Torsion Pendulum test

The torsion pendulum test (determination of the shear modulus) is used to determine the dynamic and mechanical properties of plastics in the solid state.

A distinction is made between two basic methods:
  • Torsion pendulum method (ISO 6721-2)
  • Torsional vibration – non-resonance method (ISO 6721-7)

In both cases, a plastic specimen is subjected to a shear deformation (deflection) at a constant frequency and the material response detected at periodic intervals. This results in the storage modulus G' (shear modulus) as well as the loss modulus G" and the loss factor tan δ. The storage modulus is generally determined as a function of temperature. The storage modulus curve as a function of temperature is characteristic of each plastic.

This curve can be used to identify various states of aggregation as well as softening ranges, glass transition temperatures, crystalline melting points and secondary relaxation ranges. A knowledge of where the softening range starts is very important for a part’s future use.

Results of the test method

Representation of the shear modulus curves of an amorphous and semi-crystalline thermoplastic determined using the torsion pendulum test. The various states of aggregation are also identified.

Test specimen

Flat test specimen 80 mm x 10 mm x 4 mm and 80 mm x 10 mm x 1 mm