scholarly journals Experimental study on granite acoustic emission and micro-fracture behavior with combined compression and shear loading: phenomenon and mechanism

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Yue Cao ◽  
Jinhai Xu ◽  
Liang Chen ◽  
Peng Wu ◽  
Faiz Shaikh
Keyword(s):  
Shear Stress ◽  
Acoustic Emission ◽  
Fracture Mode ◽  
Inclination Angle ◽  
Fracture Behavior ◽  
Shear Failure ◽  
Stress Component ◽  
Shear Loading ◽  
Shear Stress Component ◽  
Microcrack Initiation

AbstractOne element that is essential to consider in underground mining engineering applications is the possibility of pillar failure, which can result in deadly geological disasters, including earthquakes and surface subsidence. Pillars are commonly present under an inclined state and are significantly dependent upon combined compression and shear loading. However, many scholars regard the pure uniaxial compression strength (UCS) of rock as the main evaluation index of pillar strength, which is inconsistent with the field practice. Hence, the present study developed a novel combined compression and shear test (C-CAST) system, which was applied in the investigative acoustic emission (AE) experiments to characterize the failure mechanism and micro-fracture behavior of granite specimens at different inclination angles. The experimental results presented the exponential decrease of UCS of inclined specimens with increase in the shear stress component. Changes in the inclination angle with a range of 0°–10° produced a splitting-shear failure fracture mode from the initial splitting failure. In comparison, an increase in the inclination angle from 10° to 20° produced a single shear failure fracture mode from the initial combined splitting-shear failure. The specimens exhibited nonlinearly reduced microcrack initiation (CI) and damage (CD) thresholds following an increase in the inclination angle, suggesting the dependence of the microcrack initiation and propagation on the shear stress component. The ratio of CI and CD thresholds to inclined UCS varies within a certain range, indicating that the ratio may be an inherent property of granite specimens and is not affected by external load conditions. Additionally, the rock fracture behavior was largely dependent upon the mechanism of shear stress component, as validated by the microcrack initiation and growth. Finally, a modified empirical formula for pillar strength is proposed to investigate the actual strength of inclined pillar. Results of a case study show that the modified formula can be better used to evaluate the stability of inclined pillars.

scholarly journals An Experimental Study on Mechanical Behavior of Parallel Joint Specimens under Compression Shear

2018 ◽  
Vol 2018 ◽  
pp. 1-12
Author(s):  
Fei Wang ◽  
Ping Cao ◽  
Yu Chen ◽  
Qing-peng Gao ◽  
Zhu Wang
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Failure Mode ◽  
Shear Failure ◽  
Strain Curve ◽  
Shear Loading ◽  
Plane Shear ◽  
Joint Spacing ◽  
Dip Angle ◽  
Joint Inclination

In order to investigate the influence of the joint on the failure mode, peak shear strength, and shear stress-strain curve of rock mass, the compression shear test loading on the parallel jointed specimens was carried out, and the acoustic emission system was used to monitor the loading process. The joint spacing and joint overlap were varied to alter the relative positions of parallel joints in geometry. Under compression-shear loading, the failure mode of the joint specimen can be classified into four types: coplanar shear failure, shear failure along the joint plane, shear failure along the shear stress plane, and similar integrity shear failure. The joint dip angle has a decisive effect on the failure mode of the specimen. The joint overlap affects the crack development of the specimen but does not change the failure mode of the specimen. The joint spacing can change the failure mode of the specimen. The shear strength of the specimen firstly increases and then decreases with the increase of the dip angle and reaches the maximum at 45°. The shear strength decreases with the increase of the joint overlap and increases with the increase of the joint spacing. The shear stress-displacement curves of different joint inclination samples have differences which mainly reflect in the postrupture stage. From monitoring results of the AE system, the variation regular of the AE count corresponds to the failure mode, and the peak value of the AE count decreases with the increase of joint overlap and increases with the increase of joint spacing.

Characterization of Thermally Induced Stress in IC Packages Using PiFETs Over a Temperature Range of −180°C to 80°C

2014 ◽  
Vol 2014 (1) ◽  
pp. 000500-000504 ◽  
Author(s):  
Francy J. Akkara ◽  
Uday S. Goteti ◽  
Richard C. Jaeger ◽  
Michael C. Hamilton ◽  
Michael J. Palmer ◽  
...  
Keyword(s):  
Shear Stress ◽  
Stress Component ◽  
Shear Stress Component ◽  
Thermally Induced ◽  
Temperature Changes ◽  
Temperature Range ◽  
Induced Stress ◽  
Highly Sensitive ◽  
Stress Components

In certain applications, IC packages may be exposed to extreme temperatures and knowledge of thermally induced stress aids the prediction of performance degradation or failure of the IC. In the devices that are used in extreme conditions, the stress is caused mainly by the mismatch in expansion of various materials triggered by the different coefficients of thermal expansion. This work performed in this study is conducted using NMOS current mirror circuits that are cycled through a wide temperature range of −180°C to 80°C. These circuits are highly sensitive to stress and provide well-localized measurements of shear stress. The sensors are fabricated in such a way that the effects of certain stress components are isolated. These sensors are also temperature compensated so that only the effect of mechanical stress components is observed and changes in device performance due to temperature changes are minimal. Current readings obtained from the sensors are used to extract the shear stress component. Finite element simulations, using expected materials performance parameter information were also performed for similar packages and these results are compared to the measured results.

scholarly journals Experimental Study on Physical-mechanical Properties and Fracture Behaviors of Saturated Yellow Sandstone Considering Coupling Effect of Freeze-Thaw and Specimen Inclination

2020 ◽  
Vol 12 (3) ◽  
pp. 1029 ◽  
Author(s):  
Liang Chen ◽  
Peng Wu ◽  
Yanlong Chen ◽  
Wei Zhang
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Elastic Modulus ◽  
Failure Mode ◽  
Inclination Angle ◽  
Compression Strength ◽  
Shear Loading ◽  
Cold Regions ◽  
Freeze Thaw ◽  
Peak Compression

The effect of freeze-thaw on the physical-mechanical properties and fracture behavior of rock under combined compression and shear loading was crucial for revealing the instability mechanism and optimizing the structure design of rock engineering in cold regions. However, there were few reports on the failure behavior of rock treated by freeze-thaw under combined compression and shear loading due to the lack of test equipment. In this work, a novel combined compression and shear test (C-CAST) system was introduced to carry out a series of uniaxial compression tests on saturated yellow sandstone under various inclination angles (θ = 0°, 5°, 10°, and 15°) and the number of freeze-thaw cycles (N = 0, 20, 40, and 60). The test results showed that the P-wave velocity dramatically decreased, while the rock quality and porosity increased gradually as N increased; the peak compression strength and elastic modulus obviously decreased with the increasing θ and N, while the peak shear stress increased gradually with the increasing θ and decreased with the increase of N, indicating that the shear stress component can accelerate the crack propagation and reduce its resistance to deformation. The acoustic emission (AE) results revealed that the change of crack initiation (CI) stress and crack damage (CD) stress with the θ and N had a similar trend as that of the peak compression strength and elastic modulus. Particularly, the CI and CD thresholds at 60 cycles were only 81.31% and 84.47% of that at 0° cycle and indicated a serious freeze-thaw damage phenomenon, which was consistent with the results of scanning electron microscopy (SEM) with the appearance of some large-size damage cracks. The fracture mode of sandstone was dependent on the inclination angle. The failure mode developed from both the tensile mode (0°) and combined tensile-shear mode (5°) to a pure shear failure (10°–15°) with the increasing inclination angle. Meanwhile, the freeze-thaw cycle only had an obvious effect on the failure mode of the specimen at a 5° inclination. Finally, a novel multivariate regression analysis method was used to predict the peak compression strength and elastic modulus based on the initial strength parameters (θ = 0°, N = 0). The study results can provide an important reference for the engineering design of rock subjected to a complex stress environment in cold regions.

The Influence of Turbulence Memory on Idealized Tornado Simulations

2020 ◽  
Vol 148 (12) ◽  
pp. 4875-4892
Author(s):  
Aaron Wang ◽  
Ying Pan ◽  
Paul M. Markowski
Keyword(s):  
Boundary Condition ◽  
Shear Stress ◽  
Stress Component ◽  
Lower Boundary ◽  
Surface Friction ◽  
Surface Shear Stress ◽  
Normal Surface ◽  
Shear Stress Component ◽  
Surface Shear ◽  
Lower Boundary Condition

AbstractSurface friction contributes to tornado formation and maintenance by enhancing the convergence of angular momentum. The traditional lower boundary condition in atmospheric models typically assumes an instant equilibrium between the unresolved stress and the resolved shear. This assumption ignores the physics that turbulent motions are generated and dissipated at finite rates—in effect, turbulence has a memory through its lifetime. In this work, a modified lower boundary condition is proposed to account for the effect of turbulence memory. Specifically, when an air parcel moves along a curved trajectory, a normal surface-shear-stress component arises owing to turbulence memory. In the accompanying large-eddy simulation (LES) of idealized tornadoes, the normal surface-shear-stress component is a source of additional dynamic instability, which provides an extra pathway for the development of turbulent motions. The influence of turbulence memory on the intensity of quasi-steady-state tornadoes remains negligible as long as assumptions employed by the modified lower boundary condition hold over a relatively large fraction of the flow region of interest. However, tornadoes in a transient state may be especially sensitive to turbulence memory.Significance StatementFriction between the wind and the ground can influence atmospheric phenomena in important ways. For example, surface friction can be a significant source of rotation in some thunderstorms, and it can also help to intensify rotation when rotation is already present. Unfortunately, the representation of friction’s effects in atmospheric simulations is especially error-prone in phenomena characterized by rapid temporal evolution or strong spatial variations. Our work explores a new framework for representing friction to include the effect of the so-called turbulence memory. The approach is tested in idealized tornado simulations, but it may be applied to a wide range of atmospheric vortices.

scholarly journals Effect of High Temperature and Inclination Angle on Mechanical Properties and Fracture Behavior of Granite at Low Strain Rate

2020 ◽  
Vol 12 (3) ◽  
pp. 1255 ◽  
Author(s):  
Liang Chen ◽  
Xianbiao Mao ◽  
Peng Wu
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Elastic Modulus ◽  
Crack Initiation ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Shear Failure ◽  
Nuclear Waste Repository ◽  
Compression Stress ◽  
Peak Compression

Comprehensive understanding of the effects of temperature and inclination angle on mechanical properties and fracture modes of rock is essential for the design of rock engineering under complex loads, such as the construction of nuclear waste repository, geothermal energy development and stability assessment of deep pillar. In this paper, a novel inclined uniaxial compression (inclined UCS) test system was introduced to carry out two series of inclined uniaxial compression tests on granite specimens under various inclination angles (0–20°) and treated temperatures (25–800 °C) at 5° inclination. Experimental results revealed that the peak compression stress and elastic modulus gradually decreased, while peak shear stress increased nonlinearly with the increasing inclination angle; the peak compression and shear stress as well as elastic modulus slightly increased from 25 to 200 °C, then gradually decreased onwards with the increasing temperature. The effect of temperature on peak axial strain was the same as that on peak shear displacement. Acoustic emission (AE) results suggested that the relationship between crack initiation stress, inclination angle and treated temperature followed a similar trend as that of the peak compression stress and elastic modulus. Particularly, the crack initiation (CI) stress threshold and shear stress corresponding to CI threshold under 800 °C were only 7.4% of that under 200 °C and revealed a severe heat damage phenomenon, which was consistent with the results of the scanning electron microscopy (SEM) with the appearance of a large number of thermal pores observed only under 800 °C. The failure modes tended to shear failure with the increasing inclination angle, indicating that the shear stress component can accelerate sliding instability of rocks. On the other hand, the failure patterns with different temperatures changed from combined splitting-shear failure (25–400 °C) to single shear failure (600 and 800 °C). The study results can provide an extremely important reference for underground thermal engineering construction under complex loading environment.

Mechanical Properties and Fracture Behavior of Friction Stir Spot Welded AZ61 Magnesium Alloys

2010 ◽  
Vol 154-155 ◽  
pp. 498-507 ◽  
Author(s):  
Ben Yuan Lin ◽  
Ju Jen Liu ◽  
Lee Der Lu
Keyword(s):  
Fracture Behavior ◽  
Shear Failure ◽  
Shear Loading ◽  
Stir Zone ◽  
Welding Parameters ◽  
Tensile Shear ◽  
Friction Stir ◽  
Lower Sheet ◽  
Lap Shear ◽  
Spot Welded

In this study, the tensile shear strength and the fracture behavior of friction stir spot welded AZ61 joints in lap-shear configuration were investigated. The heat input was measured in FSSW to help analyze the effect of welding parameters on the strength. The tensile shear failure test was performed in a material testing system. The cross section of the joints and the fracture surface of the failed specimens were analyzed using optical microscopy and scanning electron microscopy. Results show that the weld diameter and the tensile shear load increase with increasing the input heat. The path of the material flow formed during FSSW process would provide a good way for crack propagation. All failed specimens in this study appear the same fracture features and show a circumferential failure mode under tensile shear loading conditions. The failure is initiated from a notch tip in the upper sheet loading side, and then propagates along the interface of the upper and lower sheets, then through the stir zone circumference; finally, a small portion of the lower sheet in the lower sheet loading side is torn off with some part of the stir zone.

Off-axis tensile strength and evaluation of the in-plane shear strength of paper

Holzforschung ◽  
2014 ◽  
Vol 68 (5) ◽  
pp. 583-590 ◽  
Author(s):  
Hiroshi Yoshihara ◽  
Masahiro Yoshinobu
Keyword(s):  
Tensile Strength ◽  
Shear Stress ◽  
Shear Strength ◽  
Stress Component ◽  
Shear Stress Component ◽  
Plane Shear ◽  
Dog Bone ◽  
Paper Filter ◽  
Failure Conditions ◽  
The Relationship

Abstract The off-axis tensile strength (OATS) of copy paper, filter paper, and sack paper was obtained from dog-bone specimens. The relationship between OATS and the off-axis angle (OAA) was predicted under several failure conditions. Additionally, the shear strengths (SS) of these papers were evaluated based on the results of OAT tests. The OATS could be accurately predicted under several Hill-type failure conditions. An equation for deriving the in-plane SS of these papers was proposed based on the tensile strength of the specimen with a 35° OAA, in which the contribution of the shear stress component was maximum.

scholarly journals Mechanical Properties and Damage in Lignite under Combined Cyclic Compression and Shear Loading

2020 ◽  
Vol 12 (20) ◽  
pp. 8393
Author(s):  
Haoshuai Wu ◽  
Haibo Bai ◽  
Yanlong Chen ◽  
Hai Pu ◽  
Kai Zhang
Keyword(s):  
Mechanical Properties ◽  
Inclination Angle ◽  
Shear Failure ◽  
Cyclic Stress ◽  
Shear Loading ◽  
Tensile Failure ◽  
Shear Tests ◽  
Volume Strain ◽  
Cyclic Compression ◽  
Upper Limit

In this paper, uniaxial cyclic compression and shear test was carried out for lignite samples. The effects of inclination angle (θ) and upper limit of cyclic stress (σmax) on mechanical properties of coal samples were analyzed, and the damage variables of coal samples were studied based on energy dissipation theory. The results show that the uniaxial compressive strength (UCS) of coal samples after uniaxial cyclic compression and shear tests decreases with the increase of the upper limit of cyclic stress and inclination angle. The shear stress component generated by the increase of inclination angle can effectively reduce the UCS and increase the damage degree of coal samples. With the increase of inclination angle, the failure mode of coal samples is changed from tensile failure (θ = 0°), the combined tensile failure and shear failure (θ = 5°) to shear failure (θ = 10°). The peak axial and radial strain of coal samples first increases rapidly and then stagnates. The peak volume strain rapid increases and then stagnates (θ = 0° and θ = 5°). When the inclination angle is 10°, the peak volume strain first decreases rapidly and then stagnates. Even if the upper limit of cyclic stress is lower than its UCS, it will still promote the propagation of micro cracks and the generation of new cracks and increase the internal damage of coal samples. With the increase of the cycle number, damage variables of coal samples after uniaxial cyclic compression and shear tests nonlinearly increase, and the growth rate decreases gradually.

Fiber Breakage in Plain Woven Glass Fabric Composites Under Tension/Shear Biaxial Cyclic Stress

2001 ◽  
Author(s):  
Hiroyuki Maeyama ◽  
Kazuya Okubo ◽  
Toru Fujii
Keyword(s):  
Shear Stress ◽  
Fiber Bundle ◽  
Stress Component ◽  
Cyclic Stress ◽  
Biaxial Stress ◽  
Fiber Bundles ◽  
Fiber Breakage ◽  
Shear Stress Component ◽  
Fabric Composites ◽  
Longitudinal Fiber

Abstract Fiber breakage occurring in fiber bundles of plain-woven glass fabric composites is investigated under tension/shear biaxial cyclic stress. The experimental results show an existence of the strong effect of biaxial stress ratio on fiber breakage and its accumulation. Under pure tension (uniaxial) loading, the variation of fiber breakage ratio with respect to loading cycles is divided into two stages in the longitudinal fiber bundles. In the first stage, the fiber breakage scarcely occurs. In the final stage, fibers in a fiber bundle are broken remarkably. Under the biaxial cyclic stress, the fiber breakage in the longitudinal fiber bundle is observed in initial fatigue stage. In the case of the biaxial stress with large shear stress component, the fiber breakage is also observed in the transverse fiber bundle. The fiber breakage is accelerated by the combined stress with large shear stress component, which is called the shear constraint effect.

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