Behavior and Fracture Mechanism of Brittle Rock with Pre-Existing Parallel Cracks

2006 ◽  
Vol 324-325 ◽  
pp. 1055-1058 ◽  
Author(s):  
M.X. Zhang ◽  
X.L. Lee ◽  
A.A. Javadi
Keyword(s):  
Fracture Mechanism ◽  
Rock Fracture ◽  
Strength Criterion ◽  
Brittle Rock ◽  
Fracture Mechanisms ◽  
Stress Equilibrium ◽  
Parallel Cracks ◽  
Micro Cracks ◽  
Griffith Theory ◽  
Almost All

There is a macro-crack and micro-crack system in rock, which affects almost all the mechanical properties of rock, especially for the fracture mechanism. The propagation of pre-existing cracks in rock samples under load is fundamental to understanding of rock fracture mechanisms. It is evident that assumption of Griffith theory was not in accord with the fact that numerous cracks exist in rock. So, it is difficult to explain how the propagation of a micro-crack developed into macro-failure by conventional theories. In order to investigate the cause and results of fracture within the rock, the stress concentration around the micro-cracks was analyzed, which resulted in propagation of wing cracks and connecting adjacent original cracks, eventually leading to macro-failure. The experiments on gypseous samples with pre-existing parallel cracks (flat rectangular in shape) under compression were carried out. The fracture mechanism and the stress equilibrium condition at brittle rock were discussed. Based on the fracture mechanism of brittle rock, a strength criterion of rock was proposed.

scholarly journals Experimental Research on Brittleness and Rockburst Proneness of Three Kinds of Hard Rocks under Uniaxial Compression

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Rongchao Xu ◽  
Yiding Jin ◽  
Yumin Zhang
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Fracture Mechanism ◽  
Large Scale ◽  
Rock Fracture ◽  
Failure Process ◽  
High Energy ◽  
Brittle Rock ◽  
Evaluation Index ◽  
Unstable Crack

Rockburst is a highly destructive geological disaster caused by excavation and unloading of hard and brittle rock mass under high geostress environment. Quantitative evaluation of rock brittleness and rockburst proneness is one of the important tasks in potential rockburst assessment. In this study, uniaxial compression and acoustic emission tests were carried out for basalt, granite, and marble, and their brittleness and rockburst proneness were quantitatively evaluated. The acoustic emission evolution characteristics of the three rocks during uniaxial compression were analyzed, and the differences of fracture mechanism of the three rocks were compared. The results show that (1) based on the brittleness evaluation index, basalt is the most brittle rock, followed by granite, and marble is the weakest; (2) based on the rockburst proneness evaluation index, combined with the macroscopic failure phenomenon and morphology of the samples, the rockburst proneness of basalt is the strongest, followed by granite, and marble is the weakest; (3) there exists a positive correlation between rockburst proneness and brittleness, and the fitting results show that they are approximately exponential; and (4) brittleness has an important influence on the rock fracture mechanism. Unlike marble, basalt and granite with strong brittleness continuously present high-energy acoustic emission signals in the stage of unstable crack propagation, and large-scale fracture events continue to occur; from the calculation results of the acoustic emission b value, the stronger the brittleness of rock, the larger the proportion of large-scale fracture events in the failure process.

Fracture Mechanism and Fracture Toughness at the Interface Between Cortical and Cancellous Bone

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Pankaj Shitole ◽  
Arpan Gupta ◽  
Rajesh Ghosh
Keyword(s):  
Fracture Toughness ◽  
Cortical Bone ◽  
Cancellous Bone ◽  
Fracture Mechanism ◽  
Fracture Mechanisms ◽  
J Integral ◽  
Single Edge ◽  
Plastic Part ◽  
Edge Notch ◽  
Sample Width

The microstructure at the interface of cortical and cancellous bone is quite complicated. The fracture mechanisms at this location are necessary for understanding the comprehensive fracture of the whole bone. The goal of this study is to identify fracture toughness in terms of J integral and fracture mechanism at the interface between cortical and cancellous bone. For this purpose, single edge notch bend (SENB) specimens were prepared from bovine proximal femur according to ASTM-E399 standard. Bone samples were prepared such that half of the sample width consists of cortical bone and other half of the width was cancellous bone; this interfacial bone is referred as a corticellous bone. Elastic–plastic fracture mechanics was used to measure fracture toughness. The J integral (both elastic and plastic) was used to quantify the fracture toughness. The plastic part of J integral value (Jpl) of corticellous specimen was 9310 J m−2, and shown to be 27 times of the J integral of the elastic part (Jel), 341 J m−2. The total J integral of the corticellous bone was found to be 9651 J m−2, which is close to two times of the cortical bone, 4731 J m−2. This study observed that J integral of corticellous bone is higher than the cortical bone since more energy is required for plastic deformation of corticellous bone due to crack branches and slowdown at the interface between cortical and cancellous bone.

scholarly journals Tensile Fracture Mechanism of Masonry Wallettes Parallel to Bed Joints: A Stochastic Discontinuum Analysis

Modelling ◽  
2020 ◽  
Vol 1 (2) ◽  
pp. 78-93
Author(s):  
Bora Pulatsu ◽  
Semih Gonen ◽  
Ece Erdogmus ◽  
Paulo B. Lourenço ◽  
Jose V. Lemos ◽  
...  
Keyword(s):  
Material Properties ◽  
Fracture Mechanism ◽  
Equations Of Motion ◽  
Constitutive Models ◽  
Numerical Approach ◽  
Tensile Fracture ◽  
Fracture Mechanisms ◽  
Contact Points ◽  
Statistical Variations ◽  
Modeling Strategy

Nonhomogeneous material characteristics of masonry lead to complex fracture mechanisms, which require substantial analysis regarding the influence of masonry constituents. In this context, this study presents a discontinuum modeling strategy, based on the discrete element method, developed to investigate the tensile fracture mechanism of masonry wallettes parallel to the bed joints considering the inherent variation in the material properties. The applied numerical approach utilizes polyhedral blocks to represent masonry and integrate the equations of motion explicitly to compute nodal velocities for each block in the system. The mechanical interaction between the adjacent blocks is computed at the active contact points, where the contact stresses are calculated and updated based on the implemented contact constitutive models. In this research, different fracture mechanisms of masonry wallettes under tension are explored developing at the unit–mortar interface and/or within the units. The contact properties are determined based on certain statistical variations. Emphasis is given to the influence of the material properties on the fracture mechanism and capacity of the masonry assemblages. The results of the analysis reveal and quantify the importance of the contact properties for unit and unit–mortar interfaces (e.g., tensile strength, cohesion, and friction coefficient) in terms of capacity and corresponding fracture mechanism for masonry wallettes.

Research Progress on Fracture Mechanism of Mechanical Products

2010 ◽  
Vol 118-120 ◽  
pp. 551-555
Author(s):  
Jiang Shao ◽  
Cheng Hui Zeng
Keyword(s):  
Ductile Fracture ◽  
Failure Mechanism ◽  
Fatigue Fracture ◽  
Cleavage Fracture ◽  
Fracture Mechanism ◽  
Research Progress ◽  
Fracture Mechanisms ◽  
Reliability Design ◽  
Mechanical Products

Based on reliability physics theory, investigation on failure mechanism is a kernel job in reliability design and analysis of mechanical products. The basic conception and classification of failure mechanism are introduced. Researches on five kinds of fracture mechanisms (ductile fracture, cleavage fracture, quasi-cleavage fracture, fatigue fracture and intergranular fracture) are discussed in detail. At last, problems are summarized and suggestions for future investigations are also made.

Investigation of Compressive and Damage Mechanisms in Fully Lamellar TiAl-Based Alloy

2012 ◽  
Vol 487 ◽  
pp. 416-422
Author(s):  
Bin Tang ◽  
Chuan Jing Chen ◽  
Zi Gong Xue ◽  
Chun Jing Wu ◽  
Shuang Shou Li
Keyword(s):  
Mechanical Property ◽  
Shear Stress ◽  
Cleavage Fracture ◽  
Tial Alloy ◽  
Fracture Mechanisms ◽  
Maximum Strain ◽  
Compression Tests ◽  
Compressive Properties ◽  
Micro Cracks ◽  
Fully Lamellar

The compressive Properties and the effect of anti-damage were studied by means of compression and pre-compression damage tests. The study indicated that：The fracture mechanisms of compression tests were quasi-cleavage fracture attributed to the normal stress and shear stress. Fracture strength, the maximum strain and the fracture energy were reduced in varying degrees, and the damage was intensified while increasing preload value. The mechanical property of the TiAl alloy degrades because of the present of the cracks, and large amount of micro-cracks appear on the surface firstly.

scholarly journals On the tensile fracture behavior of Cr coating for ATF cladding considering the effect of pre-oxidation

2021 ◽  
Vol 2076 (1) ◽  
pp. 012047
Author(s):  
Ziyan Pan ◽  
Mingduo Yuan ◽  
Zhenyu Zou ◽  
Weijian Zhang ◽  
Mingyue Du ◽  
...  
Keyword(s):  
Interfacial Strength ◽  
Tensile Fracture ◽  
Fracture Mechanisms ◽  
Failure Behavior ◽  
Premature Failure ◽  
Interfacial Cracks ◽  
Micro Cracks ◽  
Coating Microstructure ◽  
Cr Coating

Abstract In this study, the fracture mechanisms of Cr-coated Zr4 alloy samples were studied by in-situ tensile testing with high-resolution observations. Both original sample and pre-oxidized sample were studied to study the effects of pre-oxidation on the cracking and failure behavior. For the Cr-coated Zr4 sample, with the increase of tensile strain, multiple surface cracks were dominant and less interfacial cracks were formed, indicating good interfacial strength of Cr coating. For the pre-oxidized samples, there was a thin oxide layer formed on the Cr coating surface, revealing improved oxidation resistance and protection effects. However, a brittle ZrCr2 diffusion layer was formed in the same while at the Cr/Zr4 interface underneath the Cr coating, which would lead to earlier micro-cracks formed under tensile stress and evidently degrade the interfacial strength. The findings in the study indicated the importance of optimizing coating microstructure in future study to avoid forming the above-mentioned brittle diffusion interlayer and the associated premature failure.

scholarly journals Quantitative Damage and Fracture Mode of Sandstone under Uniaxial Load Based on Acoustic Emission

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Ying Xu ◽  
Qiangqiang Zheng ◽  
Xin Gao ◽  
Rongzhou Yang ◽  
Xian Ni ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Fracture Mechanism ◽  
Damage Mechanics ◽  
Shear Failure ◽  
Rock Fracture ◽  
Damage Model ◽  
Damage Models ◽  
Uniaxial Load ◽  
Damage And Fracture ◽  
Ae Signals

The damage degree and fracture mechanism of the rock are important to the bearing performance of the rock mass and the stability of the overlying structure. Most of the existing damage models for characterizing rock damage exclude the range of postpeak stress or do not consider the compaction and closure stage of the fracture, and the description of the quantitative damage of sandstone is not accurate enough. In addition, the description of the rock fracture mechanism under load is not exact enough. Aiming at the problem of quantitative damage and fracture mechanism of the loaded rock, this paper adopts acoustic emission (AE) to monitor the loading process of sandstone under uniaxial loading. In accordance with the characteristics of the AE signal, the loading stage of sandstone under uniaxial load is divided into three stages: initial hit stage, hit stability stage, and hit instability stage. By modifying the traditional damage model and combining the AE signals of the sandstone under the load, a modified damage mechanics model is obtained, which can fully express the entire loading stage. Furthermore, through the analysis of AE signals, the fracture mechanism of sandstone under uniaxial load is studied. The results show that the modified damage model can quantitatively describe the damage at different loading stages which include two areas including the fracture compaction closure stage and the postpeak stress stage. The failure and instability of sandstone under uniaxial load is mainly shear failure. The research results can provide a reference for the nondestructive testing of sandstone and engineering reliability in geotechnical engineering.

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