This is a joint research project between the NASA Langley Research Center and the Cornell Fracture Group, as part of NASA's Airframe Structural Integrity Program. The principal objectives of the research project are to develop a computational methodology to predict curvilinear fatigue crack growth and fatigue life and to simulate stable tearing for residual strength prediction of thin shell structures, for example, aircraft fuselages, for a large single crack or multiple cracks.

A general software framework for simulating arbitrary crack growth has been developed and implemented within the FRANC3D code. FRANC3D provides a general representation of a problem, consisting of a geometrical model with associated simulation attributes, which is independent of the numerical method and mesh required for stress analysis. The STAGS (Structural Analysis of General Shells) finite element code is used to perform the stress analysis.

The CFG Shares Award from NASA

The Fuselage Structural Integrity Analysis Team at the NASA Langley Research Center has received one of the 1996 NASA Group Achievement Awards. Three members of the eleven person Team, Dr. Wash Wawrzynek , Dr. David Potyondy (Ph.D., 1994), and Prof. Tony Ingraffea, are past or present members of the CFG. The nomination cited the team for "developing an accurate structural analysis methodology for predicting the structural integrity and residual strength of fuselage structures with widespread fatigue damage and long cracks." The letter from Dr. Charles Harris (Chief Engineer of the Materials Division at NASA Langley) which accompanied the award noted that "A key element of the technology is the computer software being developed by the team members from Cornell University which employs advanced numerical methods and innovative adaptive remeshing strategies for generating engineering solutions to complex structural integrity problems. " Our thanks to other members of the team for stimulating and productive collaboration: Dr. Vicki O. Britt, NASA Langley, Dr. David Dawicke, NASA Langley, Dr. James C. Newman, Jr., NASA Langley, Dr. Robert Piascik, NASA Langley, Dr. Charles Rankin, Lockheed-Martin Corp., Dr. James H. Starnes Jr., NASA Langley and Dr. Richard D. Young, NASA Langley.

• Potyondy, D.O.: A Software Framework for Simulating Curvilinear Crack Growth in Pressurized Thin Shells, Ph.D. Thesis, School of Civil and Environmental Engineering, Cornell University, Ithaca, N.Y., 1993.
• Potyondy, D.O., Wawrzynek, P.A., and Ingraffea, A.R. (1995), "Discrete Crack Growth Analysis Methodology for Through Cracks in Pressurized Fuselage Structures," International Journal for Numerical Methods in Engineering, Vol. 38, No. 10, pp. 1611-1633.
• Potyondy, D.O., Wawrzynek, P.A., and Ingraffea, A.R. (1995), "An Algorithm to Generate Quadrilateral or Triangular Element Surface Meshes in Arbitrary Domains with Applications to Crack Propagation," International Journal for Numerical Methods in Engineering, Vol. 38, pp. 2677-2701.
• Chen, C.-S., Wawrzynek, P.A., and Ingraffea, A. R. (1997), "Methodology for Fatigue Crack Growth and Residual Strength Prediction with Applications to Aircraft Fuselages," Computational Mechanics, Vol. 19, No. 6, pp. 527-532.
• Chen, C.-S., Wawrzynek, P.A., and Ingraffea, A. R. (1997), "Simulation of Stable Tearing and Residual Strength Prediction with Applications to Aircraft Fuselages," Proceedings of the FAA-NASA Symposium on Continued Airworthiness of Aircraft Structures, Atlanta, pp. 605-618.
• Carter, B.J., Chen, C-S., Ingraffea, A.R., Wawrzynek, P.A. (1997), "A topology based system for modeling 3D crack growth in solid and shell structures," Advances in Fracture Research, Vol 4, Ninth International Congress on Fracture, Sydney, Australia, Elsevier Science Publishers, pp. 1923-1934.
• Chen, C.-S., Wawrzynek, P.A., and Ingraffea, A. R. (1997) "Residual Strength Prediction of Fracture Specimens and Fuselage Structures with Multi-Site Damage," Proceedings of 25th Silver Jubilee Midwestern Mechanics Conference, Rapid City, South Dakota, pp. 2.15-2.17.
• Chen, C.-S., Wawrzynek, P.A., and Ingraffea, A. R. (1998) "Recent Advances in Numerical Simulation of Stable Crack Growth and Residual Strength Prediction," the Sixth East Asia-Pacific Conference on Structural Engineering & Construction, Taipei, Taiwan, pp. 1773-1778.
• Chen, C.-S., Wawrzynek, P.A., and Ingraffea, A. R. (1998) "Elastic-Plastic Crack Growth Simulation and Residual Strength Prediction of Thin Plates with Single and Multiple Cracks," In Fatigue and Fracture Mechanics: 29th Volume, ASTM STP 1332 (in press).
• Chen, C.-S., Wawrzynek, P.A., and Ingraffea, A. R. (1998) "Residual Strength Prediction of Fuselage Structures with Multiple Site Damage," In Proceedings of the Second Joint NASA/FAA/DoD Conference on Aging Aircraft (in press).
• Chen, Chuin-Shan: Crack Growth Simulation and Residual Strength Prediction in Thin Shell Structures, Ph.D. Thesis, School of Civil and Environmental Engineering, Cornell University, Ithaca, N.Y., 1999.
• Chen, C.-S., Krause, R., Pettit, R. G., Banks-Sills, L., and Ingraffea, A. R. "Numerical Assessment of T-stress Computation Using a P-version Finite Element Method," (in preparation).
• Chen, C.-S., Wawrzynek, P.A., and Ingraffea, A. R. (1999) "Crack Growth Simulation and Residual Strength Prediction in Airplane Fuselages," final report for NASA project NAG-1-1184 crack growth prediction methodology for multi-site damage, January.

• IUTAM Symposium: Innovative Computational Methods for Fracture and Damage, Dublin, Ireland, June 30th - July 5th, 1996
• FAA/NASA Symposium on Continued Airworthiness of Aircraft Structures, Atlanta, August 28-30, 1996
• ASTM 29th National Symposium on Fatigue and Fracture Mechanics, Stanford, California, June 24-26, 1997
• The First Joint DoD/FAA/NASA Conference on Aging Aircraft, Ogden, Utah, July 8-10, 1997
• Midwestern Mechanics Conference, Rapid City, South Dakota, September 21-24, 1997
• The Sixth East Asia-Pacific Conference on Structural Engineering & Construction, Taipei, Taiwan, January 14-16, 1998
• The Second Joint NASA/FAA/DoD Conference on Aging Aircraft, Williamsburg, Virginia, August 31-September 3, 1998
• International Conference on Computational Engineering Science, Atlanta, Georgia, October 5-9, 1998

• FRANC3D Thin Shell Tutorial Guide (DRAFT)

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