Stress in a rod with a hole for pin-joint

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Discussion Overview

The discussion revolves around the stress distribution in a rod with a hole for a pin-joint, particularly focusing on the conditions of compression and tension in the rod and boom. Participants explore the implications of these conditions on the stress at the minimum area where the hole is located.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the section of the rod with a hole for the pin is stress-free when the rod is in compression, and how this changes if the rod is in tension.
  • Another participant suggests that understanding the net area at the cross section of the holes and the stress in the main body of the rod is crucial, and asks for clarification on the conditions of compression and tension.
  • A participant cites a statement from a textbook indicating that sections of minimum area at the holes are not under stress when the boom is in compression, leading to confusion about why this is the case compared to tension scenarios.
  • It is proposed that in tension, the pin pulls on the rod, creating tensile stress throughout, including at the hole, whereas in compression, the pin pushes on the boom, resulting in no stress from the inner edge to the end of the boom.

Areas of Agreement / Disagreement

Participants express differing views on the stress conditions at the minimum area of the rod with a hole, particularly regarding the effects of compression versus tension. The discussion remains unresolved with multiple competing interpretations of the stress behavior.

Contextual Notes

Participants highlight the importance of considering the net area and the specific mechanics of how forces are applied at the pin-joint, but there are unresolved assumptions regarding the definitions of stress-free conditions and the implications of the textbook statement.

Ali Baig
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If a rod is in compression, will the minimum area on rod ( the section where there is a hole for pin) stress free? What if the rod is in tension? The rod BC is in compression and the boom AB is in tension?

http://imgur.com/a/6asfB
 
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I don't understand what you mean by stress free, but you need to look at the cross section net area of the flat ends at the holes, as well as rod stress in main body and a bunch of other stuff. Please explain why you think the rod is in compression and the boom in tension. Is this a homework or study problem?
 
It was a solved example in book Mechanics of Materials 5th Ed. by Beer. I am sorry for including it as part of question. My main question is about a statement given in the book that says
..the sections of minimum area at A and B are not under stress, since the boom is in compression, and, therefore, pushes on the pins (instead of pulling on the pins as rod BC does).
I want to ask when a given rod or boom is in compression, why we don't consider stress at minimum area (area where there is a hole for pin) but we do consider stress at the minimum area if the rod/boom is in tension? I am not able to understand this statement.
 
Oh ok , the boom is in compression and the rod is in tension. For the tension case, the pin pulls on the rod from its outer edge at the contact point, causing tensile stress throughout the rod including at the cross section of the hole which is not stress free. For the compression case, the pin pushes on the boom from its inner edge at the contact point, thus there is no stress in the boom from that inner edge to the end of the boom.
 
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