BVID KDF on Ply/Laminate Strengths 1

[Ryan_aero]

Are there situations where it is acceptable to forgo a BVID knockdown when calculating ply strength or laminate strength margins? The startup I am employed at (expendable launch vehicle industry) has historically not accounted for a strength knockdown due to impact damage. I understand it is common practice to do so since an event as simple as a dropped tool can result in BVID. My thoughts are that our approach is risky even if our structures have a relatively limited service life.

Are there situations where it can be justified to forgo a BVID knockdown for composite strength margins? Or should it be accounted for on any composites part due to defects that can occur during manufacturing?

I wanted to gather more opinions before I push to change our approach on this. Accounting for BVID will result in a weight penalty in certain areas of our vehicle (where laminate failure is critical).

Thanks,
Ryan

 

[SWComposites]

You can avoid sizing to BVID if you do a threat assessment and determine the probability of damage is low, or if you implement inspections prior to flight to detect any accidental damage. If you plan to offer launches to the government you will need to satify their requirements.

Generally space vehicles do not carry the extra weight required to size for BVID.