Influence of an Overload on the Fatigue Crack Growth in Steels (original) (raw)
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Effect on fatigue crack growth of interactions between overloads
Fatigue <html_ent glyph="@amp;" ascii="&"/> Fracture of Engineering Materials and Structures, 2002
Various types of interactions between overloads were studied in a 0.38% C low carbon steel. The retarding effect due to consecutive overloads is found to increase with the number of overloads, until it reaches a maximum. Similarly, it is found that a critical distance between overloads ensures the highest retarding effect, while shorter or longer spacing are less efficient for retarding crack growth. These effects are successfully explained using FEM calculations of the effective stress intensity factor. The kinematic hardening of the alloy, which is very efficient in ferritic±pearlitic steels, is shown to be mostly responsible for those effects. Taking into account the amplitude of kinematic hardening allows qualitative explanation of the observed effects. The order of application of the cycles during variable amplitude fatigue is thus important and should be taken into account for predicting fatigue lives.
In this study, fatigue crack growth rate in mixed-mode overload (modes I and II) induced retardation zone has been predicted by using an ''Exponential model". The important parameter of this model is the specific growth rate. This has been correlated with various crack driving parameters such as stress intensity factor range, maximum stress intensity factor, equivalent stress intensity factor, and mode mixity, as well as material properties such as modulus of elasticity and yield stress. An equation has been formulated for specific growth rate which has been used to calculate crack growth rate under mixed-mode loading conditions. It has been observed that the crack growth rate predicted by the model is in good agreement with experimental results.
Effect of Single Overload Ratio and Stress Ratio on Fatigue Crack Growth
World Academy of Science, Engineering and Technology, International Journal of Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering, 2013
In this investigation variation of cyclic loading effect on fatigue crack growth is the studied. This study is performed on 2024 T351 and 7050-T74 aluminum alloys, used in aeronautical structures. The propagation model used in this study is NASGRO model. In constant amplitude loading (CA), effect of stress ratio has been investigated. Fatigue life and fatigue crack growth rate were affected by this factor. Results showed an increasing in fatigue crack growth rates (FCGRs) with increasing stress ratio. Variable amplitude loading (VAL) can take many forms i.e. with a single overload, overload band... etc. The shape of these loads affects strongly the fracture life and FCGRs. The application of a single overload (ORL) decrease the FCGR and increase the delay crack length caused by the formation of a larger plastic zone compared to the plastic zone due without VAL. The fatigue behavior of the both material under single overload has been compared. Keywords—Fatigue crack growth, overload ...
Overload Retardation in a Structural Steel
Fatigue & Fracture of Engineering Materials and Structures, 1987
The mechanisms causing crack growth retardation after an overload were examined for BS4360 50B steel. It was found that plasticity-induced crack closure is the main cause of retardation when the pre-overload growth rate is in the mid-regime of the growth rate versus stress intensity range plot. When the pre-overload growth rate is near threshold it is argued that retardation at the surface of the specimen is primarily due to strain hardening and to the build-up of a favourable residual stress distribution in the material ahead of the crack tip. Supporting evidence for this argument is provided by a preliminary test on 2014A-T4 aluminium alloy. Plasticity-induced crack closure may be a further cause of retardation in the bulk, plane strain regions of the specimens made from BS4360 50B steel and 2014A-T4 aluminium alloy, when the pre-overload growth rate is near threshold.
Acceleration of Fatigue Crack Growth After Overload in Carbon Steel
International Journal of Modern Physics: Conference Series, 2012
The effects of an overload on fatigue crack growth behavior have been investigated by using carbon steel. Delayed retardation and acceleration of crack growth were both observed. These phenomena depended not only on overload conditions but also on the baseline stress conditions. Moreover, the mechanical properties of the materials affected the crack growth rate after overload. It was found that crack growth accelerated when tensile residual stress was distributed in front of the crack tip. The residual stress distribution is related to the crack opening geometry at the overload stage.
Effects of a single tensile overload on fatigue crack growth in a 316L steel
Fatigue <html_ent glyph="@amp;" ascii="&"/> Fracture of Engineering Materials and Structures, 1999
The aim of this study was to investigate the effects of a single tensile overload on subsequent fatigue crack growth in a 316L stainless steel. Fatigue tests were conducted under the plane stress condition, and further supplemented with compliance measurements and field emission scanning electron microscopy (FESEM) observations. Effects of a tensile overload, e.g. initial acceleration and subsequent retardation of fatigue crack growth, were explained and quantified by FESEM and compliance measurements. The FESEM observations suggest that the initial crack growth acceleration stems from void and quasi-cleavage fracture within the fatigue damage zone in the vicinity of the crack tip. Systematic compliance measurements taken during fatigue crack growth suggest that the overall crack growth retardation is related to strain hardening and residual compressive stress produced by the plastic deformation associated with the tensile overload.
Effect of band-overload on fatigue crack growth rate of HSLA steel
IOP Conference Series: Materials Science and Engineering, 2015
Fatigue crack growth behavior is important parameter of structural materials. This parameters can be used to predict their life, service reliability and operational safety in different conditions. The material used in this investigation is an HSLA steel. In this investigation effect of single overload and band-overload on fatigue crack growth of same steel are studied using compact tension (CT) specimens under mode-I condition and R=0.3. It is observed that overload and band-overload applications resulted retardation on the fatigue crack growth rate in most of the cases. It is also noticed that maximum retardation took place on application of seven successive overload cycles. Application of ten and more overload cycles caused no crack growth retardation.
Almost all load bearing components usually experience variable amplitude loading (VAL) rather than constant amplitude loading (CAL) during their service lives. A single overload cycle introduced in a constant amplitude fatigue loading retards fatigue crack growth and increases residual fatigue life. Although many models have been proposed on this subject, but life prediction under these complex situations is still under constant improvement. The present study aims at evaluating retardation in fatigue life due to application of a single tensile overload spike by adopting an exponential model. The proposed model calculates not only parameters related with overload induced retardation in fatigue crack growth, but also residual life in case of 7020-T7 and 2024-T3 aluminum alloys with reasonable accuracy without integration of rate equation. The model also covers stage-II and stage-III of post-overload period.
Analysis of overload effects and related phenomena
International journal of …, 1999
Overloads and underloads perturb steady state fatigue crack growth conditions and affect the growth rates by retarding or accelerating the growth. Clear understanding of these transient effects is important for the reliable life prediction of a component subjected to random loads. The overload effects have predominately been attributed to either plasticity induced crack closure behind the crack tip, residual stresses ahead of the crack tip, or a combination of both. These effects are critically examined in the context of the Unified Approach proposed by the authors. Recent experimental and analytical evaluation of crack closure has confirmed its negligible contribution to crack growth and has demonstrated that changes in the stresses ahead of the crack tip are more important than closure behind the crack tip. It is shown that the overload effects and other transient effects arise due to perturbation of the stresses ahead of the crack tip, and these can be accounted for by the two parametric approach emphasized in the unified theory. It is shown that related phenomena including the role of K max , the existence of propagation threshold K pr , and effects of overloads on K pr and K max etc, are all accounted for by the Unified Approach.
The Effect of Overload on Crack Growth Behaviour in Biaxial Fatigue
MATEC Web of Conferences
This paper focus on the study of biaxial fatigue cracks based on a methodology that enables evaluation of the overload effect in fatigue. The methodology is based on the experimental evaluation via full-field technique of digital image correlation of the effective stress intensity factor and the crack opening displacement (COD). The tests were performed on cylindrical specimens made of low carbon steel subjected to tension-tension and a combination of tension and torsion loads. The experimental data was used to compare the crack growth behaviour with an overload cycle under uniaxial and biaxial loading. A hybrid method was also employed to evaluate the value of the Stress Intensity Factor (SIF) before and after applying the overload. The results showed a reliable estimation of closure level and SIF for both uniaxial and biaxial loading condition. A new procedure previously developed for uniaxial loads was adapted to the study of biaxial loads. This new procedure was used to identify important differences produced by the overload event.