Introduction to the uncertainty consideration in mechanical engineering and problem positioning.

There are two major types of uncertainties in engineering :

  • random uncertainties (« statistic », « observable » or even « irreducible »), caused by a intrinsic variability of the system or of its environment (ex : a geometric imperfection, a load, a boundary conditions or even material properties) ;
  • epistemic uncertainties (or “reducible”), connected with an imperfect knowledge (ex : an inadequate number of test, a model error accompanied with an expert assessment appraisal).

The standards and other regulations which are available in a large number of sectors (civil engineering especially) make it possible to free from an explicit consideration of the uncertainties through the use of characteristic values (average or extreme) and the application of security coefficients to ensure a reliability level assumed by the standard’s author (or the competent security authority).
Nevertheless, this is not always practical :

  • Either as the innovation capacity bring by our customers which tends to push the limits out of the practical application of these prescriptions,
  • Whether as their preoccupations concerning sustainable development which lead them to justify the life extension of their system, and so commands higher margins in relation to a reliability system level.

PHIMECA Engineering control the methods and tools of quantifying these uncertainties, propagating them through their customers’ models of simulation to develop robust and reliable products. These tools, coming from applied mathematics, go from probability/statistics through response surfaces to optimization.

It is incidentally these tools themselves used by the standards’ authors to produce their recommendations.


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PHIMECA Engineering est une société d’ingénierie spécialisée dans l’évaluation et l’optimisation des performances des produits et des systèmes. Sa vocation est de proposer des solutions en ingénierie robuste et en fiabilité en s’appuyant sur un socle scientifique solide, un esprit d’entreprise et des valeurs morales partagés par tous ses collaborateurs.