Original Article Journal of Intelligent Material Systems and Structures 1–18 Ó The Author(s) 2018 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/1045389X18818775 journals.sagepub.com/home/jim Numerical and experimental investigation of damage severity estimation using Lamb wave–based imaging methods Asaad Migot 1,2 , Yeasin Bhuiyan 1 and Victor Giurgiutiu 1 Abstract In this article, estimation of crack size, shape, and orientation was investigated numerically and experimentally using Lamb waves. A hybrid global–local approach was used in conjunction with the imaging methods for the numerical simula- tion. The hybrid global–local approach allowed fast and efficient prediction of scattering wave signals for Lamb wave interaction with crack from various incident directions. The simulation results showed the directionality effect of the scattering wave signals and suggested an optimum transmitter–sensor configuration. Two imaging methods were used: one involves the synthetic time reversal concept and the other involves Gaussian distribution function. Both imaging methods show very good agreement during simulations. Experiments were designed and conducted based on the simu- lated results. A networkof eight piezoelectric wafer active sensors was used to capture the scattering waves from the crack. Both the pitch-catch and pulse-echo experimental modes were used. The directionality effect of incident Lamb waves on the imaging results was studied. The effect of summation, multiplication, and combined algorithms for each imaging method was studied. It was found that both methods can successfully predict the crack size and orientation. An attempt was made to use these imaging methods for detecting and sizing smaller sized damage (1- to 3-mm-diameter hole). It was found that these methods can successfully localize the hole, but size estimation was a bit challenging because of the smaller dimensions. The scattering waves for various hole sizes were studied. Keywords Structural health monitoring, wave propagation, synthetic time reversal, crack sizing, scattering waves Introduction State of the art In recent years, the damage quantification using Lamb waves has become one of the topical research areas. Lamb waves are suitable for fast damage detection, because they propagate at very high speeds and may complete the inspection in a very short period of time. They can propagate a long distance with very little energy loss, so they enable the inspection of large areas of structures. The analyses of Lamb wave interaction could potentially detect, localize, and estimate the size of various kinds of damage in structures (Chang et al., 2007; Masserey and Fromme, 2015; Saravanan et al., 2015). An experimental study was performed to obtain an appropriate Lamb wave mode to detect structural defects (Ghosh et al., 1998). Attempts have been made for quantifying structural defects using Lamb wave scattering field (Baghalian et al., 2017; He et al., 2016). A network of sensors was used for defect visualization in the pitch-catch experi- mental mode (Ihn and Chang, 2008). Damage index was calculated for each sensing path to characterize the defect. Crack orientation was quantitatively determined using scattered Lamb wave and by evaluating the dif- ferent amplitudes of energy peaks in the Hilbert spectra (Lu et al., 2007). A system of an electromagnetic acous- tic transducer (EMAT) array was designed for detect- ing artificial defects in large metallic structures using symmetric Lamb wave mode (Wilcox et al., 2005). The phased array filter approach was developed for damage 1 Department of Mechanical Engineering, University of South Carolina, Columbia, SC, USA 2 Department of Mechanical Engineering, College of Engineering, Thi-Qar University, Nasiriyah, Iraq Corresponding author: Asaad Migot, Department of Mechanical Engineering, University of South Carolina, 300 Main St., Columbia, SC 29208, USA. Email: amigot@email.sc.edu