EASA CS 23.613 Requirement 3

[teknomiks]

Hello,

I need some clarifications about below paragraph. I appreciate if you can help me.

1. What does quaranteed minimum value mean ? S-basis allowable ?

2. “premium selection” of the material ? Does it mean a single test of particular raw material to be used in design.

3. If I test the raw material (exact heat only) and use that values, I dont need to generate statisc based allowables.

"(e) Design values greater than the guaranteed
minimum’s required by this paragraph may be
used where only guaranteed minimum values are
normally allowed if a “premium selection” of the
material is made in which a specimen of each
individual item is tested before use to determine
that the actual strength properties of the particular
item will equal or exceed those used in design."


Thanks and Regards

 

[victorzv]

Just an opinion.

1. Guaranteed minimum means the design value is smaller than the actual property. No, it is the A- or B-basis. See subparagraphs b1 and b2 for clarification.

2. This means you prove your value through testing. No, a single test is not enough. You must comply with respective DIN, ASTM or whatever standard is acceptable for your AA.

3. It seems, testing raw material may not be enough. You may need to test the part. You will definitely require to produce some statistics on your testing.

 

[rb1957]

1) as victor above ... A-basis is best, B-basis if you're going to test (geez, i'm a poet), use S-basis if there's nothing else.

2) to me "premium selection" means you test each batch of material to validate to allowable (and reject batches that show lower strength).

3) yes, but you may need to develop a statistical story (fairy tale ?) that shows your batch testing validates the allowable. possibly test each piece of raw material ?

developing your own allowables usually takes an incredible amount of testing (and money). get your cert people's buy-in before you invest (spend) the money.

 

[SWComposites]

1. What does guaranteed minimum value mean ? S-basis allowable ?
> no, it means an A-basis or B-basis allowable. S-values are NOT statistical allowables; they are merely specification minimum values and have no statistical basis.

2. "premium selection" of the material ? Does it mean a single test of particular raw material to be used in design.
> no, it means you test every actual part that you manufacture. this is typically done by including prolong specimens in the part and testing those specimens. if the prolong specimen does not meet the design value, then the part is not acceptable.

3. If I test the raw material (exact heat only) and use that values, I don't need to generate static based allowable.
>you may not need allowables (need to get your certification authority to agree), but you cannot just test the raw material batch, you have to test a specimen or specimens from every production part, from now to forever.

You need to discuss your proposed approach with the certification authority as soon as possible.

 

[teknomiks]

Thanks fo answers, I need to update that I am trying to understand above requirement for metallic materials only. For example, when I look at MMPDS for metallic allowables, there are many S-Basis values. But I know that I cant use S-basis allowables in design. Then why they index these values in MMPDS.

Thanks again .

 

[SWComposites]

For historical purposes (many have been in MMPDS/Mil-5 for a long time), for preliminary design and for use in programs which allow the use of S-values.