The dynamic response of a weapon`s internal components to a high speed impact Page: 4 of 10

                                
device (ESD).

There are 15 major structural components in the finite element model. Table 1 lists each
component, its material, and its material model used in the finite element calculations. The
listing of a pseudo-material indicates that the density of the material was modified to obtain
the correct weight since the geometry of the component may have been slightly modified. The
only structure modelled as a rigid body was the nuclear explosives package (NEP).
As mentioned above, the finite element calculations were performed using PRONTO3D. The
capabilities of PRONTO3D used to perform these simulations were element death, rigid body
dynamics, point masses and inertias, and contact algorithms. The element death capability
was used to model the tearing, perforation, and erosion of a material. Death limits are a user-
defined criterion that enables PRONTO3D to remove an element once a predefined threshold
is exceeded. These values include effective plastic strain, von Mises stress and many others.
In each of the five accident scenarios, the death option was applied to the heat shield, the
substrate, the FSA bolts, and the FSA container and baseplate. The rigid body option was used
to model the NEP, and a point mass and point inertia were used to complete the NEP's mass
properties since the exact geometry was not modelled.
2.2 Assumptions and Approximations
One major assumption made when modelling the weapon is that a vertical plane of symmetry
exists along the axis of the weapon (see Figure 1). The FSA components were slightly
Table 1:  Major structural components, their materials, and material model.
Structural Component          Material         Material Model
1      Substrate                   Aluminum 7049       Elastic-Plastic
2      Forward Support             Titanium            Elastic-Plastic
3      FSA Baseplate               Pseudo-Material     Elastic-Plastic
4      Fireset                     Pseudo-Material     Elastic
5      Trigger                     Pseudo-Material     Elastic
6      FSA Internal Barrier        304L Stainless Steel Elastic-Plastic
7      Switch                      Pseudo-Material     Elastic
8      ESD                         Pseudo-Material     Elastic
9      FSA Container               Pseudo-Material     Elastic-Plastic
10     Modified NEP                 Pseudo-Material    Rigid
11     Heat Shield                  Carbon Phenolic    Elastic-Plastic
12     Shipping Supports            304L Stainless Steel Elastic
13     Foam                         15 lb/in3          Orthotropic Crush
14     Rail/Flat PLate              Mild Steel         Elastic
15     Bolts                        AMS 5732           Elastic-Plastic

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