Читать книгу The Rheology Handbook - Thomas Mezger - Страница 102

Plastic behavior cannot be described unequivocally using the usual scientific fundamentals of mathematics and physics since it is an inhomogeneous behavior. Therefore, it can only be presented in terms of relative values obtained from empirical tests.

Unfortunately, in many industrial laboratories the terms plastic, ideal-plastic, viscoplastic or elastoplastic still are used to mean a lot of different things. It is useful to understand what these terms might mean, but their use should be avoided when performing and analyzing scientific rheological tests. Within a limited deformation range, in most cases, samples can be characterized as viscoelastic (DIN 13343). However, if a material cannot be sheared homogeneously it is often necessary to use special relative measuring systems (see Chapter 10.6). In this case, it is better to work only with the measured raw data such as torque, rotational speed and deflection angle, instead of any rheological parameter such as shear stress, shear rate, shear deformation, viscosity, and shear modulus.