Skjuvmodul

Skjuvmodul, or shear modulus, is a material property that describes how resistant a material is to shape changes when subjected to shear. It is defined as the ratio of shear stress to shear strain in the elastic regime, expressed as G = τ/γ. The unit is the pascal (Pa), with practical values often given in gigapascals (GPa). For isotropic, linear-elastic materials, the shear modulus relates to Young’s modulus E and Poisson’s ratio ν by G = E / [2(1 + ν)].

Physically, skjuvmodul characterizes resistance to distortion without a change in volume. It is distinct from Young’s modulus, which describes elongation or compression under normal stresses. The modulus can vary with temperature, frequency of loading, and material microstructure, and it may differ along different crystallographic directions in anisotropic materials.

Measurement methods include torsion tests on cylindrical specimens, direct shear tests, biaxial shear tests, and dynamic mechanical analysis. In geophysics and materials science, resonant and indirect methods are also used. For many polymers, G can span orders of magnitude and is highly temperature-dependent; metals typically have high, relatively temperature-insensitive G values; ceramics are stiff but brittle. Rubber and other elastomers have much lower G values, varying with strain and frequency.

Applications and significance: skjuvmodul is a key input in elastic strength and wave-propagation calculations. In seismology, the shear modulus determines shear-wave velocity v_s = sqrt(G/ρ). Designers use G to predict deflections, natural frequencies, and stability of structures and components under shear loading.