Final answer:
Shear strain can be expressed in Radians (rad), Degrees (°), or as a dimensionless quantity. Newtons per square meter (N/m²) is not used for strain, as it is the unit for stress.
Step-by-step explanation:
Units used to express shear strain include Radians (rad) and Degrees (°). Additionally, shear strain is commonly expressed as a dimensionless quantity. This is because shear strain is a ratio of the change in dimension to the original dimension, and this ratio does not have units.
Newton per square meter (N/m²) is relevant for expressing shear stress, not strain. Strain typically has no units because it is a measure of deformation (change in shape or size) relative to the original dimensions of the material and is thus represented as a pure number or in angles for shear strain.