注浆微型钢管桩抗弯性能研究

为探讨注浆微型钢管桩的抗弯性能，对不同钢管管径、壁厚以及砂浆强度的12根试件，采用正交试验方案进行纯弯曲试验，基于试验结果提出极限抗弯承载力表达式，并采用有限元软件ANSYS建立模型进行验证。结果表明：注浆微型钢管桩的弯曲全过程可分为3个阶段，即，弹性阶段、弹塑性阶段和强化阶段；对注浆微型钢管极限荷载敏感性大小为，钢管管径>钢管壁厚>砂浆强度等级；不同规程计算的极限抗弯承载力与试验差异较大，本研究所提出的注浆微型钢管桩极限抗弯承载力表达式与试验结果吻合较好，钢管的抗弯承载力约占注浆微型钢管桩总抗弯承载力的78%,管内砂浆约占22%;有限元模拟结果显示，管内砂浆对微型钢管桩的抗弯性能有较大的提升，验证了所提出的注浆微型钢管桩抗弯承载力表达式的正确性。     

腹板V形加劲冷弯薄壁卷边槽钢柱试验研究

为了解腹板V形加劲冷弯薄壁卷边槽钢构件的受压性能,对8根短柱和中长柱进行了轴心受压试验研究。在试验之前首先用有限条和有限元方法对柱试件进行了详细的设计,以确保发生畸变屈曲失效。柱受压试验结果发现：所有试件均发生畸变屈曲失效破坏,同时在峰值荷载时中长柱试件有绕弱轴的弯曲产生,畸变屈曲和局部屈曲一样也有一定的屈曲后强度。在总结分析现有国内外规范计算理论的基础上,提出了基于直接强度法设计腹板V形加劲冷弯薄壁卷边槽钢轴压构件畸变屈曲承载力的计算方法。采用该建议方法计算所得结果与试验值和参数分析值吻合较好,其设计过程简便且安全可靠。     

碳/碳复合材料T型悬臂梁弯曲失效分析

首次对碳/碳复合材料T型结构件进行了悬臂梁弯曲试验。通过化学气相沉积工艺制备了宽度为40mm的T40试件和宽度为50mm的T50试件,分别对两种试件的损伤失效模式和弯曲应力进行了研究;根据结构破坏区域的应变随载荷增加的变化规律,得到了结构在弯曲过程中的损伤失效进程。结果发现,在悬臂梁弯曲载荷作用下,结构处于正应力和剪应力耦合状态,耦合应力会使宽厚比较小的结构件容易在腹板根部出现局部失稳现象。应用横力弯曲理论对结构破坏截面上腹板边缘的正应力和面内剪切应力进行了简单计算。结果表明:屈曲失效的T50试件比剪切型破坏的T40试件的最大弯曲正应力小22.93%,说明屈曲失效会使结构的弯曲强度大幅下降;而T50试件的最大剪切应力比T40试件的高31.46%,说明屈曲失效主要由材料的剪切性能控制。最后通过有限元方法对T50试件在发生剪切型破坏时的最大弯曲正应力进行了计算,计算结果与试验中发生压缩剪切破坏的T40试件相比仅相差3%,可以较好地表征T50试件的弯曲强度。     

环形钢管混凝土直杆抗弯性能研究

针对离心法生产的环形钢管混凝土桩,外径Ф400、内径Ф220,钢管厚度6mm,钢管材料Q235B,混凝土强度等级C80,运用试验和理论分析方法研究其弯曲性能.试验表明,钢管与混凝土端部界面无滑移,协同工作性能良好,弹性极限弯矩290kNm,相应的挠跨比1/450;塑性极限弯矩394kNm,相应的挠跨比1/100;在挠度达到跨度的1/30时,弯矩-挠度曲线仍然处于上升阶段,最大试验弯矩430kNm,相应的延性系数15.运用材料力学原理,忽略两种材料界面间的粘结滑移,认定受拉区混凝土开裂退出工作,推导建立其塑性抗弯承载力计算方法,计算值与试验值基本吻合.研究表明,环形钢管混凝土桩具有很高的抗弯承载力和优越的弯曲延性,具有良好的抗震性能.     

热载荷作用下梯度多孔材料梁弯曲及过屈曲力学行为的研究

基于Bernoulli-Euler梁理论,引入物理中面解耦了复合材料结构的面内变形与横向弯曲特性,研究了梯度多孔材料矩形截面梁在热载荷作用下的弯曲及过屈曲力学行为．假设沿梁厚度方向材料的性质是连续变化的,利用能量法推导了矩形截面梁的控制微分方程和边界条件,并用打靶法对无量纲化的控制方程进行数值求解．利用计算得到的结果分析了材料的性质、热载荷、边界条件对矩形截面梁非线性力学行为的影响．结果表明,对称材料模型下,固支梁与简支梁均显示出了典型的分支屈曲行为特征,而其临界屈曲热载荷值均会随着孔隙率系数的增加而单调增加．非对称材料模型下,固支梁仍显示出分支屈曲行为特征,但其临界屈曲热载荷不再随着孔隙率系数的变化而单调变化;而对于两端简支梁,发生了弯曲变形,弯曲挠度随载荷的增大而增大．     

HSSTS新管幕构件受力性能数值分析研究

针对目前管幕工法应用时存在的施工步骤繁琐、抗弯刚度较弱等问题,本文提出了一种采用H型钢连接的新型管幕结构(HSSTS);基于相关构件室内试验结果,采用ABAQUS有限元软件建立了HSSTS有限元模型,探究了其受力特征和破坏规律;并详细研究了多个部件参数对结构抗弯性能的影响,同时对构件承载力和抗弯刚度进行了多元线性回归分析。结果表明:结构具有较高的横向刚度,钢管壁厚对承载力影响明显,翼缘板厚度对其影响不明显,混凝土强度对其具有一定影响,其极限荷载环比提高百分比平均值分别为5.23%、0.29%、3.94%;基于多元线性回归理论建立的承载力和抗弯刚度回归模型的相关系数分别为0.992和0.927,表明模型拟合效果较好。     

轻质金属点阵夹层板热屈曲临界温度分析

本文针对均匀温度场下四边简支和四边固支金属点阵夹层板的临界热屈曲温度进行了求解和参数影响分析。将点阵夹芯等效为均匀连续体,并且将夹层板的剪切刚度近似为点阵夹芯的抗剪切刚度,忽略夹芯的抗弯刚度且认为夹层板主要由面板来提供抗弯刚度。对于无法获得解析解的四边固支条件,通过对未知变量进行双傅里叶展开的方法求解了Ressiner夹层板模型的临界屈曲温度,理论分析结果与有限元计算结果吻合良好。进一步分析了不同边界条件、点阵胞元构型、点阵材料相对密度、面板厚度等对临界屈曲温度的影响规律。     

用杂交应力元分析板的弹塑性屈曲

基于一个含面内初应力薄板问题的修正的Hellinger-Reissner变分原理,导出了一个十二自由度矩形杂交应力弯曲板元。并首次将杂交应力模型用于求解各向同性以及加筋平板的弹塑性欧拉屈曲问题。计算中,将Sturm序列方法与0.618加载法相结合以确定临界应力。材料性质采用Stowell塑性屈曲理论及Ramberg-Osgood应力应变关系加以反映。 计算结果与解析解、实验值均符合良好。而且比多数已知有限元解精确。这表明,用杂交应力模型求解平板的弹塑性欧拉屈曲问题可行,方便,可以获得满意结果:本文导出的单元精度高、收敛快。     

梯度多孔材料梁的非线性力学行为

基于经典梁理论以及物理中面概念,研究了机械载荷作用下梯度多孔材料梁的非线性弯曲及过屈曲问题。利用能量法导出了梯度多孔材料梁的基本方程,并用打靶法对其进行数值求解。假设梯度多孔材料性质只沿厚度方向变化,利用数值结果研究了两种不同材料模型下梯度多孔材料性质、外载荷、边界条件等因素对梯度多孔材料梁非线性弯曲及过屈曲行为的影响。数值结果表明:随着孔隙率的增大,梯度多孔材料梁的弯曲挠度增大,而且非对称材料模型下的结果高于对称材料模型下的结果;梯度多孔材料梁的临界屈曲载荷随孔隙率的增大而减小,而非对称材料模型下的结果低于对称材料模型下的结果。     

考虑不确定性因素的有限元屈曲模型验证

研究了考虑不确定性因素的有限元屈曲模型验证和确认方法,提出了不确定参数选择的相关性和敏度分析方法以及基于面积度量的模型评估方法.针对化铣整体壁板,开展了有限元屈曲模型验证研究,首先利用8件试验件,获得了壁板屈曲载荷的试验值,然后依据试验加载情况,建立了考虑试验台的壁板有限元模型,最后利用面积度量方法对有限元模型进行了验证和确认.本文的模型验证和确认方法可为其他工程结构开展类似的工作提供借鉴.     

神经网络在麦秆秆茎机械强度确定中的应用

为了避免重复性力学实验来确定麦秆茎秆机械强度, 将神经网络技术用于麦秆茎秆机械强度的计算, 建立神经网络多几何参数确定麦秆茎秆机械强度的预测模型. 详细介绍麦秆机械强度神经网络预测模型的操作过程, 并根据预测误差结果分析, 证实了该方法的有效性和可行性.     

Membrane fusion based on the geometry of the stalk model

It is a commonly accepted assumption that membrane fusion involves an hourglass-shaped local contact between two monolayers of opposing membranes, an intermediate structure called a stalk. The shape of the stalk is considered as an axisymmetrical figure of revolution in 3D space, with a planar geometry in the initial configuration. The total energy of the stalk is evaluated from the assumption that the stalk has a constant curvature. Its negative value due to the presence of spontaneous curvature promotes hemifusion. An extension of the original model developed in Markin and Albanesi [23] is proposed, in which any geometrical feature of the stalks can be expressed in explicit form, by considering the stalks as nodoid surfaces. The local stresses and induced internal moments due the membrane bending are evaluated based on the adopted parameterization.     

TG-DSC method applied to drying characteristics and heat requirement of cotton stalk during drying

Drying characteristics of cotton stalk were investigated at four temperatures (60, 80, 100 and 120?°C) using a simultaneous thermal analyzer (TG-DSC). Heat requirements of cotton stalk during drying were calculated ranging from 189 to 406?kJ/kg. Consequently, Midilli-Kucuk model showed the best fit to experimental drying data. The values of effective diffusivity ranged from 4.38?×?10^?9 to 8.15?×?10^?9?m²/s, and the activation energy was calculated to be 11.6?kJ/mol.     

A structural mechanics approach for predicting the mechanical properties of carbon nanotubes

Based on molecular mechanics, a structural mechanics model of carbon nanotubes (CNTs) was developed with special consideration given to the bending stiffness of the graphite layer. The potentials associated with the atomic interactions within a CNT were evaluated by the strain energies of beam elements which serve as structural substitutions of covalent bonds in a CNT. In contrast to the original model developed by Li and Chou (Int. J. Solids Struct. 40(10):2487–2499, 2003), in the current model the out-of-plane deformation (inversion) of the bond was distinguished from the in-plane deformation by considering a rectangular cross-section for the beam element. Consequently, the model is able to study problems where the effect of local bending of the graphite layer in a carbon nanotube is significant. A closed-form solution of the sectional properties of the beam element was derived analytically. The model was verified through the analysis of rolling a graphite sheet into a carbon nanotube. Using the present model, the buckling behavior of nanotubes under bending is simulated. The predicted critical bending angle agrees well with molecular dynamics simulations.     

液晶高弹体的光致变形与弯曲行为研究

本文研究了一类光敏液晶高弹体在紫外光照射下的变形和弯曲行为。在分析了近年发现的光敏液晶高弹体中光致变形的机理和规律的基础上，给出了该材料一维变形本构关系，研究其变形行为，进而利用铁木辛科双金属片弯曲的思想建立了梁的光致弯曲模型。     

Linear viscoelastic model for bending and torsional modes in fluid membranes

This paper develops and applies a linear viscoelastic model for bending and torsional modes of fluid membranes, based on the nonlinear Cosserat surface fluid model. The linearized fluid membrane model in spherical and cylindrical geometries is shown to decouple bending and torsional viscoelastic modes. It is found that solutions of the membrane viscoelastic model to small-amplitude oscillatory bending and torsion allows for the measurement of the bending and the torsion viscosity. The model and its potential in characterizing the bending and torsion viscoelasticity of membranes complements the on-going efforts to establish the role of curvature in dissipative process of biological membranes.     

弯曲及拉伸荷载作用下的钢管抗压溃性能研究

钢管在海洋油气资源开发中应用广泛,一般依据在位应用时的荷载进行设计,设计理论较为成熟。但在某些安装工况中的拉伸和弯曲荷载与在位荷载具有相同的量级,此时钢管的设计需要考虑安装荷载的影响。本文针对钢管在承受拉伸和弯曲荷载下的抗外压压溃性能开展研究。基于商业软件ABAQUS建立有限元模型,开展钢管压溃实验与带有弯曲荷载下的钢管压溃实验验证有限元模型的正确性,进而利用验证后的数值模型讨论拉伸、弯曲荷载和两者联合作用下对管道抗外压压溃性能的影响。结果表明,弯曲荷载是影响抗压溃性能的重要因素,弯曲荷载的增加都会使极限压溃值显著下降。管道所受拉伸荷载对抗压溃性能有一定的影响,但影响很小,在两者共同作用下极限压溃值随弯曲荷载的增加都出现先增大后减小的现象,而且极值的位置与拉伸荷载的大小和弯曲荷载有关。因此,在抗压溃设计中应重点考虑弯曲荷载对压溃的影响,可忽略拉伸荷载的影响。本文可为海洋管道的安装起到指导作用。     

A thin-sheet, combined tension and bending specimen

Validating stress intensity factor solutions for combined tension and bending is an arduous task because the necessary experimental data are not readily available. Toward this end, a tension and bending test specimen was designed to produce controllable levels of both tension stress and bending stress at the crack location. The specimen was made from 2024-T3 clad aluminum, which is commonly used in aircraft structures. The need for testing multiple specimens of various geometries and stress levels prompted the development of an analytical tool for specimen design. An extention of the Schijve line model, based on simple beam theory, was developed to calculate the stress distributions of tension and bending through the length of the specimen. A comparison of measured static strain levels with those predicted by the model showed the model to be accurate to within 5 percent, confirming its efficacy for specimen design. As expected, for the same remote stress (100 MPa), cracks in the tension and bending specimens grew faster than those in middle-cracked tension specimens.     

A Theoretical Study on Nonlinear Bending of Wires

The nonlinear bending of thin wires is a challenging topic in several applications where the final geometry of the wire after bending and springback has to be known. Typical examples are tyre manufacturing, helical spring design, spectacles frames. In order to develop analytical models able to set bending parameters for a required final shape of the wire, both account material behaviour (during the loading and unloading phases with springback effect) and geometrical nonlinearity have to be considered. In the case of plates bending, many analytical and numerical models are available in the literature, offering an accurate solution to this problem. However, the bending of thin wires could still be the subject of discussion and research. In this paper a new analytical model was developed, starting from the models available in the literature, in order to provide the designer with a simple model to predict the final shape of a wire by using mathematical codes. The model allows to predict with a higher level of accuracy the final shape of wires having different cross-sections after nonlinear bending. Since Bernoulli’s hypothesis is assumed, the model can be used in all the applications where the material behaviour of the wire guarantees that plane cross sections of the wire will remain plane after rotation due to bending, with negligible errors from the engineering point of view.     

反倾层状岩体斜坡弯曲-拉裂两种失稳破坏之判据探讨

对反倾层状岩体斜坡弯曲-拉裂的失稳破坏判据,已有研究分别基于两种力学模型进行推导,即竖直压杆弹性屈曲稳定和平直梁弯折破坏模型,但对层间错动阻力及挠度产生附加弯矩等因素未加以考虑,不尽合理。在反倾斜坡岩层受力分析基础上,建立考虑了板侧层间错动阻力的下端嵌固、上端自由的斜置等厚弹性悬臂板梁模型,统一地通过瑞利-里兹能量方法,推导了弹性屈曲临界条件和嵌固端弯折破坏临界条件。实例计算及讨论表明,弹性屈曲判据适用于陡立岩层;而中-陡反倾岩层应主要为弯折破坏,但层间的力学性质对弯折临界判据值具有较大影响。