Tackling Uncertainties in Design

- uncertain design parameters, safety concept, modelling, analysis -

by Prof. Dr. Ralf Cuntze

Modern light-weight structures are the result of an optimisation compromise between allthe product’s functional requirements such as stiffness, strength and the operationalrequirements such as lifetime. Design driving are the material properties and the failureconditions for fracture and yielding. Responsible for the quality of the structure achievedunder minimum mass requirement are a qualified analysis procedure, the input ofreliable data including the dimensioning load cases and the safety concept. At present,usually a deterministic safety concept is applied that employs factor of safety values toimplement reliability in the structure. Special task of the designer is the development ofa so-called robust structure that does not essentially change its behaviour under theusual scatter of the stochastic design parameters. Thereby, the aerospace engineerrelies on the existence of qualified processes such as qualified analysis, test,manufacturing and NDI procedures as pre-requisites for the application of a safetyconcept. Their goodness has to be checked and information carefully monitored.