PSI - Issue 8

G. Fargione et al. / Procedia Structural Integrity 8 (2018) 566–572 Author name / Structural Integrity Procedia 00 (2017) 000–000

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from which it is possible to derive the requirements to be associated with each component, and on information specified in the early stages of the design process, particularly in the System Design phase, which defines the system layout and the subdivision into components. Requirements that express the objectives of the problem (optimizing masses, costs, other performance functions), and the functional constraints within which these objectives should be pursued (loads to bear, pressures to contain, thermal flows to be transmitted), in formulating the design problem they translate into objective functions and constraint equations on requirements. The latter, together with constraints on geometric parameters and on material properties, guide the choice of material and the dimensioning of free variables in optimizing functions that express the objectives of the problem.

Fig. 1. Methodological framework: Design process context and selection procedure

2.1. Requirements specification

The functions to perform and the conditions under which they have to be performed will result in design requirements, which directly affect the choice of the material of each component. Their definition therefore requires an analysis of the functions that the system to be designed has to perform throughout the intended use life, and the ways and conditions under which these functions must be performed. These requirements may be of different types, depending on the problem under consideration. In the formulation of the design problem for the system and its components, they will constitute the set of basic requirements {R}: • Functional requirements – They express the key properties required for the system and its components, which characterize the design problem and derive from the primary needs from which the design originates. • Manufacturability and costs requirements – They interpret the ability to make components as efficiently and economically as possible, and are generally quantified by cost functions. • Mechanical-structural requirements – They ensure the stability of the structural behavior of the components, and can therefore be attributed to all mechanical phenomena to which the components are subjected, due to operating conditions. • Requirements related to physical properties of other nature - They regard the behavior related to physical phenomena of various nature (thermal, electrical, magnetic, optical).