An Elastomeric Ejection System

Abstract

The ability of elastomers to store large quantities of energy, which can subsequently be recovered very quickly, makes them attractive materials for propulsion devices. Recently the U.S. Navy has developed a torpedo ejection system based on an elastomeric mechanical capacitor. The criteria governing selection of a material for this application include high elastic energy, sufficient fatigue life, minimal creep, and resistance to deterioration by seawater. This paper describes various approaches to obtaining these material properties.

Aging of Natural Rubber in Air and Seawater

“…In Figure 6 is shown a double logarithmic plot of the fatigue life as a function of the ratio of the strain energy parameter, KW in Equation (2), for N = 1 (single extension to break) to that for fatigue testing at λ = 2.26; the exponent is 1.6. Note that if the changes in fatigue life were due only to changes in strain energy (i.e., the material per se were unchanged), the slope of Figure 6 would correspond to the β in Equation (2).…”

“…1 The development of the rubber compound has been described previously. 2 The disk has a diameter of more than 2 m and a thickness varying from 20 to 30 cm. It is to be inflated with seawater to 100% biaxial strain, and the performance must be maintained over roughly 2000 inflation cycles (ca.…”

Strains in an Inflated Rubber Sheet

“…5,6 The present study was motivated by the development of an inflated rubber disk as an ejection system for torpedoes on US Navy Virginia-class submarines. [7][8][9] During fatigue testing, the failure properties were found to be dependent on the size of the disk. Such a scaling effect indicates that biaxial deformation at the pole, which is the largest strain, does not necessarily govern the failure.…”

Unconventional Rubber Networks: Circumventing the Compromise Between Stiffness and Strength

“…It is well known that these properties pass through a maximum versus cross-link density, reflecting the countervailing effects on network integrity and embrittlement. This is illustrated Figure 1, 1 showing the tensile strength of four natural rubber compounds plotted versus the modulus at 100% extension. The practically useful range of cross-linking falls past the maximum, which means that in general, elastomer failure properties decrease with increasing modulus.…”