In situ sem testing for crack closure investigation and. Structural design taking into account fatigue damage requires a thorough knowledge of the behaviour of materials. On the significance of crack closure in fatigue crack growth a. Elber, wolf, the significance of fatigue crack closure. Following this preliminary experiment, a more complete analysis of the internal force system was made. Such shielding arises in fatigue from crack closure see for example refs. An analytical model for fatigue crack propagation prediction. For cyclic loading significantly below the fracture toughness, the cyclic deformation is the dominant part responsible for fatigue crack propagation. The model accounts for the hold time and frequency effect under high temperature fatigue crack growth.
A study of crack closure in fatigue lehigh preserve. Effect of strain hardening on fatigue crack closure in aluminum alloy. His work is currently published in international journal of fatigue. First discovered by elber 1970, 1971 crack closure has been extensively studied in the past three. Fracture mechanics of engineering materials engineering. Kk k kk max min min minmax,0 crack closure att kkop gives. Cyclic plastic work, which corresponds to an irreversible energy consumed in a cracked body is generated ahead of a crack, is required as a fatigue crack driving force. The significance of crack closure under high temperature fatigue crack growth with hold periods.
Fundamentals of and applications to fatigue analysis on the web. Elber, w resident research associate, national academy of sciences, nasa langley research center, national aeronautics and space administration, hampton, va. Crack closure concept is often used to explain the crack propagation behavior in cracked components. Elber elucidates the mechanisms and importance of crack closure in slowing the growth of a fatigue crack due to the wedging effect of plastic deformation left behind the tip of the crack. Astm stp 43 advances in fatigue crack closure measurements and analysis, 5778. Ris for refworks, endnote, procite, reference manager, zoteo, and many others. The second period starts when the fatigue crack penetrates into the subsurface material away from the material surface.
Fatigue crack closure analysis and crack propagation estimation. Advances in fatigue crack closure measurement and analysis. This report provides an overview of fatigue crack initiation in austenitic stainless steels in lwr coolant environments. Fatiguelife prediction methodology using a crackclosure. A symposium presented at the seventythird annual meeting american society for testing and materials, pp. The mechanism and estimation of fatigue crack initiation in. Apr 11, 20 the premature contact of crack surfaces attributable to the neartip plastic deformations under cyclic loading, which is commonly referred to as plasticity induced crack closure picc, has long been focused as supposedly controlling factor of fatigue crack growth fcg. On the significance of crack closure in fatigue crack growth. It is well known by much experimental data that fatigue cracks close at positive loads during constant amplitude loading cycles. Al alloy sheet fatigue crack closure under cyclic tensile loading, deriving expression for crack propagation rate in terms of effective stress amplitude.
Crack opening and closure in fatigue sciencedirect. Analysis of the importance of the crack closure in the. The significance of fatigue crack closure,damage tolerance in aircraft structure, astm stp486, astm, w. Additional topics briefly covered are timedependent crack growth. Fatigue crack closure under cyclic tension 39 applied force. The two previous chapters, chapters 6 and 7, mainly deal with fatigue in the crack initiation period. Evidence is presented that a fatigue crack growing under cyclictension can close on itself at about half the maximum load. The implications of crack closure on fatigue crack are considered.
Fatigue crack closure, observations and technical significance. Elber, the significance of fatigue crack closure, astm stp 486, astm 1970 230242. The implications of crack closure results in describing high temperature fatigue crack growth rate data is outlined. This immediately suggests that the system has a varying geometry, which in turn can only mean that the crack is closing.
List of symbols a half crack length aclose distance between the center of the crack and the contact line aq initial half crack length aaa,n rate. The analytical procedure involves the determination of the reversed plastic zone size, the crack opening and closure stresses and is based on budiansky. Elbert, the significance of fatigue crack closure, in damage tolerance in aircraft structures. A loading stage for the scanning electron microscope has been used in conjunction with the stereoimaging technique to study fatigue crack closure for a center notched specimen of an aluminum alloy. The amout of cyclic plasticity is reduced by a crack closure. Modeling of fatigue crack closure by finite element method. On the dominant role of crack closure on fatigue crack growth. Roughnessinduced crack closure in the threshold region for. Key words suggested by authors fatigue crack growth crack closure ti6al4v titanium. The applicable fatigue crack growth rate expression.
The experimental results show that crack closure cannot fully account for the effect of stress ratio, r, on crack growth, and that it cannot be regarded as the sole cause for delay. Mechanics of fatigue crack closure astm stp 982 volume 982 of astm special technical publication, american society for testing and materials, issn 00660558 volume 982 of american society for testing and materials. Crack closure is a phenomenon in fatigue loading, where the opposing faces of a crack remain in contact even with an external load acting on the material. Introduction it has been well established that crack closure is an important phenomenon in fatigue crack growth and signi. Fractographic reassessment of the significance of f atigue crack closure article in journal of astm international 26 june 2005 with 12 reads how we measure reads. The crack closure plays a role to obstruct the generation and growth of compressive plastic zone during unloading. Fatigue crack growth thresholds at negative stress ratio for.
Linear elastic fracture mechanics lefm analysis of the effect of. Astm special technical publication journal of american society for testing and materials. The presence of a crack can significantly reduce the life of a component or structure. The growth of the fatigue crack is then depending of the crack growth resistance of the material as a bulk property. Crack closure occurs from the presence of material propping open the crack faces and can arise from many sources including plastic deformation or. On the significance of crack closure in fatigue crack. Langley research center hampton, virginia 23665 technical paper presented at the eighth national symposium on fracture mechanics, providence, rhode island, august 2628, 1974.
The significance of fatigue crack closure 1971 citeseerx. Role of plasticityinduced crack closure in fatigue crack. One objective of this experimental study is to verify the existence and significance of crack closure by directly measuring the variation of crack tip opening displacement ctod and evaluating the crack opening stress levels. Topics on high and lowcycle fatigue, including fatigue crack nucleation and formation, are followed by crack propagation aspects in fatigue, crack closure, crack tip shielding, and fatigue testing. During the testing, the loading cycle is divided into a certain number of levels. Fractographic reassessment of the significance of fatigue crack closure article in journal of astm international 26 june 2005 with 12 reads how we measure reads. The purpose of this paper is to model analytically fatigue crack growth with a plasticityinduced crack closure effect in constant amplitude loading. Evidence is presented that a fatigue crack growing under cyclic. Testing procedures for fatigue crack propagation and the. This result showed that onset of crack closure detected by electricalpotential measure ment and crack openingdisplacement measurement is the same. Crack closure effects on fatigue crack propagation rates hindawi. Elber, the significance of fatigue crack closure, astm stp 486, damage tolerance in aircraft structures, american society for testing and. As the load is increased, a critical value will be reached at which time the crack becomes open.
In this model, a stripyield methodology was used to simulate creep fatigue crack growth and to quantify the influence of hold time on plasticityinduced crack closure during creep fatigue crack growth. To make life estimations for fatigue crack growth and damage tolerant design, the following information are often needed. E64708e01, standard test method for measurement of fatigue crack growth rates. In addition, the crack closure stress was estimated for a simple random load sequence. Experiments on 2024t3 aluminum alloy sheet are described which confirm the occurrence of fatigue crack closure under cyclic tensile loading. Crack closure r elber, in 1970, discovered that crack closure exists in cyclic loading, even for loads that are greater than zero this crack closure will decrease the fatigue crack growth rate by reducing the effective stress intensity range the stress intensity rate. The crack closure and opening effects can be estimated using an elastoplastic analysis based on analytical 3, 19 or numerical, 14 approaches.
In particular, a characterization of crack flank oxide. The significance of crack closure under high temperature. The phenomenon of crack closure, which involves the premature closing of fatigue cracks during the unloading portion of a fatigue cycle resulting in the development of crack. The effective stress intensity factor range is considered as a driving force of fatigue crack growth based on the traditional crack closure concept. Al alloy sheet fatigue crack closure under cyclic tensile loading, deriving expression for crack. Crack closure is the most used mechanism to model thickness and load interaction effects on fatigue crack propagation. As the creep strain rates increase, the crack opening displacement and effective stress range over which the crack is open increases. The significance of fatigue crack closure astm international. Damage tolerance in aircraft structures, astm stp 486, american society for.
The significance of fatigue crack closure 1971 by w elber venue. Fractographic reassessment of the significance of fatigue. Y a n g metallurgy department and institute of materials science, university of connecticut, storrs, ct 06268, usa abstract the research of recent years has brought about a better understanding of the nature and the significance of fatigue crack closure. Crack closure stress was estimated at stress ratios of 0. Research on fatigue crack propagation of conventional and highly crosslinked uhmwpes has confirmed a detrimental effect of increasing radiationcrosslinking levels on the resistance to crack inception and crack growth 5, 33, 35, 4042. Page 439 the significance of fatigue crack closure, damage tolerance in aircraft structures, astm stp 486, american society for testing and materials, philadelphia, 1971, pp. A closure model for predicting crack growth under creep. The increase in effective stress range depends on the level of applied stresses relative to yield strength and is influenced by the sensitivity of creep strain rates on stress. Of particular significance is the varying contri bution of crack tip shielding, with the size of the crack wake, in locally reducing the effec tive driving force experienced at the tip 14. The results show that a fatigue crack can be closed at the crack tip for up to half of the loading amplitude, leaving this portion of the cycle ineffective in propagating the crack.