PSI - Issue 72

Sergio Arrieta et al. / Procedia Structural Integrity 72 (2025) 362–369

367

and an independent Advisory Board provide ongoing oversight and evaluation of all project tests. These combined strategies serve to maintain rigorous control over both the scope and the quality of the experimental program. 5.3. Modeling Modeling plans are designed to optimize industrial impact by integrating research findings with existing and forthcoming work. WP4 focuses on five key areas: numerical analysis for test design and interpretation, data mining, review of codified methods, advancement of fatigue damage modeling (including non-codified approaches), and industrial application. A core objective is to move beyond traditional empirical fatigue assessments by developing and validating mechanistically informed models for EAF. This involves addressing complexities such as material hardening, non-zero mean stress, and variable amplitude loading waveforms (Colin et al. (2010)), which are often inadequately captured by simplified models. Ongoing analysis highlights the necessity for improved modeling of material hardening effects on mean stress, plastic loading behavior, and the environmental factor parameter. Furthermore, the exploration of non-codified methods, including crack growth modeling, contributes to a deeper understanding of EAF and endurance data interpretation, with the final goal of supporting the development of new code cases (as Asada and Nomura (2021)). 5.4. Mechanical understanding Current engineering assessments of EAF typically rely on simplified methodologies, deriving fatigue curves and cumulative usage factors (Chopra and Stevens (2018), USNRC (2018)) from experimental test results. This simplification arises from the inherent complexity and cost associated with developing mechanistic models directly from empirical data. While such models may not yet be universally adopted in engineering applications, they are crucial for validating the accuracy and applicability of simplified models and offer the potential for innovative approaches to fatigue assessment. A key objective of the INCEFA-SCALE project is to advance the development and application of these potentially less conservative mechanistic EAF models within engineering contexts. A fundamental understanding of the EAF mechanism is of greatest importance. Given the significant influence of material conditions and load distributions, the project will incorporate both microstructural analysis (Vainionpaa et al. (2023)) and FEA. Standardized microstructural analysis methodologies will be employed. As an example, within WP5, a validated procedure has been implemented to quantify fatigue striation spacing (Howe et al. (2022)). Specimens will be characterized both pre- and post-fatigue testing to identify and quantify manufacturing-induced damage and its subsequent evolution during fatigue. This characterization will yield critical data on key mechanistic aspects of fatigue, including striation spacing and damage accumulation. The integration of microstructural characterization with diverse fatigue testing protocols will enhance the mechanistic understanding of fatigue patterns characteristic of NPP components. An example of fatigue striation spacing counting is shown in Fig. 4.

Fig. 4. SEM images of fatigue fracture surface (UC10 test). Detail of striations spacing (right).

An INCEFA-SCALE evaluation model will be defined. Concurrently with INCEFA-SCALE's progression towards fatigue test standardization, results will be evaluated using existing fatigue regulations, incorporating accumulated