PSI - Issue 46

Tamás Fekete et al. / Procedia Structural Integrity 46 (2023) 189–196 Tamás Fekete / Structural Integrity Procedia 00 (2021) 000–000

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assess whether the knowledge acquired at a higher hierarchical level should be re-evaluated or not, based on the lessons learned from lower level activities/knowledge Rousseau (2018). From here, the two key postulates, selected from philosophical studies and speculations, are presented:  Postulate of Dynamic presentism : the objects that all together form our world are finite and ‘ exist dynamically ’ – Golosz (2017, 2021)–, explained more in detail by the following sub-postulates (S1)–(S3): (S1): ‘the notion of dynamic existence is “tensed” ’ –Golosz (2021)–, meaning that it is possible to talk ‘about what dynamically existed (the past), what dynamically exist (the present), and what will dynamically exist (the future)’, consequently past, present and future can obviously be differentiated; (S2): objects ‘that dynamically exist endure’, i.e., the objects ‘endure, when they persist over time, keeping their strict identity’ Golosz (2021); (S3): ‘events (which are acts of acquiring, losing, or changing properties by dynamically existing things and their collections) dynamically exist in the sense of coming to pass ’ Golosz (2021).  Dissipation postulate : ‘dissipation occurs naturally and inevitably in our world –starting from the smallest to the largest length-scales of interest–’ based in the idea of Öttinger (2017). Some important comments concerning the two postulates are made as follows: (1) the lifetime of a dynamically existing object is finite; (2) ‘… the future is (or seems to be) open, while the past is fixed’, so ‘things can impact on future events with no possibility of having an impact on the past’; (3) ‘the enduring things –one can say metaphori cally–’ … ‘convey traces of the past into the future’, because their existence is dynamic and future-oriented, while bearing traces of past interactions within them –see Golosz (2021)–. The ‘ Dynamic presentism ’ and ‘ Dissipation ’ postulates, when applied together, lead immediately to the conclusion that (4) dissipative mechanisms may have a substantial role in the memorization of traces of past events in the corresponding objects, and (5) an object's reactions to an ongoing event may be influenced by memories of its entire past life history, Steinbach (2020). The significance of the Dynamic presentism postulate is that: (1) it suggests a dynamic approach on ‘purely’ met aphysical grounds, and hence unavoidably suggests the introduction of a time-dependent description into scientific theories that are of crucial importance for further theoretical investigations; (2) it makes clear that time is an oriented (i.e. asymmetric) concept, which, at scientific level of description, can ensure that the theory based on it satisfies the requirement of temporal causality , i.e., to distinguish causes and effects over time, –see Golosz (2021) and Rakoto manana (2018)–. With the joint application of postulates, the idea of a theory is formulated that interprets the engi neering systems –i.e., LSPSs – to be described as non-equilibrium systems , where (1) temporal causality and (2) memory –see Steinbach (2020)– are present . So, the new framework theory is sought within modern thermodynamics, which is expected to provide a unified description of ageing and fracture phenomena. At this stage, Thermomechanics with Internal Variables ( TIV ), as a form of thermomechanics seems to be the best theoretical framework that could be used in the development of models for future engineering methodologies for SI problems in LSPSs . 3.2. Outline of a new Thermomechanics-based model for Structural Integrity of Large-Scale Pressure Systems To build a methodology tailored to specific engineering problems from a general physical framework theory, the most relevant engineering problems must first be identified, then a problem-specific, but still sufficiently general model should be constructed. Currently, the ‘ Achilles' heel ’ of existing LSPS SI methodologies is the lack of a funda mental model supporting concurrent and coupled modelling of ageing and fracture. In 1921, Griffith developed linear elastic fracture mechanics –Griffith (1921)–, based on global energy balance considerations. It was about 90 years, until Chen developed a modern version of Griffith's method, based on modern Thermody namics, having the following features: (1) it is based on energy representation, (2) it starts from global form of the balances. The resulting model provides a nonlinear field theory of fracture mechanics, which enables the description of strongly coupled multi-field fracture mechanics problems, including bulk dissipation –see Chen and Mai (2013)–. Next, inspired by the general theory –Chen and Mai (2013)–, a theoretical model is sketched that seems promising for solving fracture mechanics problems in the context of thermo-visco-elastoplastic material behaviour. Deformation of a solid body in ambient space is described by the mapping     , t t  x χ X , x denoting positions in Euler and X in Lagrange coordinates;  denotes the gradient in Euler, X  in Lagrange picture.   u x X is vector