Vibrational and Impact Response Properties of Agricultural Products for Non-destructive Evaluation of Internal Quality (II)
Viscoelasticity of Watermelons
1978 Volume 40 Issue 3 Pages 375-380
Details
1978 Volume 40 Issue 3 Pages 375-380
For determining the dynamic viscoelastic moduli of flesh of watermelons, the approximate equations were derived from the measured resonant frequency and halfvalue width of its cylindrical specimen. The relations between these viscoelastic moduli and the internal quality of watermelons were investigated, and these data could be applied for non-destructive evaluation of internal quality of agricultural products using vibrational and impact response.
1. By solving the equation of motion for longitudinal vibration of viscoelastic bar,
∂2ξ/∂t2-E/ρ∂2ξ/∂x2-η/ρ∂3ξ/∂x2∂t=0
the dynamic modulus and dynamic viscosity were determined approximately as follows:
E=4ρl2fr2(4+φ2)/(2n-1)2,
η=8ρl2frφ/(2n-1)2π,
where φ=1/√3Δf/fr
2. The dynamic modulus of watermelons increased with the accumulated temperature. The increase was remarkable at the center of flesh, and reached to around 280×105dyne/cm2 for matured ones. But the dynamic modulus was supposed to decline in the sphere of overmatured watermelons.
3. During the growth and development, the dynamic modulus of watermelons changed in the same inclination as the Young's modulus determined by the quasi-static test, but the value of the former was about 2.4 times as large as that of the latter.
4. The dynamic modulus at the center of flesh of watermelons had the highest correlation with sugar content, followed by that at the placental region. But no correlation was found between the dynamic modulus at the inner wall and the sugar content. Hence, the dynamic modulus at the center of flesh was considered to be useful as much as sugar content as an index of maturity.
5. In the stage of growing, the dynamic viscosity of the flesh of watermelons decreased untill the accumulated temperature reached to 700°C, and then increased. Because of no correlation with sugar content, the dynamic viscosity was not considered to be useful for the evaluation of the maturity.
