PSI - Issue 14

Kartikeya et al. / Procedia Structural Integrity 14 (2019) 514–520 Kartikeya/ Structural Integrity Procedia 00 (2018) 000 – 000

517

4

(4)

Since experimental data was available for air-blast, it was modeled using CONWEP which required equivalent mass of TNT. Since plastic explosive was used in experiments, equivalent TNT mass was calculated using energy equivalence according to US Army Technical Manual. Simulation was run for 6 milliseconds using encastre boundary condition i.e. arresting both displacement and rotation in all three directions at the outer surface of plate. This boundary condition corresponds to situation when an armor steel plate is attached to undercarriage or side of anti-landmine vehicle. 3. Results and Discussions Mesh convergence parametric study is performed using continuum shell element with reduced integration (SC8R). Reduced integration reduces the computational time with a little loss of accuracy and is advisable to use in nonlinear analysis as it prevents over-stiff element stiffness matrix. Maximum central deflection of plate is taken as critical parameter for the convergence. Meshes from coarse to fine are considered as shown in Table 2. A node set is created to request field output of displacement of the center of plate. It can be seen that central displacement is increasing and tending to experimental results with mesh refinement.

Table 2. Convergence Study Mesh

Element Generated

Central Deflection (mm)

Coarse

1600 6400

15.56 17.30 17.75

Medium

Fine

80000

Mesh refinement resulted in convergence in central deflection and refined mesh is further used for study. Using predefined empirical model and input data Abaqus created a pressure ware. When this pressure was interacted with plate surface many vibration modes were excited resulting in deformation of plate. Central deflection and equivalent plastic strain were compared with experiment results of Mehreganian et. al (2017) and were found to be in acceptable agreement as shown in Figure 1 and 2 and Table 3. Results using solid elements with two elements in thickness direction are also shown in Figure 3. As a result of using greater number of elements the results correspond to those of shell elements but with expense of increased computation time.

Figure 1. Central deflection time history.