Size effect in glass fiber reinforced and pure polyurethane foams in monotonic and creep compression

Abstract

Size effects on the monotonic and creep compression behavior of closed-cell polyurethane foams is investigated experimentally. The aim is to determine a minimum representative volume of mechanical behavior for both mechanical tests. Cubic specimens of nonreinforced and glass fiber-reinforced foams are tested in compression and creep. In the first series of tests, various sizes of samples are tested, cube with edge between 10 and 50 mm. In this case, edge effects have a variable influence depending on the sample size and the minimal size is about 40 × 40 × 40 mm³ for the nonreinforced foam and 50 × 50 × 50 mm³ for the glass fiber-reinforced one. In the second series, the mechanical behavior of more or less extended domains is analyzed from the surface of a single 50 × 50 × 50 mm³, that is, at given edge effect. The minimal size was smaller in the latter case. Influence of the loading path was investigated comparing monotonic tension and short-term creep kinetics. Unlike in monotonic compression, and in the initial creep strain, no influence of the sample size was evidenced on the creep kinetics. Surface analysis in cubic samples upon monotonic compression and creep lead to a minimum representative surface between 4 and 13 mm edge.