Select the materials to test in a tensometer:

Aluminium Approximately pure aluminium.

Copper Approximately pure copper.

Brass Cu-46 wt% Zn α-β brass.

Mild steel Fe-C alloy with lower carbon content.

Silver steel Fe-C alloy with higher carbon content.

Martensite Made from silver steel annealed at 750 ℃ and rapidly quenched in water.

Stainless steel 18.7-Cr, 70.1-Fe, 11.1-Ni wt% alloy.

Summary A summary to compare the mechanical behaviour of the metallic materials above.

Copper is ductile and necks before fracture.

The brass is tougher and can be stretched longer without failing. It is also more brittle and does not neck significantly before fracture.

This low carbon steel shows a pronounced drop in the stress required for plastic deformation following initial yield. To learn the reasons behind this, click Cottrell atmosphere .

When the alloy is made, diffusion at high temperatures allows the carbon solute atoms to diffuse towards the dislocations where there is more open space.

This creates a Cottrell atmosphere along the length of a dislocation, which pins the dislocations, retarding their movement. This results in a higher initial yield stress.

After the dislocations escape from their Cottrell atmospheres, the yield stress drops.

The general increase in yield stress after the drop is due to work hardening (see hardness section).

Silver steel is more brittle than mild steel and undegoes less necking compared to mild steel.

Martensite is very brittle and hardly undergoes any plastic deformation before fracture. Its yield stress is lower than silver steel as a result of residual stress from quenching.

Stainless steel is ductile and tough. It can be streched for a large length and absorb a lot of energy before fracture. It also necks before fracture.