Wedge Calculations

[Poveydesign]

Hi Guys,

Wondering if someone on here can help me I'm trying to calculate some wedge forces for 2 wedges acting together and the resultant force that comes from the rear of the top wedge. This is for an expanding item. I have attached a sketch which may make more sense.

Thank you in advance

Ian

 

[Jboggs]

Homework not allowed.

 

[Poveydesign]

Hi Jboggs, thank you for the reply however it is not a productive one. This isn’t homework it’s something I’m trying to calculate for work.
Do you know how to do this?

 

[3DDave]

We have to assume that all friction is dynamic friction as a start. For certain if this was homework that should have been a given.

One problem is that, by specifying the 300 kN (little k, capital N for Isaac Newton) is that unless there is an exact balance the mass will be accelerated upwards, assuming the 300 kN is high enough not to slip backwards. Also, kg is not a force; it needs to be multiplied by G (~9.81 m/sec^2 near the surface of the Earth) to produce the force.

The side force is just the force required to push the weight up the 25º hill with the given amounts of friction on the upper wedge. I think it will require an iterative solution to make a guess, starting with the sideways force that would happen if friction was zero.

If the 300 kN is not enough to cause it to move then the side force could be zero.

 

[IRstuff]

Hah, 3D, it should be little "g", big "G" is reserved by sparkies and physicists for Gauss. ;-)

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[Poveydesign]

Hi 3dDave,

Thank you for the info, to explain a little further which may help.
In the practical application I pull on the bottom wedge using a hydraulic cylinder in the 300kN direction, this moves and pushes the top wedge up, in order to control the movement it pushes against the plate highlighted by the vertical line on the wide side of the top wedge. I’m trying to work out how strong this plate needs to be, in my mind it doesn’t see a lot of force but I’m unsure how to calculate it.

Thank you

 

[3DDave]

It should be g-sub-c, but I forget which forums have subscript. and g/G was clear enough for the solution space.

 

[3DDave]

Here's a walkthrough of what looks to be a very similar problem:

https://www.youtube.com/watch?v=-EPcwWLgQ7A

https://www.youtube.com/watch?v=4kxOnBJ9tgI

Note that the force applied to the lower wedge is derived, not given. The main difference is you have 3 different friction coefficients, so need to adjust the normal angles by different amounts accordingly.