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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].
For the thin-walled assumption to be valid, the vessel must have a wall thickness of no more than about one-tenth (often cited as Diameter / t > 20) of its radius. [4] This allows for treating the wall as a surface, and subsequently using the Young–Laplace equation for estimating the hoop stress created by an internal pressure on a thin-walled cylindrical pressure vessel:
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 polar second moment of area appears in the formulae that describe torsional stress and angular displacement. Torsional stresses: = where is the torsional shear stress, is the applied torque, is the distance from the central axis, and is the polar second moment of area.
The ordinary stress is then reduced to a scalar (tension or compression of the bar), but one must take into account also a bending stress (that tries to change the bar's curvature, in some direction perpendicular to the axis) and a torsional stress (that tries to twist or un-twist it about its axis).
• The behavior of bodies under stress • Analytical, numerical, and experimental methods • Tension, compression, shear, and combined stress • Beams and curved beams • Torsion, flat plates, and columns • Shells of revolution, pressure vessels, and pipes • Bodies under direct pressure and shear stress • Elastic stability
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. For the special case of unconstrained uniaxial tension or compression, Young's modulus can be thought of as a measure of the stiffness of a structure.
The classic formula for determining the bending stress in a beam under simple bending is: [5] ... 1st torsional: ... Pipe bending; Shear and moment diagram ...