体积收缩率对光固化树脂基复合材料收缩应力的数值模拟

依据SiC晶须增强树脂基复合材料的光固化实验结果，运用材料的温度应力原理，利用降温等效体积应变与光固化体积收缩率关系的假设，建立了有限元模型。研究并分析了树脂基体中组分配比、光固化层厚和晶须增强体对成型件收缩应力的影响。结果表明：树脂基体中组分配比和晶须增强体对收缩应力的影响很大，而光固化层厚对收缩应力的影响较小。     

同轴单搭接接头破坏过程研究

在实验所得结果之基础上研究了预偏角对单搭接胶接接头破坏机制的影响,用弹塑性有限元法模型得到了不同裂纹长度时接头整体和胶层中心等效应力沿裂纹尖端的分布,并研究了外载大小、裂纹长度对应力强度因子的影响.结果表明,同轴接头和标准接头的破坏均从胶层界面开始,但同轴接头以形成较多小裂纹为主,而标准接头中裂纹沿着胶层向中部扩展,最终导致破坏;随裂纹长度的增加,接头上等效应力渐增,胶层中心峰值应力也增大,裂纹尖端的应力远高于其他部位;当裂纹扩展到临界尺寸时,接头会迅速破坏.     

金属胶接接头残余应力计算及数值分析

利用Baker模型和弹塑性有限元方法研究了胶接接头搭接区残余应力的分布.结果表明,因胶粘荆的线膨胀系数比被粘物高得多,胶层固化时被粘物阻碍了胶层的收缩,故胶层中为残余拉伸应力,被粘物中为残余压缩应力,胶层中的残余应力远大于被粘物中的残余应力.利用Baker模型和有限元计算远离自由端的胶层中的残余应力,两者吻合.被粘物中的残余应力呈中心对称,等效应力经多项式拟合后呈抛物线分布.     

Q345 中厚板 V 形折弯应力 应变分析

目的研究Q345中厚板在V形折弯时的应力应变中性层内移规律。方法通过对中厚板135°折弯过程进行数值模拟,分析了板料在成形过程中的等效应力应变及其中性层内移现象,测得了应变中性层与几何中间层之间的距离变化。在此基础上,采用厚度为16 mm的Q345板料进行物理实验,并与模拟结果进行了对比分析。结果在成形过程中,等效应力应变中性层均产生了内移现象,且应力中性层的内移量明显大于应变中性层的内移量;成形结束之后,应变中性层与几何中间层的距离为3.3 mm;实验结果显示,应变中性层的内移量为3.1 mm左右,与模拟值较为一致。结论数值模拟方法可以为应力应变中性层计算提供指导。对于中厚板折弯,采用几何中间层展开求得的坯料尺寸并不准确。     

粗糙陶瓷涂层与刚性平面滑动摩擦过程的数值模拟

陶瓷涂层在滑动接触过程中的温升对零部件的接触和力学性能有重要的影响.应用有限元法,建立了含多粗糙峰陶瓷涂层与刚性平面的滑动接触模型,并通过热机耦合计算对滑动摩擦过程进行了数值模拟,分析了滑动过程中陶瓷涂层、粘结层和基体的温度及应力分布规律,研究了相对滑动速度、初始压入量、摩擦系数和涂层厚度对各部分的温升、等效应力和接触应力的影响.结果表明:陶瓷涂层的最高温度出现在粗糙峰的滑动接触面上,其高温区也集中在粗糙峰部分;与静态接触相比,滑动接触改变了各部分内部应力的分布;粘结层和基体的最大等效应力和最高温度随着运动速度和摩擦系数的增大而升高,随涂层厚度的增加而降低;粘结层和基体在滑移前后的最大等效应力及最高温度均与压入量近似成线性关系.     

反应堆压力容器接管安全端焊接残余应力模拟及其焊接参数优化研究

目的 针对反应堆压力容器接管安全端焊接残余应力较大易导致应力腐蚀开裂的问题,探究焊接工艺参数对焊接残余应力的影响,并寻找最佳工艺参数。方法 利用有限元参数化建模方法建立反应堆压力容器接管安全端的三维热-力耦合模型,模拟其焊接过程,研究焊接残余应力的变化情况。采用正交试验设计法分析了焊接电流、焊接速度及层间冷却时间对焊后最大等效应力的影响,建立了焊后最大等效应力与焊接电流、焊接速度及层间冷却时间的二次回归模型,基于该模型利用遗传算法寻优焊接参数。结果 焊接残余应力峰值靠近熔合区位置,残余应力较高,超过了材料的屈服应力;各参数按对焊后等效残余应力峰值的影响由大到小的顺序依次为焊接速度、焊接电流、层间冷却时间。正交试验所得最佳工艺参数如下：焊接电流为610 A,焊接速度为20 mm/s,层间冷却时间为400 s,经遗传算法进一步优化后所得的最佳参数如下：焊接电流为610 A,焊接速度为23 mm/s,层间冷却时间为427 s。通过仿真验证遗传算法优化结果,得到焊接残余应力的峰值为373 MPa,比未优化前减小了44 MPa。结论 优化后的工艺参数有效降低了焊接残余应力,提高了反应堆压力容器接...     

薄膜几种重要力学性能的评价

提出了一种利用X射线应力分析技术和应变电测法测量附着膜的等效应力——等效单轴应变、屈服强度和加工硬化指数的方法。利用该方法测得一种厚度为2．5μm的TiN膜的务件屈服点σ0，1和σ0．2分别等于4．2GPa和4．4GPa，加工硬化指数72为0．36；对于一种厚度为2．4μm的铜膜，得到σ0．1-328MPa，σ0．2—415MPa，n=0．62。利用无应变剥层技术逐层剥离薄膜，同时测量基片曲率半径的变化，由此测得了一种厚度为2．3μm的TiN膜的残余应力沿层深分布。用新建立的一种利用X射线应力分析法测量薄膜泊松比的技术，测出一种TiN膜的泊松比等于0．27。给出了测量陶瓷膜的杨氏模量的设想。     

考虑油墨粘弹性的胶印机墨辊变形特性分析

胶印机输墨系统中的墨辊按照软硬相间的规律排列。为分析两墨辊间粘弹性油墨层对软质墨辊变形特性的影响,综合考虑油墨层和橡胶层的粘弹性,推导了两辊对滚的动力学模型。同时,建立了硬质墨辊-油墨层-软质墨辊的仿真模型,其中油墨层用弹簧来等效,通过设定等效弹簧的刚度及阻尼来模拟油墨层的粘弹性。对软质墨辊施加轴承约束同时对硬质墨辊施加径向位移,使两墨辊相互挤压,仿真后提取软质墨辊接触区中间节点的变形、应力、应变及等效弹簧的变形。对比不同刚度、阻尼的粘弹性油墨层对软质橡胶辊接触区变形、应力、应变及等效弹簧变形的影响,结果表明,等效弹簧(也即油墨层)的刚度和阻尼越大,软质墨辊受到运动载荷所产生的变形越大,两墨辊间的油墨厚度也越大,结果与推导的理论模型相一致。研究结果对分析印刷过程中油墨的传递特性及输墨系统的运动平稳性具有重要意义。     

玻璃与铝在不同层数结构下的阳极键合界面力学性能

运用共阳极法实现不同层数玻璃／铝的阳极键合,采用MARC非线性有限元分析软件,对三层、五层、七层、九层玻璃／铝键合试件的界面力学性能进行比较分析,探讨结合处残余应力随层数增加的变化趋势,分析结果表明,由于多层结构的对称性,最大的等效应力发生在中心处的过渡层。研究结果为MEMS器件在多层封装结构的设计提供了理论依据。     

倾斜薄壁增材过程中基板的热应力数值模拟

利用电弧增材制造技术加工倾斜薄壁时,循环热力效应下,熔覆层与基板结合处应力较为集中,易导致基板变形翘曲,严重影响零部件的成形。为了明确增材倾斜薄壁不同层间偏移量和不同基板厚度下基板的热应力演化,本文采用不锈钢焊丝在Q235基板上进行沉积试验,利用COMSOL建立有限元模型,分析基板横向温度梯度和等效应力的变化。结果表明,基板的横向温度梯度在熔覆层边缘达到最大值,在距离熔覆层中心超过5 mm后趋于最小值;随着层间偏移量的增大,基板的横向温度梯度最大值逐渐减小,但基板上的等效应力逐渐增大;随着基板厚度的增加,基板的横向温度梯度最大值逐渐减小,同一测量点的横向温度梯度和等效应力也随之减小。因此,在倾斜薄壁增材中,不同的层间偏移量主要影响基板上横向温度梯度的分布和熔覆层与基板结合处的等效应力,更大厚度的基板能够有效减小基板上的横向温度梯度,从而减小变形,这对于增材初期倾斜薄壁结构中基板的变形控制具有一定的参考意义。     

Analysis of laminated crack defect in the upsetting process of heavy disk-shaped forgings

Using nonlinear finite element method, a thermo-mechanical coupled simulation model for the formation mechanism of the laminated crack defect has been established in the upsetting of heavy disk-shaped forgings. Through numerical simulation, the distributions of stress, equivalent strain and strain rate were analysed. Meanwhile the distribution diagram of stress state evolution was obtained, and the uncoordinated deformation, under tri-lateral compression, is determined as the main reason leading to laminated crack defect. To reveal the characteristics of the uncoordinated deformation, the variations of each variable and its gradient in numerical simulation were presented, and a combined prediction model of laminated crack defect were proposed based on degree of deformation and gradient of deformation speed. Subsequently, the morphology and distribution of laminated crack were obtained in the centre of forging using the prediction model. Comparison of calculation results and experimental data indicates that both of them match well. In addition, the effect of friction coefficient on the deformation is also presented. The results show that the decreasing of friction coefficient is an effective measure to restrain the laminated crack defect.     

A 2-dimensional mixture theory for biaxially fiber reinforced composites with application to dynamic crack problems

A 2-dimensional mixture theory is developed for wave propagation in a laminated medium in which every layer is made of a fiber reinforced composite material with the angle of reinforcement alternating from layer to layer. The developed theory contains as special cases the 2-dimensional mixture theory for a laminated medium made of isotropic layers, as well as the equivalent modulus theories for bi-directionally and unidirectionally fiber reinforced composites. The developed mixture theory is applied to the problem of a semi-infinite crack in the composite which is under dynamic loading. The induced fracture mode of the crack is of mixed type and contains both Mode I and Mode II types of opening. A numerical method of solution is applied to the four coupled mixture equations of motion in the average displacements and results are given for the dynamic stress fields in the composite.     

基于复合材料层合箱梁改进解析模型计算等效刚度

提出了基于复合材料层合箱梁改进解析模型的等效刚度计算方法。在考虑三维应变效应的同时用复合材料单层的二维折算模量分量来表示三维折算模量分量,简化了复合材料层合箱梁等效刚度系数的计算,得到了由梁横截面几何尺寸和层合板刚度系数表达的等效抗弯刚度和等效抗扭刚度的解析式。该解析式适用于环向刚度一致的复合材料层合箱梁,并充分考虑了弯曲-剪切耦合和扭转-拉伸耦合效应对等效刚度的影响。通过三点弯试验和扭转试验,验证了解析式的正确性;通过与分层等效叠加法、有限元法进行对比,分析了解析式的计算精度。结合经典层合板理论,研究了铺层方式对等效刚度产生的影响及原因,预测了不同铺层复合材料层合箱梁等效刚度的变化规律。      

Bending of cross-ply laminated composites: An accurate and efficient plate theory based upon models of Lekhnitskii and Ren

Bending laminated composites results in a distinctive zig-zag shaped deformation pattern, accordingly jumping transverse shear strains at layer interfaces, but continuous courses of transverse shear stresses there. An accurate representation of this laminate-specific mechanical behavior in terms of plate theories is challenging, even more if computational efficiency is aimed for. Here, an axiomatic equivalent single layer plate theory for cross-ply laminated composites is presented, which is based on the work of Lekhnitskii and Ren and delivers accurate deformation and stress prognoses at the cost of six solution variables. Fulfilling transverse stress continuity, the infinitesimal equilibrium equations are considered in order to derive an appropriate ansatz for the transverse shear stresses including the influence of all plane stress reduced stiffness components. However, the effect of the normal stress σ_zz is neglected, and deflection w is assumed constant across the plate thickness. The equilibrium equations and corresponding boundary conditions of the plate theory are derived by application of the principle of virtual displacements. Numerical results for symmetrical and non-symmetrical composites as well as for typical sandwich plates obtained by the present theory show good agreement with corresponding exact elasticity solutions given by Pagano, even for thick plates.     

A model of composite laminated Reddy plate based on new modified couple stress theory

Based on new modified couple stress theory a model for composite laminated Reddy plate is developed in first time. In this theory a new curvature tensor is defined for establishing the constitutive relations of laminated plate. The characterization of anisotropy is incorporated into higher-order laminated plate theories based on the modified couple stress theory by Yang et al. in 2002. The form of new curvature tensor is asymmetric, however it can result in same as the symmetric curvature tensor in the isotropic elasticity. The present model of thick plate can be viewed as a simplified couple stress theory in engineering mechanics. Moreover, a more simplified model for cross-ply composite laminated Reddy plate of couple stress theory with one material’s length constant is used to demonstrate the scale effects. Numerical results show that the present plate model can capture the scale effects of microstructure. Additionally, the present model of thick plate model can be degenerated to the model of composite cross-ply laminated Kirchhoff plate and Mindlin plate of couple stress theory.     

基于等效模型的帽型复合材料加筋壁板优化设计

本工作提出了一种优化复合材料帽型加筋壁板稳定性的有效方法,该方法是基于在PATRAN软件中用单层板来模拟层合板的力学性能的想法。其中用层合板建的加筋板模型称为详细模型,改用单层板建的称为等效模型。对于航空结构中常见的帽型加筋壁板,本工作采用反映实际壁板形状的高精度有限元模型,分别建立了详细模型和等效模型。比较得出两种模型的一阶线性失稳因子和失稳应变基本一致,从而验证了将等效模型用于帽型加筋壁板结构稳定性分析的可行性。为了便于验证该优化方法的有效性,本工作只考虑加筋板的筋条厚度一致的情况。传统方法在优化蒙皮和筋条厚度时需要优化层合板的每个单层的铺层厚度和铺层顺序,本文提出的优化方法只需要解决单层板的厚度优化问题,相比本方法大大减少了设计变量。本工作用此方法优化得到了两个参数不同的复合材料帽型加筋板的最优屈曲性能,发现只需要2～4次迭代优化就可以收敛,收敛速度很快。     

用变分渐近法进行复合材料层合板仿真及三维场重构

为有效模拟和准确重构复合材料层合板三维应力/应变/变形场,基于变分渐近方法构建单斜对称的复合材料层合板渐近修正理论和重构关系。主要内容包括:基于旋转张量分解概念用一维广义应变和翘曲表示板的三维应变场,以考虑包括板翘曲变形在内的所有变形;基于变分渐近法将原三维问题分析严格拆分为非线性二维板分析(等效单层板模型)和沿法线方向的一维线性分析;通过层合板厚跨比和二维应变量阶数2个较小参数将应变能渐近修正到第二阶,并转换为Reissner形式以便于实际应用;利用生成的二维板变形和翘曲函数精确重构三维场。通过一具有20层复合层合板的柱形弯曲算例表明:基于该理论和重构过程开发的渐近变分程序VAPAS重构生成的三维应力场精确性较一阶剪切变形理论和古典层合理论更好,与三维有限元精确解相一致。     

A global-local higher order theory for multilayered shells and the analysis of laminated cylindrical shell panels

Based on the global-local superposition technique proposed by Li and Liu [Li XY, Liu D. Generalized laminate theories based on double superposition hypothesis. Int J Numer Meth Eng 1997;40:1197–212.], a global-local higher order laminated shell model is proposed for predicting both displacement and stress distributions through the thickness of laminated shells. This shell model satisfies transverse shear stress continuity conditions at interfaces as well as free surface conditions of transverse shear stresses. The merit of this model is that transverse shear stresses can be accurately predicted directly from constitutive equations without smoothing techniques. Cylindrical bending of laminated and sandwich shell panels is chosen to assess the present model wherein the results from several 2D laminated shell models and three-dimensional elasticity solution are available for comparison. In addition, thermal bending and thermal expansion of laminated cylindrical shell panels are also considered in this paper.     

Flexural analysis of cross-ply laminated plates subjected to nonlinear thermal and mechanical loadings

The objective of this paper is to present an equivalent single-layer shear deformation theory for evaluation of displacements and stresses of cross-ply laminated plates subjected to uniformly distributed nonlinear thermo-mechanical load. A trigonometric shear deformation theory is used. The in-plane displacement field uses a sinusoidal function in terms of the thickness coordinate to include the shear deformation effect. The theory satisfies the shear stress free boundary conditions on the top and bottom surfaces of the plate. The present theory obviates the need of a shear correction factor. Governing equations and boundary conditions of the theory are obtained using the principle of virtual work. Stresses and displacements for orthotropic, two-layer antisymmetric, and three-layer symmetric square cross-ply laminated plates subjected to uniformly distributed nonlinear thermo-mechanical load are obtained. Numerical results of the present theory for displacement and thermal stresses are compared with those of classical, first-order and higher-order shear deformation plate theories.     

考虑剪力滞效应的层合箱梁矩阵分析方法

给出了考虑剪力滞后及剪切变形效应条件下,复合材料薄壁层合箱梁静力行为控制微分方程组的初参数解。以此为基础,推导出了层合箱梁单元的刚度矩阵和等效结点荷载列阵,从而使薄壁层合箱梁的剪力滞、剪切变形效应分析方便地纳入了工程中广泛应用的矩阵位移法程序系统,为复合材料连续层合箱梁等复杂结构的强度及刚度分析提供了有效的计算手段。