Design a Mounting Bracket for 100kg Steel to Aluminum Plate

[HaveVun]

Homework Statement

I have to create a design to mount a steel (yield=250MPa) weight 100kg and thickness of 15 mm to aluminum plate (Yield = 100MPa) with a tap hole of 15mm in vertical direction with 6 of M6 screws.

Homework Equations

σ (bearing load) =F/A
τ (shear load) = F/A

The Attempt at a Solution

Assuming that the force came from the weight of the steel (1000N)
I treated this problem as a rivet joint
Bearing on bolt = 1000/(6*15*6) = 1.85 MPa
Bearing on aluminum plate = 1000/(6*15*6) = 1.85MPa
Shear on Bolt (on the thread) = 1000/(6*(phi*6^2)/4) = 0.59 MPa

If you look at the calculation, the stress is 100 times smaller than the material properties of the aluminum and steel. This is a very big safety factor. Does that mean I can hang a weight of 100kg with just 1 screw of M1 and still have a safety factor more than 1?? I do not see this make sense. Please advise on how to approach this.

 

[KataKoniK]

Hi there,

First of all, great job on your calculations and approach to this problem! You are correct in treating this as a rivet joint, and your calculations for bearing and shear stress are correct.

However, there are a few things to consider when designing a mounting for a weight of 100kg. First, the safety factor should not be based solely on the yield strength of the materials involved. Other factors such as the environment (temperature, humidity, etc.) and potential dynamic loads (vibrations, movement, etc.) should also be taken into account.

Secondly, the number and size of screws needed for the mounting will depend on the distribution of the weight and the forces acting on the mounting. For example, if the weight is not evenly distributed, you may need more screws to evenly distribute the load and prevent any potential failure points.

Lastly, it is always better to err on the side of caution and use a larger safety factor when designing a mounting for a heavy weight. This will ensure that the mounting can withstand any unforeseen loads or changes in the environment.

In conclusion, while your calculations show that the proposed design can technically support the weight of 100kg, it is important to consider other factors and use a larger safety factor to ensure the stability and longevity of the mounting. I suggest consulting with a structural engineer for a more thorough and accurate design. Hope this helps!