Elastic resistive component

Chemical Composition The chemical composition of the materials of construction may affect the safety of a packaging component. New materials may result in new substances being extracted into the dosage form or a change in the amount of known extractables. The chemical composition may also affect the compatibility, functional characteristics, or protective properties of packaging components by changing rheological or other physical properties (e.g., elasticity, resistance to solvents, or gas permeability). 

When the material of solid surface is to a significant extent soluble in the wetting liquid, one also observes the hysteresis phenomena. In this case changes in the profile of the solid surface occur due to a contact with the liquid phase. To understand this, let us recall Fig. III-19, from which one can see that the vertical component of the oLG vector can not be fully balanced by the surface tensions of the two other surfaces. If a liquid is in contact with a solid phase that is insoluble, this vertical component, oLG, is balanced by the elastic resistance of the solid surface. The situation is entirely different when a drop of liquid (L,) is placed onto the surface of another liquid (L2) in this case all phases are highly mobile, and the state of equilibrium is described by the vector Neuman equation ... 

The biomechanical response of the body has three components, (1) inertial resistance by acceleration of body masses, (2) elastic resistance by compression of stiff structures and tissues, and (3) viscous resistance by rate-dependent properties of tissue. For low-impact speeds, the elastic stiffness protects from crush injuries whereas, for high rates of body deformation, the inertial and viscous properties determine the force developed and limit deformation. The risk of skeletal and internal organ injury relates to energy stored or absorbed by the elastic and viscous properties. The reaction load is related to these responses and inertial resistance of body masses, which combine to resist deformation and prevent injury. When tissues are deformed beyond their recoverable limit, injuries occur. 

Force and lengthening data were used to calculate the compliance of the system (Equation (24.3)), whose plot as a function of the applied voltage is reported in Figure 24.12. These results demonstrate that, as expected, the use of the actuators actually enables electrical modulations of the system compliance. This represents a proof of concept of the intended application, showing the benefit of equipping the splint with electrically controllable elastic components over purely passive elastic components. This permits the need for manual regulation, or even substitution of the resistive components, to vary the rehabilitation exercise to be avoided. 

The mechanical properties of the HA are similar to those of the most resistant components of the bone. HA has an elastic modulus of 40-100 GPa, dental enamel 74 GPa, the dentine 21 GPa, the compact bone 18-12 GPa. Nevertheless, dense bulk compact of HA has a mechanical resistance of the order of 100 MPa in front of to the 300 MPa of the human bone, diminishing drastically this resistance in the case of porous bulk compact. 

Other elastomeric-type fibers iaclude the biconstituents, which usually combine a polyamide or polyester with a segmented polyurethane-based fiber. These two constituents ate melt-extmded simultaneously through the same spinneret hole and may be arranged either side by side or ia an eccentric sheath—cote configuration. As these fibers ate drawn, a differential shrinkage of the two components develops to produce a hehcal fiber configuration with elastic properties. An appHed tensile force pulls out the helix and is resisted by the elastomeric component. Kanebo Ltd. has iatroduced a nylon—spandex sheath—cote biconstituent fiber for hosiery with the trade name Sidetia (6). 

The material in use as of the mid-1990s in these components is HDPE, a linear polymer which is tough, resiUent, ductile, wear resistant, and has low friction (see Olefin polymers, polyethylene). Polymers are prone to both creep and fatigue (stress) cracking. Moreover, HDPE has a modulus of elasticity that is only one-tenth that of the bone, thus it increases the level of stress transmitted to the cement, thereby increasing the potential for cement mantle failure. When the acetabular HDPE cup is backed by metal, it stiffens the HDPE cup. This results in function similar to that of natural subchondral bone. Metal backing has become standard on acetabular cups. 

One way of measuring thermal shoek resistanee is to drop a piece of the ceramic, heated to progressively higher temperatures, into cold water. The maximum temperature drop AT (in K) which it can survive is a measure of its thermal shock resistance. If its coefficient of expansion is a then the quenched surface layer suffers a shrinkage strain of a AT. But it is part of a much larger body which is still hot, and this constrains it to its original dimensions it then carries an elastic tensile stress EaAT. If this tensile stress exceeds that for tensile fracture, <7js, the surface of the component will crack and ultimately spall off. So the maximum temperature drop AT is given by... 

The analytic validity of an abstract parallel elastic component rests on an assumption. On the basis of its presumed separate physical basis, it is ordinarily taken that the resistance to stretch present at rest is still there during activation. In short, it is in parallel with the filaments which generate active force. This assumption is especially attractive since the actin-myosin system has no demonstrable resistance to stretch in skeletal muscle. However, one should keep in mind, for example, that in smooth muscle cells there is an intracellular filament system which runs in parallel with the actin-myosin system, the intermediate filament system composed of an entirely different set of proteins, (vimentin, desmin, etc.), whose mechanical properties are essentially unknown. Moreover, as already mentioned, different smooth muscles have different extracellular volumes and different kinds of filaments between the cells. 

Viscoelasticity illustrates materials that exhibit both viscous and elastic characteristics. Viscous materials tike honey resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain instantaneously when stretched and just as quickly return to their original state once the stress is removed. Viscoelastic materials have elements of both of these properties and, as such, exhibit time-dependent strain. Viscoelasticity is the result of the diffusion of atoms or molecules inside an amorphous material. Rubber is highly elastic, but yet a viscous material. This property can be defined by the term viscoelasticity. Viscoelasticity is a combination of two separate mechanisms occurring at the same time in mbber. A spring represents the elastic portion, and a dashpot represents the viscous component (Figure 28.7). 

For bending, assume 12 bars al the corner provide the tension component for resisting in-plane moment. An accurate assessment of the contributing bars would be difficult because of out-of-plane bending tension on bars away from the binding corners. Because of this approximation, the in-plane response will be limited to the elastic range. 

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