Stress intensity factors for surface fatigue crack in a round bar under cyclic axial loading

Muñoz-Abella

Fatigue Fract Eng Mat Struct

2017

In the last decades, neural network approach has often been used to study various and complex engineering problems, such as optimization or prediction. In this paper, a methodology founded on artificial neural networks (ANNs) was used to calculate the stress intensity factor (SIF) in different points of the front of a semi‐elliptical crack present in a rotating shaft, taking into account the shape and depth of the crack, the angle of rotation, and the location of the point in the front. In the event of rotating machines, such as shafts, it is crucial to know the SIF along the crack front because this parameter, according to the Paris Law, is related to the performance of the crack during its propagation. Previously, it was necessary to achieve the data for the ANN training, for this a quasi‐static numerical model was made, which simulates a rotating cracked shaft with a semi‐elliptical crack. The numerical solutions cover a wide range of crack depths and shapes, and rotation angles. The values of the SIF estimated by the ANNs were contrasted with other solutions available in the literature finding a good agreement between them. The proposed neural network methodology is an alternative that offers a very good option for the SIF estimation, because it is efficient and easy to use, does not require high computational costs, and can be used to analyse the propagation of cracks contained in rotating shafts by means of the Paris Law taking into account the nonlinear behaviour of the shaft.

Section: Introductionmentioning

confidence: 99%

Neural approach to estimate the stress intensity factor of semi‐elliptical cracks in rotating cracked shafts in bending

Muñoz-Abella

Fatigue Fract Eng Mat Struct

2017

“…2 These kinds of breakdowns, [3][4][5] if not early detected, are often catastrophic and produce personal injuries or economic problems. In addition, one can find in the literature other kind of models that consider partial opening and closing of the crack during shaft rotation: this behaviour has been studied, numerically or analytically, by different authors, [9][10][11][12][13][14] always considering an aligned and balanced shaft. When a cracked shaft rotates, the transverse crack, perpendicular to the shaft axis, can open and close once per revolution depending on the loads, the global stiffness of the shaft and the local stiffness of shaft at the cracked section.…”

Section: Introductionmentioning

confidence: 99%

“…The presence of eccentric masses can be considered a very common unbalance case in rotors [11][12][13][14][15] and modifies the dynamic behaviour of the rotating shafts and may hide the presence of the cracks or, as well, can increase their effects. The presence of eccentric masses can be considered a very common unbalance case in rotors [11][12][13][14][15] and modifies the dynamic behaviour of the rotating shafts and may hide the presence of the cracks or, as well, can increase their effects.…”

Section: Introductionmentioning

confidence: 99%

“…Switching crack model can be valid for small cracks, but when the crack grows, its behaviour can be associated with a harmonic variation 8 . In addition, one can find in the literature other kind of models that consider partial opening and closing of the crack during shaft rotation: this behaviour has been studied, numerically or analytically, by different authors, [9][10][11][12][13][14] always considering an aligned and balanced shaft.…”

mentioning

confidence: 99%

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Stress intensity factor estimation for unbalanced rotating cracked shafts by artificial neural networks

Muñoz-Abella

Fatigue Fract Eng Mat Struct

2014

The knowledge of the stress intensity factor (SIF) values along a crack front is essential to calculate the crack growth rate and the remaining life of a mechanical component. In the case of a rotating shaft, usually it presents disalignments, which modify the SIF data with regard to a balanced one. This paper presents the use of an artificial neural network (ANN) for estimating the SIF at the crack front in an unbalanced shaft under rotating bending, previously, a quasi‐static numerical (finite element) model, which simulates a rotating shaft, has been developed to create the training cases for the ANN. The obtained results allow to study the influence of the unbalance of rotating shafts in the crack breathing mechanism and will allow to predict the influence of this behaviour on the values of the SIF and in the propagation of cracks.

Theoretical and Applied Mechanics Letters

“…Email: h.yuan@uni-wuppertal.de arc crack front [8][9][10][11][12][13][14][15][16] as shown in Fig. 1.…”

mentioning

confidence: 97%

Investigation on 3D fatigue crack propagation in surface-cracked specimens

Yuan

Sun

2013

In the present work the fatigue crack growth in AISI304 specimens is investigated experimentally. In 3D finite element analysis the virtual crack closure technique is applied to calculate distributions and variations of the stress intensity factor along the surface crack front. It is confirmed that the stress intensity factor along the surface crack front varies non-uniformly with crack growth. Crack growth rate is proportional to the stress intensity factor distribution in the 3D cracked specimen. The fatigue crack growth in surface cracked specimens can be described by the Forman model identified in conventional compact tension specimens. For crack growth in the free specimen surface the arc length seems more suitable to quantify crack progress. Geometry and loading configuration of the surface cracked specimen seem to not affect the fatigue crack growth substantially.Critical cracks exist mainly on surfaces of mechanical components in engineering. To predict fatigue crack growth life, characterization and verification of a surface crack through the conventional fracture mechanics specimen, such as compact tension (CT), are of interesting. From fracture analysis it is known that the stress field in a 3D surface crack differs from the conventional plane strain tip field. The stress intensity factor (SIF) depends additionally on crack front curvature, crack edge to free surface, and structure configuration. Especially, SIF may vary non-proportionally with crack growth. Predictability and accuracy of the fracture mechanics to 3D surface crack are still interesting issue for many mechanical parts under complex loading conditions.In the present work, surface crack in circular rod of stainless steel AISI304 is studied experimentally. The crack growth rate (da/dN ) versus stress intensity factor (∆K) relation with different load ratios (R) was firstly obtained from standard CT specimens. Fatigue crack growth in the CT specimens can be described by the Forman model. 1 To investigate surface crack growth, the axial tension rods are fabricated and pre-cracked. Fatigue crack growth tests on the rods were carried out at different load ratios. Backtracking method 2,3 was attempted for monitoring crack shape evolution. To obtain more accurate SIFs, beach marks on the crack surface were represented by fitting elliptical arc curves. 3D finite element meshes are generated in compliance with the crack configurations. The SIF along the whole crack front was calculated via the virtual crack closure technique (VCCT). 4-7 The relation of crack shape evolution with the SIF distribution along the crack front was discussed. Finally, the Forman model obtained from the standard CT specimen is used to predict the surface crack evolution in tensile rods.A 3D crack front can be represented by an elliptical a) Corresponding author. Email: h.yuan@uni-wuppertal.de arc crack front 8-16 as shown in Fig. 1. Here a denotes the depth of the surface crack. The elliptical crack can be described by the semi-axes, a and b. For a given crack depth, the ...