scholarly journals Paths of interactive cracks in creep conditions

2015 ◽  
Author(s):  
K. Nowak
Keyword(s):  
Damage Mechanics ◽  
Crack Path ◽  
Creep Crack Growth ◽  
Creep Condition ◽  
Continuum Damage Mechanics ◽  
Damage Parameter ◽  
Multiple Cracks ◽  
Time To Failure ◽  
Continuum Damage ◽  
Initial Cracks

The paper contains plane strain analysis of uniformly stretched plate working in creep condition. The plate contains initial defects in forms of central and/or edge cracks working in mode I. These cracks are modelled by attributing critical value of damage parameter to preset points and therefore resulting in stresses set to zero (material does not support any loading). The Continuum Damage Mechanics constitutive equations are used to describe the creep crack growth problem and Finite Element Method Abaqus system is applied to solve corresponding boundary and initial value problem. Analysis of different initial cracks configuration has been performed. The crack path is defined by points in which damage parameter equals to critical one. Time to failure of the plate with single initial crack is achieved when the crack path spans its width. This time is calculated and compared to the time to failure of initially uncracked structure. For the plate with multiple cracks the paths starting from different cracks can develop independently until they merge and/or span the plate width. In each case the damage field is analysed and the direction of crack path development is determined. The analysis of crack propagation allows for determination of a distance between initial cracks for which the interaction between them is negligible. It is demonstrated that Continuum Damage Mechanics approach allows not only to model the development of initially existing cracks but also initiation of new, cross-spanning cracks and their kinking and branching.

The role of continuum damage in creep crack growth

1984 ◽  
Vol 311 (1516) ◽  
pp. 131-158 ◽  
Keyword(s):  
Crack Growth ◽  
Damage Mechanics ◽  
Experimental Studies ◽  
Creep Crack Growth ◽  
Stress Rupture ◽  
Continuum Damage Mechanics ◽  
Continuum Damage ◽  
Creep Crack ◽  
Theoretical Predictions ◽  
Rupture Criterion

Theories that have been used to predict the rate of growth of cracks due to creep are reviewed and assessed. The need is expressed for a sounder understanding of the mechanisms by which creep crack growth takes place. The aim of this paper is to answer the question: can continuum damage mechanics provide the mechanism by which cracks grow by creep? The paper reports the results of theoretical and experimental studies on internally and externally cracked, plane strain, tension members, in an aluminium alloy, in copper and in 316 stainless steel, all of which undergo high temperature creep rupture under steady loads. Theoretical predictions of lifetimes, expressed as a representative rupture stress, of damage fields and of crack growth are made by using a previously developed finite element system (Hayhurst, Dimmer & Morrison, Phil. Trans. R. Soc. Lond . 311, 103 (1984)) based on the theory of continuum damage mechanics. The theoretical predictions are shown to be in close agreement with experimental observations. The effect of the growth of continuum damage is to produce considerable stress redistribution and to cause the nullification of stress singularities. The multi-axial stress rupture criterion of the material plays an important role in the determination of lifetimes and of the planes upon which crack propagation takes place. The numerical solution procedure is automatic but requires that the constitutive equations model the elastic response, the creep strain rates, including tertiary behaviour, and the multiaxial stress rupture criterion of the material at the appropriate stress levels. Continuum damage mechanics theory is shown to be capable of modelling the propagation of cracks through material which has suffered relatively low damage.

A precipitate evolution-based continuum damage mechanics model of creep behaviour in welded 9Cr steel at high temperature

2018 ◽  
Vol 233 (1) ◽  
pp. 39-51
Author(s):  
C Ó Murchú ◽  
SB Leen ◽  
PE O’Donoghue ◽  
RA Barrett
Keyword(s):  
Damage Mechanics ◽  
Volume Fraction ◽  
Creep Behaviour ◽  
Continuum Damage Mechanics ◽  
Time To Failure ◽  
Continuum Damage ◽  
State Variable ◽  
9Cr Steel ◽  
Mechanics Model ◽  
Physically Based

A multiaxial, physically based, continuum damage mechanics methodology for creep of welded 9Cr steels is presented, incorporating a multiple precipitate-type state variable, which simulates the effects of strain- and temperature-induced coarsening kinematics. Precipitate volume fraction and initial diameter for carbide and carbo-nitride precipitate types are key microstructural variables controlling time to failure in the model. The heat-affected zone material is simulated explicitly utilising measured microstructural data, allowing detailed investigation of failure mechanisms. Failure is shown to be controlled by a combination of microstructural degradation and Kachanov-type damage for the formation and growth of creep cavities. Comparisons with experimental data demonstrate the accuracy of this model for P91 material.

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.

Defect Assessments at Elevated Temperature

1983 ◽  
Vol 105 (3) ◽  
pp. 263-268 ◽  
Author(s):  
R. A. Ainsworth ◽  
I. W. Goodall
Keyword(s):  
Damage Mechanics ◽  
Creep Crack Growth ◽  
Continuum Damage Mechanics ◽  
Continuum Damage ◽  
Initiation Time ◽  
Creep Crack ◽  
Reference Stress ◽  
Statistical Approaches ◽  
Assessment Requirements ◽  
Fast Fracture

Methods are described for assessing acceptable defect sizes for plant in high temperature service. At one extreme of behavior, that of creep ductile response, failure is governed by continuum damage mechanics which may be analyzed using finite element methods or more approximately by reference stress techniques. In less ductile cases failure can occur through the initiation and growth of a dominant creep crack. For this case the paper outlines how the assessment requirements may be based on an estimate of the initiation time and a method for calculating this initiation time is given. When the initiation time is small, the assessment also requires an estimate of the time taken in the creep crack growth stage and both empirical correlation and statistical approaches for analyzing this stage are described. Finally the paper outlines how fast fracture and ductile instability can be included in determining repair criteria for use with the various assessment methods.

scholarly journals DESCRIPTION OF DETERIORATION PROCESSES: DAMAGE PARAMETER OF Y.N. RABOTNOV: HISTORICAL REMARKS, FUNDAMENTAL RESULTS AND CONTEMPORARY STATE

2017 ◽  
Vol 20 (3) ◽  
pp. 97-114 ◽  
Author(s):  
L.V. Stepanova ◽  
S.A. Igonin
Keyword(s):  
Damage Accumulation ◽  
Damage Mechanics ◽  
Continuum Damage Mechanics ◽  
Damage Parameter ◽  
Continuum Damage ◽  
Damage State ◽  
Detailed Review ◽  
Contemporary State ◽  
Historical Remarks

In the paper the detailed review of the present-day results related to problems of continuum damage mechanics is given. The survey shows the development of ideas of Y.N. Rabotnov who together with L.M. Kachanov introduced damage and continuity variables which characterize the damage state. In the paper the recent studies in the elasticity, plasticity and creep theories accounting for damage accumulation processes are discussed.

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