Contact:
David Hui
University of New Orleans
Dept. of Mechanical Engineering
New Orleans, LA 70148
Tel: (504) 280-6192
dhui@uno.edu

In future single stage reusable launch vehicles, light-weight composite materials will play a critical role. The structural systems of such vehicles must withstand rapid loading, vibration and high acceleration in severe environments while internally containing liquid oxygen and hydrogen under pressure at cryogenic temperatures. Currently, careful manufacturing conditions under controlled pressure and temperature in autoclaves provide satisfactory control of the development of microcracks during curing. Research is needed to characterize, monitor development and progression of microcracks under cryogenic temperature and service conditions and, finally, assess the influence of such fracture growths on the performance of such structures by fracture mechanics studies.

Image right: Polished edge of
[0/+45/90/-45]s LM21CO3
tape specimen cycled 800 times to 6000 microstrain
at –320°F

The primary concern for composites being used in the new generation of the re-entry vehicles is premature failure. Composites in space applications, whether used as rocket shell, satellite structures or cryogenic tanks, involve extreme temperatures and mechanical load variations not only on its surface, but also through the thickness. Thick-section composites typically fail at stresses and strains that are well below the expected failure limits. This early failure is often attributed to the existence of critically sized processing and/or material defects and interfacial problems in the interphase region between the matrix and the reinforcing phase.

The University of New Orleans' work in the area of "Cryogenic Microcracks Growth in Polymer Composites" focuses on the evaluation of materials suitable for use in tanks that will be manufactured and tested under thermo-mechanical loadings. The objective of this effort will be the determination of the existence and growth of microcracks. A predictive model will be developed which will establish a microcrack threshold for ultimate failure of these composite materials under various manufacturing situations.