A Fracture Mechanics Based Methodology for Fatigue Life Prediction of Single Crystal Nickel Based Superalloys

2006 ◽  
Author(s):  
Srikant Ranjan ◽  
Nagaraj K. Arakere
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Single Crystal ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
Mixed Mode ◽  
Life Prediction ◽  
Mixed Mode Loading ◽  
Intensity Factors

A comprehensive fracture mechanics based life prediction methodology is presented for FCC (Face Centered Cubic) single crystal components, based on computation of stress intensity factors (SIFs), and modeling the crystallographic fatigue crack growth process, under mixed-mode loading conditions. The 3D finite element numerical procedure presented for computing SIFs for anisotropic materials under mixed-mode loading is very general, and not just specific to FCC single crystals. Stress intensity factors for a Brazilian Disc (BD) specimen are presented for the crack on the {111} plane in the 〈101〉 and 〈121〉 directions, which represent the primary and secondary slip directions. Variation of SIFs as a function of thickness is also presented. Modeling of the crystallographic fatigue crack growth (FCG) behavior is performed by using the resolved shear stress intensity coefficient (RSSIC), Krss. This parameter is sensitive to the grain orientation and is based on the resolved shear stresses on the slip planes at the crack tip, which is useful in identifying the active crack plane as well as predicting the crack growth direction. A multiaxial fatigue crack driving force parameter, ΔKrss, was quantified, which can be used to predict the FCG rate and hence life in single crystal components subject to mixed mode fatigue loading.

A Fracture-Mechanics-Based Methodology for Fatigue Life Prediction of Single Crystal Nickel-Based Superalloys

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Srikant Ranjan ◽  
Nagaraj K. Arakere
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Single Crystal ◽  
Crack Growth ◽  
Mixed Mode ◽  
Life Prediction ◽  
Shear Stresses ◽  
Crack Plane ◽  
Mixed Mode Loading

A comprehensive fracture-mechanics-based life prediction methodology is presented for fcc single crystal components based on the computation of stress intensity factors (SIFs), and the modeling of the crystallographic fatigue crack growth (FCG) process under mixed-mode loading conditions. The 3D finite element numerical procedure presented for computing SIFs for anisotropic materials under mixed-mode loading is very general and not just specific to fcc single crystals. SIFs for a Brazilian disk specimen are presented for the crack on the {111}) plane in the ⟨101⟩ and ⟨121⟩ directions, which represent the primary and secondary slip directions. Variation of SIFs as a function of thickness is also presented. Modeling of the crystallographic FCG behavior is performed by using the resolved shear stress intensity coefficient, Krss. This parameter is sensitive to the grain orientation and is based on the resolved shear stresses on the slip planes at the crack tip, which is useful in identifying the active crack plane as well as in predicting the crack growth direction. A multiaxial fatigue crack driving force parameter, ΔKrss, was quantified, which can be used to predict the FCG rate and, hence, life in single crystal components subject to mixed-mode fatigue loading.

scholarly journals Computational Simulation of 3D Fatigue Crack Growth under Mixed-Mode Loading

2021 ◽  
Vol 11 (13) ◽  
pp. 5953
Author(s):  
Abdulnaser M. Alshoaibi
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
Mixed Mode ◽  
Intensity Factors ◽  
Linear Elastic ◽  
Growth Studies

The purpose of this research was to present a simulation modelling of a crack propagation trajectory in linear elastic material subjected to mixed-mode loadings and investigate the effects of the existence of a hole and geometrical thickness on fatigue crack growth and fatigue life under constant amplitude loading. For various geometry thickness, mixed-mode (I/II) fatigue crack growth studies were carried out to utilize a single edge cracked plate with three holes and compact tension shear specimens with various loading angles. Smart Crack Growth Technology, a new feature in ANSYS, was used in ANSYS Mechanical APDL 19.2 to predict the cracks’ propagation trajectory and their consequent fatigue life associated with evaluating the stress intensity factors. The maximum circumferential stress criterion is implemented as a direction criterion under linear elastic fracture mechanics (LEFM). According to the hole position, the results demonstrate that the fatigue crack grows towards the hole due to the unbalanced stresses on the hole induced crack tip. The results of this simulation are verified in terms of crack growth paths, stress intensity factors, and fatigue life under mixed-mode load conditions, with several crack growth studies published in the literature showing consistent results.

On the Characterization of Fatigue Crack Growth in a Plate With a Single-Sided Repair

2004 ◽  
Vol 126 (2) ◽  
pp. 192-198 ◽  
Author(s):  
C. N. Duong ◽  
C. H. Wang
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
Load Path ◽  
Intensity Factors ◽  
Analytical Work ◽  
Out Of Plane ◽  
Plane Bending

An unsupported cracked plate repaired with a reinforcement bonded on one side may experience considerable out-of-plane bending due to the load-path eccentricity. This out-of-plane bending causes the stress intensity factor at the crack tip to vary significantly through the plate’s thickness with a maximum value attained at the un-patched side of the crack. Even though significant analytical work has been done in the past to evaluate these thickness-varying stress intensity factors, however, to the authors’ knowledge, little work has been done to characterize the fatigue crack growth in a plate with a single-sided repair. The purposes of the present work are to (i) assess the accuracy of the available analytical methods for predicting the stress intensity factors of the panels with a single-sided repair and more importantly, and (ii) characterize the fatigue crack growth in these panels, using test results generated recently under the Composite Repair of Aircraft Structures (CRAS) program.

Effect fracture resistance on retardation of crack growth

2015 ◽  
Vol 6 (4) ◽  
pp. 510-521
Author(s):  
Jirí Behal ◽  
Petr Homola ◽  
Roman Ružek
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Aluminium Alloy ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
High Stress ◽  
Intensity Factors ◽  
Content Type

Purpose – The prediction of fatigue crack growth behaviour is an important part of damage tolerance analyses. Recently, the author’s work has focused on evaluating the FASTRAN retardation model. This model is implemented in the AFGROW code, which allows different retardation models to be compared. The primary advantage of the model is that all input parameters, including those for an initial plane-strain state and its transition to a plane-stress-state, are objectively measured using standard middle-crack-tension M(T) specimens. The purpose of this paper is to evaluate the ability of the FASTRAN model to predict correct retardation effects due to high loading peaks that occur during variable amplitude loading in sequences representative of an aircraft service. Design/methodology/approach – This paper addresses pre-setting of the fracture toughness K R (based on J-integral J Q according to ASTM1820) in the FASTRAN retardation model. A set of experiments were performed using specimens made from a 7475-T7351 aluminium alloy plate. Loading sequences with peaks ordered in ascending-descending blocks were used. The effect of truncating and clipping selected load levels on crack propagation behaviour was evaluated using both experimental data and numerical analyses. The findings were supported by the results of a fractographic analysis. Findings – Fatigue crack propagation data defined using M(T) specimens made from Al 7475-T7351 alloy indicate the difficulty of evaluating the following two events simultaneously: fatigue crack increments after application of loads with maximum amplitudes that exceeded J Q and subcritical crack increments caused by loads at high stress intensity factors. An effect of overloading peaks with a maximum that exceeds J Q should be assessed using a special analysis beyond the scope of the FASTRAN retardation model. Originality/value – Measurements of fatigue crack growth on specimens made from 7475 T7351 aluminium alloy were carried out. The results indicated that simultaneously evaluating fatigue crack increments after application of the load amplitude above J Q and subcritical increments caused by the loads at high stress intensity factors is difficult. Experiments demonstrated that if the fatigue crack reaches a specific length, the maximal amplitude load induces considerable crack growth retardation.

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