## Stress / Strain

Stress is expressed as force per unit area. As this suggests, it is simply the intensity of the internally distributed forces that resist a change in the shape of a material that is being, or has been, subjected to external forces. The factors which we have to bear in mind here are the intensity of the force distributed over the area, the location of the stress, and the material's internal resistance to the applied load.

The two most common stress considerations are:

Average Normal Stress Under an Axial Loading

σavg = F

A

Where F is the normal force across the area and A is the normal area.

Average Shear Stress

τavg = Fs

A

Where Fs is shear force and A is shear area.

Stress and Strain are linear as proven by Hooke's Law

Stress =σ=constant=E

Strain ε

Poisson's Ratio is used to calculate linear strain

υ= -Lateral Strain

Axial Strain

The more brittle, the lower the number e.g ceramics 0.2, rubber 0.5.

## Torsion

Torsion is the term given to the twising of a component due to torque being applied.

Torsion formula

T = GΦ = τ

J L R

T= Torque, J= Polar moment of inertia, G= Shear modulus, Φ= Angle of twist, L= Length of shaft, T= Torson shear stress, R= Radius of shaft

## Elasticity

Young's Modulus of Elasticity- Young's Modulus is the E in Hooke's Law

Young's features in Hooke's Law as the Proportional Limit.

Elasticity: Anisotropic 21, Monoclinic 13, Orthotropic 9, Transversely Isotropic 5, Cubic 3, Isotropic 2

## Density

Density = Mass

Volume

## Ultimate Tensile Strength

Tmin x a = stensile

Take the minimum tensile strength of the ASTM Grade and multiply by the stress area of the cross section of piece.

## Hardness

Young's Modulus of Elasticity- Young's Modulus is the E in Hooke's Law

Young's features in Hooke's Law as the Proportional Limit.

Elasticity: Anisotropic 21, Monoclinic 13, Orthotropic 9, Transversely Isotropic 5, Cubic 3, Isotropic 2

## Ease of Joining

Young's Modulus of Elasticity- Young's Modulus is the E in Hooke's Law

Young's features in Hooke's Law as the Proportional Limit.

Elasticity: Anisotropic 21, Monoclinic 13, Orthotropic 9, Transversely Isotropic 5, Cubic 3, Isotropic 2

## Yield Strength

Ymin x a = syield

Take the minimum yield in psi of the ASTM Grade and multiply by the stress area of the specific cross section of the piece.

## Corrosion Resistance

Young's Modulus of Elasticity- Young's Modulus is the E in Hooke's Law

Young's features in Hooke's Law as the Proportional Limit.

## Machinability

Young's Modulus of Elasticity- Young's Modulus is the E in Hooke's Law

Young's features in Hooke's Law as the Proportional Limit.

## Rigidity

The relationship between shear stress and strain in all three directions is denoted thusly:

τxx = GYxy

τyz = GYyz

τzx = GYzx

"G"= Modulus of rigidity

## Wear Resistance

Young's Modulus of Elasticity- Young's Modulus is the E in Hooke's Law

Young's features in Hooke's Law as the Proportional Limit.

## Ductility

Young's Modulus of Elasticity- Young's Modulus is the E in Hooke's Law

Young's features in Hooke's Law as the Proportional Limit.

## Weldability

Young's Modulus of Elasticity- Young's Modulus is the E in Hooke's Law

Young's features in Hooke's Law as the Proportional Limit.

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#### Aeronautical materials

## materials selection

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## Formability

Young's Modulus of Elasticity- Young's Modulus is the E in Hooke's Law

Young's features in Hooke's Law as the Proportional Limit.