Using crack face displacement to measure stress intensity: A practical approach

Abstract

This study presents a novel method for estimating the stress intensity factor (K) using direct measurements of crack face displacements. Starting from Westergaard’s analytical solutions, modifications were derived from adapting these equations for finite-width bodies in five different geometries, including centre crack plates, edge crack plates (with both single and double cracks), plates containing angled cracks, and cracks in three-point bend specimens. Finite Element Analysis (FEA) was used to determine the profile of crack face displacement at different points along each crack. It was found that for centre-cracked plates, Westergaard’s equation worked well with only slight correction needed, whilst for edge-cracked geometries, a different equation was needed to describe the displacement profile. Unlike conventional methods that require applied load or local stress–strain data, this approach provides a simple and practical means of estimating K using optical measurements of crack face displacement. The proposed equations correctly predicted K with errors less than 10% for all geometries considered. To demonstrate the practical use of this method, an experimental study was conducted to estimate the fracture toughness (K_IC) of leaf specimens using crack face displacement measurements. The results were within 3% of those obtained from conventional laboratory tests, confirming the feasibility of this approach for real-world applications. Other potential applications to different materials and structures were also proposed. These findings establish crack face displacement as a reliable parameter for fracture analysis, offering potential applications in material testing, non-destructive evaluation, and structural health monitoring.