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National Advisory Committee for Aeronautics, Technical Notes - Effect of Variation in Rivet Diameter and Pitch on the Average Stress at Maximum Load for 24S-T3 and 75S-T6 Aluminum Alloy, Flat, Z-Stiffened Panels that Fail by Local Instability

A study is made of the effect of variation in diameter and pitch of
Al7S—Th aluminum—alloy flat—head rivets on the average stress at mathmn
load for 2hS-T3 and 7SS~T6 aluminumralloy, flat, Z—stiffened panels that
fail by local instability. A curve is presented for determining the
diameter and pitch required to insure the development of a given average
stress for local instability.

An extensive investigation of the effect of variation in rivet
diameter and pitch on the average stress at maximum load for longitudi—
nally stiffened compression panels is being conducted in the Langley
Structures Research Laboratory of the National Advisory Committee for
Aeronautics. So far this investigation has consisted primarily of the
collection of experimental data to use as a guide for the establishment-
of methods for taking into account the effect of riveting on panel
strength.

The data reported (references 1 to 5) have been concerned with
2hS-T3 aluminum—alloy panels, particularly those having longitudinal,
formed, Z-section stiffeners attached with AIYS—Th flat—head rivets. The
phase of the investigation reported herein is a generalization and exten—
sion of the previous work, with the primary purpose of making the results
applicable to 7SS—T6 material.

As a first step in the generalization of the results obtained in
references 1 to S for ZhS—TB panels, a "potential strength" or maximum
attainable strength was defined as the highest average stress at maxi—
mum load arpot that can be obtained for a given panel by varying rivet

diameter and pitch to find the optimum. Curves giving the stresses for
such ideally riveted panels were then prepared from the data of refer-
ences 2, h, 5, and 6 in which just such a variation in rivet diameter
and pitch was made. The data of these papers were analyzed and the
curves derived from them were faired and cross—plotted in order to

make them as nearly representative as possible of the potential
strengths of the panels considered — namely, short, 2hS—T3 aluminumr
alloy (ocy.z h3.9 ksi), flat panels with longitudinal, formed, Z—section
stiffeners attached to the sheet with AlYS—Th flat—head rivets. The
resulting curves of arpot plotted against the ratio of stiffener
spacing to skin thickness bS/ts are given in figure 1.