- #1
sumit saurav
- 6
- 0
what is shear stress?what is its direction?
Chestermiller said:Suppose you have a surface, and an force acting obliquely on that surface. The stress vector is the force per unit area of the surface. The shear stress is the component of the stress vector in the direction tangent to the surface. This is also the same as the stress vector minus the normal component of the stress vector. Clearly, the shear stress has direction.
I don't know where you and Shyan learned mechanics, but based on a PhD in fluid mechanics and over 50 years of real world working experience in solid- and fluid mechanics, I can assure you that both normal stress and shear stress acting on a surface have direction. Of course, as with any vector, the magnitude of a vector is a scalar. Maybe that's what you are thinking of.TumblingDice said:The force vector has a direction. Shear stress is a scalar as Shyan indicated - the force per unit area - measured for example in psi. Just as with normal stress, there's no direction on shear stress.
Chestermiller said:I don't know where you and Shyan learned mechanics, but based on a PhD in fluid mechanics and over 50 years of real world working experience in solid- and fluid mechanics, I can assure you that both normal stress and shear stress acting on a surface have direction. Of course, as with any vector, the magnitude of a vector is a scalar. Maybe that's what you are thinking of.
Normal and shear stresses are simply the components of the traction vector that are normal and parallel to the area's surface as shown in the figure. Using n for the unit normal vector to the surface, and s for the unit vector parallel to it, means that
σ=T⋅n and τ=T⋅s
It's very important to recognize that σ and τ here are each scalar values, not full tensors. This is the natural result of the dot product operations involving T, n, and s. (Dot products produce scalar results.)
I can see why you have been confused. The write-up in Wiki is very confusing, and this does a disservice to students like yourself who are seeking clarity. The quantities σ and τ that they refer to are the magnitudes of the normal stress and shear stress components of the traction vector. In terms of the unit normal vector [itex]\vec{n}[/itex] and the unit vector in the tangential direction [itex]\vec{s}[/itex] (whatever direction that happens to be) to the surface, the traction vector [itex]\vec{T}[/itex] is represented as:TumblingDice said:Chester, I use topics at PF to continue learning and try to help, too. I'm thankful for more experienced members like yourself who keep the information in check. The information I wrote was based on my understanding of the shear stress wiki that Shyan linked to in post #4. I've searched further and found this:
I clipped the above from http://www.continuummechanics.org/cm/tractionvector.html
I'd like to understand better and correctly. Is this a misunderstanding of the information, or specifics of terminology, or something more?
You specify the orientation a surface by specifying the components of a unit normal to the surface.sumit saurav said:wait what should i take as direction of surface?
Shear stress is a type of stress that occurs when two surfaces slide or move against each other in opposite directions. It is caused by a force applied parallel to the surface.
Shear stress is different from other types of stress, such as tension or compression, because it acts in a parallel direction to the surface instead of perpendicular. Shear stress can also cause deformation or failure in the material, whereas tension and compression typically cause elongation or compression.
Shear stress is typically measured in units of force per area, such as newtons per square meter (N/m²) or pounds per square inch (psi).
The direction of shear stress is determined by the direction of the applied force. If the force is applied in a clockwise direction, the shear stress will act in a counterclockwise direction and vice versa.
Shear stress can be seen in many everyday situations, such as when a person cuts through a piece of paper with scissors, when a car turns around a corner, or when a strong wind blows against a building. It is also an important factor in the design and stability of structures, such as bridges and buildings.