Roland Engelhardt

An Approach to Classify Methods to Control Uncertainty in Load-Carrying Structures

Today, a wide variety of methods to deal with uncertainty in load-carrying system exists. Thereby, uncertainty may result from not or only partially determined process properties. The present article proposes a classification of methods to control uncertainty in load-carrying systems from different disciplines within mechanical engineering. Therefore, several methods were collected, analysed and systematically classified concerning their characteristic into the proposed classification. First, the classification differs between degrees of uncertainty according to the model of uncertainty developed in the Collaborative Research Centre CRC 805. Second, the classification differs between the aim of the respective method to descriptive methods, evaluative methods or methods to design a system considering uncertainty. The classification should allow choosing appropriate methods during product and process development and thus to control uncertainty in a systematic and holistic approach.

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