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Impact strength

Impact strength is an ability of the material to absorb mechanical energy in the course of deformation and destruction under the influence of impact loading. The main difference of impact loadings from tests on stretching/compression or bending is much higher speed of energy release. Thus, impact strength characterizes capability of a material to fast energy absorption.

Work before destruction or breaking of a tested sample at impact loading related to the area of its section in loading point is usually estimated. It is expressed in J/cm² or in kJ/m². Impact strength is designated by KCV, KCU, KCT. KC is the symbol of impact strength, the third symbol specifies a cut: sharp (V), with a curve radius (U), a crack (T).

The existing laboratory methods differ in:
– a way of fixing a sample at the test bench;
– a way of application of loading: falling weight, pendulum, hammer, etc.;
– presence or lack of a cut in the impact point.

For a "without cut" test a sheet of material with equal thickness in the entire area is chosen. When carrying out a "with cut" test a groove is made on a sheet surface, as a rule, on a side reverse in relation to the impact point, along all width (length) of a sample, at 1/2 thickness in depth. Impact strength at a "without cut" test can much more exceed results at a "with cut" test.

Among widespread methods of impact resistance tests we should specify the following ones:
– Charpy tests;
– Gardner tests;
– Izod tests.

Comparison of polyamides by impact strength