结构系统静强度与断裂的综合可靠性分析

基于疲劳载荷作用下裂纹扩展的随机性,建立了结构系统综合考虑静强度和断裂的可靠性分析方法,该方法给出了元件静强度失效时所对应的当量寿命,并建立了元件综合失效判别准则,分析了元件静强度失效和断裂失效之间的相关性.算例表明,随使用年限的增加,元件静强度失效和断裂失效之间的相关性也在增加;在不同的使用年限内,结构系统主要失效路径是不同的,并且在结构系统主要失效路径中既有元件静强度失效又有元件断裂失效;若只考虑静强度或断裂的结构可靠性分析,分析结果偏于危险.     

混凝土和岩石断裂及损伤国际会议

该会在奥地利维也纳工业大学举行.来自24个国家和地区的与会者共145人,有101篇文章,其中意大利最多24人,其次东道主奥地利22人.会议由维也纳工业大学第二力学所H.P.Rossmanith主持.三个大会报告是;美国西北大学S.P.Shah,“确定断裂过程区及断裂参数的实验方法”;瑞典爆轰研究基金会(SveDeFo)F.Ouchterlony,“利用岩芯试件进行岩石断裂韧性试验”;美国康奈尔大学A.R.Ingraffea在混凝土结构专题讨论会上做的“混凝土坝断裂模拟的实验研究”.9个分会是:断裂过程区(18篇),断裂能      

内聚力模型的形状对胶接结构断裂过程的影响

内聚力模型被广泛应用于粘接结构的断裂数值模拟过程中,为深入分析不同形状内聚力模型与胶黏剂性质和粘接结构断裂之间的关系,本文分别采用脆性和延展性两种类型胶黏剂,对其粘接的对接试件进行了单轴拉伸、剪切实验,以及其粘接的双臂梁试件进行了断裂实验.3种类型的内聚力模型(抛物线型、双线型和三线型)分别模拟了以上粘接结构的断裂过程,并与实验结果进行对比.结果发现:双线型的内聚力模型适用计算脆性胶黏剂的拉伸与剪切的断裂过程;指数型内聚力模型较适合计算延展性胶黏剂的拉伸和剪切的断裂过程,临界应力、断裂能和模型的形状参数是分析拉伸和剪切的重要参数;双臂梁试件的断裂过程模拟结果发现,断裂曲线与胶黏剂性质有关,内聚力模型形状参数也有影响.通过实验与计算结果分析,双线型内聚力模型更适合脆性胶黏剂粘接的双臂梁断裂计算,而三线型更适合计算延展性胶黏剂粘接的双臂梁断裂过程,此研究结果对胶黏剂的使用和粘接结构的断裂分析有很重要意义.     

混凝土断裂过程及尺寸效应分析

为研究混凝土裂纹断裂过程和最大承载力计算方法,通过实验机对四种不同尺寸混凝土紧凑拉伸断裂试件进行了加载过程实验,并对其中一个试件进行应变片跟踪测试.由实验结果分析得到了一系列关系曲线,如试件的载荷-加载点位移关系曲线,断裂损伤区变形随载荷变化曲线;并且计算了不同尺寸断裂试件的应力强度因子.结合计算粘聚裂纹应力强度因子的公式与断裂准则,完成了对承载力理论值的计算,并将其与实验峰值平均值进行对比,其结果是两者相比误差较小,表明此种计算裂纹结构最大承载力方法是可行的.     

牙齿表面微观磨损形貌的数值化分析研究

牙齿表面磨损一般通过显微镜进行形貌图像表征分析，而数值化分析牙齿表面磨损形貌的工作相对较少. 本研究中通过白光共聚焦显微镜，Solarmap Universal 软件和Tooth-Frax软件对牙齿咬合前后表面磨损形貌进行数值化分析，建立磨损前后表面尺度敏感曲线. 结果显示:牙齿表面磨损形貌可以通过轮廓分形分析法建立相应的表面尺度敏感曲线，形成表面磨损尺度敏感数字信号. 本工作的主要目的是寻求通过表面磨损数值化分析为研发牙齿磨损动态监测设备提供理论基础和技术支撑.      

基于碎点法的动态断裂分析

工程中的冲击防护结构在撞击、爆炸等冲击载荷下可能发生动态断裂并最终破坏, 抑制结构的动态断裂是提升结构防护能力的重要手段, 为此需要准确预测结构在动态载荷下的断裂行为. 数值仿真是预测动态断裂的重要手段, 然而当前工程中常用的有限元法在模拟断裂方面仍存在网格畸变和难以显式引入裂纹等问题. 碎点法是近年来提出的一种不连续型伽辽金弱形式无网格方法, 适合模拟断裂问题, 本文提出一种显式动力学格式的碎点法并将该方法应用于动态断裂分析. 一方面, 碎点法参考弱形式无网格类方法, 将求解域离散为空间中的节点和子域, 并基于支持域内的节点群构造子域的位移试函数, 因此该方法的子域具有抵抗畸变的能力. 另一方面, 碎点法参考间断伽辽金有限元法, 使用分片连续的位移试函数, 并引入内部界面数值通量修正保证方法的一致性和稳定性, 因此该方法易于在结构中显式引入裂纹. 本文首先介绍碎点法的核心思想和离散形式, 接着推导了动力学碎点法弱形式动量方程, 然后建立了碎点法的显式动力学求解格式, 最后通过算例验证动力学碎点法预测应力波传播和动态断裂行为的能力.      

工程岩体断裂构造发育程度的定量评价研究IAEG信息(会讯)

岩体断裂构造发育程度及其均匀性是影响岩体结构类型、岩体质量优劣及岩体稳定性分析以及工程岩体综合分区利用的重要因素, 因此岩体断裂构造发育程度的定量评价具有重要的工程意义。本文以三峡工程永久船闸边坡工程为例, 系统地讨论了工程岩体断裂构造发育程度的评价方法、定量评价指标的确定原则、断裂构造发育程度的分级标准等。研究表明, 根据岩体断裂构造发育特点, 综合运用多层次模糊综合评判法和人工神经网络技术是评价工程岩体断裂构造发育程度的有效方法。     

第五届国际材料力学行为会议将于1987年在中国召开

第五届国际材料力学行为会议定于1987年5月18日至22日在北京举行。征文内容: 1.材料在工程实践中的断裂研究。包括连续力学和微观判据的关系;不同韧性参数间关系及解释;板材成型中的断裂问题,包括成型性及材料发展。2.材料疲劳判据及材料特性。包括宏微观描述裂纹起始与生长;载荷及表面因素对疲劳裂纹生长的影响;焊接处的性能;表面处理提高疲劳抗力等。3.断裂的环境影响。包括化学因素对断裂行为的作用;局部环境与应力腐蚀断裂;应力腐蚀同氢脆断裂工程问题等。     

第五届国际材料力学行为会议将于1987年在中国召开

第五届国际材料力学行为会议定于1987年5月18日至22日在北京举行。征文内容: 1.材料在工程实践中的断裂研究。包括连续力学和微观判据的关系;不同韧性参数间关系及解释;板材成型中的断裂问题,包括成型性及材料发展。2.材料疲劳判据及材料特性。包括宏微观描述裂纹起始与生长;载荷及表面因素对疲劳裂纹生长的影响;焊接处的性能;表面处理提高疲劳抗力等。3.断裂的环境影响。包括化学因素对断裂行为的作用;局部环境与应力腐蚀断裂;应力腐蚀同氢脆断裂工程问题等。     

再生核质点法研究进展

概述了无网格再生核质点法的近似方案和本质边界条件的处理;综述了再生核质点法在结构动力学、大变形分析、计算流体力学、断裂及损伤力学、微机电结构分析中的应用;从工程应用和改进再生核质点法的角度提出了未来的若干研究方向.      

Investigation of root-periodontium interface stresses and displacements for orthodontic application

The orthodontic appliance (“braces”) loads a number of individual teeth; in the case of each tooth, the displacement which results is related to the form of the active force system transmitted from the appliance to the tooth crown. In this paper, a model of a single-rooted tooth together with its support structure, the periodontium, is the subject of a plane-stress study with the objective to correlate crown loading, support reaction and initial tooth-displacement direction. The analytical calculations of the interface-stress components are verified through a photoelastic analysis of the tooth/support-structure model. Center-of-rotation locations are determined as functions of the applied-force system and several interface normal-displacement patterns are included, with the goal of this study being the ability to better predict basic tooth movements from knowledge of the form of the crown loading.     

上颌双侧游离端活动义齿连接体的激光全息研究

本文采用全息干涉度量术,对五种结构的上领双侧活动义齿连接体在外力作用下的变形进行了定量分析,得出了基板对粘骨膜的压力分布情况,为活动义齿的结构设计提供了有意义的参考.     

不同年龄段天然牙的摩擦磨损行为研究

采用往复滑动摩擦磨损试验台考察了不同年龄段的天然牙同钛合金配副时的摩擦学性能.结果表明:天然牙的摩擦磨损行为同年龄密切相关,早期和中期恒牙的摩擦磨损行为相似,磨损表面主要呈现轻微擦伤迹象,中期恒牙的抗磨性能最佳;乳牙及晚期恒牙的摩擦系数变化波动较大,抗磨性能不佳,磨损表面主要呈现严重犁削和剥落特征.     

乳、恒牙釉质及本质体外摩擦行为的对比研究

采用往复式滑动摩擦磨损试验考察了人体乳、恒牙牙釉质及牙本质在人工唾液润滑下的摩擦学性能.结果表明:人体牙的摩擦磨损行为同其微观结构密切相关;恒牙釉质磨痕表面存在轻微擦伤迹象;乳牙釉质的磨损表面主要呈现裂纹和轻微犁沟,二者都存在腐蚀磨损的现象;乳牙和恒牙本质的摩擦磨损行为相似,磨损明显加剧,磨斑表面呈现严重犁削和剥落特征.     

Droplet impact on wetted structured surfaces

In this study, we numerically investigate the droplet impact onto a thin liquid film deposited on a structured surface with square pillars and cavities. The time evolution of crown geometry is strongly affected by the surface structure. When the thickness of the liquid film is larger than the structure height, the expanding speed of the crown base radius is independent of the structure width. However, if the liquid film thickness is equal to the structure height, the crown base expands slower as...     

弱粘结的斜交铺设层合圆柱壳的柱形弯曲

导出了两端简文的具有弱粘结界面的任意斜交铺设层合圆柱壳柱形弯曲问题的一个精确弹性理论解。分析中采用线性弹簧模型来表征界面的弱粘结特性。引进新的物理量改写了基本方程,导出了对应的状态空间列式,并利用变量替换技术将该状态方程转换成常系数状态方程,从而方便求解。最后给出了数值算例,并讨论了弱界面的影响。     

混凝土静态力学性能的细观力学方法述评

混凝土力学特性是大坝、海洋平台等工程结构抗震设计及仿真分析的前提条件之一,也是目前研究的薄弱环节. 混凝土是一种典型的非均质材料,其宏观力学特性由细观组成来决定.本文总结了目前研究混凝土宏观力学特性的细观力学分析方法,细观有限元法及理论分析法; 阐述了界面过渡区(ITZ)对混凝土性能的影响,简单介绍了混凝土界面过渡区问题的研究现状;介绍了作者提出的混凝土宏观力学性能研究的细观单元等效化分析方法.最后对其未来发展的一些方向和有待进一步研究的问题作了总结.      

Modelling of a single drop impact onto liquid film using particle method

The process of single liquid drop impact on thin liquid surface is numerically simulated with moving particle semi‐implicit method. The mathematical model involves gravity, viscosity and surface tension. The model is validated by the simulation of the experimental cases. It is found that the dynamic processes after impact are sensitive to the liquid pool depth and the initial drop velocity. In the cases that the initial drop velocity is low, the drop will be merged with the liquid pool and no big splash is seen. If the initial drop velocity is high enough, the dynamic process depends on the liquid depth. If the liquid film is very thin, a bowl‐shaped thin crown is formed immediately after the impact. The total crown subsequently expands outward and breaks into many tiny droplets. When the thickness of the liquid film increases, the direction of the liquid crown becomes normal to the surface and the crown propagates outward. It is also found that the radius of the crown is described by a square function of time: r_C = [c(t ? t₀)]^0.5. When the liquid film is thick enough, a crown and a deep cavity inside it are formed shortly after the impact. The bottom of the cavity is initially oblate and then the base grows downward to form a sharp corner and subsequently the corner moves downward. Copyright © 2004 John Wiley & Sons, Ltd.     

Numerical study of spherical blast-wave propagation and reflection

The objective of this study is to understand the flow structures of weak and strong spherical blast waves either propagating in a free field or interacting with a flat plate. A 5th-order weighted essentially non-oscillatory scheme with a 4th-order Runge-Kutta method is employed to solve the compressible Euler/Navier-Stokes equations in a finite volume approach. The real-gas effects are taken into account when high temperature occurs. A shock-tube problem with the real-gas effect is first tested in order to verify the solver accuracy. Moreover, unsteady shock waves moving over a stationary wedge with various wedge angles, resulting in different types of shock wave reflections, are also tested. It is found that the computed results agreed well with the existing data. Second, the propagation of a weak spherical blast wave, created by rupture of a high-pressure isothermal sphere, in a free field is studied. It is found that there are three minor shock waves moving behind the main shock. Third, the problem of a strong blast wave interacting with a flat plate is investigated. The flow structures associated with single and double Mach reflections are reported in detail. It is found that there are at least three local high-pressure regions near the flat plate. Received 27 July 2000 / Accepted 25 January 2002 – Published online 17 June 2002     

Toward more rational criteria for determination of design earthquake forces

The preliminary design of most buildings is based on equivalent static forces specified by the governing building code. The height wise distribution of these static forces seems to be based implicitly on the elastic vibration modes. Therefore, the employment of such a load pattern in seismic design of normal structures does not guarantee the optimum use of materials. This paper presents a new method for optimization of dynamic response of structures subjected to seismic excitation. This method is based on the concept of uniform distribution of deformation. In order to obtain the optimum distribution of structural properties, an iterative optimization procedure has been adopted. In this approach, the structural properties are modified so that inefficient material is gradually shifted from strong to weak areas of a structure. This process is continued until a state of uniform deformation is achieved. It is shown that the seismic performance of such a structure is optimal, and behaves generally better than those designed by conventional methods. By conducting this algorithm on shear-building models with various dynamic characteristics subjected to 20 earthquake ground motions, more adequate load patterns are introduced with respect to the period of the structure and the target ductility demand.