A copper ingot is compressed between two anvils. If the yield strength \(\sigma_{y}\) of copper is \(80 \mathrm{MPa}\) and the coefficient of friction \(\mu\) at the interface between the copper and the anvil is 0.1 , what is the maximum forming pressure at the centre of the ingot when the aspect ratio \(2 w / h\) is \(20: 1\) ?