抄録
It was reported that compressive modulus of flexible polyurethane foams seem to be an important physical property corresponding to sensory value “hardness”8, 9), and compressive modulus of this substance is anisotropic between parallel and perpendicular to rising direction7). In this paper, as a continued report of the ones above mentioned7-9), the anisotropy of compressive modulus in any direction of this substance is mainly referred. In the first half, the certification of the adaptability of elastostatics to the anisotropy of compressive modulus of foams, whose specimens are large enough to be treated homogeneously, and in the latter half, using the result of the first half conversely, the minimum largeness of specimen regarded as the homogeneous substance for compression, are discussed.
The results obtained are as follows:
1) Compressive modulus Y of foams is anisotropic in the longitude plane, but is isotropic in the equator plane (see Fig. 2). Accordingly, the anisotropy of Y depends on the complementary angle β of the latitude.
2) The anisotropy Y(β) in the longitude plane of foam is expressed as, And the results of the calculations on the above equation showed a good agreement with the observed values of Y(β). Accordingly, the reason for being of the anisotropy of Y(β) in the longitude plane is explained as K(=lz/lx)_??_1. Where, lz and lx are the sizes of cell in parallel and in perpendicular to rising direction, and Yz is compressive modulus in parallel to rising direction.
3) Any specimen to which was given direction of β for measuring of Y(β) must have at least [N]=20-odd numbers of layers of cells along the line of thickness of specimen, in order to treat it homogeneously in case of compression test. And, the minimum thickness [t] of specimen, regarded as the homogeneous substance, depends on the size of cell and β.
4) When the direction of the thickness of the specimen is in line with the diagonal line of a cell, the number of cells per unit length in the thickness of the specimen is minimum. And, [t] of this direction is enough to be applicable to any specimen having direction of β. Where, [t] is calculated from
