Basic Study on the Viscoelastic Properties of the Rice Kernel

Abstract

In order to investigate the viscoelastic property of a rice kernel, the compression and the stress relaxation tests were made by using the test pieces of the rice endosperm formed into a cylindrical shape. The experimental results obtained were summarized as follows:
(1) The beginning of the stress-strain curve obtained under a constant strain-rate compressoin test was given as a convex function due to imperfect contact between the end surfaces of the test piece and the loading plates.
(2) By the stress-strain curves obtained under various strain-rate tests, it was found that the strain at a constant stress level had a tendency to increase with decreasing strain-rate. It could be considered, as a result, that a rice endosperm had a viscoelastic property.
(3) By the stress relaxation tests, it was proved that a compression stress in the rice endosperm was remarkably relaxed with time.
(4) It could be concluded that the rice endosperm was approximately a kind of linear viscoelastic materials in the range about ε<1% or σ<2kg/mm². The relaxation property of the rice endosperm was given by the following equation, E(t)/E(0)=0.3exp(-t/τ₁)+0.7exp(-t/τ₂) where E(t): relaxation modulus, E(0): instantaneous elastic modulus, t: time, ε: nominal strain, σ: nominal stress, τ₁ and τ₂: relaxation times.