# A few questions about Direct and Shear stress

1. Feb 12, 2010

### hunterage2000

Just a few questions.

1). A bar of 2m and diameter 40mm, is subjected to an axial tensile force of 50KN. What will be the elongation and the reduction in diameter. The aluminium bar has a Modulus of Elasticity E = 70 Gpa and a poissons ratio v = 0.3

2). A 1.5m steel bar has a cross sectional area of 100mm x 50mm. If a force of 120KN is applied what will be the longitudial and lateral strain, and the change in dimension. Assume that for steel E = 200Gpa and v = 0.3.

2. Feb 12, 2010

### tiny-tim

Welcome to PF!

Hi hunterage2000! Welcome to PF!

Show us what you've tried, and where you're stuck, and then we'll know how to help!

3. Feb 12, 2010

### hunterage2000

I dont know what the formula is for working out elongation. I have looked on the web and cant find it. I tried F/AE and got 5.684x10-4. The problems come with answers and it says it should be 1.136mm but the notes on it are a bit crap so I'm just trying to arrange things to get the answer. Same with the 2nd one, its doesnt give the equations for longitudial and lateral strains. I,m not the brightest when it comes to physics.

4. Feb 12, 2010

### raymo39

well im not 100% on the stuff that youve jsut put up, but if you can figure out the change in diameter (which i gather you have) elongation can be found by using the original volume and the new diameter using cylindrical volume formulas :)

5. Feb 12, 2010

### nasu

The formula is Hooke's law. What you show here is the relative elongation (unitless). The problem requires the elongation.
elongation=(L-Lo)
relative elongation=(L-Lo)/Lo