道路外文翻譯----對柔性路面面層開裂的三維有限元分析

1、<p>　　附錄1：外文文獻(xiàn)翻譯</p><p>　　對柔性路面面層開裂的三維有限元分析</p><p>　　Hasan Ozer, Imad L. Al-Qadi* and Carlos A. Duarte</p><p>　　美國伊利諾伊大學(xué)厄本那—香檳分校，土木與環(huán)境工程系, IL 61801</p><p>　　摘要：靠近路

2、面表層的開裂是導(dǎo)致道路壽命縮短的主要因素之一。重交通荷載、施工缺陷、表層混合料的特征是導(dǎo)致路面表層開裂的主要原因。此外，形狀不規(guī)則的輪胎與路面的接觸力有可能在路面表層附近產(chǎn)生極其復(fù)雜的應(yīng)力狀態(tài)。在這種條件下預(yù)測裂紋擴(kuò)展需要對多種路面結(jié)構(gòu)狀態(tài)如應(yīng)力、應(yīng)變、位移做高精度計(jì)算。廣義有限元方法（GFEM）提供了一個計(jì)算框架，當(dāng)使用一個擴(kuò)展的策略時，裂縫在有限單元網(wǎng)格中可能沿任意方向發(fā)展。此擴(kuò)展方法在GFEM中也能提高多項(xiàng)式近似計(jì)算的精度。使用G

3、FEM時會對地表層裂縫執(zhí)行三維分析，建立持久路面結(jié)構(gòu)的大型三維模型，在不同位置插入裂縫。擁有集料規(guī)模缺陷的持久路面結(jié)構(gòu)的數(shù)值試驗(yàn)揭示了雙輪胎下路面斷裂的復(fù)雜情形。</p><p>　　關(guān)鍵詞：由上而下產(chǎn)生裂縫（top-down crack）；廣義有限元法；混合模型；持久路面；</p><p><b>　　1. 簡介</b></p><p>　

4、　靠近上面層的裂縫，即自上而下開展的裂縫（top-down cracking，以下簡稱“上貫縫”），一直被認(rèn)為是柔性路面的主要損壞形式之一。隨著長效路面，即人們所認(rèn)為的持久路面建設(shè)率的增加，這種損壞現(xiàn)象也隨之增加。這些路面常為了增加壽命而有較厚的瀝青混合料層。在這種情況下，裂縫只限于表面。然而，人們還沒有弄明白靠近路面表層的結(jié)構(gòu)層。研究“上貫縫”的學(xué)者在沒有識別裂縫產(chǎn)生的位置的情況下，就導(dǎo)致開裂的原因達(dá)成共識。不規(guī)則的輪胎接觸壓力、橫向

5、組件與溫度荷載時主要因素。由于粘結(jié)劑的老化和分離，剛度梯度的變化成了另一個增加裂縫發(fā)展的因素。</p><p>　　許多學(xué)者通過現(xiàn)場調(diào)查研究了這一復(fù)雜的現(xiàn)象。利用多種數(shù)值方法分析、實(shí)驗(yàn)室模擬和大規(guī)模的測試，De freitas et al.在2005年識別出了幾個導(dǎo)致上貫縫產(chǎn)生的原因，開始利用實(shí)驗(yàn)室、三維有限元法（FE）評估了其中的一些原因。這些原因包括粘結(jié)劑種類、粘結(jié)劑用量、集料等級、孔隙率大小、溫度。在車輪輪

6、跡帶裝置下，表層裂縫同車輪下路面的極端永久變形有關(guān)。當(dāng)時發(fā)現(xiàn)層間分離對產(chǎn)生表面裂縫影響最大。裂縫發(fā)生在行車道上。在另一個試驗(yàn)中，Rolt（2000）進(jìn)行了一個大規(guī)模的路面設(shè)計(jì)試驗(yàn)，來分析粘結(jié)層老化對于路面產(chǎn)生裂縫的影響。這項(xiàng)研究僅做了熱帶地區(qū)試驗(yàn)。研究得出在此熱帶環(huán)境下下，多種粘結(jié)層的老化是產(chǎn)生上貫縫的基本原因。Tsoumbanos（2006）在澳大利亞墨爾本地區(qū)檢查了永久路面的工作性能。根據(jù)研究調(diào)查，上貫縫逐漸成為永久路面主要的失效模

7、式。表面裂縫限制在路面層40～60mm深度之內(nèi)。從調(diào)查網(wǎng)站取得的核心數(shù)據(jù)顯示表面裂縫從垂直線沿特定角度發(fā)展。</p><p>　　Kim 等人(2009b)利用軸對稱粘彈有限元（FE）模型研究了表層沿縱向輪跡帶的開裂。在輪胎下發(fā)現(xiàn)關(guān)鍵的拉伸應(yīng)變，采用了基于能量耗散的模型來預(yù)測上貫縫。根據(jù)這個模型，在預(yù)設(shè)的關(guān)鍵位置重復(fù)加載來計(jì)算能量的耗散。當(dāng)耗散能量達(dá)到某一閾值時，裂縫就會產(chǎn)生。Myers和Roque（2011）利

8、用斷裂力學(xué)和有限元（FE）模型分析了表面輪跡帶裂縫的產(chǎn)生。根據(jù)這項(xiàng)研究的成果，裂縫發(fā)展的原因首先來至于張力，路面結(jié)構(gòu)和軸載譜對裂縫影響也很重要。將不同長度的裂縫插入二維有限元模型中，由這個研究中改進(jìn)的有限元模型進(jìn)行敏感性分析。根據(jù)敏感性分析，熱拌瀝青混合料（HMA）的厚度和剛度對裂縫的影響最小，但輪胎和地面的橫向作用應(yīng)力被認(rèn)為是導(dǎo)致橫向開裂的主要原因。</p><p>　　Sangpetngam（2004）等人使

9、用邊界元法（BEM）預(yù)測裂縫在柔性路面的產(chǎn)生。在距輪跡邊緣952.5mm處的表面插入12.7mm長的裂縫，使用模型I的應(yīng)力強(qiáng)度因子（SIF）KI作為產(chǎn)生裂縫的因素來計(jì)算。根據(jù)敏感度分析的結(jié)果，發(fā)現(xiàn)熱拌瀝青混合料層的剛度變化是使裂縫擴(kuò)張的很大的原因。這些人同時談到BEM模型在解決裂縫插入困難當(dāng)中的優(yōu)勢。Wang（2007）等人建議根據(jù)機(jī)械經(jīng)驗(yàn)法（mechanistic –empirical）將貫裂縫融入路面設(shè)計(jì)協(xié)議書中，在佛羅里達(dá)州機(jī)械經(jīng)

10、驗(yàn)法被認(rèn)為是路面失效的主要模式。他們使用散失能量比的概念來描述路面損壞及產(chǎn)生裂縫程度。層狀彈性理論被用來預(yù)測應(yīng)力及位移的發(fā)生，由此導(dǎo)致裂縫的產(chǎn)生。Al-Qadi（2008）等人，包括Elseifi（2005,2006）、Wang和AL-Qadi（2009）、Yoo和Al-Qadi（2007）等，研究了新一代的雙輪寬胎荷載對路面開裂特別是近表層失效的影響。將真實(shí)的輪胎荷載與3D動態(tài)和粘彈模型相結(jié)合，分析了剪應(yīng)力在表面開裂的產(chǎn)生的作用。&l

11、t;/p><p>　　對縱貫縫的分析以及將其納入路面設(shè)計(jì)協(xié)議中是一項(xiàng)重大的挑戰(zhàn)。主要的挑戰(zhàn)是準(zhǔn)確確定裂縫產(chǎn)生位置并精確計(jì)算出不規(guī)則輪胎接觸下的應(yīng)力應(yīng)變。傳統(tǒng)的條狀或帶狀分析無法對路面裂縫的產(chǎn)生提供必要的條件。輪胎與路面的接觸在路面表面及接近荷載的位置越來越重要。結(jié)果可能是產(chǎn)生極其復(fù)雜的拉伸與壓縮相混合的破壞模式。此外，由于接近表面的粘結(jié)劑因氧化而老化，其剛度的變化成為導(dǎo)致路表面及附近的情形變的更加復(fù)雜的又一因素。老化

12、不但改變了表面材料的剛度，而且改變了破裂的特征。因此，真實(shí)的車輪荷載應(yīng)力分析及三維模型分析對于計(jì)算交通荷載的應(yīng)力是必不可少的。其次，這個用于計(jì)算應(yīng)力、預(yù)測裂縫產(chǎn)生發(fā)展的模型應(yīng)該可以分析混合模式的斷裂問題。</p><p>　　廣義有限元（GFEM）模型、擴(kuò)展有限元模型（XFEM），與標(biāo)準(zhǔn)有限元方法不同，主要用于解決具有復(fù)雜形狀、復(fù)雜應(yīng)力狀態(tài)以及多尺度應(yīng)用程序的問題。這些方法也被稱為是統(tǒng)一分區(qū)（partition

13、of unity PoU）法，它們有可能克服困難，解決網(wǎng)格設(shè)計(jì)和有限元計(jì)算法無法攻克的例如裂縫不連續(xù)、材料接口等難題。早期用于解決三維開裂難題的GFEM、XFEM模型可以分別在Duarte、Oden（1996a）、Duarte et al.（2000，2001）、Belytschko et al.（2001）等人的工作找到。</p><p>　　本研究的主要目的是分析較厚的路面結(jié)構(gòu)下，靠近表層的結(jié)構(gòu)層（表層下結(jié)構(gòu)

14、層）在雙輪配置的荷載下的開裂問題。用GFEM作為數(shù)值工具查找三維格柵中裂縫的準(zhǔn)確位置。假定路面結(jié)構(gòu)層在總體規(guī)模上存在缺陷，這些缺陷以半便士形或圓形按不同的位置以不同方向插入路表層下的結(jié)構(gòu)層。這些裂縫規(guī)模不足全球總量的1%。在這項(xiàng)研究中假定了材料的彈性性質(zhì)，采用了線彈性斷裂力學(xué)理論。將這一方法（GFEM）擴(kuò)展到粘彈性材料是一個正在研究的項(xiàng)目。</p><p>　　注：本文節(jié)選原文對道路有限元原理及發(fā)展歷史的介紹部分

15、</p><p>　　附錄2：外文文獻(xiàn)原文</p><p>　　A three-dimensional generalised finite element analysis for the near-surface cracking problem in flexible pavements</p><p>　　Hasan Ozer, Imad L. Al-Qad

16、i* and Carlos A. Duarte</p><p>　　Department of Civil and Environmental Engineering, University of Illinois at Urbana Champaign, Urbana, IL 61801, USA</p><p>　　Department of Civil and Environment

17、al Engineering, University of Illinois at Urbana Champaign, Urbana, IL 61801, USA Near-surface cracking is one of the major distress types which results in reducing pavement service life. Heavy traffic loads, constructio

18、n deficiencies, and surface mixture characteristics are among the predominant factors contributing to nearsurface cracking. In addition, non-uniform tire-pavement contact stresses have a potential to generate extremely c

19、omplex stress states near</p><p>　　Keywords: top-down; GFEM; mixed-mode; long-lasting; pavement</p><p>　　1. Introduction</p><p>　　Near-surface cracking, also known as top-down crack

20、ing, in flexible pavements has been recognised as one of the major modes of distress types. This phenomenon increases with the increasing rates of constructing long-lasting pavement, also known in the market as perpetual

21、 pavement. These pavements usually have a relatively thick asphalt mixture layer to extend pavement life. In this case, cracking is only confined to the surface. However, the mechanisms of near-surface cracking have not

22、yet been </p><p>　　Many researchers studied this complex phenomenon by conducting field surveys, utilising various numerical methods and performing laboratory and large-scale tests. De Freitas et al. (2005)

23、identified several factors on topdown cracking initiation and evaluated some of these factors using laboratory tests and a 3D finite element (FE) analysis. These factors were identified as binder type, binder content, ag

24、gregate gradation, air void content and temperature. Surface cracks were associated with the</p><p>　　Kim et al. (2009b) investigated surface initiated longitudinal wheel-path cracking using a viscoelastic a

25、xisymmetric FE model. A critical tensile strain was identified right under the tires. A dissipated energy-based model was used to predict top-down cracking. According to this model, dissipated energy was computed under r

26、epeated applications of loading at the predefined critical locations. Crack initiation was predicted when the dissipated energy reached a certain threshold. Myers and Roque (2</p><p>　　Sangpetngam et al. (20

27、04) used the boundary element method (BEM) to predict the initiation of surface cracks in flexible pavements. A crack of 12.7mm was inserted on the surface and 952.5mm away from the tire edge. Mode-I stress intensity fac

28、tor (SIF) KI was computed as the crack driving force. According to the results from a sensitivity analysis, stiffness gradient in the HMA layer was recognised as an influential factor increasing the magnitude of crack dr

29、iving forces. The authors also comment</p><p>　　The analysis of top-down cracking and its integration into a pavement design protocol poses significant challenges. The major challenges are to identify the cr

30、itical locations of crack initiation and to develop accurate computation of stresses and strains under nonuniform contact stresses. The conventional beam or platelike analysis does not provide necessary conditions for cr

31、ack initiation on the surface of a pavement. Tire– pavement interaction becomes increasingly important on the surface and</p><p>　　The generalized FE method (GFEM) and the extended FE method (XFEM) are the t

32、wo alternatives to the standard FE method (FEM) for problems with complex geometry, loading conditions and also multi-scale applications. These methods are also known as partition of unity (PoU) methods. They are promisi

33、ng candidates to overcome mesh design and computational issues of the FEM for the problems with discontinuities such as cracks, material interfaces and so on. Early developments on the GFEM and XFEM for s</p><

34、p>　　The objective of this study is to analyse near-surface cracking under a dual tire configuration on a relatively thick pavement structure. The GFEM is utilised as the numerical tool to find critical locations for c

35、rack initiation in a 3D mesh. The pavement structure is assumed to have existing defects at the aggregate scale. These defects are in the form of half-penny and circular cracks inserted at different locations and orienta