Affiliations: Defence Research and Development Canada –
Suffield, Suffield, AB, Canada | Defence Research and Development Canada –
Atlantic, Dartmouth, NS, Canada | Director Maritime Ship Support, Ottawa, ON,
Canada | Amtech Aeronautical Ltd. Medicine Hat, AB,
Canada
Abstract: The damage sustained by rigidly-clamped square steel plates when
subjected to close-proximity underwater explosions has been investigated. The
test specimens consisted of plates 0.76 mm and 1.21 mm thick made of either
ASTM A1008 mild steel or 350 WT structural-grade steel with a low-temperature
notch-toughness requirement. The explosively-loaded area of the plates was
square, with dimensions of 254 mm X 254 mm. High-explosive charges from 1.1 g
to 50 g were used at different standoff distances to obtain different shock
strengths and bubble collapse intensities. Although the main impulsive load on
the plate was due to the shock impact, because the standoff distances were less
than twice the maximum free-field bubble radius, a strong interaction between
the detonation product bubble and the target plate caused a rapid water jet to
impinge on the plate, resulting in additional loading and damage. As a result,
four main regimes of loading and damage were identified: a) holing/petaling due
to shock loading, b) edge tearing due to shock loading only, c) edge tearing
due to the cumulative loading from shock and bubble collapse, and d) large
deformation due to shock and bubble collapse loading. The damage mechanisms and
dynamic response of the plates were measured using dynamic displacement
sensors, pressure gauges, and high-speed video. A fracture analysis was
performed on the damaged plates to analyze the mechanisms of failure. Finally,
finite-element analysis using a failure criterion based on normalized shear
stress and effective strain has been used to examine the failure limits.
