Papers by Keyword: Laser Ultrasonics

Abstract: State of the art of in-situ analysis on grain structure of metals during thermal and stress treatment is done by observation of the probe in a thermomechanical treatment system. Potential analysis methods are high energy x-ray scattering (e.g. in a synchrotron) or laser-ultrasonics (LUS). The most commonly used thermomechanical system, is the so called “Gleeble” from Dynamic Systems Inc., which is able to heat and load the material in a quite fast manner with extremely high heating rates, very high forces and fast force changes. There is a wide area of research and applications, though, where these capabilities are not fully required, a less complex deformation-and quenching dilatometer would often be sufficient. In this paper we will show the implementation of a LUS system in such a dilatometer and compare it to the “all inclusive” Gleeble system, pointing out benefits and downsides on different aspects, like the technical specifications, the needed footprint and more. A sketch of the full system and the beam path will show the general idea on the implementation of the LUS system into the dilatometer. We will also present first results of a thermal treatment on a metal sample suited for grain structure and phase transition analysis.

Abstract: Detected the cracks in porcelain insulator is a strategy to prevent failure. This study proposes a remote detect technique to inspect the cracks in on-line porcelain insulator based on laser-generation based imaging (LGBI) method. Two porcelain insulators samples A and B were designed. Samples A is a 10kv porcelain insulator work outdoors, it has five artificial notch-type defects in the cylindrical surface of porcelain insulator. Sample B is a 10kv porcelain insulator work indoor with aging cracks. All defects in two specimens were detected by laser ultrasonic visualizing inspector (LUVI). Images are quite convenient to confirm cracks morphology. The experiment proves that the cracks in porcelain insulator can be detected by LUVI system.

Abstract: Laser ultrasonics for metallurgy (LUMet) is an innovative sensor technology for in-situ measurement of microstructure evolution during thermomechanical processing. This unique sensor has been attached to a Gleeble 3500 thermomechanical simulator for dedicated laboratory studies during processing of steel, aluminum, magnesium and titanium samples. Advanced processing software has been developed for the measurement of grain size and texture evolution from laser ultrasonic signals. Results of austenite grain growth measurements in low carbon steels will be described to demonstrate the capabilities of the LUMet technique. Further, applications of the system to measure recrystallization of ferrite and austenite formation during intercritical annealing simulations of dual phase steels will be presented. The ability to rapidly acquire data both during a single test and for multiple conditions over a range of conditions from different samples has important implications on expediting process modelling and alloy design. Although certain limitations exist, the LUMet technique offers a very reliable characterization platform with a number of potential applications in metallurgical process engineering.

Abstract: This paper reports on a study of the propagation characteristics of visco-elastic, Rayleigh waves induced by laser ultrasonics in half space structures. Beginning with the Kelvin model, the characterization equation and the normal displacement of visco-elastic Rayleigh waves in are derived and the influence of the visco-elastic modulus on dispersion and attenuation are discussed. The transient response of a visco-elastic Rayleigh wave is also simulated by means of Laplace and Hankel inversion transforms. The papers results and conclusions will provide insights and guidance for estimating visco-elastic parameters

Abstract: Laser ultrasonics opened possibilities to measure thermal and mechanical property of skin which occupies an essential position and is beneficial in industrial and medical applications. This paper focuses on the thermal effect in the thermal section of the laser ultrasonic technique. A transient thermal analysis is developed and promoted to simulate the interaction between the laser pulse and human skin, using a multilayered finite element model (FEM). Chicken leg had been used and irradiated by KrF laser, the thermal reactions were detected and recorded by a thermal camera. By comparison, the thermal result of experiments and simulation matches.

Abstract: This paper describes a study of laser generated ultrasonic waves in an 2-layer elastic, isotropic biomaterial model, in order to establish a modelling technique to simulate the thermoelastic response of high-power short pulse laser beams in human skin. The theory proposed in this paper takes into consideration the fundamental understanding of the laser/material interface. A finite element model using the commercial finite element code ANSYS is used to study the effects of laser pulse duration and energy flux contribution to the surface waves. The simulation comprises a set of boundary conditions that approximate a heat flux point source located on top of the surface of the material. Because of the time scale of interest, the elastic effects do not feed back into the thermal problems, so that a sequential coupled-field analysis was performed where the thermal and elastodynamic fields are uncoupled and treated separately. The initial finite element analysis involves a transient thermal analysis using a heat flux with Gaussian spatial variation to simulate the laser pulse heating. The results from the thermal analysis were read and applied to the structural analysis where the out-of-plane displacements histories are analyzed in the skin model with varying thicknesses