scholarly journals Coseismic fault lubrication by viscous deformation

2021 ◽  
Author(s):  
Giacomo Pozzi ◽  
Nicola De Paola ◽  
Stefan B. Nielsen ◽  
Robert E. Holdsworth ◽  
Telemaco Tesei ◽  
...  
Keyword(s):  
Viscous Deformation

Effects of heterogeneity on frictional-viscous deformation and the depth-extent of the seismogenic zone

2021 ◽  
Author(s):  
Ake Fagereng ◽  
Adam Beall
Keyword(s):  
Shear Stress ◽  
Yield Strength ◽  
Fault Zone ◽  
Fluid Pressure ◽  
Local Stress ◽  
Seismogenic Zone ◽  
Depth Range ◽  
Viscous Deformation ◽  
Viscosity Contrast ◽  
Depth Extent

<p>Current conceptual fault models define a seismogenic zone, where earthquakes nucleate, characterised by velocity-weakening fault rocks in a dominantly frictional regime. The base of the seismogenic zone is commonly inferred to coincide with a thermally controlled onset of velocity-strengthening slip or distributed viscous deformation. The top of the seismogenic zone may be determined by low-temperature diagenetic processes and the state of consolidation and alteration. Overall, the seismogenic zone is therefore described as bounded by transitions in frictional and rheological properties. These properties are relatively well-determined for monomineralic systems and simple, planar geometries; but, many exceptions, including deep earthquakes, slow slip, and shallow creep, imply processes involving compositional, structural, or environmental heterogeneities. We explore how such heterogeneities may alter the extent of the seismogenic zone.</p><p> </p><p>We consider mixed viscous-frictional deformation and suggest a simple rule of thumb to estimate the role of heterogeneities by a combination of the viscosity contrast within the fault, and the ratio between the bulk shear stress and the yield strength of the strongest fault zone component. In this model, slip behaviour can change dynamically in response to stress and strength variations with depth and time. We quantify the model numerically, and illustrate the idea with a few field-based examples: 1) earthquakes within the viscous regime, deeper than the thermally-controlled seismogenic zone, can be triggered by an increase in the ratio of shear stress to yield strength, either by increased fluid pressure or increased local stress; 2) there is commonly a depth range of transitional behaviour at the base of the seismogenic zone – the thickness of this zone increases markedly with increased viscosity contrast within the fault zone; and 3) fault zone weakening by phyllosilicate growth and foliation development increases viscosity ratio and decreases bulk shear stress, leading to efficient, stable, fault zone creep. These examples are not new interpretations or observations, but given the substantial complexity of heterogeneous fault zones, we suggest that a simplified, conceptual model based on basic strength and stress parameters is useful in describing and assessing the effect of heterogeneities on fault slip behaviour.         </p>

Contact Damage of Dental Multilayers: Viscous Deformation and Fatigue Mechanisms

2005 ◽  
Vol 127 (1) ◽  
pp. 33-39 ◽  
Author(s):  
M. Huang ◽  
X. Niu ◽  
P. Shrotriya ◽  
V. Thompson ◽  
D. Rekow ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Loading ◽  
Analytical Models ◽  
Dental Ceramics ◽  
Contact Damage ◽  
Viscous Deformation ◽  
Dental Restorations ◽  
Multilayered Systems ◽  
Elastic Layers ◽  
Radial Cracks

This paper presents the results of recent experimental and finite element studies of contact damage in model dental multilayered systems with equivalent elastic properties to those of crown/join/dentin layers that are found in dental restorations. Subsurface radial cracks are observed to form after Hertzian indentation fatigue loading. In order to explain the possible failure mechanisms, the viscous deformation of the foundation (dentinlike ceramic filled polymer) and epoxy join layers are measured. Finite element and analytical models are then developed in an effort to explain the observed contact-induced deformation of the composite multilayered system. Our results suggest that: viscous deformation of the join and foundation layers can give rise to increased tensile stresses in the top elastic layers (glass or zirconia); defects at the bottom of the top layers (induced by grinding steps before crown attachment) are also shown to promote ratcheting phenomena that can lead to stress build-up in the top layers; and viscous flow of the cement can cause the subcritical crack growth in the dental ceramics.

scholarly journals Alginate/Gelatin Hydrogels Reinforced with TiO2 and β-TCP Fabricated by Microextrusion-based Printing for Tissue Regeneration

Polymers ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 457 ◽  
Author(s):  
Rodrigo Urruela-Barrios ◽  
Erick Ramírez-Cedillo ◽  
A. Díaz de León ◽  
Alejandro Alvarez ◽  
Wendy Ortega-Lara
Keyword(s):  
Mechanical Properties ◽  
Tissue Engineering ◽  
Tissue Regeneration ◽  
Average Pore Size ◽  
Three Dimensional ◽  
Engineering Applications ◽  
Average Pore ◽  
Viscous Deformation ◽  
Freeze Dried ◽  
3D Printed

Three-dimensional (3D) printing technologies have become an attractive manufacturing process to fabricate scaffolds in tissue engineering. Recent research has focused on the fabrication of alginate complex shaped structures that closely mimic biological organs or tissues. Alginates can be effectively manufactured into porous three-dimensional networks for tissue engineering applications. However, the structure, mechanical properties, and shape fidelity of 3D-printed alginate hydrogels used for preparing tissue-engineered scaffolds is difficult to control. In this work, the use of alginate/gelatin hydrogels reinforced with TiO2 and β-tricalcium phosphate was studied to tailor the mechanical properties of 3D-printed hydrogels. The hydrogels reinforced with TiO2 and β-TCP showed enhanced mechanical properties up to 20 MPa of elastic modulus. Furthermore, the pores of the crosslinked printed structures were measured with an average pore size of 200 μm. Additionally, it was found that as more layers of the design were printed, there was an increase of the line width of the bottom layers due to its viscous deformation. Shrinkage of the design when the hydrogel is crosslinked and freeze dried was also measured and found to be up to 27% from the printed design. Overall, the proposed approach enabled fabrication of 3D-printed alginate scaffolds with adequate physical properties for tissue engineering applications.

scholarly journals A viscoplastic model of creep in shale

Geophysics ◽  
2020 ◽  
Vol 85 (3) ◽  
pp. MR155-MR166
Author(s):  
Ehsan Haghighat ◽  
Fatemeh S. Rassouli ◽  
Mark D. Zoback ◽  
Ruben Juanes
Keyword(s):  
Plastic Flow ◽  
Gradient Descent ◽  
Dissipated Energy ◽  
Eagle Ford ◽  
Viscoplastic Model ◽  
Viscous Deformation ◽  
Modified Cam Clay ◽  
Time Parameters ◽  
Haynesville Formation ◽  
Cam Clay

We have developed a viscoplastic model that reproduces creep behavior and inelastic deformation of rock during loading-unloading cycles. We use a Perzyna-type description of viscous deformation that derives from a maximization of dissipated energy during plastic flow, in combination with a modified Cam-clay model of plastic deformation. The plastic flow model is of the associative type, and the viscous deformation is proportional to the ratio of driving stress and a material viscosity. Our model does not rely on any explicit time parameters; therefore, it is well-suited for standard and cyclic loading of materials. We validate the model with recent triaxial experiments of time-dependent deformation in clay-rich (Haynesville Formation) and carbonate-rich (Eagle Ford Formation) shale samples, and we find that the deformation during complex, multiscale loading-unloading paths can be reproduced accurately. We elucidate the role and physical meaning of each model parameter, and we infer their value from a gradient-descent minimization of the error between simulation and experimental data. This inference points to the large, and often unrecognized, uncertainty in the preconsolidation stress, which is key to reproducing the observed hysteresis in material deformation.

A physical theory of snow gliding

1981 ◽  
Vol 18 (1) ◽  
pp. 86-94 ◽  
Author(s):  
David M. McClung
Keyword(s):  
Rigid Body ◽  
Constitutive Equations ◽  
Slip Velocity ◽  
Physical Theory ◽  
Water Film ◽  
Point Of View ◽  
Slip Condition ◽  
Realistic Case ◽  
Viscous Deformation ◽  
Snow Gliding

Snow glide, slip of the entire snowpack over the ground, is not observed unless water reaches the ground interface. In this paper, snow gliding is approached from the point of view that a perfect slip condition is attained at the glide interface whereby a thin continuous water film is envisioned to exist between the snowpack and the ground. Two mechanisms are described by which the snowpack may move forward: (i) creep (defined as slow, viscous deformation) over roughness asperities under the condition that the snowpack conforms to the interface and (ii) rigid body sliding of the snowpack over the interface when it does not conform to the interface. Constitutive equations relating tangential drag on the snowpack to slip velocity are derived for these idealized cases, and the extension to the more realistic case where the processes compete is discussed.

scholarly journals Nonlinear Material Model for Quasi-Unidirectional Woven Composite Accounting for Viscoelastic, Viscous Deformation, and Stiffness Reduction

Polymers ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 903 ◽  
Author(s):  
Zhanyu Zhai ◽  
Bingyan Jiang ◽  
Dietmar Drummer
Keyword(s):  
Material Model ◽  
Tensile Tests ◽  
Experimental Results ◽  
Nonlinear Material ◽  
Weibull Function ◽  
Viscous Deformation ◽  
Stiffness Reduction ◽  
Viscoelastic Strain ◽  
Proposed Model ◽  
The Individual

To clarify the individual contribution of viscoelastic and viscous deformation to the global nonlinear response of composites, multilevel cyclic loading-unloading recovery tensile tests were carried out. The experimental results show that there is a linear relationship between the viscous strain and viscoelastic strain of composites, regardless of the off-axis angle or loading stress level. On the basis of experimental results, a coupled damage-plasticity constitutive model was proposed. In this model, the plasticity theory was adopted to assess the evolution of viscous strains. The viscoelastic strain was represented as a linear function of viscous strains. Moreover, the Weibull function of the effective stress was introduced to evaluate the damage variables in terms of stiffness reduction. The tensile stress-strain curves, predicted by the proposed model, showed a good agreement with experimental results.

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