Detection of fatigue crack propagation through damage characteristic FWHM using FBG sensors

Sensor Review ◽  
2020 ◽  
Vol 40 (6) ◽  
pp. 665-673
Author(s):  
Meng Zhang ◽  
Weifang Zhang ◽  
Xiaobei Liang ◽  
Yan Zhao ◽  
Wei Dai
Keyword(s):  
Crack Propagation ◽  
Strain Field ◽  
Theoretical Calculations ◽  
Damage Index ◽  
Crack Tip ◽  
Image Correlation ◽  
Content Type ◽  
Inhomogeneous Strain ◽  
Fbg Sensors ◽  
Damage Characteristic

Purpose Crack damage detection for aluminum alloy materials using fiber Bragg Grating (FBG) sensor is a kind of structure health monitoring. In this paper, the damage index of full width at half maximum (FWHM) was extracted from the distorted reflection spectra caused by the crack-tip inhomogeneous strain field, so as to explain the crack propagation behaviors. Design/methodology/approach The FWHM variations were also investigated through combining the theoretical calculations with simulation and experimental analyses. The transfer matrix algorithm was developed to explore the mechanism by which FWHM changed with the linear and quadratic strain. Moreover, the crack-tip inhomogeneous strain field on the specimen surface was computed according to the digital image correlation measurement during the experiments. Findings The experimental results demonstrated that the saltation points in FWHM curve accorded with the moments of crack propagation to FBG sensors. Originality/value The interpretation of reflected spectrum deformation mechanism with crack propagation was analyzed based on both simulations and experiments, and then the performance of potential damage features – FWHM were proposed and evaluated. According to the correlation between the damage characteristic and the crack-tip location, the crack-tip of the specimen could be measured rapidly and accurately with this technique.

Methodology for in situ stress intensity factor determination on cracked structures by digital image correlation

2010 ◽  
Vol 1 (4) ◽  
pp. 344-357 ◽  
Author(s):  
V. Richter‐Trummer ◽  
P.M.G.P. Moreira ◽  
S.D. Pastrama ◽  
M.A.P. Vaz ◽  
P.M.S.T. de Castro
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Digital Image Correlation ◽  
Intensity Factor ◽  
Digital Image ◽  
Strain Field ◽  
Image Correlation ◽  
Content Type ◽  
Cracked Structures

PurposeThe purpose of this paper is to develop a methodology for in situ stress intensity factor (SIF) determination that can be used for the analysis of cracked structures. The technique is based on digital image correlation (DIC) combined with an overdetermined algorithm.Design/methodology/approachThe linear overdeterministic algorithm for calculating the SIF based on stress values around the crack tip is applied to a strain field obtained by DIC.FindingsAs long as the image quality is sufficiently high, a good accuracy can be obtained for the measured SIF. The crack tip can be automatically detected based on the same strain field. The use of the strain field instead of the displacement field, eliminates problems related to the rigid body motion of the analysed structure.Practical implicationsIn future works, based on the applied techniques, the SIF of complex cracked plane stress structures can be accurately determined in real engineering applications.Originality/valueThe paper demonstrates application of known techniques, refined for other applications, also the use of stress field for SIF overdeterministic calculations.

Crack propagation in a PVA dual-crosslink hydrogel: Crack tip fields measured using digital image correlation

2019 ◽  
Vol 138 ◽  
pp. 103158 ◽  
Author(s):  
Mincong Liu ◽  
Jingyi Guo ◽  
Zhilong Li ◽  
Chung-Yuen Hui ◽  
Alan T. Zehnder
Keyword(s):  
Digital Image Correlation ◽  
Crack Propagation ◽  
Digital Image ◽  
Crack Tip ◽  
Image Correlation ◽  
Crack Tip Fields

scholarly journals Identification and Prediction of Mixed-Mode Fatigue Crack Path in High Strength Low Alloy Steel

Proceedings ◽  
2018 ◽  
Vol 2 (8) ◽  
pp. 504
Author(s):  
Jie Zhang ◽  
Cedric Kiekens ◽  
Stijn Hertelé ◽  
Wim De Waele
Keyword(s):  
Fatigue Crack ◽  
Digital Image Correlation ◽  
Crack Propagation ◽  
Digital Image ◽  
Mixed Mode ◽  
Standardized Test ◽  
Crack Tip ◽  
Shear Loading ◽  
Image Correlation ◽  
Crack Trajectory

The trajectory of fatigue crack growth is influenced by many parameters and can be irregular due to changes in stress distribution or in material properties as the crack progresses. Images of the surface of a standardized test specimen can be used to visualize the crack trajectory in a non-destructive way. Accurately identifying the location of the crack tip, however, is challenging and requires devoted image postprocessing. In this respect, digital image correlation allows to obtain full field displacement and strain fields by analysing changes of digital images of the same sample at different stages of loading. This information can be used for the purpose of crack tip tracking. This paper presents a combined experimental-numerical study of detection and prediction of fatigue crack propagation path by means of digital image correlation (DIC) and the extended finite element method (X-FEM). Experimental validation and analyses are carried out on a modified C(T) specimen in which a curved crack trajectory is triggered by introducing mixed-mode (tension + shear) loading. The developed tools are used for validating an automated framework for crack propagation prediction.

scholarly journals Effect of microstructure on fatigue crack tip field of laser melting deposited Ti–5Al–5Mo–5V–1Cr–1Fe titanium alloy

2018 ◽  
Vol 165 ◽  
pp. 02009
Author(s):  
Kai Wang ◽  
Rui Bao ◽  
Siyuan Ren ◽  
Dong Liu ◽  
Chuliang Yan
Keyword(s):  
Titanium Alloy ◽  
Fatigue Crack ◽  
Strain Field ◽  
Crack Tip ◽  
Image Correlation ◽  
Laser Melting ◽  
Crack Tip Field ◽  
Significant Difference ◽  
Microstructure Effect ◽  
Effect Of Microstructure

In this paper, experimental and simulated investigations were carried out to understand the effect of microstructure on the fatigue crack tip strain field of laser melting deposited Ti–5Al–5Mo–5V–1Cr–1Fe titanium alloy. The mechanical properties of the laser melting deposited material corresponding to different microstructure zones were measured by digital image correlation method under in-situ static stretching, and the results indicate that the direction of primary α lamellas has great influence on the mechanical property of each grain. The crack tip strain fields considering the influence of material microstructure under constant amplitude conditions were measured, and the strain field of plastic zone has significant difference. Crystal plasticity finite element simulation of the static tensile and crack tip field considering the microstructure effect had been conducted and compare with experiment results. The simulation results are in good agreement with the test results in both the static tension strain field and crack tip strain field.

scholarly journals In Situ Measurements for Plastic Zone Ahead of Crack Tip and Continuous Strain Variation under Cyclic Loading Using Digital Image Correlation Method

Metals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 273 ◽  
Author(s):  
Yan Zhao ◽  
Dianyin Hu ◽  
Meng Zhang ◽  
Wei Dai ◽  
Weifang Zhang
Keyword(s):  
Digital Image Correlation ◽  
Plastic Zone ◽  
Crack Propagation ◽  
Digital Image ◽  
Crack Tip ◽  
Experimental Results ◽  
Image Correlation ◽  
Specimen Preparation ◽  
Strain Variation

Fatigue crack is one of the most common damage forms for aeronautical aluminum alloy. With crack propagation, the strain fields of the whole object surface and plastic zone (PZ) ahead of the crack tip are changing continuously. For most metallic materials, the behavior of PZ around the crack tip and continuous strain variation play a vital role in crack propagation. In this work, the “continuous” strain information at and in front of the crack tip on the specimen surface was obtained quantitatively and the PZ size ahead of crack tip was in situ measured quantitatively with crack propagation by using the digital image correlation (DIC) method, which overcomes the difficulty for the in situ measurement of mechanical variables. Moreover, the method of specimen preparation was simplified by using a white matt paint with strong adhesion, but also resulted in a higher resolution being shown, even for such a large area. Furthermore, the experimental results of the PZ size from the proposed method had good agreement with the theoretical values, which overcomes the limitation that the conventional approaches only consider the quasi-static crack. Finally, the continuous strain variation behavior was analyzed from the experimental results in detail with the consideration of crack propagation.

Development of a photomicroscope method for in situ damage monitoring under ultrasonic fatigue test

2022 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Kai Tan ◽  
Victor Postel ◽  
Yujia Liu ◽  
Dongtong Yang ◽  
Sen Tang ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Early Stage ◽  
Strain Analysis ◽  
Infrared Camera ◽  
Small Crack ◽  
Image Correlation ◽  
Content Type ◽  
Damage Monitoring ◽  
Ultrasonic Fatigue

PurposeMechanical issues related to the information and growth of small cracks are considered to play a major role in very high cycle fatigue (VHCF) for metallic materials. Further efforts on better understanding in early stage of a crack are beneficial to estimating and preventing catastrophic damage for a long period service.Design/methodology/approachDependent on the ultrasonic loading system, a novel method of in situ photomicroscope is established to study the crack behaviors in VHCF regime.FindingsThis in situ photomicroscope method provides advantages in combination with fatigue damage monitoring at high magnification, a large number of cycles, and efficiency. Visional investigation with attached image proceeding code proves that the method has high resolution on both size and time, which permits reliable accuracy on small crack growth rate. It is observed that the crack propagation trends slower in the overall small crack stage down to the level of 10–11 m/cycle. Strain analysis relays on a real-time recording which is applied by using digital image correlation. Infrared camera recording indicates the method is also suitable for thermodynamic study while growth of damage.Originality/valueBenefiting from this method, it is more convenient and efficient to study the short crack propagation in VHCF regime.

The cellular level mode I fracture behaviour of spruce and birch in the RT crack propagation system

Holzforschung ◽  
2016 ◽  
Vol 70 (2) ◽  
pp. 157-165 ◽  
Author(s):  
Pekka Tukiainen ◽  
Mark Hughes
Keyword(s):  
Crack Propagation ◽  
Fracture Behaviour ◽  
Crack Tip ◽  
Cellular Level ◽  
Image Correlation ◽  
Environmental Scanning ◽  
Mode I ◽  
Microscopic Structure ◽  
Pure Mode ◽  
Displacement Fields

Abstract The effect of the microscopic structure and the moisture content (MC) of wood on its fracture behaviour has been investigated. Green and air-dried spruce (Picea abies [L.] Karst.) and birch (Betula pendula Roth.) wood were subjected to pure mode I loading in the radial- tangential (RT) crack propagation system. Tests were carried out in situ in an environmental scanning electron microscope to observe crack propagation at the cellular level. Crack-tip displacement fields were computed by digital image correlation, and crack propagation was observed from the images captured during testing. Both the MC and the microscopic structure were found to affect the fracture process. In the air-dried birch and spruce, only microcracking caused large displacements ahead of the crack-tip. In spruce, the microcracking zone was larger than in birch. In green birch and spruce, microcracking was less evident than in the air-dried specimens, and in some cases, there were notable deformations in a few cells ahead of the crack-tip before crack extension. Microcracking is considered to be the main toughening mechanism in spruce and birch in the RT crack propagation system.

scholarly journals Mechanism of Subordinate Peak Skewing of FBG Sensor during Cracks Propagation Monitoring on Aluminum Alloy Structure

2017 ◽  
Vol 2017 ◽  
pp. 1-7 ◽  
Author(s):  
Bo Jin ◽  
Weifang Zhang ◽  
Feifei Ren ◽  
Meng Zhang ◽  
Wei Dai ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Plastic Zone ◽  
Strain Gradient ◽  
Strain Distribution ◽  
Crack Tip ◽  
Fbg Sensor ◽  
Inhomogeneous Strain ◽  
Study Results ◽  
Fbg Sensors ◽  
Cracks Propagation

This study investigates the variety of the spectra features of fiber Bragg grating (FBG) around the crack tip during fatigue crack propagation. The study results reveal that the turning of the subordinate peak is significantly associated with crack lengths and corresponds to strain gradient along the FBG. Meanwhile, the strain distribution sensed by the FBG changes with the sensing section of the grating. FBG sensors could observe the monotonic plastic zone ahead of the fatigue crack tip. The cubic strain is distributed along the grating, with monotonic plastic zone propagation at the initial and terminal part of the grating, at approximately a 30% ratio of the entire grating. However, the monotonic plastic zone is sensed by the FBG, at ±15% bias of the grating center, with the quadratic strain gradient pattern along the grating. In particular, when the initial and terminal parts of the grating experience highly inhomogeneous strain distribution, the spectrum distortion occurs.

scholarly journals New experimental techniques for dynamic crack localization

2009 ◽  
pp. 255-283
Author(s):  
David Grégoire ◽  
Hubert Maigre ◽  
Fabrice Morestin
Keyword(s):  
Crack Propagation ◽  
Crack Tip ◽  
Image Correlation ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Displacement Sensors ◽  
Optical Displacement ◽  
Propagation Parameters ◽  
Tip Position

The determination of relevant constitutive crack propagation laws under dynamic loading is a rather challenging operation. In dynamic impact cases, the variations of propagation parameters and exact crack positions are difficult to control. This paper focuses on different techniques for measuring accurate crack tip position histories in dynamic crack propagation experiments. Two different methods are considered: very accurate crack tip localization by optical displacement sensors is first described for transparent materials; then, an automatic method based on digital image correlation is presented for crack localization in all brittle materials whatever their opacity.

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