NA meaning in Physics Related ?
Answer: What is Neutral Axis mean?
The neutral axis is an axis in the cross section of a beam (a member resisting bending) or shaft along which there are no longitudinal stresses or strains. If the section is symmetric, isotropic and is not curved before a bend occurs, then the neutral axis is at the geometric centroid. All fibers on one side of the neutral axis are in a state of tension, while those on the opposite side are in compression.
Since the beam is undergoing uniform bending, a plane on the beam remains plane. That is:
γ x y = γ z x = τ x y = τ x z = 0 {\displaystyle \gamma _{xy}=\gamma _{zx}=\tau _{xy}=\tau _{xz}=0}
Where γ {\displaystyle \gamma } is the shear strain and τ {\displaystyle \tau } is the shear stress
There is a compressive (negative) strain at the top of the beam, and a tensile (positive) strain at the bottom of the beam. Therefore by the Intermediate Value Theorem, there must be some point in between the top and the bottom that has no strain, since the strain in a beam is a continuous function.
Let L be the original length of the beam (span)
ε(y) is the strain as a function of coordinate on the face of the beam.
σ(y) is the stress as a function of coordinate on the face of the beam.
ρ is the radius of curvature of the beam at its neutral axis.
θ is the bend angle
Since the bending is uniform and pure, there is therefore at a distance y from the neutral axis with the inherent property of having no strain:
ϵ x ( y ) = L ( y ) − L L = θ ( ρ − y ) − θ ρ θ ρ = − y reference
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