Dacron yarn, because of its superior resistance to thermal degradation when exposed to temperatures of 350-4-OO℉. for prolonged periods, has been suggested as a replacement for nylon in decelera¬tion parachutes. Dacron's strength retention after high temperature exposure is good, but a longitudinal shrinkage of the order of 20% takes place which presents problems of parachute component dimensional stability. Secondly, this 20% shrinkage is reflected in lower strength and energy to weight ratios, thus requiring proportionately heavier para¬chutes. Furthermore, the added elongation resulting from thermal shrink¬age is composed primarily of secondary creep or permanent set. Upon deployment of the parachute the possibility exists that fabric compon¬ents might deform at the time of stress application, but not recover upon stress removal unless and until the parachute or its components are again elevated to the 350℉ level.
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