Understanding Internal Moments in Mechanics of Materials

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SUMMARY

The discussion clarifies the treatment of internal moments in mechanics of materials, specifically when analyzing elemental cubes or planar squares. It establishes that internal moments are not omitted due to cancellation but rather because they are a resultant of a distributed continuum of forces acting on the cut face. By representing these forces as a distribution rather than as a resultant, one can effectively simplify the analysis of normal, shear, and moment stresses.

PREREQUISITES
  • Understanding of normal stress and shear stress in mechanics of materials
  • Familiarity with the concept of internal moments in structural analysis
  • Knowledge of distributed forces and their effects on structural elements
  • Basic principles of frame-machine analysis
NEXT STEPS
  • Research the concept of distributed forces in mechanics of materials
  • Study the role of internal moments in structural analysis
  • Explore methods for simplifying stress analysis in elemental cubes
  • Learn about the application of shear and moment diagrams in frame-machine analysis
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Students and professionals in mechanical engineering, structural engineering, and materials science who are looking to deepen their understanding of stress analysis and internal moments in mechanics of materials.

Cyrus
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In mechanics of materials we often look at elemental cubes or planar squares, and we write the normal stress and shear stress acting on the faces. Why are the internal moments acting on each face omited? When we cut a frame-machine, we include a shear, normal and moment, why not for the elemental cube/plane?

I figured it out, someone please delete this pointless dribble.
 
Last edited:
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will it be because the internal moments cancel off each other?
 
No, the internal moment is actually a resultant of a distributed contiuum of forces acting along the face where the cut is made. So you can effectively get rid of the internal moment by drawing a distribution of the contiuum, as opposed to a resultant normal, shear and moment. Its just looking at the normal, shear and moment in a different light.
 

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