Quasi-static tearing tests of metal plating
Woertz, Jeffrey C. (Jeffrey Collin), 1969-
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Great effort is being focused on making the next generation of naval combatant ships more resistant to the effects of close-aboard explosions. The examination of the deformation modes in blast-loaded metal plating suggests that a physical model can be developed to simulate the force vs. displacement history produced by an impinging shock wave during the holing phase. Similar approaches have been successfully used to approximate damage due to grounding and ballistic penetrators. In this case, the deformation of the clamped plate is modeled in two stages: (1) dishing, which leads to disking and (2) radial crack propagation, which results in petalling. In the first stage, a thin geometrically-scaled (0.90 mm, 1.15 mm, and 1.40 mm thick by 300 mm square) mild steel sheets are dished inward using spherical indenters of radii 20 mm, 50 mm, and 75 mm. The sheets have an average tensile strength of 317 MPa and a Rockwell Superficial Hardness Number of 72 (H(N15T)72). This portion of the test approximates the initial material stretching done by a spherical wave at various standoff distances. The spherical indenter produces a circular hole, which simulates the disk of material normally ejected as a blast front penetrates a plate section. As the material reaches a critical necking thickness at the edges of the hole, radial cracks form creating petals. During the second stage, an oblique conical punch is used to simulate the expanding wave front, which drives open the petals, causing the cracks to propagate towards the plate's clamped boundaries. By measuring the resultant forces and minimizing the effects of friction, the total bending and membrane work can be reasonably estimated. Ultimately, the approximate blast damage for a given ship's hull may be related to a given charge size and standoff distance.
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