4.67 Assuming that a uniform cross-sectional beam made of steel with yield
stress = 320 MPa receives a moment M with respect to the z-axis and is in
an elastomeric state, find the moment M when (a) the yield occurs for the
first time and (b) the thickness of the internal elastic portion is 5 mm.
15 mm
Z
Figure P4.67
y
12 mm
M