### 3.2.1. Shock Equation of State

To define the pressure and energy on the Hugoniot this equation of state requires the material shock velocity-particle velocity relationship as material input. In Autodyn this is specified through

Us = C0 + Sup | (3–26)

where

Us is the shock velocity
up is the particle velocity
S is the slope of the Us – up relationship
C0 is the bulk acoustic sound speed

For the case of an orthotropic material, the bulk acoustic sound speed is calculated from the effective bulk modulus Equation 3–22 and density:

| (3–27)

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