Page 298 - Mechanical Engineer's Data Handbook

286 MECHANICAL ENGINEER’S DATA HANDBOOK

7.9.2 Toughness tests

Toughness testing consists of striking a notched test
piece with a hammer and measuring the energy
required to cause fracture. The energy is indicated on
the dial of the test machine and the force is produced
by a swinging mass.
Energy to fracture specimen
Toughness =Constant x
Energy of the swinging mass
The energy of the swinging mass is 163 J for the Izod
impact test and 294 J for the Charpy test.

Izod impact test machine and test piece

~~

Charpy test piece

/ specimen

7.9.3 Tensile test on steel
-
-
Test bar
Testing machines are used to determine the mechan-
ical properties of materials under tension, compres-
sion, bending, shear and torsion.
One of the most important tests is the tensile test,
especially that for steel. Typical curves are shown for
- ductile steel and hard steel. In the case of a ductile steel
>
such as ‘mild steel’, there is a definite yield point above
which the steel is no longer elastic. In the case of hard
steel the load-extension curve becomes non-linear and
it is necessary to specify a ‘proof stress’ for a specified
strain, e.g. 0.1%.