We discuss waves created in relatively thick plates by edge excitation at frequency-thickness (fd) products that correspond, in principle, to multiple Lamb wave modes. For relatively low values of the fd product it is clear that Lamb wave modes will be generated, while at large values of the fd product we observe a bulk (longitudinal wave) in the solid, but influenced by reflections from the pl...

This paper presents a forward calculation and analytic results of plate wave propagation in stressed plates of cubic materials. The single crystalline Ge films deposited on the Z-cut silicon wafers are investigated. Significant biaxial residual stresses in the film results from the lattice misfit between of the Ge film and the Si substrate. Phase velocity change of the acoustic waves due to mec...

Compared with conventional linear ultrasonic inspection methods, which are sensitive only to severe defects, nonlinear ultrasonic inspection methods are better for revealing micro-cracks in thin plates. However, most nonlinear ultrasonic inspection methods have only been experimentally investigated using bulk or Rayleigh waves. Numerical studies, especially numerical simulations of Lamb ultraso...

It is well known that harmonic bounded Gaussian beams undergo a transformation into two bounded beams upon reflection on a solid immersed in a liquid. The effect is known as the Schoch effect and can be found at the Rayleigh angle for thick plates and at the different Lamb angles for thin plates. Here, a study is made on the effect of pulsed Gaussian beams reflected on solids. It is found exper...

Nondestructive evaluation (NDE) of aerospace structures using traditional methods is a complex, time-consuming process critical to maintaining mission readiness and flight safety. Limited access to corrosion-prone structure and the restricted applicability of available NDE techniques for the detection of hidden corrosion or other damage often compound the challenge. In this paper we discuss our...

A time-frequency representation (TFR) is used to analyze the interaction of a multimode and dispersive Lamb wave with a notch, and then serves as the basis for a correlation technique to locate the notch. The experimental procedure uses a laser source and a dual-probe laser interferometer to generate and detect Lamb waves in a notched plate. The high fidelity, broad-bandwidth, point-like and no...

Among the various techniques available, ultrasonic Lamb waves offer a convenient method of evaluating composite materials. Since the Lamb wave velocity depends on the elastic properties of a structure, an effective tool exists to monitor damage in composites by measuring the velocity of these waves. Lamb wave measurements can propagate over long distances and are sensitive to the desired in-pla...

Structural health monitoring (SHM) is an emerging technology with great potential in structural diagnosis and prognosis. SHM systems can be passive or active. Active SHM systems rely on structural interrogation using active sensors (transducers) that can transmit and receive ultrasonic Lamb waves traveling at large distances in the structural material. Piezoelectric-wafer active sensors (PWAS) ...

As continuous health monitoring of aircraft components will provide substantial time and cost savings to the aircraft industry, the use of an integrated sensing technology with autonomous damage assessment is looked for. This study is part of the 6 STREP framework AISHA project, investigating the use of ultrasonic Lamb wave technology for the fast inspection of large shell structures. For the d...

Ultrasonic guided waves inspection using Lamb waves is suitable for damage detection in metallic structures. This paper will present experimental results obtained using guided Lamb waves to detect flaws in aluminum specimens with design features applicable to space applications. Two aluminum panels were fabricated from a variable-thickness aluminum top plate, with two bolted I-beams edge stiffe...