Analysis of dynamic mechanical response in torsion

Abstract

We investigate the dynamic response of industrial rubbers (styrene-butadiene random copolymers, SBR) in torsion and compare against common small amplitude oscillatory shear measurements by using a torsion rectangular fixture, a modified torsion cylindrical fixture, and a conventional parallel plate fixture, respectively, in two different rheometers (ARES 2kFRTN1 from TA Instruments, USA and MCR 702 from Anton Paar-Physica, Austria). The effects of specimen geometry (length-to-width aspect ratio) on storage modulus and level of clamping are investigated. For cylindrical specimens undergoing torsional deformation, we find that geometry and clamping barely affect the shear moduli, and the measurements essentially coincide with those using parallel plates. In contrast, a clear dependence of the storage modulus on the aspect ratio is detected for specimens having rectangular cross section. The empirical correction used routinely in this test is based on geometrical factors and can account for clamping effects, but works only for aspect ratios above a threshold value of 1.4. By employing a finite element analysis, we perform a parametric study of the effects of the aspect ratio in the cross-sectional stress distribution and the linear viscoelastic torsional response. We propose a new, improved empirical equation for obtaining accurate moduli values in torsion at different aspect ratios, whose general validity is demonstrated in both rheometers. These results should provide a guideline for measurements with different elastomers, for which comparison with dynamic oscillatory tests may not be possible due to wall slip issues

Chemical control of the viscoelastic properties of vinylogous urethane vitrimers

“…Stress–relaxation experiments were conducted in torsion geometry29 with a deformation of 1% and compared to the uncatalysed samples. Similar to the elastomeric networks, a much faster stress–relaxation can be observed, again without a significant change in activation energy (Supplementary Fig.…”

Characterizing viscoelastic properties of synthetic and natural fibers and their coatings with a torsional pendulum

“…Many other researchers have used torsional balances in a similar manner or used the torsional pendulum setup to directly characterize mechanical properties of different filaments and fibers 1,[30][31][32][33][34][35] . More broadly, soft matter scientists are still using torsion balances and pendulums today in their studies of different viscoelastic materials 36,37 . Many of the mentioned studies have focused on monofilament fibers.…”

“…Corresponding correction factors for different cross-section geometries (e.g. square 51 , rectangle 54 , and ellipse 53 ) and details of the modified analysis are reported in the literature 50,51,53,54 . † The torsional strain is small because R(θ 0 −θ )/L << 1 for long fibers.…”

Dynamic Mechanical Property Experiment of Viscous Material for Viscous Damping Wall

“…ARES test usually used to measure the linear mechanical property under shear strain of polymer. Polymers such as SBR and PEKK were investigated on the influences of frequencies, strain rates and strain amplitudes on modulus of polymers (Hu et al, 2008;Snijkers and Vlassopoulos, 2011;Dessi et al, 2016;Coulson et al, 2018). However, polymers are usually shear-thinning material and following the power-law whose velocity exponent is not equal to 1 (Fatkullin et al, 2011;Li et al, 2013), while rheometers assume that the velocity exponent is always equal to 1 during measuring process.…”