Polyimide Foams for Aerospace Vehicles

Abstract

Due to a demand by the aerospace industry, NASA has begun developing the next generation of polyimide foams which could be utilized to reduce vehicle weight for the X-33 and Reusable Launch Vehicle (RLV) programmes. The activity at NASA Langley Research Center focuses on developing polyimide foam and foam structures which are made using monomeric solutions or salt solutions formed from the reaction of a dianhydride and diamine dissolved in a mixture of foaming agents and alkyl alcohols. This process can produce polyimide foams with varying properties from a large number of monomers and monomer blends. The specific densities of these foams can range from 0.008 g cc−1 to 0.32 g cc−1. Polyimide foams at densities of 0.032 g cc−1 and 0.08 g cc−1 were tested for a wide range of physical properties. The foams demonstrated excellent thermal stability at 321°C, a good thermal conductivity at 25°C of 0.03 W m−1 K−1, compressive strengths as high as 0.84 MPa at 10% deflection and a limiting oxygen index of 51%. Thermomechanical cyclic testing was also performed on these materials for 50 cycles at temperatures from −253°C to 204°C. The foams survived the cyclic testing without debonding or cracking. Thermal forming of the 0.032 g cc−1 foam was performed and a minimum radius curvature of 0.0711 m was achieved. The foams exhibited excellent properties overall and are shown to be viable for use as cryogenic insulation on the next generation RLV.

Thermal-Structural Optimization of Integrated Cryogenic Propellant Tank Concepts for a Reusable Launch Vehicle

“…Concept I had an Al 2219 metallic alloy tank wall with a hybrid CI bonded to the external surface with Lord 212™ adhesive. The hybrid CI was a layer of PDL-1034 CI and a layer of TEEK CI [3]. In an actual RLV CI, the foam of the hybrid CI would be inside a honeycomb core to increase the tension strength, bondline strength, and robustness of the CI.…”

Airframe Technology Development for Next Generation Launch Vehicles

“…Another objective of this task was to conduct metallurgical analysis and mechanical property tests to evaluate candidate metallic materials for reusable cryogenic propellant tank applications. [23][24] The task conducted an assessment and modification of the expendable Space Shuttle External Tank material Al-Li alloy 2195 for reusable application. In addition, mechanisms associated with delamination fracture in Al-Li alloys were investigated.…”

A Novel High Strain Rate Sensitive Rigid Polyurethane Resin Based Syntactic Foam

“…They have been widely used in several engineering applications due to their low moisture absorption, good thermal insulation, and excellent strength to weight ratio, vibration isolation, and low radar cross-section properties [3][4][5]. As a class of advanced lightweight composites, syntactic foams have been widely employed in more and more engineering applications, e.g., civil, automobile, aeronautical, marine equipment for deep sea operations [6], aircraft components, spacecraft solid rocket booster nose cones fillings, thermal insulation for deep sea pipelines [7][8][9], core materials of sandwiches [10,11], and structural components in aerospace industry [12].…”