Abstract
The effects of gas compression and Poisson's ratio on the compressive stress-strain curves of closed cell foams have been analysed. The contributions of hardening, polymer viscoelasticity, and gas escape on creep are examined. The foam diffusivity for air was predicted from the polymer permeability and the foam density. Diffusivity values, derived from fitting creep curves of LDPE and EVA foams, are of the correct order of magnitude. Creep is dominated by the polymer viscoelasticity if the stress is less than the yield stress, but at higher stresses gas compression takes an increasing proportion of the load. Gas escape is a creep mechanism operating on a timescale that depends on the size of the foam block. The consequences of the high gas diffusivity on the creep design for polyolefin foams are discussed.
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