impulse excitation
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Author(s):  
И. И. Попов ◽  
А. В. Левченко

Постановка задачи. Работа посвящена экспериментальному определению внутреннего трения в таких материалах, как каучуковые бетоны (каутоны) на основе низкомолекулярного полибутадиенового каучука смешанной микроструктуры марки ПБН и цис-полибутадиенового низкомолекулярного каучука марки СКДН-Н, с помощью метода импульсного воздействия. Результаты. Установлено, что каутон на основе каучука марки ПБН обладает более выраженными вязкоупругими свойствами по сравнению с аналогичным материалом на основе каучука марки СКДН-Н. Введение стальной фибры снижает внутреннее трение в материале, в то время как полимерная фибра дает обратный эффект. Это связано с тем, что волокнистая пропиленовая фибра служит дополнительным демпфирующим материалом, усиливающим диссипацию энергии при динамическом нагружении. Выводы. Впервые измерено внутреннее трение для каутона и фиброкаутона. Полученные данные являются дополнительными микроструктурными характеристиками материалов, описывающими их вязкость. Определены реальные значения исследуемых величин, которые позволяют применять модели с дробными производными при расчете строительных конструкций из каутона и фиброкаутона на динамические воздействия с учетом явления вязкоупругости. Statement of the problem. The paper is devoted to the experimental identification of damping for such materials as butadiene rubber (BR) and cis-butadiene low-molecular weight rubber (SKDN-N) based concrete and fiber-reinforced rubber concrete by means of the Impulse Excitation Technique (IET). Results. It was found that BR based concrete with or without fiber-reinforcement shows more obvious viscoelastic properties than the corresponding materials based on SKDN-N rubber. The addition of steel fiber reduces internal friction in the material, while propylene fiber has the opposite effect. This is due to the fact that the fibrous propylene acts as an additional damping material, which enhances energy dissipation under dynamic loading. Conclusion. The internal friction in the rubber concrete and fiber-reinforced rubber concrete has been measured for the first time. The obtained data are the additional microstructural characteristics of polymer concrete, which describes its viscosity. The actual values of the investigated quantities have been determined, which makes it possible to use the models with fractional derivatives in the calculations of building structures made of rubber concrete and fiber-reinforced rubber concrete for dynamic loads taking into account the phenomenon of viscoelasticity.


Author(s):  
I. Popov ◽  
A. Levchenko

Statement of the problem. The paper is devoted to the experimental identification of damping for such materials as butadiene rubber (BR) and cis-butadiene low-molecular weight rubber (SKDN-N) based concrete and fiber-reinforced rubber concrete by means of the Impulse Excitation Technique (IET). Results. It was found that BR based concrete with or without fiber-reinforcement shows more obvious viscoelastic properties than the corresponding materials based on SKDN-N rubber. The addition of steel fiber reduces internal friction in the material, while propylene fiber has the opposite effect. This is due to the fact that the fibrous propylene acts as an additional damping material, which enhances energy dissipation under dynamic loading.Conclusion. The internal friction in the rubber concrete and fiber-reinforced rubber concrete was measured for the first time. The obtained data are the additional microstructural characteristics of polymer concrete, which describes its viscosity. The real values of the investigated quantities have been determined, which makes it possible to use the models with fractional derivatives in the calculations of building structures made of rubber concrete and fiber-reinforced rubber concrete for dynamic loads, taking into account the phenomenon of viscoelasticity.


2021 ◽  
Vol 11 (22) ◽  
pp. 10802
Author(s):  
Tomáš Húlan ◽  
Filip Obert ◽  
Ján Ondruška ◽  
Igor Štubňa ◽  
Anton Trník

In this study, resonant frequencies of flexurally vibrating samples were measured using the sonic resonant method (SRM) and the impulse excitation technique (IET) to assess the equivalency of these two methods. Samples were made from different materials and with two shapes (prism with rectangular cross-section and cylinder with circular cross-section). The mean values and standard deviations of the resonant frequencies were compared using the t-test and the F-test. The tests showed an equivalency of both methods in measuring resonant frequency. The differences between the values measured using SRM and IET were not significant. Graphically, the relationship between the resonant frequencies is a line with a slope of 0.9993 ≈ 1.


2020 ◽  
Vol 11 (1) ◽  
pp. 101
Author(s):  
Carlo Boursier Niutta

A new approach for the nondestructive determination of the elastic properties of composite laminates is presented. The approach represents an improvement of a recently published experimental methodology based on the Impulse Excitation Technique, which allows nondestructively assessing local elastic properties of composite laminates by isolating a region of interest through a proper clamping system. Different measures of the first resonant frequency are obtained by rotating the clamping system with respect to the material orientation. Here, in order to increase the robustness of the inverse problem, which determines the elastic properties from the measured resonant frequencies, information related to the modal shape is retained by considering the effect of an additional concentrated mass on the first resonant frequency. According to the modal shape and the position of the mass, different values of the first resonant frequency are obtained. Here, two positions of the additional mass, i.e., two values of the resonant frequency in addition to the unloaded frequency value, are considered for each material orientation. A Rayleigh–Ritz formulation based on higher order theory is adopted to compute the first resonant frequency of the clamped plate with concentrated mass. The elastic properties are finally determined through an optimization problem that minimizes the discrepancy on the frequency reference values. The proposed approach is validated on several materials taken from the literature. Finally, advantages and possible limitations are discussed.


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