The closure model developed in this paper will be called the crop model for closure, roughness, oxide, and plasticity. Nearthreshold closure is complex because multiple closure mechanisms are likely, including plasticity and oxide induced crack closure. Plasticity induced crack closure in adhesively bonded joints under fatigue loading. This transformation induced closure is strongly influenced by the size and geometry of the test specimen and of the fatigue crack. Fatigue crack growth resistance and crack closure behavior. 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. Analytical and experimental study of near threshold.
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 assessment of the role of plasticityinduced closure and residualplastic deformations, in addition to oxide debris, in threshold development was made. Oxide induced crack closure, roughnessinduced crack closure, and crack deflection are responsible for the behavior in the nearthreshold region. Fatigue crack growth resistance and crack closure behavior in two. An explanation for nearthreshold corrosion fatigue crack growth behavior, coauthor with s. A geometric model for fatigue crack closure induced by fracture roughness, met. Oxide induced closure occurs where rapid corrosion occurs during crack propagation. These steels transform from the austenitic to the martensitic lattice structure under sufficiently high deformation. The model accounts for the combined effect of plasticityinduced crack closure, oxide induced crack closure and. But real fatigue cracks close continuously from the crack tip, caused by plasticity. 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.
Special considerations will be made for nearthreshold fcg scenarios, but this model will not be limited to low. A geometric model for fatigue crack closure induced by fracture surface roughness s. The oxide debris is produced by the fretting actions of crack faces in air and is. Multimechanism crack closure simulations in various. A potential source of the kmax effects on crackgrowth rate data will be studied at high stress ratios and at high. Two methods of calculating crackopening stresses were compared. Crack closure by fracture surface asperities is often referred as roughnessinduced closure suresh and ritchie, 1982. A simple fatigue life prediction algorithm using the. The first analytical crack closure model was developed by newman in 1974, based on the dugdale crack model. Crack closure in nearthreshold fatigue crack propagation. Crack configuration analyzed with stripyield model. A crack closure model was developed that considers plasticity, roughness, and oxide induced crack closure mechanisms picc, ricc, and.
Influence of oxide induced crack closure on the threshold values. Plasticityinduced crack closure model the plasticityinduced crackclosure model, shown in figure 2, was developed for a. Quantitative dependence of oxideinduced crack closure on. Influence of oxide induced crack closure on the threshold values of fatigue crack propagation rate i. This oxide induced closure model is found to be consistent with most experimental observations of nearthreshold fatigue crack. 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. Oxideinduced crack closure, more than plasticity and fracture surface roughness closure. Furthermore, analytical results indicate closure mechanisms interact in a non. 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 above phenomena increase the values when measured. 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. A geometric model for fatigue crack closure induced by. Antunes2 1department of mechanical engineering, polytechnic institute of coimbra, rua pedro nunes, quinta da nora, 3030199 coimbra, portugal.
Modeling the interactions between multiple crack closure. Terasawa, fatigue crack growth behavior at stage 2 and examination of oxide induced crack closure, j. 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. Identification of closure from load versus displacement 54 s15. Structural failure occurs if a crack larger than a critical size exists. The model can leave several elements in the wake of the advancing crack tip. Influence of throughthickness crack shape on plasticity induced. Although there exists other closure phenomena, such as roughness induced crack closure and oxide induced crack closure, they are often assumed to be secondary.
In plasticity induced crack closure, the crack growth is governed by the effective stress intensity range. Consequently, in lr method, crack faces can produce roughsurface or fretting debris which contributes to the early crack closure and higher. Analyses will be conducted under both constantamplitude and singlespikeoverload conditions. A parameter for quantitative analysis of plasticity. 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. The analytical model is shown to provide a good description of the combined influences of crack. An evaluation of the plasticityinduced crackclosure. Nearthreshold fatigue crack growth in 2 14 cr1mo pressure vessel steel in air and hydrogen. The following is the model for estimating the fatigue crack propagation rate when. A multimechanism modeling of fatigue crack growth is presented in this paper. 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. Numerical simulation of plasticity induced crack closure.
Multimechanism crack closure simulations in various steels. 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. 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. Picc plasticity induced crack closure acronymattic. Finite element results were used to verify the analytical solutions for cracktip stress intensity factor and crack face displacements. If the plastic zone size is an order of magnitude or larger than the.
An analytical model of plasticity induced crack closure f. Finite element analysis of plasticityinduced fatigue. A model is proposed to explain the development of this wedge under plane strain conditions. The analytical model is shown to correctly predict the combined influences of crack roughness, oxide debris, and plasticity in the near. Oxideinduced crack closure, more than plasticity and fracture surface. On the other hand, plasticityinduced crack closure is. The plasticityinduced crackclosure model, shown in figure 1, was developed for a through crack in a finitewidth plate subjected to remote applied stress. Citeseerx document details isaac councill, lee giles, pradeep teregowda. 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. Both oxide wedge and roughnessinduced crack closure are microstructure sensitive. Crack closure by fracture surface asperities is often referred as roughness induced closure suresh and ritchie, 1982. Three types of crack closure mechanisms wake region material. The model accounts for the combined effect of plasticity induced crack closure, oxide induced crack closure and embrittlement effects near the crack tip.
Finite element analysis of plasticity induced fatigue. Modeling of crack closure due to plasticity and sliding in. Both alloys demonstrate an unrecrystallized pancakeshaped grain structure. Plasticityinduced crack closure an overview sciencedirect topics. Roughnessinduced crack closure in the threshold region. The implications of this model to nearthreshold fatigue crack growth behavior, in terms of the role of load ratio, environment, and microstructure. The fatigue crack closure models discussed above fundamentally assume plasticity induced crack closure picc as the only mechanism of closure.
The implications of this model to nearthreshold fatigue crack growth behavior, in terms of the role of load ratio, environment, and microstructure are discussed. Among them, newmans finite element model is the best and deserves future developments. 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. In the dugdale model, the plastic zone is replaced by a narrow strip that. Quantitative fractography results were also used to infer crack closure levels in some cases. 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. Ritchie mechanisms for fatigue crack closure under. 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. 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. Interactions of plasticity and oxide crack closure. Typical variation of 45 excess oxide thickness, d, with crack length and crack propagation rate 22. 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. Modelling crack nucleation non propagating cracks crack growth. Ritchie, metallurgical transactions a, volume 12a, august 1981, pages 14351443.
Both oxide wedge and roughness induced crack closure are microstructure sensitive. Iii fatigue models university of illinois at urbana. The effects of load ratio on threshold fatigue crack. The actual closure level of a particular crack may be a combination of more than one of these mechanism.
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. Applications of the model to crack surface roughness and oxide induced crack closure were attempted. An analytical model of plasticity induced crack closure. In general, greater size of grains promotes roughness induced crack closure ricc and oxide induced crack closure oicc is enhanced simultaneously.
Experiments have shown that oxideinduced crack closure occurs at both room and elevated temperature, and. Plasticityinduced crack closure is more prevalent in fatigue cracks under the. 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. Christensen discovered the crack closure in 1963, which was later defined by elber in 1968. On the residual life assessment of highspeed railway. Crack closure has now been accepted as a crucial retardation mechanism in fatigue crack growth. Analysis of plasticity, roughness and oxide induced crack. A model of roughnessinduced crack closure springerlink. The key finding from the work was that roughness induced crack closure effects can be. In this case, oxideinduced crack closure figure 7, roughnessinduced crack. The results gave a fairly good agreement with those obtained by finite element analysis or the dugdale model. Crack closure is a phenomenon in fatigue loading, where the opposing faces of a crack remain.
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