How to test the tension of the metric button head socket cap screws?

Tensile strength is an important indicator of the mechanical properties of screw fasteners. The tensile test of the metric button head socket cap screws is determined by testing the breaking tensile load, and then calculating the tensile strength of the screw to determine whether it meets the standard requirements. The formula for calculating tensile strength is as follows: =P/

P——Minimum tensile load

——Thread stress cross-sectional area

Among them, the calculation formula of the thread stress cross-sectional area is:

=0.7854*(D-0.9743/n)^2

D——the nominal diameter of the screw

N – the number of teeth per inch

The minimum distance from the threaded end of the metric button head socket cap screws sample of the metric button to the nut bearing surface of the clamp) that is subjected to the tensile load and the unthreaded thread length should be greater than or equal to 1 thread diameter (≥1d).

When the test force reaches the minimum tensile load specified by the standard, the metric button head socket cap screws cannot be broken. Continue to increase the load until it breaks. The break should occur within the length of the thread that is not screwed and not screwed, and should not occur where the head or the head and the stem are joined.

In the test, when the load has exceeded the minimum tensile load specified by the standard, if the test piece has produced a significant necking, the test can be aborted. However, if there is a dispute, the screw should be broken. In the case of a fully threaded screw, if the break occurs in the unthreaded threaded portion, the crack will still be considered to meet the standard requirements, even though the crack has been extended to the under corner of the head or under the head.

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