When the shaft is subjected to pure bending moment (M b), the bending stresses are given by:.When the shaft is subjected to axial tensile force (P), the tensile stress is given by:.The design of transmission shaft consists of determining the correct shaft diameter from strength and rigidity criterion.Transmission shafts are often subjected to axial tensile force, bending moment or torsional moment or their combinations.
These loads may be axial loads, bending loads or/and torsional shear loads etc. Mechanical members are generally subjected to more than one kind of loads at a time.bending couples) in such a way that magnitude of bending moment remains constant throughout the length of the beam.īending equation: The following equation is known as bending equation. Bending Stresses in BeamsĪ beam or a member is said to be under pure bending when it is subjected to two equal and opposite couples in a plane along the longitudinal axis of the beam (i.e. The expression GJ is called torsional rigidity of the shaft. Rigidity criteria: The rigidity criteria uses the last two terms of torsion equation and design is done on the basis that maximum angular twist must exceed a certain value. Strength Criteria: The strength criteria uses the first two terms of torsion equation and design is done on basis that stress induced in the shaft must not exceed the strength of material of shaft. The torsional shear stress is maximum at the outer surface while it is zero at the centroidal axis.ĭesign of shaft: The design of the shaft can be done on the basis of two criteria which are explained below:.A component subjected to the two equal and opposite couples acting in parallel planes, is called under torsion and the internal stresses produced to resist the applied stresses are called torsional shear stresses.The designer expects that the applied stress on the component will not go beyound allowable stress under normal operating conditions. The allowable stress is the actual stress value considered for determining the dimensions of the component during the design phase. Thus, it is obtained by considering a suitable factor of safety (FOS). Shear Stress: If the external force on a component in applied in such a way that it tends to slide the adjacent planes relative to each other, then resulting stresses induced are called shear stresses.įig.1: Shear failure of mechanical memberįactor of safety (FOS): It should be kept in mind while designing a component that it should have sufficient excessive strength to prevent any failure due to the accident. Orthotropic Material: Exhibits different elastic properties in orthogonal directions at a given point. Anisotropic Material: Exhibit direction dependent elastic property. Isotropic Material: Same elastic properties in any direction at a given point. Homogenous material: Same elastic properties at any point in a given directions. If σ yield ≤ σ induced ≤ σ ultimate, then yielding will occur without any failure.If σ induced ≤ σ ultimate, then fracture will not occur.If σ induced ≤ σ yield, then yielding, then yielding (permanent deformation) will not occur.Strength is defined as the maximum or limiting value of stress that a material can withstand without any failure or fracture.Stress: Stress is defined as an intensity or magnitude of an internal resisting force developed at a point under given load. Modes of failure: A mechanical component failure may be result of any one of the following failure modes: Static load: A static load is gradually applied to a mechanical component whose magnitude or direction are independent of the time.
0 kommentar(er)
