Quantification of the stress field associated with mixed-mode I/II crack initiation considering the pre-existing weak interlayers: A photoelastic experimental study using 3D printed transparent models

Abstract

Accurate identifying and describing the full-field stress distribution and fracture parameters at the crack tip in rock structures with primary fractures and weak interlayers lay the groundwork for predicting the structural failure behavior of rock masses. This study utilizes 3D printing to create flat-plate models with weak interlayers and open-inclined cracks. The ten-step phase-shift method is applied to obtain the full-field stress of the model. The stress intensity factors at the crack tip are determined using crack multiparameter stress field equations and the nonlinear over-determined least squares method, with an analysis of the method’s reliability. The study explores the effects of mechanical properties, distribution, and length of weak interlayers on the full-field stress difference and stress intensity factor at the crack tip under uniaxial compression. By conducting experiments on low-temperature uniaxial compression, we conducted an analysis of crack propagation characteristics and the influence exerted by weak interlayers. The results indicate the robust reliability of the combination of the ten-step phase-shift method, the multiparametric equation for the crack tip, and the nonlinear over-determined least squares method in evaluating stress intensity factors at the crack tip. The weak interlayer has the potential to shield the principal stress difference and stress intensity factors K_I and K_II at crack tips, with this shielding effect being influenced by the mechanical properties, distribution, and length of the weak interlayer. The T stress at the crack tip is influenced by the mechanical properties, distribution, and length of the weak interlayer. At −50 ℃, crack propagation undergoes a slow growth stage and a rapid growth stage. The presence of weak interlayers hinders the propagation of cracks and may affect the initiation direction of cracks.