Effect of plastic deformation on the microhardness

These motions result in partial disordering of the crystalline lattice and thus also in increased mobility of the segments at the intercrystalline regions. This leads to the change in the linear expansion coefficient. 

The effect of temperature on microhardness at low temperatures (for PE between —60 and 25 °C and for isotactic polypropylene (i-PP) between -20 and 25 °C) has also been studied (Perena et al, 1989 Martin et ah, 1986). While for i-PP it is possible to detect accurately the glass transition temperature, for PE it is concluded that the use of only H for recognizing the secondary relaxations in PE does not allow their precise temperature location. Here the joint use of dynamic mechanical techniques and microhardness is recommended (Perena etal, 1989). 

From the morphology of the fibrous structure of the deformed polymer (see Fig. 2.11(a)) one may conclude that the dominant deformation modes of the drawn polymer under the stress field of the indenter involve  

From the foregoing it is apparent that indentation anisotropy is a consequence of high molecular orientation within highly oriented fibrils and microfibrils coupled with a preferential local elastic recovery of these rigid structures. We wish to show next that the influence of crystal thickness on AH is negligible. The latter 

Ultra-oriented solid-state extruded fibres 

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