Meridion circulare

In terms of the measurements of Table IV the basis for a 20 A. pseudoperiod may be stated as follows The two strong meridional arcs are not hyperbolic intersections of the flat film with widely extended reciprocal disks (21), but their circular arc shape indicates clearly that their expression is caused by disorientation. That layer lines exist at these levels is indicated by the fainter diffuse lines with approximately the same axial spacing components. In addition, there is evidence for another layer line at about 5.0 A. These, along with the distinct ones, can be assigned indices 0, 2, 4, 5, and 7 to very nearly account for their relationships. 

A distinctive structural feature of PpPTA and other para-aromatic polyamide fibres is the pleated sheet, which is shown in Fig. 13c, 13d and 13e. It was for the first time observed by Ballou in dark-field images taken from meridional reflections of the ED pattern [132]. This phenomenon has been extensively studied by Dobb et al. [125]. The pleated sheet consists of parallel-oriented chains, which are hydrogen bonded along the direction of the crystallographic b-axis. They are usually oriented perpendicular to the surface of the filament, i.e., in the circular cross-section the b-axes are directed preferably along the radius, as shown in Fig. 14. The angle between adjacent planes of the pleat is about 170° and the distanee between two pleats is about 250 nm, but both values may vary along the radius of the fibre cross-section. 

The resultant friction stress exerted at the tool-sheet contact interface is assumed to be made of two in-plane components - a meridional component - due to the step down movement of the tool and a circumferential component - due to circular movement of the tool combined with the rotational speed of the tool. This last assumption, which is an untraditional way of modelling... 

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