Weibull analysis of strengths of coir fibres.

The large scatter observed in the fracture strengths of coir fibres ranging in length from 0·001 m to 0·065 m and in diameter from 0·15 × 10−3 m to 0·35 × 10−3 m, is analysed statistically using a two-parameter Weibull treatment. It was found that the strength distribution at any length (and for any diameter of fibre) can be represented satisfactorily by unimodal Weibull distributions. The plot on logarithmic coordinates of mean fracture strength () against test length for a 0·25 × 10−3 m diameter coir fibre, shows a linear relationship between 0·065 m and 0·006 m; below 0·006 m the strength is relatively independent of length. Apparently below a length of 0·006 m the flaws are evenly distributed and the mean distance between gross flaws is of the order of 0·006 m. The plot of percentage coefficient of variation against mean fracture strength shows that the experimental results fall in two parallel lines showing a discontinuity at a given strength corresponding to a length of about 0·006 m. The increase in Weibull parameter, m, with increase in diameter shows that the flaw distribution is more uniform in fibres of large diameter. This conclusion is in agreement with the fibre strength histograms plotted for various diameters. The origin of flaws in coir fibres may be from two sources: (a) growth defects and (b) processing defects. These flaws and flaw distributions in coir fibres are responsible for the observed scatter in fracture strength values