scholarly journals Simulation of near-tip crack behaviour and its correlation to fatigue crack growth with a modified strip-yield model

2008 ◽  
Vol 5 (1) ◽  
pp. 77 ◽  
Author(s):  
Lei Wang ◽  
Yongkang Chen ◽  
William Tiu ◽  
Yigeng Xu
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Yield Model ◽  
Strip Yield Model

Explicit and Implicit Lifetime Assessment Methods of 9Cr-1Mo Steel Under Combined Creep and Fatigue Loads Using a Strip Yield Model

2014 ◽  
Author(s):  
B. Andrews ◽  
G. P. Potirniche
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Constitutive Equations ◽  
Crack Extension ◽  
Cyclic Loads ◽  
Yield Model ◽  
Creep Crack ◽  
Strip Yield Model

Growing demand for clean, affordable energy has driven the power industry towards generation plants with higher thermal efficiency and higher operating temperatures. ASTM Grade 91 is a high chromium (9Cr-1Mo) creep resistant steel commonly used in high temperature pressure vessel and piping applications. These service conditions often involve a combination of stationary and cyclic loads at elevated temperatures. Lifecycle assessments of components under such conditions require modeling of both creep and fatigue behaviors. This paper develops two approaches to modeling mixed creep and fatigue crack growth for lifetime assessment of high service temperature components. Both approaches model fatigue crack growth using the Paris law integrated over the number of lifetime cyclic reversals to obtain crack extension. A strip yield model is used to characterize the crack tip stress-strain fields. The first approach employed an explicit method to approximate creep crack growth using C* as a crack tip parameter characterizing creep crack extension. The Norton power law was explicitly solved to model the primary and secondary stages of creep. The second approach used an implicit method to solve a set of constitutive equations based on properties of the material microstructure to model all creep stages. Constitutive equations were fit to experimental data collected at stresses 10–60% of yield and temperatures 550–650°C. These methods were compared to published experimental data under purely stationary loads, purely cyclic loads and mixed loading. Both models showed good agreement with experimental data in the stress and temperature conditions considered.

Numerical Simulation of Fatigue Crack Growth Based on Strip Yield Model Considering Work Hardening of Materials

2010 ◽  
Author(s):  
Koji Gotoh ◽  
Keisuke Harada
Keyword(s):  
Numerical Simulation ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Work Hardening ◽  
Plastic Material ◽  
Elastic Behaviour ◽  
Yield Model ◽  
Hardening Effect ◽  
Strip Yield Model

This paper presents the improved numerical simulation of fatigue crack growth considering the crack opening / closing behaviour based on the strip yield model with the stress intensity factor weight function. The mechanical property in the primitive model corresponds to rigid-plastic material and is replaced to the elastic - perfectly plastic material in order to describe the elastic behaviour of material around a crack tip during the unloading process. However, the simulation model based on the elastic - perfect plastic material gives poor growth estimations under rapidly changing of loading histories, e.g. the spike loading. The possibility is pointed out that insufficient considerations of work hardening effect of materials lead the excess crack closure in the numerical simulations. Authors propose the improved numerical simulation fatigue crack growth considering the work hardening effect of materials in this paper. Comparison of proposed simulation results with previous ones and with measured results confirms the primacy of proposed method over previous ones.

Improvement of Fatigue Crack Growth Simulation Based on the Strip Yield Model Considering the Strain Hardening Effect of Materials

2012 ◽  
Author(s):  
Koji Gotoh ◽  
Keisuke Harada
Keyword(s):  
Numerical Simulation ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Strain Hardening ◽  
Crack Growth ◽  
Model Comparison ◽  
Yield Model ◽  
Poor Growth ◽  
Hardening Effect ◽  
Strip Yield Model

This paper presents an improved numerical simulation procedure for fatigue crack growth based on the strip yield model with a weight function. In the previous numerical model, one-dimensional bar elements plugged up the chink corresponding to the virtual crack opening displacement in the plastic zone to describe the crack wake over fatigue crack surfaces. However, this numerical simulation method gives poor growth estimations under large variable loading histories, e.g. spike overloading. It is possible that insufficient consideration of the strain hardening effect of materials leads to excess crack closure. The authors develop the numerical simulation model of fatigue crack growth by considering the strain hardening effect of materials using the modified strip yield model. Numerical simulations of fatigue crack growth under many types of loading are performed to investigate the validity of our new proposed model. Comparison of proposed simulation results with previous results and with experimental measurements confirms the superiority of the proposed method.

scholarly journals Modeling of creep-fatigue interaction effects on crack growth at elevated temperatures

2018 ◽  
Vol 165 ◽  
pp. 05004 ◽  
Author(s):  
Gabriel P. Potirniche
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Loading ◽  
Yield Model ◽  
Strip Yield Model ◽  
Creep Fatigue ◽  
Creep Fatigue Crack ◽  
Crack Growth Rates

The well-known load frequency effect on creep-fatigue crack growth is explained by the interactions between fatigue and creep loading and is quantified using the concept of plasticity-induced crack closure. It is shown that the hold time during creep loading affects crack growth rates during subsequent fatigue cycles. Longer hold times lead to lower crack-tip opening stresses and faster crack growth rates during fatigue loading. To model the impact of hold time on crack opening stresses during fatigue loading, a strip-yield model was developed for creep-fatigue crack growth. The strip-yield model computes crack-tip opening stresses, which determine the effective stress intensity factor range and crack growth rate during the fatigue portion of each loading cycle. Maximum stress intensity factor is used to compute the crack growth rate during the creep portion of each cycle. The proposed strip-yield model is used to compute creep-fatigue crack growth rates for several structural materials, i.e., an Astroloy, aluminium alloy 2650 and 316 stainless steel. The model predictions of crack growth rates compare well with published experimental data for these alloys. This model achieves reliable predictions of crack growth rates and life prediction on components subjected to creep-fatigue loading at elevated temperatures by considering loading interaction effects.

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