# Homework Help: Stress and strain question

1. May 22, 2006

### dblanche

The Ultimate tensile strength of steel is 470MPa.

Assuming a factor of safety of 5 the maximum working load an 8.00mm diameter round steel bar should support against gravity is?

2. May 22, 2006

### Gokul43201

Staff Emeritus
And the work you have done so far towards solving the problem is... ?

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3. May 23, 2006

### dblanche

I have used every formula that I can think of, i've used the following equations:

Stress= Force / Area
470 x 10E06 = force / 5.03 x 10E-05
Force = 23624.78 N

then multiply 23624.78 by the factor of safety being 5
= 118123.9 Newtons????????????????????????????

Don't really know how to do it, could you please give us some hints?????????????????????????

4. May 23, 2006

### Gokul43201

Staff Emeritus
This is correct. You've calculated the maximum load.

There's a small error here. Should the allowable load be 5 times the maximum load ? What happens to the rod if you apply a load greater than the maximum load ?

Before you do any calculation involving numbers, first write down all the necessary equations using symbols to represent the various quantities involved. Plug in the numbers only after you've arrived at a final equation with the required unknown on one side, and all the knowns on the other.

5. May 23, 2006

### dblanche

No the allowable load would not be 5 times the maximum load, you divide this maximum load by 5 to give the maximum working load, which is 472.5 kg or 4724.96 Newtons..................................