scholarly journals Experimental Investigation on Shear Failure Mechanism of Rock Mass with Intermittent Joints

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Minghui Ma ◽  
Fenhua Ren ◽  
Wensheng Liu
Keyword(s):  
Rock Mass ◽  
Shear Strain ◽  
Failure Mechanism ◽  
Shear Failure ◽  
Shear Fracture ◽  
Shear Loading ◽  
Surface Strain ◽  
Image Correlation ◽  
Maximum Shear Strain ◽  
Natural Rock

There are a large number of discontinuous weak planes distributed in the natural rock mass, which makes the sliding failure of rock mass along the intermittent structural plane very complex. To investigate the shear failure mechanism of rock mass with intermittent joints and study the influence of different joint heights on the shear failure mode of the rock mass, direct shear tests were carried out by presetting a series of jointed rock specimens with different undulating heights. During the shear loading, digital image correlation (DIC) technology was employed to monitor the surface strain field of the specimens in real time. The results show that the fluctuation height has a significant effect on the evolution of shear strain. With the increase of shear load, the maximum shear strain of the jointed specimens with different undulating heights first increases slowly and then increases rapidly. When the undulating height is 5 mm, the failure of the specimen is dominated by the rock sliding along prefabricated joints. When the undulating height is larger than 10 mm, the shear fracture of the rock becomes dominant. With the increase of the undulating height, more penetrating cracks perpendicular to the preexisting joints appear between the serrated surfaces, and the shear fracture phenomenon is more obvious.

scholarly journals Shear failure of weak snow layers in the first hours after burial

2019 ◽  
Author(s):  
Benjamin Reuter ◽  
Neige Calonne ◽  
Ed Adams
Keyword(s):  
Shear Modulus ◽  
Shear Strain ◽  
Strain Energy ◽  
Shear Failure ◽  
Shear Fracture ◽  
Image Correlation ◽  
Published Data ◽  
Strain Rates ◽  
Weak Layer ◽  
Lag Times

Abstract. In a dry stratified snowcover slab avalanches release following failure in a weak layer below the slab. Typically, such weak layers consist either of persistent grain types or precipitation particles. Experience suggests that non-persistent instabilities often crest during or towards the end of a storm – probably because weak layers of precipitation particles strengthen rapidly. Studies so far have mainly focused on persistent grain types providing only sparse data to describe non-persistent weak layer failure. To understand differences between persistent and non-persistent weak layers we measured fracture mechanical properties relevant for avalanche release in a temporal series of laboratory tests. At defined lag times we tested small layered samples containing a weak layer of surface hoar, facets or decomposing fragmented particles in shear. Highspeed frames from the failure zone and image correlation analysis confirm that weak layers concentrate the shear strain. Failure consistently occurred after 20–30 % of strain energy was dissipated – despite shear strain rates as high 10−2 s−1. Our results of shear modulus and shear fracture toughness compare well with published data. The values for surface hoar and decomposing fragmented particles increased due to sintering. In the first hours after burial both weak layers had similarly low values, indicating they are equally fragile. Only for surface hoar and decomposing fragmented particles could we calibrate a formulation which allows for estimating the shear modulus from SMP signals.

scholarly journals Experimental Study on Shear Failure Characteristics of Jointed Rock Mass Based on Direct Shear Tests and Digital Image Correction Techniques

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Fenhua Ren ◽  
Liwei Zhang ◽  
Xinghui Wu ◽  
Wensheng Liu
Keyword(s):  
Rock Mass ◽  
Shear Strain ◽  
Shear Failure ◽  
Jointed Rock ◽  
Image Correction ◽  
Shear Tests ◽  
Maximum Shear Strain ◽  
Direct Shear Tests ◽  
Discontinuous Joints ◽  
Dip Angle

The instability of rock engineering is normally dominated by the shear failure of rock mass. The dip angle of discontinuous planes widely existing in rock mass is a key parameter affecting the shear strength and failure mode of jointed rock. This paper aims to investigate the influence of discontinuous joints on the shear failure of rock. Direct shear tests are carried out on rock-like specimens with discontinuous joints in different dip angles. During the shear tests, the strain field is monitored in real-time by digital image correction (DIC) technology. Experimental results show that the shear strength, shear strain evolution, and failure mode for the jointed specimens are affected by the dip angles of the discontinuous joints. The maximum shear strain of specimens with joint angles of 45° and 75° increases gradually with the increase of shear loading. The maximum shear strain for the specimens with joint angles of 0°, 15°, 30°, 60°, and 90° increases sharply after the shear load reaches 80% of the peak load. When the joint inclination angle is less than 45°, the crack begins to expand from the joint tip and is interconnected to form a penetrating fracture. When the joint dip angle is greater than 45°, the cracks initiate at the joint tip and then propagate at different paths resulting in multistage shearing and crushing failure.

Modelling the deformation of a high-hardness armour steel in Taylor rod-on-anvil experiments

2019 ◽  
Author(s):  
Shannon Ryan ◽  
Brodie McDonald ◽  
Nikki Scott ◽  
Rory Bigger ◽  
Sidney Chocron
Keyword(s):  
Experimental Measurement ◽  
High Speed ◽  
Elevated Temperatures ◽  
High Hardness ◽  
Shear Loading ◽  
Surface Strain ◽  
Image Correlation ◽  
High Speed Photography ◽  
Rate Dependency ◽  
Armour Steel

Abstract A high hardness armour steel (HHA) has been subjected to mechanical characterization under tension, compression, and shear loading at quasi-static and dynamic rates incorporating ambient and elevated temperatures. The resulting data has been used to derive constants for four plasticity constitutive models: Johnson-Cook (JC), Zerilli-Armstrong (ZA), modified Johnson-Cook (MJC), and a generalized J2-J3 yield surface (GYS). The resulting models have been used to predict the response of the HHA material during Taylor rod-on-anvil experiments. High speed photography and digital image correlation was used during the rod-on-anvil experiments to capture both transient deformation profiles and maximum principal strain along the surface of the rod (i.e. compression along the length of the rod). The JC, MJC, and GYS models were found to provide the best prediction of the shape of the rod (nose diameter and length), within 2% of the experimental measurement in all four rod-on-anvil experiments which did not result in fracture. The JC and GYS models, furthermore, were found to provide the best agreement with the measured transient surface strain profiles, predicting the experimental measurement to within 10% at all measurement locations and time steps for the experiment resulting in maximum deformation (impact velocity = 208 m/s). The results suggest that the added complexity of models such as the MJC and GYS, which incorporate strain hardening saturation, two-part strain rate dependency, and J3 plasticity effects, are unnecessary for HHA under the loading conditions experienced during rod-on-anvil experiments.

Shear Failure Mechanism of Infilling Rock Joints and its PFC Simulation

2015 ◽  
Vol 723 ◽  
pp. 317-321 ◽  
Author(s):  
Lei Xu ◽  
Qing Wen Ren
Keyword(s):  
Failure Mechanism ◽  
Shear Test ◽  
Shear Failure ◽  
Failure Process ◽  
Rock Joint ◽  
Rock Joints ◽  
Particle Flow Code ◽  
Rock Masses ◽  
Natural Rock ◽  
Simulation Results

Infilling rock joints widely exist in natural rock masses, and the shear failure of infilling rock joints plays an important role in the instability of rock masses. In order to study the shear failure mechanism of infilling rock joints, Particle Flow Code is used to simulate the direct shear test of infilling rock joints. The PFC models with different infilling thickness are established firstly, and then the procedures of PFC simulation are described. In the end, the shear failure process of infilling rock joints with different infilling thickness is simulated. Based on the PFC simulation results, it can be concluded that the shear failure mode changes with increasing infilling thickness, and the shearing of the infilling rock joint rarely gives birth to microcracks in rock due to the existence of the infilling material.

Improved Method Used to Investigate the Dynamic Shear Failure of AISI 1045 Steel Cylinder Under Blast Loading

2016 ◽  
Vol 08 (01) ◽  
pp. 1650003 ◽  
Author(s):  
Minzu Liang ◽  
Xiangyu Li ◽  
Fangyun Lu
Keyword(s):  
Failure Mechanism ◽  
Shear Failure ◽  
Shear Fracture ◽  
Blast Loading ◽  
Adiabatic Shear ◽  
Dynamic Shear ◽  
Improved Method ◽  
Aisi 1045 Steel ◽  
Aisi 1045 ◽  
1045 Steel

This study describes an improved method used to determine the dynamic shear failure of materials under blast loading conditions. The proposed method is a convenient and effective and generates material failure along the controlled fracture trajectories under uniform uniaxial stress conditions at a strain rate of [Formula: see text][Formula: see text]s[Formula: see text] to [Formula: see text][Formula: see text]s[Formula: see text]. The method was developed by performing experiments on AISI 1045 steel with heat treatment. Specimens were filled with composition B explosives and detonated, and fragments were recovered. Most of the macroscopic shear cracks originated at the notch tips and connected adjacent internal and external notches. The phenomena of multipath and bifurcate shear fracture trajectories were also observed. Fractography analysis of the fragments provided data on damage and failure mechanism and revealed that dynamic shear fracture was characterized by microvoids and microcracks. The adiabatic shear band of AISI 1045 steel was detected on the fracture surface boundary. This finding indicates that adiabatic shear localization is the underlying failure mechanism of the studied material.

Study on Tensile Strength of Composite Double-Lap Joint

2012 ◽  
Vol 157-158 ◽  
pp. 1519-1526 ◽  
Author(s):  
Sui Liu ◽  
Zhi Dong Guan ◽  
Xia Guo ◽  
Dong Xiu Yan ◽  
Ping Chen ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Shear Strain ◽  
Analytical Model ◽  
Shear Failure ◽  
Tensile Load ◽  
Lap Joints ◽  
Plastic Behavior ◽  
Finite Model ◽  
Lap Joint ◽  
Maximum Shear Strain

An experimental and analytical study on ultimate tensile strength of composite double-lap joints with different adhesive thicknesses is employed in the paper，test results indicate the major failure mode of joints is adhesive shear failure and the ultimate strength of joints increasing with thicker adhesive. Analytical model is developed to investigate the adhesive failure of double-lap joint based on the experiments. The model takes into account anisotropy of each ply in the composite laminates and elastic-perfectly plastic behavior of the adhesive in the joints. The validity of analytical model for calculating shear strain/stress distribution is certified by comparing with finite model results. Maximum shear strain criterion is adopted in the analytical model to predict the ultimate tensile load of double-lap joint. Good agreement of the analytical predictions with the experimental results is obtained.

scholarly journals Virtual Extensometer Analysis of Martensite Band Nucleation, Growth, and Strain Softening in Pseudoelastic NiTi Subjected to Different Load Cases

Materials ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 1458
Author(s):  
Cagatay Elibol ◽  
Martin Wagner
Keyword(s):  
Strain Softening ◽  
Nucleation Site ◽  
Shear Loading ◽  
Gauge Length ◽  
Surface Strain ◽  
Image Correlation ◽  
Localized Deformation ◽  
Stress Strain ◽  
Softening Behavior ◽  
Characteristic Features

Pseudoelastic NiTi shape memory alloys exhibit different stress–strain curves and modes of deformation in tension vs. compression. We have recently shown that under a combination of compression and shear, heterogeneous deformation can occur. In the present study, we use digital image correlation to systematically analyze how characteristic features of the nominally uniaxial engineering stress–strain curves (particularly the martensite nucleation peak and the plateau length) are affected by extensometer parameters in tension, compression, and the novel load case of shear-compression. By post-experimental analysis of full surface strain field data, the effect of the placement of various virtual extensometers at different locations (with respect to the nucleation site of martensite bands or inhomogeneously deforming regions) and with different gauge lengths is documented. By positioning an extensometer directly on the region corresponding to the nucleating martensite band, we, for the first time, directly record the strain-softening nature of the material—a specific softening behavior that is, for instance, important for the modeling community. Our results show that the stress–strain curves, which are often used as a basis for constitutive modeling, are affected considerably by the choice of extensometer, particularly under tensile loading, that leads to a distinct mode of localized deformation/transformation. Under compression-shear loading, inhomogeneous deformation (without lateral growth of martensite bands) is observed. The effects of extensometer gauge length are thus less pronounced than in tension, yet systematic—they are rationalized by considering the relative impact of differently deforming regions.

scholarly journals Determination of In-Plane Shear Properties of Laminate with V-Notch Rail Shear Test and Digital Image Correlation

2019 ◽  
Vol 2019 (3) ◽  
pp. 57-65
Author(s):  
Maciej Karny
Keyword(s):  
Shear Strength ◽  
Carbon Fiber ◽  
Digital Image Correlation ◽  
Shear Modulus ◽  
Shear Strain ◽  
Digital Image ◽  
Shear Loading ◽  
Image Correlation ◽  
Strain Gages ◽  
Plane Shear

Abstract This article presents the results of the application of Digital Image Correlation (DIC) to measurements of in-plane shear modulus and strength of three different carbon fiber reinforced laminates. Three different approaches to shear strain calculations via DIC are evaluated and compared with standard strain gage measurements. Calculation of shear strain based on averaging DIC strain values of strain gages area in most cases yielded results closest to strain gages, while measurements based on single point strain measuring differed the most from strain gages. These results are attributed to shear strain distribution in the center area of the specimen. Thermoplastic matrix fabric reinforced composite had the lowest shear strength at 5% of shear strain, but the highest ultimate shear strength and strain at failure. Of thermosetting materials, laminate reinforced with unidirectional carbon fiber had shear modulus about 10% lower, than fabric reinforced laminate, but higher ultimate strength and strain at failure. This behavior is attributed to the presence of weaves in fabric reinforcing the laminate, causing shear stiffening of the material, but lowering its ability to deform under shear loading.

Tensile characteristics of flexible PU-coated multi-axial warp-knitted fabrics

2016 ◽  
Vol 47 (1) ◽  
pp. 38-56 ◽  
Author(s):  
Lingxiao Jing ◽  
Nangkuo Guo ◽  
Haiyan Xu ◽  
Jinhua Jiang ◽  
tonghua Zhang ◽  
...  
Keyword(s):  
Failure Mechanism ◽  
Shear Failure ◽  
Small Strain ◽  
Image Correlation ◽  
Knitted Fabrics ◽  
Apparent Modulus ◽  
Coated Fabric ◽  
Plane Direction ◽  
Coated Fabrics ◽  
Warp Knitted Fabric

In practice, the coated fabric is available in many shapes and sizes, not just rectangle and plane. In order to increase the shape-shifting abilities of coated fabrics, polyurethane-coated multi-axial warp-knitted fabric (PU-CMWKF) is developed. In this paper, the tensile characteristics of PU-CMWKF were investigated. Five groups of tensile experiments, with off-axial angles of 0°, 22°, 45°, 67.5°, and 90°, were conducted under constant velocity. The failure mechanism was explored by analyzing the damaged specimens. Additionally, the deformation behavior of PU-CMWKF in three regions was investigated by utilizing the digital image correlation (DIC) system, and an orthogonal anisotropic model was used to predict the modulus and Poisson’s ratio of 22.5° and 67.5°. Research results showed that the apparent modulus of PU-CMWKF strongly depended on the cut of directions. And the failure mechanism under in-plane direction loading suggests that tensile and shear failure act together. The analytical model is validated along five directions in the representation of elastic constant under corresponding small strain.

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