Fatigue Crack Propagation Monitoring Research Articles

Monitoring of Fatigue Crack Propagation by Damage Index of Ultrasonic Guided Waves Calculated by Various Acoustic Features

Under cyclic and repetitive loads, fatigue cracks can be further propagated to a crucial level by accumulation, causing detrimental effects to structural integrity and potentially resulting in catastrophic consequences. Therefore, there is a demand to develop a reliable technique to monitor fatigue cracks quantitatively at an early stage. The objective of this paper is to characterize the propagation of fatigue cracks using the damage index (DI) calculated by various acoustic features of ultrasonic guided waves. A hybrid DI scheme for monitoring fatigue crack propagation is proposed using the linear fusion of damage indices (DIs) and differential fusion of DIs. An experiment is conducted on an SMA490BW steel plate-like structure to verify the proposed hybrid DIs scheme. The experimental results show that the hybrid DIs from various acoustic features can be used to quantitatively characterize the propagation of fatigue cracks, respectively. It is found that the fused DIs calculated by the acoustic features in the frequency domain have an improved reliable manner over those of the time domain. It is also clear that the linear and differential amplitude fusion DIs in the frequency domain are more promising to indicate the propagation of fatigue cracks quantitatively than other fused ones.

Fatigue crack propagation monitoring by Acoustic Emission signal analysis

A crucial aspect in damage evaluation of masonry structures is the analysis of long-term behaviour and for this reason fatigue analysis has a great influence on safety assessment of these structures.Acoustic Emission (AE) technique is very effective in identifying micro and macro-defects and their temporal evolution due to fatigue in several materials. This technique permits to estimate the velocity of ultrasonic waves propagation and the amount of energy released during fracture propagation to obtain information on the criticality of the ongoing process.By means of AE monitoring, an experimental analysis on two different sets of reinforced masonry walls under fatigue loading has been carried out. During these tests, the AE signals were recorded. The AE signals were analysed using Fast Fourier Transform (FFT) to examine the frequency distribution during the micro- and macro-cracking process. The evolution of the wavelength of the shear component of the AE signal was evaluated through the two characteristic peaks in the AE signals spectrum and the wave speed of the P or S waves. This wavelength evolution can provide information on the micro-crack and macro-crack progress. This procedure permits to estimate the characteristic fracture dimension in several loading conditions and for different masonry reinforcing methods.

Fatigue Crack Propagation Monitoring by Acoustic Emission Signal Analysis

The aim of this work is to analyse the mechanical response of the masonry specimens under long-term action by means of cyclic tests. To this end laboratory tests were carried out at the Non-Destructive Testing Laboratory of the Politecnico di Torino. The Acoustic Emission technique was employed to assess the damage evolution, and the mechanical properties decay in order to evaluate the extent and the evolution of micro and macro-cracking due to cyclic action until structural collapse in masonry blocks and mortar layers.

304 渦電流を用いた疲労き裂のIn-situ進展評価(学生賞 I,2.学術講演)

304 渦電流を用いた疲労き裂のIn-situ進展評価(学生賞 I,2.学術講演)

Acoustic emission monitoring of fatigue crack propagation

Abstract The monitoring of fatigue crack propagation in steel and welded steel compact tension and T-section girder test specimens, using an advanced acoustic emission system with accurate source location, is described. The compact tension test specimens were subjected to load ratios of 0.1, 0.3, 0.5 and 0.7 while the T-section girders were subjected to a load ratio of 0.3. Located acoustic emission events were filtered for a narrow band containing the fatigue crack, and separated for different regions of the applied load range. The test results indicate that acoustic emission count rates, for small percentages of the applied load range close to the peak load, show reasonable correlation with crack propagation rates. Based on these correlations it may be possible to predict the remaining service life of fatigue damaged structures from the results of short term acoustic emission monitoring.

Constructive and destructive interference in acoustic emission during fatigue crack propagation

Fatigue crack propagation monitoring with acoustic emission reveals the presence of maxima and minima in the curve of the count rate as a function of the stress intensity factor. This is explained in terms of constructive and destructive interference due to specimen geometry. A theoretical model is developed and experimental proof of the validity of the model is presented.