Microscopic techniques, micromechanical

To study the influence of these structural parameters on the micromechanical mechanisms of toughening, several techniques of electron microscopy were used. Electron microscopic techniques allow investigations not only of detailed morphology but also of the micromechanical processes of deformation and fracture (3, 9-11). 

Figure 3. Electron microscopic techniques used to study micromechanical processes in polymers (a) investigation of fracture surfaces by SEM (b) investigation by TEM of ultrathin sections prepared from deformed and selectively stained bulk material and (c) deformation of samples of different thicknesses (bulk, semithin, and ultrathin)9 using special tensile stages with SEM, HVEM, and TEM. The technique in (c) shows the possibility of conducting in situ deformation tests in the electron microscope.

Recently, several different techniques to study micromechanical properties have been applied. Besides spectroscopic and scattering techniques, the microscopic techniques of electron microscopy and atomic force microscopy are particularly useful for direct determination of micromechanical properties in polymers (2-7). A brief overview about successfully applicable techniques is given in this article. Using these techniques, micromechanical properties of different polymers that have been studied are also reviewed. 

Micromechanical theories of deformation must be based on physical evidence of shock-induced deformation mechanisms. One of the chapters in this book deals with the difficult problem of recovering specimens from shocked materials to perform material properties studies. At present, shock-recovery methods provide the only proven teclfniques for post-shock examination of deformation mechanisms. The recovery techniques are yielding important information about microscopic deformations that occur on the short time scales (typically 10 -10 s) of the compression process. 

Based on a local dissolution law, the micromechanical approach is able to discuss the effects of the local heterogeneity of the mechanical affinity on the dissolution process and to predict the evolution of the pore space morphology. Whenever it is possible to describe the latter by a scalar parameter , (22) yields its evolution (t) which captures the chemomechanical coupling in so far as it controls the evolution of the poroelastic coefficients in (13). Nevertheless, the implementation of this modelling requires to be able to determine the microscopic strain state along the fluid-solid interface by appropriate micromechanical techniques. 

Fundamental investigations into the mechanical properties of RP constituents and into the gross mechanical properties of RPs have been termed micromechanics to indicate that the part of the RP under investigation is usually only a microscopically small part of the total RP. One of the principal goals of micro mechanics research is to develop analytical techniques for predicting elastic constants, stress-strain... 

Because of its simplicity, microindentation has become a common technique to measure the micromechanical behavior of polymers and its relation with microstructure. Microhardness, H, is obtained by dividing the peak contact load by the projected area of impression, which is measured under a light microscope (imaging method). Typical loads of 10 mN, when applied to the surface... 

In the field of composite materials there are many specimens or construction elements that are large in size compared with the length of structural elements (grains, fibres, conclusions, voids etc.). Therfore, following a purely phenomenological concept, the micromechanical structure can be neglected in a first approach. The well-known homogenization techniques will be a useful tool to take into account some deterministic or stochastic ideas of the mesoscopic and microscopic levels. 

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