What is the Modulus of Elasticity?
Definition: Modulus is the initial slope of the stress-strain curve. Modulus is the ratio of the applied stress to the change in shape of an elastic body (also known as elastic or Young’s modulus ).
Tension elongation testing is commonly used to find a material’s break tension and break elongation. However, the same test will also measure a material’s modulus of elasticity or Young’s modulus.
Modulus will have units of force per area, such at MPa or psi.
Example modulii: (1kpsi = 6.9 MPa)
| Material | Modulus (SI) | Modulus (American) |
|---|---|---|
| E(Steel) | 200 GPa | 30,000 kpsi |
| E(Aluminum) | 69 GPa | 10,000 kpsi |
| E(BOPET) | 3.5-5.5 GPa | 500-800 kpsi |
| Paper | 3.5-4.2 GPa | 500-600 kpsi |
| Polypropylene | 0.7-1.7 GPa | 100-250 kpsi |
| Polyethylene | 0.2-1.4 GPa | 25-200 kpsi |
Materials like steel and aluminum will require high stresses (load over area) to get even the smallest strain or elongation, but will yield at relatively low strains, if you can apply the stress to get them there.
Other webs are elastic over a large strain range.
Once you’ve reached a web’s elastic limit, it will no longer fully recover when unloaded. In web handling, the goal is almost always to handle the web below the elastic limit and avoid any permanent damage to the web.
