A helmet has an open cell polystyrene foam liner that is designed to absorb the kinetic energy from an impact. The foam has a relative density of 10% and the Young's modulus of the solid polystyrene that the foam is made from is 1.5GPa. How much energy per unit volume, in J/m3, can the foam absorb if it is loaded in uniaxial compression to a strain of 80%? Please assume that C1=1.0 and C2=0.05.
U (in J/m3):