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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Taking a closer look on the relations for the and ˆ J J integrals, it is evident that they are thermodynamically con sistent generalization of the original J integral developed by Cherepanov (1967) and Rice (1968), also valid for dy namic crack propagation. The most significant improvement over the original theory is not necessarily the removal of the path independence of the J integral, rather the shift from strain-energy density to the corresponding thermody namic potential –in the above case, the Helmholtz free energy– in the core of the integral; note that this is not without precedent in the literature, however, due to lack of space, the issue will not be investigated further. Ageing processes cause a reduction of the thermodynamic potential through dissipation, making the structural material increasingly brittle. The presence of dissipation in ageing suggests that ageing is: (1) an inevitable feature of non-equilibrium systems and, (2) as such, it is also a dynamic phenomenon. Crack-front stability is described by a time-dependent     ..., ..., G R      criterion, which seems like the classical J I = J Ic criterion applied in today's SICs . To summarize, the model presented above appears to be promising to describe material ageing at the phenomeno logical level with a consistent account of bulk dissipation and paves the way for describing the behaviour of cracks in various dissipative ‘environments’, even for coupled multi-field problems. Hence, material damage, structural health, durability, their relationship to fracture mechanics can be interpreted and phenomenologically described in this frame work. However, it is important to note that the development of nonlinear field theories of fracture for multi-field and multi-scale problems is still in its infancy –see Chen and Mai (2013)–; an exciting and challenging research agenda for those working in the field. The development of industrially feasible models is also a challenging task for the medium-term future, whose practical significance is expected to increase in future projects. 4. Summary, Conclusions A long-standing research project at the CER in Budapest, Hungary is ongoing to develop a solid basis for future SICs of LSPSs . Methodological issues are at the heart of SICs . Despite the fact that many complex LSPSs have been built and operated over the past nearly one hundred years, guided by standards-based engineering approaches, the research has shown that there are inherent problems even at the core of these methodologies. Generalised Concept of SI is appearing to be a promising framework to provide a solid foundation for future SIC methodologies of LSPSs . The paper outlined structure of the framework, showed that philosophical considerations can be used to pave the way to a sound approach towards a theoretical basis for a modern methodology, and sketched a state-of-the-art thermome chanics-based model –based on a variant of TIV – that seems promising for future SIC methodologies of LSPSs . This model can be considered as a promising example for a phenomenology of ageing in structural materials, and concur rently opens the way towards a description of cracks in differently behaving and ageing materials. References ASME 2021, 2021. Boiler and Pressure Vessel Code Complete Set. ASME New York. Cellucci, C., 2017. Rethinking Knowledge. The Heuristic View. Vol. 4 of the series European Studies in Philosophy of Science, Springer IP AG. Chen, X.H., Mai, Y.W., 2013. Fracture Mechanics of Electromagnetic Materials. Nonlinear Field Theory and Applications. Imperial College Press, London. Cherepanov, G.P., 1967. 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