Viscoelastic characterisation of carbon black reinforced rubber using the torsion pendulum: Guidelines and temperature sweep results. (October 2022)

• Record Type: Journal Article
• Authors: Vizcaíno-Vergara, M.; Tunnicliffe, L.B.; Busfield, J.J.C.; Kari, L.
• Is Part Of: Polymer testing. Volume 114(2022)
• Publication Date: 2022-10
• Subjects: Torsion pendulum -- Carbon black filled rubber -- Temperature sweep -- Dynamic modulus -- Viscoelastic characterisation; Polymers -- Testing -- Periodicals; Polymères -- Tests -- Périodiques; 620.1920287
• DOI: 10.1016/j.polymertesting.2022.107692
• Languages: English
• ISSNs: 0142-9418

Abstract

Abstract: A comprehensive set of guidelines on the use of the torsion pendulum for the viscoelastic characterisation of carbon black reinforced rubber is presented, including the set up selection, the post processing steps and the final evaluation of the method using temperature sweep results at small strains. The torsion pendulum is based on the free vibration principle, in which the sample is instantaneously perturbed to initiate a torsional movement and then left to freely vibrate. From the frequency and damping of this impulse response function, the properties of the material can be obtained against temperature and time. However, despite the extensive use for many years of the torsion pendulum, the difficulty of activating only the desired torsional mode hinders the acquisition of accurate results. The method presented aims to improve the torsion pendulum performance and can be divided in two stages. The pre-testing phase covers the influence of the test set up and sample geometry on the measured response. The test set up will determine the frequency at which the dynamic properties are obtained, while the sample geometry will influence the torsional strain and bending deflection. The post-testing phase includes the steps to post-process the curve and the criteria to identify and select the most reliable data sets from all of the measured data. The quality of the curve is assessed in the frequency domain by evaluating the frequency components of its Fast Fourier Transform and in the time domain by evaluating its fit to an ideal exponentially decreasing sinusoidal curve. The final selection of the response functions that can be used to measure the viscoelastic properties of the rubber samples is made based on the maximum strain level and the minimum variation of the dynamic properties within one curve. The validity of the method is then tested by comparing temperature sweep results before and after the application of the presented guidelines, where a clear decrease on the results deviation can be observed. Finally, the results obtained with this method are compared to Dynamic Mechanical Analysis results over the same temperature range, where a good fit is obtained. Thus, this investigation presents a comprehensive method, useful to all torsional pendulum users aiming to measure and characterise the mechanical behaviour of viscoelastic materials. Highlights: The torsion pendulum is used for the viscoelastic characterisation of filled rubber. A new method is presented to improve the performance of the torsion pendulum. After application of the method, temperature sweep results are greatly improved. The torsion pendulum results compare very well with DMA data.