A small question regarding force/stress/area

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Discussion Overview

The discussion revolves around the application of force to a curved surface, specifically addressing how to calculate stress when a force is applied via a pin to a u-shaped hole. The scope includes theoretical considerations and practical implications in engineering contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Tina inquires whether the process for calculating stress remains the same for a curved surface as it does for a flat surface, specifically asking about the method for determining the area.
  • One participant suggests that a sketch and additional details about the orientation and dimensions of the surfaces involved are necessary for a clearer understanding.
  • Tina provides a sketch and mentions the diameter of the pin, indicating that assumptions may need to be made due to limited information.
  • Another participant notes that the stress at the contact area between the pin and the hole is complex, suggesting an approximation for compressive stress if the sizes are similar.
  • It is mentioned that the hole must be larger than the pin for a cold fit, leading to a theoretical line load scenario, and that yield strength can help determine a lower bound on the contact area.
  • A participant points out that while engineers often calculate stress using projected area, this assumption may not accurately reflect the actual stress distribution due to bending of the pin.
  • Different types of stress, including tensile, bearing, and shear stress, are highlighted as important considerations in the analysis of the problem.

Areas of Agreement / Disagreement

Participants express differing views on the appropriate method for calculating stress in this scenario, with no consensus reached on the best approach or the implications of the assumptions involved.

Contextual Notes

Participants acknowledge the need for assumptions due to limited information and the complexity of stress distribution in the context of the pin and hole interaction.

tina-duncan
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Hello friends, I have a small query regarding a force being applied to a surface...

I have a force of 0.1MN which is being applied in the -y direction onto a surface.
Now I know that if said surface was flat, I would divide the force by the area to give me the stress.

However the force is being applied to a curved surface (a u shape).
Is the process the same?
Do I just simply calculate the area of that surface or is there another procedure involved?

Many thanks,
Tina
 
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This needs a sketch and a description of how the force is applied. Does 'flat' mean horizontal, vertical or sloping? Does 'u-shape' mean 2-dimensional or 3-dimensional?
 
My apologies. Here is a rather crude sketch of the problem.
2lbiyxz.png


The load acting on the hole is supplied by a pin of diameter 0.0195m.

This is all the information that is given to me, so assumptions may have to be made I would imagine...
 
The stress on the contact area between pin and u hole is complex. If the pin and hole are of approximately equal size, an approximation can be used you could calculate your compressive stress as F/A with the area being .02x.01
If the pin is much smaller than the hole, I'll see if I can find the equation.
 
The hole has to be larger than the pin if it is to be fitted cold. Therefore the actual contact is theoretically a line load with no thickness. However, if you know the yield strength of the pin you can work out the lower bound on the contact area from that. However, this is a very common problem and most engineers calculate the stress as load/ projected area (as DTM has suggested). In assessing strength they will be using experimental data using the same nominal assumption of projected area, even though it is known to be false. There are other complications: To get the load into the pin from outside the object illustrated, the pin has to bend a little, throwing most of the stress to the edges of the hole (in a way that is indeterminate) rather than uniformly distributed as is usually assumed.
 
There are 3 diffrent types of stress you should consider for the plate: tensile, bearing, and shear stress (tear out). DTM describes the bearing stress of the bolt acting on the plate. Tear out should be fine if you follow the standards, but it's good to check anyway.
 

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