IRstuff,
This is not the same as derating. Whenever a parameter of a statistical distribution is calculated from sample data, there is some uncertainty associated with the estimate. A second sample taken from the exact same population will not give the exact same estimate as the first sample...
How does your company use confidence level in setting its reliability design inputs and test acceptance criteria?
Given that the confidence level approaches zero as the bounds approach the nominal Weibull curve, what do you consider a minimum confidence level to set as the acceptance...
Some engineers here have begun adding notes to certain component drawings to indicate that the UL report file (no number given) must be reviewed if the design is changed. The intent is to prevent mismatches between the product configuration being manufactured, and that registered with UL. From...
My favorite is the Dimensioning and Tolerancing Handbook (Drake, ed. 1999), which includes the following chapters on stack-up analysis:
9. Traditional approaches to analyzing mechanical tolerance stacks
11. Predicting assembly quality (Six Sigma methodologies to optimize tolerances)
12...
John,
IMO, ewh and KENAT are right. A cert is not a design specification or a process, it's just one possible method to verify them. If a vendor did not have an established quality system, we might choose instead to sample and test every lot.
In my experience, certs end up on drawings when...
Looking for opinions on a drawing practice related to configuration management: including revision levels of component parts on an assembly drawing. The standards and drafting guidance documents don't seem to directly address it. Advisable or not? How about if the configuration management...
The best book I've encountered for tolerance analysis is the Dimensioning and Tolerancing Handbook (Drake, et al, 1999).
http://www.amazon.com/Dimensioning-Tolerancing-Handbook-Paul-Drake/dp/0070181314
There are also a lot of good papers online at BYU's Association for the Development of...
Allen! I'm so glad to see that fault-tree.net is back up! We've found the references incredibly useful and entertaining.
Thanks for the response. Since I posted that message we've completed two analyses, and they did indeed take more than two or three pages before they were done. We've also...
FMEA resources online indicate that a common mistake is to confuse the failure mode with the effect or the cause. I've seen this happen quite a bit, and it's usually due to the fact that the cause-and-effect chain is longer than three discrete items for the failure mode in question. So what is...
In the reference listed below, the author makes a statement about Fault Tree Analysis (FTA) while discussing the use of cutsets:
I was wondering if other practicing engineers using FTA have found this to be true. We currently only use Failure Mode and Effects Analysis (FMEA) as our risk...
What are the recommended run-in procedures for small (~ 1.0 inch gearbox diameter, 96-120 DP gears) planetary gearboxes lubricated with thick (channelling) grease?
In the bearing industry, at least one manufacturer recommends that bearings be run initially at 20% of full speed until the...
This is MSC.Nastran for Windows, not NENastran or full Nastran. I've read about Nastran's superelements and Patran's displacement fields, but have access to neither at the moment.
Although I understand how to apply MPC equations, I have no idea how to formulate such equations for an arbitrary...
I'm trying to do a global-local analysis of a solid model in Nastran for Windows 2003. The global model has been solved, and the original nodes on the sub-structure boundary surfaces have 6dof constraints and displacement loads derived from the output vectors. The tricky part is trying to tie...
Section 18 of Genium's Drafting Manual is "Sheet Metal Practice". In sub-section 7.0, they show three examples. None of them include features which cross a bend, but each includes a note:
Does that number refer to a standard, or is it intended to indicate a shop procedure? (We don't work...
