  A study of methodological nature demonstrates the efficiency of a probation
test allowing for the intrinsic character of a rheological constitutive law to
be assessed. Such a law is considered here for Semi-Crystalline Polymers
exhibiting necking and for large deformation. In the framework of a
$(\dot\sigma, \sigma, \dot\varepsilon, \varepsilon)$ behavior's law, tensile
experiments conducted at an imposed constant strain rate $\dot\varepsilon_0$
bring true stress responses from which constitutive (material) parameters can
be identified from Model-Based Metrology concepts. The same experiment repeated
at various strain rates gives then access to the dependence of the non-elastic
parameters on the strain rate. Then the intrinsic law is tested severely by
considering a new set of experiments carried out for constant displacement
rates of the grips. In that case, the specimens show local strain rates which
evolve strongly during the test (by a factor of 5-10 here). The parameter
identification process requires then the introduction of the exact realized
input strain and strain-rate command into the model. Accounting for strain rate
dependency requires additionally the knowledge of the preliminary identified
strain rate dependence of the non-elastic constitutive parameters for good
predictions of the experimental response directly. This is what is proven here.
The conclusion speaks in favor of a possible upgrade of international standards
for the mechanical characterization of polymers based on constant strain-rate
tensile tests and properly applied model-based metrology.
