Tasdiqlayman“Chet tiilar” kafedras imudiri M. B. Ganikhanova

Impact Properties

In some designs, dynamic forces are likely to cause failure. For example an

alloy may be hard and have high compressive strength and yet be unable to

withstand a sharp blow. In particular, low-carbon steels are susceptible to brittle failure at certain temperatures. Most impact tests use a calibrated hammer to strike a notched or unnotched test specimen. In the former, the test result is strongly dependent on the base of the notch, where there is a large concentration of triaxial stresses that produce a fracture with little plastic flow. The impact test is particularly sensitive to internal stress producers such as inclusions, flake graphite, second phases, and internal cracks.

The results from an impact test are not easily expressed in terms of design

requirements because it is not possible to determine the triaxial stress conditions at the notch. There also seems to be no general agreement of the interpretation or

significance of the result. Nonetheless the impact test has proved especially useful in defining the temperature at which steel changes from brittle to ductile behavior.

Low-carbon steels are particularly susceptible to brittle failure in a cold environment such as the North Atlantic. There were cases of Liberty ships of World War II vintage splitting in two as a result of brittle behavior when traveling in heavy seas during the winter.