Development of nondestructive non-contact acousto-thermal evaluation technique for damage detection in materials.
This paper presents the development of a new non-contact acousto-thermal signature (NCATS) nondestructive evaluation technique. The physical basis of the method is the measurement of the efficiency of the material to convert acoustic energy into heat, and a theoretical model has been used to evaluate this. The increase in temperature due to conversion of acoustic energy injected into the material without direct contact was found to depend on the thermal and elastic properties of the material. In addition, it depends on the experimental parameters of the acoustic source power, the distance between sample and acoustic source, and the period of acoustic excitation. Systematic experimental approaches to optimize each of the experimental variables to maximize the observed temperature changes are described. The potential of the NCATS technique to detect microstructural-level changes in materials is demonstrated by evaluating accumulated damage due to plasticity in Ti-6Al-4V and low level thermal damage in polymer matrix composites. The ability of the technique for macroscopic applications in nondestructive evaluation is demonstrated by imaging a crack in an aluminum test sample.
FEM modeling of ultrasonic vibrothermography of a damaged plate and qualitative study of heating mechanisms
Abstract Ultrasonic vibrothermography (UVT), or sonic infrared imaging, is a promising technique which excites ultrasonic elastic waves to locally stimulate defects on solid specimens and is typically applied in the aerospace and automotive industries. This technique allows for defect selective imaging using thermal waves generated by ultrasound waves. Energy dissipation mechanisms turn a dynamically loaded defect into a heat source, which is identified by a thermography system. In this paper finite element method (FEM) is implemented for simulation of vibrothermography and qualitative study of crack heating caused by internal and external energy losses. External loss is modeled by considering local friction between crack surfaces and internal loss (hysteresis) is modeled by taking into account viscoelastic and thermoelastic damping in the absence of plastic deformations. Defected plate specimens with edge crack and internal crack subjected to ultrasonic waves are modeled and studied.
Photoreflectance characterization of vanadium-doped GaAs layers grown by metalorganic vapor phase epitaxy
Abstract We characterized the vanadium-doped (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy. The conductivity of the samples is checked by the Hall effect measurements, and it is n type with electrons concentration ranging from 2×10 13 to 2×10 17  cm −3 . We used the photoreflectance technique (PR) to study the effect of vanadium doping on the optical properties of GaAs. Our experimental results show that the built-in electric field F and the broadening parameter Γ 0 increase with V-doping concentration. Furthermore, the temperature dependence of the built-in electric field and the broadening parameter of GaAs:V samples have been investigated by PR. It has been observed that these parameters increase with increasing temperature. The decrease of the built-in electric field with decreasing temperature is due to the photovoltage effect.We characterized the vanadium-doped GaAs (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy.