Embed Size (px)
Citation preview
One Mechanical Design Teacher’s FEA Challenge
Paul CorderMechanical Engineering Department
Lamar UniversityBeaumont, Texas
Virtual Product Development Conference, Phoenix, AZ, April 21-22, 2009
Abstract
Engineers are problem solvers.
The teacher’s challenge is to properly introduce “tools” and their use.
Abstract
Engineers are problem solvers.
The teacher’s challenge is to properly introduce “tools” and their use.
This paper uses two Analytical (equations) and two Numerical (FEA) approaches to illustrate this challenge.
Abstract
Engineers are problem solvers.
The teacher’s challenge is to properly introduce “tools” and their use.
This paper uses two Analytical and two Numerical (FEA) approaches to illustrate this challenge.
FEA is a useful engineering design tool, but it can be dangerous if not interpreted.
Too many people do not interpret, or validate, the results of computer simulations.
Introduction
The challenge to teaching the use of computer simulation, such as FEA, is to establish the habit of validating estimates of performance made by that model.
Introduction
The challenge to teaching the use of computer simulation, such as FEA, is to establish the habit of validating estimates of performance made by that model.
The stress responses of two structural components, or objects, under load are estimated using two Analytical approaches and two Numerical, or finite element analysis, programs to analyze each object.
The Design Process
Recognition of a Societal Need
The Design Process
Recognition of a Societal Need
Definition of the Problem
The Design Process
Recognition of a Societal Need
Definition of the Problem
Synthesis of Possible Solutions
The Design Process
Recognition of a Societal Need
Definition of the Problem
Synthesis of Possible Solutions
Analysis of the Best One
The Design Process
Recognition of a Societal Need
Definition of the Problem
Synthesis of Possible Solutions
Analysis of the Best One
Evaluation w.r.t. the Problem
The Design Process
Recognition of a Societal Need
Definition of the Problem
Synthesis of Possible Solutions
Analysis of the Best One
Evaluation w.r.t. the Problem
Presentation
The Problem
Too many students are all too willing to accept the output of a computer simulation without seriously questioning the validity of the results.
The Challenge
Structural response can be estimated using
the EXPERIMENTAL approach,
the ANALYTICAL approach, and/or
the NUMERICAL approach.
The Challenge
Structural response can be estimated using the Experimental approach, the Analytical approach, and the Numerical approach.
This paper uses the latter two to illustrate the challenge in teaching the use of finite element modeling in mechanical design.
Cantilevered Beam
Mechanica FEA Model
Nastran FEA Model (Default Mesh)
Table 1: Results For Default Mesh
Table 1
Strength
Of
Materials
Theory
Of
Elasticity
Nastran
(Center)
Nastran
(Corner)
Mechanica
(Center)
Mechanica
(Corner)
xx(Top)
17,990 17,990 5,802 9,089 19,659 20,680
xx(Bottom)
-17,990 -17,990 -4,642 -4,921 -16,750 -19,630
Stresses in psi. 1” Mesh Size
Table 2: Averaged Stresses
Table 2Strength
Of
Materials
Theory
Of
Elasticity
Nastran
(Center and
Corner
Averaged)
Mechanica
(Center and
Corner
Averaged)
xx(Top)
17,990 17,990 7,446 20,170
xx(Bottom)
-17,990 -17,990 -4,782 -18,190
Stresses in psi. 1” Mesh Size
Nastran FEA Model (Default Mesh)
Nastran Finer Mesh
Nastran Model Using Finer Mesh
Table 3: Results Using Finer Mesh
Stresses in psi. 0.125” Mesh Size
Table 3Strength
Of
Materials
Theory
Of
Elasticity
Nastran
(Center and
Corner
Averaged)
Mechanica
(Center and
Corner
Averaged)
xxTop
17,990 17,990 25,191 20,170
xxBottom
-17,990 -17,990 -19,896 -18,190
Triangular Bracket
Bracket, Mechanica Model
Bracket, Nastran Default Model
Table 4: Bracket Results
Table 4Strength
Of
Materials
Theory
Of
Elasticity
Nastran
(Default Mesh)Mechanica
xx(Top)
250 305 605 743
xx(Bottom)
-250 -194 -85 -43
Observations
Must interpret results for reasonableness.
Observations
Must interpret results for reasonableness.
Computers are fast, but the results can be misleading.
Observations
Must interpret results for reasonableness.
Computers are fast, but the results can be misleading.
Proper use of the tools is challenging.
Observations
Must interpret results for reasonableness.
Computers are fast, but the results can be misleading.
Proper use of the tools is challenging.
Use Strength of Materials estimates as backup estimates of response.
Observations
Must interpret results for reasonableness.
Computers are fast, but the results can be misleading.
Proper use of the tools is challenging.
Use Strength of Materials estimates as backup estimates of response.
Calculations predict, not specify.
Observations
Must interpret results for reasonableness.
Computers are fast, but the results can be misleading.
Proper use of the tools is challenging.
Use Strength of Materials estimates as backup estimates of response.
Calculations predict, not specify.
Stress is a function of geometry, not of the material used.
Conclusions
Always interpret the results of FEA models.
Conclusions
Always interpret the results of FEA models.
Computers may only give you a bad answer quicker.
Conclusions
Always interpret the results of FEA models.
Computers may only give you a bad answer quicker.
The finite element modeling tool should be used with extreme caution.
Conclusions
Always interpret the results of FEA models.
Computers may only give you a bad answer quicker.
The finite element modeling tool should be used with extreme caution.
Always have an estimate of the response using an alternative approach.
Thank You
Paul Corder, Ph.D., P.E.Professor, Mechanical Engineering
Lamar UniversityP.O. Box 10028
Beaumont, Texas 77710 U.S.A.
409.880.8769 [email protected]
Virtual Product Development Conference, Phoenix, AZ, April 21-22, 2009
