Tobias Eifler

Approach for a Consistent Description of Uncertainty in Process Chains of Load Carrying Mechanical Systems

Uncertainty in load carrying systems e.g. may result from geometric and material deviations in production and assembly of its parts. In usage, this uncertainty may lead to not completely known loads and strength which may lead to severe failure of parts or the entire system. Therefore, an analysis of uncertainty is recommended. In this paper, uncertainty is assumed to occur in processes and an approach is presented to describe uncertainty consistently within processes and process chains. This description is then applied to an example which considers uncertainty in the production and assembly processes of a simple tripod system and its effect on the resulting load distribution in its legs. The consistent description allows the detection of uncertainties and, furthermore, to display uncertainty propagation in process chains for load carrying systems.

Modellierung von Unsicherheit in der Produktentwicklung

Fur die erfolgreiche Entwicklung von Produkten sind typischerweise eine Vielzahl von Einflussfaktoren zu beruksichtigen. Aufgrund von Unsicherheiten, z.B. fehlenden Informationen oder schwankende Einflussgrosen im Produktlebenslauf, ist eine detaillierte Analyse jedoch haufig schwierig. In diesem Beitrag wird deswegen die Wahrscheinlichkeits- mit der Moglichkeitstheorie verglichen, um die Anwendbarkeit beider Theorien fur eine quantitative Analyse von Unsicherheiten im Rahmen der Produktentwicklung zu untersuchen. Am Beispiel eines Euler-Knickstabes werden die Einschrankungen einer statistischen Analyse sowie die Vorteile der Berechnung einer unscharfen, kritischen Knicklast aufgezeigt. Das Ziel ist eine geeignete Beschreibung relevanter Unsicherheiten als Grundlage fur die Entwicklung robuster Produkte. Die vorgestellten Betrachtungen sind Teilergebnisse des Sonderforschungsbereichs 805 „Beherrschung von Unsicherheit in lasttragenden Systemen des Maschinenbaus“ der Deutschen Forschungsgemeinschaft an der Technischen Universitat (TU) Darmstadt.

An Assignment of Methods to Analyze Uncertainty in Different Stages of the Development Process

During its life cycle, each engineering product goes through different stages of planning, production and usage. Uncertainties occur in all of these phases. As defined, uncertainties in technical systems are present as far as product and process properties are not determined and deviations of these properties arise. They result either from imperfect information about output values of production processes (regarding product properties) or in terms of diverging uses of the products. Especially within the product development process, the occurring uncertainties have to be taken into account. During the early design stages, decisions that have a variously strong impact on the future product are made. Moreover, the knowledge about a future product is still low so that neither the expected processes nor the product’s properties are known. For this reason, well-known methods of probabilistic uncertainty analysis are not sufficient. They cannot be applied until the product is completely defined. A comprehensive uncertainly analysis in the product development process can be executed in an integrated process model with the Uncertainly Mode and Effects Analysis Methodology (UMEA) [1]. The underlying model of uncertainly is the basis for a comprehensive and consistent classification of uncertainly, a distinction comparable to concepts such as reliability, availability, error or risk. The model to analyze uncertainty has been exercised using the example of the product development process according to Pahl/Beitz [2]. It enables the assignment of suitable methods for the classification of uncertainty at different stages in the design process and thus different levels of abstraction. Based on this model, the quantitative methods of the probability theory are complemented by qualitative concepts such as risk analysis methods, for example, FailureMode and Effects Analysis (FMEA), Event Tree Analysis (ETA), or Hazard and Operability (HAZOP). The assignment of methods offers the possibility to analyze the classified uncertainties in the different phases of the product development process.Copyright