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Torsion of a square section bar Example of torsion mechanics. In the field of solid mechanics, torsion is the twisting of an object due to an applied torque [1] [2].Torsion could be defined as strain [3] [4] or angular deformation [5], and is measured by the angle a chosen section is rotated from its equilibrium position [6].
The torsion constant or torsion coefficient is a geometrical property of a bar's cross-section. It is involved in the relationship between angle of twist and applied torque along the axis of the bar, for a homogeneous linear elastic bar. The torsion constant, together with material properties and length, describes a bar's torsional stiffness.
The whirling frequency of a symmetric cross section of a given length between two points is given by: N = 94.251 E I m L 3 RPM {\displaystyle N=94.251{\sqrt {EI \over mL^{3}}}\ {\text{RPM}}} where: E = Young's modulus, I = second moment of area , m = mass of the shaft, L = length of the shaft between points.
Combining these two features with the length of the shaft, , one is able to calculate a shaft's angular deflection, , due to the applied torque, : = As shown, the larger the material's shear modulus and polar second moment of area (i.e. larger cross-sectional area), the greater resistance to torsional deflection.
This type of stress may be called (simple) normal stress or uniaxial stress; specifically, (uniaxial, simple, etc.) tensile stress. [13] If the load is compression on the bar, rather than stretching it, the analysis is the same except that the force F and the stress σ {\displaystyle \sigma } change sign, and the stress is called compressive ...
The following stresses are induced in the shafts. Shear stresses due to the transmission of torque (due to torsional load). Bending stresses (tensile or compressive) due to the forces acting upon the machine elements like gears and pulleys as well as the self weight of the shaft. Stresses due to combined torsional and bending loads.
Similarly, the torsional stiffness of a straight section is = where is the rigidity modulus of the material, is the torsion constant for the section. Note that the torsional stiffness has dimensions [force] * [length] / [angle], so that its SI units are N*m/rad.
Strain is the ratio of change in length to the original length, when a given body is subjected to some external force (Strain= change in length÷the original length). Stress analysis is a primary task for civil, mechanical and aerospace engineers involved in the design of structures of all sizes, such as tunnels, bridges and dams, aircraft and ...