ASTM E143 Test for Shear Modulus at Room Temperature

Introduction

ASTM E143 is used to determine the shear modulus of structural materials. This test is limited to materials where creep is negligible compared to the strain produced immediately upon loading. Further, the standard values are in SI units.

Scope

ASTM E143 calculates the shear modulus of rigidity, which determines whether a structural material complies with torsion (torsion is the twisting of an object due to an applied torque). Shear modulus assists manufacturers in designing rotating shafts and helical compression springs. This test is for materials that exhibit linear elastic stress-strain behavior. The structural material must also obey Hooke’s law, meaning that the twist angle should be proportional to the applied torque. 

The tangent or chord shear modulus value helps technicians calculate the discontinuity between stress and strain for materials that follow nonlinear elastic stress-strain behavior. However, this is outside the scope of this ASTM E143 standard. 

Elastic properties such as Young’s modulus and Poisson’s ratio are not usually determined and are generally not specified in the material’s specification.

Test Procedure

The dimensions of the test specimen are measured according to ASTM E143. The cylindrical or tubular test specimen is aligned and loaded on the fixture. An external torque is applied to the specimen, twisting the gauge length (the part of the specimen that changes during the test). 

The applied torque and the corresponding changes in the twist angle are mapped out on a stress-strain curve. The appropriate slope is calculated from the shear stress-strain curve. The slope could be derived under conditions of either increasing or decreasing torque.

Specimen Size

The technicians should choose specimens made from good, clean material. Slight imperfections near the surface, which would have a negligible effect in determining Young’s modulus, cause significant errors in the shear modulus.  

The test specimen used in ASTM E143 testing should be circular, cylindrical, or tubular. In the case of solid cylinders, the specimen should be straight and of uniform diameter for a length equal to the gauge length plus two to four diameters. Tubes should be straight and have a uniform diameter and wall thickness for a length equal to the gauge length plus at least four outside diameters. The gauge length should be at least four times the diameter.

Advantages and Disadvantages of ASTM E143

The table below provides the advantages and disadvantages of ASTM E143:

Data

The following data is calculated in ASTM E143:

The shear modulus for the circular specimen is calculated by:

G=TL/Jθ

G = shear modulus of the specimen, 

T = torque, 

L = gauge length, 

J = polar moment of inertia of the section about its center and 

θ = angle of twist, in radians. 

For a solid cylinder:

D = diameter

For a tube:

D0 = outside diameter

Di = inside diameter. 

Result Analysis

ASTM E143 calculates the shear modulus, which determines whether a structural material complies with torsion (torsion is the twisting of an object due to an applied torque).

Conclusion

The test determines the structural strength of a material to compile against torsional force. Further, it provides the shear modulus of rigidity for specimens of various geometry. Thus, it helps the manufacturer to identify the flaws in their material’s structure and enhance its quality. Contact our material testing experts and get your material tested by international standards.

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