A Continuum Model for Dynamic Tensile Microfracture and Fragmentation

1985 ◽  
Vol 52 (3) ◽  
pp. 593-600 ◽  
Author(s):  
L. Seaman ◽  
D. R. Curran ◽  
W. J. Murri
Keyword(s):  
Continuum Model ◽  
Crack Density ◽  
Volume Growth ◽  
Material Point ◽  
Detailed Simulation ◽  
Elastoplastic Materials ◽  
Material Separation ◽  
Dependent Growth ◽  
Stress Dependent ◽  
Fracture Processes

A continuum model for dynamic tensile cleavage fracture and fragmentation has been developed for detailed simulation of brittle fracture processes in elastoplastic materials. The model includes processes for nucleation of microcracks, stress-dependent growth, coalescence and fragmentation, and stress relaxation caused by the developing damage. Fracturing is characterized by a crack density with a distribution of sizes at each material point. The model extends previous work by treating more completely full material separation and stress-free volume growth, as well as multiple loadings, unloadings, and recompaction, and by describing the damage in greater microscopic detail.

An innovative method to simulate stress-induced velocity changes in anisotropic rock

2021 ◽  
Vol 11 (4) ◽  
pp. 1-18
Author(s):  
Q. Bai ◽  
H. Konietzky
Keyword(s):  
Seismic Velocity ◽  
Numerical Models ◽  
Crack Density ◽  
Bedding Plane ◽  
Anisotropic Rock ◽  
Proposed Model ◽  
Isotropic Structure ◽  
Velocity Changes ◽  
Induced Velocity ◽  
Stress Dependent

This contribution proposes a numerical microstructural modeling approach to investigate stress-induced seismic velocity changes on anisotropic rocks. By introducing pre-existing cracks with preferential orientations in bonded-particle assemblies, the transverse isotropic structure of the Whitby Mudstone is simulated. Using power-law distributed aperture and calibrated micro-properties, we successfully reproduce stress-dependent velocity changes on Whitby Mudstones with different anisotropic angles in relation to the applied loads. The proposed model also duplicates the directional dependence of wave speed with respect to the bedding plane as expected theoretically. The numerical models show that velocity increase results from the closure of pre-existing cracks due to load increase. Direct relations are established between velocity changes and opened crack density (or crack closure), which displays a similar tendency compared with theoretical predictions. This relation can be used to quantify the micromechanisms behind the velocity changes. The proposed model provides the ability to directly examine the micro-processes underlying velocity changes.

Strain and temperature dependence of crack populations in columnar-grain ice

2003 ◽  
Vol 81 (1-2) ◽  
pp. 311-318
Author(s):  
L W Gold
Keyword(s):  
Grain Boundary ◽  
Strain Rate ◽  
Crack Density ◽  
Time Range ◽  
Transgranular Crack ◽  
Transverse Isotropic ◽  
Stage Process ◽  
Columnar Grain ◽  
Dependent Growth ◽  
Growth Of Voids

It has been shown that the development of grain-boundary and transgranular crack populations in transverse isotropic columnar-grain ice by a uniaxial compressive stress is a random process. The lognormal distribution function was found to be a good descriptor of the strain dependence of the crack density and of the crack length. It is shown, in the present paper, that the populations are induced in the first 10–2 strain and within the time range for the anelastic strain. These time and strain limits, and the strain-rate, stress, temperature, and grain-size dependence of the characteristics of the crack populations, indicate a two-stage process involving the development of precursors and the formation of cracks. The increasing probability for the formation of grain-boundary cracks with increasing strain rate is consistent with a time-dependent growth of voids and an increase in the associated stress intensity factors. The increasing probability for the formation of transgranular cracks with decreasing stain rate is consistent with an increasing density of dislocations and grain distortion due to shear. PACS Nos.: 62.20MK, 62.40-x

Determination of the stress-dependent stiffness of plasma-sprayed thermal barrier coatings using depth-sensitive indentation

2003 ◽  
Vol 18 (8) ◽  
pp. 1975-1984 ◽  
Author(s):  
J. Malzbender ◽  
R. W. Steinbrech
Keyword(s):  
Crack Density ◽  
Strain Curve ◽  
Spherical Indenter ◽  
Atmospheric Plasma ◽  
Elastic Response ◽  
Elastic Behavior ◽  
Thermal Barrier ◽  
Additional Information ◽  
Stress Dependent ◽  
Plasma Sprayed

The elastic response of atmospheric plasma-sprayed coatings was investigated using Vickers and spherical indenter geometries. In both cases a strong dependency of the stiffness on the applied load (indentation depth) was observed. The stiffness of the coatings decreased with increasing load for a Vickers indenter, whereas it increased for a spherical indenter. This contrary behavior was related to the relative crack density in the deformed volume and to the stress dependence of the stiffness due to crack closure. The effect of annealing on the stiffness was quantified for both tip geometries. The heat treatment yielded additional information on the relationship between the indentation data and the microstructural defects. From the results it was concluded that the stiffness measured using a sharp indenter and small load reflected the elastic behavior of single spraying splats. With the relatively large spherical indenter, the average global stiffness of the thermal barrier coating was measured even at small loads. From the data obtained using the spherical indenter, a compressive stress–strain curve was suggested. Furthermore, values of the apparent crack density and yield strength were determined from the indentation tests.

Main the Oretical Provisions of Grain Material Separation in Air Channels with Unequal Air Flow Speed

2020 ◽  
pp. 122-133
Author(s):  
Serhii Stepanenko ◽  
◽  
Boris Kotov ◽  
Keyword(s):  
Initial Conditions ◽  
Flow Speed ◽  
Material Point ◽  
Friction Forces ◽  
Air Stream ◽  
Air Resistance ◽  
Material Separation ◽  
Round Section ◽  
Air Channels ◽  
Rational Shape

The article considers the increase of efficiency of grain materials separation in pneumatic vertical channels by determining the rational shape and parameters of material supply, as well as the geometric shape of the pneumatic channel and options for separation into fractions. Regularities of change of trajectory and speed of movement of material in pneumatic vertical channels of round section with the lower unloading of material are received. The regularities of particle motion in the form of a material point were determined taking into account air resistance forces, friction forces, Magnus and Zhukovsky forces, material moisture and density based on a theoretical study of grain fractionation in pneumatic vertical channels. Using the proposed dependences for the design of air separators, it is possible to determine the initial rate of introduction and the direction of entry of grains into the air stream, which are the initial conditions for determining the trajectory of material in air channels with lower material discharge.

scholarly journals Exploring trends in microcrack properties of sedimentary rocks: An audit of dry-core velocity-stress measurements

Geophysics ◽  
2009 ◽  
Vol 74 (5) ◽  
pp. E193-E203 ◽  
Author(s):  
Doug A. Angus ◽  
James P. Verdon ◽  
Quentin J. Fisher ◽  
J.-M. Kendall
Keyword(s):  
Aspect Ratio ◽  
Sedimentary Rock ◽  
Crack Density ◽  
Sedimentary Rocks ◽  
Rock Physics ◽  
Initial Crack ◽  
Density Tensor ◽  
Physics Model ◽  
Rock Physics Model ◽  
Stress Dependent

Rock-physics models are used increasingly to link fluid and mechanical deformation parameters for dynamic elastic modeling. We explore the input parameters of an analytical stress-dependent rock-physics model. To do this, we invert for the stress-dependent microcrack parameters of more than 150 sedimentary rock velocity-stress core measurements taken from a literature survey. The inversion scheme is based on a microstructural effective-medium formulation defined by a second-rank crack-density tensor (scalar crack model) or by a second- and fourth-rank crack-density tensor (joint inversion model). Then the inversion results are used to explore and predict the stress-dependent elastic behavior of various sedimentary rock lithologies using an analytical microstructural rock-physics model via the initial modelinput parameters: initial crack aspect ratio and initial crack density. Estimates of initial crack aspect ratio are consistent among most lithologies with a mean of 0.0004, but for shales they differ up to several times in magnitude with a mean of 0.001. Estimates of initial aspect ratio are relatively insensitive to the inversion method, although the scalar crack inversion becomes less reliable at low values of normal-to-tangential crack compliance ratio [Formula: see text]. Initial crack density is sensitive to the degree of damage as well as the inversion procedure. An important implication is that the fourth-rank crack-density term is not necessarily negligible for most sedimentary rocks and evaluation of this term or [Formula: see text] is necessary for accurate prediction of initial crack density. This is especially important because recent studies suggest that [Formula: see text] can indicate fluid content in cracks.

scholarly journals Contraction and stress-dependent growth shape the forebrain of the early chicken embryo

2017 ◽  
Vol 65 ◽  
pp. 383-397 ◽  
Author(s):  
Kara E. Garcia ◽  
Ruth J. Okamoto ◽  
Philip V. Bayly ◽  
Larry A. Taber
Keyword(s):  
Chicken Embryo ◽  
Dependent Growth ◽  
Stress Dependent ◽  
Growth Shape

Cyclic Damage Evolution in a PMC Laminate

2007 ◽  
Vol 348-349 ◽  
pp. 33-36
Author(s):  
Alan Plumtree ◽  
M. Melo
Keyword(s):  
Fatigue Damage ◽  
Damage Evolution ◽  
Damage Mechanics ◽  
Life Stage ◽  
Crack Density ◽  
Stage I ◽  
Matrix Cracks ◽  
Minimum Stress ◽  
Stress Dependent ◽  
Cyclic Damage

Using damage mechanics, cyclic damage evolution has been described and evaluated in a non-crimped glass epoxy fabric composite. A fundamental fatigue study has been carried out by progressively monitoring the fatigue damage modulus and crack density throughout the life of an [0,+45,90,-45]2 (antisymmetric) laminate cycled at a stress ratio R (minimum stress/maximum stress) of 0.1. Development of damage can be separated into two main stages. Initially, damage increases very quickly during the first 10% of life (Stage I). Afterwhich, it increases more slowly at a relatively constant rate to failure (Stage II). The changes in the fatigue modulus and crack density both show the same behaviour. A large amount of damage in the form of transverse matrix cracks develops during the first cycle. These then remain constant throughout life. By contrast, the number of shear matrix cracks increase continually. The crack density is cycle, not stress dependent. This behaviour is reflected by changes in the fatigue modulus. Using damage mechanics, a representative equation has been applied to express the progressive evolution of damage. The significance of which is that the amount of fatigue damage at the end of Stage I for any stress level can be used to predict fatigue life and the stress-life diagram for the laminate.

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