No abstract

Delamination is a common defect in composite plates that may cause significant losses in commercial applications. In this study, a hybrid damage detection method was introduced, which raised both the damage identification sensitivity level and detected quantitative damage parameters. The primary damage location was pinpointed by the wavelet transform, and the damage parameters, including location, depth, and intensity, were then isolated by the model updating process. The wavelet transform was obtained according to the signal’s nature, which leads to improvement in the wavelet transform’s operation. Then, the lifting scheme algorithm process was performed to increase the wavelet efficiency in damage detection. In addition, a proper signal, based on strain energy, was used for damage detection by the wavelet transform. Finally, the genetic algorithm method was employed in the proposed model updating method to identify the damage parameters through employing a novel error function. The selected error function was based on strain energy, having the best operation among previously identified modal criteria. Consequently, the accuracy of identifying the damage parameters was improved upon utilizing the proposed method, particularly in the presence of noise. In addition, the solution performed faster than the previously available updating methods which utilized only the genetic algorithm-based on mode shapes and natural frequencies for detecting the damage.

Delamination is a potential risk of failure considered as one of the failure modes and frequently occurs in composites due to its relatively low inter-laminar fracture toughness. In recent years, the majority of activities in this field have been focused on raising the level of sensitivity of these devising methods for detecting tiny damages. In this article, damage detection method via wavelet transform has been examined, and an appropriate procedure has been proposed to increase sensitivity of this transform for damage detection. Among the inherent impediments of classical wavelet transforms, the generality of these transforms and ignoring the studied signal can be mentioned. Consequently, various wavelet selection algorithms leading to provide appropriate wavelet functions with respect to the characteristics of the signal have been examined. As a novelty in the field, the correlation between wavelet and strain energy signal is considered as a criterion for optimal wavelet selection. In wavelet transforms, in addition to original wavelet functions, the signals used for damage detection are also of high importance. To achieve this goal, the frequency-weighted strain energy ratio signals resulting from intact and damaged forms have been exploited. Also, the edges' effects were removed through stringing of plane mode shape signals. Moreover, by summing wavelet coefficients in all scale factors plus natural frequencies, the focus can bring to the detection of one or more damages in a laminated composite plate with symmetric layup. Finally, a quantitative measure to compare different wavelets has been presented.

Damage detection using the wavelet transform was investigated and appropriate approaches to raising the method’s sensitivity level were proposed. In addition, the current study attempted to implement the impulse wavelet design algorithm in order to present appropriate wavelet function with respect to the characteristics of the signal. The initial wavelet function corresponding to the impulse response of composite plate was achieved using impulse wavelet algorithm in time domain. The function was optimized using lifting scheme method. To detect damages, an appropriate signal was selected through applying wavelet transform. To enhance damage identification, first, the edges’ effect of wavelet transform was removed, then a higher accuracy was observed by summing the wavelet coefficients in all scale factors for each mode shape and the wavelet coefficients for all mode shapes. The article also presents a quantitative measure to compare different wavelets.

A new method combining experimental and numerical data is proposed to simultaneously determine the mechanical properties and damage parameters in multilayered composite plates. Studied parameters are mechanical properties of each layer, width and length of delamination zone, location of damage’s center, and interface location of the damage. In this method, the PSO optimization procedure based on a CPAM algorithm uses vibration test data along with their corresponding numerical solution. Vibration data are the plates’ natural frequencies and mode shapes obtained in the modal laboratory. In order to efficiently investigate the studied parameters, the numerical solution is investigated by a commercial finite element package. The error function constitutes two parts, one part is included by the sum of the squared differences between experimental and numerical natural frequencies and the other is based on the mode shapes data. The mode shapes’ curvatures are also utilized to achieve high sensitivity to small faults. Moreover, by applying a Gaussian disorder model to the vibrational data, the sensitivity of the method is evaluated in the presence of unwanted noises. The results confirm the robustness of the proposed study for identifying both mechanical constants and damage parameters in composite plates.