Experimental realization of on-chip topological nanoelectromechanical metamaterials

Topological mechanical metamaterials translate condensed matter phenomena, like non-reciprocity and robustness to defects, into classical platforms. At small scales, topological nanoelectromechanical metamaterials (NEMM) can enable the realization of on-chip acoustic components, like unidirectional waveguides and compact delay-lines for mobile devices. Here, we report the experimental realization of NEMM phononic topological insulators, consisting of two-dimensional arrays of free-standing silicon nitride (SiN) nanomembranes that operate at high frequencies (10-20 MHz). We experimentally demonstrate the presence of edge states, by characterizing their localization and Dirac cone-like frequency dispersion. Our topological waveguides also exhibit robustness to waveguide distortions and pseudospin-dependent transport. The suggested devices open wide opportunities to develop functional acoustic systems for high-frequency signal processing applications

Thermographic analysis of residual stress in aluminum plates through wavelet transform

Monitoring the material properties and microstructure after mechanical processing is a crucial aspect in quality control for manufacturing industry. This study aims to estimate the residual stress occurring after drilling process in metallic specimens. The heat generated during the laser-cut process changes the grain morphology and consequently the heat conductivity in the hole proximity area. The proposed methodology lays in the context of nondestructive techniques and is based on thermography and advanced signal processing methods

Guided Wave Propagation and Breathing-Debond Localization in a Composite Structure

Carbon-fibre reinforced composite laminates are extensively used in aerospace, automotive, wind energy and marine engineering structures due to their light-weight advantage, high-energy absorption capability, fire resistance, high stiffness-to-weight ratios and construction flexibilities. This work is mainly focused on the analysis of nonlinear ultrasonic guided wave propagation and breathing-debond source localisation in a stiffened composite structure. In the process, the finite element method based 3D numerical simulations has been carried out on a stiffened composite structure using a preassigned network of piezoelectric transducers (PZT). From the analysis of the results, it is observed that the presence of plate-stiffener breathing-type debonds produces higher-harmonics in the registered PZT signals. Based on the identified differential parameters in the higher-harmonics, the breathing-debond source locations are effectively identified by using a fast and efficient baseline-free SHM strategy that uses Fast-Fourier-Transform of the registered sensor signals from the target structure to detect single as well as multiple breathing-debond locations in the stiffened composite structure