Page 42

apr16

Computation and modeling applied to ceramic materials lated motion of atoms or molecules of material. Basically, it solves Newton’s equations of motion for a set of particles. Researchers have used MD fairly extensively to explore structure and brittle fracture in glasses. They can evaluate static and dynamic properties of the system as a function of temperature. A primary requirement is an accurate representation of interatomic potential between entities. Muralidharan et al.21 provide an excellent review of the field of MD simulation of silica fracture. Ceramic-matrix composites Because of their mechanical properties at elevated temperatures, ceramic- matrix composites, particularly SiC/SiC, are particularly attractive for many applications. According to Sullivan, one of the participants at the workshop, a pressing need exists for models of oxidation behavior of materials and life prediction methodologies for SiC/SiC composites in engine environments. Sullivan noted that this approach requires obtaining a more complete understanding of the BN coating–fiber interface oxidation mechanisms and development of algorithms that permit modeling of oxidation at the constituent level. He also indicated there is a need for improved capabilities in process modeling to streamline tool design and reduce manufacturing costs. Computationally derived materials play a significant role in NASA’s 2015 Technology Roadmap.22 The Roadmap notes, “The objective of this emerging technology is to design materials that are optimized for their intended usage, accelerate materials development and integration of physics-based models of materials at multiple length scales with new experimental capabilities to fully capture the relationship between processing, microstructure, properties, and performance for structural and multifunctional materials.” The Roadmap indicates that “simulation methods can span nearly 10 orders of magnitude in length scale and 15 orders of magnitude in time scale.” Summary and ongoing questions This workshop raised many questions regarding future needs and opportunities for computation and modeling as applied to glasses, single crystals, polycrystalline ceramics, and ceramic-matrix composites. Although we have made significant progress in predicting fundamental properties of simple materials, considerable work remains. Some of the many questions follow. • What are the most important material properties and behaviors to address? • Which calculation techniques offer the most promise (e.g., DFT, ab-initio quantum mechanics, molecular dynamics)? Limitations on use of DFT have been indentified4—are these limitations being overcome? • How can temperature effects be readily incorporated into calculations? • Is fundamental data necessary for calculations easily available? • Are the results of simulation and modeling projects being archived in such a way as to make them fully accessible to the community? • What education is needed in computation and modeling for experimentalists and experts in the area? How can computation and modeling techniques be better used for discovery of new ceramics, reproducibility of ceramics, and obtaining robust descriptors of a material’s properties? About the authors Steve Freiman is president of Freiman Consulting (steve.freiman@ comcast.net). Lynnette D. Madsen is program director, Ceramics, at the National Science Foundation (lmadsen@ nsf.gov). William Hong is on the research staff in the Science and Technology Division of the Institute for Defense Analyses (whong@ida.org). Disclaimer Any opinion, finding, recommendation, or conclusion expressed in this material are those of the authors and do not necessarily reflect the views of NSF. Acknowledgments The authors gratefully acknowledge the many conversations with participants in the workshop and others on this topic. Steve Freiman and William Hong gratefully acknowledge the support of ASDR&E for this work. Chandler Becker acknowledges the work of her colleagues at NIST who contributed to the section on computation and modeling. References 1S.W. Freiman, L.D. Madsen, and J.W. McCauley, “Advances in ceramics through government-supported research,” Am. Ceram. Soc. Bull., 88 1 27–31 (2009). 2S.W. Freiman, L.D. Madsen, and J. Rumble, “A perspective on materials databases,” Am. Ceram. Soc. Bull., 90 2 28–32 (2011). 3S.W. Freiman and L.D. Madsen, “Issues of scarce materials in the United States,” Am. Ceram. Soc. Bull., 91 4 40–45 (2012). 4S.W. Freiman and L.D. Madsen, “The state of ceramic education in the United States and future opportunities,” Am. Ceram. Soc. Bull., 94 2 34–38 (Mar. 2015). 5J. Allison, “Integrated computational materials engineering: A perspective on progress and future steps,” J. Mater., 63 4 15–18 (2011). 6S.W. Freiman, J. Fong, N. A. Heckert, and J. Filliben, “A new statistical methodology for assessing mechanical reliability”; manuscript. 7“Standard practice for reporting uniaxial strength data and estimating Weibull distribution parameters for advanced ceramics,” ASTM Designation C 1239-07. Committee C28 on Advanced Ceramics, reapproved 2008. American Society for Testing and Materials, West Conshohocken, Pa. 8http://gurka.fysik.uu.se/ESP/ 9http://materialsproject.org/ 10http://aflowlib.org/ 11http://www.nsf.gov/funding/pgm_summ.jsp?pims_ id=505044&org=DMS 12The Minerals, Metals, and Materials Society, Modeling across scales: A roadmapping study for connecting materials models and simulations across length and time scales. TMS, Warrendale, Pa., 2015. 13A.J. Cohen, P. Mori-Sanchez, and W. Yang, “Insights into current limitations of density functional theory,” Science, 321, 792–94 (2008). 14S.W. Freiman and J.J. Mecholsky Jr., “The fracture energy of brittle crystals,” J. Mater. Sci., 45, 4063–66 (2010). 15E. Bitzek, J.R. Kermode, and P. Gumbsch, “Atomistic aspects of fracture,” Int. J. Fract., 191, 13–30 (2015). 16W. Wong-Ng, G.S. White, and S.W. Freiman, “Application of molecular orbital calculations to fracture mechanics: Effect of applied strain on charge distribution in silica,” J. Am. Ceram. Soc., 75, 3097–102 (1992). 17C.G. Lindsay, G.S. White, S.W. Freiman, and W. Wong-Ng, “Molecular orbital study of an environmentally enhanced crack growth process in silica,” J. Am. Ceram. Soc., 77, 2179–87 (1994). 18J.E. Del Bene, K. Runge, and R.J. Bartlett, “A quantum chemical mechanism for the water-initiated decomposition of silica,” Comput. Mater. Sci., 27, 102–108 (2003). 19J.K. West and L.L. Hench, “The effect of environment on silica fracture: Vacuum, carbon monoxide, water, and nitrogen,” Philos. Mag. A, 77, 85–113 (1998). 20G.S. White and W. Wong-Ng, “Molecular orbital calculations comparing water-enhanced bond breakage in SiO2 and Si”; in Fracture Mechanics of Ceramics, Vol. 12. Edited by R.C. Bradt, A.G. Evans, D.P.H. Hasselman. Plenum Press, New York, 1996. 21K. Muralidharan, J.H. Simmons, P.A. Deymier, and K. Runge, “Molecular dynamics studies of brittle fracture in vitreous silica: Review and recent progress,” J. Non-Cryst. Solids, 1351, 1532–42 (2005). 22http://www.nasa.gov/sites/default/files/thumbnails/ image/oct_roadmaps n 40 www.ceramics.org | American Ceramic Society Bulletin, Vol. 95, No. 3


apr16
To see the actual publication please follow the link above