基于人工神经网络的多处损伤加筋板剩余强度预测

用BP神经网络算法对多处损伤加筋板的剩余强度数据进行训练学习,将预测值和3种经典分析方法的计算值与实验值进行对比,结果表明,ANN法预测值与实验值吻合得最好,LMC修正法和WSU3修正法次之,Swift塑性区连通法最差。最后用所建立的BP网络对不同主裂纹半长和韧带长度的剩余强度进行了预测,结果发现,在其他参数不变的情况下,不管是双筋条还是三筋条加筋板,剩余强度总是随主裂纹半长的增加而成线性降低,随韧带长度的增加而成线性增加,但双筋条加筋板比三筋条加筋板对主裂纹半长和韧带长度的变化更加敏感。     

基于谱元法的加筋双层板声透射分析

首先应用谱元法(SEM)建立简支加筋双层板结构在简谐平面声波激励下的振动响应分析模型,将所得结果与有限元法(FEM)计算结果对比,表明谱元法(SEM)在求解该类问题时具有精度高和求解速度快的优点。然后应用Rayleigh积分求解加筋双层板结构路径传声的透射声功率。在筋板截面面积不变的约束条件下,研究筋板倾角与面板间距在声波正入射情况下对透射侧面板辐射声功率的影响。结果表明:筋板倾角越大,加筋双层板的透射声功率越小;在倾角小于22o的情况下,隔声性能随着面板间距的减小而提高。分析结果对加筋双层板的结构设计与隔声优化具有一定的指导意义。     

Kirchhoff型裂纹板的边界元法

本文用的复变函数理论,导出了含裂板弯曲问题的基本解。该基本解满足自由裂纹的边界条件。将其引入直接或间接积分方程中,只要对板的外边界进行离散,就可计算有限尺寸裂纹板的弯曲问题。算例表明,本文所得到的基本解用以求解裂纹板弯曲问题划分的单元较少,精度较高。本文的方法还可用以求解含有形状比较复杂的裂纹或孔洞板弯曲问题的基本解。     

双向正交加筋板声振响应解析方法研究

提出双向正交加筋板声振响应的一种解析计算方法。使用两种连续性条件,建立双向正交加筋板的耦合振动方程。利用二维傅里叶级数作为双向正交加筋板振动位移表达式,将双向正交加筋板振动微分方程化为线性方程组,求解获得双向正交加筋板的模态特性以及加筋板稳态声振响应,并通过了现有文献数据和有限元方法的验证。通过进一步的参数分析,研究加强筋在板上的排布方式对加筋板声振特性的影响。     

简谐激励下复合材料加筋板的基体微裂纹损伤演化

研究了在简谐激励作用下复合材料加筋板基体微裂纹损伤的演化行为及其对加筋板动力特性的影响。基于平均微裂纹密度和断裂力学方法, 建立了复合材料加筋板基体微裂纹演化的刚度退化准则。由于该准则考虑了载荷作用周期数的影响, 从而能够更合理地分析周期性动载荷作用下基体微裂纹损伤演化规律。采用Mindlin一阶剪切理论和复合材料模态阻尼模型, 建立了复合材料加筋板动力分析的有限元方法, 研究了在简谐激励作用下, 含分层损伤复合材料加筋板振动过程中诱发的基体微裂纹损伤的演化、 刚度退化, 频率折减和动力响应。      

阻尼夹芯复合材料加筋板的振动分析与数值模拟

以阻尼夹芯复合材料加筋板为研究对象,依据一阶剪切变形理论(FSDT)和Hamilton原理,推导板和加强筋的应变能、动能表达式,采用变分原理建立控制微分方程,根据相关边界条件和傅里叶级数求解方程。建立了ANSYS阻尼夹芯复合材料加筋板的有限元模型,该模型考虑到阻尼夹芯复合材料加筋板中阻尼材料与纤维预浸料间的结合方式,用模态应变能有限元数值模拟方法研究了结构的动力学性能,并通过对数值模拟结果与理论解的比较,验证了模型的合理性和有效性。探讨了不同的筋条尺寸、不同的筋条数量、不同的筋条分布方式对阻尼夹芯复合材料加筋板动力学性能的影响,得出了阻尼夹芯复合材料加筋板的一阶模态频率和损耗因子随不同参数的变化曲线,其结论为阻尼夹芯复合材料加筋板的优化设计提供参考。     

钢材与复合材料多形式加筋平板透声性能消声水池实测分析

以复合材料声呐导流罩加筋板结构多目标综合优化为工程背景,开展消声水池模型插入损失测试,横向对比分析钢制桁架筋材与四种复合材料筋材加筋板近场透声特性,综合讨论了筋材材质、筋材结构形式以及入射角度对加筋板近场透声性能的影响。测试及分析结果表明:桁架式加筋板近场透声性能优异且稳定;细矮型筋材可提高加筋板整体透声性能。研究结果为声呐导流罩复合材料加筋板结构的优化设计提供了参考。     

含切口复合材料加筋板的压缩剩余强度研究

通过对含穿透切口的复合材料加筋板轴向压缩试验以及有限元渐进损伤模拟分析,研究了加筋板离散源损伤的扩展模式与破坏特征。结果表明,切口前端出现了非常明显的应变集中且最先发生破坏,沿切口方向未切断筋条的屈曲和壁板边缘的突然压溃导致了加筋板的最终破坏。基于最大应变判据和Hashin判据的三维有限元渐进损伤模拟有效的表达了含切口复合材料加筋板的损伤扩展,计算结果与试验吻合较好。     

考虑屈曲的复合材料加筋壁板铺层顺序优化

提出了一种考虑屈曲的复合材料加筋壁板铺层顺序优化方法。基于复合材料加筋壁板屈曲载荷求解的能量法,系统推导了轴压载荷作用下复合材料加筋壁板蒙皮、筋条局部屈曲载荷的显示表达式,考虑了加筋壁板各板元之间的弹性支持作用及筋条下缘条的影响,引入工程法求解了加筋壁板整体屈曲载荷。基于国产自主结构分析软件HAJIF中的复合材料铺层工程数据库,以铺层参数为中间变量,利用本文提出的复合材料加筋壁板屈曲载荷求解方法,构建了考虑屈曲的复合材料加筋壁板铺层顺序优化设计流程并完成程序实现,将最小二乘法用于最优铺层顺序与工程铺层数据库的匹配。相比于传统有限元计算方法,本文提出的复合材料加筋壁板屈曲载荷求解方法具备较好的求解精度及求解效率。复合材料加筋壁板优化算例表明,采用本文提出的加筋壁板屈曲载荷分析及其优化方法,在结构重量不变的前提下,屈曲载荷提高约17%,且铺层顺序优化结果可直接从铺层工程数据库中提取并用于工程实际。      

有限板共线多孔MSD疲劳裂纹扩展有限元模拟

介绍了二维断裂分析有限元软件FRANC2D/L在疲劳裂纹扩展模拟方面的基本步骤．利用该软件对有限板中心孔边对称裂纹的疲劳裂纹扩展进行模拟计算,对比模拟结果和试验数据,发现两者吻合良好,证明了利用该方法模拟疲劳裂纹扩展的可靠性．将FRANC2D/L应用到有限板共线多孔MSD疲劳裂纹扩展的有限元模拟上,得到了各孔边裂纹的长度和疲劳扩展寿命之间的关系曲线．模拟计算结果表明,在相同条件下,有限板中心孔边对称裂纹的裂纹扩展寿命要远远高于MSD结构中中心孔边裂纹的疲劳扩展寿命;由于MSD结构中影响各孔边裂纹的因素有所差异,各条裂纹的疲劳扩展寿命也会有所不同．另外,还给出了不含主裂纹的MSD和含主裂纹的MSD两种情况下的疲劳裂纹扩展历程,通过比较得知,含主裂纹的MSD结构更容易发生裂纹的合并和贯穿致使结构发生破坏．     

A new method of crack-tip opening displacement determined based on maximum crack opening displacement

In this paper a new method is presented to determine the crack-tip opening displacement (CTOD) for the center cracked plate with uniaxial uniform tension load. The maximum crack opening displacement (MCOD) is adopted to estimate CTOD. Based on the series of calculation results by elastic–plastic finite element simulation, an explicit function expression for the CTOD versus MCOD is determined, which enables to consider the influence effects of crack geometries, plate sizes, applied loads, plane state and material properties. Hence, the presented method of CTOD determined by MCOD is suitable to any center crack finite plate of any material under uniaxial tension.     

Surface and internal cracks in a residually stressed plate

The problem of a surface or an internal crack in a plate which contains residual stresses is examined. The line spring model, which reduces a three-dimensional elasticity problem into a two-dimensional problem in plate theory, is used to model the crack. The Reissner plate theory, which takes into account transverse shear deformations, is used to model the plate. The formulation is based on Fourier Transforms which lead to a pair of singular integral equations that are solved numerically. The line spring method requires the plane strain solution to both the edge and internally cracked strip with crack surface loads representative of tension, bending, and the given residual stress distribution. For general use, plane strain solutions are presented for polynomial loading through the thickness up to the fifth order. Comparisons are made between the results given by the line spring model for the Reissner plate theory and the finite element method.     

Analysis of stress intensity factors for the tension of a centrally cracked strip with stiffened edges

This paper presents a theoretical analysis of the stress intensity factor for the tension of a centrally cracked strip reinforced with stringers along its edges. The method is based on the Laurent expansions of the complex stress potentials, and the perturbation technique is applied in determining their coefficients from the boundary conditions. Formulae of the crack tip stress intensity factors are given in forms of 36 term power series of $\text{λ}{}^2$, where λ is the ratio of the crack length to the plate width. The analysis covers, as special cases, a centrally cracked strip with free edges, that with clamped edges, and a wide plate stiffened by parallel stringers and containing a crack between every adjacent stringers. Numerical calculations are performed for various combinations of the extensional and bending rigidities of the stringers, and their stress relieving effects are examined in detail. The present method is considered to give practically exact values for λ less than 0.95 regardless of other parameters.     

Some recent fatigue and fracture mechanics research in BIAM

The paper presents a brief review of some of the major research activities on fatigue and fracture mechanics in recent years at the Beijing Institute of Aeronautical Materials. Attention is mainly given to the studies on weight function methods for analyses of two- and three-dimensional crack problems, fatigue crack growth under variable amplitude loading, small crack effects and a fracture-mechanics-based total fatigue life prediction method.Abbreviations 2(3)D two- (three-) dimensional - BIAM Institute of Aeronautical Materials, Beijing - CCT center cracked tension - COD crack opening displacement - CTOD crack tip opening displacement - FEM finite element method - LEFM linear elastic fracture mechanics - SENT single edge notched tension - SIF stress intensity factor - WFM weight function method     

The residual strength characteristics of stiffened panels containing fatigue cracks

In heavy structural members, where plane strain conditions prevail, linear fracture mechanics can be used for predicting residual strength. Aircraft structures consist largely of sheet structures with plane stress conditions where linear fracture mechanics do not seem to apply. Yet it is in the aircraft main structure that large fatigue cracks can develop and that has to be designed fail-safe. The present paper describes a method to predict the residual strength of a cracked sheet structure.Contrary to an unstiffened sheet, the sheet structure contains stiffening elements that can act as crack stoppers. This crack arresting action and its consequences for the residual strength are considered in the analysis.The paper proposes a method that relates the crack resistance of a stiffened panel to that of an unstiffened sheet. It takes full account of sheet-stringer interaction in the cracked region. A criterion for crack arrest is put forward. Ultimate panel failure after crack arrest is initiated either by subsequent unstable crack growth or by stiffener failure. Critical load conditions for both failure modes are presented. In case crack arrest does not occur, the residual strength of the unstiffened panel constitutes a safe lower bound.Computational results of the interacting rivet forces by both analytical and numerical (finite element) methods are presented. From these the load concentration in the stiffener and the reduction of the stress intensity at the crack tip can be determined. This enables the complete residual strength characteristics to be predicted.The results of residual strength tests on bonded and riveted panels with symmetric strip stiffeners or eccentric Z-stringers fully substantiate the method proposed for residual strength calculations.     

A contour integral computation of stress intensity factors in the cracked orthotropic elastic plates

Stress intensity factors in the cracked orthotropic elastic plates are obtained numerically using a reciprocal work contour integral technique. The integral representation for calculating the intensities of elastic singular stresses at cracks, notches and corners can be extended to treat the rectilinearly anisotropic crack problems. An extension of the method can be done immediately with identification of the characteristic singular solutions and construction of the corresponding complementary elastic states. A centrally cracked tension plate with various degree of orthotropy is analyzed to assess accuracy of the computational procedures newly adopted. Two cracked orthotropic plates modelling bidirectional fiber-reinforced composites are treated: symmetric Mode I type of double edge crack tension plate and mixed mode type of cantilever plate with a single edge crack.     

加强筋截面类型对轨道车辆板件结构隔声影响研究

针对轨道车辆轻量化设计后可能带来的隔声性能降低问题,研究不同截面加强筋铺设对板件隔声性能的改善效果。基于混合有限元-统计能量分析(Hybrid FE-SEA)方法建立轨道车辆加筋板结构隔声特性预测分析模型,系统分析T型、L型、I型和矩形加强筋截面类型对板件隔声性能的影响。研究结果表明,加筋板的刚度和1阶固有频率皆比均质板大,且随加强筋厚度的增大而增大;当加强筋厚度恒定时,T型加筋板的刚度和1阶固有频率最大,L型加筋板次之;敷设厚度15 mm的加强筋,板件的隔声性能最佳;当加强筋的质量、厚度、腹板面积及尺寸、翼板面积相等时,各类型加筋板的计权隔声量Rw差异不大;板件加筋后,刚度控制区的隔声量增幅3 dB~17 dB,1 250 Hz~4 000 Hz中高频段的隔声量增幅1 d B~6 d B。综合分析可知,以计权隔声量为评价标准时,在加强筋质量、腹板面积、翼板面积及尺寸相等时,敷设厚度15 mm加强筋,板件的隔声性能最佳,Rw较均质板可提高1.4 dB~1.5 dB,而加强筋厚度恒定时,T型和L型加筋板的刚度又最佳。相关研究成果可为轨道车辆板件结构加筋优化提供设计参考。     

Application of the distributed dislocation technique for calculating cyclic crack tip plasticity effects

This paper describes a method for modelling cyclic crack tip plasticity effects based on the distributed dislocation technique (DDT). A strip‐yield model is utilised to allow for the determination of the crack opening displacement, size of the plastic zones and in the case of a fatigue crack, the wake of plasticity. The DDT can be easily implemented for a wide range of cracked geometries with reliable control over the accuracy and convergence. Thickness effects can also be incorporated through a recently obtained solution for an edge dislocation in an infinite plate of finite thickness. Results for finite length cracks that have had limited growth, such that there is no plastic wake, are presented for a range of applied loads and R‐ratios. Further results are provided for a steady‐state fatigue crack in a plate of finite thickness. The present results are compared with analytical solutions and they show an excellent agreement.     

复合材料加筋板的大变形有限元分析

本文将考虑横向剪切变形的Mindlin's理论应用于复合材料加筋板的大变形分析,在Total-Lagrange坐标系下推导了八结点等参弯曲板单元和三结点等参梁单元的增量平衡方程和切线刚度矩阵,非线性问题采用增量法和Newton-Raphson迭代法相结合的方法求解.本文通过一些算例,证明了所采用单元具有良好的收敛性和足够的精度,并讨论了边界条件、纤维铺设角和加筋疏密等因素对复合材加料筋板非线性解的影响.     

Three-dimensional stress intensity factor calibration for a stiffened cracked plate

Three-dimensional finite element analyses are used in this paper to calibrate the stress intensity factor in a cracked stiffened plate subjected to remote uniform traction. An accurate numerical determination of the stress field and stress intensity variation through the thickness of a central cracked plate was first carried out in order to evaluate three-dimensional effects. A stiffened cracked plate was then analysed, taking into account the results and the conclusions obtained in the previous study. Such a structure was chosen due to the growing interest for large integral metallic structures for aircraft applications, following the continuous need for low cost and the emergence of new technologies. The J-Integral technique was used to calculate the values of the stress intensity factor along the plate thickness. The plane strain behaviour near the crack front and the variation of the opening stress are discussed.