Micromechanical deformation

Another chapter deals with the physical mechanisms of deformation on a microscopic scale and the development of micromechanical theories to describe the continuum response of shocked materials. These methods have been an important part of the theoretical tools of shock compression for the past 25 years. Although it is extremely difficult to correlate atomistic behaviors to continuum response, considerable progress has been made in this area. The chapter on micromechanical deformation lays out the basic approaches of micromechanical theories and provides examples for several important problems. 

Since the thickness and properties of the interphase strongly influence the characteristics of composites and the strength of the interaction determines the dominating micromechanical deformation process, many attempts have been made to characterize them quantitatively. Many various techniques are used for this purpose, and it is impossible to give a detailed account here. As a consequence a general overview of the most often used techniques is given with a more detailed account of some specific methods which have increased importance. A more detailed description of the surface characterization techniques can be found in a recent monograph by Rothon [15],... 

Incorporation of hard particles into the polymer matrix creates stress concentration, which induces local micromechanical deformation processes. Occasionally these might be advantageous for increasing plastic deformation and impact resistance, but usually they cause deterioration in the properties of the composite. Encapsulation of the filler particles by an elastomer layer changes the stress distribution around the particles and modifies the local deformation processes. Encapsulation can take place spontaneously, it can be promoted by the use of functionalized elastomers (see Sect. 6.3) or the filler can be treated in advance. 

The micromechanical deformation behavior of SAN copolymers and rubber-reinforced SAN copolymers have been examined in both compression [102] and in tension [103,104]. Both modes are important, as the geometry of the part in a given application and the nature of the deformation can create either stress state. However, the tensile mode is often viewed as more critical since these materials are more brittle in tension. The tensile properties also depend on temperature as illustrated in Figure 13.6 for a typical SAN copolymer [27]. This resin transforms from a brittle to ductile material under a tensile load between 40 and 60 C. 

Kim, C. M., Michler, C. H., Rosch, J., and Miilhaupt, R. 1998. Micromechanical deformation processes in toughened PP/PA/SEBS-g-MA blends prepared by reactive processing. Acta Polymerica 49 88-95. 

Micromechanical deformation Raman spectorscopy Coir, celery fibers 53... 

As the performance of the composite is profoxmdly dominated by the micromechanical deformation process, its knowledge and control are critical for the improvement of composite properties. The effect of particle characteristics and interfacial adhesion on the micromechanical deformation processes in PP-wood composites was investigated by Renner et al. [7]. They proposed a failure map as well as the practical results and considered the influence of matrix characteristics on deformation and failure in PP-natural fiber composites in other research [24]. Hietala et al. [78] studied the effect of chemical pre-treatment and moisture content of wood chips on the wood particle aspect ratio during the processing and mechanical properties of WPCs. The use of pretreated wood chips enhanced the flexural properties of the wood chip-PP composites. Moreover, the use of undried wood chips compared to dried one can improve and reduce the flexural strength and flexural modulus, respectively. On the other hand, they concluded that the use of pretreated and undried wood chips lead to the highest aspect ratio after compounding. The effect of composition and the incorporation... 

Pioneering works on the micromechanical deformation mechanisms in block copolymers date back to the mid-eighties when cavitation mechanism in styrene-butadiene (SB) diblock copolymers containing PB cylinders in a PS matrix was proposed (52,53). Based mainly on tern investigations, a two-step craze growth mechanism was proposed ... 

The interpretation of the results of such experiments starts from a visual inspection of the 2-dimensional patterns. Before elongation, the patterns are isotropical rings. As a consequence of the formation of crazes which are due to the micromechanical deformation mechanism, the isotropicity of SAXS patterns is lost and intense streaks appear along certain directions. 

Attempts have been made to manufacture particles on the nanometer scale for applications such as controlled release and intravenous delivery systems. A comparison evaluating the processability and solid dosage performance of spray-dried nanoparticles and microparticles was conducted (41). In this study, nanoparticle suspensions were prepared by wet comminution in the presence of stabilizers, converted into dried particles using a spray-drying process and subsequently compressed. Compacts prepared from microparticles and nanoparticles were found to differ in their internal structure and micromechanical deformations. 

In the following Section 3.1.1, the morphology is discussed for block copolymer nanostructures via self-assembly (Section 3.1.1.1), in dependence on the chain architecture (Section 3.1.1.2), for blends of block copolymers with a constituent homopolymer (Section 3.1.1.3), for processing-induced influences (Section 3.1.1.4), and for block copolymer nanocomposites (Section 3.1.1.5). Section 3.1.2 gives an overview of nano- and micromechanical deformation effects. 

The micromechanical deformation processes that typically occur in fiber-reinforced polymers and, therefore, the mechanical properties depend on the orientation of the fibers with respect to the direction of applied load and on the degree of phase adhesion (interfacial strength) between fiber and matrix. Figure 7.2 illustrates the situation when the fibers are arranged parallel to the applied load direction. 

Figure 9.11 Schematics of micromechanical deformation mechanisms of polystyrene in dependence on sample thickness [19] ...

The structure of foams and filled polymers was eharacterized by means of MRI. It is also possible to observe the deformation behavior of the structure of foams and filled polymers in situ. The NMR images were analyzed by image processing. Average distances between particles were estimated by the spectrum of the autocorrelation function. The displacement field was calculated by the cross-correlation function. Information about particle distances and micromechanical deformation can be obtained by NMR imaging methods by combining autocorrelation and cross-correlation. 

Pukanszky, B., Vanes, M., Maurer, H.J., Voros, G.Y., Micromechanical deformations in particulate filled thermoplastics volume strain measurements, /. Mater. Sci. 29 (1994) 2350-2355. 

In spite of the imperfections of the adsorption interaction approach, can be used successfully for the characterization of matrix/filler interaction in particulate filled polymers. In these materials debonding is usually the dominating micromechanical deformation process. Stress analysis has shown that the debonding stress (/ ) depends on the reversible work of adhesion in the following way [8] ... 

Pukanszky, B. et al.. Micromechanical deformations in particulate filled thermoplastics— Volume strain measurements. Journal of Materials Science, 1994. 29(9) 2350-2358. 

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