Recoverable strain energy

Ur recoverable strain energy per unit volume stored in the coating... 

Interfacial work of adhesion, y, can be measured by spontaneous peeling test using above equation. Spontaneous peeling thickness, tp, can be directly measured, and the recoverable strain energy, Ur, for an elastic material under a one-dimensional strain is. 

The effect of the fillers on the dynamic mechanical property of NR material was analysed by DMA in this work. The elastic modulus ( ") and the loss factor (tan 5) of the neat NR and NR composites were characterized as functions of temperature. Under an oscillating force, the resultant strain in specimen depends upon both elastic and viscous behaviour of materials. The storage modulus reflects the elastic modulus of the rubber materials which measures t recoverable strain energy in a deformed specimen, and the loss factor is related to the energy damped due to energy dissipation as heat. 

Figure 8.1 shows stress-strain curves of atactic polystyrene (PS) in compression at 295 K for two structures with different initial states well annealed, i.e., furnace cooled from Tg + 20 K to room temperature, and rapidly quenched into ice water (Hasan and Boyce 1993). In both cases there is a gradual transition to fully developed plasticity that is reached at the peak of a yield phenomenon which is more prominent in the annealed material. Both curves show several unloading histories, starting with one close to the upper yield peak. All unloading paths show prominent Bauschinger effects of plastic strain recovery that is independent of the pre-strain. These indicate the presence of strain-induced back stresses and some recoverable stored elastic strain energy. In both cases the flow stress moves toward a unique flow state attained at a strain of around 0.3. 

Strain energy n. The recoverable, elastic energy stored in a strained body and recovered quickly upon release of stress. Strain energy in a perfectly elastic material is equal to the area beneath the stress-strain curve up to the strain being considered. For Hooke s-law material, it is equal to 0.5-modulus-strain. This area, which appears to have the dimensions of stress (Pa), is actually the strain energy per unit volume (J/m ). 

A reduction of the required energy could be reached by the incorporation of conductive fillers such as heat conductive ceramics, carbon black and carbon nanotubes [103-105] as these materials allowed a better heat distribution between the heat source and the shape-memory devices. At the same time the incorporation of particles influenced the mechanical properties increased stiffness and recoverable strain levels could be reached by the incorporation of microscale particles [106, 107], while the usage of nanoscale particles enhanced stiffness and recoverable strain levels even more [108, 109]. When nanoscale particles are used to improve the photothermal effect and to enhance the mechanical properties, the molecular structure of the particles has to be considered. An inconsistent behavior in mechanical properties was observed by the reinforcement of polyesterurethanes with carbon nanotubes or carbon black or silicon carbide of similar size [3, 110]. While carbon black reinforced materials showed limited Ri around 25-30%, in carbon-nanotube reinforced polymers shape-recovery stresses increased and R s of almost 100% could be determined [110]. A synergism between the anisotropic carbon nanotubes and the crystallizing polyurethane switching segments was proposed as a possible... 

Several expressions for the function/have been proposed by different authors based on different assumptions about the driving force for the enhancement of nucleation. The suggested driving forces include shear rate, recoverable strain, the first normal stress difference, the change in free energy induced by flow, the effect of the combination of shear rate and strain, etc. 

Table 5.2 The flexural modulus, maximum stress, energy at break and hot recoverable strain of the CIM and SCORIM processed PLLA...

Run Elastic modulus (GPa) Maximun stress (MPa) Energy at break (J) Hot recoverable strain (%)... 

If a perfectly elastic specimen is subject to a dynamic strain then the work done will create strain energy which will be recovered during unloading. If the specimen is viscoelastic part of the energy will be transformed to heat which is not recoverable. During one full cycle the dissipated energy per unit volume (see Section 16.1.5.1) is... 

The various elastic and viscoelastic phenomena we discuss in this chapter will be developed in stages. We begin with the simplest the case of a sample that displays a purely elastic response when deformed by simple elongation. On the basis of Hooke s law, we expect that the force of deformation—the stress—and the distortion that results-the strain-will be directly proportional, at least for small deformations. In addition, the energy spent to produce the deformation is recoverable The material snaps back when the force is released. We are interested in the molecular origin of this property for polymeric materials but, before we can get to that, we need to define the variables more quantitatively. 

As reviewed thermoplastics (TPs) being viscoelastic materials respond to induced stress by two mechanisms viscous flow and elastic deformation. Viscous flow ultimately dissipates the applied mechanical energy as frictional heat and results in permanent material deformation. Elastic deformation stores the applied mechanical energy as completely recoverable material deformation. The extent to which one or the other of these mechanisms dominates the overall response of the material is determined by the temperature and by the duration and magnitude of the stress or strain. The higher the temperature, the most freedom of movement of the individual plastic molecules that comprise the... 

The strain response can be broken down into its elemental components of stress, which are in phase or out of phase, to derive the values for G and G". The storage modulus G is the ratio of the applied stress that is in phase with the strain (8 = 0°). This means that G is an expression of the magnitude of the energy stored in the material, recoverable per deformation cycle (68). The loss modulus G" is the ratio of the applied stress that is out of phase with the strain (8 = 90°), meaning that it is a measurement of the energy lost as viscous dissipation per deformation cycle (66-68). These two moduli are dependent on the phase angle of the system and are... 

FIGURE 17.5 Examples of stress a versus strain e for various materials that are first compressed, then decompressed (both at constant strain rate). Examples are meant to illustrate various kinds of behavior. The hatched areas indicate the deformation energy that is dissipated (not recoverable). The scales are generally different for the various frames. 

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