NON-LINEAR
CALCULATIONS

Designs may be made of plastic materials, they may allow large deformations, they may rely on membrane effects for stiffness, or they may be made up of contacting parts. In such cases, linear analysis still gives a tractable approximation. However, non-linear analysis may yield a much more accurate result. This added accuracy enables our clients to improve their designs. It is important to note that linear and non-linear analysis must yield the same result for a linear problem; our engineers are able to distinguish the necessity for non-linear analysis from cases where linear analysis will suffice.

Material non-linearity

All materials exhibit non-linear behaviour at some point. Most metal alloys like steel and aluminium have a large linear range, which makes them prime candidates for linear analysis. However above a certain load, these materials start behaving in a non-linear fashion, just like other materials like plastics. At Femtec, we know how to incorporate custom stress-strain curves for specialized materials into an analysis or approximate non-linear material behaviour from more easily obtainable values of yield strength and ultimate strength.

Geometric non-linearity

Designs may allow ‘large displacements’ of their parts and with that void one of the prerequisites for linear analysis. These large displacements may cause loads applied to the non-deformed geometry to differ significantly from those occurring after the design was deformed by that (or some other) load. The geometry and loads applied need to be updated during the analysis. At Femtec we possess the experience and mechanical insight to ensure correct load application to our models, constantly bearing possible geometric non-linearity in mind.

Membrane effects

Many constructions rely on the ‘membrane effect’ for their strength and stiffness. This effect can be visualized by a sheet held taut and bearing a load. Linear theory would have the sheet hold op the load with only its own bending stiffness, resulting in very high deformation and stresses. However, in this case the non-linear membrane affect is not negligible. While performing analyses for our clients, we recognize the occurrence of these effects and make use of the non-linear capabilities of our software where needed.

Contact analysis

Contact analysis is used when a design consists of contacting parts that either should or should not slide. Contact analysis is also frequently used if a design incorporates a critical bolted connection. It’s almost always undesirable for the two parts that are bolted together to lose connection or slide, putting excessive strain on the bolts. We are experienced in using finite element analysis with contact analysis to determine this for the most unusual bolt patterns and complicated load combinations.

Peak stresses over yield strength?
No problem!



Often the maximum allowable stress in a design is related to the yield stress of the metal it is made of. Sometimes, however, the design only needs to survive an extreme load. Non-linear analysis can be a life-saver; small peaks over yield strength might not cause any damage. Using a material model with plastic strain capability, non-linear analysis can predict the extent of permanent deformation after a load, which can prevent a costly redesign.

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