Isotropic rib stiffened shell whose ribs intersect to form equilateral triangles has advantages of high twisting rigidity of construction and simplicity of triangular pattern

Meyer, R. R.

English

NASA Technical Reports Server

July 1972	 B72-10323 
NASA TECH BRIEF 
Marshall Space Flight Center 
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. 
Isogrid Structure 
The isogrid structure is a practical design of isogrid 
shells. It is essentially an isotropic rib-stiffened shell 
whose ribs intersect to form equilateral triangles. Though 
isogrid structures are of particular interest to the aero-
space industry, methods used in their analysis can be 
applied to numerous structural design problems. In this 
case, the analysis develops the principal bending stress 
relations and discusses buckling, thermal loading, and 
optimization of cylinders and spheres for the azi-
symmetric uniform-loading case. In addition, it includes 
a number of examples and experimental results. 
The advantages of the structure for stiffened non-
rectangular plates and plates supported or loaded locally 
are the high twisting rigidity of the construction, which 
acts to distribute the loading over a wide region, and the 
simplicity of the triangular pattern, which can accommo-
date non-rectangular boundaries. From the construc-
tional point of view, a weight advantage may be obtained 
by drilling holes at the centers of the grid points where 
fillet material tends to build up. These holes could serve 
as natural attachment points for stud inserts to secure 
material and transfer local loads to the plate. 
The analysis of the isogrid structure presents the 
results of an experiment used to determine the effect of 
the amount of reinforcement at the rib nodes on the 
overall bending stiffness. The specimen used was ma-
chined from a polycarbonate plastic plate, the elastic 
modulus being determined from tensile specimens taken 
from the same sheet of material. Brake forming methods
were also evaluated in a series of three point bending 
tests, the primary object being the determination of the 
effect of spacing the support points used in the three 
point forming. 
An experimental program, using the three-dimensional 
photoelastic, stress freezing technique, is presently being 
performed. to obtain detailed information on the stress 
distribution in isogrid stiffened shells. 
Notes: 
1. Information concerning this innovation may be of 
interest to industry due to its applicability in struc-
tural design and analysis, particularly in the area of 
pressure vessels. 
2. Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A & TS-TU 
Huntsville, Alabama 35812 
Reference: B72-10323 
Patent status: 
No patent action is contemplated by NASA. 
Source: R. R. Meyer of
McDonnell-Douglas Corp.

under contract to
Marshall Space Flight Center

(MFS .21 567) 
Category 06 
This documentwas prepared underthe 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 owned rights.
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Isogrid structure

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