Bulk sample deformation

Bulk sample deformation is followed by the observation of surface changes via SEM, ESEM, AFM, or after replication by TEM. Changes inside the bulk material are studied by preparing semithin or ultrathin sections using an ultramicrotome and investigation by TEM or AFM. 

Block and clay regions of SEBS nanocomposite Modulus from Hertz model ( Sample) MPa Localized sample deformation (d), nm Modulus from JKR model ( Sample) MP Bulk modulus3 of SEBS/clay nanocomposite, MPa... 

To circumvent the limitations described above, Plummer et al. have used a different method, suitable for observation of plastic zones in bulk samples [30]. They embedded a DCB sample in a low viscosity epoxy resin with the razor blade in place. The crack tip was therefore maintained under stress while the resin was left to cure at room temperature. The sample was then trimmed for thin sectioning, stained by immersion in a Ru04 solution, and microtomed in thin sections in the region of the plastic zone for observation by TEM. While this method gave particularly good results on ductile semicrystalline systems where a deformed thin film would not have been representative of the plastic deformation mechanisms taking place in bulk samples, it should in principle be applicable fairly generally. 

As true affine deformation assumption proposed by Kuhn and Grun for crosslinked elastomershere quoted after , says that the effect of the deformation is to change the components of the vector length of each polymer chain in the same ratio as the corresponding dimensions of the bulk sample the Kratky scheme is termed pseudoaffine. In view of the above our treatment is affine deformation scheme for the vector field description of molecular orientation. 

The overall microstructure of the bulk sample following a full creep run at 1620 K was found to have changed little from that observed following the 4-h anneal. No cavitation was observed, In order to determine the reason for the break observed in the creep curve at 1620 K, a careful TEM analysis was conducted on samples taken both before the break in cuve and after, and these were compared to a sample taken from the lower temperature creep run, 1470 K, where no break was observed. The microstructure representing the material before the break was obtained by allowing the material to deform at stresses of 50,100, and 150 MPa with a final true strain of -0.9%. The sample used to represent the microstructure after the break was deformed at stresses of 50,100,150,200,250,300 and 350 MPa with a final true strain of -1.5%. High resolution electron microscopy was used to examine the grain boundaries in each sample. 

Fig. 2. Survey of (electron and scanning force) microscopic methods for investigating micromechanical processes in polymers, a indicates the applied tension stress and the arrows indicate area and direction of investigation in the microscope (see text for full details), (a) fracture surfaces— tension test, impact test, broken pieces (b) surfaces of deformed (loaded) bulk samples (c) in situ deformation of thin samples.

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