DYNAMIC ANALYSIS OF INFLATABLE DECOYS

Abstract

Decoys are compact, portable, durable, easy to handle and highly mobile. Inflatable structures/ decoys are made of high-strength fabric (polyester and nylon fabric) coated with PVC, TPU, and rubber (Neoprene/ Hypalon). The main challenge in design and analysis is deployment reliability on inflation. Material properties and the response of fabrics for inflatable structures are vital factors in creating the required material model before design and simulation. The uni-axial tension and bias-extension test methods are used to determine the fabric material model. PVC-coated polyester fabric is found suitable, and the deflation and inflation process through ABAQUS/ CAE is shown using a direct approach. Pressure is defined as a boundary condition to the cavity reference point and this method was employed in this paper. For Simulation, three models are used: (i) Simple box model, (ii) Box with pipe model and (iii) Box with internal baffles model. On inflating these models, lateral deflection corresponding to applied pressure is calculated on each surface, and structural stability is compared. It is concluded from the simulation and lab test results that the behaviour after inflation is suitable in only two models, i.e., (i) Box with pipe model and (ii) Box with internal baffles model, after observing its lateral deflection corresponding to applied pressure. However, a simple box model shows higher lateral deflection, which is undesirable for achieving the correct shape of the structure. Thermal signature testing was done on samples including iron plates, aluminium paint, aluminium pigments, steel pigments, graphite and uncoated fabric. The pure metal tapes and coatings showed better thermal signatures than non-metalised paints. Maximum changes in signatures were found in the case of aluminium metal tape It was also observed that lighter colour paints have better signatures compared to black colour; the main reason behind this output was the same environmental temperature for all the objects, and black colour showed lesser reflectivity for the infrared frequency spectrum.