Parametric Finite-Volume Micromechanics of Uniaxial Continuously-Reinforced Periodic Materials With Elastic Phases

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Mahendra Gattu ◽  
Hamed Khatam ◽  
Anthony S. Drago ◽  
Marek-Jerzy Pindera
Keyword(s):  
Finite Volume ◽  
Local Stress ◽  
Analytical Framework ◽  
Unit Cell ◽  
Local Fields ◽  
Standard Theory ◽  
Stress Concentrations ◽  
Parametric Mapping ◽  
Cell Refinement ◽  
Heterogeneous Microstructures

The finite-volume direct averaging micromechanics (FVDAM) theory for periodic heterogeneous materials is extended by incorporating parametric mapping into the theory’s analytical framework. The parametric mapping enables modeling of heterogeneous microstructures using quadrilateral subvolume discretization, in contrast with the standard version based on rectangular subdomains. Thus arbitrarily shaped inclusions or porosities can be efficiently rendered without the artificially induced stress concentrations at fiber/matrix interfaces caused by staircase approximations of curved boundaries. Relatively coarse unit cell discretizations yield effective moduli with comparable accuracy of the finite-element method. The local stress fields require greater, but not exceedingly fine, unit cell refinement to generate results comparable with exact elasticity solutions. The FVDAM theory’s parametric formulation produces a paradigm shift in the continuing evolution of this approach, enabling high-resolution simulation of local fields with much greater efficiency and confidence than the standard theory.

Quadrilateral Subcell Based Finite Volume Micromechanics Theory for Multiscale Analysis of Elastic Periodic Materials

2008 ◽  
Vol 76 (1) ◽  
Author(s):  
Xiguang Gao ◽  
Yingdong Song ◽  
Zhigang Sun
Keyword(s):  
Finite Volume ◽  
Local Stress ◽  
Equation System ◽  
Stress Concentrations ◽  
Equilibrium Equations ◽  
Direct Integral ◽  
Stress Equilibrium ◽  
Number Systems ◽  
Unit Cells ◽  
Global And Local

In this paper, we extend the finite volume direct average micromechanics to enable the use of quadrilateral subcells. To do this work, the quadrilateral subcells are used to discretize the repeating unit cells first. Then the average displacement and traction defined on the boundary of the subcell are evaluated by direct integral method. This contrasts with the original formulation in which all of the subcells are rectangular. Following the discretization, the cell problem is defined by combining the directly volume-average of the subcell stress equilibrium equations with the displacement and traction continuity in a surface-average sense across the adjacent subcell faces. In order to assemble the above equations and conditions into a global equation system, the global and local number systems, which index the boundary of subcell in different manners, are employed by the extended method. Finally, the global equation system is solved and the solutions give the formulations of the microstress field and the global elastic moduli of material. The introduction of quadrilateral subcells increases the efficiency of modeling the material’s microstructure and eliminates the stress concentrations at the curvilinear bimaterial corners. Herein, the advantage of the extension is presented by comparing the global moduli and local stress fields predicted by the present method with the corresponding results obtained from the original version.

Low Cycle Fatigue Analysis of Marine Structures

2006 ◽  
Author(s):  
Xiaozhi Wang ◽  
Joong-Kyoo Kang ◽  
Yooil Kim ◽  
Paul H. Wirsching
Keyword(s):  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Prediction Method ◽  
Local Stress ◽  
Cyclic Plasticity ◽  
Cycle Fatigue ◽  
Stress Concentrations ◽  
Damage Prediction ◽  
Marine Structure ◽  
Number Of Cycles

There are situations where a marine structure is subjected to stress cycles of such large magnitude that small, but significant, parts of the structural component in question experiences cyclic plasticity. Welded joints are particularly vulnerable because of high local stress concentrations. Fatigue caused by oscillating strain in the plastic range is called “low cycle fatigue”. Cycles to failure are typically below 104. Traditional welded joint S-N curves do not describe the fatigue strength in the low cycle region (< 104 number of cycles). Typical Class Society Rules do not directly address the low cycle fatigue problem. It is therefore the objective of this paper to present a credible fatigue damage prediction method of welded joints in the low cycle fatigue regime.

scholarly journals A-type amylose single crystals: unit cell refinement from synchrotron radiation microdiffraction data

2006 ◽  
Vol 62 (a1) ◽  
pp. s178-s178
Author(s):  
D. Popov ◽  
M. Burghammer ◽  
A. Buléon ◽  
N. Montesanti ◽  
J. L. Putaux ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Single Crystals ◽  
Unit Cell ◽  
Cell Refinement

TO DETERMINE THE PHYSICAL AND MECHANICAL PROPERTIES OF THE SOIL OF LANDSLIDE SLOPES FROM THE DEGREE OF POROSITY AND HUMIDITY

InterConf ◽  
2021 ◽  
pp. 917-933
Author(s):  
Аkbota Serikkyzy ◽  
A. Baimakhan ◽  
A. Makhanova ◽  
Baimakhan Baimakhan ◽  
G. Baimakhanova
Keyword(s):  
Mechanical Properties ◽  
Physical And Mechanical Properties ◽  
Local Stress ◽  
Saturated Soil ◽  
Degree Of Saturation ◽  
Stress Concentrations ◽  
Mountain Slope ◽  
Experimental Works ◽  
Water Saturated

The results of theoretical and experimental works devoted to the determination of the physical and mechanical properties of water–saturated soil are analyzed. On the basis of a comprehensive analysis, conclusions are formulated, and a method is proposed for determining the Young’s modulus and Poisson’s ratio for water-saturated soil, depending on humidity (degree of saturation) and porosity. Tables of data on the physical and mechanical properties of water–saturated soil are proposed. The study established the places of formation of local stress concentrations along the inclined layer. The values of dangerous stress concentrations found in various areas of the mountain slope that are vulnerable to collapse are shown in the tables.

scholarly journals Air-temperature control on diurnal variations in microseismicity at Laohugou Glacier No. 12, Qilian Mountains

2019 ◽  
Vol 60 (79) ◽  
pp. 125-136 ◽  
Author(s):  
Tao Zhang ◽  
Yuqiao Chen ◽  
Min Ding ◽  
Zhongyan Shen ◽  
Yuande Yang ◽  
...  
Keyword(s):  
Short Duration ◽  
Crack Opening ◽  
Low Frequency ◽  
Local Stress ◽  
Stress Concentrations ◽  
Night Time ◽  
Strong Negative Correlation ◽  
Near Surface ◽  
Temperature Change Rate ◽  
Trigger Algorithm

ABSTRACTWe conducted a 9-d seismic experiment in October 2015 at Laohugou Glacier No. 12. We identified microseismic signals using the short-term/long-term average trigger algorithm at four stations and classified them as long and short-duration events based on waveform, frequency, duration and magnitude characteristics. Both categories show systematical diurnal trends. The long-duration events are low-frequency tremor-like events that mainly occurred during the daytime with only several events per day. These events lasted tens of seconds to tens of minutes and are likely related to resonance of daytime meltwater. The dominant short-duration events mostly occurred during the night time with a peak occurrence frequency of ~360 h−1. Their short-duration (<0.2 s), high frequency (20–100 Hz) and dominance of Rayleigh waves are typical of events for near-surface crack opening. A strong negative correlation between the hourly event number and temperature change rate suggests that the occurrence of night-time events is controlled by the rate of night-time cooling. We estimated the near-surface tensile stress due to thermal contraction at night to be tens of kilopascals, which is enough to induce opening of surface cracks with pre-existing local stress concentrations, although we cannot exclude the effect of refreezing of meltwater produced during the day.

Two-dimensional pressure field and backflow in the annular skirt of vortex gripper

2020 ◽  
pp. 095440622097404
Author(s):  
Jianghong Zhao ◽  
Xin Li
Keyword(s):  
Flow Field ◽  
Pressure Distribution ◽  
Local Stress ◽  
Vortex Chamber ◽  
Physical Contact ◽  
Two Dimensional ◽  
Stress Concentrations ◽  
Suction Force ◽  
Maximum Value ◽  
Gap Height

The vortex gripper is a kind of pneumatic noncontact gripper that does not produce a magnetic field and heat. It can grip a workpiece without physical contact, which avoids any unintentional damage such as mechanical scratches, local stress concentrations, frictional static electricity, and surface stains. This study focused on the two-dimensional pressure distribution field on a workpiece surface under the vortex gripper. Theoretical, experimental, and computational fluid dynamics results were combined to study the backflow phenomenon in the annular skirt, which can decrease the gripper’s suction force after the maximum value is reached. First, the pressure distribution in the annular skirt was theoretically modeled. A comparison with the experimental results showed that increasing the gap height between the gripper and workpiece generates a circumferentially asymmetrical flow field in the skirt. Based on this, it was hypothesized that an airflow in the circumferential direction may exist. The experimental data and simulation results were analyzed under large gap height conditions to observe the backflow in detail and it was found that an uneven pressure distribution with positive and negative pressure regions generated by the uneven flow is the root cause of the backflow. Finally, the effect of the backflow on the flow field in two different flow regions (in the annular skirt and inside the vortex chamber) was analyzed and the reason why the suction force of the vortex gripper has a maximum value was determined.

Numerical studies of the influence of textural gradients on the local stress concentrations around fibers in carbon/carbon composites

2008 ◽  
Vol 24 (12) ◽  
pp. 2194-2205 ◽  
Author(s):  
Romana Piat ◽  
Igor Tsukrov ◽  
Thomas Böhlke ◽  
Norbert Bronzel ◽  
Tilottama Shrinivasa ◽  
...  
Keyword(s):  
Local Stress ◽  
Carbon Composites ◽  
Stress Concentrations ◽  
Numerical Studies

Comparison between Pile-Up Singularities and Stress Fields Induced by Thin Slip Bands. Application to the Prediction of Grain Boundary Microcrack Nucleation

2013 ◽  
Vol 592-593 ◽  
pp. 61-66
Author(s):  
Maxime Sauzay ◽  
Mohamed Ould Moussa
Keyword(s):  
Slip Band ◽  
Tensile Deformation ◽  
Finite Thickness ◽  
Local Stress ◽  
Stress Fields ◽  
Stress Concentrations ◽  
Griffith Criterion ◽  
Slip Bands ◽  
Pile Up ◽  
Microcrack Initiation

Slip localization is widely observed in metallic polycrystals after tensile deformation, cyclic deformation or pre-irradiation followed by tensile deformation. Such strong deformation localized in thin slip bands induces local stress concentrations in the quasi-elastic matrix around, at the intersections between slip bands (SBs) and grain boundaries (GBs) where microcrack initiation is often observed. Since the work of Stroh, such stress fields have been mostly modeled using the dislocation pile-up theory which leads to stress singularities similar to the LEFM ones. The Griffith criterion has then been widely applied, leading usually to strong underestimations of the macroscopic stress to GB crack initiation. In fact, slip band thickness is finite: 20nm-1000nm depending on material, temperature and loading conditions. Then, many slip planes are plastically activated through the thickness, and not only one single atomic plane. To evaluate more realistic stress fields, numerous crystalline finite element (FE) computations have been carried out using microstructure inputs (slip band aspect ratio, crystal and GB orientation...). A strong influence of slip band thickness close to the slip band corner has been highlighted, which is not accounted for by the pile-up theory. But far away, the thickness has a negligible effect and the predicted stress fields are close to the one predicted by the pile-up theory. Closed-form expressions are deduced from the numerous FE computation results allowing a straightforward prediction of GB stress fields. Slip band plasticity parameters, such as length and thickness, as well as crystal orientation, GB plane and remote stress are taken into account. The dependence with respect to the various parameters can be understood in the framework of matching expansions usually applied to cracks with V notches of finite thickness. As the exponent of the GB stress close-field is only about one-half of the pile-up or LEFM crack one, the Griffith criterion may not be used for GB microcrack prediction in case of finite thickness. That is why finite crack fracture mechanics is used together with both energy and stress criteria. Taking into account SB finite thickness, t>0, leads to predicted remote stresses to GB microcrack initiation three to six times lower than the ones predicted using the to pile-up theory, in agreement with experimental data.

scholarly journals Cell refinement of CsPbBr3 perovskite nanoparticles and thin films

2019 ◽  
Vol 1 (1) ◽  
pp. 147-153 ◽  
Author(s):  
Christophe Tenailleau ◽  
Sigalit Aharon ◽  
Bat-El Cohen ◽  
Lioz Etgar
Keyword(s):  
Thin Films ◽  
Phase Transformations ◽  
Structural Unit ◽  
Unit Cell ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Cell Refinement ◽  
Perovskite Nanoparticles

In this work, we performed a detailed study of the phase transformations and structural unit cell parameters of CsPbBr3 nanoparticles (NPs) and thin films.

A Preliminary Study on the Mechanical Performance of Tiled Polymer Composites

2006 ◽  
Author(s):  
M. A. Qidwai ◽  
J. N. Baucom ◽  
A. C. Leung ◽  
J. P. Thomas
Keyword(s):  
Composite Laminates ◽  
Load Transfer ◽  
Mechanical Performance ◽  
Local Stress ◽  
Superior Performance ◽  
Design Parameters ◽  
Interlaminar Stresses ◽  
Stress Concentrations ◽  
Critical Design ◽  
Composite Joint

We are developing and exploring the concept of in-plane tiling of composite laminates, called MOSAIC, to mitigate or control delamination at free edges due to interlaminar stresses. Initial mechanical testing has shown that MOSAIC composites with uniaxial graphite-fiber reinforced tiles retain the stiffness levels of traditional uniaxially reinforced composites but with reduced strength. The reduction in strength is attributed to the formation of resin-rich pockets between adjacent tiles. In this study, we have performed detailed finite element analyses to identify the critical design parameters that affect the mechanical performance of uniaxially reinforced MOSAIC composites. We have found that using continuous laminae on the outer surfaces significantly increases the overall loadcarrying capacity. Increasing aspect ratio of the pocket and decreasing material property differences between resin and tiles also cause better load transfer between tiles but may not necessarily improve overall strength due to increasing stress concentration. The tiling scheme and density of pocket placement influence the interaction of local stress concentrations. Consequently, a novel composite joint is proposed and found to have superior performance.

Sign in / Sign up

Export Citation Format

Share Document