Strain and filler ratio transitions from chains network to filler network damage in EPDM during single and cyclic loadings

Chains and filler network damage were investigated during single and multiple cycles on a series of vulcanized EPDM containing various filler contents. In both series of experiments, a strain and a filler ratio transitions for damage mechanisms were identified. For low filler content (<= 40 phr), damage mechanisms mostly occur in the elastically active rubber network consistent with the chains network alteration theory associated with irreversible chains scission/bond breakage. For high filler content (>40 phr), a strain transition occurs with damage initially located in the elastically active rubber network, but subsequently localizes in the vicinity of the filler-filler network. This is ascribed to filler re-aggregation with strain, improving its load-bearing capacity, that may release the immobilized rubber formed by the chains that are occluded and bonded to fillers. During cyclic experiments, such reversible release involving loss of weak physical bonds and chains slippage yields in a progressive cavity closing with cyclic accumulation that prevents further irreversible damage of the elastically active rubber network.