1. Aug 10, 2012

### walleye3

1. The problem statement, all variables and given/known data

What is the factor of safety of a steel hanger having an ultimate strength of 550.00 MPa and supporting a load of 64000.000N. The steel hanger in question has a cross sectional area of 7.400cm squared

2. Relevant equations

3. The attempt at a solution
i understand the equation is ulitamate stress divided by allowable stress but the cross sectional area gives me problems. please show me a the steps i should take to find the factor of safety

well i went load/ area > 64000N/7.4cm squared = 8648.65 Pa

550 MPa = 550000kPa/8.648kPa (ultimate stress/allowable stress) =63594.11
63.59 as my answer is that correct ? if not please show me where i went wrong

Last edited: Aug 11, 2012
2. Aug 10, 2012

### rock.freak667

Given the load and the area, how do you find the working stress i.e. stress due to the load?

3. Aug 10, 2012

### walleye3

Load divided by area ...right ? , when it gives me cross sectional area do I need to do anything mathematically with it or do I plug that number in ?

4. Aug 11, 2012

### rock.freak667

Well you have the formula

And you are given both. You want to get the value of stress.

5. Aug 11, 2012

### walleye3

well i went load/ area > 64000N/7.4cm squared = 8648.65 Pa

550 MPa = 550000kPa/8.648kPa (ultimate stress/allowable stress) =63594.11
63.59 as my answer is that correct ? if not please show me where i went wrong

6. Aug 11, 2012

### CWatters

Check the units. cm2 ?

7. Aug 11, 2012

### walleye3

oh , i need metres squared

8. Aug 11, 2012

### walleye3

Load/Area= 64000N/0.074m= 864864.8649 Pa > 864.864 kPa
F/S = Ultimate stress/ Allowable Stress = 550 MPa/ 864.864 kPa > 550000 kPa/ 864.864kPa = 635.938

is (635.938 ) my answer ? (factor of safety) ??

9. Aug 11, 2012

### rock.freak667

1 cm2 = 0.0001 m2

10. Aug 11, 2012

### Staff: Mentor

1.0 cm2= ?? m2

11. Aug 11, 2012

### walleye3

1 cm = 0.01 m ....

12. Aug 11, 2012

### walleye3

okay thank you... i see my mistake

13. Aug 11, 2012

### walleye3

64000 N/ 0.00074m2 = 86486486.49 Pa > 86486.48649 kPa
F/S Ultimate stress/Allowable Stress = 550 MPa/86486.48649 > 550000kPa /86486.48649= 6.359

14. Aug 12, 2012

### CWatters

Allowable / Actual