Plane-strain compression of a hexagonal rod is shown in the sketch, including a possible slip-line field. The metal has a tensile yield strength of 25,000 psi. If the von-Mises criterion applies, find the pressure P, in psi, to start flow of the metal. (I took this question from the book of Metal Forming: Mechanics and Metallurgy, 2nd ed.)

Plane-strain compression of a hexagonal rod is shown in the sketch, including a possible slip-line field. The metal has a tensile yield strength of 25,000 psi. If the von-Mises criterion applies, find...