Estimation of the Shape Evolution and the Growth History of an Embedded Crack by Fatigue Loading

2011 ◽  
Author(s):  
Koji Gotoh ◽  
Keisuke Harada ◽  
Yosuke Anai
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Estimation Method ◽  
Estimation Procedure ◽  
Fatigue Loading ◽  
Shape Evolution ◽  
Crack Growth Behaviour ◽  
Embedded Crack

Fatigue life estimation for planar cracks, e.g. part-through surface cracks or embedded cracks is very important because most of fatigue cracks found in welded built-up structures show planar crack morphologies. Fatigue crack growth behaviour of an embedded crack in welded joints is investigated in this study. The estimation procedure of crack shape evolution for an embedded crack is introduced and validation of the estimation procedure of fatigue crack growth based on the numerical simulation of fatigue crack growth with EDS concept for an embedded crack is performed. The validity of the proposed shape evolution estimation method and the fatigue crack growth simulation based on the fracture mechanics approach with EDS concept are confirmed.

scholarly journals Acoustic Emission Monitoring of Fatigue Crack Growth in Mooring Chains

2019 ◽  
Vol 9 (11) ◽  
pp. 2187 ◽  
Author(s):  
Ángela Angulo ◽  
Jialin Tang ◽  
Ali Khadimallah ◽  
Slim Soua ◽  
Cristinel Mares ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Large Scale ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Fatigue Loading ◽  
Damage Initiation ◽  
High Level

Offshore installations are subject to perpetual fatigue loading and are usually very hard to inspect. Close visual inspection from the turret is usually too hazardous for divers and is not possible with remotely operated vehicles (ROVs) because of the limited access. Conventional nondestructive techniques (NDTs) have been used in the past to carry out inspections of mooring chains, floating production storage and offloading systems (FPSOs), and other platforms. Although these have been successful at detecting and assessing fatigue cracks, the hazardous nature of the operations calls for remote techniques that could be applied continuously to identify damage initiation and progress. The aim of the present work is to study the capabilities of acoustic emission (AE) as a monitoring tool to detect fatigue crack initiation and propagation in mooring chains. A 72-day large-scale experiment was designed for this purpose. A detailed analysis of the different AE signal time domain features was not conclusive, possibly due to the high level of noise. However, the frequency content of the AE signals offers a promising indication of fatigue crack growth.

Guided Wave Acoustic Emission from Fatigue Crack Growth in Aluminium Plate

2006 ◽  
Vol 13-14 ◽  
pp. 23-28 ◽  
Author(s):  
C.K. Lee ◽  
Jonathan J. Scholey ◽  
Paul D. Wilcox ◽  
M.R. Wisnom ◽  
Michael I. Friswell ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Elastic Waves ◽  
Fatigue Cracks ◽  
Guided Wave ◽  
Experimental Results ◽  
Multiple Reflections ◽  
Alloy Plate

Acoustic emission (AE) testing is an increasingly popular technique used for nondestructive evaluation (NDE). It has been used to detect and locate defects such as fatigue cracks in real structures. The monitoring of fatigue cracks in plate-like structures is critical for aerospace industries. Much research has been conducted to characterize and provide quantitative understanding of the source of emission on small specimens. It is difficult to extend these results to real structures as most of the experiments are restricted by the geometric effects from the specimens. The aim of this work is to provide a characterization of elastic waves emanating from fatigue cracks in plate-like structures. Fatigue crack growth is initiated in large 6082 T6 aluminium alloy plate specimens subjected to fatigue loading in the laboratory. A large specimen is utilized to eliminate multiple reflections from edges. The signals were recorded using both resonant and nonresonant transducers attached to the surface of the alloy specimens. The distances between the damage feature and sensors are located far enough apart in order to obtain good separation of guided-wave modes. Large numbers of AE signals are detected with active fatigue crack propagation during the experiment. Analysis of experimental results from multiple crack growth events are used to characterize the elastic waves. Experimental results are compared with finite element predictions to examine the mechanism of AE generation at the crack tip.

Comparison of DBEM and FEM Crack Path Predictions with Experimental Findings for a SEN-Specimen under Anti-Plane Shear Loading

2007 ◽  
Vol 348-349 ◽  
pp. 129-132 ◽  
Author(s):  
Roberto G. Citarella ◽  
Friedrich G. Buchholz
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Crack Path ◽  
Shear Loading ◽  
Crack Growth Behaviour ◽  
3D Crack Growth ◽  
Corner Points ◽  
Experimental Findings

In this paper detailed results of computational 3D fatigue crack growth simulations will be presented. The simulations for the crack path assessment are based on the DBEM code BEASY, and the FEM code ADAPCRACK 3D. The specimen under investigation is a SEN-specimen subject to pure anti-plane or out-of-plane four-point shear loading. The computational 3D fracture analyses deliver variable mixed mode II and III conditions along the crack front. Special interest is taken in this mode coupling effect to be found in stress intensity factor (SIF) results along the crack front. Further interest is taken in a 3D effect which is effective in particular at and adjacent to the two crack front corner points, that is where the crack front intersects the two free side surfaces of the specimen. Exactly at these crack front corner points fatigue crack growth initiates in the experimental laboratory test specimens, and develops into two separate anti-symmetric cracks with complex shapes, somehow similar to bird wings. The computational DBEM results are found to be in good agreement with these experimental findings and with FEM results previously obtained. Consequently, also for this new case, with complex 3D crack growth behaviour of two cracks, the functionality of the proposed DBEM and FEM approaches can be stated.

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