Calculate Shear Stress for a Glued Solid Rod in .375 in. D Hole

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Discussion Overview

The discussion revolves around calculating the shear stress for a solid rod glued in a hole, specifically focusing on the geometry of the glued area and the forces applied until the glue bond shears. The scope includes homework-related calculations and technical reasoning regarding shear stress in adhesive bonds.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents a calculation for shear stress using the formula τ=F/A and provides observed values for force and calculated shear stress.
  • Another participant notes that the shear stress should depend on the area of the glued surface around the rod, suggesting that the length of the glued section is necessary for accurate calculations.
  • A different participant proposes a revised formula for shear stress that incorporates the width and height of the bond, indicating a need to adjust the initial approach.
  • Another participant challenges the previous calculations by emphasizing the importance of considering the inner surface area at the glue/rod interface and suggests visualizing the glue as a flat shape to determine the correct surface area for shear stress calculations.

Areas of Agreement / Disagreement

Participants express differing views on how to calculate the shear stress, particularly regarding the appropriate area to use in the calculations. There is no consensus on the correct method or formula to apply.

Contextual Notes

Participants mention the need for additional information, such as the length of the glued section, to accurately determine the shear stress. There are also references to the properties of different types of glue, which may affect the calculations.

Who May Find This Useful

This discussion may be useful for students or professionals interested in adhesive bonding, shear stress calculations, and the mechanics of materials in engineering contexts.

BigRedTruck
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Homework Statement


A Solid rod with .375 in. D sits glued in the hole with .38 in. D. There is glue only on the annulus of the rod. A force is applied to the back side of the rod until the glue bond is fully sheared and the rod falls out.

2wbwcon.jpg


Find the shear stress


Homework Equations



τ=F/A psi
Annulus A = π((D2/2)^2-(D1/2)^2) in^2
Force is observed values where the glue sheared in lbf

The Attempt at a Solution



Rod D Hole D Annulus A Force Shear
0.375 0.38 0.002964878 219.9 74168.31

Some other observed forces and calculated shear values
F tau
130.3 43947.84
71.61 24152.76
31.12 10496.22
52.06 17558.90


I don't have anyone around to check my numbers and these values seem really large
 
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The shear stress depends on the area of the glued surface around the rod, not the end area, You will need to be given the length of the glued section of the rod (the embedded depth or hole depth) to solve the problem by finding the surface area of the glue.

( If its super glue, it'll pull out pretty easily, because although it has pretty good tensile strength, it has rotten strength in shear)!:smile:
 
Ok so I need to change my stress formula to tau=Force/(width of the bond (D2-D1) * height of the bond)
in the first case it would be 219.9 lbf /(.005 in.*.27 in.)=162888.9 psi

I've been looking around most everything I've seen are lap joints
 
No, you are not taking the inner surface area at the glue/rod interface. Picture unwrapping the glue into a flat shape. The surface area is the rod circumference times the hole depth. Shear areas are parallel to the shear forces.
 

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