Evaluation of Creep Crack Growth Rate of P92 Welds Using Fracture Mechanics Parameters

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Masataka Yatomi ◽  
Akio Fuji ◽  
Masaaki Tabuchi ◽  
Yasushi Hasegawa ◽  
Ken-ichi I. Kobayashi ◽  
...  
Keyword(s):  
Crack Growth ◽  
Power Plants ◽  
Thermal Power ◽  
Creep Crack Growth ◽  
Creep Model ◽  
Element Analysis ◽  
Creep Crack ◽  
Fine Grained ◽  
Type Iv ◽  
Total Life

High Cr ferritic heat resisting steels have been widely used for boiler components in ultrasupercritical thermal power plants operated at about 600°C. In the welded joint of these steels, type-IV crack initates in the fine-grained heat affected zone during long-term use at high temperatures and their creep strength decreases. In this paper, creep properties and creep crack growth (CCG) properties of P92 welds are presented. The CCG tests are carried out using cross-welded compact tension C(T) specimens at several temperatures. The crack front was located within the fine-grained HAZ region to simulate type-IV cracking. Finite element analysis was conducted to simulate multiaxiality in welded joints and to compare experimental results. The constitutive behavior for these materials is described by a power-law creep model. C∗ and Q∗ parameters are used to evaluate CCG rate of P92 welds for comparison. C∗ parameters can characterize approximately 20% of the total life of CCG in P92 welds, and Q∗ parameters can characterize approximately 80% of the total life. Q∗ parameter is one of the useful parameters to predict CCG life in P92 welds.

Creep Crack Growth of P92 Welds

2008 ◽  
Author(s):  
Masataka Yatomi ◽  
Akio Fuji ◽  
Ken-ichi I. Kobayashi ◽  
Masaaki Tabuchi ◽  
Takeo Yokobori ◽  
...  
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Creep Model ◽  
Element Analysis ◽  
Creep Properties ◽  
Creep Crack ◽  
Type Iv ◽  
Growth Properties ◽  
Power Law Creep

This paper represents creep properties and creep crack growth properties for P92 welds. The CCG tests were carried out using cross-welded compact tension (C (T) specimens at several temperatures. The crack front was located at HAZ region to simulate Type IV crack. Finite element analysis was conducted to simulate multiaxiality in welded joints and compare the experimental results. The constitutive behaviour for these materials is described by a power law creep model.

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.

Virtual Methods in Creep Crack Growth Predictions in 316H Stainless Steels

2007 ◽  
Author(s):  
Masataka Yatomi ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Stainless Steels ◽  
Creep Crack Growth ◽  
Crack Propagation Rate ◽  
Creep Model ◽  
Elastic Plastic ◽  
Creep Crack ◽  
Plastic Creep ◽  
Plane Strain Crack

The paper discusses numerically based virtual techniques of creep crack growth predictions in a fracture mechanics component. The material properties used are for 316H stainless steels and the constitutive behaviour of the steel is described by a power law creep model. A damage-based approach is used to predict the crack propagation rate in compact tension (C(T)) specimens and the data are correlated against an independently determined C* parameter. Elastic-plastic-creep analyses are performed using two different crack growth criteria to predict crack extension under plane stress and plane strain conditions. The NSW and NSW-MOD strain exhaustion models are applied to compare to the experimental data and FE predictions. The plane strain crack growth rate predicted from the numerical analysis is found to be less conservative than the plane strain NSW model but more conservative than plane strain NSW-MOD model, for values of C* within the limits of the present creep crack growth testing standards. At higher loads and C* values, the plane strain crack growth rates, predicted using an elastic-plastic-creep material response, approach is considered and compared to the plane strain NSW-MOD model.

Finite Element Analysis of History-Dependent Damage in Time-Dependent Fracture Mechanics

1993 ◽  
Vol 115 (4) ◽  
pp. 339-347 ◽  
Author(s):  
P. Krishnaswamy ◽  
F. W. Brust ◽  
N. D. Ghadiali
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Operating Conditions ◽  
Time Dependent ◽  
Element Analysis ◽  
Creep Crack ◽  
Numerical Predictions ◽  
Fracture Parameters ◽  
Growing Cracks

The demands for structural systems to perform reliably under both severe and changing operating conditions continue to increase. Under these conditions time-dependent straining and history-dependent damage become extremely important. This work focuses on studying creep crack growth using finite element (FE) analysis. Two important issues, namely, (i) the use of history-dependent constitutive laws, and (ii) the use of various fracture parameters in predicting creep crack growth, have both been addressed in this work. The constitutive model used here is the one developed by Murakami and Ohno and is based on the concept of a creep hardening surface. An implicit FE algorithm for this model was first developed and verified for simple geometries and loading configurations. The numerical methodology developed here has been used to model stationary and growing cracks in CT specimens. Various fracture parameters such as the C1, C*, T*, J were used to compare the numerical predictions with experimental results available in the literature. A comparison of the values of these parameters as a function of time has been made for both stationary and growing cracks. The merit of using each of these parameters has also been discussed.

Prediction of Creep Crack Growth for Modified 9Cr-1Mo at 600°C

2012 ◽  
Author(s):  
Nak Hyun Kim ◽  
Yun Jae Kim ◽  
Woo Gon Kim ◽  
Hyeong Yeon Lee
Keyword(s):  
Prediction Model ◽  
Crack Growth ◽  
Damage Model ◽  
Creep Crack Growth ◽  
Creep Damage ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
Element Analysis ◽  
Creep Ductility ◽  
Creep Crack

This paper introduce theoretical creep crack growth prediction model and provides experimental validation of the approach for simulating creep crack growth using finite element analysis method, recently proposed by the authors. The FE creep damage model is based on the creep ductility exhaustion concept, and incremental damage is defined by the ratio of incremental creep strain and multi-axial creep ductility. A simple linear damage summation rule is applied. When accumulated damage becomes unity, element stresses are reduced to zero to simulate progressive crack growth. For validation, simulated results are compared with experimental data for a compact tension specimen of modified 9Cr-1Mo at 600°C under various loading levels. The simulated results agree well with experimental C*-da/dt data. The test data are also compared with theoretical CCG prediction model.

Evaluation of Constraint Effect on Creep Crack Growth by Advanced Creep Modeling and Damage Mechanics

2014 ◽  
Author(s):  
Simone Dichiaro ◽  
Luca Esposito ◽  
Nicola Bonora
Keyword(s):  
Numerical Simulation ◽  
Creep Rate ◽  
Crack Growth ◽  
Damage Mechanics ◽  
Crack Depth ◽  
Creep Crack Growth ◽  
Creep Model ◽  
Secondary Creep ◽  
Creep Stage ◽  
Creep Crack

Effects of constraint induced by crack depth and sample geometry on creep crack behavior of high chromium steels was investigated by numerical simulation. An advanced mechanism-based creep model formulation, which accounts for primary and secondary creep stage was used. Here, the transient creep rate is modeled considering the evolution of the internal stress with the activation energy while the steady state creep rate is modelled considering both diffusional and dislocation creep mechanisms. This formulation allows one to predict accurately creep strain accumulation over a wide range of stress and temperature. Model parameters were identified on constant load creep tests and their transferability to the multiaxial state of stress was verified comparing predicted creep life with data obtained on notched bar samples. Continuum damage mechanics was used to predict the occurrence of tertiary creep stage and crack advance. To this purpose, a non-linear damage law, as proposed in Bonora and Esposito [1] was used. The effect of the geometry constrain on creep crack growth was investigated in different sample geometries (C(T), SEN(T), SEN(B), DEN(T) and CCP(T)) for a given crack depth values, and the same biaxiality ratio for SEN(T), SEN(B) and DEN(T). Numerical simulation results were validated by comparison with available experimental data for P91 steels.

Sign in / Sign up

Export Citation Format

Share Document