Simple structural elements are explored with configurations selected to best utilize composite materials. Combination of the biaxial properties of beryllium or an isotropic composite with the uniaxial properties of one directional filamentary reinforcement is studied

Dow, N. F.

Rosen, B. W.

English

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NASA TECH BRIEF 
May 1970	 Brief 70-10054 
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 Clearinghouse for Federal Scientific and Technical 
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be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Unidirectional Composite Stiffening 
The efficient application of composite materials to 
structures requires proper selection of the reinforce-
ment pattern and material as well as the overall struc-
tural arrangement. Guidelines for the optimum de-
sign of such composite structures have been generally 
lacking, nor are they of such a nature as to be obvious 
to the designer. The more recent trends towards effi-
cient material configurations have evolved from these 
conclusions: (1) for high load intensities where 
strength requirements are important, filamentary 
composites appear most attractive, particularly when 
used as unidirectionally reinforced elements; (2) for 
plate and shell structures which failed because of 
elastic instability, the most efficient laminate varied 
with structure and loading condition, but always - con-
tained multi-directional reinforcement configurations, 
(3) the high multi-directional stiffness-to-density 
ratio of beryllium makes it more efficient than com-
posites for many shell and plate structures—partic-
ularly if the load intensities encountered are low and 
if the stiffness requirements are important. 
The problem which arises from these conclusions is 
whether a combination of the biaxial properties of 
beryllium or an isotropic composite with the uniaxial 
properties of one-directional filamentary reinforce-
ment may possibly be the ideal configuration. Based 
upon the three conclusions, several simple structural 
elements were explored whose configurations were 
selected to best utilize composite materials. 
An aluminum-alloy circular tube-column with uni-
directionally reinforced composite stiffeners was 
selected as the first model. The structural efficiency 
curve for the column was evaluated by equating the 
stress levels for two failure modes; namely, local in-
stability and column instability. Results ot the calcu-
lations indicate that the addition of boron/epoxy
three-point reinforcements permit the tube-column 
to be made substantially lighter both at high and low 
loadings. In the elastic stress range, there is appar-
ently an optimum reinforcement ratio beyond which 
higher. percentages of reinforcement do not further 
increase the efficiency. At the high stresses, the 
great strength and stiffness of the unidirectional rein-
forced composite provide an increase in efficiency at 
reinforcement ratios greater than the elastic optimum 
ratio. 
A study was also made of long supported plates con-
sisting of layers of beryllium on both sides of a 
uniaxial composite layer. All of the plates had 0° 
reinforced boron/epoxy cores. An analysis of the 
results of this study indicate that 0° reinforced 
material (prestressed if possible) should be used as 
the strength element to provide the maximum possible 
elasticity. The material used to provide the plate 
buckling resistance, the face material in a sand-
wich, should be selected on the basis of the stresses 
to be carried out; beryllium should be used at low 
stresses and composite configurations approaching 
the 0° configuration should be used at the higher 
stresses. 
Note: 
The following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: NASA CR-665 18 (N68-13962), 
Design Criteria and Concepts for 
Fibrous Composite Structures 
(continued overleal) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately ownedrights.
https://ntrs.nasa.gov/search.jsp?R=19700000050 2020-03-17T00:03:13+00:00Z
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA Code 
GP, Washington, D.C. 20546. 
Source: B. Walter Rosen and Norris F. Dow of 
General Electric Company 
under contract to
NASA Headquarters 
(HQN- 10266)
.. 
Brief 70-10054	 Category 04


Unidirectional composite stiffening

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