Mechanical Enhancement of Graded Nanoporous Structure

2021 ◽  
pp. 1-23
Author(s):  
Lijie He ◽  
Niaz Abdolrahim
Keyword(s):  
Pore Size ◽  
High Stress ◽  
Gaussian Random Field ◽  
Nanoporous Structure ◽  
Stress And Strain ◽  
Gradient Structure ◽  
High Mechanical Strength ◽  
The Past ◽  
Dynamics Simulations ◽  
Gradient Scaling

Abstract Inspired by the development of strong and ductile composite and gradient materials over the past decade, here we report the investigation of a graded nanoporous (NP) structure utilizing molecular dynamics simulations. The structure is generated by inducing a gradient scaling parameter in a Gaussian random field model. It has a large ligament/pore size toward the core and a small ligament/pore size toward the surface. The redistribution of stress and strain under tensile loading is then scrutinized and compared between the functional graded NP structure and two conventional NP structures with identical relative density but constant ligament size. During loading, the thick ligaments in the gradient structure yield at high stress, leading to the entire structure's high mechanical strength. The thin ligaments help the structure accommodate significant plastic strain by promoting uniform deformation. Both parts of the gradient structure worked collectively and resulted in the structure exhibiting a synergy of excellent strength and good deformability.

Investigation on Stress and Strain Singularity in LEFM

2006 ◽  
Vol 306-308 ◽  
pp. 31-36
Author(s):  
Zheng Yang ◽  
Wanlin Guo ◽  
Quan Liang Liu
Keyword(s):  
High Stress ◽  
Crack Tip ◽  
Plane Stress State ◽  
Stress And Strain ◽  
Linear Elastic ◽  
Geometrical Nonlinear ◽  
Maximum Crack ◽  
Elastic Fracture ◽  
Plain Strain ◽  
Strain Singularity

Stress and strain singularity at crack-tip is the characteristic of Linear Elastic Fracture Mechanics (LEFM). However, the stress, strain and strain energy at crack-tip may be infinite promoting conflicts with linear elastic hypothesis. It is indicated that the geometrical nonlinear near the crack-tip should not be neglected for linear elastic materials. In fact, the crack-tip blunts under high stress and strain, and the singularity vanishes due to the deformation of crack surface when loading. The stress at crack-tip may still be very high even though the singularity vanishes. The low bound of maximum crack-tip stress is the modulus of elastic in plane stress state, while in plain strain state, it is greater than the modulus of elastic, and will increase with the Poisson’s ratio.

Strain Measurement by X-ray Diffraction Methods

1949 ◽  
Vol 1 (3) ◽  
pp. 211-224
Author(s):  
G. B. Greenough
Keyword(s):  
Strain Measurement ◽  
Plastic Anisotropy ◽  
Stress And Strain ◽  
Routine Method ◽  
X Ray Diffraction ◽  
Strain Measurements ◽  
X Ray ◽  
The Past ◽  
Polycrystalline Metals ◽  
The Individual

SummaryMany papers have been written on the measurement of strain by X-ray diffraction methods and on the interpretation of these strains in terms of stresses. Whereas, during the past few years, the experimental methods of determining the strains have. remained largely unchanged, research has shown that the older techniques for calculating stresses from strains are not always valid.In this paper an attempt is made to describe some of the principles of strain measurement by X-ray diffraction methods to those who are unfamiliar with the methods. The types of stress and strain systems which may exist in polycrystalline metals are then considered, particular attention being paid to the effect of the elastic and plastic anisotropy of the individual crystals. Some indication is given as to how the earlier methods of interpreting X-ray strain measurements should be modified, but no rigid routine method is proposed for use in a general case.

The Propagation of Plasticity in Uniaxial Compression

1948 ◽  
Vol 15 (3) ◽  
pp. 256-260 ◽  
Author(s):  
M. P. White ◽  
LeVan Griffis
Keyword(s):  
Uniaxial Compression ◽  
Thin Sheet ◽  
High Stress ◽  
Stress And Strain ◽  
Velocity Range ◽  
Plastic Materials ◽  
The Face ◽  
Elastic Plastic Materials ◽  
The Impact ◽  
Type Of Behavior

Abstract A theoretical investigation of the mechanism of uniaxial compression impact on elastic-plastic materials is described in this paper. The method of analysis is similar in some respects to that previously given for tension impact on such materials. It is concluded that four different kinds of behavior can occur, depending upon the impact velocity. In the lowest velocity range the behavior in compression is similar to that found in tension. In this case stress and strain are propagated from the point of impact as a zone or wave front of ever-increasing length. This type of behavior ends at a velocity corresponding to the “critical” velocity found in tension impact. Within the next higher velocity range, stress and strain are propagated as a shock-type wave, or wave of very small length in which the transition from low to high stress and strain is very abrupt. At still higher impact velocities, there occurs “flowing deformation” in which the material is too weak to maintain coherency. Here there is a steady flow of the material toward and against the hammer, after which it flows in a thin sheet radially outward over the face of the hammer. The final possible state occurs at impact velocities greater than the speed of an elastic wave, so that no disturbance can escape from the hammer into the medium. Here the behavior is essentially that of a fluid, impact force being independent of strength of material.

Investigation of PDC Cutter Interface Geometry Using 3D FEM Modelling

2017 ◽  
Vol 29 ◽  
pp. 45-53 ◽  
Author(s):  
Seyed Ali Heydarshahy ◽  
Shivakumar Karekal
Keyword(s):  
Strain Distribution ◽  
High Stress ◽  
Polycrystalline Diamond ◽  
Shear Loading ◽  
Stress And Strain ◽  
3D Fem ◽  
Interface Shear ◽  
Interface Elements ◽  
Premature Failure ◽  
Stress And Strain Distribution

Polycrystalline Diamond Compact (PDC) cutters have been popularly used in recent times due to their resistance against mechanical and thermal wear. This paper was focused on interface geometries between the substrate and the diamond table. Various types of interfaces were designed, to investigate how different interface geometries influence distribution of stress and strain under shear loading. The interface geometries examined in this paper included castle interface, dent interface, honeycomb interface and chase interface. Parallel to the interface, shear loading was applied to the top of diamond table to mimic the shear loading component from the rock cutting. To apply the shear loading, two locations were considered for each of the geometries. These locations differed depending on the interface features. Stress and strain distribution and values across different interface geometries were analysed with the aid of 3D Finite Element Method (FEM). The numerical simulations indicated that stress and strain magnitudes and distribution patterns varied in relation to different geometries. Some substrates showed relatively lower plastic strain representing higher durability of the geometries. Concentration of stress and strain distribution showed the areas where one could expect weakness. It also implies that rotating the PDC cutter assemblies around their cylindrical axis helps avoiding fatigue of interface elements in regions of high stress concentration; and thus, preventing premature failure of interface elements.

Measurement of Red Cell Modulus of Elasticity by in-Vitro and Model Cell Experiments

1970 ◽  
Vol 92 (3) ◽  
pp. 604-609 ◽  
Author(s):  
T. W. Hoeber ◽  
R. M. Hochmuth
Keyword(s):  
Modulus Of Elasticity ◽  
Relaxation Times ◽  
High Stress ◽  
Red Cells ◽  
Stress And Strain ◽  
Internal Diameter ◽  
Membrane Stress ◽  
Membrane Elasticity ◽  
Model Cell

Because of the small size of the human red blood cell, it is difficult to measure the elasticity of the cell membrane. Previous techniques of measuring membrane elasticity involve high stress and strain and therefore do not adequately characterize the membrane’s elasticity near its equilibrium (biconcave) shape. In order to determine elasticity at low stress and strain, an experiment was designed to involve minimal membrane stress. In the experiment, the red cells are expelled from glass micropipettes on the order of 3 microns in internal diameter. The cell is in a folded deformed shape within the confines of the tip but once it leaves the pipette the cell returns to its biconcave shape. With the use of dimensional analysis, the characteristic relaxation times of the red cells and of geometrically similar, fluid-filled model cells are compared and a modulus of elasticity of approximately 106 dynes/cm2 is calculated.

Formation of Anodic Oxide Nanotubes in H2O2 - Fluoride Ethylene Glycol Electrolyte as Template for Electrodeposition of α-Fe2O3

2013 ◽  
Vol 832 ◽  
pp. 333-337 ◽  
Author(s):  
Zainovia Lockman ◽  
Dede Miftahul Anwar ◽  
Monna Rozana ◽  
Syahriza Ismail ◽  
Ehsan Ahmadi ◽  
...  
Keyword(s):  
Oxide Film ◽  
Ethylene Glycol ◽  
Pore Size ◽  
Surface Structure ◽  
Anodic Oxidation ◽  
Chloride Solution ◽  
Anodic Oxide ◽  
Nanoporous Structure ◽  
20 Nm

Anodic oxidation of titanium (Ti), zirconium (Zr) and niobium (Nb) foils in fluoride ethylene glycol (EG) added to it 1 H2O2 as oxidant was done to produce oxide film with nanostructures at 40 V. Whilst arrays of aligned nanotubes were successfully formed on the surface of Ti and Zr respectively, anodic Nb2O5 was found to consist of nanoporous structure with pore size of ~ 20 nm. Despite long nanotubes were formed on both Ti (2 μm) and Zr (3 μm), the surface of the nanotubes suffered from severe dissolution, thinning the wall and collapsing them. Well defined, ordered surface structure of the nanotubes is required as they will be used as template for subsequent deposition of nanoparticles. This was achieved when Ti anodised in 5 ml H2O2 fluoride EG. With excess H2O2 etching at the surface occur more uniformly forming homogenous surface structure. α-Fe2O3 were then electrodeposited on this surface at-3 V from chloride solution and the mode of formation is believed to be due to electrogeneration of base at the surface of the TiO2.

scholarly journals Effects of temperature and pore structure on the release of methane in zeolite nanochannels

RSC Advances ◽  
2019 ◽  
Vol 9 (17) ◽  
pp. 9546-9554 ◽  
Author(s):  
Xu Cheng ◽  
Zhigang Li ◽  
Ya-Ling He
Keyword(s):  
Molecular Dynamics ◽  
Pore Structure ◽  
Molecular Dynamics Simulations ◽  
Pore Size ◽  
Effects Of Temperature ◽  
Dynamics Simulations

The effects of temperature and pore size on release of methane in zeolite nanochannels is investigated by molecular dynamics simulations.

The Constitutional Crisis in Austria

1930 ◽  
Vol 24 (1) ◽  
pp. 144-157
Author(s):  
Malbone W. Graham
Keyword(s):  
Social Order ◽  
Democratic Republic ◽  
Stress And Strain ◽  
Social Revolution ◽  
Party Organization ◽  
The Past ◽  
The Social ◽  
History Of ◽  
Parliamentary Supremacy ◽  
The Government

Constitutionalism, in Austria, is not a new slogan. It was a phrase to conjure with during the entire lifetime of Francis Joseph, though in practice the whole history of the country down to the revolution of 1918 was its virtual negation. Only in the latter days of the monarchy, when the scepter passed from the hands of Francis Joseph to the inexperienced young emperor Karl, was a modicum of popular expression allowed to supplant the personal autocracy of the sovereign. The old Austria passed out of existence in 1918 without the successful implantation of a régime of liberal legality in any of its parts.The young Austrian Republic, coming into existence in the hour of the Empire's dissolution, thus inherited a legacy of unconstitutional government, and only the solidity of socialist and clerical party organization, bred of the stress and strain of clashing conceptions of the social order, gave support to the government in the days when social revolution swept almost to the doors of Vienna. It was under such circumstances that Austria entered, in 1918, upon the way of constitutionalism and sought, through her provisional instruments of government, to avoid the autocratic excesses of the past and avert the impending perils of a proletarian dictatorship.In a series of revolutionary pronouncements and decisions of her provisional assembly, she discarded, under socialist leadership, the arbitrary régime attendant on the monarchy, and, establishing a unitary democratic republic with far-reaching local self-government as a stepping-stone toward union with Germany, inaugurated a régime of unquestioned parliamentary supremacy, strict ministerial responsibility, virtual executive impotence, and extensive socialization.

Dislocation Dynamics Simulations in the Presence of Interacting Cracks

1999 ◽  
Vol 121 (2) ◽  
pp. 151-155 ◽  
Author(s):  
I. Demir ◽  
A. N. Gulluoglu
Keyword(s):  
Plastic Zone ◽  
High Stress ◽  
Dislocation Dynamics ◽  
Failure Behavior ◽  
Multiple Cracks ◽  
Accurate Analysis ◽  
High Stress Concentration ◽  
History Of ◽  
Reasonable Description ◽  
Dynamics Simulations

For an understanding failure behavior of crystalline solids, considerable interest is given to investigating interaction effects between the main crack and microcracks in the presence of mobile dislocations. Accurate analysis of these types of interaction problems may lead to accurate models for failure prevention and the history of plastic zone development. High stress concentration areas such as crack tips are the places where dislocations are subjected to higher forces. Therefore, a computer simulation technique based on dislocation dynamics has been developed to investigate the movement of dislocations in the presence of multiple cracks. Dislocation structures, dislocation distribution and strain rate results are presented as functions of applied stresses for different microcrack positions and orientations. Simulation results give a reasonable description of dislocation pattern development during deformation around the cracks and explain the shape and development of the plastic zone.

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