<DOC>
<DOCNO>
727
</DOCNO>
<TITLE>
a study of the acoustic fatigue characteristics of
some flat and curved aluminium panels exposed to random
and discrete noise .
</TITLE>
<AUTHOR>
hess,r.w., herr,r.w. and mayes,w.h.
</AUTHOR>
<BIBLIO>
nasa tn.d1.
</BIBLIO>
<TEXT>
  a study was made of the fatigue
life of simple 2024-t3 aluminumalloy
panels measuring 11 by 13
inches and exposed to both discretefrequency
noise from a siren and
random noise from an air jet .  noise
levels varied from approximately
panel variables included thickness,
edge conditions, curvature, and
static-pressure differential .
  no significant differences were noted
in the nature of failures
experienced for the two types of loadings .
at a given root-mean-square
stress level, the failure times were
generally shorter for the random
loading than for the discrete-frequency
loading .  these differences in
failure times were noted to be a function
of stress level, the larger
differences occurring at the lower stress levels .
  increases in time to failure were
obtained as a result of increased
panel thickness, increased panel curvature,
and particularly for increased
static-pressure differential across curved panels .
  for the discrete-type loading,
the location of weak points in these
simplified structural designs can be
satisfactorily accomplished but
quantitative predictions of fatigue
life are much more difficult .
</TEXT>
</DOC>
