The impact identification function of the IVI technique was validated from two aspects that are diverse structure configurations and vibration noises contamination. The validation details and the relevant discussion are described in this section:. However, in order to reveal the impact identification performance of the IVI technique comprehensively, some impact events with representative impact locations are selected and illustrated in Figure 15 and Figure For Specimen 1, impact event N1 is selected due to the consideration of boundary performance validation, and impact event N2 is selected with the consideration of general performance validation.
As well, for Specimen 2, two impact events C1 and C2 which both occurred at surrounding positions close to the cutout hole of the structure were chosen. The two impact events on a cutout structure were selected to verify the anti-discontinuity capability of the impact identification function due to the inhomogeneous property of the structure, typically, an airplane fuselage panel with a window cutout frame.
Two representative changing random vibration disturbance conditions were selected, where one is under the noise condition of signal-to-noise ratio SNR of 15 and the other one is under the noise condition of SNR of With the IRF matrix networks established, the identification results are calculated, and they match well with the actual impact forces recorded in terms of maximum amplitude, force duration and impulse. Furthermore, in order to assess the accuracies of the identification results, the relative average errors e a corresponding to the above three parameters are necessary to be compared by using the following equation:.
In view of all the impact tests performed, as for the normal structure Specimen 1 without any vibration disturbance, the corresponding average error of the maximum amplitude is 7. However, when the overall average errors of impact identifications with noise contaminations are calculated out, they are both a little more than the results of the de-noising implementation. As a result of the relative comparisons of all estimated results, it is easy to see that the results of impact identifications obtained by de-noising processing are better than those identification results with noise contaminations.
However, this causes the above situation of different errors, the main reason for which is that there exist several disturbed and unstable factors that are known or unknown resulting from vibrations while the experimental tests are being performed, for instance, nonlinear problems, vibration randomness problems, unpredictable impact conditions and the effect of stress wave propagation due to vibration, etc. What happens in the structure when impact events occur unexpectedly on a structure? How does the structural state alter? And what effects are produced in the structure? With a set of the above problems, an approach of the absorbing energy distribution in a structure provides a better solution to solve the intractable problems met, which is resulting from any impact event.
Through the absorbing energy distribution AED method, the structural state can be monitored in real-time mode. Also, the AED method can analyze and evaluate using the output data from the structural response to supply a demonstration for determining the corresponding FE model order generated due to any impact event. Accordingly, Specimen 1 was used as this demonstration to illustrate the synthesized performance of the impulse energy distribution method, which is presented in Figure Structural state monitoring and assessment when impact events occurred.
This paper presents a systematical impact inspection and structural condition monitoring scheme. By using the distributed sensors networks defined, an advanced real-time IVI technique is proposed to estimate the impact locations and force histories including the information about the force magnitudes and to visualize the structural state when impacts occurred. In the automatic identification procedure, a precise forward model for a given structure can be established rapidly through the functional module of forward model generator.
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Nevertheless, in the impact positioning and evaluation procedure, the initial impact locations can be estimated using the developed smoothed power distribution method, afterwards on the basis of the results from the initial location estimations, the accurate location coordinates of each impact can be updated further by the proposed time of flight ToF based quadrilateral sensor network positioning method.
It is worth noting that to achieve a highly reliable and highly robust impact monitoring and identification system adapting into complex and harsh engineering environments, the real-time IVI technique shows satisfactory success in predicting impact locations and estimating force histories for various types of structure configurations and under mutative vibration environment conditions, and its capability of structural state monitoring and real-time assessment is also verified.
Through all cases of the impact tests considered, the impact visualization inspection technique shows its potential as an on-board rapid diagnostic tool of accidental impact events that can cause possible damage in an aerospace composite structure. Si would like to acknowledge gratefully Zhanjun Wu from Dalian University of Technology for his kind help and advice on impact monitoring. Si is primarily responsible and the primary developer on this research, and wrote this paper. Baier dedicated his helpful advice and valuable suggestions to this research. National Center for Biotechnology Information , U.
Journal List Sensors Basel v. Sensors Basel. Published online Jul 8. Vittorio M. Passaro, Academic Editor. Author information Article notes Copyright and License information Disclaimer. Received Apr 9; Accepted Jun This article has been cited by other articles in PMC. Abstract For the future design of smart aerospace structures, the development and application of a reliable, real-time and automatic monitoring and diagnostic technique is essential.
Keywords: real time, impact monitoring, hybrid thresholding filter, fast genetic algorithm, parameter estimation, composite structures, random vibration noises, structural state awareness. Method of Approach This developed IVI approach is an automatic inspection technique based on global sensor measurements as illustrated in Figure 1 , which is adaptable to various structure configurations and various types of impact objects. Open in a separate window. Figure 1. Overview of the automatic implementation procedure of the IVI technique.
Signal Data Preprocessing In order to de-noise the original sensor signals, a mode decomposition-based filtering method—the real-time empirical mode decomposition EMD, [ 18 ] -based hybrid thresholding filter [ 19 , 20 ] is adopted to eliminate the interferences e. Figure 2. Flowchart of the real-time EMD based hybrid thresholding filtering process. Figure 3. A sensor output signal from the structural response within noise.
Impact Identification Procedure 2. Forward Model In the procedure of establishing an accurate forward model, three main functional modules are executed, as follows: 1.
Figure 4. Inverse Model Operator In order to reconstruct impact forces, the force signals from impacts can be predicted based on the inverse model operator using the output data of the structure responses. Figure 5. Impact Positioning Calculation To determine multi-impact locations and decrease the estimation time for impact location and reconstruction, an initial estimation method needs to be adopted.
Locating Impact Coordinates To update the accurate locations of impact forces acting on a structure, there exists an effective search parameter index—Time of Flight ToF , which is an important characteristic parameter that represents how the stress waves propagate in a structure. Figure 6.
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Figure 7. Demonstration of impact positioning procedure through updating quadrilateral. Figure 8. Figure 9. Impact Tests In order to obtain the various IRFs, impact experimental tests were performed on the two specimens. Figure Demonstration for the formation of IRF network on Specimen 2. Real-time visualization inspection for an unknown impact event. Results and Discussion The estimated and reconstructed results are illustrated to validate the efficacy of the IVI technique for impact source identification.
Impact Positioning and Error Evaluations To illustrate the proposed monitoring and identification scheme, Figure 12 presents a set of estimated results for impact locations on Specimen 1, and a set of estimated results for impact locations on Specimen 2 are shown in Figure Impact Identifications The impact identification function of the IVI technique was validated from two aspects that are diverse structure configurations and vibration noises contamination.
The validation details and the relevant discussion are described in this section: 1 To validate the efficacy of the impact identification function, a series of impact tests were implemented on the various CFRP panel structures Specimens 1 and 2. Structural State Awareness What happens in the structure when impact events occur unexpectedly on a structure? Conclusions This paper presents a systematical impact inspection and structural condition monitoring scheme. Author Contributions L. Conflicts of Interest The authors declare no conflict of interest. References 1. Kamsu-Foguem B.
Knowledge-based support in Non-Destructive Testing for health monitoring of aircraft structures. Zhang C.
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A strain amplitude-based algorithm for impact localization on composite laminates. Ghajari M. Identification of impact force for smart composite stiffened panels. Lee M. A numerical study into the reconstruction of impact forces on railway track-like structures. Park C. Includes guidelines showing how decisions based on manufacturing considerations affect weight and how weight optimization may adversely affect the cost.
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