After having addressed the issue of yield and tensile strength in one of our previous blog post. Secondly, there is the matter of elongation at fracture A, the tensile strength under wedge loading and head soundness.
Elongation at fracture A [%]
It is the permanent elongation measured on the fractured specimen related to the original measured length. What are the exceptions? Screws A1 to A4. Where this is measured on fullsize screws (ISO 3506).
Tensile strength under wedge loading
It is tested by means of having a wedge positioned underneath the screw head. (see the image below)
When tensioned, the screw must break:
- in the thread
- in the shank.
Bolts and screws are subjected to a wedge test to measure the ductility and head integrity.
Head soundness.
The head of the screw must withstand several hammer blows. How to make measurements? After being bent to a specified angle, the shank head fillet shall not show any signs of cracking. (see ISO 898)
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