PSI - Issue 68

T. Fekete et al. / Procedia Structural Integrity 68 (2025) 687–693

688

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T. Fekete et al. / Structural Integrity Procedia 00 (2025) 000–000

Nomenclature CM

Continuum Mechanics Continuum Thermomechanics

CTM

Digital Twin

DT

NonLinear Field Theory of Fracture Mechanics

NLFTFM

Nuclear Power Plant

NPP SIC TMF

Structural Integrity Calculation Theory of Material Forces

Moreover, the Long-Term Operation also poses a challenge for R&D , as a significantly reduced quantity of structural material is currently available for the experiments necessary to complete Structural Integrity Calculations ( SIC s) for further licensing, in comparison to previous projects. Despite the fact that the international best-practices based SIC methodology (IAEA 2006; MRKR – SHR – 2004 2004; Kang, Kupča 2010; VERLIFE 2008) has been considered reliable so far, recent results within basic sciences have highlighted the potential to extend the SIC methodology to the broader realm of material behavior. Generalized SIC methodology is based on a unified nonlinear theory of modern Continuum ThermoMechanics ( CTM ) and Fracture Mechanics ( FM ), which is referred to in the literature as the "NonLinear Field Theory of Fracture Mechanics" ( NLFTFM ) (Chen, Mai 2013). The conventional methodology for SIC s is based in classical Continuum Mechanics ( CM ), whereas the novel methodology is rooted in modern CTM . From the perspective of theoretical physics, modern CTM is a continuum field theory that has been developed with the objective of characterizing time-dependent processes in spatially inhomogeneous, non-equilibrium systems with finite state-change rates (Gyarmati 1970; Muschik, Papenfuß, Ehrentraut 2001; Podio-Guidugli 2019, Morro, Giorgi, 2023). Beyond this, modern CTM has its roots in a worldview different from CM . While classic CM is fundamentally reversible, modern CTM is a theory based on the irreversibility hypothesis , which posits that the world is inevitably irreversible (Öttinger 2017; Torromé 2021). It is worthy of note that the recently proposed methodology for SIC s could be based on the Theory of Material Forces ( TMF ) in place of the NLFTFM . This is because the TMF is also founded upon the principles of the modern CTM and incorporates FM (Maugin 2010; Steinmann 2022). Theory of Configurational Forces is another name for TMF . The theoretical foundations of the new SIC methodology are outlined in more detail in (Fekete 2023). In order to ensure the validity of the novel methodology, it is essential to assess the material parameters that can only be derived from empirical evidence through the lens of the underlying Conceptual/Theoretical framework (Bažant, Cedolin 1991, Béda, Kozák, Verhás 1995). It is essential that experiments are designed and performed in a manner that ensures the collection of sufficient information for the theoretical and numerical apparatus. Furthermore, the measurements should be evaluated on models that accurately describe the nonlinear geometric and material behavior of the test specimens with the requisite precision. A unified measuring and measurement evaluation system has recently been developed, which permits the monitoring of experiments with high temporal resolution and the acquisition of full-field data. Evaluation of measurements then becomes possible using the DT of the experimental setup (Fekete, Antók, Tatár, Bereczki 2024). Tensile test specimens were produced on a high-precision CNC machining center, and a fine-resolution coordinate map was obtained using its high accuracy coordinate measuring system. By employing full-field observation and data acquisition technology, a substantial amount of information with high temporal and spatial resolution is gathered, enabling the monitoring of the specimen’s geometric evolution and the tracking of observable patterns over time. The DT is based on the second-order theory of classic CM , which has been proven to offer an effective tool for tracking the time evolution of the specimen’s geometry and the patterns observed during measurements. The present study aims to demonstrate that the theoretical model implemented in the DT is suitable for explaining observations related to the specimen geometry, for which standard procedures –see e.g. ASTM E8/M8-24 2024– are inadequate. This is made evident by employing realistic post-production geometric dimensions of the specimens in their respective DT s, as determined through the utilization of precise measurements.