The analytical model is shown to provide a good description of the combined influences of crack roughness, oxide debris, and plasticity in the nearthreshold regime. It is reported that many mechanism models can explain the crack closure phenomenon, such as the plasticityinduced crack closure, the oxide induced crack closure, and the roughnessinduced crack closure. Crack closure by fracture surface asperities is often referred as roughness induced closure suresh and ritchie, 1982. The effects of load ratio on threshold fatigue crack. Analysis of plasticity, roughness and oxide induced crack. Applications of the model to crack surface roughness and oxide induced crack closure were attempted. In general, greater size of grains promotes roughness induced crack closure ricc and oxide induced crack closure oicc is enhanced simultaneously. Plasticityinduced crack closure is more prevalent in fatigue cracks under the. Am 1103 55 other sources of crack closure maxs open b s max s open a roughness induced crack closure ricc oxide induced crack closure oicc am 1103 56 model. Influence of oxide induced crack closure on the threshold values. Nearthreshold fatigue crack growth in 2 14 cr1mo pressure vessel steel in air and hydrogen. The oxide debris is produced by the fretting actions of crack faces in air and is. On the residual life assessment of highspeed railway. Modeling the interactions between multiple crack closure.
An advanced analytical model developed earlier has been utilized to predict interactions between plasticity and oxide crack closure mechanisms that influence nearthreshold fatigue crack growth behavior. Crack closure has now been accepted as a crucial retardation mechanism in fatigue crack growth. Analyses will be conducted under both constantamplitude and singlespikeoverload conditions. An analytical model of plasticity induced crack closure. Interactions of plasticity and oxide crack closure. Both alloys demonstrate an unrecrystallized pancakeshaped grain structure. An evaluation of the plasticityinduced crackclosure. Experiments have shown that oxideinduced crack closure occurs at both room and elevated temperature, and. Finite element analysis of plasticity induced fatigue. First, plasticity induced crack closure was analyzed. Although there exists other closure phenomena, such as roughness induced crack closure and oxide induced crack closure, they are often assumed to be secondary. Oxide induced crack closure, roughnessinduced crack closure, and crack deflection are responsible for the behavior in the nearthreshold region. In this case, oxideinduced crack closure figure 7, roughnessinduced crack.
The actual closure level of a particular crack may be a combination of more than one of these mechanism. The plasticityinduced crackclosure model, shown in figure 1, was developed for a through crack in a finitewidth plate subjected to remote applied stress. A plasticityinduced crackclosure model was used to study fatigue crack growth and closure in a thinsheet 2024t3 aluminum alloy under threshold and constantk max testing procedures. The results gave a fairly good agreement with those obtained by finite element analysis or the dugdale model. An existing geometric asperity based model for roughnessinduced crack closure under constant amplitude conditions was evaluated and extended. Ritchie, metallurgical transactions a, volume 12a, august 1981, pages 14351443.
Crack configuration analyzed with stripyield model. The fatigue crack closure models discussed above fundamentally assume plasticity induced crack closure picc as the only mechanism of closure. On the other hand, plasticityinduced crack closure is. Picc plasticity induced crack closure acronymattic. But real fatigue cracks close continuously from the crack tip, caused by plasticity. Analytical and experimental study of near threshold. Both oxide wedge and roughness induced crack closure are microstructure sensitive. A model of roughnessinduced crack closure springerlink. Typical variation of 45 excess oxide thickness, d, with crack length and crack propagation rate 22. In plasticity induced crack closure, the crack growth is governed by the effective stress intensity range. The analytical model is shown to correctly predict the combined influences of crack roughness, oxide debris, and plasticity in the near. The analytical model is shown to provide a good description of the combined influences of crack. Quantitative fractography results were also used to infer crack closure levels in some cases. Special considerations will be made for nearthreshold fcg scenarios, but this model will not be limited to low.
Three types of crack closure mechanisms wake region material. Identification of closure from load versus displacement 54 s15. The concept of oxide induced crack closure is utilized to explain the role of gaseous and aqueous environments on corrosion fatigue crack propagation at ultralow, nearthreshold growth rates in bainitic and martensitic 2 14 cr1 mo pressure vessel steels. Structural failure occurs if a crack larger than a critical size exists. A geometric model for fatigue crack closure induced by.
A model is proposed to explain the development of this wedge under plane strain conditions. Finite element results were used to verify the analytical solutions for cracktip stress intensity factor and crack face displacements. Quantitative dependence of oxideinduced crack closure on. A parameter for quantitative analysis of plasticity. Crack closure in nearthreshold fatigue crack propagation. Consequently, in lr method, crack faces can produce roughsurface or fretting debris which contributes to the early crack closure and higher. Influence of throughthickness crack shape on plasticity induced. Influence of oxide induced crack closure on the threshold values of fatigue crack propagation rate i. Plasticity induced crack closure is included by modifying an existing analytical model, and an oxide layer in the crack mouth is modeled as a uniform layer. Antunes2 1department of mechanical engineering, polytechnic institute of coimbra, rua pedro nunes, quinta da nora, 3030199 coimbra, portugal.
The concept of oxide induced crack closure is utilized to explain the role of gaseous and aqueous environments on corrosion fatigue crack propagationat ultralow, nearthreshold growth rates in. This oxide induced closure model is found to be consistent with most experimental observations of nearthreshold fatigue crack. Plasticity induced crack closure in adhesively bonded joints under fatigue loading. Multimechanism crack closure simulations in various. A crack closure model was developed that considers plasticity, roughness, and oxide induced crack closure mechanisms picc, ricc, and. Terasawa, fatigue crack growth behavior at stage 2 and examination of oxide induced crack closure, j. Oxideinduced crack closure, more than plasticity and fracture surface roughness closure. This transformation induced closure is strongly influenced by the size and geometry of the test specimen and of the fatigue crack. Among them, newmans finite element model is the best and deserves future developments. The key finding from the work was that roughness induced crack closure effects can be. Plasticityinduced crack closure an overview sciencedirect topics. Two methods of calculating crackopening stresses were compared. It is shown that at low load ratios, nearthreshold growth rates are significantly reduced in moist environments such as air or water. For oxide induced fatigue crack closure, an oxide film forms on the surface in the wake region and makes contact while under tensile loads.
An analytical model of plasticity induced crack closure f. Fatigue crack growth resistance and crack closure behavior in two. The model can leave several elements in the wake of the advancing crack tip. Fatigue crack growth resistance and crack closure behavior. Numerical simulation of plasticity induced crack closure. A geometric model for fatigue crack closure induced by fracture surface roughness s. The effects of load ratio on threshold fatigue crack growth of aluminum alloys john andrew newman abstract the integrity of nearly all engineering structures are threatened by the presence of cracks. An explanation for nearthreshold corrosion fatigue crack growth behavior, coauthor with s.
The model accounts for the combined effect of plasticityinduced crack closure, oxide induced crack closure and. The results of an analytical closure model that considers contributions and interactions between plasticity, roughness, and oxide induced crack closure mechanisms are presented and compared with experimental data. Plasticityinduced crack closure model the plasticityinduced crackclosure model, shown in figure 2, was developed for a. Oxideinduced crack closure, more than plasticity and fracture surface. Iii fatigue models university of illinois at urbana. Nearthreshold closure is complex because multiple closure mechanisms are likely, including plasticity and oxide induced crack closure. A 2dimensional, elasticplastic finite element model has been developed to simulate plasticity induced crack closure in slanted and deflected cracks growing outside the small scale yielding ssy regime.
The first analytical crack closure model was developed by newman in 1974, based on the dugdale crack model. If the plastic zone size is an order of magnitude or larger than the. Researchers in the past have focused on modeling and understanding a variety of closure mechanisms like plasticity induced crack closure, roughness induced crack closure, oxide induced crack closure etc. Modelling crack nucleation non propagating cracks crack growth. Finite element analysis of plasticityinduced fatigue. Oxide induced closure occurs where rapid corrosion occurs during crack propagation. These models ignore the role of other known closure mechanisms like roughness induced crack closure ricc, oxide induced crack closure and transformation induced crack closure. The concept of oxide induced crack closure is utilized to explain the role of gaseous and aqueous environments on corrosion fatigue crack propagationat ultralow, nearthreshold growth rates in bainitic and martensitic 2 14 cr1 mo pressure vessel steels. Citeseerx document details isaac councill, lee giles, pradeep teregowda.
Crack closure is a phenomenon in fatigue loading, where the opposing faces of a crack remain. Special attention is devoted to the physical origin, the consequences for the experimental determination and the prediction of the effective crack driving force for fatigue crack propagation. An assessment of the role of plasticityinduced closure and residualplastic deformations, in addition to oxide debris, in threshold development was made. The model accounts for the combined effect of plasticity induced crack closure, oxide induced crack closure and embrittlement effects near the crack tip. Christensen discovered the crack closure in 1963, which was later defined by elber in 1968. Crack closure by fracture surface asperities is often referred as roughnessinduced closure suresh and ritchie, 1982. The following is the model for estimating the fatigue crack propagation rate when. The development of oxide debris behind the crack tip causing oxide induced crack closure is relevant at low stress intensity factor ranges, in the nearthreshold regime. The implications of this model to nearthreshold fatigue crack growth behavior, in terms of the role of load ratio, environment, and microstructure. A multimechanism modeling of fatigue crack growth is presented in this paper.
Both oxide wedge and roughnessinduced crack closure are microstructure sensitive. A geometric model for fatigue crack closure induced by fracture roughness, met. The implications of this model to nearthreshold fatigue crack growth behavior, in terms of the role of load ratio, environment, and microstructure are discussed. Multimechanism crack closure simulations in various steels. Furthermore, analytical results indicate closure mechanisms interact in a non. Nasa langley research center hampton, virginia usa abstract a plasticityinduced crackclosure model was used to study fatigue crack growth and closure in thin 2024t3 aluminum alloy under constantr and constantkmax threshold. The oxide layer can only contribute to crack closure when the specific mass density of the oxide is lower than that of the original material steel, since some of the original material is consumed to form the oxide and it is the excessive volume that causes the wedging effect.
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