A couple questions regarding force and free body diagram

Click For Summary

Discussion Overview

The discussion revolves around questions related to force and free body diagrams, specifically focusing on the behavior of stress and strain graphs during compressive testing of materials and the proper construction of free body diagrams in a mechanical context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant notes that the shallow gradient in the stress and strain graph may be due to initial slack in the attachment of the compressive element to the testing machine.
  • Another participant questions the equilibrium of the free body diagram for segment AB, suggesting it is not correct, while stating that the diagram for segment BC appears accurate.
  • A participant expresses uncertainty about the forces and moments acting on segment 1, specifically questioning whether a bending moment could arise from the force Fcl.
  • There is a reminder that for segment 1 to be in equilibrium, all forces and moments must sum to zero, indicating that something may be missing in the participant's analysis.
  • Several participants suggest that the original poster should move their question to the homework section for potentially better responses.

Areas of Agreement / Disagreement

Participants express differing views on the correctness of the free body diagrams, with some asserting inaccuracies while others provide suggestions for improvement. The discussion regarding the shallow gradient in the stress-strain graph does not reach a consensus, as it remains an area of exploration.

Contextual Notes

There are unresolved assumptions regarding the setup of the compressive testing and the specific forces acting on the segments in the free body diagrams. The discussion does not clarify all necessary conditions for equilibrium in the diagrams presented.

Who May Find This Useful

Individuals interested in material testing, mechanics, and the construction of free body diagrams may find this discussion relevant.

Junkwisch
Messages
30
Reaction score
0
Hey guy, I would like to ask a few question about force and free body diagram.

First question, I conduct a compressive experiment a few day back, using compression machine to test the strength of different materials e.g., Aluminium, PVC and Ceramic. However there is one thing that I don't under stand in regards to this experiment. When the machine start working, the stress and strain graph somehow start up with a very shallow gradient instead of a straight linear gradient which one would expected for the elastic region (modulus of elasticity). This shallow gradient exists for all three experiments. I asked my lab adviser, which he hold me that this is normal. However, it still stuck me about where this shallow gradient come from... can anyone give me a clue for its existence.

The second question has something to do with a question I found on a textbook in regards to drawing a free body diagram. I'm a newbie at this and I'm not certain whether this is the right way to draw it. Can anyone give me a head up. (The question and my work out is in attach files)

Best Regards
Junkswischen
 

Attachments

  • 10013618_532860006831782_3022290809424675420_n.jpg
    10013618_532860006831782_3022290809424675420_n.jpg
    39.5 KB · Views: 591
  • 10173804_532860533498396_3172914506026644089_n.jpg
    10173804_532860533498396_3172914506026644089_n.jpg
    19.5 KB · Views: 581
Physics news on Phys.org
1) I assume that depending on how you attached the compressive element to the testing machine there was some initial slack to be taken up before the full compression load could be applied.

2) Your free body diagram for AB is not in equilibrium. The FBD for BC is looks right.
 
You should put it in the homework section of the forum. You will get better responses.
 
Ah, I see that make sense why the graph start out shallow.

For question 2, I thought the one that has a mistake in is segment 2. Is there any other force/moment involves in segment 1? I thought the only force acting on it will be Fcl and Fbc, could there be a bending moment caused by Fcl in segnment A?
 
In order for segment 1 to be in equilibrium you have to sum all the forces in both directions to zero and to sum the moments to zero. So you are missing something.
 
Seth.T said:
You should put it in the homework section of the forum. You will get better responses.

Moved. :smile:
 
  • Like
Likes   Reactions: 1 person
Berkeman, Kudos to keeping this forum neat :)!
 

Similar threads

Free body diagram for two-force members
  • · Replies 13 ·
Replies
13
Views
3K
Free body diagram of a preloaded system with a gasket
  • · Replies 2 ·
Replies
2
Views
2K
Engineering Should one include friction in this free-body diagram?
  • · Replies 3 ·
Replies
3
Views
2K
Why are moments not included in free body diagrams?
  • · Replies 31 ·
2
Replies
31
Views
2K
Undergrad Force Generated By Leg Muscles in Free Body Diagrams
  • · Replies 8 ·
Replies
8
Views
2K
Free body diagram from whole system-direction of forces in free-body d
  • · Replies 1 ·
Replies
1
Views
3K
Truss Free Body Diagram & initial conditions
  • · Replies 5 ·
Replies
5
Views
2K
Free body diagram of a beam construction
  • · Replies 3 ·
Replies
3
Views
2K
Potential Mistake in Free-Body Diagram
  • · Replies 5 ·
Replies
5
Views
2K
Free Body Diagram of Mass-Spring System
  • · Replies 5 ·
Replies
5
Views
2K