Design and analysis of a high-performance shipping container for large payloads Page: 3 of 11
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The impact simulations involve modelling nonlinear phenomena such as large
deformations, nonlinear material response of metals and foams, and material self-contact.
In addition, the combination of thin shell-like structures and regions of solid material in
the H1636A necessitates use of both solid and shell type elements. The three-dimensional
transient solid dynamics code PRONTO was selected because it is well suited to handle
Modelling the Containment Vessel
One of the goals of this study was to predict CV integrity. The system will be considered
to have failed if the CV cracks, or if the tape joint fails, both of which imply a loss of
containment. As an approximation of the CV response, the axially oriented stiffeners
were not modelled. Instead, the stiffened region was thickened to provide equivalent
stiffness. Because of the high computational costs that would be required, detailed
modelling of the tape joint was not feasible for this type of study. As an approximation,
the tape joint region was modelled to provide stiffness equivalent to that of the combined
stiffness of the two layers of the actual joint.
Modelling of the Double-Walled Outer Drum of the Overpack
Upon impact of the system, the outer drum acts as a membrane, confining the foam as it
is crushed. The response of the foam, which accounts for 40 percent of the system mass,
and provides the vast majority of the energy-absorbing capability of the system, is
significantly different for confined and unconfined crush. Therefore the membrane
confinement provided by the drum greatly influences the overall response of the system.
In addition to providing membrane confinement, the drum can also undergo bending,
localized buckling and folding, and tearing.
Several factors affect the local buckling, bending, and membrane stiffnesses of the drum
wall. The local buckling stiffness and the bending stiffness of the drum are related to the
cube of the drum wall thickness, while the membrane stiffness of the drum is linearly
related to the drum thickness. In addition, the local buckling stiffness of the outer drum
in the finite element model is dependent on the size of the shell elements used to model
the outer drum walls, and the constraints on the elements (i.e., whether or not the shell
elements are attached to the solid elements used to model the foam). In the H1636A, the
foam is enclosed within the two concentric thin metal walls of the double-walled outer
drum and can move (in an accident situation) relative to the drum walls. Such a condition
is most closely approximated in a finite element model with a contact relation defined
between the outer surface of the foam and the surface of the drum walls, which allows the
drum walls to separate from the foam. In addition, if a sufficient number of elements are
used to model the drum walls, the buckling and folding behavior can be closely
approximated. With the further addition of elements, tearing can also be simulated.
However, this approach greatly increases the computational cost of the model. To capture
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York, A.R. II & Slavin, A.M. Design and analysis of a high-performance shipping container for large payloads, article, May 1, 1995; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc736215/m1/3/: accessed November 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.