TORSION TEST ON STRUCTURAL STEEL BASICS AND TUTORIALS

TORSION TEST ON STRUCTURAL STEEL BASIC INFORMATION
What Is Torsion Test Of Steel?


The torsion test (ASTM E143) is used to determine the shear modulus of structural materials. The shear modulus is used in the design of members subjected to torsion, such as rotating shafts and helical compression springs.

In this test a cylindrical, or tubular, specimen is loaded either incrementally or continually by applying an external torque to cause a uniform twist within the gauge length. The amount of applied torque and the corresponding angle of twist are measured throughout the test.


Below shows the shear stress–strain curve.


The shear modulus is the ratio of maximum shear stress to the corresponding shear strain below the proportional limit of the material, which is the slope of the straight line between R (a pretorque stress) and P (the proportional limit). For a circular cross section, the maximum shear stress shear strain and the shear modulus (G) are determined by the equations:



where

T = torque
r = radius

J = polarmoment of inertia of the specimen about its center, for a solid circular cross section.

0 = angle of twist in radians
L = gauge length



The test method is limited to materials and stresses at which creep is negligible compared with the strain produced immediately upon loading. The test specimen should be sound, without imperfections near the surface.

Also, the specimen should be straight and of uniform diameter for a length equal to the gauge length plus two to four diameters. The gauge length should be at least four diameters.

During the test, torque is read from a dial gauge or a readout device attached to the testing machine, while the angle of twist may be measured using a torsiometer fastened to the specimen at the two ends of the gauge length.

A curve-fitting procedure can be used to estimate the straight-line portion of the shear stress–strain relation.

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