Strain Gradient Effect in Cone Indentation

2002 ◽  
Vol 741 ◽  
Author(s):  
Anthony A. DiCarlo ◽  
Henry T. Y. Yang ◽  
Srinivasan Chandrasekar
Keyword(s):  
Strain Gradient ◽  
Indentation Size ◽  
Strain Fields ◽  
Strain Gradients ◽  
Element Simulation ◽  
Macro Scale ◽  
Self Similar ◽  
Rotational Strain ◽  
Indentation Strain

ABSTRACTA size effect is known to exist in the strength and hardness of metals at small length scales. For example, the hardness of a pyramid indentation at the macro-scale is constant and typically independent of indentation size due to the self-similar feature of the indentation. But, at the meso-scale, this hardness has been observed to increase with decreasing indentation size. This increase has been attributed to the influence of strain gradient on the flow stress. At this point, the contribution of a rotational gradient to the hardness is unclear.This study investigates the sensitivity of the hardness to rotational strain gradients through a Cosserat continuum. Finite element simulation of cone indentation is employed to conduct this investigation. The effect of varying indentation strain fields is modeled using indentation with cones of varying angles. The results demonstrate the role of rotational gradients in indentation.

scholarly journals Time dependence of cellular responses to dynamic and complex strain fields

2019 ◽  
Vol 11 (1) ◽  
pp. 4-15 ◽  
Author(s):  
Sophie Chagnon-Lessard ◽  
Michel Godin ◽  
Andrew E Pelling
Keyword(s):  
Strain Gradient ◽  
Strain Field ◽  
Local Strain ◽  
Cellular Responses ◽  
Strain Fields ◽  
Strain Gradients ◽  
Biologically Relevant ◽  
Physical Cues ◽  
History Of ◽  
Strain Direction

Abstract Exposing cells to an unconventional sequence of physical cues can reveal subtleties of cellular sensing and response mechanisms. We investigated the mechanoresponse of cyclically stretched fibroblasts under a spatially non-uniform strain field which was subjected to repeated changes in stretching directions over 55 h. A polydimethylsiloxane microfluidic stretcher array optimized for complex staining procedures and imaging was developed to generate biologically relevant strain and strain gradient amplitudes. We demonstrated that cells can successfully reorient themselves repeatedly, as the main cyclical stretching direction is consecutively switched between two perpendicular directions every 11 h. Importantly, from one reorientation to the next, the extent to which cells reorient themselves perpendicularly to the local strain direction progressively decreases, while their tendency to align perpendicularly to the strain gradient direction increases. We demonstrate that these results are consistent with our finding that cellular responses to strains and strain gradients occur on two distinct time scales, the latter being slower. Overall, our results reveal the absence of major irreversible cellular changes that compromise the ability to sense and reorient to changing strain directions under the conditions of this experiment. On the other hand, we show how the history of strain field dynamics can influence the cellular realignment behavior, due to the interplay of complex time-dependent responses.

Społeczne i kulturowe determinanty funkcjonowania państwa u progu XXI wieku

1970 ◽  
Vol 21 (282) ◽  
pp. 3-18
Author(s):  
Michał Strzelecki
Keyword(s):  
Political Institutions ◽  
Common Good ◽  
The State ◽  
Political Conflicts ◽  
Role Of The State ◽  
Macro Scale ◽  
The Common ◽  
Civic Awareness ◽  
Political Scene

The contemporary state crisis is a derivative of complex economic and social processes. His indicators include not only the visible increase in the intensity of political conflicts (both on a micro and macro scale), the revival and development of separatist tendencies, and the weakening of the role of the state as the basic instrument of organizing collective life. It is also increasing fragmentation of the political scene, the development of particularisms, weakening and progressive dysfunctionality of existing political institutions, increasing economic rivalry and the collapse of the generally accepted axiological system, which is accompanied by increasingly clear questioning of the idea of the common good and progressing pragmatism and egoism. An important element is therefore the disappearance of civic awareness and activity. The intensification of these disturbing tendencies is certainly not supported by the modern education system, whose hallmarks are commercialization and economization, withdrawal of the state and professionalization.

New expanding cavity model for indentation hardness including strain-hardening and indentation size effects

2006 ◽  
Vol 21 (5) ◽  
pp. 1317-1326 ◽  
Author(s):  
X.-L. Gao
Keyword(s):  
Strain Hardening ◽  
Young’S Modulus ◽  
Strain Gradient ◽  
Young's Modulus ◽  
Indentation Hardness ◽  
Cavity Model ◽  
Indentation Size ◽  
New Model ◽  
Plastic Materials ◽  
Classical Plasticity

An expanding cavity model (ECM) for determining indentation hardness of elastic–strain-hardening plastic materials is developed. The derivation is based on a strain gradient plasticity solution for an internally pressurized thick-walled spherical shell of an elastic linear-hardening material. Closed-form formulas are provided for both conical and spherical indentations. The formulas explicitly show that indentation hardness depends on Young's modulus, yield stress, strain-hardening index, and strain gradient coefficient of the indented material as well as on the geometry of the indenter. The newly formulated ECM can capture the indentation size effect, unlike classical plasticity based ECMs. The new model reduces to existing classical plasticity based ECMs (including Johnson's ECM for elastic-perfectly plastic materials) when the strain gradient effect is not considered. The presently developed ECM is validated by comparing with existing experimental hardness data. The numerical results obtained using the new model reveal that the hardness is indeed indentation size dependent when the indentation radius is very small: the smaller the indentation, the larger the hardness. Also, the indentation hardness is seen to increase with the Young's modulus and strain-hardening level of the indented material for both conical and spherical indentations. The strain-hardening effect on the hardness is observed to be significant for materials having strong strain-hardening characteristics. In addition, it is found that the indentation hardness increases with decreasing cone angle of the conical indenter or decreasing radius of the spherical indenter. These trends agree with existing experimental observations and model predictions.

The stabilizing role of higher-order strain gradients in non-linear thermoviscoplasticity

1991 ◽  
Vol 86 (1-4) ◽  
pp. 65-81 ◽  
Author(s):  
N. Charalambakis ◽  
A. Rigatos ◽  
E. C. Aifantis
Keyword(s):  
Higher Order ◽  
Strain Gradients ◽  
Non Linear

Child

2016 ◽  
Author(s):  
Rebekah Sheldon
Keyword(s):  
Children's Literature ◽  
Young Adult ◽  
Young Adult Literature ◽  
Human Life ◽  
Children’S Literature ◽  
Human Action ◽  
Young Adult Fiction ◽  
Self Similar ◽  
To Come

In the conclusion of The Child to Come, the book asks, ‘What happens when the life figured by the child--innocent, self-similar human life at home on a homely Earth--no longer has the strength to hold back the vitality that animates it?’ This chapter looks at two kinds of texts that consider this question: Anthropocene cinema and Young Adult Fiction. By focusing on the role of human action, the Anthropocene obscures a far more threatening reality: the collapse of the regulative. In relation, both children’s literature and young adult literature grow out of and as disciplinary apparatuses trained on that fraught transit between the presumptive difference of those still in their minority and the socially necessary sameness that is inscribed into fully attained adulthood.

Structure Modulation in Confined Nanoparticles: The Role of the Strain Gradient

2020 ◽  
Vol 124 (39) ◽  
pp. 21810-21817
Author(s):  
Chengwu Zou ◽  
Ce Hu ◽  
Hang Zhou ◽  
Shanqing Li ◽  
Xingfang Luo ◽  
...  
Keyword(s):  
Strain Gradient ◽  
Structure Modulation

The importance of Hall effect on the magnetized thin accretion disc

2019 ◽  
Vol 492 (2) ◽  
pp. 1770-1777
Author(s):  
Maryam Ghasemnezhad
Keyword(s):  
Hall Effect ◽  
Equatorial Plane ◽  
Radial Direction ◽  
Vertical Structure ◽  
Accretion Rate ◽  
Accretion Disc ◽  
Mhd Equations ◽  
Self Similar ◽  
Similar Solutions

ABSTRACT To study the role of Hall effect on the structure of accretion disc, we have considered a toroidal magnetic field in our paper. To study the vertical structure of the disc, we have written a set of magnetohydrodynamic (MHD) equations in the spherical coordinates (r, θ, ϕ) based on the two assumptions of axisymmetric and steady state. Also, we employed the self-similar solutions in the radial direction to obtain the structure of the disc in the θ-direction. We have solved a set of ordinary differential equations in the θ-coordinate with symmetrical boundary conditions in the equatorial plane. In order to describe the behaviour of Hall effect, we introduced the ΛH parameter that was called the dimensionless Hall Elsasser number. The strength of the Hall effect is measured by the inverse of dimensionless Hall Elsasser number. We have shown that the strong Hall effect decreases the accretion rate or infall velocity and size of inflow part. It has also been found the Hall effect is maximum in the equatorial plane and gets the value close to zero near the boundary, and it has the antidiffusive nature. The results display that the strong Hall effect makes the standard accretion sub-Keplerian disc becomes thinner. Our solutions have shown the Hall effect leads to transport magnetic flux outward in the upper layer of the disc and it produces outflows in the surface of the disc.

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