A multistage damage detection method is introduced in this work that uses piezoelectric lead zirconate titanate (PZT) transducers to excite/sense the Lamb wave signals. A continuous wavelet transformation (CWT), based on the Gabor wavelet, is applied to accurately process the complicated wave signals caused by the damage. For a network of transducers, the damage can be detected in one detection cell based on the signals scattered by the damage, and then it can be quantitatively estimated by three detection stages using the outer tangent circle and least-squares methods. First, a single-stage damage detection method is carried out by exciting a transducer at the center of the detection cell to locate the damaged subcell. Then, the corner transducers are excited in the second and third stages of detection to improve the damage detection, especially the size estimation. The method does not require any baseline signal, and it only utilizes the same arrangement of transducers and the same data processing technique in all stages. The results from previous detection stages contribute to the improvement of damage detection in the subsequent stages. Both numerical simulation and experimental evaluation were used to verify that the method can accurately quantify the damage location and size. It was also found that the size of the detection cell plays a vital role in the accuracy of the results in this Lamb-wave-based multistage damage detection method.

A damage estimation method based on continuous wavelet transformation (CWT) of the normalized Lamb wave signals is proposed here. Lamb waves are actuated and sensed using piezoelectric (lead zirconate titanate, PZT) transducers arranged in the form of square detection cells on a plate-like structure. Excitation sequences based on pitch–catch and pulse–echo configurations are tested for the same arrangement of the transducers. The possibilities of the existence of damage for each actuator–senor pair are formed by using the normalized coefficient of CWT. The size of the possible damage region is directly controlled through envelopes defined by the coefficients of CWT, and no additional parameter is required to define its size. The aggregate damage image is constructed by the fusion of damage possibilities from all actuator–sensor pairs using damage indices based on conjunctive and compromised fusion schemes. The results indicate that the proposed method can estimate the location and severity of multiple damage with signals directly from the damaged plate, without the need of baseline signals from the undamaged plate, and the time-compensated signals provide better damage imaging than the raw signals. The most accurate and computationally inexpensive combination is the pulse–echo configuration with damage index based on conjunctive image fusion scheme. The method is computationally inexpensive and can be applied for multiple damage estimations in large structures to reduce the evaluation cost and inspection time during on-line structural health monitoring.

Cardiovascular diseases have been a leading cause of death for the past several decades. A comparison of blood flow patterns through diseased and treated arteries can be beneficial in diagnosis and treatment. The computational fluid dynamic (CFD) analysis was utilized to numerically simulate the blood flow dynamics of stenosed and stented carotid artery bifurcation. Two lumen models were generated: first with the stenosis and then a stent was introduced to remove the abnormality. The control volume method was implemented to discretize the blood domain, and then the steady-state velocity inlet was used based on the measured blood flow rate. The transitional flow was observed in the post-stenotic region due to the high Reynold’s number near peak systole; however, the flow exhibited laminar characteristics at the peak diastole. Four distinct locations downstream of the stenosis were used to compare the results. The internal carotid artery (ICA) stenosis resulted in high wall shear stresses, irregular flow patterns, and low-pressure areas. The velocity and pressure profiles oscillated in the immediate vicinity downstream of the stenosis. The stented model showed minimal pressure and velocity fluctuations, as well as minimal wall shear stresses. Additionally, for the stented model, the flow could not enter the transitional regime under both conditions. The proposed simulation methodology can be utilized until the abnormalities in the carotid artery geometry are removed and normal blood flow characteristics are achieved, which then become the basis for an optimal design of a carotid artery stent.

The effective damage detection does not only require the location of damage but also its size. Most of the existing damage detection methods for composite structures are imaging methods, which only focus on the damage localization but provide no information about its extent. The methods which focus on damage size can accurately estimate the circular damage but cannot quantify a