PSI - Issue 54

T. Fekete et al. / Procedia Structural Integrity 54 (2024) 314–321 T. Fekete, D. Antók, L. Tatár, P. Bereczki Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction

Preserving Structural Integrity ( SI ) of Large-Scale Pressure Systems ( LSPS s) is of utmost importance. This is done by Structural Integrity Calculations ( SIC s). The aim of the SIC s is to assure fail-safe operation of these systems during their entire Service Lifetime ( SL ). The Technically Allowable Lifetime ( TAL ) of a LSPS is the time during which it can perform its intended functions safely, under normal conditions and in case of various –low probability– accidents. The expected TAL of a LSPS is predicted by SIC s, that simulate system behaviour considering the cumulated impact of past operational history and expected future load patterns. For a system, SL ≤ TAL . Due to the very high value of LSPS s Long-Term Operation ( LTO ) is economically preferable, however it is a challenge for the engineering scientific community, making the need to increase the accuracy of SIC s even more urgent. SIC s are driven mainly by FEM simulations. Digital Twins ( DT s) offer a great and promising opportunity to improve the performance of SIC s on a previously unseen level. The effectiveness of SIC s depends on the predictive ability of the underlying theoretical framework, reliability of FE models and the quantity and quality of the information obtained from material tests supporting these calculations.

Nomenclature

Digital Twin

DT FE

Finite Element(s)

Finite Element Method

FEM

Structural Integrity

SI

Structural Integrity Calculation/Computation

SIC

Service Lifetime

SL

Large-Scale Pressure System

LSPS LTO

Long Term Operation

Technically Allowable Lifetime

TAL

2. Theoretical considerations

2.1. Paradigm Shift in the Methodology for SICs

The SIC methodology in its ‘classic approach’ is based on a disciplinary based phenomenological paradigm –see top of Figure 1.–. A shift from this approach to a more advanced, modern Thermodynamics/Thermomechanics-based paradigm is emerging, as shown in Figure 1. For this new paradigm, a new theoretical framework is developed, based on the work of Chen and Mai (2013), Verhás (1997), Maugin (2010) and Steinmann (2022), distinguishing between short and long timescales and considering geometric and material nonlinearities. This theoretical framework covers the same four relevant phenomena as the classic approach –i.e., heat transport, mechanics, fracture mechanics and ageing–, but modern Thermodynamics is transdisciplinary in nature, integrating the description into a holistic whole. The basic field equations considered in the framework are as follows: • The equation of motion and the kinematical model ‒ second-order Boltzmann Continuum, with large deformation ‒ ; • The balances of mass, linear momentum, angular momentum and energy –1 st law of thermodynamics–; • Constitutive laws, taking into account the 2 nd law of thermodynamics –the dissipation requirement–. For a more detailed description of the governing equations, see Fekete (2023). Solutions to these equations describe a Thermodynamic process –Papenfuß (2020)–. The Conceptual Framework of SI is the Theoretical Frame with its associated Computational Framework. To ensure that a Computational Model correctly represents the behaviour of the engineering structure being investigated, all necessary material tests should be designed, performed, and evaluated within this Conceptual Framework –see Bažant and Cedolin (1991), Sih (1991) and Béda, Kozák, Verhás (1995)–. In other words, the concept of measurement and evaluation should be consistent with the Conceptual Framework.