[TODO] Fix Bend Calculator

[gbowne1]

To repro this issue:

$ python3 app.py
Select a calculator:

1. Bend Calculator
2. Lathe Calculator
3. Sheet Metal Calculator
4. Speed and Feed Calculator
5. Punch Tonnage Calculator
6. Quit
   Enter your choice:

Enter 1 as the choice:

enter these values:

Enter your choice: 1
Enter length in inches: 1
Enter width in inches: 2
Enter thickness in inches: .125
Enter bend angle in degrees: 45
Enter inner radius in inches: .125
Enter K-factor: 0.38
Enter tensile strength in pounds per square inch: 53700
Enter die opening in inches: 1

which should be ok for 1018 steel I couldn't find good numbers for tensile strength of 1018 except that it was suggested to be between 53,700ppsi and 90,000ppsi and I also couldnt find good numbers for K-factor for 1018.

The issue here is that this does not really return any valid data, it is only accepting inputs. It just returns you to the program after entering the die opening in inches.

Are K-Factor, tensile strength calculated numbers? What do we do with the numbers once we enter in all this data?