Izod impact test, fracture resistance

The impact strength is a measure of the energy needed to break a sample. The term toughness is sometimes used to describe the impact strength of a material. The notched izod impact test is a single point test that measures the resistance of a material to impact from a swinging pendulum. Izod impact is defined as the kinetic energy needed to initiate fracture and continue the fracture until the speci-... 

Keywords instrumented impact test, Charpy test, Izod test, fracture resistance, striker, strain gages, dynamic testing... 

Impact resistance n. ( ) Ability of a coating to resist a sudden blow. Ability to resist deformation from impact. (2) The relative durability of plastics article to fracture under stresses apphed at high speeds. A widely used ASTM impact test, www.astm.org, employs the Izod pendulum striker swung from a fixed height to strike a specimen in the form of a notched bar mounted vertically as a cantilever beam. The Charpy tester, an alternative in D 256, uses a specimen in the form of a horizontal beam supported at both ends. ASTM lists some several different impact tests for plastics and plastics products. 

Standardized notched impact tests such as the Izod and Charpy tests (ASTM, ISO, DIN) are the most commonly used to characterize the impact strength of plastic materials. It is very difficult to use measured data from tests using idealized laboratory specimens to predict impact behavior of end-use polymeric material. The apparent lack of good correlation between measured impact fracture energy and end-use impact resistance is due to the extreme complexity of microscopic fracture processes. In particular, the influence of specimen geometry is sometimes poorly matched with the type of failure mechanism of defects present in the actual molded part subjected to end-use impact forces. 

Two quantities can be measured to describe a material s resistance to crack propagation fracture toughness, IQ, and strain energy release rate, G. Different stress states can be applied, with the most common being the opening mode (Mode I). Materials can also be tested in inplane shear (Mode n) and in torsional shear (Mode III). Testing in these modes typically involves strain rates much lower than those associated with impact teste such as the Charpy and Izod methods. Other methods... 

---