It is one of most important assumptions made in ory of simple bending that is modulus of elasticity that is Young?s modulus [E] is same in both tension and compression for material and stress in a beam do not exceed elastic limit.

In a simply supported beam, re is compressive stress above neutral axis and tensile stress below it. It bends with concavity upwards. Hence bending stress distribution is not uniform over section.

eV (volumetric strain) = 3× linear strain = 3×e
The volumetric strain is algebraic sum of all linear(or) axial strain when a solid to be subjected to equal normal sources of same type of all faces we will have ?x, ?y and ?z equal in value. In this case volumetric strain will be 3 times linear strain in any of three axes.

After reaching ultimate stress, stress strain curve suddenly falls with rapid increase in strain and specimen breaks. The stress corresponding to breaking point is known as breaking stress and it is denoted by G.

The strength of two beams of same material can be compared by section modulus values. The strength of beam depends on material, size and shape of cross section. The beam is stronger when section modulus is more, strength of beam depends on Z.

The product of modulus of rigidity (C) and polar moment of inertia (J) is called torsional rigidity and it produces a twist of one radian in a shaft of unit length.

The moment due to dead load in case of continuous beams at middle of interior spans is w L² / 24.

Principal stress is a magnitude of direct stress, across a principal plane which is a particular plane having no shear stress at all.

In a cantilever beam maximum compressive stress occurs at bottom most fibre and maximum tensile stress occurs at top most fibre and zero at neutral axis hence tensile stresses lies above neutral axis.

The product of young?s modulus (E) of material and moment of inertia (I) of beam section about its neutral axis is called flexural rigidity.
Units for E are N/m²
Units for I are m⁴
Their product is Nm².