Effect of Inertia on Finite Near-Tip Deformation for Fast Mode-III Crack Growth

1985 ◽  
Vol 52 (2) ◽  
pp. 281-286 ◽  
Author(s):  
J. D. Achenbach ◽  
N. Nishimura
Keyword(s):  
Explicit Expression ◽  
Crack Growth ◽  
Finite Deformation ◽  
Crack Tip ◽  
Dynamic Strain ◽  
Mode Iii ◽  
Moving Crack ◽  
Crack Line ◽  
Transition Boundary ◽  
Small Strains

The combined effects of finite deformation and material inertia have been analyzed for fast crack growth under antiplane loading conditions. A steady-state dynamic solution has been obtained for the finite strain on the crack line, from the moving crack tip to the moving transition boundary with the zone of small strains. The crack propagates in a material with a response curve in uniform shear that is linear at small strains, and which remains constant once a critical strain has been exceeded. The corresponding quasi-static solution is given in the full zone of large deformation. For the dynamic formulation, an explicit expression for the crack-line strain has been obtained by expanding the displacement in a power series in the distance to the crack line, with coefficients that depend on the distance to the moving crack tip. Substitution in the equation of motion yields a nonlinear ordinary differential equation for the relevant coefficient, which can be solved rigorously. The finite deformation crack-line fields have been matched to appropriate small-strain fields at the transition boundary. The principal result is that the dynamic strain remains bounded at the crack tip, apparently due to the effect of material inertia. The crack-line strain has been plotted for several crack-tip speeds. It decreases with higher crack-tip speed. An explicit expression has been given for the extent of the zone of finite deformation, as a function of the crack tip speed and the far-field loading.

scholarly journals Study on the Influence of the Gurson–Tvergaard–Needleman Damage Model on the Fatigue Crack Growth Rate

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1183
Author(s):  
Edmundo R. Sérgio ◽  
Fernando V. Antunes ◽  
Diogo M. Neto ◽  
Micael F. Borges
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Plastic Strain ◽  
Crack Growth ◽  
Damage Model ◽  
Crack Tip ◽  
Strength Parameter ◽  
Stress Intensity Factor Range

The fatigue crack growth (FCG) process is usually accessed through the stress intensity factor range, ΔK, which has some limitations. The cumulative plastic strain at the crack tip has provided results in good agreement with the experimental observations. Also, it allows understanding the crack tip phenomena leading to FCG. Plastic deformation inevitably leads to micro-porosity occurrence and damage accumulation, which can be evaluated with a damage model, such as Gurson–Tvergaard–Needleman (GTN). This study aims to access the influence of the GTN parameters, related to growth and nucleation of micro-voids, on the predicted crack growth rate. The results show the connection between the porosity values and the crack closure level. Although the effect of the porosity on the plastic strain, the predicted effect of the initial porosity on the predicted crack growth rate is small. The sensitivity analysis identified the nucleation amplitude and Tvergaard’s loss of strength parameter as the main factors, whose variation leads to larger changes in the crack growth rate.

Modeling the Interactions of Hydrogen, Stress and Dissolution in Near-Neutral pH Stress Corrosion Cracking of Pipelines

2006 ◽  
Author(s):  
Frank Y. Cheng
Keyword(s):  
Stress Corrosion ◽  
Dissolution Rate ◽  
Crack Growth ◽  
Anodic Dissolution ◽  
Hydrogen Concentration ◽  
Stress Corrosion Cracking ◽  
Crack Tip ◽  
Corrosion Cracking ◽  
Neutral Ph ◽  
Ph Stress

A thermodynamic model was developed to determine the interactions of hydrogen, stress and anodic dissolution at the crack-tip during near-neutral pH stress corrosion cracking in pipelines. By analyzing the free-energy of the steel in the presence and absence of hydrogen and stress, it is demonstrated that a synergism of hydrogen and stress promotes the cracking of the steel. The enhanced hydrogen concentration in the stressed steel significantly accelerates the crack growth. The quantitative prediction of the crack growth rate in near-neutral pH environment is based on the determination of the effect of hydrogen on the anodic dissolution rate in the absence of stress, the effect of stress on the anodic dissolution rate in the absence of hydrogen, the synergistic effect of hydrogen and stress on the anodic dissolution rate at the crack-tip and the effect of the variation of hydrogen concentration on the anodic dissolution rate.

Finite Element Simulation of Stable Fatigue Crack Growth Using Critical CTOD Determined by Preliminary Finite Element Analysis

2014 ◽  
Vol 891-892 ◽  
pp. 1675-1680
Author(s):  
Seok Jae Chu ◽  
Cong Hao Liu
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Finite Element Simulation ◽  
Crack Growth ◽  
Crack Tip ◽  
Stress Intensity Factor Range ◽  
Crack Tip Opening Displacement ◽  
Element Analysis ◽  
Element Simulation

Finite element simulation of stable fatigue crack growth using critical crack tip opening displacement (CTOD) was done. In the preliminary finite element simulation without crack growth, the critical CTOD was determined by monitoring the ratio between the displacement increments at the nodes above the crack tip and behind the crack tip in the neighborhood of the crack tip. The critical CTOD was determined as the vertical displacement at the node on the crack surface just behind the crack tip at the maximum ratio. In the main finite element simulation with crack growth, the crack growth rate with respect to the effective stress intensity factor range considering crack closure yielded more consistent result. The exponents m in the Paris law were determined.

Estimation of Crack Growth Life in Rail with a Squat Defect

2009 ◽  
Vol 417-418 ◽  
pp. 313-316 ◽  
Author(s):  
Hyun Kyu Jun ◽  
Won Hee You
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Rail Steel ◽  
Crack Tip ◽  
Cost Effective ◽  
Rolling Contact ◽  
Hertzian Contact ◽  
Maintenance Strategy ◽  
Whole Life Cycle

Rolling contact fatigue initiated defects such as surface corrugation, head check, squat, are one of growing problems in high speed railway line. A squat is generally developed below the rail surface and grows parallel to surface until it turns down into rail. Estimation of critical crack size and crack growth rate is an essential to prevent rail from failure and develop cost effective railway maintenance strategy. In this study, we predict crack growth rate of a rail with a squat defect. For this purpose, a rail model with a squat defect is developed. Timoshenko’s beam theory is applied to calculate the global bending stress at the crack tip and Hertzian contact model is applied to calculate the local contact stresses at the surface of rail by simulating rolling over a railway wheel on a rail. Stress intensity factors are calculated from the total stress at the crack tip. Fatigue crack growth curve of 60kg rail steel is applied to calculated crack growth rate. Software to predict crack growth life through whole life cycle is developed. We expect that we can make a more cost effective rail maintenance strategy by considering the crack growth analysis for a defective rail.

scholarly journals In-situ SEM and optical microscopy testing for investigation of fatigue crack growth mechanism under overload

2018 ◽  
Vol 165 ◽  
pp. 13013
Author(s):  
Wei Zhang ◽  
Liang Cai
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Optical Microscopy ◽  
Crack Growth ◽  
Load Condition ◽  
Crack Tip ◽  
Initial Crack ◽  
Crack Growth Behavior ◽  
Single Overload

In this paper, the in-situ scanning electron microscope (SEM) and optical microscopy experiments are performed to investigate the crack growth behavior under the single tensile overload. The objectives are to (i) examine the overload-induced crack growth micromechanisms, including the initial crack growth acceleration and the subsequent retardation period; (ii) investigate the effective region of single overload on crack growth rate. The specimen is a small thin Al2024-T3 plate with an edge-crack, which is loaded and observed in the SEM chamber. The very high resolution images of the crack tip are taken under the simple variable amplitude loading. Imaging analysis is performed to quantify the crack tip deformation at any time instant. Moreover, an identical specimen subjected to the same load condition is observed under optical microscope. In this testing, fine speckling is performed to promote the accuracy of digital imaging correlation (DIC). The images around the crack tip are taken at the peak loads before, during and after the single overload. After that, the evolution of local strain distribution is obtained through DIC technique. The results show that the rapid connection between the main crack and microcracks accounts for the initial crack growth acceleration. The crack closure level can be responsible for the crack growth rate during the steady growth period. Besides that, the size of retardation area is larger than the classical solution.

Dynamic Strain Effects in Elastomers

1963 ◽  
Vol 36 (2) ◽  
pp. 407-421 ◽  
Author(s):  
Glenn E. Warnaka
Keyword(s):  
Elastic Modulus ◽  
Mechanical Behavior ◽  
Strain Amplitude ◽  
Loss Factor ◽  
Dynamic Strain ◽  
Dynamic Mechanical ◽  
Small Strains ◽  
Dynamic Mechanical Behavior ◽  
Elastomeric Materials ◽  
Practical Engineering

Abstract Many common elastomeric materials have two ranges of dynamic-mechanical behavior. Such materials behave as viscoelastomers at very small strains and as plastoelastomers at strains of practical engineering interest. The change from viscoelastic to plastoelastic behavior occurs at dynamic strain amplitudes of 0.001 inches per inch to 0.005 inches per inch. In the plastoelastic range, the dynamic elastic modulus decreases with increasing dynamic strain amplitude. Loss factor reaches a maximum in the plastoelastic range.

Characterization of Crack Tip Damage Zone Formation on Alloy 625 During Fatigue Crack Growth at 750°C by Transmission EBSD Method

2017 ◽  
Author(s):  
Yuji Ozawa ◽  
Tatsuya Ishikawa ◽  
Yoichi Takeda
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Power Plants ◽  
Crack Path ◽  
Damage Zone ◽  
Crack Tip ◽  
Loading Frequency ◽  
Zone Formation ◽  
Alloy 625

In order to clarify the mechanism of fatigue crack growth in alloy 625, which is a candidate material for use in advanced ultra supercritical power plants, the crack tip damage zone formation after a crack growth test conducted in high temperature steam was investigated. It was observed that the oxide thickness at the crack tip tended to increase with decreasing cyclic loading frequency. The crack path was a mix of transgranular and intergranular fractures. According to the grain reference orientation deviation (GROD) maps, it was revealed that the density of geometrically necessary dislocations (GNDs) in the matrix along the crack path and ahead of crack tip increased with an increase in the fatigue crack growth rate (FCGR) due to environmental effects. It was observed that (1) mobile dislocations at the crack surface were blocked due to the thick oxide layer, resulting in an increase in the density of GNDs, and (2) an increase in the density of GNDs might induce stress concentration at the crack tip, deformation twinning, and the acceleration of FCGRs.

Features of Dynamic Deformation of an Elastoviscoplastic Material in the Vicinity of a Moving Crack Tip

2020 ◽  
Vol 55 (6) ◽  
pp. 885-891
Author(s):  
N. D. Verveiko ◽  
S. E. Krupenko ◽  
A. I. Shashkin
Keyword(s):  
Dynamic Deformation ◽  
Crack Tip ◽  
Moving Crack
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