A fracture mechanics analysis of fatigue crack growth in a complex cross section

1996 ◽  
Vol 3 (4) ◽  
pp. 249-265 ◽  
Author(s):  
A.I Rifani ◽  
A.F Grandt
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Cross Section ◽  
Complex Cross ◽  
Complex Cross Section ◽  
Mechanics Analysis

Fracture Mechanics Analysis of a Single Crystal Turbine Blade

2010 ◽  
Author(s):  
X. Wu ◽  
W. Beres ◽  
Z. Zhang ◽  
P. A. S. Reed
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Single Crystal ◽  
Crack Growth ◽  
Turbine Blade ◽  
Maximum Temperature ◽  
J Integral ◽  
Single Crystal Turbine Blade ◽  
Mechanics Analysis

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.

Effective Modeling of Fatigue Crack Growth in Pipelines

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.

Fatigue Life Prediction Based on Probabilistic Fracture Mechanics: Case Study of Automotive Parts

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
Mahboubeh Yazdanipour ◽  
Mohammad Pourgol-Mohammad ◽  
Naghd-Ali Choupani ◽  
Mojtaba Yazdani
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Probabilistic Models ◽  
Fatigue Loading ◽  
Critical Fields ◽  
Propagation Of Uncertainty ◽  
Automotive Parts ◽  
Crack Growth Model

This paper studies the stochastic behavior of fatigue crack growth analytically and empirically by employing basic models in fracture mechanics. The research estimates the crack growth rate probabilistically, quantifies the uncertainty of probabilistic models under fatigue loading in automotive parts, and applies the simulations on W319 aluminum alloy, which has vast applications in automotive components’ products. Walker and Forman correlations are used in the paper. The deterministic simulations of these models are verified with afgrow code and validated experimentally with fatigue data of W319 aluminum. Then, the models are treated probabilistically by considering the models’ parameters stochastic. Monte Carlo (MC) simulation is employed to investigate the models under stochastic conditions. The paper is quantifies the propagation of uncertainty with calculating the standard deviations of crack lengths via cycles. The proposed procedure is useful for selecting a proper probabilistic fatigue crack growth model in specific applications and can be used in future fatigue studies not only in the automotive industry but also in other critical fields, to obtain more reliable conclusions.

Assessment of Pipeline Fatigue Crack-Growth Life

2006 ◽  
Author(s):  
Carl E. Jaske
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Flaw Size ◽  
Stress Intensity Factor Range ◽  
Loading History ◽  
Fatigue Crack Growth Life ◽  
Number Of Cycles

This paper describes an accepted approach for predicting fatigue crack-growth life in pipelines. Fatigue life is computed as the number of cycles for a crack-like flaw to grow from an initial size to a final critical size. This computation is performed by integrating a fracture-mechanics model for fatigue crack growth. The initial flaw size is estimated either from inspection results or by using fracture mechanics to predict the largest flaw that would have survived a hydrostatic pressure test. The final flaw size is estimated using fracture mechanics. Fracture-mechanics models for computing fatigue crack growth and predicting flaw size are reviewed. The anticipated cyclic loading must be characterized to perform the crack-growth calculations. Typically, cyclic loading histories, such as pressure cycle data, are analyzed and used to estimate future loadings. To utilize the crack-growth models, the cycles in the loading history must be counted. The rainflow cycle counting procedure is used to characterize the loading history and develop a histogram of load range versus number of cycles. This histogram is then used in the fatigue crack-growth analysis. Results of example calculations are discussed to illustrate the procedure and show the effects of periodic hydrostatic testing, threshold stress intensity factor range, and pressure ratio on predicted fatigue crack-growth life.

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