100 years after Griffith - Challenges in the Theory of Rupture | K. Ravi-Chandar
One hundred years have passed since the pioneering work of Griffith on the theory of rupture. This ground breaking work on modeling brittle fracture in glass spawned an enormous effort to understand, characterize, model, and predict the failure behavior in a wide range of materials and structures. Advances in fracture characterization, modeling and simulations, inspection for crack identification, standardization of material characterization, and fracture critical design methods that have been developed over the last sixty years have made possible the safe operation of engineered systems for applications ranging from transportation and power generation to microelectronic devices, adhesion, and numerous other applications. Standard methods have been established by various institutions, such as the American Society for Testing and Materials and the European Structural Integrity Society, for characterizing fracture properties of materials. Specifications in terms of fracture toughness and fatigue characteristics are commonly employed in selecting materials for application. The philosophy of fracture critical and/or flaw-tolerant structural design is now firmly embedded in the design of high-performance structures. Reliability assessments of structures in operation are carried out routinely with the tools developed by fracture researchers over the past century.
This remarkable success in engineering applications opens the field to new challenges that can be tackled with the foundations now well laid; here is a short, but by no means exhaustive, list of open areas. First, when significant inelastic deformations are encountered or in heterogeneous materials, even the basic formulations are still being refined. For example, continuum damage models, cohesive zone models, phase-field models, peridynamics models and others have been under intense development in recent years as a substitute for the classical fracture models; since these models are easily incorporated in numerical codes and are capable of simulating crack growth automatically, there has been significant interest in implementing such models. Corresponding developments in the characterization of material properties to incorporate such models in practical applications appear to be lagging, but are certainly an important part of the characterization. Second, new areas such as nanoscale and biological materials and structures, microelectronics devices and manufacturing processes, earthquake modeling and prediction, high strain rate fragmentation and other applications provide numerous opportunities for fracture research. Third, the assumption of a preexisting crack that is at the core of traditional fracture analyses completely avoids the issue of nucleation of flaws in a material/structure under loading. However, it is well recognized that most systems spend a significant fraction of their lifetime in the stage where flaws get nucleated from defects at some scale and become identifiable cracks for which the fracture mechanics analysis is well suited. This is one of the primary reasons for the underestimation of the lifetime of structures, and is particularly important in small scale structures. Lastly, there remains a large gap between the way fracture is viewed from mechanics and materials engineering, and the way it is viewed from the point of view of fundamental physics. Seen from mechanics and materials engineering, the fracture process zone, where material separates and the crack opens up, is a region of such enormous complexity that precise descriptions appear difficult. It is presumed that crack motion can be described completely in terms of fields such as stress and strain outside the process zone – the outer problem. This approach has been highly successful for a wide range of engineering problems when the fracture properties are obtained from calibration experiments. From the point of view of materials physics, it is natural to ask how crack motion is dictated by process zone details down to the level of atomic motions or at some mesoscale level above this in terms of void nucleation and growth etc – the inner problem. There are a number of worthy attempts at bridging the inner and outer problems, and this remains an area of important research activity. Thus, the future directions for the discipline are waiting to be charted by the imagination of the intellectual community in this field.
The International Journal of Fracture is an outlet for original analytical, numerical and experimental contributions which provide improved understanding of the mechanisms of micro and macro fracture in all materials, and their engineering implications. The journal presents papers from engineers and scientists working in various aspects of fracture, as well as occasional review papers in these areas. Innovative and in-depth engineering applications of fracture theory are also encouraged.
Professor Krishnaswamy Ravi-Chandar holds the M.C. (Bud) and Mary Beth Baird Endowed Chair in Department of Aerospace Engineering and Engineering Mechanics at The University of Texas at Austin. His research interests are in the general area of mechanics of materials; he has made seminal contributions to dynamic fracture and failure. He has published nearly 170 articles in journals, books, and conference proceedings on fracture mechanics, high strain-rate mechanical behavior, dynamic instabilities, fragmentation, ductile failure, multiscale experimental methods, inverse problems in material characterization, and other topics. A list of his publications can be found on Google Scholar.
Dr. Ravi-Chandar is the Editor-in-Chief of the International Journal of Fracture (2000 – present). He served as President of the International Congress on Fracture (2005-2009) and served on the Executive Committee of the Applied Mechanics Division of the ASME from 2003-2008, serving as Chair in 2007-2008. He was the President of the American Academy of Mechanics (2011-2014), and is a member of the US National Committee on Theoretical and Applied Mechanics (2003 – present; Vice-Chair: 2017-2019; Chair 2019-2020; Past-Chair, 2021-2022) and the Congress Committee of the International Union of Theoretical and Applied Mechanics (IUTAM; 2010 – 2018). He has been elected as a Fellow of the American Society of Mechanical Engineers, Society for Experimental Mechanics, the American Academy of Mechanics, the International Congress on Fracture and the Indian Structural Integrity Society. He received the Murray Medal from the Society for Experimental Mechanics in 2004, the Drucker Medal from the ASME in 2015 and the Prager Medal from the Society for Engineering Science in 2020.