Calculation of minimum crack size for growth under RCF between wheel and rail

Fracture toughness and Fatigue Crack Growth (FCG) experimental data represent the basis for accurate designs and integrity assessments of components containing crack-like defects. Considering ductile and high toughness structural materials, crack growing curves (e.g. J-R curves) and FCG data (in terms of da/dN vs. ΔK or ΔJ) assumed paramount relevance since characterize, respectively, ductile fracture and cyclic crack growth conditions. In common, these two types of mechanical properties severely depend on real-time and precise crack size estimations during laboratory testing. Optical, electric potential drop or (most commonly) elastic unloading compliance (C) techniques can be employed. In the latter method, crack size estimation derives from C using a dimensionless parameter (μ) which incorporates specimen’s thickness (B), elasticity (E) and compliance itself. Plane stress and plane strain solutions for μ are available in several standards regarding C(T), SE(B) and M(T) specimens, among others. Current challenges include: i) real specimens are in neither plane stress nor plane strain - modulus vary between E (plane stress) and E/(1-ν2) (plane strain), revealing effects of thickness and 3-D configurations; ii) furthermore, side-grooves affect specimen’s stiffness, leading to an “effective thickness”. Previous results from current authors revealed deviations larger than 10% in crack size estimations following existing practices, especially for shallow cracks and side-grooved samples. In addition, compliance solutions for the emerging clamped SE(T) specimens are not yet standardized. As a step in this direction, this work investigates 3-D, thickness and side-groove effects on compliance solutions applicable to C(T), SE(B) and clamped SE(T) specimens. Refined 3-D elastic FE-models provide Load-CMOD evolutions. The analysis matrix includes crack depths between a/W=0.1 and a/W=0.7 and varying thicknesses (W/B = 4, W/B = 2 and W/B = 1). Side-grooves of 5%, 10% and 20% are also considered. The results include compliance solutions incorporating all aforementioned effects to provide accurate crack size estimation during laboratory fracture and FCG testing. All proposals revealed reduced deviations if compared to existing solutions.

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Influences of Residual Stress, Surface Roughness and Peak-Load on Micro-Cracking: Sensitivity Analysis

Metals ◽

10.3390/met11020320 ◽

2021 ◽

Vol 11 (2) ◽

pp. 320

Author(s):

Jairan Nafar Dastgerdi ◽

Fariborz Sheibanian ◽

Heikki Remes ◽

Hossein Hosseini Toudeshky

Keyword(s):

Residual Stress ◽

Surface Roughness ◽

Crack Formation ◽

Peak Load ◽

Crack Size ◽

Effective Parameters ◽

Load Range ◽

Load Effect ◽

Damage Initiation ◽

Load Conditions

This paper provides further understanding of the peak load effect on micro-crack formation and residual stress relaxation. Comprehensive numerical simulations using the finite element method are applied to simultaneously take into account the effect of the surface roughness and residual stresses on the crack formation in sandblasted S690 high-strength steel surface under peak load conditions. A ductile fracture criterion is introduced for the prediction of damage initiation and evolution. This study specifically investigates the influences of compressive peak load, effective parameters on fracture locus, surface roughness, and residual stress on damage mechanism and formed crack size. The results indicate that under peak load conditions, surface roughness has a far more important influence on micro-crack formation than residual stress. Moreover, it is shown that the effect of peak load range on damage formation and crack size is significantly higher than the influence of residual stress. It is found that the crack size develops exponentially with increasing peak load magnitudes.

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Bearing Anomaly Recognition Using an Intelligent Digital Twin Integrated with Machine Learning

Applied Sciences ◽

10.3390/app11104602 ◽

2021 ◽

Vol 11 (10) ◽

pp. 4602

Author(s):

Farzin Piltan ◽

Jong-Myon Kim

Keyword(s):

Machine Learning ◽

Variable Structure ◽

Vibration Signal ◽

Crack Size ◽

Approximation Technique ◽

Digital Twin ◽

Average Accuracy ◽

Machine Learning Approach ◽

The Impact ◽

Signal Approximation

In this study, the application of an intelligent digital twin integrated with machine learning for bearing anomaly detection and crack size identification will be observed. The intelligent digital twin has two main sections: signal approximation and intelligent signal estimation. The mathematical vibration bearing signal approximation is integrated with machine learning-based signal approximation to approximate the bearing vibration signal in normal conditions. After that, the combination of the Kalman filter, high-order variable structure technique, and adaptive neural-fuzzy technique is integrated with the proposed signal approximation technique to design an intelligent digital twin. Next, the residual signals will be generated using the proposed intelligent digital twin and the original RAW signals. The machine learning approach will be integrated with the proposed intelligent digital twin for the classification of the bearing anomaly and crack sizes. The Case Western Reserve University bearing dataset is used to test the impact of the proposed scheme. Regarding the experimental results, the average accuracy for the bearing fault pattern recognition and crack size identification will be, respectively, 99.5% and 99.6%.

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Quantitative acoustic emission investigation on the crack evolution in concrete prisms by frequency analysis based on wavelet packet transform

Structural Health Monitoring ◽

10.1177/14759217211018871 ◽

2021 ◽

pp. 147592172110188

Author(s):

Zonglian Wang ◽

Keqin Ding ◽

Huilan Ren ◽

Jianguo Ning

Keyword(s):

Acoustic Emission ◽

Frequency Band ◽

Wavelet Packet ◽

Strain Energy Release ◽

Crack Size ◽

Frequency Bands ◽

Emission Signal ◽

Damage Process ◽

Concrete Materials ◽

Stage 1

To gain an insight into the evolution of micro-cracks in concrete materials, a quantitative acoustic emission investigation on the damage process of concrete prisms subjected to three-point bending loading was performed. Each of the monitored acoustic emission signals was processed by a two-level wavelet packet decomposition into four different frequency bands (AA2, DA2, AD2, and DD2), and the energy coefficients R1, R2, R3, and R4 that parameterize their characteristic frequency bands were calculated. By analyzing variations in energy coefficients of the lowest frequency band (AA2), R1, and the energy coefficients of the highest frequency band (DD2), R4, the whole damage process was divided into three stages: crack initiation, crack growth, and crack coalescence. An inverse relationship between the frequency of the acoustic emission signal emitted by the propagating crack and the crack size in concrete materials was acquired based on the damage theory of brittle materials and the strain energy release theory. The statistical analysis results of the experimental data indicated that the average of R1 increased in turn, and the average of R4 correspondingly decreased in turn from Stage 1 to Stage 3. It revealed that the frequencies of acoustic emission signals decreased gradually with the evolution of the damage of concrete prisms, which is in a good agreement with the theoretical analysis result.

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Effect of Rotational Stiffness Evolution at Crack Part on Critical Crack Size in SFR

Volume 6: Materials and Fabrication, Parts A and B ◽

10.1115/pvp2012-78061 ◽

2012 ◽

Author(s):

Takashi Wakai ◽

Hideo Machida ◽

Shinji Yoshida

Keyword(s):

Evaluation Method ◽

Large Diameter ◽

Crack Size ◽

Evolution Model ◽

Piping System ◽

Rotational Stiffness ◽

Critical Crack ◽

Rotational Spring Model ◽

Size Evaluation ◽

Critical Crack Size

This paper describes the efficiency of the deployment of rotational stiffness evolution model in the critical crack size evaluation for Leak Before Break (LBB) assessment of Sodium cooled Fast Reactor (SFR) pipes. The authors have developed a critical crack size evaluation method for the thin-walled large diameter pipe made of modified 9Cr-1Mo steel. In this method, since the SFR pipe is mainly subjected to displacement controlled load caused by thermal expansion, the stress at the crack part is estimated taking stiffness evolution due to crack into account. The stiffness evolution is evaluated by using the rotational spring model. In this study, critical crack sizes for several pipes having some elbows were evaluated and discuss about the effect of the deployment of the stiffness evolution model at the crack part on critical crack size. If there were few elbows in pipe, thermal stress at the crack part was remarkably reduced by considering the stiffness evolution. In contrast, in the case where the compliance of the piping system was small, the critical crack size could be estimated under displacement controlled condition. As a result, the critical crack size increases by employing the model and LBB range may be expected to be enlarged.

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Nondestructive Detection of a Crack in a Triangular Cantilever Beam Based on Frequency Measurement

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.353-358.2285 ◽

2007 ◽

Vol 353-358 ◽

pp. 2285-2288

Author(s):

Fei Wang ◽

Xue Zeng Zhao

Keyword(s):

Cantilever Beam ◽

Natural Frequencies ◽

Frequency Measurement ◽

Crack Size ◽

Force Sensors ◽

Rotational Spring ◽

Cantilever Deflection ◽

Crack Location ◽

Small Force ◽

Point Of Intersection

Triangular cantilevers are usually used as small force sensors in the transverse direction. Analyzing the effect of a crack on transverse vibration of a triangular cantilever will be of value to users and designers of cantilever deflection force sensors. We present a method for prediction of location and size of a crack in a triangular cantilever beam based on measurement of the natural frequencies in this paper. The crack is modeled as a rotational spring. The beam is treated as two triangular beams connected by a rotational spring at the crack location. Formulae for representing the relation between natural frequencies and the crack details are presented. To detect crack details from experiment results, the plots of the crack stiffness versus its location for any three natural modes can be obtained through the relation equation, and the point of intersection of the three curves gives the crack location. The crack size is then calculated using the relation between its stiffness and size. An example to demonstrate the validity and accuracy of the method is presented.

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Effect of virtual crack size on the crack deflection criterion at a bi-material interface under wedge loading

Mechanics Research Communications ◽

10.1016/j.mechrescom.2008.09.004 ◽

2009 ◽

Vol 36 (2) ◽

pp. 193-198 ◽

Cited By ~ 2

Author(s):

Jong-Bong Kim ◽

Hyunho Shin ◽

Woong Lee ◽

Kyong Yop Rhee

Keyword(s):

Crack Size ◽

Crack Deflection ◽

Material Interface

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Determination of Critical Crack Size Utilizing a Fracture Mechanics Test in Equipment Under Fatigue

Volume 6: Materials and Fabrication, Parts A and B ◽

10.1115/pvp2009-77937 ◽

2009 ◽

Author(s):

Irene Garcia Garcia ◽

Radoslav Stefanovic

Keyword(s):

Heat Treatment ◽

Fracture Mechanics ◽

Crack Size ◽

Operational Experience ◽

Element Analysis ◽

Critical Crack ◽

Circumferential Welds ◽

Fea Model ◽

Critical Crack Size

Equipment that is exposed to severe operational pressure and thermal cycling, like coke drums, usually suffer fatigue. As a result, equipment of this sort develop defects such as cracking in the circumferential welds. Operating companies are faced with the challenges of deciding what is the best way to prevent these defects, as well as determining how long they could operate if a defect is discovered. This paper discusses a methodology for fracture mechanics testing of coke drum welds, and calculations of the critical crack size. Representative samples are taken from production materials, and are welded employing production welding procedures. The material of construction is 1.25Cr-0.5Mo low alloy steel conforming to ASME SA-387 Gr 11 Class 2 in the normalized and tempered condition (N&T). Samples from three welding procedures (WPS) are tested: one for production, one for a repair with heat treatment, and one for repair without heat treatment. The position and orientation of test specimen are chosen based on previous surveys and operational experience on similar vessels that exhibited cracks during service. Fracture mechanics toughness testing is performed. Crack finite element analysis (FEA) model is used to determine the path-independed JI-integral driving force. Methodology for the determination of critical crack size is developed.

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