This indicates that the elber s model can fit well when the stress ratio is relatively small 0. Crack closure r elber, in 1970, discovered that crack closure exists in cyclic. An evaluation of the plasticityinduced crackclosure. Nasa langley research center hampton, virginia usa abstract a plasticityinduced crack closure model was used to study fatigue crack growth and closure in thin 2024t3 aluminum alloy under constantr and constantkmax threshold. Some effects of crack closure on the mechanism of fatigue crack propagation under cyclic tension loading, ph. The present fatigue crack growth curves are also compared to curves using several crack closure models katcherkaplan model, schijve model, and benguediab model. Fatigue life prediction based on crack closure and. Mechanics of fatigue crack closure, astm stp 982 edited by j. They used a polyester resin model of an sen specimen to measure crack tip stresses by a photoelastic technique.
Load interaction effects on fatigue crack growth stoyan ivanov stoychev, ph. Nasa langley research center hampton, virginia usa abstract an assessment of the plasticityinduced crackclosure concept is made, in light of some of the questions that have been raised on the validity of the concept, and the. The significance of fatigue crack closure 1971 citeseerx. A geometric model for fatigue crack closure induced by fracture surface roughness. According to elber s understanding of crack closure 4,9, as the crack propagates due to cyclic loading, a. A model for crack closure a model for crack closure chen, d. He assumed that crack growth cannot take place under cyclic loads until the fatigue crack is fully opened. Understanding fatigue crack propagation in aisi 316 n weld using elbers crack closure concept. Dugdalebarenblatt stripyield model for the crack tip plasticity dugdale, 1960, barenblatt, 1962, budiansky and hutchinson, 1978.
The replicas show that when closure occurs the crack does not close back from the crack tip but at discrete contact points along the crack faces. In 1970, elber25, 26 discovered that a contact between the fracture. The crack closure levels were compared between the polycrystalline and the two 111 oriented specimens. Paper open access fatigue crack growth rate of an alcu. Many industries will continue to use simpler and less accurate theories, leaving thecontinued work in crack closure as an area of basic research.
The crack closure theory is one approach toward this problem that has received considable attention. Crack closure is a phenomenon in fatigue loading, where the opposing faces of a crack remain. Elber s proposal that crack closure occurred at discrete points on the fracture surfaces was supported by the work of cheng and brunner6. K, as the crack driving force to consider the rratio effect.
In particular, after discovering crack closure under tension loads, elber. An analytical model of plasticity induced crack closure. A crack closure study on 2024 t351 aluminum alloy by the. A model to quantify fatigue crack growth by cyclic damage. The fe model was used to simulate the effects of some fundamental factors. The onedimensional crack closure model describes the mechanics of a partially closed fatigue crack below the crack opening stress in terms of stresses and displacements in response to an externally applied tensile load and a local closure. In this work, an aluminum alloy and a steel, which have vastly different mechanical behaviors, are used to generate different stress states and premature crack closure to allow the validity of miniature specimen fcp data to be critically examined. D western michigan university, 2005 the fatigue crack propagation rate can be either increased or decreased by the. 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. The observed closure mechanism is therefore quite different from the generally accepted model. Elber modified the pariserdogan equation to allow for crack closure with the introduction of the opening stress intensity level at which contact occurs.
Nevertheless, elbers concept of effective stress range has. Initially elber 1, 2 suggested that crack closure was associated with the effective stress intensity range, using u. An evaluation of elber type crack retardation models. Analytical models that lend theoretical support to the existence of crack closure phenomenon in fa tigue crack growth, and provide some rationality for the adoption of an effective stressintensity range, based on closure effects, for the correla. The crack closure model developed in this work is novel in both the elds of nde and fracture mechanics. Although many results supported the crack closure model, the concept of. The results show a good calibration of cracking curves for low stress intensity factor. But assuming it is the only mechanism is equivalent to suppose that the rate. Wang, jia cai li, yiu wing mai, lin ye 217 a critique on evaluating fatigue crack propagation properties using miniature specimens. Crack opening displacement profiles were used to identify the loads at which each mode opened. A crack opening stress equation for fatigue crack growth. The implications of crack closure on fatigue crack are considered.
K parameter which was assumed as a linear function of stress ratio, r, independent of k m a x and. Read effects of crack closure on fatigue crack growth predictions for 2024t351 aluminum alloy panels under spectrum loading, international journal of fatigue on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at. An evaluation of the plasticityinduced crackclosure concept. Pdf an evaluation of elbertype crack retardation models.
Pdf crack closure effects on fatigue crack propagation rates. First discovered by elber 1970, 1971 crack closure has been extensively studied in the past three. Kk k kk max min min minmax,0 crack closure att kkop gives. Elber firstly introduced the crack closure concept that has significant influence on fatigue crack propagation 11. An elasticplastic analysis of fatigue crack closure in modes. On the dominant role of crack closure on fatigue crack. Various analytical models for crack closure are also compared in this study. Crack closure seems to be able to explain th e influence of mean stress in both regimes i and ii of. Mechanics of fatigue crack closure edited by newman j. Fatigue life prediction based on crack closure and equivalent. A fatigue crack closure model and measurement technique. Crack tip constraint factors, to account for threedimensional stateofstress effects. A comparative analysis of driving force models for fatigue. In the early seventies elber 1, 2 introduced the crack closure and opening concepts.
Introduction it has been well established that crack closure is an important phenomenon in fatigue crack growth and signi. Considerable emphasis has been placed on the role of plastic deformation in the wake of the crack, although. Christensen discovered the crack closure in 1963, which was later defined by elber in 1968. Proposal of a fatigue crack propagation model taking into account. A new quadrature q method for crack closure estimation, based on. Comparative study between crack closure model and willenborg model for fatigue prediction under overload e. Research article crack closure effects on fatigue crack. Elber introduced the crack closure concept firstly and developed the relationship between the fatigue crack growth rate and the effective stress intensity factor. Since newman, finite element and difference analysis have been conducted to obtain a basic understanding of crack growth and crack closure processes. In 1970, elber introduced the concept of crack closure and the effective cyclic stress intensity factor. Astm special technical publication journal of american society for testing and materials.
K effective to explain the effects of load ratio rk min k max on fatigue crack growth. Fatigue crack closure for inclined and kinked cracks springerlink. The phenomenon of crack closure was first discovered by elber in 1970. K parameter which was assumed as a linear function of stress ratio, r, independent of k. An analytical model of plasticity induced crack closure f. Crack closure is the premature closure of a crack by the presence of an obstacle within it such as might result from plastic deformation, facets, oxide or metal particles. An evaluation of elbertype crack retardation models. In this paper, a general method is proposed to predict fatigue life based on the crack closure model and the eifs, in which the small crack effect is also considered. A nodel for fatigue crack closure process is proposed, which involves an elastic wedge placed into an elastic crack to simulate the. An elasticplastic analysis of fatigue crack closure in. Plastic zones associated with the fatigue crack growth were determined for all specimens using an anisotropic yield criterion. Based on the experimental observations, elber proposed a crack closure model which used an effective stress intensity factor range. For this reason, coefficients of elber model must be adjusted to have an intrinsic curve using aliaga et al. 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.
Understanding fatigue crack propagation in aisi 316 n weld. The first analytical crack closure model was developed by newman in 1974, based on the dugdale crack model. In the dugdale model, the plastic zone is replaced by a narrow strip that. A nodel for fatigue crack closure process is proposed, which involves an elastic wedge placed into an elastic crack to simulate the obstruction of crack closure due to asperities or oxide debris. The concept of crack closure was first proposed by elber j5,61 in 1970. Below this level there is no movement at the crack tip and hence no growth. Crack closure considering the small crack effect may re. Comparative study between crack closure model and willenborg. Carpinteri, 1981, 1982, which in principle can be adapted to capture the delicate interplay between bulk cyclic plasticity, closure, and gradual decohesion at the crack tip nguyen et al. A combined model of short crack closure accounting for both plasticity and roughness induced crack closures. As the load is increased, a critical value will be reached at which time the crack becomes open.
A crack closure study on 2024 t351 aluminum alloy by the moire method chweigoong tseng iowa state university follow this and additional works at. 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. Therefore, it is necessary to derive an empirically based crack growth model that account for the effect of the crack tip plastic deformation on fatigue crack growth behavior. Experimental results from gcmod and acoustic emission techniques. Experiments on 2024t3 aluminum alloy sheet are described which confirm the occurrence of fatigue crack closure under cyclic tensile loading. A vibration fatigue analysis model considering interaction. The crack closure concept was first proposed by elber 1 in 1971. Pompetzki, a comparison of measurement methods and numerical procedures for the experimental characterization of fatigue crack closure. Application of a proposed theoretical model jose a. 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. The traditional opening load or elber approach, 11, the acr technique, 12, the 2. Crack closure is the most used mechanism to model thickness and load interaction effects on fatigue crack propagation. Fatigue crack closure analysis and crack propagation estimation. A simple crack closure model for predicting fatigue crack growth under flight.
Fatiguelife prediction methodology using a crackclosure. The crack closure and opening effects can be estimated using an elastoplastic analysis based on analytical 3, 19 or numerical, 14 approaches. The compatibility of crack closure and kmax dependent models. Feb 01, 2017 crack closure is not only important under small. The stress state dependence of crack closure is discussed. A crackclosure model for predicting fatiguecrack growth under aircraft spectrum loading, nasa tm. Crack closure effects on fatigue crack propagation rates. Based on this estimated closure force, the crack opening displacement was calculated. Research article crack closure effects on fatigue crack propagation rates. Crack closure elber was one of the first to attempt to describe, with the aid of a physical model, the connection between load sequence, plastic deformation by way of crack closure and crack growth rate. Crack closure effects on fatigue crack propagation rates hindawi.
Tavares 1 institute of science and innovation in mechanical and industrial engineering, university of porto, rua dr. They are studied in part i and ii of the dissertation accordingly. An evaluation of elber type crack retardation models 2001014063. Elber indicated that fatigue cracks are closed during a portion of the tensile load cycle and developed an equation between the fatigue crack growth rate and the effective intensity factor. Analyses of fatigue crack growth and closure near threshold. Basic crack solutions required for closure model crack.
To better model the closure effects on crack retardation. A model for crack closure, engineering fracture mechanics. 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. This result showed that onset of crack closure detected by electricalpotential measurement and crack openingdisplacement measurement is the same. In the transition regime, the crack closure load decreases and can decrease into the compression regime of the load amplitude for high and low cyclic fatigue loadings. Keff, which is taken as thecrack propagation driving force and is. Basic crack solutions required for closure model crack solutions. Thesis, virginia polytechnic institute and state university, blacksburg, va, may 1974. The wheeler model the wheeler model is used to define the. After growing the fatigue crack under zero to tension. Volume 2, issue 1, pages 37, pages in3, pages 4544in4.