Bayesian prediction and probabilistic model of fatigue cracks in steel structures

2019 ◽  
Vol 103 ◽  
pp. 335-346 ◽  
Author(s):  
Meng-Cheng Chen ◽  
Wei Fang ◽  
Chao Yang ◽  
Li Xie
Keyword(s):  
Probabilistic Model ◽  
Fatigue Cracks ◽  
Steel Structures ◽  
Bayesian Prediction

Application of Plastic Optical Fiber Fatigue Sensor in Real-Time Monitoring of Fatigue Cracks in Steel Structures

2020 ◽  
Vol 15 (7) ◽  
pp. 864-869
Author(s):  
Ying Liu
Keyword(s):  
Signal Processing ◽  
Optical Fiber ◽  
Real Time ◽  
Fatigue Cracks ◽  
Steel Structures ◽  
Luminous Flux ◽  
Plastic Optical Fiber ◽  
Signal Processing Algorithm ◽  
New Type ◽  
Fatigue Sensor

Plastic optical fiber (POF) is a new type of sensing material. Compared with traditional quartz optical fiber, it has the advantages of good tenacity, low cost, easy processing, and high sensitivity. A new type of POF-Fatigue sensor (nPOF-Fs) is designed by using POF, which is based on the changes the luminous flux. The change in the relative displacement of the two ends of the fiber is obtained through the change in the luminous flux in the POF, which is later converted into an electrical signal by the photoelectric conversion device. By collecting and analyzing the signals, accurate measurement of the dynamic response of the workpiece is achieved. Combined with the signal processing algorithm that can detect and monitor the crack expansion of steel structures under cyclic loading based on the RMS envelope and Hilbert transform filters, the fatigue crack can be monitored in real-time. The results obtained by nPOF-Fs are fundamentally coincide with the results acquired by the COD sensor. In view of the higher cost of monitoring with the COD sensor, the use of a POF sensor combined with a signal processing algorithm in monitoring the occurrence and expansion of fatigue cracks has great potential in the field of structural monitoring.

Efficient detection method of fatigue cracks in steel structures

2018 ◽  
Vol 2018.17 (0) ◽  
pp. 206
Author(s):  
Yushi YAMANE ◽  
Noboru SASAKI ◽  
Hideki ENDO ◽  
Tsuyoshi ASHIDA ◽  
Tsutomu MORIMOTO ◽  
...  
Keyword(s):  
Detection Method ◽  
Fatigue Cracks ◽  
Steel Structures ◽  
Efficient Detection

Applications of Probabilistic Fracture Mechanics to Offshore Structures

1988 ◽  
Vol 41 (2) ◽  
pp. 61-84 ◽  
Author(s):  
Finn Kirkemo
Keyword(s):  
Fracture Mechanics ◽  
Model Updating ◽  
Fatigue Cracks ◽  
Limit State ◽  
Steel Structures ◽  
Local Stress ◽  
Offshore Structures ◽  
And Performance ◽  
Fatigue Limit State ◽  
Life Predictions

For offshore structures the fatigue limit state is governing the structural dimensions of several members and joint connections. Safety against fatigue failure is achieved through a combination of design requirements and performance of in-service inspections with repair of detected fatigue cracks. A review of uncertainties involved in fatigue life predictions by fracture mechanics is presented with particular reference to steel structures. Sources of uncertainties considered are: environmental conditions, hydrodynamic loading, global structural analysis, local stress calculation at fatigue sensitive points, and fatigue crack growth modeling by fracture mechanics. A probabilistic model using the fracture mechanics in probabilistic form is presented. This model accounts for uncertainties in loading, initial and critical defect sizes, material parameters, and in the uncertainty related to computation of the stress intensity factor. Failure probabilities are computed by first-order reliability methods and sensitivity factors are determined. Model updating based on in-service inspection results is formulated. Uncertainties with respect to detecting a crack and to correctly sizing a crack are included. Experience on application of the analysis method is presented.

Sensitive Ultrasonic NDE of Tightly Closed Small Cracks in Carbon Steel Structures

2006 ◽  
Vol 321-323 ◽  
pp. 644-648
Author(s):  
S. Reaz Ahmed ◽  
Masumi Saka
Keyword(s):  
Carbon Steel ◽  
Fatigue Cracks ◽  
Ultrasonic Method ◽  
Steel Structures ◽  
Steel Plates ◽  
Highly Sensitive ◽  
Small Cracks ◽  
Ultrasonic Nde ◽  
Comparison Of The Results ◽  
Load Conditions

Nondestructive evaluation of tightly closed small cracks in carbon steel has been investigated under no load conditions. The investigation has been carried out by using a new ultrasonic method of testing, which has the capability of dealing with smaller tight cracks sensitively. Tight closure of small fatigue cracks in carbon steel plates is realized when the measured responses are compared with the calculated responses of the identical open cracks. Highly sensitive characteristic of the present method is verified through the comparison of the results with those obtained by the standard ultrasonic method of testing.

The Potential for Non-Conservative Results From the Probabilistic Fracture Mechanics Analyses Is Assessed Based on the Collected Observation of Fatigue Cracks in Offshore Steel Structures

2017 ◽  
Author(s):  
Ole Tom Vårdal
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Structural Integrity ◽  
Fatigue Cracks ◽  
Steel Structures ◽  
Lessons Learned ◽  
Probabilistic Methods ◽  
Growth Potential

In structural integrity management, it is essential to know the fatigue crack growth potential. The lessons learned from use of refined fatigue analyses, fracture mechanics and probabilistic methods for platforms in-service are presented. For ageing offshore units of semi-submersible design, the inspection history of more than 20 000 NDT inspections and detection of close to 1000 fatigue cracks, are used in this study. These experience data are used to assess the potential for Non-conservative estimate for the fatigue crack growth potential.

scholarly journals Strengthening of steel structures with fatigue cracks using adhesively bonded non-prestressed and prestressed CFRP lamellas

2019 ◽  
Author(s):  
Yvonne Ciupack ◽  
Lukas Ledecky ◽  
Yann Kasper ◽  
Achim Geßler ◽  
Matthias Albiez ◽  
...  
Keyword(s):  
Fatigue Cracks ◽  
Crack Tip ◽  
Steel Structures ◽  
Positive Influence ◽  
Fatigue Tests ◽  
Small Scale ◽  
Adhesively Bonded ◽  
Repair Welding ◽  
Reinforcement Measures ◽  
Adhesive Materials

In comparison to classic strengthening methods of fatigue-damaged steel structures, adhesively bonded CFRP lamellas show several advantages. Compared to bolted reinforcement measures and the drilling of the crack tip, crosssectional weakening is avoided. Heat-induced, negatively acting residual stresses and distortions, usually occurring during repair welding, can also be excluded. Therefore, the effectiveness of adhesively bonded CFRP lamellas to enhance the remaining lifetime of fatigue damaged steel structures is examined in a German research project. Selected results are presented in this paper. To characterize the steel, CFRP and adhesive materials, different tests on small scale specimens are carried out. With the help of fatigue tests on CT-samples the remaining fatigue lifetimes of specimens strengthened with adhesively bonded CFRP lamellas is compared to the remaining lifetimes of specimens strengthened by established methods such as drilling the crack tip and repair welding. Based on the evaluation of the crack propagation after the rehabilitation measures, the great potential of adhesively bonded CFRP reinforcements can be deduced. By prestressing the lamellas, the remaining lifetime can generally be increased further. The combination of adhesively bonded CFRP lamellas together with established rehabilitation methods shows a particularly high positive influence on the remaining lifetime of the CT-specimens.

Design of Crack Removal Profiles Based on Shape Development of Surface Defects

2003 ◽  
Author(s):  
J. Efrai´n Rodri´guez-Sa´nchez ◽  
William D. Dover ◽  
Feargal P. Brennan
Keyword(s):  
Surface Defects ◽  
Fatigue Cracks ◽  
Plate Thickness ◽  
Steel Structures ◽  
Tubular Joints ◽  
Notch Geometry ◽  
Repair Procedure ◽  
Profile Design ◽  
Bending Loading ◽  
Surface Plate

A crack removal has the purpose to stop crack propagation and prevent future crack reinitiation, thus fatigue life of the component is extended. A profile design for the removal of fatigue cracks that grow under bending loading is presented. The design is based on the preferred shape development of surface defects under bending loading. Preferred shape development of surface defects was experimentally identified and validated with observations previously reported by other authors. The design of a crack removal profile consists on determining a notch geometry and its dimensions to cut out a crack. The crack removal profile presented here induces crack reinitiation, if it would occur, on the surface plate at the notch ends rather than in the bottom of the notch, so original plate thickness is reinstalled for propagation and inspection is easier. This repair procedure is recommended for the removal of fatigue cracks in tubular joints of offshore jackets steel structures.

Comparison of Calibration Functions for Short Edge Cracks under Selected Loads

2017 ◽  
Vol 754 ◽  
pp. 353-356 ◽  
Author(s):  
Stanislav Seitl ◽  
Petr Miarka ◽  
Lucie Malíková ◽  
Martin Krejsa
Keyword(s):  
Fatigue Crack ◽  
Fatigue Cracks ◽  
Steel Structures ◽  
Initial Crack ◽  
Pure Bending ◽  
Short Edge ◽  
Four Point Bending ◽  
Linear Fracture ◽  
Long Time ◽  
Edge Cracks

Attention to the fatigue cracks in steel structures and bridges has been paid for long time. In spite to efforts to eliminate the creation and propagation of fatigue cracks throughout the designed service life, cracks are still revealed during inspections. Note, that depending on location of initial crack, the crack may propagate from the edge or from the surface. The theoretical model of fatigue crack progression is based on linear fracture mechanics. Steel specimens are subjected to various load (tension, three-and four-point bending, pure bending etc.). The calibration functions for short edge cracks are compared for various load and the discrepancies are discussed.

Fatigue strength of a groove weld on steel backing

1984 ◽  
Vol 11 (4) ◽  
pp. 692-700 ◽  
Author(s):  
K. A. Baker ◽  
G. L. Kulak
Keyword(s):  
Finite Element Analysis ◽  
Fatigue Strength ◽  
Fatigue Cracks ◽  
Steel Structures ◽  
Fatigue Loading ◽  
Test Results ◽  
Fabrication Technique ◽  
Element Analysis ◽  
Fillet Weld ◽  
Local Stresses

Groove welding made from one side is a common fabrication technique for joints in steel structures. If a steel backing bar is used, current (1983) North American specifications require that it be removed after welding and the weld ground flush if the detail is to be located transversely to the direction of stress and fatigue loaded. This is an expensive, and in some cases impractical, procedure. In the investigation reported herein, data concerning the fatigue strength of a groove weld with steel backing bar detail have been obtained experimentally. The backing bar was attached with intermittent fillet welds. A finite element analysis has been used to assist in interpretation of the test results.The analysis showed that high local stresses are present at the toe of the fillet weld. However, high stresses also exist at the flush-ground face of the groove weld, and the test results indicated that all fatigue cracks started at this side of the detail. When this detail is present in a structure and subjected to a fatigue loading, category C of the AASHTO or CSA specifications will provide a suitable basis for design. Key words: failure, fatigue, steel, welding.

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