"Determine working stress and greatest allowable load"

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



The maximum load in a tensile test on a mild steel specimen of diameter 12.5 mm is 95 kN, calculate the ultimate tensile stress. Also, determine the working stress and greatest allowable load on a rod of the same material 25 mm in diameter, given that the factor of safety is to be 3.5.



2. Relevant equations







3. The attempt at a solution



I'm only in the first term of my course and still new to this. I believe i've worked out the ultimate tensile strength here;



Pi x 6.252^2 = 122.718mm^2

95000/122.718 = 774.1326



now, where i'm struggling is the second two parts. Am i using the same force for this, the 95 kN or do i need to work out a new force using factor of safety and the new diameter?



I know factor of safety = Stress at Failure/Max working stress.



Greatest allowable load, is this the same as maximum load?



What i have tried and found out to be wrong is;



Pi x 12.5^2 = 490.87

95000/490.87 = 193.534



193.534/3.5 = 55.3



I'm not asking for the answer. Just a point in the right direction would be great.



Thanks.