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• December 16, 2016 Create Date
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National Advisory Committee for Aeronautics, Technical Notes - A Study of Elastic and Plastic Stress Concentration Factors Due to Notches and Fillets in Flat Plates

Six large 2h8—T3 aluminum-alloy-sheet spectnens containing various
notches or fillets were tested in tension to determine their stress
concentration factors in both the elastic and plastic ranges.

The elastic stress concentration factors were found to be slightly
higher than those calculated by Neuber‘s method and those obtained
photoelastically by Frocht. The results showed further that the stress
concentration factor decreases as strains at the discontinuity enter
the plastic range.

A generalization of Stowell's relation for the plastic stress
concentration factor at a circular hole in an infinite plate was applied
to the specimen shapes tested and gave good agreement with test results.

Theoretical studies of stress concentrations around discontinuities
in flat plates have been limited because of .analytical difficulties to
certain geometric shapes (references 1 to 6) and, until recently, to
the realm of stresses in the elastic range. Experimental studies on
the subject are scarce, such investigations being limited by available
loading and strain measuring equipment (references 7 to 11). The present
investigation was undertaken to obtain experimentally stress concentration
data in both the elastic and plastic ranges for sheet specimens containing
a variety of notches and fillets.

A formula has been presented by Stowell (reference 12) for the
stress concentration factor in the plastic range for a circular hole in.
an infinite plate. When the formula is written in a generalized form it
appears to be applicable to the specimen shapes of this investigation
and to other configurations.

Since the maximum stress in a panel containing a stress concentration
occurs at a point and the stress distribution around the point follows 1
a gradient, it is essential for reliable measurements that the ratio
of notch dimensions to gage length of the strain gages be as large as
possible. Therefore, in order to obtain a high ratio and to be able
to use strain gages of-practical dimensions, the spechmens were made
148 by 112 inches.