An elastic mechanics model and computation method for geotechnical material

Internal friction characteristic is one of the basic properties of geotechnical materials and it exists in mechanical elements all the time. However,until now internal friction is only considered in limit analysis and plastic mechanics but not included in elastic theory for rocks and soils. We consider that internal friction exists in both elastic state and plastic state of geotechnical materials,so the mechanical unit of friction material is constituted. Based on study results of soil tests,the paper also proposes that cohesion takes effect first and internal friction works gradually with the increment of deformation. By assuming that the friction coefficient is proportional to the strain,the internal friction is computed. At last,by imitating the linear elastic mechanics,the nonlinear elastic mechanics model of friction material is established,where the shear modulus G is not a constant. The new model and the traditional elastic model are used simultaneously to analyze an elastic foundation. The results indicate that the displacements computed by the new model are less than those from the traditional method,which agrees with the fact and shows that the mechanical units of friction material are suitable for geotechnical material.

Finite Deformation and Viscoelasticity Modeling and Test

A model is considered as a representation of compressive and incompressive elastomeric materials in nonlinear behavior. Applications are done on one hand by the characterisation of polyurethane 60 - 65 shore A (a compressive material), and on the other hand by the characterisation of polyurethane 95 shore A and fluorosilicone, both incompressive materials. The Rivlin energy expression is used for incompressive materials. Linear vibrations superposed on static large deformation, which is most often the real using state of elastomeric materials, are studied. Relative experimental and numerical results presented show good predictions.

INCREMENTAL MICRO-MECHANICAL MODEL OF PLAIN WOVEN FABRIC

Warp yarns and weft yarns of plain woven fabric are the principal axes of mate- rial of fabric. They are orthogonal in their original con?guration, but are obliquely crisscross in deformed con?guration in general. In this paper the expressions of incremental components of strain tensor are derived, the non-linear model of woven fabric is linearized physically and its geometric non-linearity survives. The convenience of determining the total deformation is shown by the choice of the coordinate system of the principal axes of the material, with the convergence of the incremental methods illustrated by examples. This incremental model furnishes a basis for numerical simulations of fabric draping and wrinkling based on the micro-mechanical model of fabric.

水位差法模拟波浪荷载作用下大直径圆筒稳定性离心模型试验研究

某人工岛护岸工程采用大直径圆筒结构,结构直径和高度尺寸较大,工程所处位置波浪条件恶劣。采用水位差法等效模拟波浪荷载,开展波浪荷载作用下大圆筒施工期稳定特性离心模型试验研究,结果表明,在25 a一遇波吸力荷载作用下,筒体位移模式近似平移,侧向位移量约353 mm,筒顶沉降约为187 mm,施工阶段钢圆筒整体稳定;筒壁环向拉应力均值约为90 MPa,处于钢圆筒材料允许应力范围内;筒壁海侧土压力值随水位差增大至峰值后趋于稳定,表明筒体与周围邻近土体之间没有新的相对位移趋势,大直径钢圆筒护岸结构在波浪荷载作用下是稳定安全的。

洞桩法地铁车站边桩结构受力机制的模型试验设计

为了方便学生更形象地理解洞桩法地铁车站边桩结构的受力机制,该文以广州地区某洞桩法地铁车站工程为依托,设计了一种简化的洞桩法车站边桩结构模型试验。基于该试验方法,演示分析了边桩结构在洞桩法车站开挖过程中的施工力学行为规律,并对比研究了不同桩型布置参数下的桩后土压力、边桩结构的力学和变形规律。通过该试验,为学生展示了洞桩法边桩结构模型的设计、制作、试验具体操作及数据监测的全过程,从而让学生更好地掌握洞桩法车站边桩结构力学行为演变规律,以及采用不同边桩布置型式的力学行为差异。

偏心拉伸实验的理论分析与实验研究

偏心拉伸实验是一种综合性、研究性的材料力学实验项目。为了增加材料力学实验课程的难度和深度,通过理论分析推导偏心拉伸应力公式,并指出偏心拉伸试样的实际中性层并不再是几何中性层;利用ABAQUS软件模拟了偏心拉伸试样的应力分布;通过自制的一种可以在电子万能试验机上进行偏心拉伸实验的装置并利用电测法测试了试样横截面上各点的应变。结果表明:偏心拉伸实验的理论计算结果、实验结果和模拟结果基本吻合,3种数据之间的偏差较小;而且,应力在试样横截面上几乎呈线性分布,左边受压缩,右边受拉伸,左边的应力最小,右边的应力最大。

隧道突涌水灾害缩尺物理模型试验研究综述

随着我国经济的快速发展,隧道工程建设越来越多地面临着大埋深、高地应力、高地温、高渗透压力等复杂地质环境,运用物理模型试验开展复杂环境下隧道突涌水灾变机理与安全防控研究已成为岩石力学的热点问题。结合近年来国内外针对隧道突涌水灾变缩尺物理模型试验开展的研究工作,重点对该类物理模型的流固耦合相似理论、相似材料研制、渗透压加载方法等内容进行了系统梳理,并对下一步的可能发展方向进行展望。参考部分文献和突水典型案例后,总结了流固耦合相似准则和高地应力下的相似准则、相似材料选用方案及材料配比、试验中的水压加载方案,认为未来关注的重点包括考虑温度场的物理模型试验相似准则的研究和涌水涌泥与突水突泥间渐变过程的研究2个方面。

磁流变抛光技术研究进展

表面质量是精密零部件最重要的性能之一,零件的表面质量主要是由加工过程中不同的工艺参数和方法决定的。传统的磨抛工艺由于作用在工件上的力很大、嵌入的磨料颗粒、对工艺的控制有限等原因很难使表面粗糙度降低到精密零部件的要求精度。磁流变抛光(MRF)提供了一种新型高效的方法使工件加工质量达到预期的精度水平。MRF对工艺控制具有更大的灵活性,并且可以在不破坏表面形貌的情况下完成加工。综述了磁流变抛光液组分对加工效果的影响、材料去除模型的建立和发展、不同的MRF加工方式和未来磁流变抛光技术发展的新方向,最后总结了目前MRF技术存在的问题总结,并提出了MRF技术未来可能的发展方向。

考虑结合面特性影响的机床整机有限元静力学分析模型

针对机床数字化设计中典型结合面建模精度误差较大的问题,提出了一种采用虚拟材料等效结合面静力学特性的方法,建立了考虑结合面特性影响的机床整机有限元静力学分析模型,并完成了相应的静刚度测试实验。首先,综合考虑了弹塑性变形机制和摩擦力的影响,提出了一种新的结合面法向和切向刚度的分析模型;其次,根据不同类型结合面的特点,采用虚拟材料模拟结合面的刚度特性,建立了刚度特性与虚拟材料弹性模量和泊松比的关系,并将其应用于精密数控机床整机的静刚度分析;最后,开展了整机工艺系统的静刚度测试实验,得到了主轴末端X、Y、Z三个方向的刚度分别为26.60 N/μm、41.87 N/μm和40.17 N/μm,并将其与仿真数据进行了对比。研究结果表明:不考虑结合面影响的模型相对误差将近17%,而考虑结合面影响的模型相对误差在5%以内,验证了考虑结合面特性影响的机床整机有限元静力学分析模型的有效性;采用虚拟材料等效结合面静力学特性的方法可作为机床数字化设计的一种可行的方法。

大型梁式承台模型试验及跨中挠度简化计算方法研究

为了解大型梁式承台的力学性能,以某快速化改造工程的大型梁式承台为背景,按照缩尺比1∶10制作梁式承台模型进行力学性能试验,结合有限元计算,分析梁式承台结构受力、破坏模式、开裂情况等,并研究不同跨高比条件下梁式承台的受力特性。结果表明:在跨中荷载作用下,梁式承台受力大致可以分为线弹性阶段、裂缝发展阶段和屈服阶段3个阶段;线弹性阶段截面应力分布已不满足平截面假定,剪切效应对结构变形的影响不可忽略;模型最终破坏模式为弯曲破坏;裂缝主要表现为跨中弯曲裂缝和斜裂缝;跨高比越小,梁式承台剪切刚度越大。为考虑剪切效应对梁式承台变形的影响,拟合得出梁式承台跨中挠度的简化计算方法,将该方法计算值及规范计算值与试验值进行对比,可得在裂缝发展阶段,规范计算值与试验值偏差较大,所提方法计算值与试验值偏差较小,该方法可用于线弹性阶段及裂缝发展阶段梁式承台跨中挠度的初步估算。

试样厚度对小冲杆试验力与材料强度相关性的影响

为了研究试样厚度对小冲杆试验力与材料强度相关性的影响,针对不同厚度(0.1~0.5 mm)的小冲杆试样,使用无屈服平台的虚拟材料进行了有限元模拟。通过提取并分析有限元模拟结果中固定挠度下的小冲杆试验力,证明了小冲杆试验力与材料屈服强度和抗拉强度的双线性关系,且厚度的变化不会影响该相关关系的皮尔逊相关系数。随机生成了屈强比在0.55~0.9之间,屈服强度在200~1000 MPa之间的100种虚拟材料,并通过有限元模拟获得了大量数据,进而采用退火粒子群算法得出了固定挠度下小冲杆试验力和材料强度的关联系数。采用4种真实材料验证了小冲杆试验力与材料强度呈双线性关系的结论。

Model of fractured medium and nondestructive control of composite materials

Non-destructive testing of composites is an important issue in the modern aircraft industry.Composites are susceptible to the barely visible impact damage which can affect the residual strength of the material and occurs both during production and operation.The continuum model for describing the damaged zone is presented.The slip theory relations used for a continuous distribution of slip planes are applied.At the initial stage,the isotropic background model is used.This model allows the material slippage along the fractures based on the Coulomb friction law with the small viscous addition.In this regime,the govern system of equations becomes rigid.To overcome this difficulty,the explicit-implicit grid-characteristic scheme is proposed.The standard ultrasound diagnostic procedure of damaged composite materials is successfully simulated.Compared with the trivial free-surface fracture model,different reactions on the compression and stretch waves are registered.This approach provided an effective way for the simulation of complex dynamic behavior of damage zones.

HTPB复合固体推进剂老化研究进展

综述了HTPB推进剂在老化试验和表征方法、老化机理、模型构建和寿命预测方面的国内外研究现状,通过对国内外的HTPB推进剂研究历程进行对比,分析了与国外研究整体趋势的差异。从检索文献来看,与国外研究进展相比,国内研究整体上具有起步晚、发展快的特点。在此基础上,展望了今后的研究方向,包括多因素耦合的老化机理探究、老化快速评价、先进监测手段、寿命预测模型优化以及防老化等方面,以期为HTPB推进剂的老化研究提供更多参考。

Research on the macro-and meso-mechanical properties of frozen sand mold based on Hertz-Mindlin with Bonding model

In this study,macro-and meso-mechanical properties of frozen sand molds were discussed based on the Hertz-Mindlin with Bonding(HMB)model.Plackett-Burman,steepest ascent,and central composite designs were utilized to propose a parameter calibration methodology.The effects of mesoscopic parameter variations on the compressive strength and average gradient of stress-strain were investigated through response surface method analysis.Results showed that the relative error between the simulated and measured repose angle is 3.1%under calibrated intrinsic contact parameters.The compressive strength and average stress-strain gradient primarily depend on the normal and shear stiffness per unit area,as well as the particle size and porosity of the silica sand.Furthermore,taking load-displacement curves of three frozen sand molds with different geometric characteristics as the target value,the reliability and effectiveness of the frozen sand mold HMB model were verified through uniaxial compression tests and discrete element simulations.

钢结构涂装层的力学试验与本构模型研究

为研究钢结构桥梁涂装层的力学本构模型,以长效型涂装体系为试验对象进行单轴拉伸试验,得到面漆、中间漆、底漆和复合涂层的应力-应变曲线。通过无量纲化处理获得长效型涂装体系上升段本构方程的统一表达形式,并对每种漆膜具体的适用条件给出了相应的本构方程。结果表明:H06-X环氧富锌底漆(含80%锌)和长效型复合涂层的应力-应变曲线分为弹塑性阶段、应变强化阶段和破坏阶段;H06-C2环氧厚浆云母氧化铁中间漆的应力-应变曲线分为应变强化阶段和破坏阶段;E01-JY氟碳面漆的应力-应变曲线分为近似线弹性阶段和破坏阶段。依据应力-应变曲线得到了底漆、中间漆、面漆和复合涂层的弹性模量、泊松比、剪切模量、单轴拉伸强度和拉伸断裂应变等力学性能特征参数,发现单轴拉伸强度底漆最强,中间漆次之,面漆最差;变形性能面漆最佳,中间漆次之,底漆最差。

复合材料整体成型大后掠机翼设计与验证研究

根据机翼设计及材料工程力学性能要求,基于给定的机翼外形设计并制造了一种满足工程应用要求的全复合材料整体模压成型机翼结构。通过有限元仿真分析和工程静力学试验方法对该机翼结构进行了全面验证,有限元仿真分析结果与工程静力学试验结果吻合良好,满足复合材料工程力学许用值要求及机翼最大变形不大于半翼展长8%的刚度设计需求,该机翼的力学承载性能得到了充分验证。

A comprehensive testing method for global stability analysis of high arch dams

Hydropower projects are rapidly developing in China at present, and a number of high daras and large reservoirs are currently under construction or will soon be built. These large projects are mainly located on the great rivers in West China with complicated topographical and geological conditions. Evaluation of stability and safety of these high dam projects is an important topic. Geomechanical model test is one of the main methods to study the global stability of high dam and foundation. In this paper, a comprehensive testing method that combines overloading and strength reduction in a model is proposed. In this method, both the influence of excessive flooding and the effects of strength reduction of rock masses and weak structural planes on dam stability are considered. Thus, the comprehensive testing method can accurately incorporate multiple factors that affect the global stability of high dam and its foundation. Based on the failure testing principle and model similarity theory, a similarity relation formula for safety evaluation through comprehensive test is established. A new model material, temperature-dependent analogous material, is also developed. By rising the temperature and reducing the strength of the mod,~l material, the mechanical behaviors resulting from gradual strength reduction can be simulated. Thus, the comprehensive testing method is realized in a single model. For case studies, the comprehensive geomechanical model test is conducted for Jinpinlg I and Xiaowan high arch dam projects.

MAKING OF THE EQUIVALENT MATERIALS USED FOR STUDYING ROCK RIPPABILITY

Based on the characteristics of the ripping of rock, the simulated conditions that would be satisfied by the prototype ripping and the model ripping have been derived in this paper. In order to .nanufacture the satisfying equivalent materials for the model ripping, a new method has been set up, and the materials, which can simulate the prototype rock "Hawkesbury sandstone", have been made by using the methed.

基于支持向量机的机械零件寿命预测模型研究

机械零件的使用寿命是一个重要的问题,直接影响机械设备的安全和稳定运行。传统试验方法确定机械零件的寿命需要耗费大量的时间和资源,而且在试验过程中难以考虑到各种复杂的实际工作环境和使用条件。采用支持向量机的方法来预测机械零件的寿命,通过机械零件退化特征构造时间更新方程分析推断材料在不同工作条件下的寿命。研究结果可以为机械设备的设计和维护提供参考依据与分析方法。

柔性泡沫对振杆密实法模型试验边界效应的影响分析

为研究柔性泡沫材料对刚性模型箱边界效应的改善效果,在模型箱侧壁分别内衬了聚氨酯、聚苯乙烯和珍珠棉3种泡沫,开展了振杆密实法处理可液化地基的室内模型试验.采用2-范数偏差法对振动加速度场进行分析,通过将加速度时程信号功率谱密度对频率进行积分处理,估算出边界材料耗散的能量.结果表明,聚氨酯泡沫吸收和散射的能量约为输入水平的53.9%,其对刚性模型箱边界效应的改善作用优于聚苯乙烯泡沫和珍珠棉泡沫.柔性泡沫主要通过减少弹性波向模型土层中的反射来减弱模型箱的边界效应.泡沫材料与土体的波阻抗越接近,减少弹性波反射的能力越强.