I might also add that I found this definition today in NASA-STD-5002:
Limit Load: The maximum anticipated load experienced by a structure during a loading event, load regime, or mission. The factors of safety are not included in the limit load.
Update: and found this a couple hours later...
Thanks Sparweb.
It sounds like there are differing approaches to what should be called limit load. Some say don't include factors, and other say do include them. One of the confusions that can come with including a yield safety factor in the limit load, is that you then have to divide it out...
Yes, that is clear now how burying factors into the loads can be problematic.
This has been insightful. Thanks all for the time you've taken to help me. It has really cleared things up in my brain.
this is a lousy terminology > You can see part of the source of my confusion. I thought it was understood industry-wide that when you multiply by safety factors, only then does it become "design" loads.
I generally use service DL and LL and factored DL and LL > This is a pretty clean way of...
I assumed you mean "there is no factor applied to LL to get to DLL"? If so...
That is interesting. I'm doing a bolted joint analysis and a NASA Standard (NASA-STD-5020) gives these definitions:
Limit Load: The maximum expected applied load, including load transferred across joints as a result...
I'm a little embarrassed that I haven't figured this out thus far into my career, but alas, here I am.
Let me start by stating (in simple terms) what I think is true on this topic:
1. The limit load LL is the maximum expected applied load that could occur during service.
2. The design...
Thanks Greg. After some trial and error with some test data today, I feel good about my earlier hypothesis: take the RSS of the FFT values within a one-third octave band. I realized this is because the square root of the area under a frequency step (say from 20 Hz to 21 Hz) in the PSD is the...
Hello. I'm relatively new to vibration analysis, and I am trying to understand how to bin a narrow band FFT into one-third octave bands. My measured data has units of lbf, and lbf-in. Most of the information on this topic is acoustics related, but I can't find much for other units that aren't...
I may have answered my own question. I was writing lbf-RMS and realized that the base unit (g or lbf) should probably just be written as it would be normally. So in my options above, no capital G. Then according to the IEEE recommended unit symbol recommendations: "In general, most...
I do vibration analysis and testing, so we use the units of g-rms often. I see all sorts of ways to write this and I want to know once and for all what the right way to write it is. Options:
1. Grms
2. G-rms
3. gRMS
4. g-RMS
5. grms
6. g-rms
7. GRMS
8. G-RMS
I can't find an official source...
Thank you all for your input. Greg, I did just what you suggested. It is surely overestimating the input, but it is conservative. Overall, it was a minimal increase, something like 0.1 g-rms increase, so I'm not worried about it. I appreciate the time you spent to reply everybody.
Suppose you have an assembly that will go on a launch vehicle and be subjected to random vibration. Also suppose the input random vibration PSD (acceleraton spectral density) is given in the launch vehicle coordinate system, with the X-axis aligning with the axial direction, and Y-axis aligning...
r13, rb is correct, flaw is not the same as stress.
rb, they will not want a detailed crack growth analysis if I can show that it meets the requirements of "non-fracture critical, low-risk". Only parts with a "fracture critical" classification need a crack growth analysis. I'm trying to...
Thank you all for your replies so far.
I feel like I probably gave you too much information without enough background. The fracture requirements document NASA-STD-5019 has different fracture classifications. Two of them are Non-Fracture Critical (NFC) or Fracture Critical (FC). If a part is...
Thanks rb1957. I agree that I don't need NASGRO for this. Our company is purchasing it in case we need to actually perform crack growth analysis. What I'm attempting to do with the net section stress analysis is to show that our parts are not fracture critical to begin with and doesn't need a...
Hello all. I'm working a project bound for outer space that has fracture requirements associated with it (NASA-STD-5019). One of these I'm trying to show for my parts is to show "parts have total net-section stresses, e.g., maximum principal or von Mises, whichever is larger, at limit load...
Thank you for your responses.
BrianE22, that is a good point. That reminds me of free body diagrams I've seen of a bolt that shows the distribution of the force spread out among the the first few threads. The first few take the majority of the load. Of course. Had you asked me that I...
I am trying to calculate the stiffness of a custom screw using K = EA/L, but while specifying the length, I'm having a hard time visualizing how a fastener elongates along its length when preloaded into various plate configurations.
As a simple example, suppose you have two plates that are...
Ah, net! I think I like that even a bit better than effective. I missed your first reply.
Tmoose. Yes, prevailing = running. That is a good description for the layman. Thanks for sharing.
Effective torque has a nice ring to it. I'll note it as a possible name. However, what about the application with inserts with no locking feature and thus no running torque present? Effective torque sounds a little confusing. Installation torque sounds more appropriate for the "no running...
