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National Advisory Committee for Aeronautics, Technical Notes - Stress Analysis of Monocoque Fuselage Bulkheads by the Photoelastic Method

Since the monocoQue and the semimonocoque types of
construction have come into general use, many analytical
methods of stress analysis of stiffening rings and bulk— _
heads hate been publiShed. The simplest type, the circu—
lar ring of constant bending stiffness, offers some aha:—
lytical difficulty although many special cases 5f loading
for this type have been treated (references 1,2, and 3).
Certain general methods of analysis of noncircular, non~"' "
unifarm rings have been discussed (references 4 and 5).
but the use of these’methods involVes either extremely
complicated analysis or laborious graphical methods._ In
actual aircraft structures circular ring bulkheads of I
uniform section are usually not the most efficient design.

In many actual cases the analysis of the bulkheads is
further complicated by the attachment of floor beams, wing
2 , NACA Technical Note-239; 87.0

beams, and other members. These members, if tied into the
bulkhead, tend to increase the number of redundancies.

This increase affects the stress distribution in the bulk—
head and greatly.complicatee the problem of analysis. Al—
though seme'of the analytical methods discussed in the ref—
erences may be used in the general case, they are so labo—
rious and the possibilitv of error is so great that they
are impractical for use.in routine design.

Several years ago it was pointed out (reference 6)
that the photoelastic method could be used for the solution
of this bulkhead problem. The purpose of the investiga—
tion reported herein is to develop a technique for the pho—
to_olIastic solution of the problem. The present report
‘d_eals with the Construction of the models, the methods of
‘leading. certain short cuts in the ana.lysis of bending mo—
ment that seem to be justified, and the effect of certain
_ variables on the accuracy of the test method.