盾构隧道衬砌结构应力与变形的三维数值模拟与模型试验研究

结合广州地铁三号线盾构隧道工程实例,提出钢筋混凝土衬砌结构三维非线性有限元计算模型,应用非线性有限元程序ANSYS分析了上部和周围土体荷载作用下衬砌的应力场与变形情况。结构计算模型采用三维实体单元,考虑了衬砌与周围土体的共同作用、土体和钢筋混凝土材料的非线性性质,通过模型刚度折减考虑了管片接头的不连续性对衬砌应力和变形性质的影响。为验证数值分析结果,进行了衬砌结构的相似模型试验。给出了衬砌结构的应力场、应变场、结构整体位移以及裂纹的分布图。     

以非电量电测原理与技术测试汽车油箱总成油管在不同温度下的应变分布规律

研究汽车油箱总成中的油管在不同温度场下应变、应力变化规律,为汽车油箱总成中油管新材料的研究,为提高产品质量提供科学依据。在汽车油箱总成中的油管上粘贴电阻应变片,以应变电测法测量油管上各测点的应变值。得出了油管在20℃-60℃、-30℃-20℃范围内各个测点的应力值。得出了一些结论,对实验结果进行分析讨论。     

搭接区端部细观结构对受拉复合材料单搭接头力学响应的影响

在复合材料单搭接头的加工过程中,在搭接区端部会形成一些细观结构,从而在这些区域常存在比较严重的应力集中。应用实验和有限元方法研究了胶瘤和复合材料端部毛刺这2 种搭接区端部细观结构对受拉复合材料层合板单搭接头力学响应的影响。应用数字图像相关方法测量了搭接区端部的应变场分布情况,同时利用基于子模型技术的非线性有限元方法分析了搭接区端部细观结构的作用。实验结果与有限元分析结果吻合较好。实验和有限元结果都表明胶瘤分担了部分载荷,可以降低搭接区端部的应力集中。复合材料端部毛刺的作用与毛刺的具体结构关系密切,不同结构的毛刺对搭接区端部应力应变分布的影响是不同的。     

无应力奇异性条件下的界面应力集中问题研究

应用有限元分析技术,对无应力奇异性条件下的双材料粘接接头的应力集中问题进行了数值研究。首先,根据特征方程分析求解出消除接头界面端和界面角奇异应力场的材料组合和几何条件;据此提出了几种无应力奇异性影响并且为宏观等截面的双材料粘接接头几何模型。然后在轴对称假设条件下,对上述模型理想粘接界面上的应力分布进行了分析,着重讨论了材料组合和界面几何形状对这些应力大小的影响。结果表明:由于材料性能错配,界面上的应力集中现象不可避免,其大小依赖于材料组合和界面几何形状。这些分析结果对于指导界面几何形状优化设计,最终提高界面强度具有一定的参考价值。     

风力发电机弹性支承有限元分析

橡胶材料的非线性力学特性直接影响到风力发电机弹性支承的减振性能。通过橡胶拉伸和压缩实验获得应力-应变数据,借助有限元软件对数据进行拟合,得到橡胶材料恰当的本构模型。依据弹性支承的实际使用工况,选用合理的橡胶材料模型参数,采用整体、四分之一截面和轴对称的三种模型进行计算结果的对比分析。并针对用四分之一模型分析风力发电机弹性支承的非线性垂向、横向刚度和固有频率等特性,通过试验;验证了有限元模型和计算方法的有效性。     

基于非线性有限元法的印刷纸力学特性研究

利用流变学的基本理论,对印刷纸压缩流变特性进行理论分析和实验研究,表明印刷纸应力应变呈现出非线性关系,是典型的材料非线性问题.应用薄板非线性理论,对印刷纸粘弹性力学行为进行数值模拟研究,得出增量平衡方程.运用分析软件ANSYS建立有限元模型,得出应力应变关系曲线.有限元分析结果与理论分析和实验结果相一致,验证了模型的有效性.     

工字形截面悬臂钢梁的稳定性研究

在钢梁的稳定问题上近年来存在着两种不同的理论,对这两种理论应用于悬臂梁的情况进行了比较。应用非线性力学对稳定问题的变分原理,提出了考虑钢梁内各种应力的非线性应变能的新的总势能公式。对纯弯下单轴对称工字形截面的钢梁进行了研究,将以往两种理论及本文提出的理论在这个问题上存在的问题进行了讨论。对单轴对称截面悬臂梁作用于端部集中荷载的情况,从两种不同的总势能出发,编制了有限元程序,结果与文献的试验结果进行了比较。还提出了受横向荷载的双轴对称截面梁的新的临界弯矩计算公式,与文献公式和有限元结果进行了比较,结果说明本文的公式更精确,在形式上更加简单。     

超磁致伸缩驱动器磁滞非线性数值模拟研究

针对超磁致伸缩驱动器(giant magnetostrictive actuator,GMA)具有磁滞非线性现象,以经典Jiles-Atherton模型为基础,建立了包含偏置磁场强度和预压应力的GMA磁滞非线性模型,进行了数值仿真分析,得到了偏置磁场强度和预压应力对GMA磁化强度曲线和磁致伸缩应变曲线的影响规律。结果表明,偏置磁场强度对磁化强度曲线和磁致伸缩应变曲线的形状影响较大,调整偏置磁场强度的大小,可改变磁化强度曲线的线性区间,并能抑制或消除磁致伸缩应变曲线的倍频效应;预压应力对磁化强度曲线和磁致伸缩应变曲线的形状影响较小,施加不同的预压应力,可改变磁化强度曲线和磁致伸缩应变曲线的变化率。这与现有试验得到的结论相吻合,验证了所建磁滞非线性模型的合理性。     

镍基合金材料塑性对应力腐蚀裂纹尖端应力应变场影响的研究

为了解材料塑性对高温水环境下核电关键结构材料应力腐蚀裂纹扩展的影响,利用大型非线性有限元软件,对镍基合金中由氧化膜和基体金属构成的应力腐蚀裂纹尖端应力应变场进行了分析,得出了材料屈服应力对应力腐蚀裂纹尖端应力应变场的影响规律.结果表明:在同样的外载条件下,随着材料屈服应力的增大,裂尖基体金属的应力增大而塑性应变减小;而...     

2219铝合金焊接接头软化模型的建立与应用

通过2219铝合金TIG焊接接头不同区域的微区拉伸试验以及母材在热循环过程中不同温度下的拉伸试验,获得了相应的屈服强度和抗拉强度,建立了基于温度、温度历史及应变强化效应的接头软化模型。将此软化模型应用到TIG焊接接头残余应力的有限元模拟中,并将应力模拟值与X射线衍射应力实测值进行对比。结果表明,与常规模型相比,软化模型中的残余应力分布水平出现了不同程度的降低,此外,残余应力在焊缝附近区域、起弧端与收弧端区域及横向分布上下降幅度较为明显。与实测值相比,应用接头软化模型计算得到的焊接残余应力分布与之更为接近,提高了残余应力的计算精度,验证了接头软化模型的有效性。     

基于失效评定图(FAD)研究含疲劳裂纹T型圆钢管节点的安全性

失效评定曲线(FAD)常用来评价焊接结构在出现裂纹后的安全性,为了验证这种曲线在评价焊接管结构在节点部位出现疲劳裂纹后安全性的适用性,采用实验测试和有限元分析的方法研究了3个含疲劳裂纹的T型管节点试件在静力作用下的极限承载能力及破坏过程。3个T型管节点试件首先进行疲劳实验在焊趾处产生表面裂纹,然后通过在支管端部施加轴向拉力作用检测节点的破坏过程。基于自行开发的含表面裂纹T型管节点的有限元网格自动产生程序以及ABAQUS分析软件,研究了在管节点破坏过程中表面裂纹最深点的应力强度因子大小,并通过实验的荷载-位移曲线确定了T节点试件的塑性极限承载力。在这些结果的基础上,验证了FAD在评价含疲劳裂纹的焊接管节点安全性方面的适用性。研究结果标明:FAD在评价含疲劳裂纹管节点的安全性方面是安全可靠的,但偏于保守。     

KK节点中表面裂纹应力强度因子的数值分析

海洋平台中的管节点在出现疲劳裂纹后,其残余寿命的估算依赖于对焊缝处表面裂纹应力强度因子的精确计算。首先介绍了包含表面裂纹的KK节点的有限元网格产生方法。采用了五种不同类型的单元,即六面体单元、四分之一结点的裂纹单元、棱柱单元、棱锥单元以及四面体单元来形成KK节点焊缝处表面裂纹的网格。然后通过交互J积分法计算出了KK节点表面裂纹的应力强度因子分布情况。     

管节点承载力的非线性有限元分析

本文提出了运用四边形等参壳元构造管节点有限元模型,用自动步长增量法来计算管节点的极限承载力：在ＡＤＩＮＡ程序的基础上开发了前处理和后处理程序,使管节点（包括空间管节点）的有限元分析的成本大大降低;平面管节点的算例表明本文方法与实验结果相吻合,在此基础上本文提出并计算了圆管与矩形管管节点。     

Fatigue crack growth analyses of offshore structural tubular joints

This study investigated various aspects of a fatigue crack growth analysis, ranging from the stress intensity factor solutions to the simulation of a fatigue crack coalescence process of a tubular joint weld toe surface flaw. Fracture mechanics fatigue crack growth analyses for offshore structural tubular joints are not simple, because of the difficulty to calculate the stress intensity factors due to their geometric complexity. The fully mixed-mode stress intensity factors of nine weld toe surface cracks of an X-shaped tubular joint under tension loading were calculated by detailed three-dimensional finite element analyses. Using these stress intensity factor solutions, a fatigue crack growth study was performed for the X-joint until (the crack surface length grew to two times the tube thickness. Through this study, the crack shape change during the fatigue crack propagation was investigated in detail. Fatigue life calculations were also performed for a range of crack geometries using the stress intensity factor solutions of the nine flaws. These calculations indicate that the natural fatigue crack growing path for a crack is its quickest growing path. The study demonstrated that detailed fracture mechanics fatigue analyses of tubular joints can be practical using the finite element method.     

An investigation on strain/stress distribution around the overlap end of laminated composite single-lap joints

The damages of laminated composite single-lap joints often begin from their overlap ends because strain/stress concentrations often occur at the overlap ends. This paper presents the results of a combined experimental and finite element (FE) investigation on the strain/stress distributions around the overlap ends of laminated composite single-lap joints. Digital image correlation (DIC) technique is used to measure the strain fields near the overlap ends. A three-dimensional geometrically nonlinear FE model based on the submodel technique is developed to predict the deformation of single-lap joints. A reasonable agreement is achieved between the results from experimental measurements and FE analysis. Additionally, some FE models are built to investigate the effects of the mesostructures at the overlap ends on the stress concentrations around the overlap ends.     

AN IMPROVED PROCEDURE FOR THE DETERMINATION OF HOT SPOT STRESSES IN TUBULAR JOINTS

Abstract— A conventional finite element method may show a weakness when determining the hot spot stress distributions in the brace/chord intersection region of offshore tubular joints. This is because the chosen element displacement functions do not implicitly satisfy the conditions which prevail on the free surfaces. A procedure has been proposed to modify the conventional finite element method so as to allow the hot spot stresses, which occur at the free boundary of the weld toe of tubular joints, to be determined with improved accuracy. The results obtained by this modified method are compared with both an experimental and a traditional finite element solution. The comparison shows that the modified solution is in better agreement with the experimental data as compared with the traditional solution.     

Nonlinear analysis of adhesively bonded tubular single-lap joints for composites in torsion

The nonlinear analysis of tubular single-lap adhesive joints with composite adherends was performed by incorporating the nonlinear behavior of the adhesive into the analysis. For this purpose, the stress and strain in the laminated composite tube were first calculated under a general loading scheme, and then the iterative solution of the joints was derived by including the nonlinear properties of the adhesive. The stress distributions in the adhesive were investigated for different types of composite adherends and compared with the results of the linear analysis. The effect of the bonding length on torque transmission capability was also taken into consideration. The results indicate that the nonlinear analysis relieves the stress concentration at the edge of the joint, resulting in a more accurate prediction of joint strength.     

管道修复用管状纺织复合材料的力学性能分析

管状纺织复合材料作内衬管修复受损管道,是通过气压或水压翻转衬于管道中的,在翻衬过程中,由于翻衬压强的作用,管状纺织复合材料要承受复杂的应力与应变。本文中通过有限元方法对管状纺织复合材料翻衬时的应力和应变情况进行了分析,而且有限元模拟值分别与理论值和试验值进行了比较。结果表明：管状纺织复合材料在翻转时,翻转的头端,应力和应变不稳定,有应力集中的情况,因此在翻转头端最容易发生管状纺织复合材料的破裂;在管状纺织复合材料几何参数与组分材料一定的情况下,可通过有限元方法,给出不同翻衬压强值下其可修复管道的管径范围。     

Prediction of stress distribution along the intersection of tubular T-joints by a novel structural stress approach

The Zero Point Structural Stress (ZPSS) approach is improved to calculate the structural stress for the fatigue life assessment of tubular joints. In the ZPSS approach, the stress distribution perpendicular to the stress classification line (SCL) can be obtained directly by post-processing the finite element (FE) results. The applicability and accuracy of the approach is verified by comparing the FE results with fatigue experimental test data. High fit degree parametric equations for stress concentration factor calculation are derived based on the ZPSS approach for stress analysis of tubular T-joints in engineering.     

Numerical and experimental study of ratcheting in cold expanded plate of Al‐alloy 2024‐T3 in double shear lap joints

In this paper strain ratcheting in cold expanded flat plate of Al‐alloy 2024‐T3 in double shear lap joints was studied both experimentally and numerically. In the experimental part, two types of symmetric strain‐controlled and asymmetric stress‐controlled cyclic tests were performed. Also, the cold expanded double shear lap joints subjected to cyclic stress‐controlled tests. The required parameters for simulating the cyclic plastic behaviour of Al‐alloy 2024‐T3 were obtained on the basis of the experimental responses. In the numerical part, a combination of nonlinear isotropic and nonlinear kinematic hardening model (Chaboche) was implemented in the commercial finite element code of ABAQUS, using the subroutine UMAT written in FORTRAN. The results of simulations give an accurate prediction of ratcheting for all types of loading. The obtained results show that increasing the mean stress increases the strain ratcheting. It is clearly shown that the cold expansion process decreases the magnitude of strain ratcheting remarkably compared with “as drilled” specimens and the decrease is bigger for larger cold expansion sizes. Also, it is shown that the middle plane has the highest amount of ratcheting compared to the pin entrance plane and exit plane of the plate hole.