An Analysis of Elevated Temperature Fatigue and Creep Crack Growth

1976 ◽  
Vol 98 (4) ◽  
pp. 473-479 ◽  
Author(s):  
M. Do¨ner
Keyword(s):  
Elevated Temperature ◽  
Crack Growth ◽  
Growth Rates ◽  
Creep Crack Growth ◽  
Crack Tip ◽  
Creep Damage ◽  
Material Constant ◽  
Temperature Oxidation ◽  
Oxidation Damage ◽  
Crack Growth Rates

Existing crack growth laws which consider time and temperature effects are examined. Based on phenomenological observations, as well as mechanistic considerations, one of these laws is modified in order to provide an improved, universal elevated temperature crack growth law. It is assumed that there are essentially three processes through which crack growth rates are affected: decrease in strength and modulus with temperature, oxidation damage at the crack tip and creep damage at the crack tip. The rate controlling mechanism(s) which may be associated with each of these processes are discussed. The type of experiments which are needed for the determination of material constant(s) that describe the contribution from each process are outlined. The modified crack growth law, when applied to publish data on HS-188 alloy, results in a prediction of the crack growth rates within a factor of 2.5, in the temperature range of 873–1144 K and at cycle frequencies ranging from 0.01 to 10 Hz.

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.

Assessment of Creep Crack Growth Rates for Grade 91 Weld Joint at 550°C

2018 ◽  
Author(s):  
Woo-Gon Kim ◽  
Jae-Young Park ◽  
Hyeong-Yeon Lee ◽  
Eung-Seon Kim ◽  
Seon-Jin Kim
Keyword(s):  
Crack Growth ◽  
Weld Joint ◽  
Growth Rates ◽  
Creep Crack Growth ◽  
Tensile Creep ◽  
Fracture Parameter ◽  
Creep Crack ◽  
Elevated Temperature Design ◽  
Grade 91 ◽  
Crack Growth Rates

This study presents assessment of creep crack growth rates (CCGRs) for the base metal (BM), weld metal (WM), and heat affected zone (HAZ) of Gr. 91 weld joint, which was prepared by a shield metal arc weld (SMAW) method. A series of tensile, creep, creep crack growth (CCG) tests were performed for the BM, WM, and HAZ at the identical temperature of 550°C. The CCGR laws for the BM, WM and HAZ were constructed and compared in terms of a C*-fracture parameter. In addition, the CCGR law tested for BM was compared to that of RCC-MRx code. For a given value of C*, the WM and HAZ were almost similar in the CCGR, but they were significantly faster than the BM. This reason was closely attributed to the higher creep rate in the WM and HAZ than the BM. Currently elevated temperature design (ETD) code in French, RCC-MRx was found to be non-conservative in the CCGR when compared with the present investigation.

Computational Modelling of High Temperature Steady State Crack Growth Using a Damage-Based Approach

2003 ◽  
Author(s):  
Masataka Yatomi ◽  
Noel P. O’Dowd ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Computational Study ◽  
Creep Crack Growth ◽  
Computational Modelling ◽  
Crack Tip ◽  
Creep Damage ◽  
Creep Model ◽  
Manganese Steel

In this work a computational study of creep crack growth in a carbon manganese steel is presented. The constitutive behaviour of the steel is described by a power law creep model and the accumulation of creep damage is accounted for through the use of a well-established model for void growth in creeping materials. Two dimensional finite element analyses have been performed for a compact tension specimen and it has been found that the predicted crack growth rate under plane strain conditions approaches that under plane stress conditions at high C* levels. Furthermore it has been shown, both experimentally and numerically, that an increase in test temperature causes the convergence of the cracking rate to occur at higher values of C*. This trend may be explained by the influence of crack-tip plasticity, which reduces the relative difference in constraint between plane stress and plane strain conditions. The constraint effect has been quantified through the use of a two-parameter characterisation of the crack tip fields under creep conditions.

The Influence of Metallurgical and Mechanical Pre-Damage on Creep-Crack and Fatigue-Crack Growth Rates of CrMoV Steel

2004 ◽  
Author(s):  
Masaru Sekihara ◽  
Shigeo Sakurai
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Creep Crack Growth ◽  
Creep Crack ◽  
The Relationship ◽  
Crack Growth Rates

The effects of mechanical degradation on the creep- and fatigue-crack growth rates in power plants operated long-term were studied. Creep-crack growth tests and fatigue-crack growth tests were performed using creep-pre-strained and repetitive-strained CrMoV rotor-steel specimens. It was found that the creep-crack growth rates, da/dt, of the creep-pre-damaged specimens were larger than those of virgin specimens under constant load. It was also found that under the same stress intensity factor K, da/dt in the case of about 10%-crept and creep void induced specimens was increased five times, while in the case of 0.8%- and 2.8%-crept specimens, it only increased a little. However, all the data fell in a narrow scatter band in the relationship between C* and da/dt. The effect of long-term operating degradation appeared on the creep- and fatigue-damage under the Slow-Fast waveform. Also the crack density was larger in the damaged specimens compared with the virgin specimens. Other results showed that the fatigue-crack growth rates, da/dN, of creep- and fatigue-pre-damaged specimens were larger than those of virgin specimens. Under the same stress intensity factor range ΔK, da/dN in a specimen with approximately 10%-creep was increased 20 times. Moreover da/dN in fatigue-pre-damaged specimens was accelerated 10 times. However, the results of the strain-controlled crack growth test fell in a narrow scatter band in the relationship between J integral range ΔJ and da/dN. These results suggest that the creep remaining lives and fatigue remaining lives of mechanically damaged CrMoV steel can be estimated using the C* & ΔJ values considering the creep rate and the deformation rate of the pre-damaged materials and the da/dt and da/dN values of the virgin material.

Prediction of creep crack growth from uniaxial creep data

1984 ◽  
Vol 396 (1810) ◽  
pp. 183-197 ◽  
Keyword(s):  
Crack Growth ◽  
Growth Rates ◽  
Process Zone ◽  
Creep Crack Growth ◽  
Creep Process ◽  
Uniaxial Tensile ◽  
Creep Data ◽  
Creep Ductility ◽  
Creep Crack ◽  
Crack Growth Rates

In this paper uniaxial tensile creep data are used in conjunction with fracture mechanics concepts to predict creep crack growth rates in materials having a wide range of creep ductilities. A model is proposed of creep damage accumulation in a process zone ahead of the crack tip. The model allows all stages of creep to be incorporated in an approximate manner and creep ductility to be stress and stress-state sensitive. Good agreement is obtained with experimental crack growth data on a range of low alloy steels, a stainless steel, an aluminium alloy and a nickel-base superalloy. It is found that cracking rate is insensitive to the creep process zone size but inversely proportional to creep ductility. Crack growth rates under plane strain conditions are shown to be about fifty times those for plane stress loading.

Cohesive Zone Modeling of Hydrogen Assisted Cracking in a 15-5 PH Steel and Comparison With Experiments

2015 ◽  
Author(s):  
Giovambattista Bilotta ◽  
Mandana Arzaghi ◽  
Gilbert Hénaff ◽  
Guillaume Benoit ◽  
Clara Moriconi ◽  
...  
Keyword(s):  
Crack Growth ◽  
Growth Rates ◽  
Cohesive Zone ◽  
Hydrogen Pressure ◽  
Crack Tip ◽  
Gaseous Hydrogen ◽  
Zone Model ◽  
Loading Frequency ◽  
High Hydrogen ◽  
Crack Growth Rates

Gaseous hydrogen substantially reduces fracture properties such as threshold stress intensity factor and crack growth resistance in the precipitation-hardened martensitic stainless steel investigated in this study. Fatigue crack propagation tests were performed on CT specimens under different atmospheres (hydrogen pressures from 0.09 to 40 MPa) on the Hycomat test bench, at the Pprime Institute in Poitiers, France. A strongly enhanced crack growth regime was identified at high hydrogen pressure and low-frequency loading. Crack growth rates obtained at a constant load under same pressure levels suggest that a combination of tensile stresses above a threshold (KIscc) and fatigue cycles contribute to the hydrogen embrittlement at the crack tip. These experimental results were compared to the finite element simulation results obtained by a recently developed cohesive zone model at the crack tip. A specifically developed traction-separation law which is suitable to describe the gradual degradation of cohesive stresses under monotonic and cyclic loadings, and which is furthermore sensitive to the hydrogen concentration was used. The effects of the different testing conditions, in terms of loading frequency and hydrogen pressure, on the modeling results are discussed. It was shown that the model qualitatively predicts the detrimental influence of gaseous hydrogen on the crack growth rates.

Three Dimensional Criterion for Creep Crack Propagation in C(T) Specimen

2016 ◽  
Vol 853 ◽  
pp. 142-147
Author(s):  
Wen Ming Ye ◽  
Xu Teng Hu ◽  
Wan Lin Guo ◽  
Ying Dong Song
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Growth Rates ◽  
Three Dimensional ◽  
Creep Crack Growth ◽  
Growth Control ◽  
Compact Tension ◽  
Thickness Effect ◽  
Creep Crack ◽  
Crack Growth Rates

Experimental of two kinds of compact tension (CT) specimens’ creep crack propagation are carried out in this paper. Traditional fracture mechanics and three-dimensional fracture theory are compared and the results show that: The K-Tz two-parameter model can eliminate the thickness-effect on the crack growth rates in the relatively low K range, however when K exceed certain values the effect of thickness for crack growth rates still exists; The Ct and Ct-Tz model can describe the thickness-effect of creep crack growth rates in regions of high Ct; When the crack tip stress intensity factor K of the two kinds of thickness (B=5 mm, B=10 mm) specimens equal to 35 and 31 respectively, this material’s creep crack growth control parameter change from K to Ct.

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