Influence of mechanical strain

In this context, some experimental results relevant to these open questions of enzymatic degradation will be presented and will be discussed from the viewpoint of cellulose chemistry, together with a summary of our recent work on thermohydrolysis and acid hydrolysis of cellulose, performed in connection with research on cellulose powder manufacture (7). After a short survey of the experimental techniques applied, this contribution will be centered on three problems (1) the interaction of chain degradation and cross-linking in thermal and thermo-hydrolytic treatments of cellulose, (2) the influence of mechanical strain... 

The influence of mechanical strain and structural stress on the rate of weight loss and the decrease in DP in acid hydrolysis is in agreement with some considerations of Elema (17), who discussed the role of structural stresses in connection with weak links in the cellulose chain. It may be mentioned here, however, that our results on heterogeneous acid hydrolysis did not yield further evidence of these weak links. ... 

Y.F. Li, G.C. Farrington, C. Laird, Cyclic response-electrochemical interaction in mono- and polycrystalline AISI 316L stainless steel in sulfuric acid solution—I. The influence of mechanical strain on the transient dissolution behavior during corrosion fatigue, Acta MetaU. 41 (1993) 693—708. 

The asymmetric shape of the main band results from a third, intermediate band. However, its exact position could not be determined. The positions of the bands and their intensities indicate that the main band results from an electronic excitation of the amide ion, whereas the shoulder originates from a simultaneous excitation of a stretching vibration. The deduced intermediate band probably results from the simultaneous excitation of the deformational vibration of amide [36]. The influence of mechanical strain and exposure to an external electric field on the intensities of the UV bands of amide ions in crystalline alkali halides at helium temperature were also investigated. The amide ion is optically anisotropic light is absorbed more strongly, when its vector is perpendicular to the plane of the ion than when the vector is in the plane of the ion [15, 16]. The reestablishment of the amide equilibrium orientation after switching off the electric field was studied by electro-birefringence [16]. 

Influence of mechanical strain on chemical reactions in polymer... 

Table VII. Influence of Disintegration and of Mechanical Strain on Acid and Enzymatic Hydrolysis of a Machine-Dried Spruce Sulphite Dissolving Pulp...

Burke EM, Human JD, Weimer JJ, Cheney AB, Rigsbee JM, Lucas LC (2001) Influence of coating strain on calcium phosphate thin-lllm dissolution. J Biomed Mater Res 57 41-47 Burr DB, Mori S, Boyd RD, Sun TC, Blaha JD, Lane L, Parr J (1993) Histomorphometric assessment of the mechanisms for rapid ingrowth of bone to HA/TCP coated implants. J Biomed Mater Res 27 ... 

Associative nucleophilic substitution at phosphorus contained in a six-membered ring is not a rapid process relative to the analogous reaction of acyclic compounds. Whereas associative reactions of five-mem bered sp>ecies are dominated by the influence of special strain effects, the same is not true for six-membered species. One must therefore bear in mind that other competitive processes may become significant in the reaction of six-membered ring phosphorus compounds with nucleophiles. For example, it has been suggested that the cAMP derivative [92] is hydrolysed by a dissociative Sf l mechanism (Scheme 32) (Bottka and Tomasz, 1985). 

FIGURE 8.18 Influence of pre-strain on the dynamic Young s modulus at standard conditions (65% RH, 21 °C). (From Meredith R., Mechanical Properties of Textile Fibers, Inter-science Publishers, New York, 1956.)... 

S. P. Timoshenko and J. N. Goodier, Theory of Elasticity, (McGraw Hill, New York 1970). V. D. Weyl, Influence of Internal Strains on Texture and Mechanical Strength of Porcelains, (in German), Ber. Deut. Keram. Ges., 36, 319 324 (1959). 

Ligaments and tendons operate in the presence of various types and levels of mechanical strains that are expected to influence the behavior of cells residing in these tissues. Mesenchymal stem cells (MSCs) have been shown to preferentially differentiate into ligament fibroblasts in the presence of mechanical forces when cultured in bioreactors that generated mechanical strains that resemble the native ligament stretching conditions [87]. 

Ta bl e 1.12 The influence of mechanical load on the change in strain at break relative to the initial value in polyamide 610 under thermal-oxidative exposure [70]... 

Failures modes in adhesives joints, attending the locus of failure and the directional stability of crack propagation, have been considered. Special attention has been paid to the microscopical features left on the fractured surfaces. Influence of the strain rate and the loading mode on the joint has been discussed. Fatigue and creep failure mechanisms have been briefly introduced. 

Within the scope of this paper the influence of the strain rate and temperature on mechanical properties like the modulus of semi-crystalline materials in both static and dynamic load situations are investigated with regard to modelling the non-linear viscoelastic deformation behavior of polymers. 

In the intrinsic mechanical response of glassy polymers, two time dependencies need to be considered and we have already encountered both. The first is the rate dependence of the intrinsic properties. The influence of the strain rate on the intrinsic behavior of PC is presented in Figure 18 (left), and with increasing strain rate the yield stress increases, similarly to the observations in tensile testing (see Figure 4, left). In the post-yield region, the curves shift upward at higher strain rates by the same amount as the yield stress. 

Figure 20 Influence of mechanical rejuvenation on the failure behavior of PS. Left Engineering stress versus strain curves. Right Macroscopic failure modes of as-received and rejuvenated samples.

Thin-film XRD is important in many technological applications, because of its abilities to accurately determine strains and to uniquely identify the presence and composition of phases. In semiconduaor and optical materials applications, XRD is used to measure the strain state, orientation, and defects in epitaxial thin films, which affect the film s electronic and optical properties. For magnetic thin films, it is used to identify phases and to determine preferred orientations, since these can determine magnetic properties. In metallurgical applications, it is used to determine strains in surfiice layers and thin films, which influence their mechanical properties. For packaging materials, XRD can be used to investigate diffusion and phase formation at interfaces... 

These differences on the stress-strain behavior of P7MB and PDTMB show the marked influence of the mesomorphic state on the mechanical properties of a polymer. When increasing the drawing temperatures and simultaneously decreasing the strain rate, PDTMB exhibits a behavior nearly elastomeric with relatively low modulus and high draw ratios. On the contrary, P7MB displays the mechanical behavior typical of a semicrystalline polymer. 

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