Abstract
The reflected waves received from ultrasonic waves propagating in materials contain information that constitutes the physical properties, material composition, defects, and degradation states. When measuring the dynamic viscoelasticity, the traditional bottom reflection method (BRM) cannot be used to measure the bottom irregular samples. In this paper, the storage modulus, loss modulus, and loss tangent are extracted by the surface reflection method (SRM) to evaluate the elastomer sample viscoelasticity. A theoretical study on the phase change caused by multiple reflections in the case of non-thin layer coupling is conducted. Based on this research, the experimental system is built. The results show that considering the thickness of the coupling layer can optimize the determination of viscoelasticity and reduce the error of the viscoelastic evaluation results of an elastomer with the traditional BRM. Finally, based on the principle of the SRM, the density of the elastomers is measured, and the feasibility and overall efficiency of this method are verified by experiments.
Highlights
At present, rubber materials are widely used in transportation, the military, and national defense because of their characteristics of superelasticity, large deformation, softness, wear resistance, and insulation [1,2,3,4,5]
Rubber materials are usually used in poor environments; for example, they may be exposed to high temperatures, high pressure and high impacts when used as automobile tires, mine conveyor belts, and tank shock absorbing materials, so they are prone to fatigue and damage
The analysis shows that the storage modulus L0 obtained by the surface reflection method (SRM) is basically the same as that of the bottom reflection method (BRM) but has some error; by adding the coupling layer thickness to the optimization calculation method, the errors of the two evaluation methods are reduced
Summary
Rubber materials are widely used in transportation, the military, and national defense because of their characteristics of superelasticity, large deformation, softness, wear resistance, and insulation [1,2,3,4,5]. The internal damping mechanism is a significant evaluation index for material safety performance and to characterize it, viscoelasticity as a main mechanical property of rubber materials cannot be ignored. The conventional ultrasonic method needs to evaluate viscoelasticity through internal attenuation and sound velocity measurement of the material is essential [12,13], which requires cutting the test sample. These methods are very inconvenient to carry out in the field, and the requirements on the bottom state of the material are too high in terms of the shape of the Materials 2019, 12, 1875; doi:10.3390/ma12111875 www.mdpi.com/journal/materials. The accuracy was confirmed by experiments and the practical obstacle of the ultrasonic evaluation method of viscoelasticity was eliminated
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