Fatigue crack growth modelling by successive blocking of dislocations

1992 ◽  
Vol 437 (1900) ◽  
pp. 375-390 ◽  
Keyword(s):  
Plastic Zone ◽  
Crack Growth ◽  
Driving Force ◽  
Transition Point ◽  
Growth Modelling ◽  
Microstructural Parameter ◽  
Critical Position ◽  
Crack Driving Force ◽  
Short Cracks ◽  
The Moment

Work hardening and the study of instability is incorporated into the description of the growth of a crack in terms of the successive blocking of the plastic zone by slip barriers, such as grain boundaries, and the subsequent initiation of the slip in neighbouring grains. A simple equation is derived to determine the critical position of the crack tip in relation to the grain boundary where the plastic zone is blocked at the moment of slip transmission. The intermittent pattern of decelerating and accelerating behaviour of short cracks and the existence of non-propagating cracks is explained. Instability in crack growth is seen to occur when the rate of hardening is insufficient to compensate for the increase in crack driving force in relation to the increase in crack length. This is associated with fracture toughness. The transition point between the short and long crack régimes is seen to occur when the size of the plastic zone is of the order of the microstructural parameter.

scholarly journals Short fatigue crack growth in welded joints described by the effective cyclic J-integral

2018 ◽  
Vol 165 ◽  
pp. 09002
Author(s):  
Désiré Tchoffo Ngoula ◽  
Michael Vormwald
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Residual Stresses ◽  
Crack Growth ◽  
Welded Joints ◽  
Driving Force ◽  
J Integral ◽  
Crack Driving Force ◽  
Short Fatigue Crack

The purpose of the present contribution is to predict the fatigue life of welded joints by using the effective cyclic J-integral as crack driving force. The plasticity induced crack closure effects and the effects of welding residual stresses are taken into consideration. Here, the fatigue life is regarded as period of short fatigue crack growth. The node release technique is used to perform finite element based crack growth analyses. For fatigue lives calculations, the effective cyclic J-integral is employed in a relation similar to the Paris (crack growth) equation. For this purpose, a specific code was written for the determination of the effective cyclic J-integral for various lifetime relevant crack lengths. The effects of welding residual stresses on the crack driving force and the calculated fatigue lives are investigated. Results reveal that the influence of residual stresses can be neglected only for large load amplitudes. Finally, the predicted fatigue lives are compared with experimental data: a good accordance between both results is achieved.

A Fatigue Crack Driving Force Parameter

2008 ◽  
Author(s):  
Ying Xiong ◽  
Zengliang Gao ◽  
Junichi Katsuta ◽  
Takeshi Sakiyama
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Driving Force ◽  
Crack Tip ◽  
Force Model ◽  
Crack Driving Force ◽  
R Ratio ◽  
Two Parameter ◽  
Better Than

Most of the previous parameters that utilized as a crack driving force were established in modifying the parameter Kop in Elber’s effective SIF range (ΔKeff = Kmax–Kop). This paper focuses on the physical meaning of compliance changes caused by plastic deformation at the crack tip, the test was carried out for structural steel under constant amplitude loading, and differences of several parameter ΔKeff in literature are analyzed quantificationally. The effect of actual stress amplitude at the crack tip on fatigue crack growth is investigated, and improved two-parameter driving force model ΔKdrive(=Kmax)n(ΔK^)1−n) has been proposed. Experimental data for several different types of materials taken from literature were used in the analyses. Presented results indicate that the parameter ΔKdrive is equally effective or better than ΔK(=Kmax-Kmin), ΔKeff(=Kmax-Kop) and ΔK*(=(Kmax)α(ΔK+)1−α) in correlating and predicting the R-ratio effects on fatigue crack growth rate.

Crack Tip Shielding from a Plastic ‘Inclusion’

2011 ◽  
Vol 465 ◽  
pp. 1-8
Author(s):  
M. Neil James ◽  
C.J. Christopher ◽  
Yan Wei Lu ◽  
K.F. Tee ◽  
Eann A Patterson
Keyword(s):  
Plastic Deformation ◽  
Fracture Mechanics ◽  
Plastic Zone ◽  
Crack Growth ◽  
Displacement Field ◽  
Driving Force ◽  
Applied Load ◽  
Elastic Stress ◽  
Ductile Material ◽  
Crack Tip Shielding

This paper presents a very brief overview of the philosophy underlying a plastic inclusion approach to defining the boundary stresses imposed on the applied elastic stress or displacement field by the plastic deformation attendant on crack growth in a ductile material. It leads to two new fracture mechanics parameters, KR and KS. KR defines a retardation component arising from wake contact and the Poisson’s contraction associated with the plastic zone, whilst KS describes a compatibility-induced component arising from shear at the elastic-plastic interface. These additional components imply that KF is not directly comparable with KI, as it describes the net driving force on the crack from the applied load.

Fatigue Crack Growth Prediction under Spectrum Load in an Aluminium Alloy using Crack Driving Force K*eff Approach

2020 ◽  
Vol 12 (3) ◽  
Author(s):  
B. Shailesh Kamath ◽  
A.R. Anilchandra ◽  
T. Sivaranjani ◽  
K. Badari Narayana ◽  
C.M. Manjunath
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Aluminium Alloy ◽  
Crack Growth ◽  
Driving Force ◽  
Fatigue Load ◽  
Single Edge ◽  
Crack Driving Force ◽  
Load Sequence ◽  
Better Than

Fatigue Crack Growth (FCG) behaviour in a Single-Edge-Notched Tension (SENT) specimen of 2024-T3 aluminium alloy under a standard mini-FALSTAFF spectrum load sequence was experimentally determined. Further, the FCG behaviour was predicted using cycle-by-cycle method and compared with experimental results. Prediction procedure involved are rain-flow counting of fatigue load cycles, estimation of crack driving force for each of the counted cycle and prediction of crack extension per cycle from constant amplitude crack growth rate equation. In the present work, a new crack driving force (CDF) K*eff involving Kujawski’s crack driving force K* in conjunction with Elber’s crack closure concept was used to account for load interaction effects. FCG prediction was also made using conventional CDF ΔKeff (Elber’s) approach. A good correlation was observed between experimental and predicted FCG behaviour under spectrum loads by the proposed K*eff approach. Also, this prediction was observed to be better than that predicted by conventional ΔKeff approach.

Assessment of Fully Plastic J and C*-Integral Solutions for Application to Elastic-Plastic Fracture and Creep Crack Growth

1993 ◽  
Vol 115 (3) ◽  
pp. 228-234 ◽  
Author(s):  
D. R. Lee ◽  
J. M. Bloom
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Driving Force ◽  
Creep Crack Growth ◽  
J Integral ◽  
Finite Element Program ◽  
Hardening Material ◽  
Crack Driving Force ◽  
Elastic Plastic ◽  
Creep Crack

A critical part of the assessment of defects in power plant components, both fossil and nuclear, is the knowledge of the crack driving force (K1, J, or C*). While the determination of the crack driving force is possible using finite element analyses, crack growth analyses using finite element methods can be expensive. Based on work by Il’yushin, it has been shown that for a power law hardening material, the fully plastic portion of the J-integral (or the C*-integral) is directly related to an h1 calibration function. The value of h1 is a function of the geometry and hardening exponent. The finite element program ABAQUS was used to evaluate the fully plastic J-integral and determine the h1 functions for various geometries. The Ramberg-Osgood deformation theory plasticity model, which may be used with the J-integral evaluation capability, allows the evaluation of fully plastic J solutions. Once it was established that the grid used to generate the h1 functions was adequate (based on the more recent work of Shih and Goan), additional runs were made of other configurations given in the EPRI Elastic-Plastic Fracture Handbook. Differences as great as 55 percent were found when compared to results given in the Handbook (single-edge crack plate under tension and plane stress with a/b = 0.5). Effects of errors in h1 on predicted failure load and creep crack growth are discussed.

scholarly journals Fatigue Crack Growth Behavior of PWA 1484 Single Crystal Superalloy at Elevated Temperatures

1995 ◽  
Author(s):  
Jack Telesman ◽  
Louis J. Ghosn
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Driving Force ◽  
Narrow Band ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Mode I ◽  
Fatigue Crack Growth Behavior ◽  
Crack Driving Force

A study was done to determine the fatigue crack growth behavior of a PWA 1484 single crystal nickel base superalloy in a temperature range of 427°C to 871°C. Two distinctive failure modes were observed which were a function of both temperature and frequency. At lower temperatures and higher frequencies crack growth occured on the {111} octahedral slip planes at an oblique angle to the loading direction. Higher temperatures and decrease in frequencies favored a Mode I type failure process. The failure mode transitions were explained by invoking arguments based on environmental damage mechanisms. The fatigue crack growth rate data were analyzed using three different crack driving force parameters. The parameters investigated consisted of the Mode I stress intensity parameter corrected for the inclined crack trajectory, and two different octahedral Mode II parameters which are based on the calculation of resolved shear stresses on the {111} slip systems. The Mode I ΔK parameter did a fair job in correlating the data but did not collapse it into a single narrow band. The two octahedral crack driving force parameters, ΔKRSS and a newly proposed ΔKOCT, collapsed all the data into a single narrow band. In addition to correlating the fatigue crack growth rates, the two octahedral parameters also predicted the {111} planes on which the crack growth took place.

A Finite Element Study of the Effect of Crystal Orientation and Misalignment on the Crack Driving Force in a Single-Crystal Superalloy

2016 ◽  
Author(s):  
Christian Busse ◽  
Jordi Loureiro Homs ◽  
David Gustafsson ◽  
Frans Palmert ◽  
Björn Sjödin ◽  
...  
Keyword(s):  
Finite Element ◽  
Single Crystal ◽  
Crack Growth ◽  
Driving Force ◽  
Crystal Orientation ◽  
Plastic Anisotropy ◽  
Casting Process ◽  
Material Model ◽  
Crack Growth Behavior ◽  
Crack Driving Force

The elastic and plastic anisotropy of the single-crystalmaterials bring many difficulties in terms of modeling, evaluation and prediction of fatigue crack growth. In this paper a single-crystal material model has been adopted to a finite element-environment, which is paired with a crack growth tool. All simulations are performed in a three-dimensional context. This methodology makes it possible to analyze complex finite element-models, which are more application-near than traditional two-dimensional models. The influence of the crystal orientation, as well as the influence of misalignments of the crystal orientation due to the casting process are investigated. It is shown that both the crystal orientation and the misalignment from the ideal crystal orientation are important for the crack driving force. The realistic maximum limit of 10° misalignment is considered. It can be seen that crack growth behavior is highly influenced by the misalignment. This knowledge is of great interest for the industry in order to evaluate the crack growth in single-crystal components more accurately.

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