Cyclic strengthening of polypropylene under strain-controlled loading

Cyclic viscoplasticity of semicrystalline polymers with finite deformations

“…This figure reveals that (i) maximum and minimum stresses decrease with number of cycles n (stress-softening), (ii) the rate of decay in minimum stress exceeds noticeably that in maximum stress, (iii) hysteresis energy is reduced with number of cycles; its decrease is rather weak at small strains and becomes pronounced with growth of k max . These conclusions are in agreement with observations in cyclic tests with strain-controlled programs (Drozdov, 2011).…”

Cyclic deformations of polypropylene with a strain‐controlled program

“…2. This figure shows that loading and unloading curves (i) slowly move down with n (which is conventionally treated as cyclic softening [2, 17]) and (ii) rotate counter‐clockwise (which provides indication of cyclic strengthening [18–20]), whereas (iii) hysteresis energy (calculated as the area between subsequent loading and retraction paths) strongly decreases with n .…”

“…Most of these works concentrated on the time‐ and rate‐dependent response of polymers in cyclic tests with (i) mixed programs, where a sample was loaded up to some maximum strain ε max and unloaded down to a fixed stress σ max and (ii) stress‐controlled programs (ratcheting [13]), in which oscillations were performed between minimum and maximum stresses σ max > σ min > 0 [10, 11, 14–16]. Only a few publications [2, 17, 18] focused on cyclic tests with strain‐controlled programs (oscillations between fixed minimum ε min and maximum ε max strains).…”

Mullins'' Effect in Semicrystalline Polymers: Experiments and Modelins

“…On the contrary, parameters R 1 and R 3 increase with number of cycles (at least, after an initial period of decay). This increase is associated with damage growth in the crystalline phase (fragmentation of weak lamellae and alignment of broken lamellar pieces along the loading direction [5]). …”