THE ROLE OF THE

Design Concerns and Imperatives 53
table 4.2
Finite element analysis versus testing
Finite element analysis testing
Building FE model and running analysis are
cheaper and faster
4.6 Fea PerFormance PredIctIons
and some Key deFInItIons
Building and testing physical parts is costly and
takes a long time
No parts are physically involved Tests are usually destructive
Multiple analysis must be done to account for part
and build variations
Evaluation of different design alternatives is very
easy
Multiple physical tests must be done to account
for part and build variations
Evaluation of different design alternatives is a
long and costly process
Design optimization is easier Design optimization cannot be done easily
Accuracy: The ability of the FEA to predict actual behavior, mainly affected by the
quality of model inputs, mesh refinement, and others.
Convergence: Technique for obtaining greater accuracy from an FEA by iteratively
refining the mesh in areas of greatest concern until outputs
stabilize.
Isotropic: In FEA, this concept is assumed. It is a material that has the same strength
in all directions (as opposed to anisotropic materials).
Modulus of elasticity (E): Also known as Young’s modulus, a numerical constant
unique to each material that describes the elastic properties of the material
when loaded in the compression or in tension.
Poisson ratio: The ratio of transverse contraction strain to longitudinal extension
strain in a stretched bar. The maximum possible value is 0.5 (around 0.5 for
rubber, 0.33 for aluminum, 0.28 for common steels, and 0.1–0.4 for polymer
foams).
Singularity: Geometrically, the term used to describe a discontinuity such as
a fillet or part wall that causes an FEA result to diverge as the mesh is
refined.
Stiffness: A measure of the force required to deform a material in the elastic range.
To increase stiffness, a chemist or engineer will use a material with a higher
Young’s modulus.
Strain: Ratio of the change in length of a part to its original length (∆l/L).
Strength: A measure of a material’s ability to resist loads without deforming permanently.
To increase strength, a material with a higher yield stress must
be used.
Stress: Force per unit area in newtons per square meter (pascal) or pounds per square
inch. If the material is stretched, then it is in tension. Compressive stress is
often examined as well.