scholarly journals An Efficient Time Reversal Method for Lamb Wave-Based Baseline-Free Damage Detection in Composite Laminates

2018 ◽  
Vol 9 (1) ◽  
pp. 11 ◽  
Author(s):  
Liping Huang ◽  
Junmin Du ◽  
Feiyu Chen ◽  
Liang Zeng
Keyword(s):  
Damage Detection ◽  
Time Reversal ◽  
Lamb Wave ◽  
Composite Laminates ◽  
Narrow Band ◽  
Great Influence ◽  
Time Intervals ◽  
Wide Range ◽  
Reconstructed Signal ◽  
Short Time

Time reversal (TR) concept is widely used for Lamb wave-based damage detection. However, the time reversal process (TRP) faces the challenge that it requires two actuating-sensing steps and requires the extraction of re-emitted and reconstructed waveforms. In this study, the effects of the two extracted components on the performance of TRP are studied experimentally. The results show that the two time intervals, in which the waveforms are extracted, have great influence on the accuracy of damage detection of the time reversal method (TRM). What is more, it requires a large number of experiments to determine these two time intervals. Therefore, this paper proposed an efficient time reversal method (ETRM). Firstly, a broadband excitation is applied to obtain response at a wide range of frequencies, and ridge reconstruction based on inverse short-time Fourier transform is applied to extract desired mode components from the broadband response. Subsequently, deconvolution is used to extract narrow-band reconstructed signal. In this method, the reconstructed signal can be easily obtained without determining the two time intervals. Besides, the reconstructed signals related to a series of different excitations could be obtained through only one actuating-sensing step. Finally, the effectiveness of the ETRM for damage detection in composite laminates is verified through experiments.

Microwave-enhanced metal- and acid-catalysed hydrogen isotope exchange reactions

1998 ◽  
Vol 76 (6) ◽  
pp. 726-728 ◽  
Author(s):  
Jean M Barthez ◽  
Anton V Filikov ◽  
Lottie B Frederiksen ◽  
Marie-Loire Huguet ◽  
John R Jones ◽  
...  
Keyword(s):  
Hydrogen Isotope ◽  
Isotope Exchange ◽  
Exchange Reactions ◽  
Time Intervals ◽  
Considerable Potential ◽  
Hydrogen Isotope Exchange ◽  
Wide Range ◽  
Homogeneous Acid ◽  
Acid Catalysed Reactions ◽  
Short Time

The benefits of using microwaves to accelerate the rates of hydrogen isotope exchange reactions are illustrated by reference to heterogeneous and homogeneous metal-catalysed reactions as well as to homogeneous acid-catalysed reactions. The results show that good incorporation of deuterium is obtained in very short time intervals, typically <20 min, and that the approach has considerable potential for the labeling of a wide range of compounds with both deuterium and, by implication, tritium.Key words: microwave enhanced deuteriations, hydrogen isotope exchange.

scholarly journals COASTAL PROCESSES FROM SPACE PHOTOGRAPHY

1970 ◽  
Vol 1 (12) ◽  
pp. 39
Author(s):  
Maynard M. Nichols
Keyword(s):  
Large Scale ◽  
Salt Water ◽  
Remote Sensing Data ◽  
Vantage Point ◽  
Coastal Processes ◽  
Time Intervals ◽  
Wide Range ◽  
The World ◽  
Routine Basis ◽  
Short Time

Photographs taken from space provide a new source of data concerning coastal processes By utilizing the high vantage point and broad view orbiting space cameras can record little known large-scale processes at short time intervals Major outflow plumes, fresh-salt water "fronts", turbidity maxima and massive effluents are among the wide range of features displayed It is shown from selected examples how coastal processes can be evaluated from space photography and how the information may be of use for solving certain problems as a supplement to field and other remote sensing data By 1972 satellite photography will be available on a routine basis for many coasts of the world Engineers are urged to consider the potential for improving their information which space photography has to offer.

Time reversibility of Lamb waves in thin plates with surface-bonded piezoelectric transducers is temperature invariant at the best reconstruction frequency

2020 ◽  
pp. 147592172096512
Author(s):  
Bhabagrahi Natha Sharma ◽  
Santosh Kapuria ◽  
A Arockiarajan
Keyword(s):  
Temperature Dependence ◽  
Lamb Wave ◽  
Lamb Waves ◽  
Dominant Role ◽  
Excitation Frequency ◽  
Piezoelectric Transducers ◽  
Time Reversibility ◽  
Adhesive Layers ◽  
Wide Range ◽  
Reconstructed Signal

The Lamb wave time-reversal method has been widely proposed as a baseline-free method for damage detection in thin-walled structures. Under varying thermal environments, it would require that the time reversibility of Lamb waves is temperature invariant. In this study, we examine the temperature dependence of Lamb waves and its time reversibility using experiments and finite element simulations on isotropic plates with surface-bonded piezoelectric wafer transducers for actuation and sensing. The study is conducted at three different temperatures of the system from 25°C to 75°C for a wide range of excitation frequency. The results indicate that the time reversibility can undergo significant changes due to temperature variations depending on the excitation frequency. However, at the best reconstruction frequency corresponding to the maximum similarity of the reconstructed signal with the original input signal (proposed recently as the probing frequency), the change in the percent similarity with temperature is insignificant. The results also demonstrate that changes in the physical properties of both adhesive layers and piezoelectric transducers with temperature play a dominant role in influencing Lamb wave amplitudes. However, only the change in the characteristics of the adhesive layers is responsible for the temperature dependence of the time reversibility of Lamb waves.

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