PSI - Issue 14

Akhilesh Kumar Jha et al. / Procedia Structural Integrity 14 (2019) 416–428 Akhilesh Kumar Jha et al. / Structural Integrity Procedia 00 (2018) 000–000

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brought to rest instantaneously and the shock wave propagates through the projectile. As the shock wave propagates it brings the material behind the shock wave to rest. The pressure in the shock compressed region is known as Hugonoit Pressure.

Fig. 1. (a) Initial impact phase; (b) Shock propagation; (c) Steady state flow; (d) Pressure decay process.

Although the magnitude of the pressure is very high, it last only a few microseconds. There exists a pressure gradient at the edge of the projectile, which makes the particles to go flow steadily and in the outward direction. After several reflection of release waves, a steady flow condition is established. As the impact continues, there will be a decay phase, where the pressure reduces to zero and is the termination phase. 3. Numerical modelling 3.1. Bird Model The bird material has been replaced with an equal mass of water, as birds mostly consists of water and air trapped in the bones and lungs. The bird geometry is represented as a cylinder with hemispherical ends as this geometry resembles the pressure time history of the real bird during the impact tests as shown in Fig. 2. The bird characteristic such as diameter, cylinder length and density are obtained by using empirical formulas. A bird with mass equal to 2 pounds has been considered in this analysis as per the certification requirement. � � �� � ���� (2) ��� �� � ��� � �� � �� �� � � � ��� � � (3) � ��� � ������ � ����� � ����� (4)