Requirement for "Checkstress"

[TDI]

I'm currently involved in the "Checkstress" activity for a civil aircraft project. I know that checkstress is meant to be an independant check of the stress analysis but is it a EASA/FAA/JAA requirement to do this and if so can anyone point me towards the necessary documentation defining the requirement?

 

[rb1957]

i don't know if there is a formal requirement for this ... i'm pretty sure that it is a european thing (i haven't heard the term over this side of the pond).

i see it as an analysis exercise (a very useful one) to have a 2nd pair of eyes analyze a structure and prepare the formal certification stress analysis reports (as opposed to the "sizing" calcs done during the design development).

good luck

 

[Lurchaolot]

I would agree with rb1957 - there is very little to show for the need for "check-stress" only ever seen this in BAe on the A340 stress/design stages. All/most of the preliminary stress calcs were done in people's personal folders (mine included - on the A330/340 trailing edge structure), often changed & updated & difficult for anyone to make sense of. So for a formal documentation esp to the British CAA (who are very fussy about presentation) it all had to be pulled together & made coherent for certification.

 

[Aerodesign]

In an ideal world Checkstress would be a check on an existing fully populated calc file. Typically this includes FEM checks and gross -error checks on assumptions. In reality the CS phase is often used for a final iteration of the stressing, maybe using updated loads. If the original analysis is followed, incorporating the new loads as you go it also forms a check on the method. Any significant varaitions to the results are flagged as this may indicate an error somewhere.

I am not aware of any empirical requirements docuemnt for CS, Airbus issue their own CS stressing methods, i.e. methods that have to be used for CS otehrwise the results are not accepted. Sometimes an alternate method is submitted to the methods group, which can allow non-Airbus CS methods to get thru.

So, your CS list remains ellusive, l suggest that an ad-hoc requirement list would include: External loads, FEM validation, Internal loads, stressing methods, spreadsheet validation, assumption checks, inclusion of post-test factors, compliance checklist, RF summary and (if Airbus) production of ACD4 ACD6 and final stress dossiers, for the authorities.

I may have left something out, but its a start.

 

[inertia4u]

For Airbus, Checkstress is an *independent* check. This check is completed by pulling all geometry from the solid models (not using data from the design phase), using Checkstress approved stress methods following a "Statement of Requirements" and other design requirements.

It entails reporting, calculating and making sure the following are confirmed correct:

1. Geometry
2. Material Allowables
3. Loads
4. Analysis

The above list is the *minimum* that your checkstress should entail.


-----
Nert

 

[Camille70874]

At FokkerCheck Stressing is standard for (almost) all engineering items and all projects (Airbus, Boeing, Gulfstream etc.). It is indeed an "independent" check and the depth of the checking depends on the importancy of the structure involved (class 1 or class 3 items).