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Avoiding Finite Element Analysis Errors

Abstract

Finite Element Analysis (FEA) is a numerical method for calculating stress and strain (and other quantities) in structures that cannot be easily analyzed any other way. FEA Analysts use complex software to create a mathematic representation of the physical structure being studied, apply loads to the structure and then solve for the resulting displacements and stresses. In years past, FEA was performed by highly trained analysts with master’s level engineering degrees or higher. Today, the combination of competitive market pressures, powerful computer hardware and well designed software has resulted in CAD designers being asked to perform FEA early in the design process. To enable these designers to perform FEA analysis, solid modeling software vendors have incorporated FEA into their solid modeling and design drafting packages. Unfortunately, while the software is easy to use, CAD designers usually do not have the education in specialized mechanics and high level mathematics necessary to understand the calculations being performed by the FEA software. Even more important, without special training, they do not have the ability to recognize the potential for errors in the FEA results. Errors may occur during the modeling and analysis process due to limitations of the software as well as user error. Understanding and avoiding these errors dramatically improves the chances the designer will successfully utilize FEA software.

Autodesk Inventor Professional 9 now includes FEA capability from ANSYS, Inc. Earlier versions of this software (without FEA) were used at Purdue University – College of Technology at New Albany (PUNA) to instruct students in solid modeling and design drafting. With new and ever expanding software capabilities, CAD instructors had to determine how to prepare engineering technology students to use to software appropriately. Today, after students learn to use the software, they are given assignments that demonstrate the potential weaknesses of FEA software. This paper discusses the assignments and compares simple problems solved in Inventor to exact results to show how simple mistakes result in poor FEA results. It also includes a discussion of the implementation of FEA in Inventor and strategies for educating engineering technology students in FEA.

Introduction

Finite Element Analysis (FEA) is a method for solving the equations that describe the behavior of elastic solids when subject to loads. Finite Element software that employs this procedure allows engineers to calculate stress and strain in objects that cannot be easily analyzed by manual calculations. The FE method was first described by R. Courant in 1943 to solve a torsion problem but it failed to gain widespread use due to the volume of calculations needed.1 FEA requires an extremely large number of calculations to solve and is only practical today due to modern advances in computer speed and capacity. In the 1970’s, general purpose finite element software was developed due to the increasing availability and power of digital computers. Digital computers in the form of mainframe computers provided an efficient tool to perform finite element calculations. Since then, computer hardware has rapidly increased in speed and storage capacity and the FEA software has gained better interfaces, pre and post processing of the data and improved graphics.2

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Dues, J. (2006, June), Avoiding Finite Element Analysis Errors Paper presented at 2006 Annual Conference & Exposition, Chicago, Illinois. 10.18260/1-2--532