STRESS INTENSITY FACTORS FOR CRACKS

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• STRESS INTENSITY FACTORS FOR CRACKS
• STARTING FROM RIVET HOLES

Stefan D Pastrama, Paulo M S T de
Castro University Politehnica of Bucharest,
Romania IDMEC, Universidade do Porto, Portugal
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• the work

combined compounding weight function
determination of the stress intensity factor in
finite width strips with cracked holes (two
symmetrically equal cracks, and a single
crack) compounding method is used for
calculating the stress intensity factor for
remote uniform tension weight function method
is used in the case of point load applied on the
hole surface
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geometries and loading
2R/W 0.1, 0.16 and 0.2 a/R 1.01, 1.02, 1.04,
1.06, 1.08, 1.1, 1.15, 1.2, 1.25, 1.3, 1.4 and 1.5
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compounding
the structure containing n boundaries is
separated into ancillary configurations,
containing only one boundary which interacts
with the crack, and having known solutions
Kn the stress intensity factor for the cracked
structure having the n-th boundary, K0 the
stress intensity factor in the absence of all
boundaries. Ki interaction term (usually
negligible)
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hole effect
the hole has a significant effect on the
displacement at the crack tip a crack having an
equivalent length 2a has to be introduced in the
ancillary configurations to replace the cracked
hole
the general non-dimensional equation of the
compounding method
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ancillary configurations
K0 , K1 and K2 taken from handbooks Ki
calculated using the stress concentration factor
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results
normalized stress intensity factors Q12 for two
cracks, 2R/W 0.1
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weight function method
K for a cracked structure in a certain loading
case
KIr(a) stress intensity factor for another
loading (the reference loading) uIr(x,a) half
of the crack face displacement field in the
reference case) h(x,a) the weight function
independent of the loading ?(x) crack line
stress in the un-cracked structure in the case
for which K is calculated
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application point load case
?(x) is determined using finite element analyses
and curve fitting techniques The reference stress
intensity factor is taken from the previous case
(uniform traction) The reference crack face
displacement is calculated using the approximate
expression of Petroski and Achenbach
?0 characteristic stress for the reference
case F(a/L) correction factor in the expression
of Kir G(a/L) function obtained from the
equation of self consistency K KIr
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results
normalized stress intensity factors Q12 for a
single crack, 2R/W 0.1 (a a R)
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conclusions
stress intensity factor for a finite width strip
with a central cracked hole was determined using
a combination of the compound and weight function
techniques two loading cases, (uniform remote
tensile stress and point load on the hole
surface) were considered results were compared
with those from the literature, where
available accuracy was excellent, proving that
these two methods can be utilized for calculating
the stress intensity factor for many other
loading cases, thus providing important
information for subsequent studies, especially
for fatigue loads.