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  1. mech2926

    Book on stress analysis of plastics

    Hi, I'm looking for recommendations for a good book on stress analysis of plastics. Analysis of plastics is a new field to me so I'm interested in analysis methods and failure criteria. Basically, how to go about analyzing a plastic part for structural adequacy. Calculating stress is not an...
  2. mech2926

    Parallel computing in MSC NASTRAN

    I use NX Nastran, which is almost the same thing as MSC but not exactly. For parallel processing I use the command "PARALLEL". This can be inserted in one of several places. You can put it in the analysis deck (which I think is your bdf file) as one of the first few lines in the file, in...
  3. mech2926

    Stress occuring in cooling plastic (settle a debate!)

    These are my opinions: In scenario 1, since the bar is 1% longer when you clamp it, it is also 1% wider, so in the end state, scenario 1 is stretched more in the transverse direction at the clamps than scenario 2. I would use the average thermal expansion coefficient between the two...
  4. mech2926

    Dynamic / Impact loads

    I've never thought of it that way before; I always considered "impact" to be a type of "dynamic load." I'm a mechanical engineer; perhaps this differentiation is specific to structural/civil engineering? Perhaps the distinction has to do with whether kinetic energy is significant. If you drop...
  5. mech2926

    Pressure fatigue in B31.3 piping

    Thank you all for your posts. The system I'm working on uses stainless steel (304, 316). Thermal expansion and pressure are the only loads that are expected to occur cyclicly. For these materials, since yield is about half of ultimate stress, and allowable stress is much lower than yield...
  6. mech2926

    Pressure fatigue in B31.3 piping

    Pressures are less than or equal to 2400 psig. There would be temperature cycles occuring simultaneously with the pressure cycles. I'm assuming the cycling would be over a period of years.
  7. mech2926

    Pressure fatigue in B31.3 piping

    Is evaluation for pressure fatigue necessary for B31.3 piping in "normal" service? I've been looking through the Code and pressure fatigue seems to mainly be a concern for high-pressure piping (defined as P/SE > .385) and/or piping with "thick" walls. I could just go ahead and calculate...
  8. mech2926

    How to define temperature on surface dependent on y-axis position?

    This is kind of a late post but maybe it will help. I've never done that in Femap before but you might look at creating a Data Surface. If you're in the "Create Loads on Nodes" dialog box, on the right side are 3 options under "Method." One of these is Data Surface. Check out section 7.2.5.1...
  9. mech2926

    Response spectrum

    hacksaw, I'm not familiar with "excitation spectra"--is that a graph of the input acceleration (what would be the floor motion in my case)? What I have is a response spectrum, which is the response of a spring-mass-damper mounted to the floor (the x-axis represents the frequency of the...
  10. mech2926

    Response spectrum

    If the system's modes are in the flat part on the right end of the response spectrum, then I think they are above the forcing frequencies. I think that the magnitude of the spectrum on the right end is equal to the peak input acceleration (the acceleration of the ground). Since the system...
  11. mech2926

    Response spectrum

    TERIO, Thank you, that definitely helps. A lot of the math in the NRC document is over my head (I have only a humble bachelor's degree), but I'll see what I can learn from it. Maybe you can clarify something that has been bothering me for a while and is related to this subject. One of the...
  12. mech2926

    Response spectrum

    IRstuff, I'm not sure I understand your question. I'm coming from the perspective of using a static analysis rather than a response spectrum analysis. That's why I wanted to make sure that the approach I mentioned was conservative; if it's not then I need to find another way, or add some fudge...
  13. mech2926

    mode interaction

    Sorry for the delay; thank you all for your replies. I'll try to clarify: Yes, I was asking whether adding the relief valve will change the system modes. The main excitation frequencies of concern are from earthquake, and the ZPA is around 30 Hz. So the valve would be fine by itself because...
  14. mech2926

    mode interaction

    Hi, I have a question on mode interaction. There is a several thousand pound vertical vessel attached to a skid which is secured to the floor. Attached to the vessel are several piping assemblies. The piping assemblies weigh quite a bit less than the vessel. The first few modes of the system...
  15. mech2926

    Response spectrum

    Hi, I have a question on response spectra. I have attached a figure showing an arbitrary response spectrum. Assume that my component's first mode is at the vertical red line. If I assume that all the mass is participating in that mode, and apply the acceleration (in my Nastran model) shown by...
  16. mech2926

    skid-mounted equipment seismic loads

    I need to analyze some skid-mounted equipment for earthquake. The skid is bolted to the floor of a building. Would this be considered a "nonstructural component" in ASCE 7-05? Thanks
  17. mech2926

    applicability of Static Coefficient method IEEE-344 (seismic)

    Hi, I would like to get some clarification on the static coefficient method in IEEE-344. I've read the standard, and it explains that the static coefficient method is a simpler, more conservative method than a dynamic analysis such as response spectrum analysis. It also says that for...

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