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Design and Construction of Optical Laser Shadowgraphy System for Measuring the Internal Friction of High Elasticity Solids
Hussam Hassan, Deia Moubarak, Jamal Khaliel, Hany Ayoub, Ahmed Abdel-Rahaman, Sherif Khairy, Tarek El-Rasasi and Yahia Elbashar

This paper discusses a non-contact method for measuring the internal friction of high elasticity solid materials using pulse excitation technique. The sample that measured is prepared in the form of 200mm long string, having a homogenous circular cross section of 3mm diameter. A mechanical pulse is delivered to the fixed-fixed end sample by mean of a punch by a small solenoid motor plunger. A laser beam is used to generate a shadowgraph for the vibrating sample with silicone photodiode. The obtained electric signal is fed to a storage oscilloscope to capture the natural resonance amplitude decay profile of the test sample. The internal friction is obtained by mathematical analysis of the acquired data. This method is reliable, low cost, and accurate and suiting a wide variety of rubbery materials and elastomers. It is intended to alternate the torsion pendulum method that suite only for low elasticity materials that resists creep under pendulum weights.

Keywords: Dynamic elasticity, internal friction, pulse excitation technique, laser shadowgraphy, low cost, non-Doppler laser vibrometry

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