The Izod impact strength test is an

ASTM ASTM International, formerly known as American Society for Testing and Materials, is a standards organization that develops and publishes voluntary consensus technical international standards for a wide range of materials, products, systems and s ...

standard method of determining the impact resistance of materials. A pivoting arm is raised to a specific height (constant

potential energy In physics, potential energy is the energy of an object or system due to the body's position relative to other objects, or the configuration of its particles. The energy is equal to the work done against any restoring forces, such as gravity ...

) and then released. The arm swings down hitting a notched sample, breaking the specimen. The energy absorbed by the sample is calculated from the height the arm swings to after hitting the sample. A notched sample is generally used to determine impact energy and notch sensitivity. The test is similar to the

Charpy impact test In materials science, the Charpy impact test, also known as the Charpy V-notch test, is a standardized high strain rate test which determines the amount of energy absorbed by a material during fracture. Absorbed energy is a measure of the materi ...

but uses a different arrangement of the specimen under test. The Izod impact test differs from the Charpy impact test in that the sample is held in a cantilevered beam configuration as opposed to a three-point bending configuration. The test is named after the English engineer Edwin Gilbert Izod (1876–1946), who described it in his 1903 address to the

British Association The British Science Association (BSA) is a charity and learned society founded in 1831 to aid in the promotion and development of science. Until 2009 it was known as the British Association for the Advancement of Science (BA). The current Chief ...

, subsequently published in ''Engineering''.Izod, Gilbert, 'Testing brittleness of steel', ''Engineering'', 25 September 1903, pp. 431-2

The need for impact tests

Impact Impact may refer to: * Impact (mechanics), a large force or mechanical shock over a short period of time * Impact, Texas, a town in Taylor County, Texas, US Science and technology * Impact crater, a meteor crater caused by an impact event * Imp ...

, by definition, is a large force applied for a very short time, resulting in a sudden transfer of

momentum In Newtonian mechanics, momentum (: momenta or momentums; more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. ...

and energy, and its effect is different when the same amount of energy is transferred more gradually. Everyday engineering structures are subjected to it and may develop cracks that, over time, propagate to a point where catastrophic failure would result. Impact tests are used in comparing the shear

fracture toughness In materials science, fracture toughness is the critical stress intensity factor of a sharp Fracture, crack where propagation of the crack suddenly becomes rapid and unlimited. It is a material property that quantifies its ability to resist crac ...

of various materials under the same test conditions, or of one material versus temperature to determine its

ductile Ductility refers to the ability of a material to sustain significant plastic deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic deformation, which is reversi ...

-to-

brittle A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. ...

transition temperature where a steep descent in impact strength with decreasing temperature is observed. A material's toughness is a factor of its ability to absorb energy during relatively slow plastic deformation, though the rate at which strain occurs matters. Brittle materials have low toughness as a result of the small amount of plastic deformation they can endure at any rate. However, ductile materials may behave like brittle materials under high-energy impact, hence the need for this kind of test. The test conditions are governed by many variables, most importantly: * the dimensions of the usually rectangular cross section of the sample below the notch; * the height of the hammer at the start position, determining its velocity at impact; * the mass of the hammer which together with the velocity determines its kinetic energy at impact; * the sharpness, or tip curvature, of the notch; * the temperature of the sample.

ASTM test for plastics

The

ASTM International ASTM International, formerly known as American Society for Testing and Materials, is a standards organization that develops and publishes voluntary consensus technical international standards for a wide range of materials, products, systems and s ...

standard for Izod Impact testing of plastics is ASTM D256. The results are expressed in energy lost per unit of thickness (such as ft·lb/in or J/cm) at the notch. Alternatively, the results may be reported as energy lost per unit cross-sectional area at the notch (J/m or ft·lb/in). In Europe, ISO 180 methods are used and results are based only on the cross-sectional area at the notch (J/m). The dimensions of a standard specimen for ASTM D256 are 63.5 × 12.7 × 3.2 mm (2.5 × 0.5 × 0.125 in). The most common specimen thickness is , but the width can vary between .

The need for impact tests

ASTM test for plastics

See also

References

Further reading