Material properties
Material properties
(OP)
I'm running stress analyses for two types of equipment racks in which I'm given the following information about the materials used: one rack is made of 1" 4130 steel square tubing (mil-s-4130) and the other rack is made of 1" 1010 mild steel square tubing. I'm assuming that this is not enough information, as I would also need to know the type of treatment (ie. annealed...). Am I correct in this assumption or is there a reliable source to find this information? Thanks in advance!





RE: Material properties
RE: Material properties
Was it welded by someone with AWS qualifications or cousin Eddie? Has anyone told you the wall thickness of tube used? Textbook information is useless until you know the rack's origin.
There is a "big picture" to consider when doing a structural analysis on something like an equipment rack. In some circles is referred to as the "burden of proof", but we're engineers and don't usually say it that way. Anyhow, if you assume the role of providing the "proof" to the Administrator (assumed to be the FAA in this case) then you must handle facts more than assumptions, and minimize the harm from possibly wrong assumptions where you can.
Trying to come up with an analysis for a multiply-redundant structure like a welded rack is difficult unless you want to go all-out with FEA. Even doing so, you cannot overcome the unknowns such as welding technique.
As I suggested (and so did the others) in the other thread you started, a structural load test is the preferred way to prove its strength. It eliminates (almost) all doubt.
Steven Fahey, CET
RE: Material properties
RE: Material properties
You cannot do a proper structural analysis until all of your weldment materials, heat treatments and weld joints have been specified in detail.
MIL-HDBK-5, sec. 8.2.2 gives allowables for the fusion welded section of mild and alloy steel. You will also need to apply the appropriate knock down factors for substandard weld conditions like undercuts, porosity, lack of penetration, etc. Unless the finished weldment is stress relieved, you should also assume there will be some residual stress within the parts due to the welding.
Hope that is helpful.
Terry
RE: Material properties
RE: Material properties
At some point someone will have to decide on allowables. In the absence of any more information the only safe thing to do is use the minimum possible, which is probably annealed.
It is more complicated if you are sizing the part rather than just analysing it structurally. You can get a force distribution and then set thicknesses, etc., when allowables are known; however, very few real-world structures like racks are statically determinate. The alternative is to set some sizes based on known available material conditions, and specify material condition as well as sizes. This may well depend on post-weld heat treatment to regain quenched and tempered strengths, which will distort the part with this sort of low alloy steel. Advice from a metallurgist is advisable before putting too much time into it. An initial stick model with bars is easily adapted to new tube section properties and could be built and left with essentially guessed sections until more is known.