Correlation Analysis Between Time-Dependent Creep Crack-Tip Stress and Constraint Effect on Creep Crack Initiation Time

2020 ◽  
Author(s):  
Seung-Ho Lee ◽  
Hyun-Woo Jung ◽  
Yun-Jae Kim ◽  
Kamran Nikbin ◽  
Robert A. Ainsworth
Keyword(s):  
Crack Initiation ◽  
Correlation Analysis ◽  
Creep Crack Growth ◽  
Crack Tip ◽  
Compact Tension ◽  
Time Dependent ◽  
Initiation Time ◽  
Constraint Effect ◽  
Creep Crack ◽  
Crack Tip Stress

Abstract In this study, to qualify the constraint effect on creep crack initiation, the correlation analysis between proposed constraint parameter Q’ using time-dependent creep crack-tip stress and creep crack initiation time variable Ai was performed. Ai implies the influence of constraint effect on creep crack initiation. The procedure to calculate the Ai and the Q’-parameter was presented. To evaluate various status of constraint effect, creep crack growth tests for twenty-one compact tension specimens of Type 316H stainless steel at 550°C were investigated. The results of correlation analysis explain the reason for the different initiation time at the same C* level in respect of constraint effect.

TDFAD Analysis of Creep Crack Initiation in 0.5CMV/2.25CrMoV Steel Weldments

2019 ◽  
Author(s):  
M. Ejaz ◽  
C. M. Davies
Keyword(s):  
Crack Initiation ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Parent Material ◽  
Time Dependent ◽  
Creep Crack ◽  
Material Condition ◽  
Weld Material ◽  
Failure Assessment ◽  
Dependent Failure

Abstract The time dependent failure assessment diagram (TDFAD) is a convenient methodology to simultaneously assess whether a component is likely to fail by brittle, ductile or creep fracture, plastic collapse or creep rupture. In this work, creep toughness data, Kmatc, have been derived from experimental creep crack growth (CCG) tests on compact tension fracture mechanics specimens made of a weldment consisting of 0.5CMV parent material, 2.25CrMo, where the starter crack was located in the heat affected zone (HAZ). Time dependent failure assessment diagrams (TDFADs) are then constructed for each material condition and creep crack initiation (CCI) time predictions were obtained for the CCG tests performed on the weldment samples using both a TDFAD based on either parent and weld material data. The TDFAD based on the weld data provided the most conservative prediction of CCI times thus is recommended for use for weldment samples.

Quantification and Prediction of Residual Stresses in Creep Crack Growth Specimens

2014 ◽  
Vol 777 ◽  
pp. 25-30 ◽  
Author(s):  
Ali Mehmanparast ◽  
Catrin M. Davies ◽  
Kamran Nikbin
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Crack Tip ◽  
Creep Damage ◽  
Compact Tension ◽  
Life Assessment ◽  
Creep Crack ◽  
Fatigue Crack Growth Test

An important issue to be considered in the life assessment of power plant components is the effects of prior creep damage on subsequent fatigue crack growth and fracture behavior. To examine these effects, creep damage has been introduced into 316H stainless steel material by interrupting creep crack growth (CCG) tests on compact tension, C(T), specimens at 550 °C. During the CCG tests, the specimen is loaded in tension, crept and unloaded after a small amount of crack extension. This process introduces compressive residual stress fields at the crack tip, which may subsequently affect the fatigue crack growth test results. In this work, neutron diffraction (ND) measurements have been conducted on interrupted CCG test specimens, which contain creep damage local to the crack tip, and the results are compared to predictions obtained from finite element (FE) simulations. Reasonable agreement has been found between the FE predictions and ND measurements.

Numerical Investigation on Creep Crack Growth of Brazed Joint Using Different Damage Models

2016 ◽  
Vol 853 ◽  
pp. 231-235
Author(s):  
Yun Luo ◽  
Qian Zhang ◽  
Wen Chun Jiang
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Rupture Life ◽  
Damage Model ◽  
Creep Crack Growth ◽  
Creep Damage ◽  
Initiation Time ◽  
Creep Crack ◽  
Damage Models ◽  
Brazed Joint

In this paper, four types of creep damage models (Kachanov-Robotnov, Liu-Murakami, Cocks-Ashby and Wen-Tu model) were used to study the creep crack growth (CCG) behavior in compact tension (CT) specimen of Hastelloy C-276/BNi-2 brazed joint. The results show that the creep damage model has a great influence on the CCG behavior of brazed joint. The crack-tip stress states, da/dt-C* curves, crack initiation time and rupture life are different for the different damage models. The Kachanov-Rabotnov model can lead to higher CCG rate and shorter rupture life, while the Cocks and Ashby model can reduce CCG rate and prolong the rupture life. The model order in terms of the CCG rate from high to low is K-R, L-M, W-T, C-A model, which is opposite order of crack initiation time. In the simulation of CCG of brazed joint, a precious damage model should be employed for life prediction.

Analysis of Creep Crack Growth Behavior of the Brazed Joint Using Continuum Damage Mechanics Approach

2018 ◽  
Author(s):  
Yu-Cai Zhang ◽  
Wenchun Jiang ◽  
Shan-Tung Tu ◽  
Xian-Cheng Zhang ◽  
Guo-Yan Zhou
Keyword(s):  
Crack Initiation ◽  
Diffusion Zone ◽  
Damage Mechanics ◽  
Creep Crack Growth ◽  
Continuum Damage Mechanics ◽  
Crack Growth Behavior ◽  
Continuum Damage ◽  
Initiation Time ◽  
Creep Crack ◽  
Brazed Joint

Creep crack growth behavior of the Inconel625/BNi-2 brazed joint considering the diffusion zone at 650 °C was investigated by a continuum damage mechanics approach based on the finite element method. The results show that creep crack nucleate and develop at the region of the brazing filler metal. The crack initiates at about 0.2 mm ahead of the crack tip. When the load is 1000 N, the crack initiation time of the CT specimen is 1664 hour. While when the load is 1135 N, the crack initiation time is only about 891 hour. The simulated results correspond well with the experimental data, presenting that the used finite element method can accurately simulate the creep damage behavior of the brazed joint. When the mechanical properties of the diffusion zone are not considered, the crack initiation time and fracture time decrease significantly compared to the result with properties of the diffusion zone included, indicating that the result from the conventional simulating method without considering the diffusion zone is quite conservative compared to the experimental life of the component.

TDFAD Analysis of Creep Crack Initiation in Pre-Strained and As-Received Type 316H Stainless Steel

2012 ◽  
Author(s):  
C. M. Davies ◽  
D. W. Dean ◽  
A. Mehmanparast
Keyword(s):  
Stainless Steel ◽  
Crack Initiation ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Small Scale ◽  
Creep Crack ◽  
Material Condition ◽  
Failure Assessment ◽  
Dependent Failure ◽  
Tension Fracture

The time dependent failure assessment diagram (TDFAD), an extended form of the low temperature FAD used in the R6 procedure, has been developed to allow creep crack initiation to be predicted using a FAD-based approach. The TDFAD has a number of advantages compared to other methods for predicting creep crack initiation time: detailed calculations of crack tip parameters such as C* are not needed; it is not necessary to establish the fracture regime in advance and the TDFAD can indicate whether initiation occurs under small-scale or widespread creep conditions. The TDFAD approach relies on the availability of appropriate creep toughness, Kcmat, values. In this work, creep toughness data have been derived from experimental creep crack growth (CCG) tests on compact tension fracture mechanics specimens made of Type 316H stainless steel in as-received (AR) material and material that has been pre-compressed (PC) by up to 8% plastic strain. The influence of material pre-conditioning on creep toughness is examined. TDFADs are then constructed for each material condition and creep crack initiation (CCI) time predictions are obtained for the CCG tests performed on the Type 316H steel at 550 °C. The influence of material condition on the predicted CCI mode is examined and discussed.

The Effect of Discontinuous Crack in Creep Crack Growth Tests

2013 ◽  
Author(s):  
Nak Hyun Kim ◽  
Yun Jae Kim ◽  
Catrin M. Davies ◽  
Ali Mehmanparast ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Main Crack ◽  
Plastic Material ◽  
Creep Crack Growth ◽  
Crack Tip ◽  
Limit Load ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
Elastic Plastic ◽  
Creep Crack

Discontinuous cracks ahead of the leading crack tip may be present in observedcertain creep crack growth tests as well as in components. In this work, a single crack of different dimensions and distance from the leading crack has been numerically modeled in a compact tension specimen using elastic, elastic-plastic and elastic-plastic-creep loading. In order to examine their effects on fracture mechanics parameters a sensitivity analysis was performed to determine the effects of size and distance of the secondary crack with respect to the main crack. t The elastic analysis shows that the compliance is insensitive small cracks ahead of the main crack. Limit load analyses, assuming an elastic-perfectly plastic material, show that the limit load decreases due to the presence of discontinuous cracks ahead of the main crack. Theload versus plastic load-line displacement response of the specimen was significantly influenced by discontinuous cracking. The J contour parameter and C*-integral have been evaluated at the three crack tips and the average of all of them derived for the appropriate contours were compared with the valuesobtained from on ASTM E1820(1) and E1457(2). Whilst the average values of the contour integral are similar to the ASTM J and C* values there is significant differences in J and C* for the individual crack tip values. This need to be further evaluated in future work.

Analysis of 316H Creep Crack Initiation Data at 550℃ using A Crack Tip Constraint Parameter

2021 ◽  
pp. 107746
Author(s):  
Seung-Ho Lee ◽  
Hyun-Woo Jung ◽  
Yun-Jae Kim ◽  
Kamran Nikbin ◽  
Robert A. Ainsworth
Keyword(s):  
Crack Initiation ◽  
Crack Tip ◽  
Creep Crack ◽  
Crack Tip Constraint

The Analysis of the Stress Field and Crack of Rock under the Blast Loading

2010 ◽  
Vol 168-170 ◽  
pp. 1252-1255
Author(s):  
Zhong Guo Zhang ◽  
Ya Dong Bian ◽  
Bin Gao
Keyword(s):  
Stress Field ◽  
Crack Initiation ◽  
Crack Extension ◽  
Crack Tip ◽  
Blast Loading ◽  
Crack Arrest ◽  
The Stability ◽  
Crack Tip Stress

The crack tip stress field of rock is analyzed under blast loading, and the crack arrest criterion, the conditions of rock crack initiation and crack extension are presented in this paper. The study will help the design of maintaining the stability of stope drift active workings.

Modeling and Simulation of Creep Crack Growth in High Chromium Steels

2014 ◽  
Author(s):  
Nicola Bonora ◽  
Luca Esposito ◽  
Simone Dichiaro ◽  
Paolo Folgarait
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Chromium Steel ◽  
Creep Model ◽  
Model Parameters ◽  
Approximate Methods ◽  
High Chromium ◽  
Creep Crack ◽  
Wide Range

Safe and accurate methods to predict creep crack growth (CCG) are required in order to assess the reliability of power generation plants components. With advances in finite element (FE) methods, more complex models incorporating damage can be applied in the study of CCG where simple analytical solutions or approximate methods are no longer applicable. The possibility to accurately simulate CCG depends not only on the damage formulation but also on the creep model since stress relaxation, occurring in the near tip region, controls the resulting creep rate and, therefore, crack initiation and growth. In this perspective, primary and tertiary creep regimes, usually neglected in simplified creep models, plays a relevant role and need to be taken into account. In this paper, an advanced multiaxial creep model [1], which incorporates damage effects, has been used to predict CCG in P91 high chromium steel. The model parameters have been determined based on uniaxial and multiaxial (round notched bar) creep data over a wide range of stress and temperature. Successively, the creep crack growth in standard compact tension sample was predicted and compared with available experimental data.

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