Experimental Demonstration of a 'Viscoelastic Crossover'Phenomenon. The Reflection of Stress Pulses at the Boundary between Nearly-Elastic and Lossy Viscoelastic Media Whose Impedances Are Matched.

摘要

Observations were made of the longitudinal stress pulses reflected from an interface between two viscoelastic rods. The incident medium (polystyrene) was nearly elastic,while the reflecting medium (unplasticized polyvinyl chloride) was fairly lossy,having a frequency-dependent,complex extensional-wave impedance. The frequency at which the impedances of the two materials are equal in magnitude is termed the 'crossover'frequency and is temperature-dependent. Fourier components well above the crossover frequency are reflected substantially in phase,while those well below this frequency are reflected nearly out of phase. By varying the temperature,and hence the crossover frequency,the reflected pulses were made to vary from essentially-positive at room temperature to essentially-negative at 55C. At an intermediate temperature,the reflected pulse had a minimum amplitude and a shape significantly different from that of the incident pulse (this case is the viscoelastic analog of impedance matching for elastic media). The experimental results serve to demonstrate the viscoelastic-crossover effect predicted by Kolsky and Lee. (Author)