OPTIMUM DESCRIPTION OF YARN AXISGEOMETRY IN WOVEN COMPOSITES

摘要

Quantitative composite structure description is an important task from both thetheoretical and practical point of view. Among all in principle applicable methods for yarnaxis description or approximation the Discrete Fourier Transform (DFT) appears as the bestsuitable one, since it respects yarn periodicity or quasi-periodicity and its output, thespectrum, has a simple and straightforward physical meaning. It can be applied at least in twoways for quasi-periodic function and general closed curve description. On the other hand, theDFT should be used carefully; otherwise unwanted effects appear, such as spectrum leakagethat complicates simple and efficient use of outputs. This effect takes a place, when noninteger number of periods is sampled. Main application of DFT are presented in the paper:efficient yarn axis approximation, spectrum filtering for removing of experimental errors (likesample bending), effective approximation of general form of closed curve that is a contour ofvoid cuts in composite structure. Also method for leakage reduction is shown. Practical resultsare mainly in graphical form.