Static elastic energy

Elastic deformations within the solid can also produce static friction between surfaces that would not otherwise interlock. Figure lb illustrates a system where the spacing between peaks on the top surface is stretched to conform to the bottom surface. This could occur at the scale of either macroscopic asperities [21] (Section Vll) or individual surface atoms (Section 111). The elastic energy required to displace each peak into an opposing valley must be compensated by the gain in potential energy due to interactions between the surfaces. This... 

For the monomer polymerization at room temperature, the adhesive was augmented with a redox system of 3% BP and 0.75% DMA. To study, explain, and predict the development of the elastic failure of the polymer in the adhesive interlayer, an improved method of investigating adhesive layer crack resistance with modeling of the formation and growth of a crack at the adhesive-honded joint loading was used [119]. Five adhesive-bonded joints with the adhesive mixture compositions shown in Table 3.1 were subjected to static tests for crack resistance at room temperature. The characteristics of the static crack resistance of the adhesive-bonded joint Kic is the coefficient of the stresses intensity Gic is the intensity of the elastic energy release ic is the opening in the crack tip) were determined at the moment of onset of the crack in double-cantilever specimens DCB (Fig. 3.5). The specimen cantilevers were made of PMMA of TOCH type. 

W stat= /o2/2E = (rngf-lllES is the elastic energy in the case when the same load is applied under static conditions... 

When a polyelectrolyte gel is deformed by an external force, not only the elastic energy of the polymer chains but also its static energy changes considerably. Hence, the mechanical properties of a gel (e.g., W)ung s modulus) receive a significant contribution from static interaction as well as entropic elasticity. 

In the region of phase separation, the lest or uset can be shifted imder shear flow. Early observations showed phase separation of homogeneous solutions imder shear and a hypothesis was presented that predicted an increase in the free energy of mixing due to elastic energy increase [238]. In many polymer-polymer blends, miscibihty has been observed by shearing an initially (static) phase separated blend close to the lest. It was hypothesized by Wolf [239] that the application of shear to a phase separated blend reduces the particle size of the discontinuous phase to a point, where the particle dimensions approach the radius of gyration and thus an apparent miscible system. 

The energy criterion for fracture is simply an extension of Griffith s hypothesis which describes quasi-static crack propagation as the conversion of the work done, Wd, by the external force and the available elastic energy stored in the bulk of the specimen, U, into surface free energy, y. It may be written ... 

Stress-strain relationships for soil are difficult to model due to their complexity. In normal practice, response of soil consists of analyzing compression and shear stresses produced by the structure, applied as static loads. Change in soil strength with deformation is usually disregarded. Clay soils will exhibit some elastic response and are capable of absorbing blast-energy however, there may be insufficient test data to define this response quantitatively. Soil has a very low tensile capacity thus the stress-strain relationship is radically different in the tension region than in compression. 

The static tests considered in Chapter 8 treat the rubber as being essentially an elastic, or rather high elastic, material whereas it is in fact viscoelastic and, hence, its response to dynamic stressing is a combination of an elastic response and a viscous response and energy is lost in each cycle. This behaviour can be conveniently envisaged by a simple empirical model of a spring and dashpot in parallel (Voigt-Kelvin model). 

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