The basic idea of damage detection using Lamb wave propagation in thin-walled structures is to extract the damage features from the response signal in the presence of damage by comparing it with the baseline response signal of the structure in the undamaged condition. The presence of damage causes scattering of signals, resulting in a change in the time of flight and the amplitude of the response signal. However, a change in the environmental temperature can also alter the response signal, leading to a false alarm, if not suitably compensated, which is difficult. To address this issue, the idea of developing baseline-free damage detection techniques has been explored in the recent past, and the time reversibility process (TRP) of Lamb waves has emerged as one of the widely studied baseline-free techniques. Under varying thermal environments, it would require that the time reversibility of Lamb waves is temperature invariant.
In the present work, we examine the temperature dependence of Lamb waves and its time reversibility using experiments and finite element simulations on isotropic plates with surface-bonded piezoelectric wafer transducers for actuation and sensing. The study is conducted at three different temperatures of the system from 25˚C to 75˚C for a wide range of excitation frequencies. The results indicate that the time reversibility can undergo significant changes due to temperature variations depending on the excitation frequency. However, at the best reconstruction frequency corresponding to the maximum similarity of the reconstructed signal with the original input signal (proposed recently as the probing frequency), the change in the percent similarity with temperature is insignificant. Furthermore, it is essential to know the best reconstruction frequency of the system beforehand for the effective and optimized design of such a guided wave based structural health monitoring system. For this purpose, an analytical model is presented for the generation, sensing, and time-reversible process of Lamb waves in thin isotropic plates with surface-bonded piezoelectric wafer transducers, incorporating the shear-lag effect of the bonding layer and inertia effects of the system in transducer modeling. The model is validated by comparing it with the 2D coupled piezoelasticity-based finite element simulation and experimental data.