Forces/Moments on Complex Beam System

In summary, I am having a lot of trouble getting my head around this small part of my project, and would appreciate any help I can get.
  • #1
Graham1874
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To give a bit of context, I am doing my final year university project on micro-mechanical interactions between an AFM probe and a sample surface. I do not have notes for a system this complicated, as we always considered our systems to be rigid bodies. I was always relatively clueless at mechanics so this particular small part of my project is a nightmare for me!

I have labelled the Free Body Diagram attached, but the following information should help to explain further:

Section A has a downwards-vertical displacement being applied, and can be considered a rigid body, fixed in all other DOFs.
A key feature of this system is the bending cantilever beam (Section B as marked in FBD).
It begins with an angle of 13 degrees from the horizontal axis, the inclined beam can be seen on the image FBD.
Section C (probe tip) can also be assumed to be a rigid body.
Section D is the sample surface which can be assumed rigid and fixed in all DOFs.

How do I get to the solution for finding Fz/Fy components and moments on the sample surface from the probe tip?

I have not given values for the system because I want to use the help provided to work through it myself.

As I say, this is a relative nightmare for me and I don't really know where to start, so all help will be greatly appreciated.

I'm sure I'll need to provide more information to helpers, so these will be answered in EDITS below.
 

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  • #2
The diagram looks a bit odd because you show a straight and bent version of the beam yet A is in the same place. In consequence, the angle at which B joins A seems to change. I assume that is not the case.
You show Fy. Is there friction to be taken into account at the probe? If not, there will be no Fy; if there is it is going to complicate matters.
 
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  • #3
haruspex said:
The diagram looks a bit odd because you show a straight and bent version of the beam yet A is in the same place. In consequence, the angle at which B joins A seems to change. I assume that is not the case.
You show Fy. Is there friction to be taken into account at the probe? If not, there will be no Fy; if there is it is going to complicate matters.

Hi haruspex,

You're right, my diagram is incorrect with respect to the illustrated bending section. Linked to this, I am not sure if the probe tip will move in the negative y-direction (horizontal) to accommodate for the horizontal component of the length being decreased due to the bending? If this question doesn't make sense then please let me know and I will try to clarify.

With regards to your question about friction: I am still questioning whether friction shall be taken into account. I want to study the system in static equilibrium, so I think that friction might need to be included, otherwise the beam would straighten itself by moving the probe tip (Section C) in the positive y-direction as Section A is displaced downwards (unless my intuition is incorrect?).

I should add, I posted this question in the Homework forum and Nidum is kindly trying to help me so would you be inclined to join the discussion there? Might be best to finish the clarifications here before moving to the other thread. However, it is here for your interest: https://www.physicsforums.com/threa...al-eng-forces-moments-on-complex-beam.883145/

Thanks for you reply! I would appreciate any further input, or if you have any other questions then please feel free to ask.
 
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FAQ: Forces/Moments on Complex Beam System

1. What are the different types of forces on a complex beam system?

The different types of forces on a complex beam system include:

  • Point forces: These forces are applied at a single point on the beam and have a specific magnitude and direction.
  • Distributed forces: These forces are spread out along the length of the beam and have a varying magnitude and direction.
  • Concentrated moments: These moments are applied at a single point on the beam and cause rotational motion.
  • Distributed moments: These moments are spread out along the length of the beam and cause varying amounts of rotational motion.

2. How do you calculate the maximum bending moment on a complex beam system?

The maximum bending moment on a complex beam system can be calculated by using the equation Mmax = PL/4, where P is the maximum point load applied to the beam and L is the length of the beam.

3. What is the difference between a shear force and a bending moment?

A shear force is a force that is applied parallel to the cross-section of the beam, causing it to shear or slide. A bending moment is a moment that is applied perpendicular to the cross-section of the beam, causing it to bend or flex.

4. How do you determine the reactions at the supports of a complex beam system?

To determine the reactions at the supports of a complex beam system, you must first draw a free body diagram of the beam. Then, you can use the equations of equilibrium (sum of forces and sum of moments) to solve for the reactions at the supports.

5. What is the use of moment of inertia in analyzing complex beam systems?

Moment of inertia is a property of a beam that represents its resistance to bending. It is used to calculate the bending stress and deflection of the beam under various loading conditions. In complex beam systems, moment of inertia is especially important in determining the stability and strength of the structure.

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