The use of piezoelectric wafer active sensors (PWAS) for embedded ultrasonic nondestructive evaluation (NDE) is described. PWAS structure and principle of operation are presented. The interaction between PWAS and ultrasonic Lamb waves is modeled and analyzed, and excitation “sweet spots” for preferentially exciting certain Lamb wave modes are identified. Recent trends in guided-wave ultrasonic ...

This paper presents a 3D boundary element model (BEM), formulated in the frequency domain, to simulate heat diffusion by conduction in the vicinity of 3D cracks. The model intends to contribute to the interpretation of infrared thermography (IRT) data results and to explore the features of this nondestructive testing technique (NDT) when it is used to detect and characterize defects. The defect...

This paper reports the simulation of phased array ultrasonic wave propagation using Finite Difference Time Domain (FDTD) method to image crack like defects in Aluminum Blocks and Stainless Steel elbow sections. Inclined crack like defects have been considered for the simulation. Experiments were also performed on an Aluminum block with inclined embedded cracks various sizes in order to validate...

A series of molecular dynamics simulations using the embedded atom method is conducted to investigate crack propagation under mode I loading in a Ni single crystal with and without defects. The crack system (0 0 1)[1 0 0] in a slab of 160 000 atoms was studied. Defects consisting of lines of vacancies were introduced near the crack tip. Critical loads and strain energy distributions around the ...

Piezoelectric wafer active sensors (PWAS) are inexpensive, non-intrusive un-obtrusive devices that can be surface-mounted on existing structures, or inserted in a new composite structure. The PWAS can be used in both active and passive modes. In active mode, the PWAS generate Lamb waves that can exist as either traveling waves or standing waves. As traveling waves, PWAS-generated Lamb waves can...

The use of embedded piezoelectric-wafer active-sensors for in-situ structural health monitoring of thin-wall structures is presented. Experiments performed on aircraft-grade metallic specimens of various complexities exemplified the detection procedures for nearfield and far-field damage. For near-field damage detection, the electro-mechanical (E/M) impedance method was used. Systematic experim...

A finite-element procedure is developed to analyze plane ductile fracture problems in the presence of largescale yielding near the crack tip. Strain and stress singularities near the crack tip, corresponding to the strainhardening material model, are embedded in elements near the crack tip. The developed elastic-plastic incremental finite-element method is based on a hybrid displacement model. ...

An evolutionary approach for fatigue crack detection in cantilever type of machine structure is investigated in this paper. Fault like fatigue crack detection has received a great attention in recent years. A surface transverse open edge crack is considered for this study. Actual fatigue crack may behave like a non-linear due to opening and closing under vibration. But due to small level of vib...

An integral equations method for a three-dimensional crack in a finite or infinite body is achieved by means of Kupradze potentials. Surface and through cracks can be studied according to this approach with only the assumption that the body has a linear, elastic, homogeneous and isotropic behavior. Both singular surface integrals and line integrals appear in the derived equations. For surface a...