EFFECT OF POROSITY OM MECHANICAL-PROPERTIES OF RUBBER

Cylindrical samples, with different shape factors and levels of porosity, were prepared from a model EPDM compound and tested in compression. The modulus was reduced considerably with the introduction of porosity, especially when the shape factor was high. The stress-strain curves showed nonlinearity which depends on the shape factor and porosity level, and is related to bubble closure. The apparent modulus of bonded blocks was found to consist of two components: homogeneous compression modulus and a hydrostatic contribution. The first was obtained by compression of blocks between lubricated compression plates. It can be predicted from analytical expressions adapted from composite theories for high density foams in tension. The second arises from the pressure buildup inside the bonded blocks and depends on the shape factor and the porosity level. These moduli, after correcting for compressibility, were used to develop approximate relations describing the stress-strain curves of porous bonded blocks. The stress-strain curves of samples with different shape factors and levels of porosity could be predicted from experimental data or FEA estimates.