Abstract

Observed Trends in the Practice of Finite Element Structural Analyses 

Aerospace structures are complex, high-performance structures. As such, there is an increased reliance on modeling and analysis and considerable emphasis on accurate analyses of these structures. Advances in reliable and efficient computing and modeling tools are enabling analysts to model complex three-dimensional configurations and perform analyses rapidly and efficiently. Many of the early-career engineers of today are very proficient in the usage of modern computers, computing engines, and complex software and visualization tools. However, the current trends also suggest that there is blind acceptance, at many levels, of the results of the finite element analyses (FEA). There appears to be a general lack of understanding of engineering mechanics formulations and numerical algorithm fundamentals that serve as the foundations of FEA software systems.  Current-day analysts are adept at meshing but often neglect developing a well-thought-out plan for modeling and analysis. Products of an FE analysis need to be identified to guide the FE meshing and modeling approaches. Understanding load paths and modeling uncertainties are necessary aspects of successful FEA simulations.   Most pitfalls are observed in identifying proper boundary and interface conditions, coupling regions of plate/shell interfaces, recognizing singularities, and bolts and bolt modeling. Improper use and interpretation of primary and secondary variable results, linear and nonlinear analyses and inertia relief methods are also frequently observed.

The objective of this presentation is to show some current trends, identify some steps that need to be taken to ensure that these trends are reversed and eliminated, and ensure the use of high-quality FE analysis and results are restored. Guidelines and suggestions for senior engineers and educators are offered. Analysts need to study software developers’ manuals, actively pursue verification and validation of their finite element models, experiment with various elements to develop their own library of elements with good performance characteristics. Senior engineers and educators need to ensure that the young engineers receive proper grounding in classical methods, finite element theory, simple yet bounding modeling approaches, hand-calculation techniques, and procedures for evaluating finite element results.

As the practice of FEA for aerospace structures is very broad, the scope of this presentation is limited to the performance and use of basic linear elastic stress analysis tools. Other challenges, beyond the scope of this presentation, are composite structures requiring careful definition of material data, stacking sequences and patterns, and local coordinate system definition; thermal stress and strain simulations that often produce non-intuitive solutions; contact modeling including sliding friction to account for assembly preload that may require the use of unsymmetric equation solvers; material and geometric nonlinearities, and even the choice between implicit and explicit methods.   These challenges compound those of linear elastic FEA.

About the Speaker

Dr. Ivatury S. Raju, NASA 

Technical Fellow

Raju has been working in the fields of fracture and structural mechanics at the Langley Research Center since 1975.  In 1994, he was selected as the Branch Head of the Mechanics of Materials Branch in the Materials Division.  The branch was engaged in the development of methodologies to characterize, predict, and improve durability and damage tolerance of Metallic and Composite materials.  After reorganization in late 1998, he became the Branch Head of the Analytical and Computational Methods Branch in the Structures and Materials Competency (SMC).  The branch was engaged in the development of analytical and computational methods to accurately predict the response of aerospace structures to external loads and development of the next generation of accurate analysis methods.  In 2002, Dr. Raju assumed the position of Senior Technologist in SMC. During the past 20 years he participated in four failure investigations and he is currently completing one such investigation.

Dr. Raju has a B.S. degree in Mechanical Engineering, M.S., and Ph.D. degrees in Aeronautical Structures and a M.S. in Engineering Administration from the George Washington University.  In 2000, Dr. Raju, on a NASA Fellowship, attended Program in Management Development at Harvard University.  Dr. Raju serves on editorial boards of International Journals Computer Modeling in Engineering and Sciences and Computational Mechanics. Dr. Raju is a Fellow of the AIAA.