PSI - Issue 42

T. Fekete et al. / Procedia Structural Integrity 42 (2022) 1684–1691

1685

2

T. Fekete et al.: Extending reliability of FEM simulations… / Structural Integrity Procedia 00 (2019) 000–000

Nomenclature

Continuum Mechanics of Solids

CMS DSC

Design Safety Calculation

Digital Twin

DT

Finite Element Method Information Technology

FEM

IT

Representative Volume Element

RVE

Structural Integrity

SI

Structural Integrity Calculation

SIC

1. Introduction

Finite element ( FE ) simulations are widely used in both academy and industry to predict the strength performance and the expected behavior of components under severe malfunctions or accidents. Most challenging task of these simulations is predicting the Structural Integrity ( SI ) limits of components and systems. Although nonlinear Continuum Mechanics of Solids ( CMS ) is a promising approach for describing the mechanical behavior of structural materials even in the large deformation regime, the potential predictive capabilities of these methods are difficult to achieve. A common, long-standing problem in applications is that plastic the flow curves obtained from measurement results are often –especially for large deformations– not accurate and reliable enough. A significant part of the problem is caused by the limited quantity and quality of the information obtained from tensile tests performed with the extensometers and complied with industrial standards. To resolve the problem, a research project has been initiated in Hungary, targeting the objective to determine the plastic flow curves from the results of tensile tests supported by full field measurement techniques, using an evaluation methodology based on the Digital Twin ( DT ) philosophy. A measurement system with full-field measurements is used. The DT of the measurement system is also in operation. The goal of the progression is to achieve a level of accuracy of the constitutive models, developed from observations by using full-field measurement techniques. Furthermore, it should guarantee a good match between the observed shape of a specimen and the results of calculations performed on the DT over the whole observed geometry. The development of the method is ongoing. As a by-product of the work carried out so far, an evaluation procedure has been developed which is based on correction methods found in the literature, requiring significantly less resources than the evaluation for matching over the entire geometric model, but leading to results with satisfactory accuracy for many applications. The rest of the paper will first explain theoretical foundations of the development, then present the correction-based evaluation procedure and some typical results. Before moving to the main topic, the question may be posed here whether, in describing the development of a method for evaluating a routine materials testing method –i.e., tensile testing– it is worth explaining the theoretical basis of the work, and if so, why. The answer is yes , it is appropriate, because observing and measuring are selective: there is always a particular point of view behind them, expressed by theory, which is the basis for what to observe, what to measure and how to interpret it –see Cellucci (2018)–. That means that theory and measurements –although at first sight they may appear to be independent to certain people– are not independent, but strongly interrelated; neither theory gives a complete knowledge of the material, nor the knowledge determined by measurements. Yet, by combining theory with the results of measurements, knowledge about the material multiplies. This phenomenon is expressed in modern physics by saying that theory and measurements are entangled –see Wilczek (2016)–. By presenting the theory, the conceptual framework in which measurements and their results are interpreted, is made explicit. Based on the theory, numerical procedures are developed to make the observations traceable on the DT . Strength problems of engineering design and the simulations needed to predict expected behavior of engineering equipment are formulated in terms of CMS . Engineering models are derived from the fundamental theory along different approximations and these models are then applied to solve practical engineering problems. Nowadays, the 2. Theoretical Foundations