Energy and Motion Control

Elastomers are used in the construction industry to control noise and shock and vibration and are used in many applications strictly to accommodate motion. In any application of elastomeric materials, the method of applying the elastomer can either help or hinder the desired end result. Basically, elastomers are used in situations of shear, compression, buckling, and bulk. The particular application will dictate which would be best. 

For economic reasons, designers typically reduce the mass of a structure, but doing so reduces the lateral reaction forces that the structure can withstand. This happens as the structure is allowed to deflect more or an energy-absorbing device is applied. An elastomer is ideal in such an environment because it will not corrode. Metal components can thus be totally encapsulated in an elastomer and then bonded to all-metal surfaces. The elastomer can be used in conditions of shear, compression, or buckling. In examining 

The calculations for kc and ks adjust for such design parameters as strain, bulk compression, and bending by the elastomer section, as developed over many years of sample testing. A way to forego the pain of getting there is to let k, =. 98 and kc = 1.0, using a. 69 MPa shear-modulus elastomer as follows  

For compression, the shape factor (SF), which is the projected load area of the product divided by the elastomer area that is free to move (known in the industry as the bulge area, or BA), is the major design parameter. For this example the shape factor is calculated thus  

Applying a 20 percent maximum compression strain to the product results in a maximum compression deflection of 102 cm (41 in.). This allows a maximum compression load of only 19 kg (42 lb.), hardly sufficient to support a building or a bridge. 

Elastomers are frequendy subjected to dynamic loads where heat energy and motion control systems are required. One of the serious dynamic loading problems frequendy encountered in machines, vehicles, moving belts, and other products is vibration-induced deflection. Such effects can be highly destructive, particularly if a product resonates at one of the driving vibration frequencies. 

One of the best ways to reduce and in many cases eliminate vibration problems is by the use of viscoelastic plastics. Some materials such as polyurethane plastics, silicone elastomers, flexible vinyl compounds of specific formulations, and a number of others have very large hysteresis effects (Chapter 3). By designing them into the structure it is possible to have the viscoelastic material absorb enough of the vibration inducing energy and convert it to heat so that the structure is highly damped and will not vibrate. 

Plastics exhibit a spectrum of response to stress and there are certain straining rates that the material will react to almost elastically. If this characteristic response corresponds to a frequency to which the structure is exposed the damping effect is minimal and the structure may be destroyed. In order to avoid the possibility of this occurring, it is desirable to have a curve of energy absorption vs. frequency for the material that will be used. 

Making one gear in a gear train or one link in a linear drive mechanism an energy absorber can use the same approach as the belt. The viscoelastic damping is a valuable tool for the designer to handle impulse loading that is undesirable and potentially destructive to the product. 

When products are subjected to dynamic loads where energy and motion controls are required use is made of thermoplastic elastomer (TPE) components. These products involve buildings (Fig. 2.11), bridges, highways, sporting goods, home appliances, automobiles, boats, aircraft, and spacecraft. 

Viscoelastic damping The same approach can be used in designing power transmitting units such as belts. In most applications it is desirable that the belts be elastic and stiff enough to minimize heat buildup and to minimize power loss in the belts. In the case of a driver which might be called noisy in that there are a lot of erratic pulse driven forces present, such as an impulse operated drive, it is desirable to remove this noise by damping out the impulse and get a smooth power curve. 

Tliere is another type of application where the damping effect of plastic structures can be used to advantage. It has a long although not obvious history. The early airplanes used doped fabric as the covering for wings and other aerodynamic surfaces. The dope was cellulose nitrate and later cellulose acetate that is a damping type of plastic. Conse- 

The age-old problem of predicting what will happen to any material after it is subjected to service also exists with plastics. Different data on plastics are available, but typical of so-called progress, there is never sufficient or adequate useful information to predict the service life of products being designed. It is suggested that rather than assume that a lack of data exists, one should determine what is logically available and apply it most efficiently. A potential example of improper design with plastics concerns toys. 

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Bucksbee, J. H., The Use of Bonded Elastomers for Energy and Motion Control in Construction, Lord Corp., 1988. 

CFD may be loosely thought of as computational methods applied to the study of quantities that flow. This would include both methods that solve differential equations and finite automata methods that simulate the motion of fluid particles. We shall include both of these in our discussions of the applications of CFD to packed-tube simulation in Sections III and IV. For our purposes in the present section, we consider CFD to imply the numerical solution of the Navier-Stokes momentum equations and the energy and species balances. The differential forms of these balances are solved over a large number of control volumes. These small control volumes when properly combined form the entire flow geometry. The size and number of control volumes (mesh density) are user determined and together with the chosen discretization will influence the accuracy of the solutions. After boundary conditions have been implemented, the flow and energy balances are solved numerically an iteration process decreases the error in the solution until a satisfactory result has been reached. 

Strong interactions are observed between the reacting solute and the medium in charge transfer reactions in polar solvents in such a case, the solvent effects cannot be reduced to a simple modification of the adiabatic potential controlling the reactions, since the solvent nuclear motions may become decisive in the vicinity of the saddle point of the free energy surface (FES) controlling the reaction. Also, an explicit treatment of the medium coordinates may be required to evaluate the rate constant preexponential factor. 

The molecular dynamics unit provides a good example with which to outline the basic approach. One of the most powerful applications of modem computational methods arises from their usefulness in visualizing dynamic molecular processes. Small molecules, solutions, and, more importantly, macromolecules are not static entities. A protein crystal structure or a model of a DNA helix actually provides relatively little information and insight into function as function is an intrinsically dynamic property. In this unit students are led through the basics of a molecular dynamics calculation, the implementation of methods integrating Newton s equations, the visualization of atomic motion controlled by potential energy functions or molecular force fields and onto the modeling and visualization of more complex systems. 

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