scholarly journals Experimental Investigation of Sandstone under Cyclic Loading: Damage Assessment Using Ultrasonic Wave Velocities and Changes in Elastic Modulus

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Sen Yang ◽  
Nong Zhang ◽  
Xiaowei Feng ◽  
Jiaguang Kan ◽  
Dongjiang Pan ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Damage Assessment ◽  
Crack Density ◽  
Density Parameter ◽  
Velocity Measurements ◽  
Ultrasonic Velocities ◽  
Damage Development ◽  
Irreversible Damage ◽  
Low Level ◽  
Wave Velocities

This laboratory study investigated the damage evolution of sandstone specimens under two types of cyclic loading by monitoring and analyzing changes in the elastic moduli and the ultrasonic velocities during loading. During low-level cyclic loading, the stiffness degradation method was unable to describe the damage accumulations but the ultrasonic velocity measurements clearly reflected the damage development. A crack density parameter is introduced in order to interpret the changes in the tangential modulus and the ultrasonic velocities. The results show the following. (1) Low-level cyclic loading enhanced the anisotropy of the cracks. This results from the compression of intergranular clay minerals and fatigue failure. (2) Irreversible damage accumulations during cyclic loading with an increasing upper stress limit are the consequence of brittle failure in the sandstone’s microstructure.

An Overall Approach for Microcrack and Inhomogeneity Toughening in Brittle Solids

1999 ◽  
Vol 15 (2) ◽  
pp. 57-68
Author(s):  
Huang Hsing Pan
Keyword(s):  
Poisson Ratio ◽  
Crack Density ◽  
Mean Field ◽  
Analytic Form ◽  
Density Parameter ◽  
Brittle Solids ◽  
The Matrix ◽  
Microcrack Toughening ◽  
Average Quantity ◽  
The Mean

ABSTRACTBased on the weight function theory and Hutchinson's technique, the analytic form of the toughness change near a crack-tip is derived. The inhomogeneity toughening is treated as an average quantity calculated from the mean-field approach. The solutions are suitable for the composite materials with moderate concentration as compared with Hutchinson's lowest order formula. The composite has the more toughened property if the matrix owns the higher value of the Poisson ratio. The composite with thin-disc inclusions obtains the highest toughening and that with spheres always provides the least effective one. For the microcrack toughening, the variations of the crack shape do not significantly affect the toughness change if the Budiansky and O'Connell crack density parameter is used. The explicit forms for three types of the void toughening and two types of the microcrack toughening are also shown.

Modelling of the damage development in carbon/epoxy laminates subjected to combined seawater ageing and mechanical loading

2016 ◽  
Vol 232 (9) ◽  
pp. 761-768 ◽  
Author(s):  
N Carrere ◽  
N Tual ◽  
T Bonnemains ◽  
E Lolive ◽  
P Davies
Keyword(s):  
Applied Load ◽  
Epoxy Composite ◽  
Damage Model ◽  
Crack Density ◽  
Damage Threshold ◽  
Multiscale Approach ◽  
Damage Development ◽  
Finite Fracture Mechanics ◽  
Physically Based ◽  
Kinetics Of

In this study, a damage model that accounts for the effect of seawater ageing is proposed. The model is based on a failure criterion that takes into account the effect of the ply thickness, while the kinetics of the damage development are based on a Finite Fracture Mechanics approach. The stiffness degradation is identified by a multiscale approach. The parameters of the model are physically based which facilitates the identification and the coupling with the ageing. These and their evolution as a function of the time of immersion in seawater have been identified for a carbon/epoxy composite. The changes in crack density as a function of the applied load for three ageing times are quite well predicted by the model. The model explains why the damage threshold is strongly influenced by the ageing while the kinetics of the crack propagation remain quasi-constant.

scholarly journals Distribution of crack density parameter in Central Betic Cordillera (Southern Spain)

2013 ◽  
Vol 196 (1) ◽  
pp. 22-33 ◽  
Author(s):  
Inmaculada Serrano ◽  
Federico Torcal ◽  
José Morales
Keyword(s):  
Crack Density ◽  
Betic Cordillera ◽  
Southern Spain ◽  
Density Parameter

The relation between seismic P‐ and S‐wave velocity dispersion in saturated rocks

Geophysics ◽  
1994 ◽  
Vol 59 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Gary Mavko ◽  
Diane Jizba
Keyword(s):  
Wave Velocity ◽  
Large Scale ◽  
Velocity Dispersion ◽  
Seismic Velocity ◽  
Ultrasonic Velocities ◽  
S Wave ◽  
Local Flow ◽  
Wave Velocities ◽  
Shear Compliance

Seismic velocity dispersionin fluid-saturated rocks appears to be dominated by tow mecahnisms: the large scale mechanism modeled by Biot, and the local flow or squirt mecahnism. The tow mechanisms can be distuinguished by the ratio of P-to S-wave dispersions, or more conbeniently, by the ratio of dynamic bulk to shear compliance dispersions derived from the wave velocities. Our formulation suggests that when local flow denominates, the dispersion of the shear compliance will be approximately 4/15 the dispersion of the compressibility. When the Biot mechanism dominates, the constant of proportionality is much smaller. Our examination of ultrasonic velocities from 40 sandstones and granites shows that most, but not all, of the samples were dominated by local flow dispersion, particularly at effective pressures below 40 MPa.

Damage and Thixotropy in Asphalt Mixture and Binder Fatigue Tests

2012 ◽  
Vol 2293 (1) ◽  
pp. 8-17 ◽  
Author(s):  
Félix Pérez-Jiménez ◽  
Ramon Botella ◽  
Rodrigo Miró
Keyword(s):  
Cyclic Loading ◽  
Strain Amplitude ◽  
Fatigue Testing ◽  
Complex Modulus ◽  
Asphalt Mixture ◽  
Viscoelastic Behavior ◽  
Fatigue Cracking ◽  
Asphalt Mixtures ◽  
Asphalt Binders ◽  
Irreversible Damage

Fatigue cracking is considered one of the main damage mechanisms in asphalt pavement design. Design methods use fatigue laws obtained by laboratory testing of the materials involved. Typically, these tests consist of subjecting the asphalt mixture to cyclic loading until failure occurs. However, failure is associated not with specimen fracture (which is unusual), but with a slight decrease in the mechanical properties of the material, usually in the complex modulus. As a consequence, it is important to differentiate between real damage to the material and changes in its viscoelastic behavior and thixotropy. It is also crucial to account for the healing that occurs in asphalt material after rest periods. The above considerations are important in the fatigue testing of asphalt binders because these materials show pronounced viscoelastic behavior and thixotropy, especially when subjected to cyclic loading. This paper demonstrates that in many cases what is taken for fatigue failure during testing (i.e., a decrease in the complex modulus below half of its initial value) is actually thixotropy. Thus, the complex modulus can be recovered by reducing the loading or, as in this study, the strain applied. In contrast, asphalt mixtures experience irreversible damage, and depending on the asphalt binder, the thixotropic effects are more or less pronounced. This paper analyzes the failure criteria currently used in the fatigue testing of asphalt mixtures and binders and evaluates the parameters chosen, namely, complex modulus (G*) and phase angle (δ) to characterize asphalt binders (G*sin δ). A cyclic uniaxial tension–compression test under strain-controlled conditions was performed. Three test modalities were used: time sweeps (constant strain amplitude until total failure), increasing strain sweeps (increase in strain amplitude every 5,000 cycles), and up-and-down strain sweeps (alternating increases and decreases in strain amplitude).

scholarly journals Development of vertical and horizontal disk transducers for wave velocity measurements in a large rectangular specimen

2019 ◽  
Vol 92 ◽  
pp. 02001
Author(s):  
Troyee Tanu Dutta ◽  
Masahide Otsubo ◽  
Reiko Kuwano ◽  
Takeshi Sato
Keyword(s):  
Wave Velocity ◽  
Small Strain ◽  
Elastic Wave Velocity ◽  
Coarse Grained ◽  
Velocity Measurements ◽  
Compression Waves ◽  
Wave Velocities ◽  
Triaxial Apparatus ◽  
Horizontal Wave ◽  
Toyoura Sand

For the accurate design of structures subjected to both static and dynamic loadings, elastic wave velocity and small strain stiffness are essential parameters. Numerous techniques have been developed to estimate wave velocities of geomaterials. Bender elements which are widely adopted for wave velocity measurements are invasive in nature and are not suitable for coarse-grained materials. In the present study, new design configuration of disk transducer has been introduced to measure both vertical and horizontal wave velocities for coarse granular soils considering multidirectional oscillation of propagating waves. An innovative arrangement of both compression and shear type elements has been installed in a large-sized triaxial apparatus having rectangular specimens of size 236×236×500 mm to assess the wave velocities. The materials described are Toyoura sand (D50 = 0.24 mm) and Oiso gravel (D50 = 11.8 mm). This arrangement enables measurements of nine types of wave velocities, and thus the stiffness anisotropy to be quantified. For Oiso gravel, horizontal wave velocities are greater than vertical wave velocities for both shear and compression waves. For Toyoura sand, shear wave velocities are higher in horizontal direction of propagation, whereas similar compression wave velocities are observed from both horizontal and vertical directions.

scholarly journals Linking permeability to crack density evolution in thermally stressed rocks under cyclic loading

2013 ◽  
Vol 40 (11) ◽  
pp. 2590-2595 ◽  
Author(s):  
I. Faoro ◽  
S. Vinciguerra ◽  
C. Marone ◽  
D. Elsworth ◽  
A. Schubnel
Keyword(s):  
Cyclic Loading ◽  
Crack Density ◽  
Density Evolution ◽  
Thermally Stressed
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