Elastic modulus

About: Elastic modulus is a research topic. Over the lifetime, 33153 publications have been published within this topic receiving 810247 citations.

Entropic elastic processes in protein mechanisms. I. Elastic structure due to an inverse temperature transition and elasticity due to internal chain dynamics.

Abstract: Numerous physical characterizations clearly demonstrate that the polypentapeptide of elastin (Val1-Pro2-Gly3-Val4-Gly5)n in water undergoes an inverse temperature transition. Increase in order occurs both intermolecularly and intramolecularly on raising the temperature from 20 to 40 degrees C. The physical characterizations used to demonstrate the inverse temperature transition include microscopy, light scattering, circular dichroism, the nuclear Overhauser effect, temperature dependence of composition, nuclear magnetic resonance (NMR) relaxation, dielectric relaxation, and temperature dependence of elastomer length. At fixed extension of the cross-linked polypentapeptide elastomer, the development of elastomeric force is seen to correlate with increase in intramolecular order, that is, with the inverse temperature transition. Reversible thermal denaturation of the ordered polypentapeptide is observed with composition and circular dichroism studies, and thermal denaturation of the crosslinked elastomer is also observed with loss of elastomeric force and elastic modulus. Thus, elastomeric force is lost when the polypeptide chains are randomized due to heating at high temperature. Clearly, elastomeric force is due to nonrandom polypeptide structure. In spite of this, elastomeric force is demonstrated to be dominantly entropic in origin. The source of the entropic elastomeric force is demonstrated to be the result of internal chain dynamics, and the mechanism is called the librational entropy mechanism of elasticity. There is significant application to the finding that elastomeric force develops due to an inverse temperature transition. By changing the hydrophobicity of the polypeptide, the temperature range for the inverse temperature transition can be changed in a predictable way, and the temperature range for the development of elastomeric force follows. Thus, elastomers have been prepared where the development of elastomeric force is shifted over a 40 degrees C temperature range from a midpoint temperature of 30 degrees C for the polypentapeptide to 10 degrees C by increasing hydrophobicity with addition of a single CH2 moiety per pentamer and to 50 degrees C by decreasing hydrophobicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Upper mantle seismic wave velocity' Effects of realistic partial melt geometries

Abstract: We investigate seismic wave velocity reduction resulting from the presence of partial melt in the upper mantle The amount of shear and bulk modulus reduction produced by the presence of a connected network of realistically shaped and naturally organized melt inclusions is found using finite element calculations The geometries of the inclusions are taken directly from laboratory experiments of mantle melting, with finite element meshes constructed to conform to these shapes The shear and bulk moduli of the composite material are found for both the unrelaxed (isolated inclusions) and relaxed (pressure equalized inclusions) cases by assigning appropriate material properties to the fluid Modulus reduction from deformation simulations of a solid containing realistically shaped and ellipse- shaped melt inclusions quantify the effect of melt pocket cuspateness and melt pocket organization on seismic velocity reduction The three-dimensional response is estimated from two-dimensional distributions of the melt phase by determining the mode II and mode III components of elastic modulus reduction separately and summing their effects In general, cuspate and naturally organized melt inclusions cause greater velocity reduction It is shown that V? and Vs reduction per percent partial melt are at least 36% and 79%, respectively Even higher values for velocity reduction are possible above 1% melt fraction if melt exists only in tubules below 1% melt fraction The lower, more conservative values of velocity reduction are 070% greater for Vp and 84% greater for Vs than the analytically determined values for ellipsoidal inclusions Somewhat greater effects are possible if nonrandom organization of melt occurs on scales greater than our model

Mechanical properties of carbon nanotube/polymer composites

Abstract: The remarkable mechanical properties of carbon nanotubes, such as high elastic modulus and tensile strength, make them the most ideal and promising reinforcements in substantially enhancing the mechanical properties of resulting polymer/carbon nanotube composites. It is acknowledged that the mechanical properties of the composites are significantly influenced by interfacial interactions between nanotubes and polymer matrices. The current challenge of the application of nanotubes in the composites is hence to determine the mechanical properties of the interfacial region, which is critical for improving and manufacturing the nanocomposites. In this work, a new method for evaluating the elastic properties of the interfacial region is developed by examining the fracture behavior of carbon nanotube reinforced poly (methyl methacrylate) (PMMA) matrix composites under tension using molecular dynamics simulations. The effects of the aspect ratio of carbon nanotube reinforcements on the elastic properties, i.e. Young's modulus and yield strength, of the interfacial region and the nanotube/polymer composites are investigated. The feasibility of a three-phase micromechanical model in predicting the elastic properties of the nanocomposites is also developed based on the understanding of the interfacial region.