Strain-induced network chains damage in carbon black filled EPDM

This paper presents an experimental method to follow in-situ the chains network alteration of filled vulcanized rubbers induced by deformation. Macroscopic damage is first investigated on a series of EPDM by quantifying void fraction via Digital Image Correlation (DIC). In-situ DIC void fraction and the swollen pore fraction measured ex situ, i.e. on mechanically tested specimen, show analogous dependence on applied deformation. From such observation, Flory-Rehner equation is used by substituting fraction of swollen specimen by DIC void fraction to access to in-situ changes in network chains density, nu. Below the stretching ratio lambda = 3, reversible voids and accompanied by slight decrease of nu. Above lambda = 3, irreversible voids are associated with significant decrease of nu. Transition from reversible to irreversible voiding is finally ascribed to increased pore size of damaged elastically active chains network domains, as revealed by ex situ thermoporosimetry.