HP 50g User Manual page 752

At this point the program MOHRCIRCL starts calling the sub-programs to
produce the figure. Be patient. The resulting Mohr's circle will look as in the
picture to the left.
Because this view of PICT is invoked through the function PVIEW, we cannot get
any other information out of the plot besides the figure itself. To obtain
additional information out of the Mohr's circle, end the program by pressing
$. Then, press š to recover the contents of PICT in the graphics
environment. The Mohr's circle now looks like the picture to the right (see
above).
Press the soft-menu keys @TRACE and @(x,y)@. At the bottom of the screen you will
find the value of corresponding to the point A( x, xy), i.e.,
= 0,
(2.50E1, 5.00E1).
Press the right-arrow key (™) to increment the value of and see the
o
corresponding value of ( ' , ' ). For example, for = 45 , we have the
xx xy
values ( ' , ' ) = (1.00E2, 2.50E1) = (100, 25). The value of ' will be
xx xy yy
o o
found at an angle 90 ahead, i.e., where = 45 + 90 = 135 . Press the ™
key until reaching that value of , we find ( ' , ' ) = (-1.00E-10,-2.5E1) = (0,
yy xy
25).
To find the principal normal values press š until the cursor returns to the
intersection of the circle with the positive section of the -axis. The values found
o
at that point are = 59 , and ( ' , ' ) = (1.06E2,-1.40E0) = (106, -1.40).
xx xy
Now, we expected the value of ' = 0 at the location of the principal axes.
xy
What happens is that, because we have limited the resolution on the
o
independent variable to be = 1 , we miss the actual point where the shear
stresses become zero. If you press š once more, you find values of are =
o
58 , and ( ' , ' ) = (1.06E2,5.51E-1) = (106, 0.551). What this
xx xy
Page 22-37