Polymer crystals slip systems

For polyamide 6 crystals the slip systems are (001) [010] chain slip at 16.24 MPa, (100)[010] chain slip at 23.23 MPa and (001)[100] transverse slip [71]. Relatively little attention was paid to the plastic deformation of other semicrystalline polymers [98,110]. In particular, there are only a few papers [111,112] describing the investigations of the yield behavior and plastic resistance of oriented iPP. 

The detailed knowledge concerns the system of crystallographic slips operating in polymer crystals, critical resolved shear stresses, twinimig, martensitic transformation and succession of activation of individual slip mechanisms [111,160,161]. 

Slip bands and kink bands were first studied in compression of oriented nylon 6,6 and 6,10 by Zaukelies, and subsequently in tensile specimens of oriented high density polyethylene (HOPE) by Kurakawa and Ban and Keller and Rider Zaukelies interpreted the angle between kink bands in oriented nylon and the compression axis in terms of Orowan s theory of crystal kinking, postulating dislocation mechanisms for the process. Keller and Rider ° and Kurakawa and Ban were impressed by the appearance of deformation bands in high density polyethylene in directions close to the IDD. In this polymer system the... 

Incompressibility of the fluid has generally been assumed throughout the book, albeit this is not always stated explicitly. This is a satisfactory approximation for most non-Newtonian substances, notable exceptions being the cases of foams and froths. Likewise, the assumption of isotropy is also reasonable in most cases except perhaps for liquid crystals and for fibre filled polymer matrices. Finally, although the slip effects are known to be important in some multiphase systems (suspensions, emulsions, etc.) and in narrow channels, the usual no-slip boundary condition is regarded as a good approximation in the type of engineering flow situations dealt with in this book. 

In crystalline polymer systems the tough response, besides cavitation and crazing, is crystallographic in natme. Crystallographic slips ai-e the main plastic deformation mechanisms that require generation and motion of crystallographic dislocations. The concepts of generation of monolithic and half-loop dislocations plausibly explain the observed yield stress dependences on crystal thickness, temperatm-e and strain rate. 

---