Hydroforming is a process in which water at high pressure is introduced into a hollow steel part with the objective of expanding the steel part out against a die.
It is desired to use this process to change a circular steel tube into a square steel tube. The outside diameter of the circular steel tube is 2.75 inches and the wall thickness is 0.1 inches. The tube is made from steel with a yield stress of 80 ksi and an elastic modulus of 29,000 ksi.
(a) Calculate the water pressure at which the steel begins to yield. Treat the tube as a thin walled pressure vessel.
(b) Calculate the average strain in the wall of the tube when the shape has changed to a 2.75 inch square.