Dynamic Indentation Characteristics for Various Spacings and Indentation Depths: A Study Based on Laboratory and Numerical Tests

Laboratory and numerical study tests were conducted to investigate the dynamic indentation characteristics for various spacings and indentation depths. First, laboratory tests indicate that the increase in the indentation depth first resulted in enlarged groove volumes, caused by fiercer rock breakages between indentations for a fixed spacing; then, the groove volume slightly increased for further increase in indentation depth, whereas the increase in spacing restrained rock breakages and resulted in shrunken grooves. In addition, the numerical study agreed well with laboratory tests that small chips formed at the shallow part of the rock specimen at the early indentation stage, and then, larger chips formed by the crack propagation at deeper parts of the rock specimens when the indentation depth increased. With further increase in indentation depth, crushed powders instead of chips formed. Moreover, the numerical analysis indicates that crack propagation usually leads to the decrease of the indentation force and the dissipation of the stress concentrations at crack tips, whereas the cessation of crack propagation frequently resulted in the increase of the indentation force and the stress concentrations at crack tip with the increase in indentation depth.

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A 3DEC Numerical Analysis of the Interaction Between an Uneven Rock Surface and Shotcrete Lining

Rock Mechanics and Rock Engineering ◽

10.1007/s00603-021-02399-x ◽

2021 ◽

Author(s):

Ping Zhang ◽

Ering Nordlund

Keyword(s):

Numerical Study ◽

Support Effect ◽

Influential Factors ◽

Numerical Analyses ◽

Numerical Code ◽

Rock Surface ◽

Stress Concentrations ◽

Circular Tunnel ◽

Rock Tunnels ◽

Shotcrete Lining

AbstractRock tunnels excavated using drilling and blasting technique in jointed rock masses often have a very uneven and rough excavation surface. Experience from previous studies shows that the unevenness of a rock surface has a large impact on the support effect of shotcrete lining. However, clear conclusions regarding the effect of 2D and 3D uneven surfaces were not obtained due to limited studies in the literature. The numerical analyses reported in this paper were made to investigate the influence of the surface unevenness of a circular tunnel opening on the support effect of shotcrete using a 3D numerical code (3DEC). The models were first calibrated with the help of observations and measured data obtained from physical model tests. The influential factors were investigated further in this numerical study after calibration had been achieved. The numerical analyses show that, in general, the unevenness of a tunnel surface produces negative support effects due to stress concentrations in recesses (compressive) and at apexes (tensile) after excavation. However, shotcrete sprayed on a doubly waved uneven surface has better support effect compared to shotcrete sprayed on a simply waved tunnel surface. The development of shear strength (specifically frictional strength) on the uneven interface between the shotcrete and the rock contributes to this effect, in the condition where bonding of the shotcrete does not work effectively. The interface is a crucial element when the interaction between the rock and shotcrete is to be simulated. When an entire tunnel surface is covered by shotcrete with high modulus, more failures will occur in the shotcrete especially when rock surface is uneven. Based on the numerical model cases examined, some recommendations on how to incorporate tunnel surface conditions (2D or 3D unevenness) in the design of a shotcrete lining are given.

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Fracture in Bulk Amorphous Alloys

MRS Proceedings ◽

10.1557/proc-554-185 ◽

1998 ◽

Vol 554 ◽

Cited By ~ 5

Author(s):

J. A. Horton ◽

J. L. Wright ◽

J. H. Schneibel

Keyword(s):

Crack Propagation ◽

Crack Growth ◽

Shear Bands ◽

Bulk Amorphous Alloy ◽

In Situ Tem ◽

X Ray Diffraction ◽

Transmission Electron ◽

Crack Tips ◽

Temperature Fracture

AbstractThe fracture behavior of a Zr-based bulk amorphous alloy, Zr-10 Al-5 Ti-17.9 Cu-14.6Ni (at.%), was examined by transmission electron microscopy (TEM) and x-ray diffraction forany evidence of crystallization preceding crack propagation. No evidence for crystallizationwas found in shear bands in compression specimens or at the fracture surface in tensile specimens.In- situ TEM deformation experiments were performed to more closely examine actualcrack tip regions. During the in-situ deformation experiment, controlled crack growth occurredto the point where the specimen was approximately 20 μm thick at which point uncontrolledcrack growth occurred. No evidence of any crystallization was found at the crack tips or thecrack flanks. Subsequent scanning microscope examination showed that the uncontrolledcrack growth region exhibited ridges and veins that appeared to have resulted from melting. Performing the deformations, both bulk and in-situ TEM, at liquid nitrogen temperatures (LN2) resulted in an increase in the amount of controlled crack growth. The surface roughness of the bulk regions fractured at LN2 temperatures corresponded with the roughness of the crack propagation observed during the in-situ TEM experiment, suggesting that the smooth-appearing room temperature fracture surfaces may also be a result of localized melting.

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Numerical Study on the Fatigue Crack Propagation Behavior in Flattened Martensite Dual Phase Steel

Journal of the Japan Society of Naval Architects and Ocean Engineers ◽

10.2534/jjasnaoe.6.387 ◽

2007 ◽

Vol 6 (0) ◽

pp. 387-397 ◽

Cited By ~ 1

Author(s):

Tarou Osawa ◽

Daisuke Ueno ◽

Hanako Shimoike ◽

Tsugio Hashimoto ◽

Mitsuo Nakashima ◽

...

Keyword(s):

Fatigue Crack ◽

Crack Propagation ◽

Fatigue Crack Propagation ◽

Dual Phase Steel ◽

Numerical Study ◽

Dual Phase ◽

Fatigue Crack Propagation Behavior ◽

Propagation Behavior ◽

Crack Propagation Behavior

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Micro-mechanical modeling using DEM to study the effect of mechanical properties on crack propagation for snow slab avalanches

10.5194/egusphere-egu21-11482 ◽

2021 ◽

Author(s):

Bobillier Gregoire ◽

Bergfled Bastian ◽

Gaume Johan ◽

van Herwijnen Alec ◽

Schweizer Jürg

Keyword(s):

Mechanical Properties ◽

Steady State ◽

Crack Propagation ◽

Sensitivity Study ◽

Tensile Fracture ◽

Crack Speed ◽

Stress Concentrations ◽

Snow Layer ◽

Stress Regime ◽

Weak Layer

<p>Dry-snow slab avalanche release is a multi-scale process starting with the formation of localized failure in a highly porous weak snow layer below a cohesive snow slab, which can be followed by rapid crack propagation within the weak layer. Finally, a tensile fracture through the slab leads to its detachment. About 15 years ago, the propagation saw test (PST) was developed. The PST is a fracture mechanical field test that provides information on crack propagation propensity in weak snowpack layers. It has become a valuable research tool to investigate the processes involved in crack propagation. While this has led to a better understanding of the onset of crack propagation, much less is known about the ensuing propagation dynamics. Here, we use the discrete element method to numerically simulate PSTs in 3D and analyze the fracture dynamics using a micro-mechanical approach. Our DEM model reproduced the observed PST behavior extracted from experimental analysis. We developed different indicators to define the crack tip that allowed deriving crack speed. Our results show that crack propagation in level terrain reaches a stationary speed if the snow column is long enough. Moreover, we define stress concentration sections. Their length evolution during crack propagation suggests the development of a steady-state stress regime. Slab and weak layer elastic modulus, as well as weak layer shear strength, are the key input parameters for modeling crack propagation; they affect stress concentrations, crack speed, and the critical length for the onset of crack propagation. The results of our sensitivity study highlight the effect of these mechanical parameters on the emergence of a steady-state propagation regime and consequences for dry-snow slab avalanche release. Our DEM approach opens the possibility for a comprehensive study on the influence of the snowpack mechanical properties on the fundamental processes for avalanche release.</p>

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Numerical Study on Progressive Failure of the Marble Plate Based on the Thin-Layer Tri-Node Jointed Element

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.255-260.1867 ◽

2011 ◽

Vol 255-260 ◽

pp. 1867-1872

Author(s):

Jing Hua Qi ◽

Zhen Nan Zhang ◽

Xiu Run Ge

Keyword(s):

Crack Propagation ◽

Thin Layer ◽

Numerical Study ◽

Progressive Failure ◽

Triangular Element ◽

Compressive Loads ◽

Joint Element ◽

The Common ◽

Edge Cracks ◽

Good Agreement

In order to model the mechanical behavior of joints efficiently, a thin-layer tri-node joint element is constructed. The stiffness matrix of the element is derived in the paper. For it shares the common nodes with the original tri-node triangle element, the tri-node joint element can be applied to model the crack propagation without remeshing or mesh adjustment. Another advantage is that the cracked body is meshed without consideration of its geometry integrity and existence of the joints or pre-existed crack in the procedure of mesh generation, and then the triangular element intersected by the crack or joint is automatically transformed into the tri-node joint element to represent pre-existed cracks. These make the numerical simulation of crack propagation highly convenient and efficient. After CZM is chosen to model the crack tip, the mixed- energy simple criterion is used to determine whether the element is intersected by the extended crack or not, the extended crack is located in the model. By modeling the marble plates with two edge cracks subjected to the uniaxial compressive loads, it is shown that the numerical results are in good agreement with the experimental results, which suggests that the present method is valid and feasible in modeling rock crack propagation.

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