Elasticity mechanical properties

To understand elastic mechanical properties, the discussion of the storage of energy of deformation provides a powerful approach. Dynamic mechanical measurements at higher strain on filled silicone elastomers show that the energy of deformation may be related to an entropic and an enthalpic part. The entropic part is mainly due to the restriction of the conformational space of the polymer chain by the presence of the solid silica particles. Whereas the enthalpic part of the energy of deformation is related to... 

A mechanism to explain what propels the membrane forward, called the elastic Brownian ratchet model, is based on the elastic mechanical property of an actin filament (Figure... 

The elastic mechanical properties of carbon fibre-reinforced laminates are highly dependent on the properties of the fibres and the matrix chosen and on the direction of loading relative to the fibre orientation. In a unidirectional laminate, with all fibres orientated in one direction and loaded parallel to the fibres, the properties are mainly dependent on those of the fibres and can be estimated by the rule of mixtures, taking into account the volume fractions of the fibres and the matrix. Equation [5.1] shows that E, the Young s modulus parallel to the fibres is simply given by... 

FIGURE 3 Influence of CNF on elastic mechanical properties of vulcanized EPDM. 

The technological importance of thin films in snch areas as semicondnctor devices and sensors has led to a demand for mechanical property infonnation for these systems. Measuring the elastic modnlns for thin films is mnch harder than the corresponding measurement for bnlk samples, since the results obtained by traditional indentation methods are strongly perturbed by the properties of the substrate material. Additionally, the behaviour of the film under conditions of low load, which is necessary for the measnrement of thin-film properties, is strongly inflnenced by surface forces [75]. Since the force microscope is both sensitive to surface forces and has extremely high depth resolntion, it shows considerable promise as a teclnhqne for the mechanical characterization of thin films. 

Polymers have found widespread applications because of their mechanical behaviour. They combine the mechanical properties of elastic solids and viscous fluids. Therefore, they are regarded as viscoelastic materials. Viscoelastic... 

In the last three chapters we have examined the mechanical properties of bulk polymers. Although the structure of individual molecules has not been our primary concern, we have sought to understand the influence of molecular properties on the mechanical behavior of polymeric materials. We have seen, for example, how the viscosity of a liquid polymer depends on the substituents along the chain backbone, how the elasticity depends on crosslinking, and how the crystallinity depends on the stereoregularity of the polymer. In the preceding chapters we took the existence of these polymers for granted and focused attention on their bulk behavior. In the next three chapters these priorities are reversed Our main concern is some of the reactions which produce polymers and the structures of the products formed. 

Much more information can be obtained by examining the mechanical properties of a viscoelastic material over an extensive temperature range. A convenient nondestmctive method is the measurement of torsional modulus. A number of instmments are available (13—18). More details on use and interpretation of these measurements may be found in references 8 and 19—25. An increase in modulus value means an increase in polymer hardness or stiffness. The various regions of elastic behavior are shown in Figure 1. Curve A of Figure 1 is that of a soft polymer, curve B of a hard polymer. To a close approximation both are transpositions of each other on the temperature scale. A copolymer curve would fall between those of the homopolymers, with the displacement depending on the amount of hard monomer in the copolymer (26—28). 

Biomechanical Machines. The mechanical properties of fibrous polypeptides could be put to use for the commercial production of fibers (qv) that are more elastic and resiUent than available synthetics (see Silk). The biochemical properties of proteins could also be harnessed for the conversion of mechanical energy to chemical energy (35). 

Nonoxide fibers, such as carbides, nitrides, and carbons, are produced by high temperature chemical processes that often result in fiber lengths shorter than those of oxide fibers. Mechanical properties such as high elastic modulus and tensile strength of these materials make them excellent as reinforcements for plastics, glass, metals, and ceramics. Because these products oxidize at high temperatures, they are primarily suited for use in vacuum or inert atmospheres, but may also be used for relatively short exposures in oxidizing atmospheres above 1000°C. 

A fully automated microscale indentor known as the Nano Indentor is available from Nano Instmments (257—259). Used with the Berkovich diamond indentor, this system has load and displacement resolutions of 0.3 N and 0.16 nm, respectively. Multiple indentations can be made on one specimen with spatial accuracy of better than 200 nm using a computer controlled sample manipulation table. This allows spatial mapping of mechanical properties. Hardness and elastic modulus are typically measured (259,260) but time-dependent phenomena such as creep and adhesive strength can also be monitored. 

AHoy base Rare-earth addition, % AST M Grade Condition Density, g/cc Ultimate tensile strength, MPa Typical mechanical properties, RT Yield Elongation, % strength, MPa Elastic modulus, GPa... 

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