Comparative investigation of shock pressure, shock duration, pressure decay time, and elastic energy of both porous gelatin and pure gelatin in shock state

Abstract

Bird strike is an unavoidable threat in the aviation industry. Real birds are typically replaced with 10 wt. % pure gelatin or porous gelatin to simplify bird strike experiments and meet repeatability requirements. Porous gelatin is obtained by adding chemical agents to gelatin solution, which then solidifies, it can be regarded as pure gelatin filled with tiny pores. The differences in shock state characteristics between these two substitutes remain unclear.

In this paper, flyer plate impact experiments are conducted separately for the two types of gelatin, obtaining $u_s-u_p$Hugoniot. Considering the continuous release waves, the analytical solutions are provided for the pressure decay time and elastic energy anywhere within the gelatin, during the shock state. Numerical models of gelatin strike rigid target are conducted to extract the shock pressure and elastic energy during the shock state. The differences in mechanical properties of gelatin are analysed to understand that result in variations in pressure, shock duration, decay time, and elastic energy.

It is evident that the shock pressure of pure gelatin is higher than that of porous gelatin. The shock duration of porous gelatin is longer, and its smaller bulk modulus causes the release wave more gradual, resulting in longer shock decay time. The analytical solution of pressure decay time tends to be overestimated, the faster expansion of porous gelatin during pressure release exacerbates this discrepancy, resulting in a greater difference between the analytical solution and numerical model of elastic energy.