Effect of low temperature on the initiation and growth of fatigue cracks in 08kp steel with different grain size

Ostash, О. P.; Kostyk, E. M.; Levina, I. N.

doi:10.1007/bf00720650

Cited by 8 publications

(17 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…8a, b), which is in agreement with the characteristic distance d* = 220 Ixm for this alloy [I0]. According to the microfractographic estimate, the size of an initial macrocrack in low-carbon steel at a temperature of 77 K reaches 170~tm (Figs.8c, d), which, in fact, corresponds to d* = 150~tm for this steel in a multicyclic range [3]. However, it is known that the transition from a microcrack to a macrocrack is usually not clearly defined [ i 8] and, for this reason, it is difficult to record the transition on microfractograms.…”

Section: X] -3/2supporting

confidence: 56%

“…In plastic steels, a fatigue microcrack is always formed at AOy > %.2 and the quantity d* is constant over the whole range of durabilities N i [3].…”

Section: X] -3/2mentioning

confidence: 98%

“…3). In some cases, the parameter d* can be found by analysis of the microfractograms [3,10]. In the fracture of D I6T aluminum alloy, one observes, for example, a specific zone of laminations over the slip plane with a length of about 200 lam (Figs.…”

Section: X] -3/2mentioning

confidence: 99%

“…The value of d* is considerably (by an order) greater than the original structural parameters of the material [5,7], for example, the grain size and the distance between inclusions of the secondary phase. At the same time, for quasibrittle materials (or plastic materials at low temperatures), they can coincide [3]. At normal and low (down to 77 K) temperatures, the growth of grains leads to a decrease in the parameter d* [15].…”

Section: Phenomenological Model Of Nucleation Of a Fatigue Macrocrackmentioning

confidence: 99%

“…At the same time, it is necessary to take into account the following fact: if the microstructural barrier of the material is considered as the main factor for its endurance limit, then it is impossible to explain some experimental data. For example, there exist qualitatively opposite dependences of the fatigue limit t~ R of a smooth specimen and the fatigue threshold Kth of a cracked specimen on the grain size for the same material [3]. It is also known [4] that for a given loading amplitude, the growth rate of microstructuraily short and physically small cracks is greater than that of macrocracks and only in the case where the size of the former is greater (sometimes, by a factor of several times) than the size of the grain, the distance between inclusions, etc., they have the same growth rates [5].…”

mentioning

confidence: 94%

See 4 more Smart Citations

Unified model of nucleation and growth of fatigue cracks. Part 1. Use of force parameters of fracture mechanics of materials in the stage of crack nucleation

Ostash¹,

Panasyuk²,

Kostyk³

1998

Mater Sci

Self Cite

View full text Add to dashboard Cite

According to the phenomenological model of nucleation of a fatigue macrocrack, the process is considered as a two-parameter process. The process is described by the local stress or strain range and a certain linear parameter of the material. We propose the corresponding parameters, namely, the local stress range At~. and the characteristic size d" of the prefracture zone. The formation of this zone is caused by the anomaly of the yield strength of the material in subsurface layers, the microstructure, the loading amplitude, the cyclic strain hardening, and the environment. The quantity d* is a constant of the material, which is independent of the geometry of notch and specimen. The boundary of the prefracture zone is considered as a macrobarrier that determines the growth of microstructuraliy short and physically small cracks. The moment when a physically small crack oversteps the boundary of the prefracture zone is defined by the quantitative criterion (ao= d* ) of the initial size a 0 of a macrocrack in the material. The proposed dependences of ( A~., At,.) and (d*, Ni) can be regarded as a basis for the determination of characteristics of resistance of the material to the nucleation of a fatigue macrocrack.Due to the rapid development of fracture mechanics, especially structural fracture mechanics, in the past ten years considerable progress has been made in understanding the phenomena of fatigue of metals. A detailed analysis of successes and failures concerning the solution of this problem is given in [1,2]. By summing our own data and literature data, we propose to consider fatigue of materials as a process that consists of the following main stages: 1) nucleation and growth of microstructurally short cracks, 2) growth of physically small cracks and formation of a macrocrack, and 3) growth of the macrocrack up to total fracture of the body.Within the framework of this approach, the endurance limit of the material is estimated by the maximum stresses for which a crack in the material does not grow, i.e., the crack is retarded by certain physical barriers (crack resistance of the material). These barriers are caused by the microstructure of the material (boundaries of grains and twins, sizes of pearlitic colonies and martensitic packs, etc.). Thus, the endurance limit is, to a great extent, connected with a certain linear parameter of the structure of the material, in particular, with the distance between structural barriers [2]. At the same time, it is necessary to take into account the following fact: if the microstructural barrier of the material is considered as the main factor for its endurance limit, then it is impossible to explain some experimental data. For example, there exist qualitatively opposite dependences of the fatigue limit t~ R of a smooth specimen and the fatigue threshold Kth of a cracked specimen on the grain size for the same material [3]. It is also known [4] that for a given loading amplitude, the growth rate of microstructuraily short and physically small cracks is greater than that ...

show abstract

Section: X] -3/2supporting

confidence: 56%

“…In plastic steels, a fatigue microcrack is always formed at AOy > %.2 and the quantity d* is constant over the whole range of durabilities N i [3].…”

Section: X] -3/2mentioning

confidence: 98%

Section: X] -3/2mentioning

confidence: 99%

Section: Phenomenological Model Of Nucleation Of a Fatigue Macrocrackmentioning

confidence: 99%

mentioning

confidence: 94%

See 3 more Smart Citations

Unified model of nucleation and growth of fatigue cracks. Part 1. Use of force parameters of fracture mechanics of materials in the stage of crack nucleation

Ostash¹,

Panasyuk²,

Kostyk³

1998

Mater Sci

Self Cite

View full text Add to dashboard Cite

show abstract

Determination of period of initiation of a fatigue macrocrack at stress raisers

Ostash

1991

Mater Sci

View full text Add to dashboard Cite

A unified model of initiation and growth of fatigue macrocracks. part 3. stage of growth of a macrocrack

Ostash¹,

Panasyuk²

1999

Mater Sci

Self Cite

View full text Add to dashboard Cite

From a common viewpoint, fatigue fracture of materials is simulated by the process of initiation of an initial macrocrack of length a i = d* (d* is the constant of the material), which is successively (stepwise) repeated at the stage of its growth. As a result, the diagram "range of local stresses -period of initiation of an initial macrocrack" or "range of local strains -period of initiation of an initial macrocrack," which was determined for notched specimens, can be used for the construction of the diagram "growth rate of a macrocrack -range of the stress intensity factor" or "growth rate of a macrocrack -range of local strains," respectively, if the crack is presented as a sharp notch with effective rounded radius Peff = d* of the tip.For estimation of the endurance of a structural material, the endurance limits ~R and ~g of smooth and notched specimens, respectively, and the threshold of cyclic crack resistance Kth of specimens with a macrocrack are the most widespread characteristics. It often occurs that these characteristics correlate with other mechanical and physical parameters of materials in different ways. The reason for this lies in the fact that the characteristics are determined at various stages of fatigue fracture on the basis of fracture criteria for the limiting state of macro-or microvolumes of the material. At present, the opinion exists that the regularities of the processes of initiation and growth of a macrocrack are significantly different and, for this reason, are separately studied. To our mind, the process of fatigue of materials (the initiation of a macrocrack and its propagation) can be studied from a common viewpoint by using unified approaches and parameters and by interpreting the growth of a fatigue macrocrack as the stepwise repeated act of its initiation.In this context, it is worth noting the models of growth of fatigue cracks, which are based on the assumption that a crack can be regarded as a sharp notch [1, 2] with a rounded radius p = P* of the tip, where p* is the constant of the material [2]. The growth of a fatigue macrocrack is considered as a sequence of acts of its reinitiation in the vicinity of the tip of a sharp notch. This growth is described by the parameters that were found with smooth and notched specimens by using the well-known Neuber and Manson-Coffin approaches [1,2]. However, the parameter p* has no clear physical meaning, and methods for direct determination of its value are unknown up to now [2]. The problem of initiation of fatigue cracks was not considered in the works mentioned above.Let us postulate that the formation rate of the unit surface of a fatigue crack is a single-valued function of local strain both in the process of initiation of a macrocrack and in the course of its growth. From the viewpoint of the unified approach to initiation and propagation of fatigue macrocracks, investigations based on the above statement are of high priority. The structure of this function was established at the stage of growth of a macrocrack [3]. However, it w...

show abstract

Effect of low temperature on the initiation and growth of fatigue cracks in 08kp steel with different grain size

Cited by 8 publications

References 1 publication

Unified model of nucleation and growth of fatigue cracks. Part 1. Use of force parameters of fracture mechanics of materials in the stage of crack nucleation

Unified model of nucleation and growth of fatigue cracks. Part 1. Use of force parameters of fracture mechanics of materials in the stage of crack nucleation

Determination of period of initiation of a fatigue macrocrack at stress raisers

A unified model of initiation and growth of fatigue macrocracks. part 3. stage of growth of a macrocrack

Contact Info

Product

Resources

About