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Thread: Temperature and its affect on Plastics

  1. #1
    Associate Engineer
    Join Date
    Jul 2012

    Temperature and its affect on Plastics

    Hello All.

    I have the understanding that plastics, such as Nylon, will become more flexible and "weaker" (low tensile strength) with higher temperatures. In turn, they become more brittle and stronger (high tensile strength) with lower temperatures.

    I believe this also applies to their compressive strengths, correct?

    If we were to mount a nylon part to "something" using a bolt, which material property of the nylon should we most concern ourselves with?

    My initial thought is that you would determine the axial force applied by the bolt and then calculate the stress of the "affected area" (the area of plastic underneath the bolt's head). You would then compare this stress to the compressive strength of the material, correct? Assuming you are below the compressive strength, one would think you are in good shape.

    Now, lets take this same part and assemble it while it is very cold outside. The chances are that the part will crack during assembly due to being very brittle. By "chances" I mean I have seen this happen. This seems to go against my approach/theory above because the compressive strength of the material should be higher. How can one account for brittleness?

    Thanks for your help.

  2. #2
    Technical Fellow
    Join Date
    Feb 2011
    Hi and welcome. I suggest Magic!

    Seriously, check the Nylon manufacturer's information on useable temperature range and live within that. It would take some very fine Magic to step outside those specs and still have the thing flexible enough not to crack at lower temps. If it is already cracking, I seriously doubt changing clamping loads will assist much. It may for a short time, but eventually the Nylon will give up the fight at those temps.

    Also, Nylon is hygroscopic to varying degrees depending on grade and you may also want to take that into consideration. Maybe looking at some other Polymers may prove useful instead. Stuff used in off-road vehicle suspensions etc may be better for the project.

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