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National Advisory Committee for Aeronautics, Technical Notes - Effect of Open Circular Holes on Tensile Strength and Elongation of Sheet Specimens of a Magnesium Alloy

The effect of open circular holes on the tensile strength and
elongation of sheet specimens of magnesium alloy.AM—C5ES in both the
annealed and the hard—rolled condition was investigated. Tests were
made to study the effect of variable ratio of hole diameter to total
specimen width and also the effect of spacing and arrangement of the
holes.

It was found that greater reductions in strength were exhibited
by the annealed material than by the hard—rolled material; conversely,
the hard—rolled material showed the greater reductions in elongation.
In general the results were similar to those of aluminum—base alloys
(NACA TN 1974) except that the l-inch—wide, single—hole specimen of the
annealed material had a reduction in strength of about 19 percent com-
pared with a maximum reduction of about ll percent for any of the
aluminum alloys tested.

In the design of aircraft assemblies of aluminum— and magnesiume
alloy sheet the effect of stress concentration at perforations such as
rivet and bolt holes becomes important. The lightweight design of air-
craft components demands small margins of safety to be used and this
in turn requires suitable allowance in design for any strength reduc-
tions resulting from stress concentrations. An investigation (refer—
ence l) of the type reported herein has been made on several aluminum
alloys in sheet form and this report is an extensibn of that work to
include a magnesium alloy.

The purpose of this investigation was to study the effect of open
circular holes on the tensile strength and elongation of sheet specimens
of magnesium alloy AM-C528 in both the annealed (AM- 0528- O) and the hard-
rolled (AM-052s-H) condition. Tests were made to study the effect of
variable ratio of hole diameter to total specimen width and also the
effect of spacing and arrangement of the holes. The evaluation of the
effect of open circular holes on specimens such as those tested in this
investigation will not be equivalent to that in the case of a riveted
or bolted joint but will nevertheless serve to indicate the necessary
precautions against such stress concentrations.