Effect of Constraint Induced by Specimen Geometries on Crack Growth Behavior Under Creep-Fatigue Interaction

2018 ◽  
Author(s):  
Lei Zhao ◽  
Lianyong Xu
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Growth Rates ◽  
Crack Tip ◽  
Crack Growth Behavior ◽  
Growth Behaviour ◽  
Crack Growth Behaviour ◽  
Creep Fatigue ◽  
Crack Growth Rates

Creep-fatigue interaction would accelerate the crack growth behaviour and change the crack growth mode, which is different from that presenting in pure creep or fatigue regimes. In addition, the constraint ahead of crack tip affects the relationship between crack growth rate and fracture mechanics and thus affects the accuracy of the life prediction for high-temperature components containing defects. In this study, to reveal the role of constraint caused by various specimen geometries in the creep-fatigue regime, five different types of cracked specimens (including C-ring in tension CST, compact tension CT, single notch tension SENT, single notch bend SENB, middle tension MT) were employed. The crack growth and damage evolution behaviours were simulated using finite element method based on a non-linear creep-fatigue interaction damage model considering creep damage, fatigue damage and interaction damage. The expression of (Ct)avg for different specimen geometries were given. Then, the variation of crack growth behaviour with various specimen geometries under creep-fatigue conditions were analysed. CT and CST showed the highest crack growth rates, which were ten times as the lowest crack growth rates in MT. This revealed that distinctions in specimen geometry influenced the in-plane constraint level ahead of crack tip. Furthermore, a load-independent constraint parameter Q* was introduced to correlate the crack growth rate. The sequence of crack growth rate at a given value of (Ct)avg was same to the reduction of Q*, which shown a linear relation in log-log curve.

Estimation of Crack Growth Rate by J-Integral Range for Type SUS304 Stainless Steel Plate in Creep-Fatigue Tests at High Temperature

2014 ◽  
Author(s):  
Madoka Funai ◽  
Osamu Watanabe ◽  
Akihiro Matsuda
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Loading ◽  
Fatigue Tests ◽  
J Integral ◽  
Creep Fatigue ◽  
Integral Range ◽  
Crack Growth Rates

In structures having stress concentration under cyclic loading, a small crack initiates and it grows and propagates. Evaluating crack growth is important to estimate the remaining life of cracked components. The present paper shows the estimation of crack growth rate under creep-fatigue loading with some patterns of strain holding times. Creep-fatigue tests of the perforated plate having initial crack were conducted with the different strain holding time under strain-controlled loading at 550°C. The crack growth was observed from the photographs taken at each cycle. The crack growth per one cycle of creep-fatigue loading was evaluated by the creep-fatigue crack propagation law which used increment J-integral range. Comparing the crack growth rates of experimental with those of predicted, the crack growth rates were predicted by using increment J-integral range with the accuracy was factor of 2.

scholarly journals Predicting creep-fatigue crack growth rates in Alloy 709 using finite element simulations of plasticity and creep-induced crack closure

2018 ◽  
Vol 165 ◽  
pp. 13005 ◽  
Author(s):  
Jose Ramirez ◽  
Gabriel P. Potirniche ◽  
Henry Pugesek ◽  
Nicholas Shaber ◽  
Martin Taylor ◽  
...  
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Growth Rates ◽  
Creep Fatigue ◽  
Creep Fatigue Crack ◽  
Crack Growth Rates

This paper reports on a computational study and experimental validation of creep-fatigue crack growth rates at high temperature in two structural materials. The objectives are to develop a methodology to predict creep-fatigue crack growth rates using plasticity-induced crack closure under creep-fatigue loading conditions by characterizing the effect of hold time on crack growth rates during cyclic loading. In this study, the computation of fatigue crack growth rates is based on the crack closure phenomenon. The total crack growth rate during creep-fatigue loading is based on the addition of fatigue crack growth rate during cyclic loading and creep crack growth rate during hold time. The study identifies the effects of frequency and shape of loading cycle on crack-tip opening stresses induced by the combined action of the plasticity-induced crack closure and creep relaxation at the crack tip. Two-dimensional finite element analyses of compact tension specimens are performed to simulate crack growth under cyclic and time-dependent loading conditions. Elastic-plastic-creep material behavior is considered in these simulations. Closure levels are computed for high temperature structural materials such as 9Cr-1Mo steel and Alloy 709. The numerical predictions provide satisfactory agreement with experimental data of creep-fatigue crack growth rates in modified 9Cr-1Mo and Alloy 709 steels at high temperatures.

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.

Fatigue Crack Growth Behavior of Titanium Alloy Ti-6Al-4V and Weldment

2001 ◽  
Vol 123 (3) ◽  
pp. 141-146 ◽  
Author(s):  
Mamdouh M. Salama
Keyword(s):  
Growth Rate ◽  
Titanium Alloy ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Titanium Alloys ◽  
Crack Growth ◽  
Growth Rates ◽  
Offshore Structures ◽  
Crack Growth Rates

Optimization of weight, cost, and performance of deepwater offshore structures demands the increased utilization of high strength, light weight, and corrosion resistant materials such as titanium alloys. Titanium alloy Ti-6Al-4V has been considered for several critical components such as risers and taper joints. Because of the novelty of use of titanium alloys in the offshore industry, there is currently no standard governing design of titanium components for offshore structures. Since these structural components are subjected to a complex spectrum of environmental loading, assessment of defect tolerance using fatigue crack growth analysis is generally considered an important design parameter. In this paper, more than 60 crack growth data sets from 20 independent laboratories were collected and analyzed to develop crack growth rate equations for use in defect assessment. These data include the results of fatigue testing of both base material and welded joints in air and seawater with and without cathodic protection and at different R-ratios and test frequencies. The results suggest that for crack growth rates above 10−7 in./cycle, crack growth of Ti-6Al-4V appears to be independent of testing condition and materials processing. At the low crack growth rate (below 10−7 in./cycle), the review revealed that data are very limited. These limited data, however, suggest that the crack growth threshold is dependent on the R-ratio and slightly dependent on material processing. Comparison between crack growth rates of steel and titanium alloy (Ti-6Al-4V) showed that the two materials have very similar behavior.

Fatigue Crack Growth in Type 316 Stainless Steel at High Temperature

1971 ◽  
Vol 93 (4) ◽  
pp. 976-980 ◽  
Author(s):  
P. Shahinian ◽  
H. H. Smith ◽  
H. E. Watson
Keyword(s):  
Growth Rate ◽  
Stainless Steel ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
316 Stainless Steel ◽  
Arrhenius Relation ◽  
Crack Growth Rates

The dependence of fatigue crack growth rates on range of stress intensity factor (ΔK) in Type 316 stainless steel was investigated over the temperature range of 75 to 1100 deg F. The data for the most part could be described by a power law relationship. An increase in temperature generally increased crack growth rate for a given ΔK and decreased fatigue life. The dependence of crack growth rate on temperature is not described adequately by an Arrhenius relation over the range investigated. On the other hand, by normalizing ΔK with respect to Young’s modulus, E, the crack growth rates for the various temperatures tend to fall within a single band.

Experimental Study on Fatigue Crack Growth and Residual Strength of Steel 30CrMnSiNi2A under Mixed Corrosive Environments

2008 ◽  
Vol 33-37 ◽  
pp. 261-266
Author(s):  
Sheng Nan Wang ◽  
Yi Li ◽  
Jian Bo Qin ◽  
Ya Long Liu ◽  
Yue Quan Zhou
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Residual Strength ◽  
Growth Rates ◽  
Critical Crack Length ◽  
Corrosive Environments ◽  
Crack Growth Rates

The effects of five single and three mixed corrosive environments on the fatigue crack growth and residual strength of steel 30CrMnSiNi2A were experimentally studied. The crack growth rates in corrosive environments, obtained by using Paris equation, were compared with crack growth rate in lab air. The results showed that the interactions of aggressive environments with fatigue loads caused the accelerations of fatigue crack growth rates in steel 30CrMnSiNi2A. But the effects of various environments on the fatigue crack growth rate are different. Among the environments the most detrimental one was oil-box zone, followed by cookroom&washroom, tank seeper, 3.5%NaCl, moist air, high altitude and dried air. Also, the test data showed the less effect of various corrosive environments on critical crack length, that is, no direct infection of corrosive environments on residual strength capability dominated by fracture toughness.

scholarly journals Orientation Dependence of Hydrogen Accelerated Fatigue Crack Growth Rates in Pipeline Steels

2018 ◽  
Author(s):  
Eun Ju Song ◽  
Joseph A. Ronevich
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Growth Rates ◽  
Orientation Dependence ◽  
Gaseous Hydrogen ◽  
Crack Growth Rates

One of the most efficient methods for supplying gaseous hydrogen long distances is by using steel pipelines. However, steel pipelines exhibit accelerated fatigue crack growth rates in gaseous hydrogen relative to air. Despite conventional expectations that higher strength steels would be more susceptible to hydrogen embrittlement, recent testing on a variety of pipeline steel grades has shown a notable independence between strength and hydrogen assisted fatigue crack growth rate. It is thought that microstructure may play a more defining role than strength in determining the hydrogen susceptibility. Among the many factors that could affect hydrogen accelerated fatigue crack growth rates, this study was conducted with an emphasis on orientation dependence. The orientation dependence of toughness in hot rolled steels is a well-researched area; however, few studies have been conducted to reveal the relationship between fatigue crack growth rate in hydrogen and orientation. In this work, fatigue crack growth rates were measured in hydrogen for high strength steel pipeline with different orientations. A significant reduction in fatigue crack growth rates were measured when cracks propagated perpendicular to the rolling direction. A detailed microstructural investigation was performed, in an effort to understand the orientation dependence of fatigue crack growth rate performance of pipeline steels in hydrogen environments.

Influence of Environment and Creep on Fatigue Crack Growth in a High Temperature Aluminum Alloy 8009

1994 ◽  
Vol 116 (1) ◽  
pp. 45-53 ◽  
Author(s):  
K. V. Jata ◽  
D. Maxwell ◽  
T. Nicholas
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Hold Time ◽  
Maximum Load ◽  
Frequency Effects ◽  
Crack Growth Rates

Frequency effects on fatigue crack growth rates are examined in aluminum alloy 8009 in sheet and extruded product forms. The investigations show that frequency effects on the fatigue crack growth rates are pronounced in the sheet but minimal in the extrusion. The influence of creep cracking on fatigue crack growth rate is studied through tests with a 60 s hold-time at maximum load at several stress intensity ranges. A 60 s hold-time at maximum load at 315°C tends to retard fatigue crack growth in both the sheet and the extrusion. The mechanism by which this retardation occurs is attributed to stress relaxation at the crack tip. At 204°C a 60 s hold at Pmax accelerates crack growth rate in the sheet but not in the extrusion. Vacuum and laboratory air tests show that fatigue crack growth rates in vacuum are lower than in air by about a factor of four. A 60 s hold-time at minimum load has only a minor effect on the fatigue crack growth rates at 315°C and no effect at 204°C, confirming the absence of any strong environmental contribution to crack growth rate. Fracture modes in fatigue, creep crack growth and hold-time at Pmax are significantly different. The fractographic results are discussed in relation to the mechanical property data.

Environment Induced Cracking of Turbine Disc Steel: Effect of Organic Acids on Corrosion Fatigue of 3.5NiCrMoV Steels in High Temperature Water

2007 ◽  
Vol 345-346 ◽  
pp. 999-1002
Author(s):  
W.Y. Maeng
Keyword(s):  
Growth Rate ◽  
Acetic Acid ◽  
High Temperature ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Growth Rates ◽  
High Temperature Water ◽  
Turbine Disc ◽  
Crack Growth Rates ◽  
Temperature Water

Organic acids (acetic and formic acid) are produced by the decomposition of ETA (Ethanol Amine, C2H7NO) used as pH controller of secondary water in nuclear power plants. Corrosion Fatigue (CF) tests (R=0.2, 0.1Hz) were conducted to evaluate the effect of acetic acid on the CF crack growth rate in high temperature water at 150°C. Acetic acid significantly influenced the environmental cracking behavior of turbine disc steels in high temperature water. The CF crack growth rates of turbine disc steels increase as the organic acid concentration increase to a critical saturation pH value (~pH 4). Beyond the saturation value of pH, the CF crack growth rates decrease significantly. The higher CF crack growth rate of the higher pH solution in water of intermediate content range (pH 4~pH 5) of acetic acid is due to the higher content of H+ enhancing the reduction reactions. Crack tip blunting prevents the CF cracks from growing with increasing rate in the solution of organic acid concentrations beyond the critical value.

Fatigue crack growth of rails for railways

2003 ◽  
Vol 217 (2) ◽  
pp. 89-97 ◽  
Author(s):  
L F M da Silva ◽  
D J Stewardson ◽  
F M F de Oliveira ◽  
P M S T de Castro
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Statistical Analysis ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
The European Union ◽  
Significant Difference ◽  
Crack Growth Rates

Fatigue crack growth rates of rails from four European rail manufacturers are presented. The tests performed, on which the present paper is based, are part of the contribution to a project on the fatigue crack growth rate qualifying criteria of rails for railways—SMT4-CT98-2240—part-funded by the European Union. Six different laboratories were involved in measuring the scatter in fatigue crack growth rates. The tests were carried out under a stress ratio of 0.5, with test temperature and relative humidity recorded but not controlled beyond the ambient laboratory condition. The cyclic test frequency was either 10 or 15 Hz. The crack length was measured manually (optical microscope) which requires interruptions to the test overnight. Statistical analysis revealed that interruptions to tests may cause interference with the results. The data were analysed by three procedures: formal methods used were the secant method and the seven-point incremental polynomial technique; in addition, statistical analysis of a more investigative type using running regressions was utilized. It was found that there was no significant difference between the crack growth rate in samples from four different manufacturers.

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