Solving Oneaxial Shear Test: Find Shear Force

[Zasha]

I´m really struggling to find the shear force here.
1. Homework Statement
Hight h of a specimen = 100mm and diameter is 54mm.
Max force F=144,6 N and deformation is δ=5mm

Homework Equations

I have to find ε=δ/h
Area of specimen before deformation=54mm*100mm=5400mm
σ_z =(F(1-ε))/A
Shear force = σ_z /2

The Attempt at a Solution

ε=δ/h=5/100=0.05
A=5400mm
σ_z =(F(1-ε))/A=(144,6(1-0.05))/5400=0,025N/mm²
Shear Force=0,025/2=0,0127N/mm² which gives 12,7kN/m². The right answer is 30kN/m².

Any thoughts?

 

[haruspex]

I, for one, would need more description. What is the shape of the specimen? Where are the forces applied? Where is the deformation measured?