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impact strength[′im‚pakt ‚streŋkth]
the ability of a material to absorb mechanical energy in the process of deformation and fracture under impact loading. The term “impact strength, ” as well as the term “impact energy, ” is also applied to the amount of energy absorbed before fracture.
To determine impact strength, a bending impact test is commonly used. The specimen in this case has a prismatic bar shape, and a transverse notch is cut in one side of the specimen. The impact strength is regarded as the work required for the fracture of the specimen. In the USSR the work is generally referred to the cross-sectional area of the specimen at the base of the notch and is expressed in joules per square meter, newton-meters per square meter, or kilogram-force-meters per square centimeter.
Impact strength is one of the most important strength characteristics of a metal. When the test temperature is lowered over a series of tests, a sharp drop in impact strength indicates the brittle temperature of the material. Reliable performance of the material is possible only at temperatures above the brittle temperature.
In another type of bending impact test that is sometimes used, a small fatigue crack is produced in advance at the base of the notch; the crack is 1.5 mm in length. In this case a measurement is made of the specific work required for fracture of the specimen. Compared with the impact strength as measured in the first type of test described, the impact strength measured in this way provides a more sensitive characterization of the brittleness of high-strength materials. (See alsoMECHANICAL PROPERTIES OF MATERIALS.)
S. I. KISHKINA