The asymptotically singular stress state found at the tip of a rigid, squar
e inclusion embedded within a thin, linear elastic disk has been determined
for both uniform cooling and an externally applied pressure. Since these l
oadings are symmetric, the singular stress held is characterized by a singl
e stress intensity factor K-a, and the applicable K-a calibration relations
hip has been determined for both a fully bonded inclusion and an unbonded i
nclusion with frictionless sliding. A lack of interfacial bonding has a pro
found effect on inclusion-tip stress fields. When the inclusion is fully bo
nded, radial compression dominates in the region directly in front of the i
nclusion tip and there is negligible tensile hoop stress. When the inclusio
n is unbonded the radial stress at the inclusion tip is again compressive,
but now the hoop tensile stress is of equal magnitude. Consequently, an epo
xy disk containing an unbonded inclusion appears to be more likely to crack
when cooled than a disk containing a fully bonded inclusion. Plastic-plast
ic calculations show that when the inclusion is unbonded, encapsulant yield
ing has a significant effect on the inclusion-tip stress state. Yielding re
lieves stress parallel to the interface and greatly reduces the radial comp
ressive stress in front of the inclusion. As a result, the encapsulant is s
ubjected to a nearly uniaxial tensile stress at the inclusion tip. For a ty
pical high-strength epoxy, the calculated yield zone is embedded within the
region dominated by the elastic hoop stress singularity. A limited number
of tests have been carried out to determine if encapsulant cracking can be
induced by cooling a specimen fabricated by molding a square, steel insert
within a thin epoxy disk. Test results are in qualitative agreement with an
alysis. Cracks developed only in disks with mold-released inserts, and the
tendency for cracking increased with inclusion size. (C) 2001 Published by
Elsevier Science Ltd.