Experimental investigation on mechanical properties of yellow sandstone samples containing two coplanar fissures under multistage constant-amplitude-cyclic loading#br#
LI Kesheng1，LIU Chuanxiao2
(1. State Key Laboratory for Geomechanics and Deep Underground Engineering，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China；2. College of Water Conservancy and Civil Engineering，Shandong Agricultural
University，Tai?an，Shandong 271018，China)
摘要This work aims to elaborate the mechanical properties and damage characteristics of yellow sandstone samples containing two coplanar fissures under diverse dynamic loading frequencies. To this end，multistage constant-amplitude-cyclic loading experiments were conducted on fissured sandstone，and the fatigue mechanical properties and deformation of the rock，the evolution of acoustic emission(AE) parameters during the loading process，the microstructural characteristics of the fractured surface of specimens，as well as the role of loading frequency on fatigue damage mechanism，were analyzed. The results show that：(1) The peak strength，the fatigue life，and axial strain of the specimens increase with growing frequency. (2) The strain of the specimen increases in a stepwise manner with longer time，and at the last fatigue stage，the specimen deformation rises dramatically until the specimen fails. (3) The accumulative AE ringing counts of the samples show a quadratic function increase with higher loading frequency，and the samples under high loading frequency capture more ringing counts before failure compared to those under low loading frequency. (4) The ultimate failure mode of the specimen is related to both the pre-existing flaws and the loading frequency，that is，the samples under low loading frequency conditions perform few cracks and unclear propagation path，and it is clearly observed that the cracks coalescence directly between the two inner tips of the pre-existing flaws. Samples under high frequency conditions exhibit complex failure mode，i.e.，wing cracks appear at pre-existing fissures tip，and the outer wing cracks respectively extend to the specimen ends，while the inner wing cracks gradually extend after indirect coalescence. (5) As the dynamic loading frequency climbs，the microscopic features of the fractured surface of the specimen evolves from dominant intergranular fracture，to the coexistence of intergranular fracture，transgranular fracture，and cleavage fracture，and to dominant transgranular fracture.
Abstract：This work aims to elaborate the mechanical properties and damage characteristics of yellow sandstone samples containing two coplanar fissures under diverse dynamic loading frequencies. To this end，multistage constant-amplitude-cyclic loading experiments were conducted on fissured sandstone，and the fatigue mechanical properties and deformation of the rock，the evolution of acoustic emission(AE) parameters during the loading process，the microstructural characteristics of the fractured surface of specimens，as well as the role of loading frequency on fatigue damage mechanism，were analyzed. The results show that：(1) The peak strength，the fatigue life，and axial strain of the specimens increase with growing frequency. (2) The strain of the specimen increases in a stepwise manner with longer time，and at the last fatigue stage，the specimen deformation rises dramatically until the specimen fails. (3) The accumulative AE ringing counts of the samples show a quadratic function increase with higher loading frequency，and the samples under high loading frequency capture more ringing counts before failure compared to those under low loading frequency. (4) The ultimate failure mode of the specimen is related to both the pre-existing flaws and the loading frequency，that is，the samples under low loading frequency conditions perform few cracks and unclear propagation path，and it is clearly observed that the cracks coalescence directly between the two inner tips of the pre-existing flaws. Samples under high frequency conditions exhibit complex failure mode，i.e.，wing cracks appear at pre-existing fissures tip，and the outer wing cracks respectively extend to the specimen ends，while the inner wing cracks gradually extend after indirect coalescence. (5) As the dynamic loading frequency climbs，the microscopic features of the fractured surface of the specimen evolves from dominant intergranular fracture，to the coexistence of intergranular fracture，transgranular fracture，and cleavage fracture，and to dominant transgranular fracture.
2023, Vol. 42 
