112 H. LeKuch et al. Fig. 11.1 901D LLC isolated rack and display console Fig. 11.2 Examples of equipment mounted to the test deck on the rack. Input is measured on the deck near the fixture. Velocity and displacement-time are calculated by integration of the acceleration time history. Physical measurements of the deflection of the isolators and/or relative movement of the rack are often made using clay cones, or equivalent, that ‘squash’ in shock. 11.2 Seamount Isolators Identified by its unique tall arch shape, Seamounts exhibit large deflection capabilities in all directions [2, 3]. The isolators are molded at Shock Tech’s facilities in Monsey, NY. Repeated load cycling tests have verified the mount’s durability and accurate shock control. The proprietary elastomer compound used in the mount is a compressible, moderately well damped neoprene having a predictable rate of strain energy dissipation and nominal temperature variation [4]. Three mounts are shown in Fig. 11.3. Dimensions of each are 7 inches high, 8 inches wide and 4.5 inches deep. A large range of stiffness can be achieved in each direction by modifying the configuration and contour of the arch. To a vertical shock, energy control is mainly accomplished by buckling of the mount in compression and extension in tension. In the lateral directions, the mount undergoes off-axis deformation of its arch shape and progressive shear of the elastomer material. Tension, shear and roll exhibit nearly linear stiffness. Damping is strain dependent but usually accounted for as a velocity dependent force in shock calculations. Dynamic stiffness is greater than static stiffness by a measured factor. There are several families of Seamounts including thin wall and thin wall versions—Fig. 11.4. The half-arch mount is used with light loads and in 901D internally isolated racks. As noted, shock attenuation effectiveness of the isolator is a function of the rate of energy absorption and dissipation in elastic deformation of isolator shape and material. By modifying these factors, the stiffness and hysteresis curves can be shifted and/or modified for more energy capacity and load carrying capability in limited space. The stiffness rate is strongly influenced by the transition from bearing on the column-like section to ‘ovalizing’ of the arch. There is also a close relationship of the durometer of the elastomer compound and mount stiffness. The Seamount is modular; multiple isolators
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