Mechanische Spannungen in Mikroparakristallen

The Fourier diffraction method of Warren-Averbach, developed to measure external stress-induced strains of polycrystalline materials, can also be applied to analyse internal distortions of microparacrystals. In one case a function that is proportional to the distance p² can be obtained whilst in the second case a function proportional to |p| in the physical space can be derived. More complicated problems arise when both types of distortions occur at the same time, which happens if microparacrystals are exposed to external stresses. This is discussed here for examples of unannealed extruded polyethylene and composite material such as carbon resin fibres. The Warren plot shows that the microparacrystals under investigation suffer rheological transformations, which can no longer be explained by a convolution integral of the reflection profiles with the distribution function of their mean net-plane distance s. The measured function of p can satisfactorily be derived from an empirically detected formula being applied to the convolution product of reciprocal values of the two distortions 1/g²p and 1/ε²p², the physical meaning of which still remains an open question.