The Small Punch Creep-Recovery Test (SPCRT) is a novel miniature test used to estimate
the viscoelastic properties of polymers and biomaterials. The current investigation related to the
SPCRT is limited to Finite Element Method (FEM) simulations and experimental tests on PVC. The
aim of this investigation was focused on: (i) extending the experimental tests to other polymers with
dissimilar viscoelastic properties; (ii) deepening the influence of non-linear viscoelastic properties in
the estimation capabilities of the SPCRT; and (iii) developing a numerical methodology to estimate
and take into account the viscoelastic recovery produced during the unloading step of compressive
creep-recovery tests (CCRT) and SPCRTs. The experimental tests (CCRTs and SPCRTs) were done on
polyethylene PE 500, polyoxymethylene POM C, nylon PA 6, and polytetrafluoroethylene (PTFE),
with a range of creep loads, in the case of CCRTs, in the whole elastic regime and the surroundings
of the yield strength of each material. The experimental results confirmed that the SPCRT was an
accurate and reliable testing method for linear viscoelastic polymers. For a non-linear viscoelastic
behavior, SPCRT estimated the viscoelastic properties obtained from CCRTs for creep loads near the
yield strength of the polymer, which corresponded with large-amplitude viscoelastic properties in
dynamic creep testing. In order to consider the viscoelastic recovery generated in the unloading
step of CCRTs and SPCRTs, a Maxwell-Wiechert model with two branches was used, simulating
the different steps of the experimental tests, and solving numerically the differential equation of the
Maxwell-Wiechert model with the Runge-Kutta-Fehlberg (RKF) numerical method. The coefficients
of the elements of the Maxwell-Wiechert model were estimated approaching the straining curve
of the recovery step of the simulation with the same curve registered on each experimental test.
Experimental CCRTs with different unloading times demonstrated that the use of this procedure
derived in no influence of the unloading step time in the viscoelastic properties estimation.
