Cracking mechanisms of a medium-grained granite under mixed-mode I-II loading illuminated by acoustic emission
01 Sep 2021-International Journal of Rock Mechanics and Mining Sciences (Pergamon)-Vol. 145, pp 104852
TL;DR: In this article, the authors investigate the effect of the loading condition and granite heterogeneity on the cracking mechanism and find that the microcracks under mixed-mode I-II loading do not nucleate as easily as compared with that in mode I case.
About: This article is published in International Journal of Rock Mechanics and Mining Sciences.The article was published on 2021-09-01. It has received 14 citations till now. The article focuses on the topics: Acoustic emission & Stress intensity factor.
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TL;DR: In this article , the effects of water and fissures on rock's mechanical properties and corresponding acoustic emission characteristics were studied. But the results of this paper lay theoretical foundations for monitoring and pre-warning of engineering rock failure in water environment.
18 citations
TL;DR: In this paper, the authors analyzed the effects of pre-existing thermal microcracks on the microcracking mechanisms of Hong Kong granite under mode I loading, and found that the presence of the thermal micro-cracks aggravates the micro crack damage.
13 citations
TL;DR: In this paper , three different asymmetric notched semi-circular bending specimens (ANSCB) were designed by adjusting the angle and the distance between supporting rollers to conduct asymmetric three-point bending tests.
Abstract: In this paper, to investigate mixed-mode I-II fracture behaviors, three different asymmetric notched semi-circular bending specimens (ANSCB) were designed by adjusting the angle and the distance between supporting rollers to conduct asymmetric three-point bending tests. Several aid technologies, including acoustic emission (AE), digital image correlation (DIC), crack propagation gauge (CPG), and scanning electron microscopy (SEM), was utilized to monitor and assess the fracture characteristic. Meanwhile, the fractal dimension of the fracture surface was assessed based on the reconstructed digital fracture surface. The results show that mixed-mode I-II ANSCB three-point bending fracture is a brittle failure with the characteristics of the main crack being rapidly transfixed and the bearing capacity decreasing sharply. Based on the DIC method, the whole fracture process consists of a nonlinear elastic stage, fracture process zone, crack initiation stage and crack propagation stage. The crack initiation is mainly caused by the tension-shear strain concentration at the pre-existing crack tip. At the microscale, the crack propagation path is always along the grain boundary where the resultant stress is weakest. According to the monitoring of the AE, it can be found that micro-tensile cracks are mainly responsible for the asymmetric three-point bending fracture. The data obtained by CPG suggest that the subcritical crack growth rate is positively correlated to the ultimate load. In addition, asymmetric loading leads to a coarser fracture surface, and thus a higher fractal dimension of the fracture surface. The current study can provide a better understanding of the mixed-mode I-II fracture behaviors of rock.
8 citations
TL;DR: In this article , the effects of cyclic freeze-thaw (F-T) on the microcracking behavior of sandstone under mode I loading were investigated and the results showed that the damage degree does not significantly increase until the F-T cycle number exceeds a threshold between 60 and 90.
5 citations
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TL;DR: A method is described for the minimization of a function of n variables, which depends on the comparison of function values at the (n 41) vertices of a general simplex, followed by the replacement of the vertex with the highest value by another point.
Abstract: A method is described for the minimization of a function of n variables, which depends on the comparison of function values at the (n 41) vertices of a general simplex, followed by the replacement of the vertex with the highest value by another point. The simplex adapts itself to the local landscape, and contracts on to the final minimum. The method is shown to be effective and computationally compact. A procedure is given for the estimation of the Hessian matrix in the neighbourhood of the minimum, needed in statistical estimation problems.
27,271 citations
4,211 citations
TL;DR: In this paper, the authors investigated the general problem of crack extension in a combined stress field where a crack can grow in any arbitrary direction with reference to its original position, and showed that the direction of crack growth and fracture toughness for the mixed problem of Mode I and Mode II are governed by the critical value of the strain-energy-density factor.
Abstract: This paper deals with the general problem of crack extension in a combined stress field where a crack can grow in any arbitrary direction with reference to its original position. In a situation, when both of the stress-intensity factors,k
1,k
2 are present along the crack front, the crack may spread in any direction in a plane normal to the crack edge depending on the loading conditions. Preliminary results indicate that the direction of crack growth and fracture toughness for the mixed problem of Mode I and Mode II are governed by the critical value of the strain-energy-density factor,S
cr. The basic assumption is that crack initiation occurs when the interior minimum ofS reaches a critical value designatedS
cr. The strain-energy-density factorS represents the strength of the elastic energy field in the vicinity of the crack tip which is singular of the order of 1/r where the radial distancer is measured from the crack front. In the special case of Mode I crack extensionS
cr is related tok
1c alone asS
cr = (κ − 1)k
1
2
/8μ. In general,S takes the quadratic forma
1 1
k
1 + 2a
1 2
k
1
k
2 +a
2 2
k
2 whose critical value is assumed to be a material constant. The analytical predictions are in good agreement with experimental data on the problem of an inclined crack in plexiglass and aluminum alloy specimens. The result of this investigation provides a convenient procedure for determining the critical crack size that a structure will tolerate under mixed mode conditions for a given applied stress.
2,066 citations
TL;DR: In this article, the failure process in a brittle granite sample can be stabilized by controlling axial stress to maintain a constant rate of acoustic emission, and the post-failure stress curve can be followed quasi-statically, extending to hours the fault growth process.
Abstract: The failure process in a brittle granite sample can be stabilized by controlling axial stress to maintain a constant rate of acoustic emission. As a result, the post-failure stress curve can be followed quasi-statically, extending to hours the fault growth process which normally would occur violently in a fraction of a second. Using a procedure originally developed to locate earthquakes, acoustic emission arrival-time data are inverted to obtain three-dimensional locations of microseisms. These locations provide a detailed view of fracture nucleation and growth.
870 citations
TL;DR: A review of the successes and limitations of acoustic emission (AE) studies as applied to the fracture process in rock with emphasis on our ability to predict rock failure is presented in this paper.
867 citations