Stress relaxation, transition layer

Another view is the inhibition layer theory, which holds that the structure of the stress relaxation transition layer between the matrix and the packing is not a flexible deformation layer, but an interfacial layer with a modulus between that of the matrix and the packing. The treatment agent is a part of the interfacial area, and this part is a substance with a medium modulus that is between that of the high-modulus reinforcing material and the low-modulus matrix. It has the effect of transferring stress uniformly and reducing interfacial stress, so that it can enhance the performance of the composite materials. The inhibition layer theory is not widely accepted because it lacks the necessary experimental basis. ... 

That bonds are formed between particles is inferred by the fact that the gel layers are able to bear considerable stresses. These bonds are sensitive to the presence of stresses and allow stress relaxation to occur. The relation between stress relaxation and cracking on one hand and particle shape on the other hand is not known. The relative ease of preparing y-alumina membranes might be due to the relative ease of rearrangement of the particles and easy stress relaxation in plate-shaped boehmite particles and the isomorphous transitions to plate-shaped y-alumina at about 300°C, the transition also being accompanied by a relatively small volume change [2-4]. With spherical particles (titania, zirconia) stress relaxation might be more difficult. The easier formation of defect poor composites of alumina and titania (with spherical particles) supports the beneficial effect of plate-shaped particles. 

The transition layer theory holds that additional stress would be generated on the interface between the filler and the matrix during molding of composites because of different expansion coefficients of the filler and the matrix. In addition, under the action of external loading, the uneven distribution of stress in the composite material can produce a stress concentration phenomenon in some parts of the interface. Therefore, there is a transition layer in the interface area that plays an important role in stress relaxation. 

The solidihed layer yields and returns to the liquid phase if the shear stress excesses the critical value, which initiates the sliding. When the stress is relaxed as a result of slip, the solid phase resumes again. The periodic transition between the solid and liquid states has been interpreted in the literature as a major cause of the stick-slip motion in lubricated sliding. Understanding the stick-slip and static friction in terms of solid-liquid transitions in thin films makes a re-... 

The dynamic mechanical thermal analyzer (DMTA) is an important tool for studying the structure-property relationships in polymer nanocomposites. DMTA essentially probes the relaxations in polymers, thereby providing a method to understand the mechanical behavior and the molecular structure of these materials under various conditions of stress and temperature. The dynamics of polymer chain relaxation or molecular mobility of polymer main chains and side chains is one of the factors that determine the viscoelastic properties of polymeric macromolecules. The temperature dependence of molecular mobility is characterized by different transitions in which a certain mode of chain motion occurs. A reduction of the tan 8 peak height, a shift of the peak position to higher temperatures, an extra hump or peak in the tan 8 curve above the glass transition temperature (Tg), and a relatively high value of the storage modulus often are reported in support of the dispersion process of the layered silicate. 

The La-//ii transition may be considered a result of competition between the spontaneous tendency of the lipid layers to bend and the resulting hydrocarbon chain packing strain thus, membranes exist in a state of fmstrated curvature stress (17). Respectively, the La-Hn transition is believed to be driven by the relaxation of the curvature of the lipid monolayers toward their spontaneous curvature. Conversely to the Lp-Lc transition, the La-H II transition temperature decreases with the hydrocarbon chain length increase (Fig. 3a). At sufficiently long chains. 

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