Johns Hopkins University
Baltimore, MD 21218
Modeling Ductile Fracture Toughness and Fracture Surface Roughness
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? (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? I will report on recent calculations of mode I ductile crack growth aimed at addressing these questions. At room temperature, ductile fracture of structural metals generally occurs by the nucleation, growth and coalescence of micron scale voids. In the calculations, an elastic-viscoplastic constitutive relation for a progressively cavitating plastic solid is used to model the material. A characteristic length is needed, if only from dimensional considerations, to predict fracture toughness and in the calculations this is introduced via a discretely modeled microstructural feature such as the spacing of inclusions that nucleate voids. The crack growth resistance is quantified in terms of JIC and the tearing modulus, TR. The Hurst exponent of the correlation function of the fracture surface height distribution, a quantity typically used to characterize the fracture surface roughness, is also calculated. In addition, we go beyond the characterization of fracture surface roughness by the correlation function and investigate the full statistics of the fracture surface roughness. Possible connections between quantitative measures of crack growth resistance and quantitative measures of fracture surface roughness are explored and related to the nature of the ductile crack growth process.
About the Speaker
Alan Needleman completed his Ph.D. in Engineering at Harvard University in 1970. He then spent five years in Applied Mathematics at MIT before moving to Brown University where he became Florence Pirce Grant University Professor in 1996. He retired from Brown in June 2009 and is now Professor of Materials Science and Engineering at the University of North Texas. His contributions include the development of a ductile fracture computational methodology, the development of cohesive surface methods for fracture analysis and creation of a framework that enables using discrete dislocation plasticity to solve general boundary value problems. Professor Needleman was awarded a Guggenheim Fellowship in 1977, and is a member of the National Academy of Engineering and of the American Academy of Arts and Sciences. He has been awarded the Prager Medal by the Society of Engineering Science, the Drucker and Timoshenko Medals by the American Society of Mechanical Engineers and has been recognized by ISI as a Highly Cited Author in both the fields of Engineering and Materials Science. Professor Needleman also holds honorary doctorates from the Technical University of Denmark and Ecole Normale Superior de Cachan (France).
Faculty Host: Prof. Somnath Ghosh, 203 Latrobe, 410-516-7833, [email protected]
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