scholarly journals Investigating the effects of confining pressure on graphite material failure modes and strength criteria

2020 ◽  
Vol 52 (7) ◽  
pp. 1571-1578
Author(s):  
Yanan Yi ◽  
Guangyan Liu ◽  
Tongzhen Xing ◽  
Guang Lin ◽  
Libin Sun ◽  
...  
Keyword(s):  
Failure Modes ◽  
Confining Pressure ◽  
Material Failure ◽  
Graphite Material ◽  
Strength Criteria

Off-axial failure analysis of polytetrafluoroethylene-coated woven glass fibers under different loading rates

2016 ◽  
Vol 47 (3) ◽  
pp. 310-330 ◽  
Author(s):  
Xu Junhao ◽  
Zhang Yingying ◽  
Xue Jigang
Keyword(s):  
Tensile Strength ◽  
Failure Modes ◽  
Loading Rate ◽  
Glass Fibers ◽  
Material Failure ◽  
Failure Strength ◽  
Strength Criteria ◽  
Elongation At Break ◽  
Loading Rates ◽  
Axial Tensile

This paper presents the research on off-axial tensile behaviors of polytetrafluoroethylene-coated woven glass fibers under different loading rates. First, groups of off-axial tensile tests were carried out, and the corresponding failure mechanisms were analyzed. Then, the effect of loading rate on the tensile behaviors of off-axial specimens was studied. Finally, several current strength criteria were compared to predict the material failure strength under different loading rates. Results show the tensile behaviors of polytetrafluoroethylene-coated woven glass fibers are typical orthotropic. The material failure strength is strongly related with failure modes and yarn orientations. Three typical failure modes are observed in the tests, including interface failure, yarn breakage, and composite failure. The loading rate has significant effects on the material tensile strength and the elongation at break. With loading rate increasing, the tensile strength increases and the elongation at break decreases. The tensile strength shows a good linear correlation with the loading rate’s logarithm. Most of current quadratic strength criteria can be used to predict the material failure strength, except for the specimens of small bias angles. This is because traditional quadratic criteria are always based on the strain energy theory of homogeneous materials, which may not reflect the failure mechanisms of coated fabrics and other important details.

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.

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.

scholarly journals Permeability Characteristic and Failure Behavior of Filled Cracked Rock in the Triaxial Seepage Experiment

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Xinyu Liu ◽  
Zhende Zhu ◽  
Aihua Liu
Keyword(s):  
Growth Rate ◽  
Rock Mass ◽  
Failure Modes ◽  
Peak Stress ◽  
Confining Pressure ◽  
Strength Characteristics ◽  
Failure Behavior ◽  
Compression Tests ◽  
Secondary Cracks ◽  
Safety And Stability

Filling is commonly found in natural cracked rock mass. As the weakest part of the rock, the filling properties directly affect the rock deformation and strength, permeability, and so on and affect the safety and stability of the rock mass engineering. In this study, a single slit has been preset in sandstones and filled with different physical properties materials. Based on the laboratory triaxial seepage test, the permeability and strength characteristics of filled cracked sandstones are analyzed, and the failure modes are obtained. The main findings of this study are as follows: (1) The permeability coefficient peak value of the filled cracked rock appears before the stress peak. (2) At the same confining pressure growth rate, the peak stress growth rate of the filled cracked rock is generally higher than that of the intact rock and the strength growth rate of the cracked rock increases with the length of the fracture. The strength characteristics of the filling in the uniaxial compression tests and triaxial seepage tests are significantly affected by the hydraulic properties. (3) The strength and permeability coefficients of cracked rock filled with cement mortar are more sensitive to the change of confining pressure, while under the same condition, the ones of cracked rock filled with gypsum mortar are stable. (4) According to the failure mechanism, under the seepage stress, the secondary cracks can be divided into 3 types and the failure modes can be divided into 2 types.

scholarly journals Cracking Behaviors and Mechanical Properties of Rock-Like Specimens with Two Unparallel Flaws under Conventional Triaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Huilin Le ◽  
Shaorui Sun ◽  
Chenghua Xu ◽  
Liuyang Li ◽  
Yong Liu
Keyword(s):  
Mechanical Properties ◽  
Inclination Angle ◽  
Failure Modes ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Critical Value ◽  
Tensile Failure ◽  
Rock Bridge ◽  
Bridge Length

Flaws existing in rock masses are generally unparallel and under three-dimensional stress; however, the mechanical and cracking behaviors of the specimens with two unparallel flaws under triaxial compression have been rarely studied. Therefore, this study conducted comprehensive research on the cracking and coalescence behavior and mechanical properties of specimens with two unparallel flaws under triaxial compression. Triaxial compressive tests were conducted under different confining pressures on rock-like specimens with two preexisting flaws but varying flaw geometries (with respect to the inclination angle of the two unparallel flaws, rock bridge length, and rock bridge inclination angle). Six crack types and eleven coalescence types in the bridge region were observed, and three types of failure modes (tensile failure, shear failure, and tensile-shear failure) were observed in experiments. Test results show that bridge length and bridge inclination angle have an effect on the coalescence pattern, but the influence of bridge inclination angle is larger than that of the bridge length. When the confining pressure is low, coalescence patterns and failure modes of the specimens are greatly affected by flaw geometry, but when confining pressure rose to a certain level, the influence of confining pressure is larger than the effect of flaw geometry. The peak strength of the specimens is affected by flaw geometry and confining pressure. There is a critical value for the bridge length. If the bridge length is larger than the critical value, peak strengths of the samples almost keep constant as the bridge length increases. In addition, as the bridge inclination angle increases, there is an increase in the probability of tensile cracks occurring, and with an increase in the confining pressure, the probability of the occurrence of shear cracks increases.

Experimental, theoretical, and numerical studies on the response of square plates subjected to blast loading

2011 ◽  
Vol 46 (8) ◽  
pp. 805-816 ◽  
Author(s):  
K H Safari ◽  
J Zamani ◽  
S M R Khalili ◽  
S Jalili
Keyword(s):  
Blast Wave ◽  
Failure Modes ◽  
Scaling Law ◽  
Blast Loading ◽  
Material Failure ◽  
Perfectly Plastic ◽  
Numerical Studies ◽  
Fluid Solid Interaction ◽  
Interaction Problem ◽  
Dynamic Plasticity

This article presents the results of experimental and analytical studies on the response of steel and aluminium square plates with different thicknesses subjected to blast loading. Based on the blast wave details and the scaling law for explosions, a method of determining the blast load is proposed in which ballistic pendulums do not need to be utilized for obtaining the blast wave impulses. The loads applied to the plates are assumed to be the quasi-exponential pressure pulses, which are the same as the explosion overpressures. The theoretical solutions are presented using a rigid, perfectly plastic idealization and are exact within the context of dynamic plasticity. The dynamic energy imparted to structures can cause material failure. The presented investigation considers such a failure for fully clamped plates subjected to a blast loading idealized as an initial velocity distributed uniformly throughout the area. The predicted deflections and general failure modes of the plates are presented and compared with experimental results. Moreover, a numerical simulation is carried out by modelling an FSI (fluid–solid interaction) problem. Results are compared with each other and a better agreement between numerical results with experimental ones is observed.

scholarly journals Dynamic Rock-Breaking Process of TBM Disc Cutters and Response Mechanism of Rock Mass Based on Discrete Element

2022 ◽  
Vol 2022 ◽  
pp. 1-10
Author(s):  
Qinglong Zhang ◽  
Yanwen Zhu ◽  
Canxun Du ◽  
Sanlin Du ◽  
Kun Shao ◽  
...  
Keyword(s):  
Rock Mass ◽  
Failure Modes ◽  
Confining Pressure ◽  
Rock Breaking ◽  
Disc Cutter ◽  
Repeated Loading ◽  
Response Mechanism ◽  
Disc Cutters ◽  
Crack Penetration ◽  
Cutter Spacing

Rock-breaking efficiency of full-face rock tunnel boring machine (TBM) is closely related to the performance of the disc cutter and the characteristics of the rock mass. In the point of view of mesomechanics, the particle flow code (PFC) is used to establish a numerical model of the rock mass and the disc cutter, and the process of TBM disc cutter intrusion into the rock mass is analyzed. The dynamic response mechanism and crack evolution process of the rock mass under the action of the disc cutter are studied on the basis of micromechanics, and the relationship between the rock mass crack, penetration, and cutting force during the intrusion of the disc cutter is revealed. The sensitivity analysis is carried out on the confining pressure conditions and the influence parameters of the disc cutter spacing. The results show that the rock breaking by disc cutter undergoes the transformation characteristics of compaction, shearing, and tension failure modes, and the failure process of the rock mass is the joint action of tension and shear. In the whole process of rock breaking, the disc cutter has the phenomenon of repeated loading-unloading alternation and leaping rock breaking; after the penetration of the disc cutter reached 9.0 mm, penetration creaks begin to appear on the surface of the rock mass; the penetration was obviously reduced with the increase of confining pressure, and it is mainly the penetration cracks on the surface; after the disc cutter spacing reaches 100.0 mm, there is no penetration crack between the two disc cutters. The research conclusion can provide a reference for the disc cutter optimization design.

scholarly journals Experimental Study on the Mechanical Behavior of Yunnan Limestone in Natural and Saturated States

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Xutao Zhang ◽  
Mingyang Ren ◽  
Zhaobo Meng ◽  
Baoliang Zhang ◽  
Jinglong Li
Keyword(s):  
Elastic Modulus ◽  
Mechanical Behavior ◽  
Water Content ◽  
Failure Modes ◽  
Shear Failure ◽  
Mechanical Response ◽  
Deformation Modulus ◽  
Confining Pressure ◽  
Hyperbolic Function ◽  
Test Results

Rock material is a kind of mineral assemblage with complex structural heterogeneity, whose mechanical behavior is strongly affected by water or moisture content. In this work, we carried out a series of laboratory tests to investigate the mechanical response (e.g., deformation, strength, and failure characteristics) of Yunnan limestone in natural and saturated states. Our test results show that (1) after saturation, the stiffness and strength of Yunnan limestone degenerate considerably. Compared with the natural condition, the elastic modulus, deformation modulus, and tensile modulus decrease by about 30% on average, and uniaxial compressive strength and tensile strength also decrease by about 15% and 20%, respectively. While Poisson’s ratio is less affected by water content, it can be regarded as a constant; (2) the elastic modulus and deformation modulus of Yunnan limestone are significantly affected by confining pressure, and the relationship between them and confining pressure satisfies the law of hyperbolic function; (3) the peak strength envelope of Yunnan limestone has significant nonlinear characteristics, which can be well described by generalized Hoek-Brown strength criterion. However, the generalized Hoek-Brown criterion does not apply to the residual strength, which shows a linearly increasing trend with the increasing confining pressure; (4) the failure modes of Yunnan limestone are significantly dependent on confining pressure but insensitive to water content. With the increasing confining pressure, the failure modes of Yunnan limestone transform from splitting failure, tension-shear mixed failure, single inclined plane shear failure to Y-shaped or X-shaped conjugated shear failure. The test results can provide important experimental data for the establishment of the constitutive model of Yunnan limestone, which will contribute to obtain more reliable results for stability assessment of Xianglu Mountain Tunnel.

scholarly journals Experimental Investigation on Failure Modes and Mechanical Properties of Rock-Like Specimens with a Grout-Infilled Flaw under Triaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Huilin Le ◽  
Shaorui Sun ◽  
Feng Zhu ◽  
Haotian Fan
Keyword(s):  
Mechanical Properties ◽  
Rock Mass ◽  
Epoxy Resin ◽  
Failure Modes ◽  
Shear Failure ◽  
Fractured Rock ◽  
Triaxial Compression ◽  
Friction Angle ◽  
Confining Pressure ◽  
Compression Tests

Flaws existing in rock mass are one of the main factors resulting in the instability of rock mass. Epoxy resin is often used to reinforce fractured rock mass. However, few researches focused on mechanical properties of the specimens with a resin-infilled flaw under triaxial compression. Therefore, in this research, epoxy resin was selected as the grouting material, and triaxial compression tests were conducted on the rock-like specimens with a grout-infilled flaw having different geometries. This study draws some new conclusions. The high confining pressure suppresses the generation of tensile cracks, and the failure mode changes from tensile-shear failure to shear failure as the confining pressure increases. Grouting with epoxy resin leads to the improvement of peak strengths of the specimens under triaxial compression. The reinforcement effect of epoxy resin is better for the specimens having a large flaw length and those under a relatively low confining pressure. Grouting with epoxy resin reduces the internal friction angle of the samples but improves their cohesion. This research may provide some useful insights for understanding the mechanical behaviors of grouted rock masses.

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