scholarly journals Stress concentration analysis in rock pillars in the framework of non-local elastic model with structural parameter

2021 ◽  
Vol 773 (1) ◽  
pp. 012007
Author(s):  
VI Altukhov ◽  
SV Lavrikov ◽  
AF Revuzhenko
Keyword(s):  
Stress Concentration ◽  
Structural Parameter ◽  
Elastic Model ◽  
Non Local ◽  
Rock Pillars

scholarly journals Non-local criteria for the borehole problem: Gradient Elasticity versus Finite Fracture Mechanics

Meccanica ◽  
2021 ◽  
Author(s):  
A. Sapora ◽  
G. Efremidis ◽  
P. Cornetti
Keyword(s):  
Stress Concentration ◽  
Fracture Mechanics ◽  
Elastic Material ◽  
Fracture Criterion ◽  
Biaxial Loading ◽  
Gradient Elasticity ◽  
Energy Conditions ◽  
Material Behaviour ◽  
Finite Fracture Mechanics ◽  
Non Local

AbstractTwo nonlocal approaches are applied to the borehole geometry, herein simply modelled as a circular hole in an infinite elastic medium, subjected to remote biaxial loading and/or internal pressure. The former approach lies within the framework of Gradient Elasticity (GE). Its characteristic is nonlocal in the elastic material behaviour and local in the failure criterion, hence simply related to the stress concentration factor. The latter approach is the Finite Fracture Mechanics (FFM), a well-consolidated model within the framework of brittle fracture. Its characteristic is local in the elastic material behaviour and non-local in the fracture criterion, since crack onset occurs when two (stress and energy) conditions in front of the stress concentration point are simultaneously met. Although the two approaches have a completely different origin, they present some similarities, both involving a characteristic length. Notably, they lead to almost identical critical load predictions as far as the two internal lengths are properly related. A comparison with experimental data available in the literature is also provided.

Theoretical Modeling of Steel Strip Reinforced Flexible Pipe With Swaging End Fitting by Taking Into Account Stress Concentration Effect

2019 ◽  
Author(s):  
Yifan Gao ◽  
Wei Chen ◽  
Yong Bai
Keyword(s):  
Stress Concentration ◽  
Internal Pressure ◽  
Steel Strip ◽  
Displacement Discontinuity ◽  
Concentration Effect ◽  
Elastic Model ◽  
Thin Wall ◽  
Burst Strength ◽  
Joint Area ◽  
Stress Concentration Effect

Abstract A new theoretical model was proposed to calculate the burst pressure of steel strip reinforced flexible composite pipes (steel strip PSP) based on the thin wall cylindrical shell theory and the squeeze pressure expression between layers was derived. The radial displacement discontinuity of pipe wall in pipe-end fitting joint area takes in account in this model which could result in Stress Concentration Effect (SCE) in reinforcement layers. The SCE is caused by swaging end fitting clamped tightly at the end of the pipe. The result of the hoop strain in the joint area calculated by this model is greater than the one calculated by the classic elastic model, which leads to relative conservative burst strength of the pipe. The hoop stress variation via internal pressure on innermost reinforcement layer is introduced to predict the burst strength of the pipe. As the stress in the joint area reaches its ultimate strength, the strain on the same layer in the point far away from this area (x→∞) is extracted and the corresponding internal pressure is obtained as the burst strength of the pipe. The calculated data from two models were compared with the experiment results and the proposed new model showed better accuracy than the classic elastic model. Final additional parametric studies were conducted, while the effect of the pipe diameter, the winding angle, the number and thickness of the reinforcement layer on the burst strength of the pipe were studied. Useful conclusions were drawn for the design and application of the steel strip PSP in offshore engineering.

THE USE OF NONLOCAL CRITERIA IN FORECASTING FRACTURE OF QUASI-BRITTLE MATERIAL WITH A HOLE UNDER COMPRESSION

2019 ◽  
Vol 85 (4) ◽  
pp. 50-56
Author(s):  
Sergey V. Suknev
Keyword(s):  
Stress Concentration ◽  
Brittle Fracture ◽  
Fracture Zone ◽  
Large Scale ◽  
Failure Criteria ◽  
Material Specimen ◽  
Fictitious Crack ◽  
Non Local ◽  
The Mean ◽  
Nonlocal Criteria

The study is aimed at the development of the new failure criteria for quasi-brittle materials in conditions of stress concentration. The possibility of using non-local failure criteria for description of the brittle, quasi-brittle and ductile fracture of the materials with notches is analyzed. The general feature of these criteria consists in the introduction of the internal dimension characterizing the structure of the material, which provides the possibility of describing a large-scale effect in conditions of the stress concentration and thereby expand the area of their application compared to traditional criteria though it is limited to the cases of brittle or quasi-brittle fracture with a small pre-ffacture zone. To broaden the scope of their application to quasi-brittle fracture with a developed pre-fracture zone we propose to abandon the hypothesis about the size of the pre-fracture zone as a constant related only to the structure of the material. A number of the new nonlocal criteria, which are the development of the criteria of the mean stress and fictitious crack, are developed, substantiated from the physical standpoint, and proved experimentally. These criteria contain a complex parameter characterizing the size of the pre-fracture zone and taking into account not only the structure, but also the ductile properties of the material, specimen geometry and loading conditions. The expressions for the critical pressure in the problem of tensile crack formation upon compression of the samples of geomaterials with a circular hole are derived. The results of calculations match rather well the experimental data on the destruction of drilled gypsum slabs.

Toward High-Resolution Low-Voltage SEM

1988 ◽  
Vol 46 ◽  
pp. 218-219
Author(s):  
Zhifeng Shao
Keyword(s):  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Limiting Factor ◽  
Operating Voltage ◽  
Probe Radius ◽  
Non Local ◽  
Electron Microscopes ◽  
Image Position ◽  
Scanning Electron Microscopes

Recently, low voltage (≤5kV) scanning electron microscopes have become popular because of their unprecedented advantages, such as minimized charging effects and smaller specimen damage, etc. Perhaps the most important advantage of LVSEM is that they may be able to provide ultrahigh resolution since the interaction volume decreases when electron energy is reduced. It is obvious that no matter how low the operating voltage is, the resolution is always poorer than the probe radius. To achieve 10Å resolution at 5kV (including non-local effects), we would require a probe radius of 5∽6 Å. At low voltages, we can no longer ignore the effects of chromatic aberration because of the increased ratio δV/V. The 3rd order spherical aberration is another major limiting factor. The optimized aperture should be calculated as

Chromatic aberration and low-voltage SEM

1987 ◽  
Vol 45 ◽  
pp. 546-547
Author(s):  
Zhifeng Shao ◽  
A.V. Crewe
Keyword(s):  
Electron Energy ◽  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Primary Electron ◽  
Probe Size ◽  
Non Local ◽  
Optical Treatment ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes

For scanning electron microscopes, it is plausible that by lowering the primary electron energy, one can decrease the volume of interaction and improve resolution. As shown by Crewe /1/, at V0 =5kV a 10Å resolution (including non-local effects) is possible. To achieve this, we would need a probe size about 5Å. However, at low voltages, the chromatic aberration becomes the major concern even for field emission sources. In this case, δV/V = 0.1 V/5kV = 2x10-5. As a rough estimate, it has been shown that /2/ the chromatic aberration δC should be less than ⅓ of δ0 the probe size determined by diffraction and spherical aberration in order to neglect its effect. But this did not take into account the distribution of electron energy. We will show that by using a wave optical treatment, the tolerance on the chromatic aberration is much larger than we expected.

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