A fracture mechanics analysis of fatigue crack growth data for various materials

Single crystal superalloy turbine blades exhibit anisotropic behaviors, and the stress at the fir-tree root often reaches the yield stress of the material when the turbine operates at the peak rotational speed and at the maximum temperature. The nonlinear behavior of the material character at these operating conditions poses a significant challenge to prediction of the blade behavior using the conventional linear elastic fracture mechanics approach. In this paper a fracture mechanics analysis was performed for a single crystal turbine blade using the J-integral concept. First of all, the elastic-perfectly plastic J-integral and CTOD was used to correlate with the fatigue crack growth rates obtained in a single crystal blade in [100] and [110] directions, with the [001] direction as the loading direction under typical service conditions. The weight function method was used to evaluate the stress intensity factor for a crack growing along the serration bottom of the blade fir-tree root under small-scale yielding conditions and the crack growth analysis was performed using the correlated fatigue crack growth data. In addition, crack growth simulations were also performed using the Zencrack software. The simulated crack growth profile was compared with the actual crack profile on the component.

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Effective Modeling of Fatigue Crack Growth in Pipelines

Volume 6: Materials and Fabrication, Parts A and B ◽

10.1115/pvp2012-78575 ◽

2012 ◽

Author(s):

Steven J. Polasik ◽

Carl E. Jaske

Keyword(s):

Fatigue Crack ◽

Stress Intensity ◽

Fatigue Crack Growth ◽

Fracture Mechanics ◽

Crack Growth ◽

Growth Models ◽

Critical Parameters ◽

Operating Pressure ◽

Mechanics Model ◽

Key Variables

Pipeline operators must rely on fatigue crack growth models to evaluate the effects of operating pressure acting on flaws within the longitudinal seam to set re-assessment intervals. In most cases, many of the critical parameters in these models are unknown and must be assumed. As such, estimated remaining lives can be overly conservative, potentially leading to unrealistic and short reassessment intervals. This paper describes the fatigue crack growth methodology utilized by Det Norske Veritas (USA), Inc. (DNV), which is based on established fracture mechanics principles. DNV uses the fracture mechanics model in CorLAS™ to calculate stress intensity factors using the elastic portion of the J-integral for either an elliptically or rectangularly shaped surface crack profile. Various correction factors are used to account for key variables, such as strain hardening rate and bulging. The validity of the stress intensity factor calculations utilized and the effect of modifying some key parameters are discussed and demonstrated against available data from the published literature.

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Effect of Hardness and Tensile Mean Stress on Fatigue Crack Growth in Beryllium Copper

Journal of Mechanical Engineering Science ◽

10.1243/jmes_jour_1969_011_041_02 ◽

1969 ◽

Vol 11 (3) ◽

pp. 343-349 ◽

Cited By ~ 2

Author(s):

L. P. Pook

Keyword(s):

Growth Rate ◽

Fatigue Crack ◽

Crack Growth Rate ◽

Fatigue Crack Growth ◽

Residual Stresses ◽

Crack Growth ◽

Fatigue Crack Growth Rate ◽

Mean Stress ◽

Growth Data ◽

Beryllium Copper

Some fatigue crack growth data have been obtained for age-hardened beryllium copper. The fatigue crack growth rate was found to be very dependent on the hardness and tensile mean stress. This dependence is believed to be associated with the intense residual stresses surrounding Preston-Guinier zones.

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