Filament reinforced composite materials have high strength, high stiffness and low density. Tubes fabricated from process described have advantages of having smooth inner and outer surfaces, lower dimensional variation than tolerances set for extruded aluminum tubing and void free composites

Davis, J. G., Jr.

English

NASA Technical Reports Server

Finished Tube 
July 1972	 B72-10340 
NASA TECH BRIEF 
Langley Research Center	
-4r 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Fabrication of Uniaxial Filament-Reinforced Epoxy 
Tubes for Structural Application 
Teflon	 Heat 
Rod	 Shrinkable 
Teflon Sleeve 
The high strength, high stiffness, and low density of 
filament-reinforced composite materials have stimulated 
considerable interest in their potential application to 
aerospace structures. During the course of research on 
composite materials, a unique process was developed for 
fabricating uniaxial filament-reinforced epoxy tubes of 
suitable quality for structural application. 
The diagram illustrates the process. Strips of pre-
impregnated tape (a single ply of uniaxial filaments, 
rovings, or yarns embedded in a viscous epoxy resin) are 
cut and aligned on a Teflon rod which serves as a re-
movable mandrel. Care is taken to align the filaments
parallel to the longitudinal axis of the mandrel. The 
width of each strip is equal to the circumference of the 
tube, and plies are added until the desired wall thick-
ness is obtained. In the second step, a heat-shrinkable 
Teflon sleeve is slipped over the mandrel and tape. The 
diameter of the Teflon sleeve should be just large enough 
to permit the sleeve to be slipped over the tape without 
damaging the outer ply. The third step consists of heat-
ing the Teflon sleeve with air from an electric heat gun. 
Complete shrinkage occurs at exposure to temperatures 
of 177°C (350°F) with partial shrinkage occuring at 
temperatures as low as 93°C (2000F). As the sleeve 
(continued overleaf) 
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shrinks tightly on the composite material, air entrapped 
between the plies is squeezed out the end of the sleeve. 
In addition, the Teflon sleeve serves as a mold which 
forms a smooth outer surface on the filament-reinforced 
tube. In step four, the entire assembly is inserted in a 
close-fitting steel tube which prevents the mandrel from 
sagging while the epoxy resin is cured at an elevated 
temperature. The steel tube and assembly are heated in a 
circulating-air oven for the final epoxy cure. In step five, 
the assembly is removed from the steel tube, the Teflon 
sleeve is peeled from the outer surface of the tube, and 
the Teflon mandrel extracted. 
Tubes fabricated by this process have several advan-
tages. They have very smooth inner and outer surfaces 
which are the result of molding against Teflon surfaces. 
The dimensional variation is less than the tolerances set 
for extruded aluminum tubing. The results of void 
content determinations indicate that composites are 
essentially void-free. Compressive and column buckling 
tests show that boron-epoxy tubes fabricated using the 
process described herein weigh approximately one-half 
as much as aluminum tubes designed for the same 
loadings.
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Langley Research Center 
Langley Station Mail Stop 139A 
Hampton, Virginia 23365 
Reference: TSP72-1 0340 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Langley Research Center 
Langley Station 
Hampton, Virginia 23365
Source: J. G. Davis, Jr. 
Langley Research Center

(LAR-1 0203) 
B72-10340	 Category 04
	
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Fabrication of uniaxial filament-reinforced epoxy tubes for structural application

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