Fatigue crack initiation from notch root (local-strain damage accumulation process on crack initiation)

1986 ◽  
Vol 23 (6) ◽  
pp. 983-989 ◽  
Author(s):  
Furuya Yasubumi ◽  
Shimada Heihachi
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Damage Accumulation ◽  
Notch Root ◽  
Fatigue Crack Initiation ◽  
Local Strain ◽  
Accumulation Process

Field Effects in Fatigue Crack Initiation: Long Life Fatigue Strength

1991 ◽  
Vol 113 (2) ◽  
pp. 188-194 ◽  
Author(s):  
S. D. Sheppard
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
Notch Root ◽  
Fatigue Crack Initiation ◽  
Stress Fields ◽  
Complex Geometries ◽  
The Finite Element Method ◽  
Long Life

This work is focused on explaining observed fatigue crack initiation behavior in notched members in terms of the stress state in a finite volume at the notch root. In principle, this is no different than the work of several other researchers. What is different is the manner in which the stress fields were predicted; namely using the finite element method. By using this approach, no approximations were necessary as to the form of the stress field at the notch root. This implies that this approach is extendable to complex geometries and to the finite life regime where plastic flow is expected at the notch root.

scholarly journals Thermomechanical fatigue crack initiation in disc alloys using a damage approach

2018 ◽  
Vol 165 ◽  
pp. 19007 ◽  
Author(s):  
Daniel Leidermark ◽  
Robert Eriksson ◽  
James P. Rouse ◽  
Christopher J. Hyde ◽  
Svjetlana Stekovic
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Damage ◽  
Damage Accumulation ◽  
Fatigue Crack Initiation ◽  
Stable State ◽  
Thermomechanical Fatigue ◽  
Good Prediction ◽  
Constitutive Behaviour ◽  
Fatigue Damage Accumulation

A fatigue crack initiation model based on damage accumulation via a fatigue memory surface in conjunction with a plastic strain energy parameter was evaluated for thermomechanical fatigue loading in a gas turbine disc alloy. The accumulated damage in each hysteresis loop was summed up, and it was assumed that the damage at the stable state is repeated until failure occurs. Crack initiation occurs when enough fatigue damage has been obtained, and the number of cycles can thus be directly determined. The fatigue damage is highly coupled to the constitutive behaviour of the material, where the constitutive behaviour was modelled using a non-linear hardening description. Based on this, a stable state was achieved and the obtained damage could be extracted. A user-defined material subroutine was implemented, incorporating both the constitutive description and the fatigue damage accumulation. The framework was adopted in a finite element context to evaluate the thermomechanical fatigue crack initiation life of the disc alloy RR1000. From the evaluation it could be seen that a good prediction of the thermomechanical fatigue life was achieved compared to performed experiments.

A New Extreme-Value Probabilistic Framework for Predicting Fatigue Crack Initiation Life of Notched Components

2011 ◽  
Author(s):  
Gbadebo Owolabi ◽  
Horace Whitworth
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Strain Field ◽  
Life Prediction ◽  
Notch Root ◽  
Fatigue Crack Initiation ◽  
Fatigue Life Prediction ◽  
Probabilistic Framework ◽  
Notched Components

Traditional deterministic methods for predicting the fatigue life of notched components require a number of approximations based on heuristics and phenomenological data rather than solid theoretical underpinning and still yield unsatisfactory and inconsistent results when applied to complex components under service loads. Microstructural inhomogeneities in the materials are still an important issue, but are not explicitly accounted for in the traditional deterministic methods. Recent developments in computational crystal plasticity and microstructure-scale modeling have provided deeper understanding of the complex correlations between properties and structures and further indicate the limitations of conventional fatigue life prediction approaches. These modeling approaches have the potential to substantially reduce the need for costly large scale experimental programs to determine scatter in fatigue, for example. At present, however, there is a lack of simulation-based strategy for considering interactive effects of stress/strain field gradients at the notch-root and microstructure-scale behavior in predicting notch-root fatigue crack initiation. In this paper, the distribution of a shear-based fatigue indicator parameter computed within a well-defined fatigue damage process zone at the notch are used along with a novel probabilistic mesomechanics approach to obtain the probability distribution of fatigue crack initiation of notched components, thus extending fatigue life prediction to explicitly incorporate microstructure sensitivity via probabilistic arguments. The new probabilistic framework presented in this paper takes into account the complete plastic shear strain field around the notch root and also links the variation in the materials microstructure and associated slip activations to observable scatter in fatigue strength of the notched component. The use of such probabilistic approach can be beneficial as it avoids conservatism that may result from the use of deterministic approach for fatigue life prediction.

Local Crack-Tip Strain Concept for Fatigue Crack Initiation and Propagation

1987 ◽  
Vol 109 (2) ◽  
pp. 101-106 ◽  
Author(s):  
Heihachi Shimada ◽  
Yasubumi Furuya
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Notch Root ◽  
Fatigue Crack Initiation ◽  
Crack Tip ◽  
Local Strain ◽  
Strain History ◽  
Crack Initiation And Propagation ◽  
Fine Grid ◽  
Initiation And Propagation

The existence of the unified local strain field where we can substantially combine the two fatigue stages, crack initiation and propagation, was experimentally confirmed. Using the fine-grid-method, the changes of local notch-root or crack-tip strain and these histories were investigated until the small elemental block of material was broken by crack initiation and propagation. It became clear that the crack-tip strain behavior and its fracture process showed the similarity with local strain damage accumulation on crack initiation process. Especially, when the local strain history in the “elemental size, ρ*” adjacent to the crack-tip was taken into account, very good agreement of two stages could be obtained, ρ* depended on the kind of material. Based on this result, we have proposed a new idea termed “local crack-tip strain concept” that has the possibility for more simple, one parameter approach for future fatigue life analysis. It qualitatively differs from the currently used macroscopic, two parameters approach by combining the gross-strain (Δεtotal) fatigue life curve and fracture mechanics parameter (ΔK).

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