Practice Questions

Poisson's ratio for aluminum is 0.31-0.34. It is the ratio of transverse strain to longitudinal strain and ranges from 0.0 to 0.5 for most materials. A value of 0.5 indicates a perfectly incompressible material.

The modulus of rigidity has the same unit as stress, pressure, and modulus of elasticity. Elastic modulus (E) is the ratio of stress and strain, while rigidity modulus (G) is the ratio of shear stress and shear strain. Stress is the force applied to a certain cross-sectional area, and pressure is the force applied perpendicular to the surface of an object per unit area. The unit for all of these is N/m² or Pascal.

Stress, pressure and modulus of elasticity

Brittle materials fail in torsion at a 45° plane forming an angle with the longitudinal axis due to their weak tensile strength. Ductile materials fail in torsion due to principle shear stress, with the failure plane perpendicular to the longitudinal axis. Brittle materials fail in compression due to shear at a 45° plane from the axis, while ductile materials fail in tension due to shear at a 45° plane forming cup and cone failure. In compression yielding, short compression members fail in compression with a failure plane at 90° to the compressive load.

Along a plane perpendicular to its longitudinal axis

Along the longitudinal direction of the member

Along surface forming 45° angle with the longitudinal axis

Poisson's ratio is the ratio of transverse strain to longitudinal strain. Stainless steel: 0.30-0.31, Steel: 0.27-0.30, Cast iron:0.21-0.26, Cork: 0.0, Rubber: 0.5.

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