scholarly journals Analysis on the Behavior of Nonpropagating Fatigue Cracks under Steep Stress Gradients

2014 ◽  
Vol 2014 ◽  
pp. 1-7
Author(s):  
Hao Wu ◽  
Qiuying Lu
Keyword(s):  
Material Properties ◽  
Notch Root ◽  
Fatigue Cracks ◽  
Stress Gradient ◽  
Local Stress ◽  
Characteristic Size ◽  
Short Crack ◽  
Stress Gradients ◽  
Applied Loading ◽  
Experimental Values

A mechanism for the formation of nonpropagating fatigue cracks ahead of a notch root is presented. The stress gradients near the elongated notch root along with the propagation of short crack and the resulting nonpropagating crack lengthsanpcare estimated. The local stress which is higher than the unnotched material fatigue limitS0initiates the crack from a notch root and local steep stress gradient as a very important element leads to the nonpropagating crack. The value ofanpcdepends on the material properties, and specimen geometry as well as applied loading. The characteristic size of the short cracka0which depends on the material properties associates with the fatigue stress concentration factorKf. The estimated values ofanpcare in fairly good agreement with the experimental values available.

Pemodelan Numerik Perilaku Lentur Dan Defleksi Elemen Balok Ferrogeopolymer

2021 ◽  
Vol 1 (1) ◽  
pp. 1-12
Author(s):  
Bill J. Ebenheazar ◽  
Remigildus Cornelis ◽  
Partogi H. Simatupang
Keyword(s):  
Material Properties ◽  
Cement Mortar ◽  
Small Diameter ◽  
Wire Mesh ◽  
Beam Model ◽  
Thin Wall ◽  
Numerical Result ◽  
Number Of Layers ◽  
Geopolymer Cement ◽  
Experimental Values

Ferro-gepolymer is a type of thin-wall reinforced element constructed of geopolymer cement mortar reinforced with closely spaced relatively small diameter mesh in layers. In this investigation, the flexural and the deflection behavior of the ferro-geopolymer beams were determined numerically and the results compared to the experimental values. All the experimental material properties adopted for numerical modeling. The numerical model of all the five beams was 600 mm effective span, 100 mm width, and 100 mm height. Each specimen of the beam model having different layers of wire mesh that are 3, 5, 7, 9, and 11. The results showed that the greater the number of layers, the variation between numerical and experimental results follows the same path without much difference. The numerical result showed that the greater the number of layers, the strength was increases but insignificant.

The Use of Strain Energy and Fracture Correlation to Determine Life Expectancy for Notched Components

2009 ◽  
Author(s):  
Onome Scott-Emuakpor ◽  
Tommy George ◽  
Charles Cross ◽  
M.-H. Herman Shen
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Cross Section ◽  
Strain Energy ◽  
Notch Root ◽  
Stress Gradient ◽  
Strain Curve ◽  
Experimental Results ◽  
Cyclic Process ◽  
Notched Components

An energy-based method for predicting fatigue life of half-circle notched specimens, based on the nominal applied stress amplitude, has been developed. This developed method is based on the understanding that the total strain energy dissipated during a monotonic fracture and a cyclic process is the same material property, where the density of each can be determined by measuring the area underneath the monotonic true stress-strain curve and measuring the sum of the area within each Hysteresis loop in the cyclic process, respectively. Using this understanding, the criterion for determining fatigue life prediction of half-circle notched components is constructed by incorporating the stress gradient effect through the notch root cross-section. Though fatigue at a notch root is a local phenomenon, evaluation of the stress gradient through the notch root cross-section is essential for incorporating this method into finite element analysis minimum potential energy process. The validation of this method was carried out by comparison with both notched and unnnotched experimental fatigue life of Aluminum 6061-T6 (Al 6061-T6) specimens under tension/compression loading at the theoretical notch fatigue stress concentration factor of 1.75. The comparison initially showed a slight deviation between prediction and experimental results. This led to the analysis of strain energy density per cycle up to failure, and an improved Hysteresis representation for the energy-based prediction analysis. With the newly developed Hysteresis representation, the energy-based prediction comparison shows encouraging agreement with unnotched experimental results and a theoretical notch stress concentration value.

scholarly journals Facilitation costs and benefits function simultaneously on stress gradients for animals

2018 ◽  
Vol 285 (1885) ◽  
pp. 20180983 ◽  
Author(s):  
Olivier Dangles ◽  
Mario Herrera ◽  
Carlos Carpio ◽  
Christopher J. Lortie
Keyword(s):  
Conceptual Framework ◽  
Environmental Conditions ◽  
Species Interactions ◽  
Stress Gradient ◽  
Species Interaction ◽  
Positive Interactions ◽  
Costs And Benefits ◽  
Strong Basis ◽  
Stress Gradients ◽  
High Resource

Understanding the variation in species interactions along environmental stress gradients is crucial for making robust ecological predictions about community responses to changing environmental conditions. The facilitation–competition framework has provided a strong basis for predictions (e.g. the stress-gradient hypothesis, SGH), yet the mechanisms behind patterns in animal interactions on stress gradients are poorly explored in particular for mobile animals. Here, we proposed a conceptual framework modelling changes in facilitation costs and benefits along stress gradients and experimentally tested this framework by measuring fitness outcomes of benefactor–beneficiary interactions across resource quality levels. Three arthropod consumer models from a broad array of environmental conditions were used including aquatic detritivores, potato moths and rainforest carrion beetles. We detected a shift to more positive interactions at increasing levels of stress thereby supporting the application of the SGH to mobile animals. While most benefactors paid no significant cost of facilitation, an increase in potato moth beneficiary's growth at high resource stress triggered costs for benefactors. This study is the first to experimentally show that both costs and benefits function simultaneously on stress gradients for animals. The proposed conceptual framework could guide future studies examining species interaction outcomes for both animals and plants in an increasingly stressed world.

Computer-Aided Visioplasticity Solution to Axisymmetric Extrusion Through Curved Boundaries

1972 ◽  
Vol 94 (4) ◽  
pp. 1225-1230 ◽  
Author(s):  
A. H. Shabaik
Keyword(s):  
Material Properties ◽  
Extrusion Ratio ◽  
Strain Rates ◽  
Exit Section ◽  
Flow Function ◽  
Curved Boundaries ◽  
Circular Arc ◽  
Conical Die ◽  
Stress Components ◽  
Experimental Values

A procedure for smoothing the experimental values of the flow function ψ in axisymmetric extrusion through curved boundaries was developed. The analysis was applied to a 45 deg conical die with a 6:1 extrusion ratio and a circular arc of 0.33-in. radius and 0.033-in. land at the exit section. An analytical expression of ψ in terms of r and z was obtained and used in the calculation of velocity and strain rate components in axisymmetric extrusion of a superplastic of the eutectic of lead–tin. The stress components were obtained from the known values of the strain rates by considering equilibrium and plasticity equations and material properties.

Stress That Counteracts Electromigration: Threshold Versus Kinetic Approach

1994 ◽  
Vol 356 ◽  
Author(s):  
E. Glickman ◽  
N. Osipov ◽  
A. Ivanov
Keyword(s):  
Plastic Flow ◽  
Material Properties ◽  
Effective Viscosity ◽  
Threshold Stress ◽  
Stress Gradient ◽  
Material Constant ◽  
Induced Stress ◽  
Net Flux ◽  
Constant Yield ◽  
Coble Creep

AbstractThe paper analyzes electromigration (EM) conditions and material properties that determine the maximum EM induced stress, σa, and stress gradient, ∇σ, which counteract EM flow in interconnects.The first systematic data on the drift velocity vs. stripe length, L, current density, j, and temperature are presented for Al lines. In contrast to the conventional approach to the Blech problem with σa taken to be a material constant (“yield strength”), the observations suggest that σa increases with j. The stress adjustment is shown to result from the imperative coupling of the net flux of material directed to the downwind end of the stripe with the flux of plastic flow (creep) responsible for stress relaxation. The effect of parameters of the constitutive equation assumed to describe the plastic flow kinetics, namely that of strain rate exponent, threshold stress, and creep, effective viscosity, on the stress cya is considered. To account for the creep viscosity, η, obtained unpassivated aluminum stripes from EM experiments, a model for the attachment-controlled Coble creep is suggested.

Effect of Time Spacing and Hatch Spacing on Thermal Material Properties and Melt Pool Geometry in Additive Manufacturing of S316L

2019 ◽  
Author(s):  
Elham Mirkoohi ◽  
Daniel E. Sievers ◽  
Steven Y. Liang
Keyword(s):  
Heat Transfer ◽  
Additive Manufacturing ◽  
Material Properties ◽  
Metal Additive Manufacturing ◽  
Melt Pool ◽  
Experimental Values ◽  
Melt Pool Size ◽  
Transfer Mechanisms ◽  
Hatch Spacing ◽  
Metal Additive

Abstract A physics-based analytical solution is proposed in order to investigate the effect of hatch spacing and time spacing (which is the time delay between two consecutive irradiations) on thermal material properties and melt pool geometry in metal additive manufacturing processes. A three-dimensional moving point heat source approach is used in order to predict the thermal behavior of the material in additive manufacturing process. The thermal material properties are considered to be temperature dependent since the existence of the steep temperature gradient has a substantial influence on the magnitude of the thermal conductivity and specific heat, and as a result, it has an influence on the heat transfer mechanisms. Moreover, the melting/solidification phase change is considered using the modified heat capacity since it has an influence on melt pool geometry. The proposed analytical model also considers the multi-layer aspect of metal additive manufacturing since the thermal interaction of the successive layers has an influence on heat transfer mechanisms. Temperature modeling in metal additive manufacturing is one of the most important predictions since the presence of the temperature gradient inside the build part affect the melt pool size and geometry, thermal stress, residual stress, and part distortion. In this paper, the effect of time spacing and hatch spacing on thermal material properties and melt pool geometry is investigated. Both factors are found statistically significant with regard to their influence on thermal material properties and melt pool geometry. The predicted melt pool size is compared to experimental values from independent reports. Good agreement is achieved between the proposed physics-based analytical model and experimental values.

Effects of Steady Spatial Wall Shear Stress Gradients on Endothelial Cell Morphology in Three-Dimensional Models

2007 ◽  
Author(s):  
Leonie Rouleau ◽  
Monica Farcas ◽  
Jean-Claude Tardif ◽  
Rosaire Mongrain ◽  
Richard Leask
Keyword(s):  
Endothelial Cells ◽  
Shear Stress ◽  
Endothelial Cell ◽  
Wall Shear Stress ◽  
Cell Morphology ◽  
Flow Direction ◽  
Stress Gradient ◽  
Spatial Gradient ◽  
Stress Gradients ◽  
Wall Shear

Endothelial cell (EC) dysfunction has been linked to atherosclerosis through their response to hemodynamic forces. Flow in stenotic vessels creates complex spatial gradients in wall shear stress. In vitro studies examining the effect of shear stress on endothelial cells have used unrealistic and simplified models, which cannot reproduce physiological conditions. The objective of this study was to expose endothelial cells to the complex shear shear pattern created by an asymmetric stenosis. Endothelial cells were grown and exposed for different times to physiological steady flow in straight dynamic controls and in idealized asymmetric stenosis models. Cells subjected to 1D flow aligned with flow direction and had a spindle-like shape when compared to static controls. Endothelial cell morphology was noticeable different in the regions with a spatial gradient in wall shear stress, being more randomly oriented and of cobblestone shape. This occurred despite the presence of an increased magnitude in shear stress. No other study to date has described this morphology in the presence of a positive wall shear stress gradient or gradient of significant shear magnitude. This technique provides a more realistic model to study endothelial cell response to spatial and temporal shear stress gradients that are present in vivo and is an important advancement towards a better understanding of the mechanisms involved in coronary artery disease.

Local Investigation of Microstructure-Induced Fatigue Damaging

2009 ◽  
Vol 417-418 ◽  
pp. 521-524
Author(s):  
Michael Marx ◽  
Wolfgang Schäf ◽  
Markus T. Welsch ◽  
Horst Vehoff
Keyword(s):  
Electron Microscope ◽  
Crack Initiation ◽  
Scanning Electron Microscope ◽  
Crack Propagation ◽  
Focused Ion Beam ◽  
Fatigue Cracks ◽  
Ion Beam ◽  
Short Crack ◽  
Beam Technique ◽  
Scanning Electron

From the emission of dislocations till short crack propagation fatigue is a local process determined by the microstructure. In this paper we present experiments based on refined applications of the scanning electron microscope and focused ion beam technique, which give detailed information about crack initiation and the interaction of short fatigue cracks with microstructural elements.

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