Clash-Berg Modulus - ASTM D1043
The torsional stiffness of a material under specified conditions. Clash-Berg Modulus is also known as the apparent shear modulus, G, of a material.
Rectangular specimens are subjected to a longitudinal torque sufficient to cause a deflection of 5 to 100° (10 to 100° for non-rigid materials).
The Clash-Berg Modulus is calculated using specimen geometry, applied torque, and deflection angle using the equation:
G = (917TL) / (ab³uφ)
where a is the specimen width (larger cross-section dimension), b is the thickness (smaller cross-section dimension), L is the specimen length, T is the applied torque, u is a factor depending on the ratio of a to b, and φ is the deflection angle.
The factor u is calculated using:
u = 5.33 - [(3.6 b/a)(1 - (b4/12a4))]