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Thread: Stress calculations and deflection

  1. #1
    Associate Engineer
    Join Date
    Oct 2011

    Stress calculations and deflection

    Hi, I am in my final year of college and am in the process of making my final year project. Now I calculated the bearing stress as well as the shear stress at the location of the bolts and it should support a weight of 2953lb providing I did my calculations right (Only needs to support a person weighing around 200lb). Now I am wondering how I can determine the amount of deflection in the beam, specifically as I have slots cut out as shown in the picture. The whole assembly is supported at 6 locations at the end. I am just stumped and am looking to where to start the calculations. I am not asking for someone to do the calculations just to steer me in the right direction. I will be using 1/4-20 Cap screws rated at a tensile strength of 70,000psi and 6061 aluminum 1/4" x 1" high which has a yield strength of 35,000 psi. Thanks for the help.

    Calculations so far:

    P(shear) = 1(.25*3.14*.25^2)(70,000psi) P(bearing) = 1(.25*.25)(1.35*35000psi)
    P(shear) = 3430lbs P(bearing) = 2,953 lbs

    Edit: Used Catia to simulate a 200lb uniform load on the center beam with supports only at the end where it is connected to a solid ground. Would this in fact be the deflection if I were to strictly stand on the center beam (extremely unlikely but for ease of calculations)? But in general, if I were to be supported by all 9 beams could I divide the weight by 9 as if it were equally distributed or is my logic completely off? (I am not an engineer and know very little about stresses in beams and such so please forgive my ignorance). With the 200lb force, it claims it will deflect 0.062" at the most at the center. I understand that this is a static load applied and realistically I should factor it by quiete a bit more, I just don't know at what value. (It is going to be the board for something called a flexboardz, which is similar to a longboard).

    Last edited by AAAkings; 10-24-2011 at 07:56 PM.

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