Fibre-orientation measurements in short-glass-fibre composites - II: a quantitative error estimate of the 2D image analysis technique

Fibre-orientation measurement by two-dimensional (2D) image analysis of pol ished cross-sections is a rapid and highly efficient method for determining the fibre orientation distribution over large sample areas. In a recent pa per, a new technique was presented for measuring fibre orientation to a hig h level of accuracy by the use of a confocal microscope. In this paper, the confocal technique is used to evaluate independently the performance of th e 2D image analysis technique and the errors are presented in full. The res ults reveal a significant systematic error in orientation measurements and the effect of image resolution is considered. A method is proposed for corr ecting this systematic error and its validity is verified experimentally. A technique for determining the sampling error of a fibre-orientation measur ement is presented, enabling the calculation of confidence limits about the derived orientation tensor components. It is shown how confidence limits a id the comparison of two fibre-orientation measurements of similar samples. Furthermore, the sampling error should enable a more meaningful comparison of numerical simulation of injection moulded composites and their experime ntally manufactured counterparts. (C) 2001 Elsevier Science Ltd. All rights reserved.