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HOMEWORK 31.B - SP 24
15 thoughts on “HOMEWORK 31.B - SP 24”
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How exactly do we find the yield strength for part B when determining the factor of safety?
Since we are given the material, we can search up the material properties of the Aluminum Alloy 6061-T6.
Did you guys just use 10000 ksi for the young's modulus after converting from GPa?
Yep, I just used the values for Young's Modulus and the Yield Strength for the alloy from page 7 of the Period 30 Notes -- Young's Modulus is 10000 ksi and yield strength is 40 ksi.
Will we be given such properties like the yield strength on an exam?
Likely - it would be unfair to require us to memorize values such as the Young's Modulus or yield/ultimate strength for any possible material, and previous problems have provided us those. This assignment is probably just testing our ability to seek out the correct values given a standardized material.
I'm assuming we use the largest of the three stresses calculated in part A to determine the factor of safety right? That way the ratio between what the material can handle and the largest load we apply to it is the smallest
Yes, because the member with the smallest factor of safety would be the first to yield. Calculating each factor of safety to prove none yields would also work, though
From my understanding, to determine whether it is yielding, we need to compare the largest axial stress among the three components with the yielding stress. However, it seems that we are not provided with this information in the question. Anyone knows a reliable source that I can find that information?
I currently looked up on Google, and it says to be 35 ksi, but I am not sure that it is the value that I want. Feel free to correct me if I am wrong!
Are we supposed to find the shear stress and shear strain in addition to the normal stress and axial strain, or just the normal stress and axial strain? I'm confused because the problem statement simply says to find the "stress and strain"
from reading the question my to go to strategy would be to calculate stress and strain for each rod member using relevant formulas, considering their diameters. Then, compare stresses with material's yield stress to determine failure or compute the factor of safety.
In (b), we just need to calculate FS and compare it to 1 right? If it is bigger than 1 then it is safe
Yes, as long as the FOS is greater than one the bar will not "yield"
you can calculate it by taking (Allowable Stress/working stress)
where allowable is relevant to the material used and working is your largest stress which is member 1 in this problem
For this problem, because section BC has the highest force and smallest cross sectional area, BC is the only one you need to check for the Factor of Safety right?
For this problem, I would make sure the values you get after converting are Young's Modulus is 10000 ksi and yield strength is 40 ksi. Also, I would start by using the piece that has the smallet safety factor.