Technical information

11 / 62

© Ferrometal 08/2015
7.75
Kysy saatavuus /
Ask for availability
Suomi +358- 10 308 11 Latvia & Lithuania +371- 672 80 581
Eesti +372- 6990 470
4. Mechanical properties
Screw’s mechanical properties are presented in short in this section. Identifying these properties, it is essential to know terminology used.
Tensile strength Rm (N/mm2)
Tensile strength of a screw is the stress in which it can break. Breaking is allowed to happen in the screw’s shank or thread but not under the head. If testing is done with full-
size screws, the result is always approximate. To determine tensile strength accurately, machined test rod have to be pulled. Excluding stainless steel screws (material groups
A1…A5) which are always tested at full size (DIN ISO 3506).
Yield strength Re (N/mm2)
Yield strength indicates the tensile strength from which elongation begins to increase. Screw starts to yield when moving between elastic and plastic reformation area of the
material. Machined test rod should be used to determine also the accurate yield strength.
Tensile-elongation diagram for class 5.6 screw:
Venymä
Jännitys
Myötölujuus Max. vetomurtolujuus
Venymä
Jännitys
0,2% -raja
Max. vetomurtolujuus
Elongation
Tensile
Yield strength Max. tensile strength
Elongation
Tensile
0,2% -limit
Max. tensile strength
0,2% -limit Rp0,2 (N/mm2)
The yield strength of harder material is difficult to define since there is no clear point where the elongation begins. Therefore it is taken into use term 0,2% -limit, where per-
manent elongation of 0,2% is remained after relief. This value is used for class 8.8 and harder screws.
Tensile-elongation diagram for class 8.8 screw:
Venymä
Jännitys
Myötölujuus Max. vetomurtolujuus
Venymä
Jännitys
0,2% -raja
Max. vetomurtolujuus
Elongation
Tensile
Yield strength Max. tensile strength
Elongation
Tensile
0,2% -limit
Max. tensile strength