Novel direct measurement of mode I fracture toughness in brittle geomaterials using the Internal Edge-Notched Ring (IENR) test: Insights from coupled experimental and numerical studies

This study proposes the Internal Edge-Notched Ring (IENR) test as a novel method for determining Mode I fracture toughness (K IC ) of brittle geomaterials, with gypsum used as a representative material. The IENR configuration features a simple, compact geometry that requires minimal machining. Ring specimens (60 mm inner and 200 mm outer diameter) with notch lengths of 15, 30, and 45 mm were tested under compressive loading via high-stiffness plates engaging semi-cylindrical slots, inducing radial tensile stresses. Cracks consistently initiated at the notch tip and extended through the ligament, confirming Mode I behavior. K IC values remained nearly constant across different notch lengths, and a strong linear relationship between tensile strength and fracture toughness was observed (σ t = 7.02 K IC ). For comparison, Notched Brazilian Disc (NBD) specimens with varying notch lengths (15, 30, and 45 mm) were also tested, yielding slightly higher K IC values—likely due to less uniform tensile stress at the notch tip. Numerical simulations using PFC2D showed excellent agreement with experimental results in both fracture patterns and K IC values, validating the IENR test as a reliable and efficient method for characterizing fracture toughness in brittle construction materials. • -The Internal Edge-Notched Ring test is a novel way to measure fracture toughness in brittle materials like gypsum. • This innovative method has a simple design that needs minimal machining for practical use. • Cracks consistently initiated at notch tips, confirming expected Mode I fracture behavior. • Fracture toughness values remained stable across different notch lengths, proving method reliability. • Numerical simulations matched experimental results closely, supporting the validity of this new testing method.