K型管状接头随机疲劳强度和裂纹扩展规律的研究

分析了K型焊接管状接头受轴向和面外弯曲载荷作用下的随机疲劳问题。通过将焊趾处的表面裂纹的初始尺寸和材料常数作为随机变量处理,并计及焊缝的影响,共产生500个随机样本,最终得到裂纹扩展寿命和裂纹形状变化影响的统计计算结果,并与有关实验数据比较,给予了回归分析。同时,也考察了裂纹扩展规律。     

适时搭梯 整体架构 激活思维——以“折黄金矩形”教学设计为例

本文以“折黄金矩形”为例,探索如何在折纸活动中“适时搭梯,整体架构,激活思维”,达到有效的教学效果.黄金分割被认为是建筑和艺术中最理想的比例,“黄金矩形”是由黄金分割引出的基本图形,而通过折纸的方式得到黄金矩形,继而以“再生”为性质,将从另一个崭新的角度加深学生对于黄金分割的再认识.     

轴向应力波与弹塑性材料圆柱壳的动力屈曲

将弹塑性圆柱壳动力屈曲作为由于轴向应力波的传播而导致的分叉问题进行研究,找出该壳发生屈曲的机理,并讨论对各种支承的弹性和弹塑性壳在轴向阶梯载荷和脉冲载荷冲击下的屈曲问题.     

含温度载荷的管板变形的解析解

根据换热器结构形式建立了用于计算管板变形的力学模型,参考ASMEⅧ-1计算管板的有效弹性常数,并将外筒和换热管束分别等效为会因温度和压力载荷产生轴向变形的弹簧和弹性基础.应用Ritz法建立了管板挠度的解析解,将该解析解与三个不同规模换热器的有限元分析结果进行对比.结果表明,建立的解析解与有限元分析结果吻合良好,验证了推...     

初封载荷下封隔器胶筒表面自由变形特性分析

研究了封隔器胶筒在自由变形阶段受初封载荷作用下内、外表面发生位移变形的特性.依据连续介质力学理论，建立自由变形阶段的有限变形数学模型，给出了胶筒在初封轴向载荷下内、外表面径向变形的过程，得到胶筒非线性变形解析解.通过数值计算，在求解出胶筒外表面自由变形解析式的基础上，进一步分析了容易被忽略的胶筒内表面非线性变形规律和相关参数变化对其密封性能的影响.该变形特性分析可适用于不同型号的封隔器胶筒，为胶筒的密封和可靠性设计提供重要理论依据.     

利用折纸来改善数学教学——从芳贺第一定理谈起

1 .前言提起折纸 ,我们往往会想到用一张四方的纸来折自然界的各种动植物或现实世界中人类的各种创造物等 ,在手工课上 ,学生如果拿到一张纸 ,没有老师的指示 ,他们也会情不自禁地折出一些作品来 ,但利用折纸来改善数学教育 ,对许多中小学数学教师来说可能是一件新鲜事 .在我国 ,折纸中的数学问题作为课题学习或研究性学习的材料 ,已引起部分数学教师及数学教育研究人员的关注 ,部分数学教育工作者在自己的教育科研实践中作了一些尝试 .但这些活动大多以折正多边形及立体为主 ,即主要关注怎样折各种几何图形 ,而对折痕线或折纸过程中所得平…     

矩形折纸中的风采探究

近几年来,折纸成为中考的热点,难点,它不但考查学生灵活运用数学知识的能力,而且也考查了学生看图、识图、动手操作能力.解决这类问题的关键是:把握折纸实质上是以折痕为对称轴的轴对称,充分利用翻折前后的两个图形全等,问题就容易解决了.下面谈谈矩形折纸中的数学问题. 一、折叠出正方形 矩形最基本的折纸,就是用一张长方形纸片折一个正方形. 如图1,可以折出正方形, 二、折叠出菱形 例1已知:如图2所示的一张矩形纸片ABCD(AD＞AB),将纸片折叠一次,使点A与点C重合,再展开,折痕EF交AD边于点E,交BC边于点F,分别连接AF和CE.     

基于压电阻抗技术的金属材料弹性变形检测研究

基于压电阻抗技术的结构健康监测原理,对低碳钢圆棒试样单轴拉伸弹性变形过程中安装在其上的压电材料的阻抗信息进行了分析,探究采用压电阻抗谱中峰值频率变化表征金属材料弹性变形(也即材料应力)状态的方法的可行性.将压电材料片作为主动传感器,粘贴在圆棒的端部圆截面(受压变形区)和杆中部(拉伸变形区)两种位置,分别测取园棒试样不同拉伸伸长情况下的阻抗信号.分析试验结果发现:随着弹性伸长变形量的增加,端部压电导纳(阻抗的倒数)谱中对应峰值频率减小,而杆中部压电导纳谱中对应峰值频率增加,两个部位的压电导纳频率变化接近线性规律.由此可得出结论:可以利用压电阻抗(导纳)技术,通过测量部位的压电导纳谱信息,以频率为特征参数对结构件的应力状态进行监测;通过端面压电材料输出导纳谱信息中频率改变量,可实现对轴杆类构件轴向应力状态进行监测,这个方法特别适合于埋入式螺栓,混凝土中预应力钢筋等轴向力的监测.     

轴向拉伸细长杆的非线性力学模型

聚酯系泊缆是深海工程中具备一定抗弯刚度、易拉伸变形的细长杆件结构.聚酯缆的轴向变形属大拉伸范畴,分析中应当区分变形前后状态,特别是缆索长度的改变使得基于小拉伸假设的细长杆模型需要予以改进.因此,基于Garrett细长杆模型,应用总体坐标和斜率取代Euler-Bernoulli(欧拉 伯努利)梁元的转角,解决缆索在空间中大转动变形的几何非线性问题;使用轴向拉伸变形前后物质点对应的方法,借助单元两个节点和一个中点,以及3个二次多项式形函数描述轴向拉伸变形下细长杆元的运动微分方程.通过与轴向拉伸悬臂梁的对比分析,验证了该拉伸杆元的收敛性和准确性.     

重力载荷作用下柔性梁的结构变形与承载力分析

柔性体在承受外载荷作用时,会通过自身变形,降低所承受的外载荷.为了研究重力载荷作用下柔性梁的结构变形与承载力之间的定量关系,首先建立模拟实验分析重力载荷在梁上的分布形式;基于Timoshenko梁的大变形本构方程,建立承受重力载荷作用下大变形梁的控制方程;通过量纲分析,确定研究两个无量纲变量,结构变形数与Cauchy数...     

Effect of fiber orientation and cross section of composite tubes on their energy absorption ability in axial dynamic loading

The crushing behavior of composite tubes in axial impact loading is investigated. Tubes of circular and rectangular cross section are simulated using an LS-DYNA software. The effect of fiber orientation on the energy absorbed in laminated composite tubes is also studied. The results obtained show that rectangular tubes absorb less energy than circular ones, and their maximum crushing load is also lower. The composite tubes with a [+θ/ -θ] lay-up configuration absorb a minimum amount of energy at θ = 15°. The simulation results for a rectangular composite tube with a [+30/–30] lay-up configuration are compared with available experimental data. Cylindrical composite tubes fabricated from woven glass/polyester composites with different lay-ups were also tested using a drop-weight impact tester, and very good agreement between experimental and numerical results is achieved.     

Influence of induced magnetic field on peristaltic flow in an annulus

This paper looks at the influence of the induced magnetic field on peristaltic transport through a uniform infinite annulus filled with an incompressible viscous and Newtonian fluid. The present theoretical model may be considered as mathematical representation to the movement of conductive physiological fluids in the presence of the endoscope tube (or catheter tube). The inner tube is uniform, rigid, while the outer tube has a sinusoidal wave traveling down its wall. The flow analysis has been developed for low Reynolds number and long wave length approximation. Exact solutions have been established for the axial velocity, stream function, axial induced magnetic field, current distribution and the magnetic force function. The effects of pertinent parameters on the pressure rise and frictional forces on the inner and outer tubes are investigated by means of numerical integrations, also we study the effect of these parameters on the pressure gradient, axial induced magnetic field and current distribution. The phenomena of trapping is further discussed.     

在受轴向周期扰动作用下双壁碳纳米管动力屈曲的研究

对双壁碳纳米管受轴向周期扰动的动力响应进行了研究．采用连续体模型研究双壁碳纳米管的动力屈曲问题,考虑了壁间van der Waals力和周围弹性介质对轴向动力屈曲的影响．给出了受轴向周期扰动的屈曲模型及临界应变和临界频率．发现双壁碳纳米管由于壁间van der Waals力的作用较单壁碳纳米管具有较低的临界应变．van der Waals力和周围弹性介质将影响双壁碳纳米管不稳定区,van der Waals力使受轴向周期性扰动的双壁碳纳米管的临界频率增大,周围弹性介质对双壁碳纳米管的临界频率影响不大．     

一类指定应力问题的变分原理与应用

针对有限元分析中对应力或内力有指定条件的问题,引入非弹性应变作为实现指定应力条件的附加未知量,在小变形条件下描述了指定应力条件应当满足的弹性力学控制方程;以位移和未知非弹性应变作为独立变量,建立了具有指定应力条件问题的势能变分原理和虚功方程;以位移、弹性应变、未知非弹性应变和应力为独立变量,建立了一个含四类变量的广义变...     

Model based optimization of a statistical simulation model for single diamond grinding

We present a model for simulating normal forces arising during a grinding process in cement for single diamond grinding. Assuming the diamond to have the shape of a pyramid, a very fast calculation of force and removed volume can be achieved. The basic approach is the simulation of the scratch track. Its triangle profile is determined by the shape of the diamond. The approximation of the scratch track is realized by stringing together polyhedra. Their sizes depend on both the actual cutting depth and an error implicitly describing the material brittleness. Each scratch track part can be subdivided into three three-dimensional simplices for a straightforward calculation of the removed volume. Since the scratched mineral subsoil is generally inhomogeneous, the forces at different positions of the workpiece are expected to vary. This heterogeneous nature is considered by sampling from a Gaussian random field. To achieve a realistic outcome the model parameters are adjusted applying model based optimization methods. A noisy Kriging model is chosen as surrogate to approximate the deviation between modelled and observed forces. This deviation is minimized and the results of the modelled forces and the actual forces from conducted experiments are rather similar.     

Selection of optimum design for conical segmented aluminum tubes as energy absorbers: Application of MULTIMOORA method

The optimum design for energy absorbers requires considering different criteria. Therefore, the design process can benefit from Multiple-Attribute Decision-Making (MADM) approach. Thin-walled structures can be particularly employed as energy absorbers in automobiles to dissipate energy and protect passengers from the peak crush load caused by severe collisions. The present study investigates a thin-walled conical segmented aluminum tube which consists of several circular sections with different thicknesses. To achieve the optimum design, a number of conical segmented tubes were modeled by finite element method. Energy absorption, initial peak load, crush force efficiency (the ratio of mean load to maximum load), mass of the structure and deformation type as the conflicting objective functions were defined as attributes/criteria. The numeric logic (NL) technique was applied to determine the weight of various criteria. Furthermore, the MULTIMOORA method, as a well-accepted MADM model, was utilized to obtain the optimum design for a conical segmented tube. The design variables included wall thickness, lengths of sections, and taper angle. Drawing a comparison between the top rank conical segmented tube and the top rank conical simple tube revealed that the conical segmented tube could increase the efficiency of the crush load up to 23.8% and reduce the initial peak load and mass of the tube up to 54% and 17.54%, respectively.     

A Prediction Model for Skin Wound Suture Forces With Uncertain Material Parameters北大核心CSCD

To evaluate the forces required for the suture of skin wounds quickly and effectively, the nonlinear finite element method was used to calculate the suture forces for skin wounds with different sizes and material parameters. With the calculated results as samples, the prediction model for skin wound suture forces was constructed by means of the EBF neural network model. Given the uncertain skin material parameters influencing the reliability of numerical results, the Monte-Carlo method was used to analyze the uncertainty propagation of skin material parameters. Finally, the prediction analysis and measuring experiment of wound suture forces were carried out with pig skin specimens to verify the reliability of the method. The results showed that, the suture force increases first and then decreases according to the suture point sequence, and the peak force occurs before the center of the wound. For a 40 mm×10 mm wound, the peak suture force is about 1.7 N, and that for a 40 mm×14 mm wound is about 2.5 N. Influenced by the uncertainty of material parameters, the prediction results of suture forces fluctuate by as much as ±0.6 N. The proposed theoretical prediction model provides an effective solution to the problem of parameter uncertainty propagation for biological soft tissue materials such as skins, and makes an important mechanical reference for robotic surgical suture. © 2023 Editorial Office of Applied Mathematics and Mechanics. All rights reserved.     

Modeling of progressive failures in quasi-brittle media based on a temporal stress-redistribution mechanism

A new attempt is made to simulate progressive failure processes in heterogeneous brittle materials such as concrete, ceramics, rocks etc., by considering the time-dependence of stress redistributions induced by local breakages. Two mechanisms of stress redistribution are incorporated into the proposed model in order to account for the influence of each local breakage on the remaining specimen: (1) one is the immediate release of internal forces in the breaking element, which is assumed to happen within an infinitesimal time when compared with the characteristic time of external loadings. The release of such internal forces is hence suddenly applied to the remaining specimen, which is considered to take time to deform correspondingly due to material viscosity. This deformation delay is implemented by introducing a viscous force (VF) field prevailing in the entire specimen. (2) The other is the gradual release of previously stored VF fields, whose characteristic time is assumed to be material-dependent. Here the release of VF is approximated as stepwise for simplicity. The proposed model is found to be capable of overcoming the unreasonably-low-ductility problem encountered in many existing lattice models when it comes to the uniaxial tensile test. Furthermore, the force–displacement response obviously depends on the ratio of the VF releasing time to the characteristic time of external loading, showing trends agreeing with experimental observations. Compared with results without viscosity, the failure pattern is more scattering, and the force–displacement curve has a higher peak load and a more ductile post-peak tail.     

Response of multiwall carbon nanotubes to impact loading

Dynamic behaviors of multiwall carbon nanotubes (MWCNTs) with finite length are investigated using an analytical method. Multiple elastic shells and linearized model of van der Waals forces are used for development a comprehensive continuum dynamic model of MWCNTs. By applying Laplace transform, analytical solution for thin and thick MWCNTs under dynamic loading are obtained. Dynamic responses of 3-, 9-, and 11-layer MWCNTs under external pressure shock are examined and accuracy of results are verified by comparison the results with those obtained by numerical methods. Both displacement and stress analysis are performed for layers of MWCNTs and frequencies of oscillations are obtained. Also, effects of axial wave created by external pressure shock are studied in MWCNTs with two-dimensional analyses. Dynamic responses of MWCNTs with initial axial displacement are also proposed and the propagation of the axial wave through the length of tubes is illustrated. Furthermore, wave propagation velocity is found by analysis of time history diagram.     

Nonlocal elasticity effect on column buckling of multiwalled carbon nanotubes under temperature field

Based on nonlocal theory of thermal elasticity mechanics, an elastic multiple column model is developed for column buckling of MWNTs with large aspect ratios under axial compression coupling with temperature change. The present model treats each of the nested tubes as an individual column interacting with adjacent nanotubes through the intertube van der Waals forces. The thermal effect is incorporated in the formulation. In particular, an explicit expression is derived for the critical axial strain of a double-walled carbon nanotube which clearly demonstrates that small scale effects contribute significantly to the thermo-mechanical behavior of multiwalled carbon nanotubes and cannot be ignored.