Improvement and verification of crack propagation prediction theory for rock mate-rials under compressive load

LI Xiulei; DIAO Hang; CHEN Chen; HUANG Feng; LING Tianqing; ZENG Bin

doi:10.16186/j.cnki.1673-9787.2023070006

Abstract：Objectives The objective was to improve the accuracy of crack propagation prediction for rock materials by addressing deficiencies in the traditional maximum circumferential stress criterion(MTS crite-rion),which disregarded the non-singular stress term(T-stress)in the crack tip's stress field and the crack geometrical properties.Methods Based on the conventional MTS criterion,a new fracture criterion for non-closed fractures in rocks was established by considering the effects of T-stress and fracture geometry properties on the fracture tip stress field.Uniaxial compression tests were conducted on rock specimens with non-closed cracks in the center.The predicted criterion values were compared with the measured crack angle(θ),and the influence of fracture geometry and T-stress on crack initiation and the crack tip stress field was analyzed to assess the validity of the proposed criterion.Results The results of the research indi-cated that only considering fracture geometry features led to an increase in the crack width-length ratio(b/a),causing a rise in the stress intensity factor(KI).This increase resulted in tension fractures forming due to tensile action at the fracture tip,thereby increasing the type Ⅰ cracks in the composite fracture.When the geometric characteristics of the crack and T-stress were introduced simultaneously,an increase in the crack width ratio(b/a)reduced the crack angle θ and increased the maximum peripheral stress(σθ)max.With the introduction of T-stress,the crack starting angle(θ)and the crack starting load are closer to the actual value,then the T-stress plays a crucial role in suppressing crack initiation.Additionally,the crack starting angle(θ)gradually transitioned from positive to negative cracking with the increase of the crack dip angle(β).Conclusions The crack initiation criterion,considering T-stress and crack geometry,can more accurately predict the crack initiation angle(θ)within the range of 0° to 60° of the crack dip angle(β).