测量加筋沥青混凝土内的裂缝扩展

利用2种不同的方法加筋沥青罩面:①在沥青混合料中加入短切玻璃纤维改善沥青混凝土的特性,②采用玻璃格珊加筋沥青混凝土.应用断裂力学方法分析沥青路面裂缝扩展机理.采用沥青混合料设计试验、三点弯曲试验和疲劳裂缝扩展试验,确定加筋沥青混凝土的临界应力强度因子KIC,测量每一种沥青罩面抗裂系统的裂缝扩展速率.本研究的主要特点是提出复合型抗裂罩面系统,分析了多层加筋沥青罩面裂缝扩展过程,推荐了若干沥青路面抗裂系统.结果证明,加筋材料可以提高沥青罩面的抗裂特性,复合型抗裂罩面系统能够有效地阻止反射裂缝的扩展.     

Evaluation of accelerated deterioration in NAPTF flexible test pavements

Previous research studies have successfully demonstrated the use of artificial neural network （ANN） models for predicting critical structural responses and layer moduli of highway flexible pavements. The primary objective of this study was to develop an ANN-based approach for backcalculation of pavement moduli based on heavy weight deflectometer （HWD） test data, especially in the analysis of airport flexible pavements subjected to new generation aircraft （NGA）. Two medium-strength subgrade flexible test sections, at the National Airport Pavement Test Facility （NAPTF）, were modeled using a finite element （FE） based pavement analysis program, which can consider the non-linear stress-dependent behavior of pavement geomaterials. A multi-layer, feed-forward network which uses an error-backpropagation algorithm was trained to approximate the HWD back- calculation function using the FE program generated synthetic database. At the NAPTF, test sections were subjected to Boeing 777 （B777） trafficking on one lane and Boeing 747 （B747） trafficking on the other lane using a test machine. To monitor the effect of traffic and climatic variations on pavement structural responses, HWD tests were conducted on the trafficked lanes and on the untrafficked centerline of test sections as trafficking progressed. The trained ANN models were successfully applied on the actual HWD test data acquired at the NAPTF to predict the asphalt concrete moduli and non-linear subgrade moduli of the medium-strength subgrade flexible test sections.     

适应西藏高原环境的沥青抗紫外线老化试验研究

紫外线是导致西藏高原沥青路面早期损害的主要原因之一．根据实测的紫外线辐射水平,进行了不同掺量的3种纳米级抗紫外线老化剂（TiO2,CeO2和炭黑）的SBR沥青紫外线老化试验．针对老化后的沥青,进行了常规指标（TFOT后的针入度比、软化点）和SHRP指标的评价．针对已老化不同时间（500,1000和1500h）的、掺加0．8％炭黑的沥青,分别进行了红外光谱分析．采用灰色关联分析法,确定了抗紫外线老化剂的最佳掺量．结果表明,TiO2和CeO2不仅是好的紫外线吸收或屏蔽剂,而且是一种强氧化剂;炭黑是良好的抗紫外线老化剂,其最佳掺量为沥青质量的0．8％;沥青紫外线老化主要发生在老化前期,老化时间越长老化越严重．     

用于开启桥的轻质环氧沥青混凝土桥面铺装力学性能(英文)

拟定质量替代百分数分别为0%,15%,25%,40%,70%的碎石型陶粒环氧沥青混合料和圆型陶粒环氧沥青混合料,进行高温抗车辙性能、水稳定性及低温弯曲性能试验.采用有限元方法分析开启桥在行车和开启2种状态下的力学响应.最后成型含钢桥面板、防水黏结层及环氧沥青混凝土的复合结构试件来验证2451型环氧沥青黏结料的界面黏结强度.研究结果表明,质量替代百分数分别为0%,15%,25%,40%,70%的陶粒环氧沥青混合料均能满足钢桥面铺装的力学性能要求.替代百分数为70%的圆型陶粒环氧沥青混合料由于其在减轻铺装质量等方面的优势被推荐为开启桥桥面铺装用的首选材料.桥面铺装层间剪应力随着开启角度的增大而增大,并在开启角度达到最大值85°时达到峰值.通过室内试验结果可知,天津响螺湾立转式开启桥在桥面铺装铺筑完成并养生3d后可进行首次开启.     

Towards fully automatic modelling of the fracture process in quasi-brittle and ductile materials: a unified crack growth criterion

Fully automatic finite element （FE） modelling of the fracture process in quasi-brittle materials such as concrete and rocks and ductile materials such as metals and alloys, is of great significance in assessing structural integrity and presents tremendous challenges to the engineering community. One challenge lies in the adoption of an objective and effective crack propagation criterion. This paper proposes a crack propagation criterion based on the principle of energy conservation and the cohesive zone model （CZM）. The virtual crack extension technique is used to calculate the differential terms in the criterion. A fully-automatic discrete crack modelling methodology, integrating the developed criterion, the CZM to model the crack, a simple remeshing procedure to accommodate crack propagation, the J2 flow theory implemented within the incremental plasticity framework to model the ductile materials, and a local arc-length solver to the nonlinear equation system, is developed and implemented in an in-house program. Three examples, i.e., a plain concrete beam with a single shear crack, a reinforced concrete （RC） beam with multiple cracks and a compact-tension steel specimen, are simulated. Good agreement between numerical predictions and experimental data is found, which demonstrates the applicability of the criterion to both quasi-brittle and ductile materials.     

汽车座椅的安全性设计

座椅是影响汽车安全性的重要部件，汽车座椅安全性设计的目标就是尽可能避免座椅安全功能失效情况的发生。在讨论汽车座椅安全性设计主要内容的基础上，分析了有限无法在座椅安全性设计中的应用，并举例说明采用有限元法进行座椅安全性设计的一般过程，对汽车座椅的安全性设计有指导意义。     

改善沥青路面平整度的几点施工技术措施

沥青混凝土面层平整度的好坏,直接影响到行车的舒适性。而实际施工中由于对平整度这一指标控制不严,开放交通后,时常有行车抖动、跳车及失重感等现象发生,不仅使行车舒适性受到影响,而且在长期行车栽荷的作用下,容易继续发展为搓板、拥抱,引发交通事故,导致路面过早破坏。本文简述了沥青路面不平整的原因,从施工的各个环节分析了保证路面平整度的主要技术措施。     

温度影响下的橡胶沥青应力吸收层的应力分析

高温开裂已经成为沥青路面的主要危害之一。橡胶沥青是良好的沥青改性剂,其具有吸收应力,改善沥青高温性能、延长路面使用寿命、延缓反射裂缝等优点。利用ABAQUS有限元软件,选取15℃、20％和60℃下沥青路面的热特性参数,分析在不同温度下橡胶沥青应力吸收层对半刚性基层路面结构和柔性基层路面结构的应力应变规律,推荐合理的沥青路面结构层设计参数,为工程实践提供理论依据。     

反复张力下V形切口圆条的表面裂纹的疲劳扩展

研究目的：在相同的反复张力下,研究V形切口圆条表面裂纹的疲劳扩展规律。研究方法：1.构建V形切口圆条模型（图1）,基于线性二次元将模型表面离散成一个个网格点（图2）;2.以AZ-6A-T5镁合金为例,利用J积分计算应力强度因数,利用NASGRO裂纹增长率模拟裂纹的疲劳扩展;3.通过研究不同的裂纹纵横比和对应的应力强度因数之间的相关性来研究裂纹的扩展。重要结论：1.在裂纹扩展时裂纹纵横比的初始值对断裂形状的发展有重要影响;2.裂纹纵横比对疲劳负荷寿命的作用比缺口半径更加明显;3.当裂纹前缘演变成一条直线形时可观察到不稳定的裂纹扩展;4.裂纹深度一定时,断裂纵横比越小,疲劳负荷寿命越短;5.当裂纹纵横比为0.6-0.7时,出现了不稳定的裂纹扩展。     

Calculation Model of Equivalent Strength for Induced Crack Based on Double-K Fracture Theory and Its Optimizing Setting in RCC Arch Dam

By means of fracture testing on roller-compacted concrete (RCC) three-point bending beams with two different specimen sizes, the P-CMOD complete curve for RCC was gained. Furthermore, by applying double-K fracture theory, KIC^ini,KIC^un, as well as the critical effective crack length and the critical crack tip opening displacement, were evaluated. Based on the double-K fracture parameters above, the calculation model of equivalent strength for induced crack was established, thus the calculation method on its initiation, stable propagation and unstable fracture was ascertained. Moreover, the finite element simulation analysis of stress field in ShaPai arch dam and the on-site observational splaying points of induced crack at different altitudes validated the reliability of the model. Finally, crack inducer‘s optimal setting in RCC arch dam was studied. It improves the design level of induced crack in RCC arch dam and satisfies the necessity of engineering practice.     

Finite element simulation of stress intensity factors in elastic-plastic crack growth

INTRODUCTION The finite element method (FEM) has been widely employed for solving linear elastic and elas-tic-plastic fracture problems. The evaluation of stress intensity factors in 2D geometries by FEM is a tech-nique widely used for non-standard crack configura-tions. Basically, there are two groups of estimation methods, those based on field extrapolation near the crack tip (Chan et al., 1970; Shih et al., 1976) and those using the energy release when the crack propagates. However…     

沥青路面微波加热器电磁仿真与实验分析

为了研究微波加热再生沥青路面时的热电效率和再生温度分布的均匀性,设计了一种波导激励腔,并应用于微波加热器的结构设计.运用波导传输线理论,确定了激励腔的结构尺寸.采用IE3D分别对磁控管探头(天线)与短路板间距、不同喇叭长度和口面尺寸、不同沥青混合料介电性能和加热腔口面与沥青路面不同距离4种情况进行了电磁仿真.结果表明:...     

正交异性钢桥面铺装有限元模拟和优化分析

为了确定正交异性钢桥面铺装受力状态并为设计提供参考,运用子模型有限元法分析了桥梁整体变形及局部轮载作用下铺装内部受力状态及应变分布特点.为优化设计铺装层结构,分析了铺装层模量对其应变状态影响.分析结果表明:大跨径钢桥整桥变形对铺装层受力状态影响很小,钢桥面铺装设计的控制受力因素是轮载局部作用下铺装层的横向应变,铺装层模量对铺装层的受力状态有显著影响,通过提高铺装层刚度过渡层的结构优化设计措施可以显著改善铺装层的受力状态,降低铺装层的应变水平.分别对环氧沥青混凝土、SBS改性沥青SMA和Rosphalt改性沥青混凝土的模量及疲劳性能进行了试验评价,可以为桥面铺装结构组合设计提供参考数据.     

Fracture behavior characteristic of ceramic reinforced metal-base coatings

The fracture behavior of a ceramic reinforced metal-base coating prepared by high velocity arc spraying (HVAS)technology in three-point bending test was studied.Moreover,finite element analysis(FEA)was adopted to analyze the stress distribution in the crack front.It can be found that the crack norrnal to the interface in the coatings occurred at the location where a fixed moment of force was reached.So the critical moment can be taken as thecoating cracking criterion,which was confirmed by FEA results.In addition,the stress levels at three different locations where cracks occurred near the interface are almost the same.The results will provide reference for the design of coatings and the structure integrity evaluation of coating/substrate systems.     

筋条部分开裂复合材料加筋板后屈曲性态的有限元分析

采用参考面单元技术并引入虚拟杆单元,建立筋条局部脱胶开裂复合材料梁／板结构后屈曲分析的有限元简化模型。着重研究不同开裂尺寸和位SLM置对复合材料层合加筋板后屈曲承载能力的影响。计算表明：开裂位置相同,开裂尺寸增加会导致后屈曲承载能力降低;开裂尺寸相同,随着其位置由筋条中心向端部移动,加筋板的后屈曲承载能力逐渐上升;值得注意的是,筋条端部开裂使加筋板的后屈曲承栽能力显著降低,其影响远大于筋条中心位置开裂。     

基于离散元方法的沥青混合料虚拟断裂试验(英文)

为了深入研究沥青混合料开裂特性, 设计了基于沥青混合料二维数字试件的断裂虚拟试验. 在考虑混合料二维截面的集料数量级配和集料不规则形状的基础上, 通过生成程序建立了沥青混合料的二维虚拟试件; 运用离散元方法, 建立了混合料二维离散元模型, 并进行了虚拟的中点弯曲小梁断裂试验; 为了验证虚拟试验方法的正确性, 在实验室内进行了沥青混合料小梁的中点弯曲断裂试验. 室内实体试验与虚拟试验结果的比较发现, 虚拟断裂试验获得的混合料断裂强度与室内试验结果一致, 表明虚拟断裂试验可以作为混合料断裂性能分析的辅助手段.     

Optimal design of pressure vessel using an improved genetic algorithm

As the idea of simulated annealing （SA） is introduced into the fitness function, an improved genetic algorithm （GA） is proposed to perform the optimal design of a pressure vessel which aims to attain the minimum weight under burst pressure constraint. The actual burst pressure is calculated using the arc-length and restart analysis in finite element analysis （FEA）. A penalty function in the fitness function is proposed to deal with the constrained problem. The effects of the population size and the number of generations in the GA on the weight and burst pressure of the vessel are explored. The optimization results using the proposed GA are also compared with those using the simple GA and the conventional Monte Carlo method.     

Flat-type permanent magnet linear alternator: A suitable device for a free piston linear alternator

We proposed the flat-type permanent magnet linear alternator （LA） for free piston linear alternators （FPLAs） instead of the tubular one. Using the finite element method （FEM）, we compare these two kinds of LAs. The FEM result shows that the flat-type permanent magnet LA has higher efficiency and larger output specific power than the tubular one, therefore more suitable for FPLAs, and that the alternator design can be optimized with respect to the permanent magnet length as well as the air gap.     

ABAQUS在贫混凝土基层沥青路面结构计算中的应用

主要介绍了有限元通用软件ABAQUS在贫混凝土基层沥青路面中的应用问题．介绍了贫混凝土基层沥青路面温度应力的计算原理,以通用有限元软件ABAQUS为基础,采用三维有限元法,对开级配大粒径沥青碎右缓解层沥青路面的温度应力进行分析,探讨了路面结构层参数对温度应力的影响规律,为寻求开级配大粒径沥青碎石缓解层沥青路面的结构设计方法提供理论基础及依据．     

轻钢结构临建房屋骨架结构有限元计算分析

以轻钢结构临建房屋骨架结构试验为基础,采用有限元分析软件Ansys提出轻钢结构临建房屋的有限元计算模型建立方法,并对轻钢结构临建房屋骨架结构的水平侧移进行计算和分析。计算结果表明,所采用的有限元计算模型建立方法正确合理,且轻钢结构临建房屋骨架结构在设计荷载作用下的水平侧移不能满足规范要求。