending and membrane effects in the top foil, coupled radial and circumferential deflections in the corrugated sub-foil, and the equivalent viscous dissipation of Coulomb friction effects in the foil structure. The approach is used to investigate the effects of top-foil thickness on minimum film thickness in a bearing.     

金属陶瓷可转位刀片的有限元分析

采用有限元法，建立金属陶瓷可转位刀片复杂结构的三维有限元模型，加载求解，进行位移场和应力场分析，计算出刀具的最大位移、应力、应变等，以进行金属陶瓷可转位刀具的抗弯强度和抗压强度校核，可有利于对切削过程中的力学特性进行深入研究，为金属陶瓷可转位刀具的设计提供理论基础。     

Cyclic damage model for E-shaped dampers in the seismic isolation system

The objective of this study is to apply a constitutive damage model for cyclic response of E-shaped dampers as well as metal and metallic plate dampers in order to be used in more broad areas such as material and component levels. The seismic isolation system used as sliding bearings and metallic dampers undergoes almost elastoplastic behavior due to seismic excitation. Accordingly, a two surface damage model is applied to understand inelastic behavior and to evaluate the potential damaged state of E-shaped dampers in the seismic isolation system. This damage model is originally formulated through a thermodynamic approach based on the entropy production equation. The cyclic damage model proposed in this study can be implemented into a user subroutine in the finite element (FE) software ABAQUS. Finally, the numerical results for E-shaped energy dissipation devices in the seismic isolation system are compared with the experimental test results so as to check the validity of the proposed model.     

Effect of continuum damage mechanics on springback prediction in metal forming processes

The influence of considering the variations in material properties was investigated through continuum damage mechanics according to the Lemaitre isotropic unified damage law to predict the bending force and springback in V-bending sheet metal forming processes, with emphasis on Finite element (FE) simulation considerations. The material constants of the damage model were calibrated through a uniaxial tensile test with an appropriate and convenient repeating strategy. Holloman’s isotropic and Ziegler’s linear kinematic hardening laws were employed to describe the behavior of a hardening material. To specify the ideal FE conditions for simulating springback, the effect of the various numerical considerations during FE simulation was investigated and compared with the experimental outcome. Results indicate that considering continuum damage mechanics decreased the predicted bending force and improved the accuracy of springback prediction.     

不同强度理论在曲轴疲劳研究中的对比应用

采用有限元法对曲轴在弯矩载荷作用下的应力状态进行分析,并结合插值法对曲轴的应力分布进行拟合计算,在此基础上采用临界距离法与不同强度理论对相同材料、不同圆角半径的曲轴的结构疲劳特性进行预测研究,并对预测结果进行试验验证。研究结果表明：当基于第一强度理论与临界距离法对圆角半径不同的曲轴的疲劳特性进行预测时,无论是临界点法还是临界线法都会造成较大误差;而当基于第三及第四强度理论与临界距离法进行预测时,临界线法比临界点法的预测精度更高,分析认为这是由曲轴的破坏类型造成的。     

一种计算轮毂疲劳损伤的数值模拟新算法

针对轮毂结构复杂和周期载荷的特点,采用刚性元法简化轮毂有限元模型, 基于材料疲劳损伤规律、应变等效假设理论和有限元方法,提出了一种计算旋转轮毂结构疲劳损伤的新算法。该算法采用拟合得到的损伤演化材质参数和ANSYS的二次开发工具对轮毂的疲劳损伤过程进行数值计算,在得到裂纹全寿命的同时,给出裂纹群扩展路径,真实地模拟了轮毂动态旋转损伤进程。试验研究证明了该方法的可行性和有效性。