If you’ve ever felt this way after reviewing a material data sheet, then this next Impact Plastics Blog series focused on “Understanding your Data Sheet” is for you. In this next blog series we will explore ASTM tests commonly found on material data sheets for thermoplastic resins. Our last post discussed density and specific gravity – now we move onto another commonly encountered specification – Impact Resistance. Continue reading to learn more!
One of the ASTM test methods for plastic commonly seen on data sheets is a test for impact resistance. This test is often seen with the designation ASTM D256 and is referred to as “Notched Izod Impact Strength.” The use of this test can be a quick and easy quality control check to determine if a material complies with certain impact requirements or to compare toughness from material to material. A material’s toughness is a factor of its ability to absorb energy during plastic deformation. Brittle materials, for example, have low toughness as a result of the minimal amount of deformation they can endure. Impact toughness of a given material can also be impacted by temperature changes – in general, impact toughness decreases the lower the temperature gets.
To conduct this test, the notched specimen is clamped into the pendulum impact test fixture with the notched side of the specimen facing the
The energy absorbed by the specimen during breakage is known as the breaking energy, and the results are expressed in energy lost per unit of thickness at the notch (ft-lb or J/cm), or as energy lost per unit cross-sectional area at the notch (J/m^2 or ft-lb/in^2), indicating a given material’s impact resistance. ASTM D256 requirements dictate that a minimum of five individual data points be collected to determine the average impact resistance for a particular material. The higher the value the tougher the material.
Since many thermoplastic materials exhibit lower impact strength at reduced temperatures, this test is often conducted at lower temperatures to simulate the intended end-use environment of the material. To conduct this test at low temperatures, the specimens are conditioned at the specified temperature in a freezer, quickly removed, and impacted one at a time.
Do you have a packaging project that requires some guidance on materials? Visit our website and learn more about our materials or get in touch with our sales team today!