Étude de l’amorçage des fissures de fatigue sur des éprouvettes en acier à très haute résistance possédant des défauts de formes et de dimensions différentes

Baus, A.; Lieurade, H. P.; Sanz, Gerardo; Truchon, Michel

doi:10.1051/metal/197774100565

Cited by 4 publications

(2 citation statements)

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“…3b) at the stage of growth of a fatigue macrocrack, it is necessary to know the interrelation between the ranges Ao~, and AK in the vicinity of the tip of a macrocrack. For this purpose, we use the approximate formula [11,18] 2AK AK AOy(0) : : 1.128 r='…”

Section: Case Of Given Stresses Acy Ementioning

confidence: 99%

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

Ostash¹,

Panasyuk²

1999

Mater Sci

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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...

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Section: Case Of Given Stresses Acy Ementioning

confidence: 99%

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

Ostash¹,

Panasyuk²

1999

Mater Sci

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“…At present no exact closed solutions exist for the stress-strain state of such specimens with notches. Because of the lack of such solutions some investigators apply solutions of corresponding problems for the infinite plane with a semi-infinite crack to edge notch specimens, and determine the maximum notch tip stress aymax through the stress intensity factor for the crack of equivalent length (equal to the notch depth) according to the formula [1,3] rJ,,,,,,x = 1.l28K1/,h.…”

Section: Many Structural Elements and Machine Parts Working Under Cycmentioning

confidence: 99%

A New Approach to the Determination of the Macrocrack Nucleation Period Near a Stress Concentrator

Panasyuk

Ivanitska

Ostash

1993

Fatigue Fract Eng Mat Struct

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The stress-strain state of a rectangular plate with a central circular hole and a disc with an edge notch is analyzed both for elastic and elastic-plastic behaviour when cracks emanate from the contours of these concentrators. Stress intensity factors are determined as well as the value of the inelastic deformation at stress concentration zones. The parameters describing the process of crack nucleation are established. The computational results are compared with experimental data when evaluating the period of macrocrack nucleation. NOMENCLATURE a,b = plate length and width d* = the material constant E = Young's modulus G = elastic shear modulus h = thickness of a plate or a disc K, = stress intensity factor (SIF) for the opening mode crack K,$ = SIF for the opening mode of a crack emanating from the concentrator L, = concentrator contour (K = 0); plate or disc contour ( K = I); crack contour ( K = 2.3) I = crack length 1, = length of equivalent crack f , = length of plastic zone 1, = length of a crack emanating from the concentrator N, = number of loading cycles before crack nucleation N ( t K ) , T(tK) = stress components on the L, contour R = disc radius or hole radius in the plate t , = current coordinate of the contour L, u(t,), o(t,) = displacement vector components S , , 86, = notch tip opening displacement (NTOD) and NTOD range (in point A) p = Poisson ratio p = notch radius in the disc uys = yield stress of the material u : , Au:= normal stress and normal stress range at the characteristic distance d* from the concentrator tip uyvmax = maximum stress at the concentrator tip uy(x) = normal stress component along the concentrator axis O(z), Y ( 2 ) = Kolosov-Muskhelishvili complex stress function

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Fatigue in Lubricants Environment

Poudou

Nouail

Ayel

et al. 1983

Fracture Mechanics Technology Applied to Material Evaluation and Structure Design

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Étude de l’amorçage des fissures de fatigue sur des éprouvettes en acier à très haute résistance possédant des défauts de formes et de dimensions différentes

Cited by 4 publications

References 0 publications

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

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

A New Approach to the Determination of the Macrocrack Nucleation Period Near a Stress Concentrator

Fatigue in Lubricants Environment

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