HP 50g Graphing Calculator - Manual (Page 753)

Page 22-38
information tell us is that somewhere between φ = 58
o
and φ = 59
o
, the shear
stress, τ’
xy
, becomes zero.
To find the actual value of φ n, press $. Then type the list corresponding to
the values { σx σy τxy}, for this case, it will be
{ 25 75 50 } [ENTER]
Then, press @CC&r. The last result in the output, 58.2825255885 o
, is the actual
value of φ n.
A program to calculate principal stresses
The procedure followed above to calculate φ n, can be programmed as follows:
Program PRNST:
«
Start program PRNST (PRiNcipal STresses)
INDAT Enter data as in program MOHRCIRC
CC&r Calculate σc, r, and fn, as in MOHRCIRC
“ φ n” TAG Tag angle for principal stresses
3 ROLLD Move tagged angle to level 3
R C DUP Convert σc and r to (σc, r), duplicate
C R + “ σPx” TAG Calculate principal stress σPx, tag it
SWAP C R - “ σPy” TAG Swap,calculate stress σPy, tag it.
» End program PRNST
To run the program use:
J
@PRNST Start program PRNST
25˜ Enter σx = 25
75˜ Enter σy = 75
50` Enter τxy = 50, and finish data entry.
The result is:
Ordering the variables in the sub-directory
Running the program MOHRCIRCL for the first time produced a couple of new
variables, PPAR and EQ. These are the Plot PARameter and EQuation variables