HP 48gII User Manual page 751

with respect to segment AB. The coordinates of point A' will give the values
(σ' ,τ' ), while those of B' will give the values (σ' ,τ' ).
xx xy yy xy
The stress condition for which the shear stress, τ' , is zero, indicated by
xy
segment D'E', produces the so-called principal stresses, σ P (at point D') and
xx
σ P (at point E'). To obtain the principal stresses you need to rotate the
yy
coordinate system x'-y' by an angle φ , counterclockwise, with respect to the
n
system x-y. In Mohr's circle, the angle between segments AC and D'C
measures 2φ .
n
The stress condition for which the shear stress, τ' , is a maximum, is given by
xy
segment F'G'. Under such conditions both normal stresses, σ' = σ' , are
xx yy
equal. The angle corresponding to this rotation is φ . The angle between
s
segment AC and segment F'C in the figure represents 2φ .
s
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