Resolved Shear Stress VS General Shear Stress -Contradiction?

In summary: Both equations are derived from mechanics of materials principles in Chapters 6 and 7 of the textbook Materials Science and Engineering: An Introduction by William D. Callister. In summary, the resolved shear stress equation is specific to a certain orientation, while the equation for shear stress in general applies to any orientation.
  • #1
ltkach2015
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1
TERMS:
Slip Plane: is the plane that has the densest atomic packing—that is, has the greatest planar density.
Slip Direction: corresponds to the direction in this plane that is most closely packed with atoms—that is, has the highest linear density.

NOMENCLATURE:
θ = angle of the slip plane as measured from cross section of material
λ = angle of that the applied force makes with the slip direction
φ = it has been said that is the angle between the normal vector and the applied force
θ = angle of the slip plane as measured from the cross section of the material
φ = θ =?; would this be so?
[A][/o] = Area of the materials cross section
A = Area of the slip plane

ASSUMPTIONS:
-uniaxial tensile stress of a material with moderate ductility
-quasi-staticQUESTION:
Can you show the relationship between shear stress for a typical uniaxial tensile stress (mechanics of materials) to the resolved shear stress geometrically?

It is derived from mechanics of materials principles in Chapter 6 that shear stress is τ = σsinθcosθ. Following that chapter 7 introduces resolved shear stress τ=σcosλcosφ.

I can do both derivations but I cannot relate the two.ATTEMPT:

1) Derivation of Resolved Shear Stress

-ensure that slip direction lies on slip plane via dot product of the normal vector of the slip plane and the slip direction == 0 (orthogonal)

-Load in direction of slip direction:
V = σcosλ

-The shear stress is that load across its surface area:
τ=σcosλ/A;
Ao = Acosθ
=> A = Ao/cosθ

-The Shear Stress
τ = V/A
=> τ=σcosλcosφ.2) Derivation of Shear Stress in General:

I know how to derive via a force balance (equations of equilibrium) that gave the following result:

=> τ = σsinθcosθ
SO:
is it true that τ=σcosλcosφ == τ = σsinθcosθ

END.

TEXTBOOK: Materials Science and Engineering: An Introduction: William D. Callister. Chapter 6 & 7.
Thank you!

 

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  • #2
No, these two equations are not the same. The resolved shear stress equation (τ=σcosλcosφ) is derived for a specific case where the slip direction and slip plane are orthogonal to each other. The equation for shear stress in general (τ = σsinθcosθ) applies to any orientation of the slip plane and slip direction.
 

1. What is the difference between resolved shear stress and general shear stress?

Resolved shear stress refers to the component of shear stress acting in a specific direction, often perpendicular to a surface. General shear stress, on the other hand, refers to the overall shear stress acting on a material regardless of direction.

2. Are resolved shear stress and general shear stress contradictory concepts?

No, they are not contradictory. Resolved shear stress is a specific component of general shear stress. Think of it as a piece of a larger puzzle - they work together to describe the overall stress on a material.

3. When is it more appropriate to use resolved shear stress versus general shear stress?

The use of resolved shear stress or general shear stress depends on the specific application and context. Resolved shear stress may be more useful when analyzing the behavior of materials in specific directions, while general shear stress may provide a more comprehensive understanding of overall stress on a material.

4. How do resolved shear stress and general shear stress affect material properties?

Both resolved shear stress and general shear stress can cause deformation and failure of materials. The magnitude and direction of these stresses can affect the strength, ductility, and other mechanical properties of a material.

5. What are some practical applications of understanding resolved shear stress and general shear stress?

Understanding these concepts is essential in engineering and materials science, as they can help predict the behavior of materials under different types of stress. This knowledge is used to design and improve structures and materials, such as buildings, bridges, and aircraft, to withstand the forces they may encounter.

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