Prediction of Fatigue Crack Growth of Aged Hardening Al-Alloys under Variable Amplitude Loading

2014 ◽  
Vol 891-892 ◽  
pp. 1729-1735
Author(s):  
Mustapha Benachour ◽  
Boumedienne Zeggai ◽  
Nadjia Benachour ◽  
Mohamed Benguediab ◽  
Abdelkader Belmokhtar
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Al Alloys ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
R Ratio ◽  
Single Overload ◽  
Crack Growth Rates

In this investigation, variable amplitude loading effect was studied on aged hardening Al-alloys in series 2000 and 7000. Generalised Willenborg model was used in order to show loading interaction effects (overload effects). Variable amplitude loading under different form of spectrum has affected highly the fatigue life and fatigue crack growth rates. Fatigue lives were increased and fatigue crack growth rates (FCGRs) were decreased in increasing of overload ratio in single overload case. In application of overload band, the fatigue lives and FCGRs were affected by band overload and R-ratio of them when level in FCGRs was increased.

Fracture and Fatigue Tolerant Steel Pressure Vessels for Gaseous Hydrogen

2010 ◽  
Author(s):  
Kevin A. Nibur ◽  
Chris San Marchi ◽  
Brian P. Somerday
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Maximum Load ◽  
Pressure Vessels ◽  
Hydrogen Gas ◽  
R Ratio ◽  
History Of ◽  
Crack Growth Rates

Fatigue crack growth rates and rising displacement fracture thresholds have been measured for a 4130X steel in 45 MPa hydrogen gas. The ratio of minimum to maximum load (R-ratio) and cyclic frequency was varied to assess the effects of these variables on fatigue crack growth rates. Decreasing frequency and increasing R were both found to increase crack growth rate, however, these variables are not independent of each other. Changing frequency from 0.1 Hz to 1 Hz reduced crack growth rates at R = 0.5, but had no effect at R = 0.1. When applied to a design life calculation for a steel pressure vessel consistent with a typical hydrogen trailer tube, the measured fatigue and fracture data predicted a re-inspection interval of nearly 29 years, consistent with the excellent service history of such vessels which have been in use for many years.

Analysis of the Effect of Load Ratio on Fatigue Crack Growth

2011 ◽  
Vol 181-182 ◽  
pp. 330-336 ◽  
Author(s):  
Ying Xiong
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Multiaxial Fatigue ◽  
Cyclic Plasticity ◽  
Plasticity Model ◽  
R Ratio ◽  
Crack Growth Rates ◽  
Fatigue Criterion

In this paper, fatigue test and numerical simulation are carried out for Q345 weld joint under constant amplitude loading at different R-ratio using the compact tension samples with 3.8mm thickness. The result indicates that fatigue crack growth rates in the base metal is not sensitive to R-ratio, but the fatigue crack growth rates increases in the weld zone with R-ratio increasing. The effect of R-ratio on fatigue crack growth is analyzed based on J-S cycle plasticity model and Jiang’s multiaxial fatigue criterion. The finite element method (FEM) is used for the stress-strain analysis with the implementation of an accurate J-S cyclic plasticity model. With the detailed stresses and strains, fatigue damage assessment is made using a Jiang’s multiaxial fatigue criterion.

Fatigue Crack Growth Rates for Ferritic Steels Under Negative R Ratio

2016 ◽  
Author(s):  
Kunio Hasegawa ◽  
Vratislav Mares ◽  
Yoshihito Yamaguchi ◽  
Yinsheng Li
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Growth Rates ◽  
Ferritic Steels ◽  
R Ratio ◽  
Asme Code ◽  
Reference Curves ◽  
Crack Growth Rates

Reference curves of fatigue crack growth rates for ferritic steels in air environment are provided by the ASME Code Section XI Appendix A. The fatigue crack growth rates under negative R ratio are given as da/dN vs. Kmax, It is generally well known that the growth rates decreases with decreasing R ratios. However, the da/dN as a function of Kmax are the same curves under R = 0, −1 and −2. In addition, the da/dN increases with decreasing R ratio for R < −2. This paper converts from da/dN vs. Kmax to da/dN vs. ΔKI, using crack closure U. It can be obtained that the growth rates da/dN as a function of ΔKI decrease with decreasing R ratio for −2 ≤ R < 0. It can be seen that the growth rate da/dN vs. ΔKI is better equation than da/dN vs. Kmax from the view point of stress ratio R. Furthermore, extending crack closure U to R = −5, it can be explained that the da/dN decreases with decreasing R ratio in the range of −5 ≤ R < 0. This tendency is consistent with the experimental data.

Fatigue Crack Growth Rate Analysis in a Titanium Alloy

2008 ◽  
Vol 385-387 ◽  
pp. 5-8
Author(s):  
Alexander M. Korsunsky ◽  
Daniele Dini ◽  
Michael J. Walsh
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Complex Load ◽  
R Ratio ◽  
Lower Amplitude ◽  
Crack Growth Rates

Reliable prediction of fatigue crack growth rates in aerospace materials and components underpins the so-called defect-tolerant approach to lifing. In this methodology the presence or appearance of defects and cracks in components is accepted. However, safe operation is guaranteed by regular inspections and health monitoring, and ensuring (by means of reliable modelling) that no crack may grow far enough to reach the critical size in the interval between inspections. Under such circumstances it is clear that particular attention has to be paid to the development and validation of predictive modelling capabilities for fatigue crack propagation. The situation is complicated by the fact that it is often a challenge to represent correctly the in-service loading experienced by a cracked component. In practice, on top of the major cycles associated with each flight (LCF component), cycles of higher frequency and lower amplitude are also present (HCF component). Sensitivity to dwell at maximum load is also often observed. Furthermore, it is well established that complex load sequences involving overloads and underloads result in fluctuations of fatigue crack growth rates (retardation and acceleration) that must be accounted for in crack growth calculations. In the present study we consider the application of an approach due to Noroozi et al. [1] to the analysis of R-ratio effects in Ti-6Al-4V material, on the basis of the experimental crack growth rate data collected under the auspices of AGARD programme [2]. The approach shows promising results, and has the capacity to capture loading sequence effects.

Reference Curve of Fatigue Crack Growth for Ferritic Steels Under Negative R Ratio Provided by ASME Code Section XI

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Kunio Hasegawa ◽  
Vratislav Mares ◽  
Yoshihito Yamaguchi
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Growth Rates ◽  
Ferritic Steels ◽  
Reference Curve ◽  
R Ratio ◽  
Asme Code ◽  
Crack Growth Rates

Reference curves of fatigue crack growth rates for ferritic steels in air environment are provided by the ASME Code Section XI Appendix A. The fatigue crack growth rates under negative R ratio are given as da/dN versus Kmax. It is generally well known that the growth rates decreases with decreasing R ratios. However, the da/dN as a function of Kmax are the same curves under R = 0, −1, and −2. In addition, the da/dN increases with decreasing R ratio for R < −2. This paper converts from da/dN versus Kmax to da/dN versus ΔKI, using crack closure U. It can be obtained that the growth rates da/dN as a function of ΔKI decrease with decreasing R ratio for −2 ≤ R < 0. It can be seen that the growth rate da/dN versus ΔKI is better equation than da/dN versus Kmax from the view point of stress ratio R. Furthermore, extending crack closure U to R = −5, it can be explained that the da/dN decreases with decreasing R ratio in the range of −5 ≤ R < 0. This tendency is consistent with the experimental data.

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