Fracture Mechanics Consideration of Residual Stresses Introduced by Coldworking Fastener Holes

1980 ◽  
Vol 102 (1) ◽  
pp. 85-91 ◽  
Author(s):  
W. H. Cathey ◽  
A. F. Grandt
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fracture Mechanics ◽  
Test Specimen ◽  
Crack Size ◽  
Analysis Method ◽  
Constant Amplitude ◽  
Mechanics Analysis ◽  
Maximum Crack ◽  
Fatigue Crack Growth Life

Aluminum test specimens are prepared with precracked fastener holes, coldworked by means of an oversized mandrel, and then cycled to failure under constant amplitude loading. A simplified fracture mechanics analysis is performed to predict the fatigue crack growth life caused by the coldworking process. As discussed here, the analysis method is capable of obtaining reasonable estimates for the test specimen fatigue life and of determining the maximum crack size which can be “permanently” arrested by the coldworking process.

Fracture Mechanics Analysis of Fatigue Crack Repaired Joints

2004 ◽  
Author(s):  
J. Efrai´n Rodri´guez-Sa´nchez ◽  
William D. Dover ◽  
Feargal P. Brennan ◽  
Alejandro Rodri´guez-Castellanos
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fracture Mechanics ◽  
Structural Integrity ◽  
Offshore Structures ◽  
Assessment Process ◽  
Tubular Joints ◽  
Mechanics Analysis ◽  
Crack Repair ◽  
Inspection Data

Fatigue life predictions based on fracture mechanics calculations are required to satisfy an increasing level of safety demanded by industry. These predictions are mainly used to schedule NDT inspections and with inspection data make structural integrity assessments. The periodic inspection-assessment process can lead to the implementation of a fatigue crack repair by crack removal. Fracture mechanics analysis is used again to determine whether or not a repair will be effective. For the case of tubular joints, in offshore structures, once repairs have been shown to be ineffective it is usually required to install a clamp to maintain the continuity of joint members if the structure is still required for production. In this paper a fracture mechanics analysis of crack repaired joints based on Y factors is presented. The analysis is used to predict fatigue life after crack removal and is validated against T-butts experimental data. The analysis is also extrapolated for the prediction of fatigue life of crack repaired tubular joints.

Fracture Mechanics Analysis of Fatigue Crack Repaired Joints

2004 ◽  
Vol 127 (2) ◽  
pp. 182-189 ◽  
Author(s):  
J. Efraín Rodríguez-Sánchez ◽  
William D. Dover ◽  
Feargal P. Brennan ◽  
Alejandro Rodríguez Castellanos
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fracture Mechanics ◽  
Structural Integrity ◽  
Offshore Structures ◽  
Assessment Process ◽  
Tubular Joints ◽  
Mechanics Analysis ◽  
Crack Repair ◽  
Inspection Data

Fatigue life predictions based on fracture mechanics calculations are required to satisfy an increasing level of safety demanded by industry. These predictions are mainly used to schedule NDT inspections and with inspection data make structural integrity assessments. The periodic inspection-assessment process can lead to the implementation of a fatigue crack repair by crack removal. Fracture mechanics analysis is used again to determine whether or not a repair will be effective. For the case of tubular joints, in offshore structures, once repairs have been shown to be ineffective it is usually required to install a clamp to maintain the continuity of joint members if the structure is still required for production. In this paper a fracture mechanics analysis of crack repaired joints based on Y factors is presented. The analysis is used to predict fatigue life after crack removal and is validated against T-butts experimental data. The analysis is also extrapolated for the prediction of fatigue life of crack repaired tubular joints.

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.

A Probabilistic Micromechanical Code for Predicting Fatigue Life Variability: Model Development and Application

2005 ◽  
Vol 128 (4) ◽  
pp. 889-895 ◽  
Author(s):  
K. S. Chan ◽  
M. P. Enright
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Initiation ◽  
Crack Growth ◽  
Model Development ◽  
Fatigue Crack Initiation ◽  
Crack Size ◽  
Crack Initiation Life ◽  
Variability Model

This paper summarizes the development of a probabilistic micromechanical code for treating fatigue life variability resulting from material variations. Dubbed MICROFAVA (micromechanical fatigue variability), the code is based on a set of physics-based fatigue models that predict fatigue crack initiation life, fatigue crack growth life, fatigue limit, fatigue crack growth threshold, crack size at initiation, and fracture toughness. Using microstructure information as material input, the code is capable of predicting the average behavior and the confidence limits of the crack initiation and crack growth lives of structural alloys under LCF or HCF loading. This paper presents a summary of the development of the code and highlights applications of the model to predicting the effects of microstructure on the fatigue crack growth response and life variability of the α+β Ti-alloy Ti-6Al-4V.

Aeromechanical Modeling of Rotating Fan Blades to Investigate High-Cycle and Low-Cycle Fatigue Interaction

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Priyanka Dhopade ◽  
Andrew J. Neely
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Low Cycle Fatigue ◽  
Numerical Approach ◽  
Combined Loading ◽  
Design Stage ◽  
Cycle Fatigue ◽  
Mechanics Analysis ◽  
The Individual ◽  
Loading Spectrum

Gas turbine engine components are subject to both low-cycle fatigue (LCF) and high-cycle fatigue (HCF) loads. To improve engine reliability, durability and maintenance, it is necessary to understand the interaction of LCF and HCF in these components, which can adversely affect the overall life of the engine while they are occurring simultaneously during a flight cycle. A fully coupled aeromechanical fluid–structure interaction (FSI) analysis in conjunction with a fracture mechanics analysis was numerically performed to predict the effect of representative fluctuating loads on the fatigue life of blisk fan blades. This was achieved by comparing an isolated rotor (IR) to a rotor in the presence of upstream inlet guide vanes (IGVs). A fracture mechanics analysis was used to combine the HCF loading spectrum with an LCF loading spectrum from a simplified engine flight cycle in order to determine the extent of the fatigue life reduction due to the interaction of the HCF and LCF loads occurring simultaneously. The results demonstrate the reduced fatigue life of the blades predicted by a combined loading of HCF and LCF cycles from a crack growth analysis, as compared to the effect of the individual cycles. In addition, the HCF aerodynamic forcing from the IGVs excited a higher natural frequency of vibration of the rotor blade, which was shown to have a detrimental effect on the fatigue life. The findings suggest that FSI, blade–row interaction and HCF/LCF interaction are important considerations when predicting blade life at the design stage of the engine. The lack of available experimental data to validate this problem emphasizes the utility of a numerical approach to first examine the physics of the problem and second to help establish the need for these complex experiments.

Research on Fatigue Life of Autofrettaged Thick-Walled Cylinder in Probabilistic Fracture Mechanics

2012 ◽  
Vol 249-250 ◽  
pp. 36-39 ◽  
Author(s):  
Ai Jun Chen ◽  
Zi Chu Cha ◽  
Zhi Qun Wang
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Bauschinger Effect ◽  
Fatigue Cracks ◽  
Analysis Method ◽  
Intensity Factors ◽  
Probabilistic Fracture Mechanics ◽  
Best Fit ◽  
Elliptical Cracks ◽  
Walled Cylinder

Based on the theory of probabilistic fracture mechanics and Monte Carlo simulation, reliability analysis method for fatigue life of autofrettaged thick-walled cylinder was given. The forms of fatigue cracks in bore of autofrettaged thick-walled cylinder were considered as semi-elliptical cracks. The autofrettage residual stress solution was suitable for the thick-walled cylinder made of steel with strain hardening and Bauschinger effect. The stress intensity factors of thick-walled cylinder were calculated according to weight function method. The analysis of the examples showed that lognormal distribution is the best fit for fatigue life. Finally, the fatigue life of autofrettaged thick-walled on the condition of different reliabilities and confidences were presented.

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