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Optical Synchronous Laser Shadow Vibrometry for Measuring the Young’s Modulus of Tungsten at Elevated Temperatures
H.S. Ayoub, A.F. El-Sherif, A.M. Mokhtar, H.H. Hassan, S.A. Khairy and Y.H. Elbashar

This paper presents the use of an improved laser shadowgraphy method for measuring the dynamic elastic moduli of tungsten, from room temperature to near melting point. The method is based on measuring the frequency of impulse induced longitudinal vibration of a tungsten filament, subject to joule heating. The natural resonance frequency of the filament is obtained by lock-in synchronous photo-detection of the laser-generated filament shadowgraph. The correlation between the filament natural frequency and its temperature lead to the calculation of shear modulus at variable temperatures, the tensile and bulk moduli of tungsten. The results were compared to those obtained by laser Doppler vibrometry (LDV) of a tungsten wire induced by pulsed current technique. Our method permitted a wider measuring temperature range and an easier calculation procedure. The used setup was simple, non-destructive, non-contacting and accurate, enabling low-cost vibrometry measurements that help in future synthesis and test of new grades of refractory materials, deployed as plasma-facing material in the latest fusion reactor or super alloys in critical applications.

Keywords: Semiconductor laser, tungsten, Young’s Modulus, elasticity moduli, shadowgraphy, laser vibrometry, elevated temperatures, lock-in amplifier

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