On the Change in Strength of Netting Cords Immersed in the Sea-I

Relation between the Strength of Synthetic Netting Cords and the Temperature, and Comparison of Power of Various Kind of Cords Changing when Immersed in the Sea

Abstract

A series of field experiments has been carried out in order to clarify how the strength of netting cords changes while immersed either continously or intermittently in the sea for a long time.
Materials of the cords tested in the study include four kind of synthetic cords and three sorts of natural cords, the specifications of which are shown in Table 1. One of the synthetic cords, Amilan, is constructed with fibres made from carbolic acid and has the same chemical construction as Nylon; Cremona and kaneviyan, both Polyvinyl synthetic cords, the fibre of which is made from carbide; Saran consists of Vinyle chloride synthetic fibre.
The test materials were classified into A₁, A₂, B₁ and B₂, according to the ways as explained in foot notes of Figs. 2 and 3 and in the following.
Dying of the natural netting cords was conducted more carefully than usual, treating five times with 4% cutch solution and fixing twice with 1% K₂Cr₂O₇ solution.
One half of each kind of the natural cords thus treated was regarded as A group together with a part of non-dyed synthetic cords, and the test of the natural and synthetic cords (B guoup) was dyed wtth coal tar.
An installation employed for immersing the sample cords is illustrated in Fig. 1 (a, b). Breaking strength and elasticity of the cords were tested every 30 or 45 days, the results of which are as follows.
(1) Relation of the breaking strength or elaslticity with the experimental preiod and the temperature at the time of testing has been obtained as in Figs. 2 and 3.
(2) It has been confirmed in another laboratory experiment of synthetic cords that the breaking strength of the cords is reduced, but their elasticity increases, in proportion to the temperature of the cords when they are tested. The relation between breaking strength S or elasticity E and temperature θ may be expressed by the following experical formulace.
S=a+bθ E=a'+b'θ
(3) The breaking strength and elasticity are reduced as time elasps, even when these synthetic cords are stored as they stand. It seems, however, that the relations as shown in paragraph 2 hold still good, and that although each value of a, b, a' and b' decreases little by little under the same condition during two to three years of storage, there has hardly occurred any change in the value of b/a and of b'/a'.
(4) When the breaking strength at θ°C of the cord which has been left in a room for t days is written as S_θt, and the breaking strength of the cord at θ°C and t=0 as S_θo, they can be shown by the following formulae; because b_o/a_o=b/a=m, where m is constant.
S_θt=a(1+mθ)
Hcnce, the change of the breaking strength is
S_θt/S_θo=a/a_o=ƒ_(t)/a_o
In the same way as above, the elasticity at θ°C after t days and at θ°C, t=0 can be written as following.
E_θt=a'(1+nθ) E_θo=a'_o(1+nθ)
Therefore, the change in the elasticity is
E_θt/E_θo=a'/a'_o=4_{( ?? )}/a'_o