PSI - Issue 60

Prince Jeya Lal Lazar et al. / Procedia Structural Integrity 60 (2024) 185–194 Author name / StructuralIntegrity Procedia 00 (2019) 000–000

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The design of protective structures to mitigate the effects of blast requires an insight into the structural response of the sandwich panel. Earlier research [9] revealed that sandwich panels with square honeycomb cores offered higher resistance to dynamic crushing. Structures like triangular and square honeycombs [10], and prismatic and lattice truss structures [11-13] are also reported in literature for blast mitigation applications. In addition, high-strength austenitic and super-austenitic stainless steels with enhanced tangent modulus and strain hardening rate are widely preferred for sandwich materials for blast mitigation applications [14]. During a blast, the generated shock wave decays as it propagates away from the source of detonation. The incident impulse induces a plastic deformation on the front face of the sandwich panel which is restricted by the core [15]. The crushing of the core is dominated by the relative density, unit cell topology, and crush strength of the core material [16, 17]. The blast impulse is neutralized through mechanical energy dissipation by the plastic deformation of the front face sheet and the core of the sandwich panel. The current research deals with exploring the structural integrity of super-austenitic stainless steel sandwich panels with square honeycomb cores subjected to surface and underwater explosions. All the numerical simulations were performed using Abaqus Explicit finite element solver [18]. The effects of blast impulse are explored by varying the mass of the charge and the standoff distance. In addition, the structural integrity of the sandwich panel is evaluated by varying the core thickness and its effects on plastic deformation for varying blast intensity. Nomenclature ! Shock front pressure "#$ Atmospheric pressure " Arrival time % Time duration of the positive phase l Time decay constant Impulse Shock factor & Flow stress , , , , Material constants $ Melting temperature # Transition temperature 2. Numerical Simulations 2.1. Surface Explosion The intensity of the shock wave generated during a surface explosion depends on the mass of the explosive charge. During a surface explosion, a rapid expansion of gases generates a shock wave propagating outwards with a velocity equivalent to the detonation velocity of the explosive charge (approx. 7200 m/s) [6]. Significant damage is encountered in a positive pressure regime and the effects of the impulse in a negative pressure regime are ignored [19]. The impulse of the shock wave typically lasts for milliseconds beyond which the shock wave decays exponentially. From the modified Friedlander equation, free-field pressure–time response is described by [19] as; ( ) = ( ' − "#$ )21− #(# ! # " 4 2 ((#(# ! + ) 4 (1) Where λ is the constant associated with the time decay of the shock wave. The characteristics of a typical surface explosion are presented in Fig. 1. The specific impulse (I) encountered by the front face of the panel during the positive phase of the explosion can be estimated using Equation 2. This research used the CONWEP algorithm developed by the US Army Corps of Engineers [8] to simulate the surface explosions. = ∫ ( ) # ! ,# " # ! (2)