Evaluation of Mechanical Parameters

In order to correlate the macroscopic response of the material to its structure it is necessary to assess the deformation of the sample close to the beam position. For this purpose a method has been devised by Stribeck et al. [2]. A pattern of parallel fiducial marks is stamped on the sample. A video camera monitors the sample during deformation (Fig. 3.1). This method gives precise values of the macroscopic elongation provided the sample is kept straight and the contrast among the fiducial marks is sufficient. The pseudo-color representation provides good visual contrast. The center of the X-ray beam on the sample is marked by a cross in the image. Close 

Zeinolebadi, In-situ Small-Angle X-ray Scattering Investigation of Transient Narwstructure of Multi-phase Polymer Materials Under Mechanical Deformation, Springer Theses, 

Assuming constant volume during mechanical loading, the actual cross-section, A(f), is calculated from 

Here A (0) is the initial cross section of the sample. Let F (t) the actual force recorded by the tensile machine. Then the true stress, a, is 

The true stress averaged over one cycle, a, is also calculated in order to assess fatigue in the load-cycling tests. The averaging is done by running-average command of Xmgrace.  

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