講座題目：提高抵抗裂紋擴(kuò)展能力：韌性,、粗糙度與微結(jié)構(gòu)設(shè)計(jì)

Toughness, Roughness and the Possibility of Microstructure Design for Improved Crack Growth Resistance

報(bào) 告 人：Alan Needleman

時(shí) 　 間：2019年10月21日(周一)15:00-17:00

地 　 點(diǎn)：中關(guān)村校區(qū)研究生教學(xué)樓101報(bào)告廳

主辦單位：研究生院,、先進(jìn)結(jié)構(gòu)技術(shù)研究院

報(bào)名方式：登錄北京理工大學(xué)微信企業(yè)號(hào)---第二課堂---課程報(bào)名中選擇“【百家大講堂】第247期：提高抵抗裂紋擴(kuò)展能力：韌性、粗糙度與微結(jié)構(gòu)設(shè)計(jì)”

【主講人簡(jiǎn)介】

  Alan Needleman,，美國(guó)德克薩斯A&M大學(xué)材料科學(xué)與工程學(xué)院特聘教授,。1966年于賓夕法尼亞大學(xué)獲得學(xué)士學(xué)位，1971年于哈佛大學(xué)在J.W. Hutchinson教授指導(dǎo)下獲得固體力學(xué)博士學(xué)位,。Needleman教授曾先后于麻省理工學(xué)院,、布朗大學(xué)等任教，并于2015年加入美國(guó)德克薩斯A&M大學(xué)擔(dān)任特聘教授,。其已發(fā)表學(xué)術(shù)論文300余篇,，涉及結(jié)構(gòu)材料的變形與斷裂模擬,，孔洞形核,、生長(zhǎng)和交匯引起的延性斷裂，晶體材料塑性變形的多尺度模擬,，時(shí)間相關(guān)和率相關(guān)的塑性流動(dòng)模擬,，塑性材料中裂紋擴(kuò)展以及動(dòng)態(tài)裂紋擴(kuò)展等領(lǐng)域。他于1989年當(dāng)選美國(guó)機(jī)械工程學(xué)會(huì)會(huì)士,、1995年當(dāng)選美國(guó)力學(xué)學(xué)會(huì)會(huì)士,，并于2000年當(dāng)選美國(guó)工程院院士、2006年當(dāng)選美國(guó)人文與科學(xué)院院士,，于2018年當(dāng)選 ASME榮譽(yù)會(huì)員,。

Alan Needleman is the Distinguished Professor of Department of Materials Science & Engineering at Texas A&M University. He earned a B. S. at the university of Pennsylvania. He completed his Ph.D. in solid mechanics at Harvard University under the supervision of Professor J. W. Hutchinson. He used to work at MIT and Brown University and he joined the Texas A&M university as the Distinguished Professor. He has published over 300 scientific papers on such subjects as computational modeling of deformation, fracture processes in structural materials, ductile fracture by void nucleation, growth and coalescence, multi-scale modeling of plastic deformation of crystalline solids, modeling of time and rate dependent plastic flow, crack growth in plastically deforming solids and dynamic crack growth. In 1989, he was advanced to Fellow grade in the American Society of Mechanical Engineers. In 1995, he was elected as fellow of American Academy of Mechanics. In 2000, Needleman was elected to the U.S. National Academy of Engineering. In 2006, he was elected as a member of American Academy of Arts & Sciences. In 2018, he was elected as Honorary Member of ASME.

【講座信息】

  在斷裂的力學(xué)與物理領(lǐng)域中存在兩個(gè)基本問(wèn)題：一,、材料微觀結(jié)構(gòu)特征與其抵抗裂紋擴(kuò)展的能力之間存在怎樣的關(guān)系？二,、材料微觀結(jié)構(gòu)特征與斷裂表面的粗糙度之間存在怎樣的關(guān)系,？而由此可以提出另外一個(gè)問(wèn)題：材料抵抗裂紋擴(kuò)展的能力和斷裂表面粗糙度之間是否存在對(duì)應(yīng)關(guān)系？1984年,，Mandelbrot及其同事發(fā)現(xiàn)斷裂表面表現(xiàn)出自仿射,、類分形的特征?；谶@一觀測(cè)結(jié)果以及圖像分析的進(jìn)展,，物理學(xué)界進(jìn)行了大量對(duì)斷裂表面粗糙度的定量表征工作，試圖將分形維數(shù)與抵抗裂紋擴(kuò)展能力聯(lián)系起來(lái),。盡管這一嘗試在當(dāng)時(shí)沒(méi)有成功,，但從它出發(fā)可以提出一個(gè)基本問(wèn)題，即斷裂表面粗糙度的何種度量（如果存在的話）可以與材料抵抗裂紋擴(kuò)展能力建立聯(lián)系,?；趯?duì)延性斷裂問(wèn)題的模擬，主講人Needleman教授提出了一種斷裂表面粗糙度的統(tǒng)計(jì)度量,，該度量可以與抵抗裂紋擴(kuò)展能力建立定量關(guān)系,，并且也可以與可測(cè)、可控的微觀結(jié)構(gòu)特征建立聯(lián)系,。模擬中考慮了兩種理想化的微觀結(jié)構(gòu)：一種涉及穿過(guò)分布式第二相顆粒的裂紋擴(kuò)展,，另一種涉及沿晶界的裂紋擴(kuò)展。最后將討論通過(guò)材料微觀結(jié)構(gòu)設(shè)計(jì)來(lái)提高其抵抗裂紋擴(kuò)展的能力,。

Two fundamental questions in the mechanics and physics of fracture are: (i) What is the relation between observable features of a material's microstructure and its resistance to crack growth? and (ii) What is the relation between observable features of a material's microstructure and the roughness of the fracture surface? An obvious corollary question is: What is the relation, if any, between a material's crack growth resistance and the roughness of the corresponding fracture surface? In 1984, Mandelbrot and co-workers showed that fracture surfaces exhibit self-affine, fractal-like scaling properties. This observation, together with advances in image analysis, precipitated a significant body of work in the physics community on the quantitative characterization of fracture surface roughness with the aim of relating the fractal dimension to crack growth resistance. While this effort was not successful, it raised the question of what measure, if any, of fracture surface roughness can be related to crack growth resistance. I will describe work on modeling ductile fracture that reveals a measure of the statistics of fracture surface roughness that can be quantitatively related to crack growth resistance and how this quantity relates to a measurable and (hopefully) controllable microstructural feature. Simulation results for two idealized microstructures will be discussed: one microstructure involves crack growth through a distribution of second phase particles and the other involves crack growth along grain boundaries. The implications for designing material microstructures with improved crack growth resistance will be discussed.