Rheometers or dynamic mechanical analyzers capable of combining two drives (rotational and linear drive) have opened new horizons in the characterization of novel composite materials [1,2]. The determination of complex Young’s modulus |E*| and complex shear modulus |G*| is possible for a single sample in a continuous measurement run thanks to the combination of both linear and rotational measuring drive in the instrument. These measurements can be performed in clamping fixtures for cylindrical or rectangular specimens by torsion, extension, or compression mode [3,4]. Additional combinations allow to include frequency, temperature and humidity sweeps to the measurements. Besides the frequency domain, experiments can be also performed in the time domain in form of creep- or relaxation tests.

This type of multi-task measurement is interesting for isotropic materials since they offer an indirect method to obtain the viscoelastic Poisson’s ratio and its dependence on time and temperature [3,4]. In the case of anisotropic materials as polymer matrix composites, they are particularly useful since it is possible to evaluate, within one single run, extensive information on the viscoelastic properties of the material in both longitudinal and transversal directions. This contribution shows several application examples in which axial and rotational measurements are combined in one single experiment to obtain a more complete information about the thermo-mechanical response of the material. Special emphasis is given to anisotropic materials as polymer matrix composites. A new parameter, ζ = tanδT/ tanδE, is introduced as an indicator of anisotropy. ζ, directly inferred from the phase shift angle in extensional δE, and torsional direction δT appears as a novel dynamic fingerprint that adds one more dimension to the viscoelastic characterization of anisotropic materials.

[1] D. Jiao, et al., Nat. Commun., 2021, 12, 1312.

[2] J. Meurer, et al., Macromol. Chem. Phys., 2021, 2000462.

[3] J.R. Agudo et al., Journal of Rheology, 2023, 67, 6. [4] M. Müller-Pabel, J.R. Agudo, and M. Gude, Polym. Test., 2022, 114, 107701.

[4] M. Müller-Pabel, J.R. Agudo, and M. Gude, Polym. Test., 2022, 114, 107701.