Tests on Polymers: Hardness Test
Hardness is the resistance of a material against scratch and plastic deformation. There is no unit of measurement for hardness.
As a general rule, the hardness measurement method is intended to deform the material with a harder material than itself. The less the resulting deformation is, the higher the hardness of the material is. The hardness value is calculated by dividing the vertical force applied to the material by the area on which it acts on the material surface. Calculation is made by conducting the hardness test with loads applied at 3 different points in case the material area has no homogeneous properties.
Due to the difficulty in achieving a permanent deformation in polymer materials, the hardness value is calculated with the penetration value while the load continues to be applied and while the hardness is measured.
The Shore hardness value is used to measure the hardness of polymer materials. Shore-A and Shore-D scales are usually used to measure the hardness of polymers, elastomers, rubbers, fabrics an sponges.
Using the Shore-A method, the hardness of soft materials, such as elastomer, vinyl, rubber, rubber, leather, PVC, silicone rubber, teflon and neoprene, is usually measured, and
SUsing the Shore-D method, the hardness of more rigid materials, such as polyester, ABS, nylon, polyurethane, polyamide, kevlar, acrylic, wood and polystyrene, is measured. The Shore-D method is used to measure the hardness of engineering plastics.
The hardness value of very rigid polymers is measured by the Rockwell hardness method. This method is carried out by applying various loads between 15 and 150 kg through diamond conical or steel ball tips of various diameters on the material and then the hardness is calculated over the depth of the trace formed on the material. Every 1 μm change along the depth of the resulting trace corresponds to approximately 2 Rockwell values. For this reason, the depth measurement system should be very precise.