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  1. #1
    What would be the most rigid of these flatbar?
    Flexing as if you were using them as a bridge and standing in middle. I'm sure there is a tech term for it, but I don't know it.

    25mm thick aluminium 500x100mm

    10mm thick 500 x100mm mild steel

    10mm thick 500x100mm stainless steel.

    Thanks in advance.

  2. #2
    That's easy -

    https://en.wikipedia.org/wiki/Three-point_flexural_test

    Unless you expect someone else to do the work for you?
    You think that's too expensive? You're not a Model Engineer are you? :D

  3. #3
    I was kinda hoping not to spend 250K+ on a test rig to find out. Lol

    Just looking for advice for people that work with metals what they thought.

  4. #4
    Would depend on the aluminium alloy to some extent but Youngs modulus of steel is roughly 3x that of Aluminium.

    There is not really a particularly significant difference in modulus between stainless/mild.

    Flexural modulus is usually fairly in line with Youngs modulus in metals. Polymers can vary more.

    https://www.engineeringtoolbox.com/y...lus-d_773.html

    Edit - as it pertains to machine design, the general rule of thumb I've seen bandied around is that you need twice the thickness of aluminium to achieve similar stiffness to steel. No idea where that rule of thumb started though nor how accurate it is when considering all the different variables in real applications.
    Last edited by Zeeflyboy; 17-12-2017 at 07:57 PM.

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  6. #5
    Quote Originally Posted by PaisleyPCdoctor View Post
    I was kinda hoping not to spend 250K+ on a test rig to find out. Lol

    Just looking for advice for people that work with metals what they thought.
    And in giving dimensions and materials you are asking them to perform standard calculations based on set formulae which are easily found.
    It isn't Rocket Science and if yo want to pay my hourly rate I will look up the equations and do the calculations for you.

    Around 8 years ago I wanted to know about material thicknesses in cylinders for a variety of diameters and pressures and looked up the required mechanical engineering equations, if you were to ask this on a mechanical engineering forum I'd expect an "off the cuff" answer but generally speaking by asking this here you are just expecting someone else to do your work for you, and someone might, but without seeing their working how will you know if the answer is any good?
    You think that's too expensive? You're not a Model Engineer are you? :D

  7. #6
    Just out of interest, took your dimensions and applied a load of 200N to mild steel and 6061 alu:


    Click image for larger version. 

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    Click image for larger version. 

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    10mm Steel deflection = 0.06861 mm

    25mm Alu deflection = 0.01471 mm


    So according to that simulation, the 25mm alu would deflect less.

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  9. #7
    Quote Originally Posted by Zeeflyboy View Post
    Just out of interest, took your dimensions and applied a load of 200N to mild steel and 6061 alu:


    Click image for larger version. 

Name:	Screen Shot 2017-12-17 at 20.14.15.jpg 
Views:	84 
Size:	114.1 KB 
ID:	23425


    Click image for larger version. 

Name:	Screen Shot 2017-12-17 at 20.14.00.jpg 
Views:	76 
Size:	126.0 KB 
ID:	23426


    10mm Steel deflection = 0.06861 mm

    25mm Alu deflection = 0.01471 mm


    So according to that simulation, the 25mm alu would deflect less.
    That is amazing! Totally opposite from what I thoughtModulus of Elasticity. I have the 25mm aluminium, but thought I'd be better buying steel. Excellent news. Thanks for you efforts- totally appreciated.

  10. #8
    Good man!
    Someone else was willing to do the basic maths for you!
    You should do a degree course now! :D
    Last edited by magicniner; 17-12-2017 at 08:42 PM.
    You think that's too expensive? You're not a Model Engineer are you? :D

  11. #9
    Quote Originally Posted by magicniner View Post
    And in giving dimensions and materials you are asking them to perform standard calculations based on set formulae which are easily found.
    It isn't Rocket Science and if yo want to pay my hourly rate I will look up the equations and do the calculations for you.

    Around 8 years ago I wanted to know about material thicknesses in cylinders for a variety of diameters and pressures and looked up the required mechanical engineering equations, if you were to ask this on a mechanical engineering forum I'd expect an "off the cuff" answer but generally speaking by asking this here you are just expecting someone else to do your work for you, and someone might, but without seeing their working how will you know if the answer is any good?
    Do you actually help anyone on this forum or just troll members with snipes, criticisms and general vinegar titted grumpiness?
    #boring

  12. #10
    Yes,
    I'm glad you ask, actually I answer lots of direct relevant questions with well thought out technical answers from people who aren't lazy clueless wakners who can't be bothered to carry out a basic Google search to see if there is a good answer just sitting there for them on the net.
    But I guess you are too lazy to search and discover that too!
    #SLACKER!
    ;-)
    You think that's too expensive? You're not a Model Engineer are you? :D

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