Evaluating the fracture resistance of rocks is essential for predicting and preventing catastrophic failure of cracked structures in rock engineering.This investigation developed a brittle fracture model to predict te...Evaluating the fracture resistance of rocks is essential for predicting and preventing catastrophic failure of cracked structures in rock engineering.This investigation developed a brittle fracture model to predict tensile mode(mode I)failure loads of cracked rocks.The basic principle of the model is to estimate the reference crack corresponding to the fracture process zone(FPZ)based on the maximum normal strain(MNSN)ahead of the crack tip,and then use the effective crack to calculate the fracture toughness.We emphasize that the non-singular stress/strain terms should be considered in the description of the MNSN.In this way,the FPZ,non-singular terms and the biaxial stress state at the crack tip are simul-taneously considered.The principle of the model is explicit and easy to apply.To verify the proposed model,laboratory experiments were performed on a rock material using six groups of specimens.The model predicted the specimen geometry dependence of the measured fracture toughness well.More-over,the potential of the model in analyzing the size effect of apparent fracture toughness was discussed and validated through experimental data reported in the literature.The model was demonstrated su-perior to some commonly used fracture models and is an excellent tool for the safety assessment of cracked rock structures.展开更多
RECENTLY, a number of papers have been published concerning the asymptotic independentproperties of V X<sub>i</sub> and sum from 1 X<sub>i</sub> of weakly dependent stationary sequence {X<su...RECENTLY, a number of papers have been published concerning the asymptotic independentproperties of V X<sub>i</sub> and sum from 1 X<sub>i</sub> of weakly dependent stationary sequence {X<sub>i</sub>}.In this letter, let {X<sub>i</sub>} be a standard normal sequence of random variables with zero meanand unit variance and write r<sub>ij</sub>=cov（X<sub>i</sub>, X<sub>j</sub>）.展开更多
The problem of eliminating edge-chipping at the entrance and exit of the hole while drilling brittle materials is still a challenging task in different industries. Grinding- aided electrochemical discharge machining ...The problem of eliminating edge-chipping at the entrance and exit of the hole while drilling brittle materials is still a challenging task in different industries. Grinding- aided electrochemical discharge machining （G-ECDM） is a promising technology for drilling advanced hard-to-ma- chine ceramics, glass, composites, and other brittle mate- rials. Edge-chipping at the entrance of the hole can be fully eliminated by optimizing the machining parameters of G-ECDM. However, edge-chipping at the exit of the hole is difficult to eliminate during the drilling of ceramics and glass. This investigation suggests some practical ways to reduce edge-chipping at the exit of the hole. For this pur- pose, a three-dimensional finite element model was developed, and a coupled field analysis was conducted to study the effect of four parameters, i.e., cutting depth, support length, applied voltage, and pulse-on time, on the maximum normal stress in the region where the edge- chipping initiates. The model is capable of predicting the edge-chipping thickness, and the results predicted by the model are in close agreement with the experiment results. This investigation recommends the use of a low voltage and low pulse-on time at the hole entrance and exit when applying G-ECDM to reduce the edge-chipping thickness. Moreover, the use of a full rigid support in the form of a base plate or sacrificial plate beneath the workpiece can postpone the initiation of chipping by providing support when the tool reaches the bottom layer of the workpiece, thereby reducing the edge-chipping thickness.展开更多
基金he authors thank the financial support fromthe Key Program of National Natural Science Foundation of China(GrantNo.52039007)the Youth Science and Technology Innovation Research Team Fund of Sichuan Province(Grant No.2020JDTD0001).
文摘Evaluating the fracture resistance of rocks is essential for predicting and preventing catastrophic failure of cracked structures in rock engineering.This investigation developed a brittle fracture model to predict tensile mode(mode I)failure loads of cracked rocks.The basic principle of the model is to estimate the reference crack corresponding to the fracture process zone(FPZ)based on the maximum normal strain(MNSN)ahead of the crack tip,and then use the effective crack to calculate the fracture toughness.We emphasize that the non-singular stress/strain terms should be considered in the description of the MNSN.In this way,the FPZ,non-singular terms and the biaxial stress state at the crack tip are simul-taneously considered.The principle of the model is explicit and easy to apply.To verify the proposed model,laboratory experiments were performed on a rock material using six groups of specimens.The model predicted the specimen geometry dependence of the measured fracture toughness well.More-over,the potential of the model in analyzing the size effect of apparent fracture toughness was discussed and validated through experimental data reported in the literature.The model was demonstrated su-perior to some commonly used fracture models and is an excellent tool for the safety assessment of cracked rock structures.
文摘RECENTLY, a number of papers have been published concerning the asymptotic independentproperties of V X<sub>i</sub> and sum from 1 X<sub>i</sub> of weakly dependent stationary sequence {X<sub>i</sub>}.In this letter, let {X<sub>i</sub>} be a standard normal sequence of random variables with zero meanand unit variance and write r<sub>ij</sub>=cov（X<sub>i</sub>, X<sub>j</sub>）.
文摘The problem of eliminating edge-chipping at the entrance and exit of the hole while drilling brittle materials is still a challenging task in different industries. Grinding- aided electrochemical discharge machining （G-ECDM） is a promising technology for drilling advanced hard-to-ma- chine ceramics, glass, composites, and other brittle mate- rials. Edge-chipping at the entrance of the hole can be fully eliminated by optimizing the machining parameters of G-ECDM. However, edge-chipping at the exit of the hole is difficult to eliminate during the drilling of ceramics and glass. This investigation suggests some practical ways to reduce edge-chipping at the exit of the hole. For this pur- pose, a three-dimensional finite element model was developed, and a coupled field analysis was conducted to study the effect of four parameters, i.e., cutting depth, support length, applied voltage, and pulse-on time, on the maximum normal stress in the region where the edge- chipping initiates. The model is capable of predicting the edge-chipping thickness, and the results predicted by the model are in close agreement with the experiment results. This investigation recommends the use of a low voltage and low pulse-on time at the hole entrance and exit when applying G-ECDM to reduce the edge-chipping thickness. Moreover, the use of a full rigid support in the form of a base plate or sacrificial plate beneath the workpiece can postpone the initiation of chipping by providing support when the tool reaches the bottom layer of the workpiece, thereby reducing the edge-chipping thickness.
