scholarly journals Mechanical Properties and Failure Modes of Rock Specimens with Specific Joint Geometries in Triaxial Unloading Compressive Test

2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Guoyong Duan ◽  
Jianlin Li ◽  
Jingyu Zhang ◽  
Eleyas Assefa ◽  
Xushu Sun
Keyword(s):  
Failure Modes ◽  
Failure Mechanisms ◽  
Confining Pressure ◽  
Maximum Tensile Stress ◽  
Considerable Effect ◽  
Joint Orientation ◽  
Deformation And Failure ◽  
Practical Engineering ◽  
Griffith’S Theory ◽  
Rock Specimens

The effects of disconnected joints on the mechanical characteristics of rock masses are interesting and challenging aspects of rock mechanics. The prime objective of this study is to investigate the effect of joint orientations and joint connectivity rates on the strength, deformation, and failure mechanisms of rock specimens under unloading condition. To establish the relationships between different factors (confining pressure, joint orientation, and joint connectivity) and failure mechanisms, a series of triaxial unloading tests were performed. The results showed that the joint orientation had a more considerable effect than the joint connectivity on the strength and deformation of the specimens. Generally, three different types of failures were observed (i.e., shear, mixed, and split). Finally, Griffith’s theory was utilized to analyze the maximum tensile stress around the crack. The findings of this paper can also be used for practical engineering problems.

scholarly journals Mechanical Properties and Failure Modes of Thick-Walled Cylinder Granites with Different Apertures under Triaxial Compression

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Wei Chen ◽  
Wen Wan ◽  
Shuailong Lian ◽  
Senlin Xie ◽  
Yu Zhou ◽  
...  
Keyword(s):  
Failure Modes ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Outer Wall ◽  
Surrounding Rock ◽  
Compression Tests ◽  
Deformation And Failure ◽  
Triaxial Compressive Strength ◽  
Walled Cylinder

Roadway excavation changes the original equilibrium stress state of the rock mass, resulting in the loading and unloading of the surrounding rock near the free surface. After the excavation, the tangential stress increases and the radial stress decreases, which mainly cause deformation and collapse of the roadway. In order to study the strength characteristics of the surrounding rock after the excavation, one effective way is to carry out triaxial compression tests on small surrounding rock samples. Therefore, this paper focuses on the triaxial compression mechanical propertiesof thick-walled cylinder granites with an electrohydraulic, servo-controlled rock mechanics testing system (MTS-815). It studies how different pore sizes and confining pressures affect the triaxial compressive strength (TCS), deformation, and failure modes of granite samples. The results are as follows: (1) Under triaxial compression, the stress-strain curves have no obvious yield stage, and the peak TCS increases with the confining pressure (σ3). When σ3 is low, there is little difference in the TCS between the complete specimen and the thick-walled cylinders. When σ3 reaches 30 MPa∼40 MPa, the TCS of samples with apertures of 15 mm and 20 mm are obviously lower. The σ3 has an obvious influence on the elastic modulus of thick-walled cylinder granites. (2) Shearing and splitting are the main failure modes under triaxial compression. When σ3 is low, shear failure appears. As σ3 reaches 30 MPa∼40 MPa, split failure occurs. The area of the fracture surface increases with σ3. (3) As σ3 grows, the influence parameter (m) of the three-dimensional Hoek-Brown criterion increases. Under the same σ3, the value of m presents a decreasing trend from the outer wall to the inner wall, which means the bearing capacity keeps getting lower and lower. As a result, the inner wall is most likely to be damaged. The theoretical analysis results agree well with the tests.

scholarly journals The mechanical behaviour of rock specimens with specific edge crack distributions under triaxial loading conditions

2019 ◽  
Vol 16 (5) ◽  
pp. 962-973 ◽  
Author(s):  
Guoyong Duan ◽  
Jianlin Li ◽  
Jingyu Zhang ◽  
Zuosen Luo ◽  
Liangpeng Wan ◽  
...  
Keyword(s):  
Mechanical Behaviour ◽  
Shear Failure ◽  
Axial Stress ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Loading Conditions ◽  
Compression Tests ◽  
Joint Orientation ◽  
Failure Patterns ◽  
Rock Specimens

Abstract Research on the mechanical behaviour of rock masses with multiple joints has become a popular topic and has practical applications in natural slope stability. This paper aims to clarify the influence of joint geometry, joint orientation and joint connectivity ratio on the mechanical behaviour of rock specimens containing two pre-existing joints. Triaxial compression tests were conducted under various confining pressures to simulate the variation in external conditions. An exponential criterion was used to describe the relationship between the axial stress and confining pressure. The experimental crack propagation was explored by varying the joint orientation, joint connectivity ratio and confining pressure. The structural plane with a greater angle of inclination controlled the failure of the rock sample. Two failure patterns were observed under the loading conditions: shear failure and mixed failure. The failure surface trajectory presented similar deviations with the increase in joint inclination angle, joint connectivity ratio and confining pressure, which also accelerates the transition from mixed failure to shear failure. The experimental results highlight the significance of elucidating the influence of structural planes in practical engineering to predict the stability of natural slopes.

Methodology for Analysis of Schottky Diode Failures

2010 ◽  
Author(s):  
Bhanu P. Sood ◽  
Michael Pecht ◽  
John Miker ◽  
Tom Wanek
Keyword(s):  
Failure Mode ◽  
Schottky Diode ◽  
Failure Modes ◽  
Schottky Diodes ◽  
Failure Mechanisms ◽  
Forward Voltage ◽  
Fast Switching ◽  
Voltage Drops ◽  
The Common

Abstract Schottky diodes are semiconductor switching devices with low forward voltage drops and very fast switching speeds. This paper provides an overview of the common failure modes in Schottky diodes and corresponding failure mechanisms associated with each failure mode. Results of material level evaluation on diodes and packages as well as manufacturing and assembly processes are analyzed to identify a set of possible failure sites with associated failure modes, mechanisms, and causes. A case study is then presented to illustrate the application of a systematic FMMEA methodology to the analysis of a specific failure in a Schottky diode package.

scholarly journals An Extension Strain Type Mohr–Coulomb Criterion

2021 ◽  
Author(s):  
Manfred Staat
Keyword(s):  
Failure Modes ◽  
Peak Stress ◽  
Fracture Initiation ◽  
Failure Surface ◽  
Confining Pressure ◽  
Biaxial Compression ◽  
Simple Extension ◽  
Strain Criterion ◽  
Shear Component ◽  
Extension Strain

AbstractExtension fractures are typical for the deformation under low or no confining pressure. They can be explained by a phenomenological extension strain failure criterion. In the past, a simple empirical criterion for fracture initiation in brittle rock has been developed. In this article, it is shown that the simple extension strain criterion makes unrealistic strength predictions in biaxial compression and tension. To overcome this major limitation, a new extension strain criterion is proposed by adding a weighted principal shear component to the simple criterion. The shear weight is chosen, such that the enriched extension strain criterion represents the same failure surface as the Mohr–Coulomb (MC) criterion. Thus, the MC criterion has been derived as an extension strain criterion predicting extension failure modes, which are unexpected in the classical understanding of the failure of cohesive-frictional materials. In progressive damage of rock, the most likely fracture direction is orthogonal to the maximum extension strain leading to dilatancy. The enriched extension strain criterion is proposed as a threshold surface for crack initiation CI and crack damage CD and as a failure surface at peak stress CP. Different from compressive loading, tensile loading requires only a limited number of critical cracks to cause failure. Therefore, for tensile stresses, the failure criteria must be modified somehow, possibly by a cut-off corresponding to the CI stress. Examples show that the enriched extension strain criterion predicts much lower volumes of damaged rock mass compared to the simple extension strain criterion.

Analysis of the Relationship Between Rail Seat Load Distribution and Rail Seat Deterioration in Concrete Crossties

2014 ◽  
Author(s):  
Matthew Greve ◽  
Marcus S. Dersch ◽  
J. Riley Edwards ◽  
Christopher P. L. Barkan ◽  
Jose Mediavilla ◽  
...  
Keyword(s):  
Load Distribution ◽  
Failure Modes ◽  
Failure Mechanisms ◽  
Past Research ◽  
Concrete Surface ◽  
Hydraulic Pressure ◽  
Valuable Insight ◽  
Increased Risk ◽  
Abrasive Erosion ◽  
Field Experimentation

One of the most common failure modes of concrete crossties in North America is the degradation of the concrete surface at the crosstie rail seat, also known as rail seat deterioration (RSD). Loss of material beneath the rail can lead to wide gauge, rail cant deficiency, and an increased risk of rail rollover. Previous research conducted at the University of Illinois at Urbana-Champaign (UIUC) has identified five primary failure mechanisms: abrasion, crushing, freeze-thaw damage, hydro-abrasive erosion, and hydraulic pressure cracking. The magnitude and distribution of load applied to the rail seat affects four of these five mechanisms; therefore, it is important to understand the characteristics of the rail seat load distribution to effectively address RSD. As part of a larger study funded by the Federal Railroad Administration (FRA) aimed at improving concrete crossties and fastening systems, researchers at UIUC are attempting to characterize the loading environment at the rail seat using matrix-based tactile surface sensors (MBTSS). This instrumentation technology has been implemented in both laboratory and field experimentation, and has provided valuable insight into the distribution of a single load over consecutive crossties. A review of past research into RSD characteristics and failure mechanisms has been conducted to integrate data from field experimentation with existing knowledge, to further explore the role of the rail seat load distribution on RSD. The knowledge gained from this experimentation will be integrated with associated research conducted at UIUC to form the framework for a mechanistic design approach for concrete crossties and fastening systems.

scholarly journals Physical modelling of failure in composites

2016 ◽  
Vol 374 (2071) ◽  
pp. 20150280 ◽  
Author(s):  
Ramesh Talreja
Keyword(s):  
Composite Materials ◽  
Failure Modes ◽  
Structural Integrity ◽  
Failure Mechanisms ◽  
Local Stress ◽  
Physical Modelling ◽  
Stress Fields ◽  
Systematic Analysis ◽  
Composite Failure ◽  
Failure Theories

Structural integrity of composite materials is governed by failure mechanisms that initiate at the scale of the microstructure. The local stress fields evolve with the progression of the failure mechanisms. Within the full span from initiation to criticality of the failure mechanisms, the governing length scales in a fibre-reinforced composite change from the fibre size to the characteristic fibre-architecture sizes, and eventually to a structural size, depending on the composite configuration and structural geometry as well as the imposed loading environment. Thus, a physical modelling of failure in composites must necessarily be of multi-scale nature, although not always with the same hierarchy for each failure mode. With this background, the paper examines the currently available main composite failure theories to assess their ability to capture the essential features of failure. A case is made for an alternative in the form of physical modelling and its skeleton is constructed based on physical observations and systematic analysis of the basic failure modes and associated stress fields and energy balances. This article is part of the themed issue ‘Multiscale modelling of the structural integrity of composite materials’.

Stiction Failure Mechanisms of the Micromachined Electrostatic Comb-Drive Structures

2011 ◽  
Vol 80-81 ◽  
pp. 850-854
Author(s):  
Yi Shen Xu ◽  
Ji Hua Gu ◽  
Zhi Tao
Keyword(s):  
Failure Modes ◽  
Failure Mechanisms ◽  
Mems Devices ◽  
Comb Drive ◽  
Interfacial Forces ◽  
Restoring Forces ◽  
Critical Investigation

Stiction is one of the most important and almost unavoidable problems in MEMS, which usually occurs when the restoring forces of the microstructures are unable to overcome the interfacial forces. Stiction could compromise the performance and reliability of the MEMS devices or may even make them malfunction. One of the pivotal process of advancing the performance and reliability of MEMS is to comprehend the failure modes and failure mechanisms of these microdevices. This article provides a critical investigation on the stiction failure mechanisms of the micromachined electrostatic comb-drive structures, which is significant to improve the reliability of microdevices, especially for microfilters, microgrippers, microaccelerometers, microgyroscopes, microrelays, and so on.

Materials Failure Logic Models—A Procedure for Systematic Identification of Material Failure Modes in Mechanical Components

1982 ◽  
Vol 104 (3) ◽  
pp. 626-634 ◽  
Author(s):  
D. L. Marriott ◽  
N. R. Miller
Keyword(s):  
Failure Modes ◽  
Planning Process ◽  
Service Failure ◽  
Failure Mechanisms ◽  
Material Failure ◽  
Cad System ◽  
Logic Models ◽  
Identification Technique ◽  
Mechanical Components ◽  
Systematic Identification

This paper addresses the problem of improvement of mechanical component reliability by the systematic identification of material failure mechanisms. Experience shows that, in many cases of service failure, failure was caused by a known mechanism which was overlooked, either by design, or elsewhere in the planning process. This paper describes one approach to designing mechanical components against failure by material deterioration, but may have application to other fields. It is based on a finding from the examination of case studies which shows that material failures follow logic structures which can be described by Boolean algebra expressions. These structures are defined as Material Failure Logic Models (MFLM’s), and can be used as a means of systematically identifying potential failure mechanisms in a complex process. The identification technique is based on the observation that MFLM’s are insensitive to the precise causes of the individual events. The paper deals primarily with problems of defining MFLM’s. Some examples of MFLM’s are given. A brief discussion is presented of a CAD system under development at the University of Illinois at Urbana-Champaign.

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