Dynamic strain softening

Figure 6.7. Example of dynamic strain softening of amorphous nanocomposite above neat matrix T. Hydroxyapatite spherical and platelet uanoparticles were used as filler. Experimental points were adopted from reference [79]...

Kalfus J and Jancar J (2007) Viscoelastic response of nanocompoate poly(vinyl acet-ate)-hydroxyapatite with varying particle shape-dynamic strain softening and modulus recovery, Polym Comp 28 743-747. 

A number of experimental data have shown that a great variety of filled rubber vulcanizates exhibit the dynamic strain softening effect schematically illustrated in Figure 5.42, at given frequency and temperature. The limiting... 

It is worth noting that dynamic strain softening is observed on filled vulcanizates whatever is the strain mode, i.e., shearing, tensile of uniaxial compression. The shear modulus G =G +iG" is explicitly considered here, but the same considerations would in principle apply as well to the tensile modulus E =E +iE" or the compliance / =/A/."... 

As shown in Figure 5.50, Equation 5.59a meets reasonably well the dynamic strain softening of G however Equation 5.59b cannot meet the asymmetric shape of experimental G" vs. strain curves. 

A5.2 Kraus Deagglomeration-Reagglomeration Model for Dynamic Strain Softening... 

A5.3 Ulmer Modification of the Kraus Model for Dynamic Strain Softening Fitting the Model... 

Dynamic strain softening data on SBR/60 phr black cpds [M. Gerspacher, C.P. O Farrell, C. Tricot, L. Nikiel, H.A. Yang. ACS Rubb. Div Mtg, Louisiana, KY, 1996. Paper 74]... 

AS.5.2 Modeling the Dynamic Strain Softening Effect Elastic modulus ... 

Figure 6.10 shows typical dynamic properties of vulcanized PDMS-silica systems, as investigated through strain sweep experiments at constant frequency and temperature. As can be seen, dynamic strain softening is observed in a qualitatively similar manner to other filled polymers. It follows that models, which successfully fit conventional filled rubbers (e.g., carbon black filled compounds), are expected to well suit such data. This is indeed the case, as shown by the curves in Figure 6.10, drawn by fitting the Kraus-Ulmer equations, i.e.. 

Dynamic strain softening as observed on PDMS-silica systems 0.078% vinyl-pendant PDMS (M =140,000 g/mol Mw=390.000 g/mol) 300 m2/g silica peroxide crosslinked. (Experimental data from L. Dujourdy, PhD Thesis, University of Grenoble, France, 1996.)... 

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