焊接箱形截面不锈钢柱相关稳定性能分析

采用有限元法对焊接箱形截面不锈钢柱的局部与整体相关稳定性能进行分析,研究利用板件的屈曲后强度,以实现更为经济合理的构件截面设计。建立了可以准确模拟不锈钢非线性材料力学性能、截面焊接残余应力和构件的局部与整体几何初始缺陷等因素的精确有限元数值模型,并依据试验结果对模型的可靠性进行了验证。基于验证可靠的有限元模型,开展了系统参数分析,同时补充了大量的数值计算数据点。根据得到的试验和有限计算结果,对相关稳定承载力的理论计算方法进行了比较分析,表明现有的方法应用较为复杂,而且可能高估构件的相关稳定承载力。针对奥氏体型和双相型两类不锈钢提出了通用的计算修正系数,给出了新的直接强度法计算公式,经试验与有限元计算结果验证,表明其能够准确计算焊接箱形截面不锈钢柱的相关稳定承载力。     

RTM整体成型复合材料翼盒的固有模态及稳定性

采用基于水溶性型芯的RTM成型技术制备了整体化的复合材料翼盒, 并对翼盒进行了自由振动模态试验; 采用三维壳单元, 建立了翼盒固有模态及稳定性有限元分析模型, 该模型分析的翼盒固有模态与试验结果吻合很好, 验证了有限元模型的有效性; 为研究翼盒固有模态及稳定性的铺层效应, 采用该模型分析计算了4种铺层方案的翼盒的固有模态及稳定性。研究结果表明: 对称铺层蒙皮有利于提高翼盒轴向压缩与轴向扭转屈曲载荷及固有频率, 而不利于面外弯曲和弯扭组合情况; 腹板减薄和增加腹板45°铺层均不利于提高, 甚至会大幅度降低屈曲载荷及固有频率, 弯扭组合加载最容易导致失稳。     

Finite element buckling analysis of rotationally periodic laminated composite shells

A finite element (FE) buckling analysis of rotationally periodic laminated composite shells is performed in this paper. Because the buckling mode of such structures is characterized as rotationally periodic, a corresponding FE buckling analysis scheme is proposed to reduce the computational expenses. Moreover, a new kind of relative degrees‐of‐freedom element is developed, which can be connected to other solid elements with ease and can yield satisfactory results with a relatively coarse FE mesh. Numerical results of two laminated cylindrical shells subjected to lateral pressure are compared with theoretical ones. The good agreement of them shows the validity of this new computational strategy. Finally, a practical structure is analysed to demonstrate the advantage of this method. Copyright © 2001 John Wiley & Sons, Ltd.     

Experimental Investigations of Compressed Sandwich Composite/Honeycomb Cylindrical Shells

This article explains in some details the behaviour of thick, deep cylindrical sandwich panels subjected to compressive loads. In general, experimental results indicated that two different forms of failure have been observed – the first corresponds to the overall buckling and the second to the facesheet wrinkling. The obtained experimentally damages of shells are verified and validated with the use of the FE analysis, 2-D and 3-D both in the linear and non-linear approach. The unidirectional strain gauges were applied to detect the initiation of the overall buckling mode.     

单轴对称楔形工字钢梁的平面外稳定

该文推导了楔形变截面梁弯扭屈曲的非线性应变能,并依据得到的总应变能进行有限元分析公式的推导。对楔形悬臂梁,中间截面最大的楔形变截面简支梁承受集中荷载和均布荷载的情况进行了分析,与ANSYS基于板壳理论的有限元分析结果进行对比,验证了该文理论的正确性和精度。最后依据该文理论分析了两端简支的楔形工字钢梁受不等端弯矩作用下的临界弯矩,拟合了高精度的临界弯矩计算公式,该公式形式与等截面梁的相同,物理意义明确,便于工程应用。     

Finite element models for brush-debris interaction in road sweeping

In this paper, 2-D and 3-D finite element (FE) models for particle removal mechanisms are constructed to study the interaction between brush tines and debris in road sweeping processes. A 2-D contact FE analysis is first performed to analyse the contact behaviour between a flicking brush tine and an object to sweep. Using this model, the removal mechanisms are studied and analysed. Furthermore, the effect of brush penetration on debris removal is investigated. The 2-D sweeping model is extended to an accurate 3-D contact model, which overcomes some geometric errors in the 2-D model. From the results, it is suggested that the major removal mechanisms are a horizontal dragging force and a rolling moment generated by the external forces. It is also found that penetration has a positive contribution when it is relatively small in a non-sticky environment. Furthermore, in this environment, it is found that sweeping loads have a small effect on the removal process as either flicking tines or cutting tines can produce adequate removal loads.     

Modeling buckling distortion of DP600 overlap joints due to gas metal arc welding and the influence of the mesh density

This paper presents a computational framework for the modeling of buckling distortion of 1 mm thick DP600 overlap joints due to gas metal arc welding. The results have been compared to experiments and show good agreement. The simulations have been repeated for various FE meshes and different linear finite elements. It is shown that not only the distortion amplitude but also the buckling mode is mesh-dependent. In order to explain this behavior, an eigenmode calculation of the first two modes is undertaken as a basis for comparison and shows that the geometrical stiffness of the finite elements has an influence which is also dependent on the expected buckling mode. It is shown that for an adequate model of the expected distortion, a fine resolution is required everywhere where bending is to be expected. Dependent on the buckling mode, this could hold for the whole structure. However, it is also shown how the computation time can be reduced significantly for a controlled loss in accuracy by optimizing the FE mesh.     

Delamination buckling and postbuckling in composite cylindrical shells under combined axial compression and external pressure

A series of finite element analyses on the delaminated composite cylindrical shells subject to combined axial compression and pressure are carried out varying the delamination thickness and length, material properties and stacking sequence. Based on the FE results, the characteristics of the buckling and postbuckling behaviour of delaminated composite cylindrical shells are investigated. The combined double-layer and single-layer of shell elements are employed which in comparison with the three-dimensional finite elements requires less computing time and space for the same level of accuracy. The effect of contact in the buckling mode has been considered, by employing contact elements between the delaminated layers. The interactive buckling curves and postbuckling response of delaminated cylindrical shells have been obtained. In the analysis of post-buckled delaminations, a study using the virtual crack closure technique has been performed to find the distribution of the local strain energy release rate along the delamination front. The results are compared with the previous results obtained by the author on the buckling and postbuckling of delaminated composite cylindrical shells under the axial compression and external pressure, applied individually.     

Mechanical property evaluation of single-walled carbon nanotubes by finite element modeling

Computational simulation for predicting mechanical properties of carbon nanotubes (CNTs) has been adopted as a powerful tool relative to the experimental difficulty. Based on molecular mechanics, an improved 3D finite element (FE) model for armchair, zigzag and chiral single-walled carbon nanotubes (SWNTs) has been developed. The bending stiffness of the graphene layer has been considered. The potentials associated with the atomic interactions within a SWNT were evaluated by the strain energies of beam elements which serve as structural substitutions of covalent bonds. The out-of-plane deformation of the bonds was distinguished from the in-plane deformation by considering an elliptical cross-section for the beam elements. The elastic stiffness of graphene has been studied and the rolling energy per atom has been calculated through the analysis of rolling a graphene sheet into a SWNT to validate the proposed FE model. The effects of diameters and helicity on Young’s modulus and the shear modulus of SWNTs were investigated. The simulation results from this work are comparable to both experimental tests and theoretical studies from the literatures.     

A Case Study on Mud-Weight Design with Finite-Element Method for Subsalt Wells

This paper presents a case study for the design of a mud-weight window (MWW) with three-dimensional (3-D), finite-element (FE) tools for subsalt wells. The trajectory of the target well penetrates a 7 km thick salt body. A numerical scheme has been proposed for calculating the shear failure gradient (SFG) and fracture gradient (FG) with 3-D FE software. User subroutines have been developed to address non-uniform pore-pressure distribution. A series of FE calculations were performed to obtain the MWW of the target wellbore, which consists of the SFG and FG for the subsalt sections. Although no reverse faulting structure exists in the region at the salt base, the stress distribution at some region of the salt base has characteristics of a reverse fault. Additional analyses of the results show that this type of reverse-faulting stress pattern exists only in a small range of depth and width under the salt body. The stress pattern appears to be normal outside of that region. Consequently, a 3-D solution of the MWW along the trajectory has abnormal values at a certain salt base section, which can be 10% greater than the value predicted by 1-D software.     

Limit Load of Soil-Root Composites

This paper studies the influence of root reinforcement on shallow soil protection by using Finite Element (FE) method. Taking the root-soil composite as a periodic material, the homogenization method is used to construct a Representative Volume Element (RVE) that consists of roots and soil. This RVE is discretized by a two-dimensional (2-D) FE mesh, while special formulation is established so that this model is capable of describing three-dimensional (3-D) deformations when the strain is invariant along the fiber axis. The important effect of debonding on the interface between the fiber and the matrix is also considered by using a special interface element. To verify the validity of the proposed computational model, triaxial tests were conducted, where the root-soil composite was subjected to axial and lateral pressures. Good agreement of limit loads has been achieved between the numerical and the experimental results.     

三跨斜交T梁动力特性分析

以107国道深圳元朗斜交桥为背景,首先对全桥进行环境振动测试,利用频域中的峰值法（PP）和时域中的随机子空间识别法（SSI）识别出三跨斜交T梁桥的频率、振型和阻尼比;利用ANSYS软件建立了全桥三维有限元模型,进行理论模态分析并和实测结果进行比较,并进一步分析了不同斜交角时动力特性的差异,探讨了此类斜交桥的动力特性。     

Closed-form plastic collapse loads of pipe bends under combined pressure and in-plane bending

Based on three-dimensional (3-D) FE limit analyses, this paper provides plastic limit, collapse and instability load solutions for pipe bends under combined pressure and in-plane bending. The plastic limit loads are determined from FE limit analyses based on elastic-perfectly-plastic materials using the small geometry change option, and the FE limit analyses using the large geometry change option provide plastic collapse loads (using the twice-elastic-slope method) and instability loads. For the bending mode, both closing bending and opening bending are considered, and a wide range of parameters related to the bend geometry is considered. Based on the FE results, closed-form approximations of plastic limit and collapse load solutions for pipe bends under combined pressure and bending are proposed.     

步长自适应技术在棒线材热连轧过程模拟中的应用

利用数值仿真技术建立平-立轧制三维热力耦合有限元模型,对304不锈钢棒线材热连轧过程粗轧6道次实际工况进行仿真计算.基于刚性体推动模型,采用步长自适应技术根据模型的运算需要选择适合的时间步长.步长自适应技术能够在轧件轧制过程时采用较小的时间步长,在道次间隙时使用较大的时间步长.计算结果表明,采用步长自适应技术所建立的有限元模型可以在保证计算结果精度的前提下,显著地提高运算效率.     

复合材料层合板屈曲稳定性优化设计及其灵敏度计算方法

笔者在有限元分析基础上研究了以屈曲稳定性作为约束条件或优化目标的复合材料层合板结构优化设计及其灵敏度分析方法,重点讨论了屈曲临界荷载灵敏度对内力场和载荷的依赖关系及其在铺层优化、尺寸优化和形状优化问题中的不同计算方法,并在JIFEX软件中实现了复杂结构复合材料层合板优化设计方法。数值算例验证了本文算法和程序的有效性。     

On internal stability problems in structured materials

Summary Internal instability of structured materials and elements is occasionally observed and has been verified by experiments. The specific problems in this contribution treated analytically and numerically consist of internal instability phenomena of prestressed elastic materials and the so-called membrane buckling of thin elastic plates and shells. A stability theory taking into consideration independent local rotations is outlined; this theory is then used to treat the membrane buckling of cylindrical shells and the in-plane buckling of rectangular plates. It is shown that under certain circumstances, the in-plane buckling mode may precede the out-of-plane buckling deformation. To simulate the internal stability phenomena numerically, a number of discrete models of structured materials are considered; based on these models numerical Finite Element (FE) buckling analyses are carried out, including linear analyses for the membrane buckling of a circular cylindrical shell model and the in-plane buckling analysis of a flat plate. The FE simulations effectively afford buckling loads and buckling modes.     

Buckling behavior of carbon nanotube-based intramolecular junctions under compression: Molecular dynamics simulation and finite element analysis

Intramolecular junctions (IMJs) formed by connecting two arbitrary carbon nanotubes (CNTs) can act as functional building blocks in circuits and components of CNT-based electronics devices. While extensive studies have been conducted on the atomic structural as well as electrical properties of IMJs and great advances have been achieved, mechanical response of IMJs under large deformation, which may exert significant effects on their electrical properties, are still not fully explored. In this paper, both molecular dynamics (MD) simulation and finite element (FE) analysis are employed to investigate the buckling behavior of IMJs under axial compression. The strain rate effects are firstly studied in the MD simulations. It is found that the critical compressive strain is not sensitive to the strain rate of relatively low range, but it exhibits a strong dependency upon the strain rate under high speed compression. In particular, a different failure mode may occur under ultra-high loading velocities. Based on the discussion on the strain rate effects, a reasonable loading velocity is suggested to be adopted in the subsequent MD simulations. In this study, the results of both the MD simulations and the FE analyses indicate that the critical compressive strain is dependent upon the length, radial dimensions of the IMJ but insensitive to the chirality of the IMJ. The comparison between the results of the MD simulations and the FE analyses also confirms that the FE analysis is able to provide useful insights into the compressive behavior of CNT-based IMJs with a much less computational cost.     

基于弯曲刚度最大分层临界载荷的层压板局部屈曲预测

提出了一种预测含特定分层损伤层压板发生局部屈曲时整体应变的方法。认为含分层子板的局部屈曲载荷由其弯曲刚度最大的分层决定, 因而含有相同最大弯曲刚度分层的不同子板具有相同的屈曲载荷。在已知弯曲刚度最大分层的屈曲载荷的情况下, 根据层压板的轴向刚度公式, 计算出发生局部屈曲时弯曲刚度最大的分层与完好的基板分别承受的载荷, 即得到总载荷, 进而得到层压板的整体应变。用ABAQUS有限元分析软件建立含分层损伤的层压板模型, 使用准静态加载进行了多种分层深度和分层位置下的局部屈曲仿真, 所得局部屈曲载荷符合上述推论。用所提方法预测发生局部屈曲时的整体应变, 结果与有限元结果吻合较好, 此方法可用于建立分层参数识别的参照样本库。     

复杂型面测量中测头中心的轨迹曲面及测头半径的三维补偿

根据球形测头的中心轨迹与被测曲面互为等距曲面的关系，采用双三次Ｂ样条曲面建立了描述测头中心轨迹的数学模型，并提出了一种新的三维测头半径补偿方法。     

Piston seizure investigation: Experiments,modeling and future challenges

The complex problem of seizure failure of piston has been investigated experimentally with numerical simulation of thermal elasto-hydrodynamic lubrication (EHL). Metallurgical investigations in terms of chemical composition, chemical analysis and hardness were carried out for piston, rings and liner. In the thermal EHL model, an attempt has been made to include the complete physics of the problem. Boundary conditions in the piston secondary motion model were imported from finite element (FE) model (thermo-mechanical deformation of piston and liner) and engine conjugate heat transfer simulations using computational fluid dynamics (CFD). The FE and CFD model were validated experimentally. The predicted wear marks on piston and liner from the analysis compares well with the test results. Results suggest that high operating temperatures and significant reduction in thin film lubrication clearances accelerate the seizure failures. Further tests were conducted with coated piston to mitigate the high temperature effects. Future directions and challenges in terms modeling such complicated physics have been discussed. The authors believe that there exists a theoretical gap in modeling the seizure physics and hence, advanced theories should be developed to enhance the understanding of this complex seizure mechanism.