Investigation Internal Friction of High Elasticity Solids using Laser Shadowgraphy

Document Type : Original Article


1 Basic Science Department, Thebes High Institute of Engineering Cairo 11434, Egypt.

2 Department of Physics, Faculty of Science, Cairo University, Egypt.

3 Laser Photonics Research Center, Engineering Physics Department, Military Technical College, Cairo, Egypt.

4 Physics Department, Faculty of Science, Benha University, Egypt.


This paper discusses a non-contact method for measuring the internal friction of high elasticity solid materials using pulse excitation technique. The measured sample is prepared in form of 200mm long string, having a homogenous circular cross section of 3mm wide. A mechanical pulse is delivered to the fixed- fixed end sample by mean of a punch from a small solenoid motor plunger. A laser beam is used to generate a shadowgraph for the vibrating sample on an silicone photodiode. The obtained electric signal is fed to a storage oscilloscope to capture the natural resonance amplitude decay profile of the tested 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 suites only low elasticity materials that resists creep under pendulum weights.