Lamb wave

Active sensor wave propagation technique is a relatively new method for in-situ nondestructive evaluation (NDE). Elastic waves propagating in material carry the information of defects. These information can be extracted by analyzing the signals picked up by active sensors. Due to the physical property of wave propagation, large area can be interrogated by a few transducers. This simplifies the process

Environmental factors such as temperature and humidity influence the efficacyo fd efect imaging procedures based on the identification of changes between an intact state and the current state of as ample/compo-nent/structure in the presence of ad efect. In this paper,w ef ocus on the Reconstruction Algorithm for Proba-bilistic Inspection of Damage (RAPID)a nd propose an onlinear Lamb wave version of RAPID to visualize a delamination in acomposite structure without having to knowanything about the intact state, i.e. abaseline free RAPID. Once the optimal frequencyselection of Lamb wavesinapitch-catch configuration mode is performed, lowa nd high excitation amplitude signal responses within as parse array at that frequencya re evaluated along each transducer-receiverpath by analyzing aset of damage sensitive parameters: the correlation coefficient, the energy of the scaling subtracted signal, and the third harmonic ratio. Processing of this information leads to acor-responding probabilistic damage map of the area within the sparse array.The obtained results from av alidation experiment demonstrate the capability of this nonlinear variant of RAPID for the identification of adelamination in acomposite structure.

Wind turbine blade failure is the most prominent and common type of damage occurring in operating wind turbine systems. Conventional nondestructive testing systems are not available for in situ wind turbine blades. We propose a portable long distance ultrasonic propagation imaging (LUPI) system that uses a laser beam targeting and scanning system to excite, from a long distance, acoustic emission sensors installed in the blade. An examination of the beam collimation effect using geometric parameters of a commercial 2 MW wind turbine provided Lamb wave amplitude increases of 41.5 and 23.1 dB at a distance of 40 m for symmetrical and asymmetrical modes, respectively, in a 2 mm-thick stainless steel plate. With this improvement in signal-to-noise ratio, a feasibility study of damage detection was conducted with a 5 mm-thick composite leading edge specimen. To develop a reliable damage evaluation system, the excitation/sensing technology and the associated damage visualization algorithm are equally important. Hence, our results provide a new platform based on anomalous wave propagation imaging (AWPI) methods with adjacent wave subtraction, reference wave subtraction, reference image subtraction, and the variable time window amplitude mapping method. The advantages and disadvantages of AWPI algorithms are reported in terms of reference data requirements, signal-to-noise ratios, and damage evaluation accuracy. The compactness and portability of the proposed UPI system are also important for in-field applications at wind farms.► Portable long distance laser ultrasonic propagation imaging (LUPI) system. ► A new anomalous wave propagation imaging (AWPI) methods based platform was developed. ► It provided enhancement and accuracy in damage visibility, localization and size. ► The system feasibility was verified considering a 2 MW commercial wind turbine system. ► LUPI system shows applicability for in-field long distance wind turbine applications.