# Help with Tensile testing

1. Aug 5, 2016

### Elitisi Piuela

• Homework posted in wrong forum, so no template
I'm asked to design a rod, it is aluminium and it is to withstand force of 200kN.
maximum allowable stress is 170MPa with a strain of 0.0025mm.mm^-1
rod must be at least 3.8m long but must deform elastically no more than 6mm when the force is applied.

UTS = 170 MPa
e = 0.0025mm.mm^-1
F = 200kN
Lf = 6mm + 3.8m (?)
Lo = 3796.5087mm (?)
Gauge length = Lo ??
I'm unsure about the gauge length, Lo and Lf
do i need to also consider the force 200kN

2. Aug 6, 2016

### haruspex

Applied how? I'll assume this is tension.
I'm not quite sure what that is saying. Is it that at a tension of 200kN the stress must be no more than 170MPa? What does that tell you about the cross-section?
I'm unclear how those two relate. The first seems to say that at 200kN tension the rod must not extend more than 0.25%, while the second says it must not extend more than 6/38 %, or about .15%.
Since it must withstand that force, that seems a rather crucial consideration.

3. Aug 6, 2016

### Elitisi Piuela

I've come up with Lo = 3796.51mm and Ao = 0.0012msquared
using the formulas:
e = Δgaugelength/initial length (taking that Δgaugelength = 3.8m + 6mm)
σ = P/Ao (P=0.2MN , σ = 170MN/msquared)

is this right????

4. Aug 6, 2016

### haruspex

That satisfies the max allowable stress, but what will the extension be if at that stress it extends 2.5 mm/m?