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.

An Engineering Approach to the Prediction of Creep Crack Growth

1986 ◽  
Vol 108 (2) ◽  
pp. 186-191 ◽  
Author(s):  
K. M. Nikbin ◽  
D. J. Smith ◽  
G. A. Webster
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Elevated Temperatures ◽  
Process Zone ◽  
Creep Crack Growth ◽  
Crack Tip ◽  
Creep Damage ◽  
Creep Ductility ◽  
Creep Crack

This paper is concerned with assessing the integrity of cracked engineering components which operate at elevated temperatures. Fracture mechanics parameters are discussed for describing creep crack growth. A model is presented for expressing growth rate in terms of creep damage accumulation in a process zone ahead of the crack tip. Correlations are made with a broad range of materials exhibiting a wide spread of creep ductilities. It is found that individual propagation rates can be predicted with reasonable accuracy from a knowledge only of the material uni-axial creep ductility. An engineering creep crack growth assessment diagram is proposed which is independent of material properties but which is sensitive to the state of stress at the crack tip. Approximate bounds are presented for plane stress and plane strain situations and it is shown that crack growth rates about fifty times faster are expected under plane strain conditions than when plane stress prevails.

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.

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.

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.

scholarly journals Crack Growth Behavior in NiTi Shape Memory Alloys Under Mode-I Isothermal Loading: Effect of Stress State

2018 ◽  
Author(s):  
Behrouz Haghgouyan ◽  
Ibrahim Karaman ◽  
Sameer Jape ◽  
Alexandros Solomou ◽  
Dimitris C. Lagoudas
Keyword(s):  
Finite Element ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Crack Tip ◽  
Stress Conditions ◽  
Mode I ◽  
Niti Shape Memory Alloys

Fracture behavior in nickel-titanium (NiTi) shape memory alloys (SMAs) subjected to mode-I, isothermal loading is studied using finite element analysis (FEA). Compact tension (CT) SMA specimen is modeled in Abaqus finite element suite and crack growth under displacement boundary condition is investigated for plane strain and plane stress conditions. Parameters for the SMA material constitutive law implemented in the finite element setup are acquired from characterization tests conducted on near-equiatomic NiTi SMA. Virtual crack closure technique (VCCT) is implemented where crack is assumed to extend when the energy release rate at the crack-tip becomes equal to the experimentally obtained material-specific critical value. Load-displacement curves and mechanical fields near the crack-tip in plane strain and plane stress cases are examined. Moreover, a discussion with respect to the crack resistance R-curves calculated using the load-displacement response for plane strain and plane stress conditions is presented.

Modelling Crack Growth in the Life Assessment of Elevated Temperature Components

2007 ◽  
Vol 348-349 ◽  
pp. 709-712
Author(s):  
Kamran M. Nikbin
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Plane Strain ◽  
Elevated Temperatures ◽  
Creep Crack Growth ◽  
Crack Propagation Rate ◽  
Life Assessment ◽  
Manganese Steel ◽  
Growth Data ◽  
Creep Crack

Modelling of Creep Crack Growth (CCG) using analytical and numerical methods is relevant to life assessment procedures of components operating at elevated temperatures. This paper compares an analytical crack prediction and a numerical based virtual CCG technique used in fracture mechanics components with sample experimental results. Two approaches are presented. First the well developed strain exhaustion model called the NSW and the modified NSW-MOD models which predict plane stress/strain bound crack initiation and growth rates for engineering alloys and the second a damage-based approach used to numerically predict the crack propagation rate in Finite Element models of fracture mechanics specimens. The results from both methods are correlated against an independently determined C* parameter. As an example the NSW and the extended NSW-MOD strain exhaustion models are applied to compare to the experimental data and FE predictions for two steels at Carbon-Manganese steel tested at 360 oC and a weld 316H stainless steel at 550 oC. For values of C* within the limits of the present creep crack growth data presented 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.

Numerical Prediction of Constraint Effect of Creep Crack Growth

2009 ◽  
Author(s):  
Masataka Yatomi ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Creep Crack Growth ◽  
Constraint Effect ◽  
Three Point Bending ◽  
Creep Crack ◽  
Reference Stress ◽  
Edge Notch ◽  
Stress And Strain Rate

This paper presents the effect of constraint on creep crack growth (CCG) using FE analysis based on the stress and strain rate state at the crack tip. The comparison is made by modelling C(T) specimen tests under plane stress and plane strain conditions using creep properties of three different steels (C-Mn steel, P91 steel, and 316H austenitic steel). In addition, in order to examine the constraint effect on CCG due to geometry single edge notch specimen (SENT), centre cracked tension specimen (CCT) and three point bending (3PB) specimen have also been analysed. In all cases it is found that when the reference stress under plane strain conditions is higher than the yield stress, there is little difference between CCG rates under plane stress and plane strain.

Modeling of Plane Strain Fatigue Crack Closure

1991 ◽  
Vol 113 (1) ◽  
pp. 31-40 ◽  
Author(s):  
Huseyin Sehitoglu ◽  
Wei Sun
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Plane Strain ◽  
Crack Closure ◽  
Plane Stress ◽  
Crack Opening ◽  
Crack Tip ◽  
Crack Advance ◽  
Crack Opening Load ◽  
Opening Load

Mechanisms and models proposed for plane strain fatigue crack closure are evaluated. A mechanism based on out-of-plane plastic strain component, εzp, in plane strain is shown not to be adequate in explaining closure over a wide range of applied load levels. In the second model, partial relief of compressive stresses in front of the crack tip upon crack advance is forwarded as responsible for crack closure in plane strain. It is argued that this model would hold only if the crack advanced into a compressive stress zone which is highly improbable. A third model based on compressive strain accumulation in the x-direction, εxp, (transverse or crack growth direction) is studied. Material ahead of the crack tip contracts in the transverse direction and this mechanism provides residual material for crack surfaces as the crack advances. Stress-strain history and material displacements as crack advances are presented for plane strain conditions that lend further support to the third model. The results are obtained with a specialized finite element analysis with provisions for crack advance and crack closure. The crack opening load corresponding to relief of compressive residual stresses behind the crack tip is determined for plane stress and plane strain cases under R= − 1, 0 and 0.3 loading. The load at which stresses ahead of the crack tip become tensile, Pt, is also determined for plane stress and plane strain conditions and is found to exceed the crack opening load in all cases. The relevance of this parameter on fatigue crack growth behavior is discussed.

Improved Compliance Solutions for C(T), SE(B) and Clamped SE(T) Specimens Including Side-Grooves, Varying Thicknesses and 3-D Effects

2014 ◽  
Author(s):  
Gustavo Henrique B. Donato ◽  
Felipe Cavalheiro Moreira
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Potential Drop ◽  
Crack Size ◽  
Growth Conditions ◽  
Size Estimation ◽  
Unloading Compliance ◽  
Integrity Assessments ◽  
Elastic Unloading

Fracture toughness and Fatigue Crack Growth (FCG) experimental data represent the basis for accurate designs and integrity assessments of components containing crack-like defects. Considering ductile and high toughness structural materials, crack growing curves (e.g. J-R curves) and FCG data (in terms of da/dN vs. ΔK or ΔJ) assumed paramount relevance since characterize, respectively, ductile fracture and cyclic crack growth conditions. In common, these two types of mechanical properties severely depend on real-time and precise crack size estimations during laboratory testing. Optical, electric potential drop or (most commonly) elastic unloading compliance (C) techniques can be employed. In the latter method, crack size estimation derives from C using a dimensionless parameter (μ) which incorporates specimen’s thickness (B), elasticity (E) and compliance itself. Plane stress and plane strain solutions for μ are available in several standards regarding C(T), SE(B) and M(T) specimens, among others. Current challenges include: i) real specimens are in neither plane stress nor plane strain - modulus vary between E (plane stress) and E/(1-ν2) (plane strain), revealing effects of thickness and 3-D configurations; ii) furthermore, side-grooves affect specimen’s stiffness, leading to an “effective thickness”. Previous results from current authors revealed deviations larger than 10% in crack size estimations following existing practices, especially for shallow cracks and side-grooved samples. In addition, compliance solutions for the emerging clamped SE(T) specimens are not yet standardized. As a step in this direction, this work investigates 3-D, thickness and side-groove effects on compliance solutions applicable to C(T), SE(B) and clamped SE(T) specimens. Refined 3-D elastic FE-models provide Load-CMOD evolutions. The analysis matrix includes crack depths between a/W=0.1 and a/W=0.7 and varying thicknesses (W/B = 4, W/B = 2 and W/B = 1). Side-grooves of 5%, 10% and 20% are also considered. The results include compliance solutions incorporating all aforementioned effects to provide accurate crack size estimation during laboratory fracture and FCG testing. All proposals revealed reduced deviations if compared to existing solutions.

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