Comparison of a Fracture Toughness Test (Mode II) with FDEM Fracture Simulations Using Quantitative Laboratory and Numerical Data

Mode II fracture toughness is a key parameter in geomechanical modeling. To evaluate whether the Double-edge Notched Brazilian Disk Test is suitable for its determination, a 2D numerical model was created and compared with laboratory DNBD tests, where fracture propagation was recorded using a high-speed camera. The numerical model closely matches observed fracture patterns for all rock samples, correctly classifying valid patterns as predominantly shear fractures and confirming the DNBD test's reliability for Mode II fracture toughness. Force-strain curve comparisons were challenging due to the wooden spacers in the lab tests, but apparent similarities emerged. Therefore, the DNBD test is considered suitable for determining Mode II fracture toughness if valid and invalid fracture patterns are distinguished. However, one numerical model for one granite produced an invalid pattern, matching the predominantly invalid failures of this rock in the lab. This raises the question of whether specific rock-mechanical properties influence the likelihood of invalid fracture patterns in DNBD tests.