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Conditions for approval required by: Julien Gauther
Certification of Aerospace Products to international quality Standards
Certification of Aerospace Products to international quality Standards
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Tensile tests were carried out on ISO MJ4 screws. EN2576 specifies that tensile tests are not applicable to bolts/screws with nominal diameter lower than 5.
Minimum tensile load for EN4634-040 is theoretically 6,85 kN instead of 8.57 kN. Indeed, EN4634 screws have countersunk heads. 6,85 kN is obtained by considering EN4634 screws, MJ4, 900 MPa UTS and allowance coefficient k=0,8, see EN2576, annex B. Even though annex B is informative, minimum tensile loads applicable to protruding and countersunk head bolts cannot be the identical for the same diameter and material strength class.
Minimum tensile load for EN4634-080 is theoretically 30,01 kN instead of 37.52 kN. Indeed, EN4634 screws have countersunk heads. 30,01 kN is obtained by considering EN4634 screws, MJ8, 900 MPa UTS and allowance coefficient k=0,8, see EN2576, annex B. Even though annex B is informative, minimum tensile loads applicable to protruding and countersunk head bolts cannot be the identical for the same diameter and material strength class.
What are your thoughts?
Many thanks in advance
Best regards
Julien
Hello Julien,
For EN4634-040 we need to take k=0.8, you are right. We will update the test value to 6.85 kN on Coc.
But for EN4634-080 we take the value in Table 7 in EN2576. There is no indicated that countersunk head bolts are sent to Annex B. Would it be correct to take 30.01 kN for diameter 8 as you said? This will lower the test conditions.
Thank you for your advice,
Best Regards.
Buse.
Hello Buse,
Many thanks for your speed!
EN2576, table 7, note a) states: “See Annex B (informative) for tensile strength areas, stress rupture areas and load formulae.”
Sub-clause B.2.2.1 shows that, depending on bolt/screw head style, an allowance coefficient is applied.
For sure, EN2576 is not as clear as ISO9152, ISO9154, ISO7689 or ISO8168 since in these ISO technical specifications, we do have different minimum tensile load requirements depending on head styles in relevant tables.
Keith,
What do you think about this?
Many thanks in advance
Best regards
Julien
Hi both. It is certain that the screws are compliant as they meet the the tensile requirements for a protruding head, even though they are countersunk heads. In my opinion, the 0.8 factor should be applied as indicated in Annex B as the countersunk head cannot be expected to be as strong as the full protruding head, like a hexagon or a double hexagon. In any case, the 4mm thread size does not need to be tensile tested.
Following the discussion with Phil Edwards and Julien Gauther, we have agreed that this qualification is acceptable and I will add the following note to the report in the qualification test report section:
“It is noted that Lisi tensile tested these screws to the full requirement of a protruding head screw, where the specification only requires a countersunk head screw to meet 80% of the protruding head load.”
Many thanks to all of you.
All is clear now.
Approved from my side.
Best regards
Julien