Vendors and companies involved in 3D printing/Additive manufacturing continuously introduce new materials suitable for these machines. These materials offer a range of characteristics fitting to a design.  We’re going to examine a material’s flexibility/stiffness under load, otherwise wise known as its elastic modulus or Young’s modulus.  (As an aside, a modulus is literally a “measure.” Young’s modulus is a specific measure of the ratio of tensile stress to tensile strain. It is differentiated from the elastic modulus because there are a number of ways to measure elasticity).

Young’s modulus is a way to determine how stiff or how flexible a material is, and how readily it will return to its original shape when a load is removed. A stiff material is considered to have a high modulus of elasticity.  A flexible material is considered to have a low modulus.

The equation for Young’s modulus is:

E = σ / ε = (F/A) / (ΔL/L0) = FL0 / AΔL

Where:

E is Young’s modulus, usually expressed in Pascal (Pa)

σ is the uniaxial stress

ε is the strain

F is the force of compression or extension

A is the cross-sectional surface area or the cross-section perpendicular to the applied force

Δ L is the change in length (negative under compression; positive when stretched)

L0 is the original length

Even though the SI unit for Young’s modulus is Pa, values can be expressed as megapascal (MPa), Newtons per square millimeter (N/mm2), gigapascals (GPa), or kilonewtons per square millimeter (kN/mm2). The usual English unit is pounds per square inch (PSI) or mega PSI (Mpsi).

A consideration with Young’s modulus, especially with 3D printing involves the orientation of the part.  How you place a part on the 3D printer’s print bed (whether Z axis or X-Y axis), will affect the isotropic and anisotopic properties of the part. Isotropic materials show the same mechanical properties in all directions. Anisotropic materials show mechanical properties depending on whether force is loaded along the material’s grain or perpendicular to it. As many engineers discover, simply being aware of part orientation can instill isotropic properties to a design regardless of a materials stiffness or flexibility.