Studies on the basic characteristics of South African merino wool. I. Breaking strength and tensile strength

Abstract

A series of South African Merino wool samples, representing wools from different parts of the Union, was analysed for breaking strength and tensile strength. The method of determination, using Doehner's instrument, consisted of bundle tests, this giving average values for larger samples and lots. A portion of the analysis is devoted to the breaking strength and tensile strength of fibres within the same staple. It is shown that the average breaking strength of the coarse fibres within the staple is 6.66 (± .504) grammes. That of the fine fibres is 4.38 (± .300) grammes, so that the course fibres are 52 per cent. stronger per fibre than the fine fibres. The practical significance of this is discussed. Breeding aspects are discussed and it is shown that the Merino breeder, in striving for uniformity of fibre fineness, will tend to attain uniformity in fibre length and also in the breaking strength of the fibres. The average tensile strength of the coarse fibres within the staple is 1.32 (± 0·058) and that of the fine fibres is 1·46 (± ·070), (expressed as grammes per square cm. x 10⁶). When fibres within the same staple are considered, there is a significant correlation of · 9508 ( ± · 7938) between fibre diameter and breaking strength and a significant negative correlation of - ·4822 ( ± ·0456) between fibre diameter and tensile strength. The average breaking strength (per fibre) of representative South African Merino wool samples ranges from 1 to 11 grammes with a mean of 5 ·50 grammes. The tensile strength of South African .Merino wool varies from 0 · 6 to 1· 6 ( x 10⁶) grammes per square centimetre with an average of 1· 243 ( x 10⁶) grammes per square centimetre of fibre. The latter figure can also be expressed as 8 tons per square inch or 12 · 4 kilogrammes per square millimeter of fibre. When different samples are considered there is a significant correlation (r = 0 · 896 ± 0 · 0186) between fibre fineness and breaking strength, but an insignificant correlation ( r= -0.1780±0.0911) between fibre fineness and tensile strength. The regression coefficient of the breaking load on fibre fineness is 0 · 445 ( ± · 0208) indicating that, on an average, every increase of 1µ in fibre fineness is associated with an increase of 0 · 445 grammes in the breaking strength.