Two-scale model for the effect of physical aging in elastomers filled with hard nanoparticles

Quantifying the Contributing Factors toward Signal Fatigue in Nanocomposite Strain Sensors

“…39 This fluidization is caused by local heating from internalized friction in and around the glassy filler network as a result of bulk sliding of polymer chains by one another and chains sliding off of or on filler interfaces. 34,39,41,42 In contrast, for brittle epoxy-based nanocomposites, cycling also leads to softening; however, hysteresis effects are due to the propagation of voids and an increase in crack density. 46 For these materials, (ΔR/R 0 ) R is found to increase with cycle number as opposed to decrease because of complete material failure.…”

“…The reported softening that occurs during cycling is known as the Mullins effect . Similar to the Payne effect, the Mullins effect is the result of the structural evolution of glassy and soft microstructures inside a polymer/filler system as a function of repetitious strains. , Softening can be attributed to a stress relaxation mechanism that in the past was modeled by Kraus as the number of connections in a filler network inside a housing polymer matrix as function of strain amplitude. , However, it has been noted that this softening is not permanent and stiffness maybe be partially recovered in nanocomposites as crystalline regions are reported to “rebirth” ambiently over a long time scale (∼10 6 s) at a rate that is temperature-dependent. , …”

“…Fillers inside polymer elastomer systems can be said to be surround or covered by crystalline polymer described as a “glassy layer” and form interconnected networks containing “glassy bridges” (red region) that adjoin neighboring fillers (grey rectangles) inside the bulk amorphous structure (Figure A). ,,− According to percolation theory, at a critical loading level of fillers, this network will enable the conduction of electrical current. − During loading for an elastomeric-based nanocomposite, fluidization of the glassy layers and bridges occurs (Figure B), resulting in a change in filler network structure impacting subsequent response to additional loading cycles (Figure C) . This fluidization is caused by local heating from internalized friction in and around the glassy filler network as a result of bulk sliding of polymer chains by one another and chains sliding off of or on filler interfaces. ,,, In contrast, for brittle epoxy-based nanocomposites, cycling also leads to softening; however, hysteresis effects are due to the propagation of voids and an increase in crack density . For these materials, (Δ R / R 0 ) R is found to increase with cycle number as opposed to decrease because of complete material failure …”

“…36,37 However, it has been noted that this softening is not permanent and stiffness maybe be partially recovered in nanocomposites as crystalline regions are reported to 'rebirth' ambiently over a long time scale (~10 6 s) at a rate that is temperature dependent. 38,39 Fillers inside polymer elastomer systems can be said to be surround or covered by crystalline polymer described as a 'glassy layer' and form interconnected networks containing 'glassy bridges' (red region) that adjoin neighbouring fillers (grey rectangles) inside the bulk amorphous structure (Fig 2A). 36,38,[40][41][42] According to percolation theory, at a critical loading level of fillers, this network will enable the conduction of electrical current.…”

“…[43][44][45] During loading for a elastomeric-based nanocomposite, fluidisation of the glassy layers and bridges occur (Fig 2B ), resulting in a change in filler network structure impacting subsequent response to additional loading cycles (Fig 2C). 39 This fluidisation is caused by local heating from internalised friction in and around the glassy filler network as a result of bulk sliding of polymer chains by one another and chains sliding off of or on filler interfaces. 34,39,41,42 In contrast, for brittle epoxy-based nanocomposites, cycling also leads to softening however hysteresis effects are due to the propagation of voids and an increase in crack density.…”