Defining the Best Strain Gauge Placement through Numerical Simulations of the Mechanical Behavior of the Modified-WOL Specimen

Resumo

In structural steels, cracks are an inevitable occurrence, demanding an examination of their ability to resist crack propagation under expected loads and various environmental conditions. The process of experimentally determining fracture toughness comes at a significant expense, involving the use of multiple specimens and extended testing periods, which hinders the swift acquisition of crucial parameters. An alternative approach entails the execution of a constant displacement test using the Modified-WOL specimen, which is equipped with an instrumented bolt for self loading. The primary objective of this method is to provide the Threshold Stress Intensity Factor for Environment-Assisted Cracking, utilizing only a single specimen. The incorporation of electronic instrumentation is essential for obtaining reliable, real-time data. Despite its importance, a consensus is lacking in the literature regarding the best location for sensor installation on the Modified-WOL specimen, potentially influencing its mechanical response. This study aims to explore the mechanical behavior of the three components constituting the Modified-WOL specimen test in accordance with the guidelines outlined by ISO 7539-6. Employing the Finite Element Method with two- and three-dimensional models, this investigation utilizes the Augmented Lagrangian method for formulating the contact regions. Additionally, quarter-point singular elements are employed to accurately represent stress singularity behavior at the crack tip. The numerical computation of fracture parameter (KI) is conducted using the Displacement Correlation Technique. Comparative analyses are then carried out between the numerical and the analytical values of KI determined based on the ISO 7539-6 standard. The findings demonstrate alignment with empirical literature values, ultimately contributing to the identification of the best location for strain gauge installation among the highlighted regions of considerable interest.