Akira Kosugi

Accuracy Evaluation of Surface Temperature Profiling by a Laser Ultrasonic Method

Accuracy in measuring surface temperature distributions by a laser ultrasonic method is examined. Surface temperature distributions of an aluminum plate whose single side is heated up to 110 °C are estimated by the inverse analysis coupled with surface acoustic wave (SAW) measurements, and the results are compared with those measured by an infrared radiation method. A random fluctuation in the temperature estimated by the ultrasonic method is observed and decreases with an increase in the distance from the heating area. The standard deviation in fluctuation is estimated to be about 2 °C at the heating area. Furthermore, the systematic errors in the temperature estimation due to the deviations in the temperature dependence of SAW velocity and thermal diffusivity are investigated. It is found that the temperature dependence of SAW is an important factor affecting the systematic error, but the influence of the deviation in thermal diffusivity is negligible.

Noncontact Monitoring of Surface Temperature Distribution by Laser Ultrasound Scanning

A laser ultrasound scanning method for measuring a surface temperature distribution of a heated material is presented. An experiment using an aluminum plate heated up to 120 °C is carried out to verify the feasibility of the proposed method. A series of one-dimensional surface acoustic wave (SAW) measurements within an area of a square on the aluminum surface are performed by scanning a pulsed laser for generating SAW using a galvanometer system, where the SAWs are detected at a fixed location on the surface. An inverse analysis is then applied to SAW data to determine the surface temperature distribution in a certain direction. The two-dimensional distribution of the surface temperature in the square is constructed by combining the one-dimensional surface temperature distributions obtained within the square. The surface temperature distributions obtained by the proposed method almost agrees with those obtained using an infrared radiation camera.

Noncontact Temperature Profiling of Rotating Cylinder by Laser-Ultrasound

In the fields of engineering and manufacturing industries, it is often required to know quantitative information about surface and internal temperatures of rotating objects. In this work, a new ultrasonic method for measuring such temperatures of a heated rotating cylinder is presented. A laser-ultrasonic technique which provides noncontact ultrasonic measurements is employed in the present method. To make a quantitative evaluation of the internal temperature distribution in the radial direction of a heated rotating cylinder having axisymmetric temperature distribution, an effective method consisting of surface temperature measurements with a laser-ultrasonic technique and one-dimensional unsteady heat conduction analyses with a finite difference calculation is developed. To demonstrate the feasibility of the method, experiments with heated steel cylinders of 100 mm and 30 mm in diameter rotating at 300 min− 1 are conducted. A pulsed laser generator and a laser Doppler vibrometer are used for generating and detecting surface acoustic waves (SAWs) on the steel cylinder, respectively. Measured SAWs are used for determining both surface and internal temperatures of the cylinder. The estimated temperature distributions during heating almost agree with those measured by an infrared radiation camera. Thus, it has been shown that the noncontact temperature measurement technique with laser ultrasound is a promising tool for on-line monitoring of heated rotating cylinders.

Application of Laser Ultrasound to Noncontact Temperature Profiling of a Heated Hollow Cylinder

A new ultrasonic method to monitor the temperature distributions of a thick-walled hollow cylinder whose inner surface is heated is presented. This method basically consists of laser ultrasonic measurements and a heat conduction analysis of the heated hollow cylinder. Both longitudinal wave (LW) and surface acoustic wave (SAW) are used for estimating the temperature distribution of the cylinder. To demonstrate the validity of the proposed method, a numerical simulation and an experiment are carried out. In the numerical simulation, a steel hollow cylinder (the inner and outer diameters are 20 mm and 100 mm, respectively) is uniformly heated by a constant heat flux at the inner surface. It has been verified in the simulation that temperature distributions estimated by the proposed method completely agreed with the theoretical results. In the experiment, an aluminum hollow cylinder (the inner and outer diameters are 20 mm and 50 mm, respectively) is heated by pouring molten metal at 300 °C into the hollow cavity of the cylinder. A laser ultrasonic system is used for measuring both LW and SAW of the heated cylinder. It has also been demonstrated that the proposed method can measure the change in the temperature distribution during heating.

A Feasibility Study on Generation of Acoustic Waves Utilizing Evanescent Light

A new approach of generating acoustic waves utilizing evanescent light is presented. The evanescent light is a non-propagating electromagnetic wave that exhibits exponential decay with distance from the surface at which the total internal reflection of light is formed. In this research, the evanescent light during total internal reflection at prism surface is utilized for generating acoustic waves in aluminium and the feasibility for ultrasonic measurements is discussed. Pulsed Nd:YAG laser with 0.36 J/cm2 power density is used and the incident angle during the total internal reflection is arranged to be 69.0° for generating the evanescent light. It has been demonstrated that the amplitude of the acoustic waves by means of evanescent light is about 1/14 as large as the one generated by the conventional pulsed laser. This reveals the possibility of using a laser ultrasonic technique with near-field optics.

Ultrasonic Thermometry for Temperature Profiling of Heated Materials

In the fields of materials science and engineering, there are growing demands for monitoring temperature and its distribution of heated materials. This is basically because temperature is one of important factors that dominate material properties and related characteristics such as mechanical, electrical and chemical behaviours. In general, temperature monitoring is required for not only the surface but also the inside of heated materials. In this work, a new ultrasonic method for monitoring temperature gradients of materials during heating or cooling is presented. The method consists of ultrasonic pulse-echo measurements and an inverse analysis for determining one-dimensional temperature distributions along the direction of ultrasound propagation either inside or on the surface of heated materials. To demonstrate the practical feasibility of the method, several experiments with heated materials have been made and successful results of internal temperature profiling are obtained. In addition, non-contact methods with a laser ultrasonic technique for monitoring surface temperature distributions of heated materials are proposed and their potentials are demonstrated. Thus, it is highly expected that the ultrasonic thermometry is a promising means for on-line temperature profiling of industrial materials processed at elevated temperatures.

Feasibility Study on Noncontact Monitoring of Temperature Distributions of Rotating Tool

In the fields of materials science and engineering, measuring temperature has become one of the most fundamental and important issues. In particular, there are growing demands for monitoring temperature gradient and its transient variation of materials being processed at higher temperatures because the temperature state during processing crucially influences the quality of final products. Such temperature monitoring is also required for rotating machining processes such as tuning, milling and friction stir welding (FSW). In this work, a new noncontact method for monitoring temperature distribution of a heated rotating cylindrical object is presented. A laser-ultrasonic technique is employed in the method. Surface temperature measurements for the cylindrical object using the laser-ultrasonic technique and heat conduction analyses are combined together for making quantitative evaluation of temperature distribution in the radial direction of the cylindrical object. To demonstrate the feasibility of this method, an experiment with a steel cylinder of 100 mm in diameter rotating at 300 min-1 and heated up to 100 °C on the surface is carried out. A pulsed laser generator and a laser Doppler vibrometer are used for generating and detecting surface acoustic waves (SAWs) on the steel cylinder, respectively. Measured SAWs are used for determining both surface and internal temperatures of the cylinder. As a result, the estimated temperature distributions during heating almost agree with those measured by an infrared radiation camera.