Finite Element Analysis

Finite Element Analysis (FEA) is a technique by which the stresses, deflections and reaction forces in objects can be estimated. The technique involves dividing the object into relatively small elements whose individual behaviour is easily calculated. The behaviour of all of the small elements is then put together to estimate the stresses and deflections in the entire object.

For complicated problems, especially those involving complicated geometry, contact between components and inelastic materials, it is the least expensive means of obtaining reasonable answers.

Common engineering uses of FEA are:

Testing the performance of a design under specified conditions
Optimisation ie. reduction of the material used in a component without compromising performance

Failure analysis

Stresses through an aircraft tie-down anchor point. Red regions are highly stressed. The calculated stresses were below the material strength, indicating that the part would survive the specified loads.

This component was manufactured and installed at the Brisbane International Airport. It passed its proof load test, as predicted by the Finite Element Analysis.

Skillful definition of the problem, division of the object into elements and selection of appropriate elements is required to obtain a sufficiently accurate solution using the minimum computational effort. Interpretation of the results, based on an understanding of how they are calculated, is frequently required to relate the calculated results to actual behaviour.

What Can Be Simulated?

Stress, Strain, and Displacement
Buckling
Modal or natural frequency analysis
Frequency response (eg. response to forced vibration)
Transient response analysis
Contact surfaces (eg. threads)
Thermal behaviour
Fatigue analysis
Types of Analyses

FEA analyses can be classified as either linear or non-linear. Linear static is the most common and least intensive of all FEA analyses. This characterisation essentially determines what element features or properties are updated throughout a solve.

The main areas characterising nonlinear analyses are:

Material. eg. non-constant elastic modulus, material hardening, not homogenous, thermal-strain coupling, hyperelastic materials like rubbers, creep, high strain rates.
Boundary conditions eg. load direction dependent on geometry.
Geometry eg. geometric stiffening, large scale deflection, contact and penetration effects.
Mesh eg. very large deformation of mesh, bulk material forming.
Nonlinear FEA requires significantly more user skill and computing resources than does linear FEA. Solution of nonlinear models generally requires convergence of iterative processes involving incremental load and or time stepping. Such solutions are generally undertaken as a final, more accurate stage following initial linear runs.

Common Misconceptions

Meshing is not everything in FEA. Other important determinant model inputs include boundary conditions and material properties. Just because a particular model geometry meshes, this will not guarantee that realistic data will result from an analysis.

FEA does not replace testing. Like any other computer simulation environment FEA is based upon many mathematical and physical models as well as a variety of empirical models. It is often said that FEA actually augments testing. Testing provides qualification of the FEA results. Generally, in most New Product Development situations FEA will reduce testing requirements on final products as confidence levels are usually increased.

FEA is not easy. With the recent developments in increased usability of 3D modeler and FEA packages, there has been a general trend towards an expectation of painless, and speedy results gratification. FEA technology is fundamentally complex and should not be attempted without a reasonable physical understanding of the problem being solved and knowledge of the limitations of the models involved.

Learning the software interface is not equivalent to understanding the technology.

Click here for selected FEA case studies conducted by e3k

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