Drop weight and dynamic tear tests are widely used in the steel industry to determine material characteristics such as fracture resistance, transition temperature ranges and suitability of use of a steel for a specific application. During these tests the specimens are cooled or heated over a range of temperatures in order to determine the highest temperatures at which the sample fractures. Below this Nil Ductility Transition Temperature (NDTT) the material will consistently fracture, but above the material does not.
The American Petroleum Institute (API) 5L test standard is used to determine the fracture ductility of metal line pipe. Specimens are cut from sections of pipe, soaked at a prescribed temperature and tested within 10 seconds. ASTM E 436, similar to API 5L, is used to establish the temperature range over which ferritic steels will undergo a fracture mode transition from ductile to brittle. In both standards a determination regarding ductile to brittle behavior is based upon visual inspection of the specimens in conjunction with, at times, a calculation to determine the percentage of shear seen the materials fracture.
Dynamic tear tests, performed according to ASTM E 604, provide a measurement of the amount of energy absorbed during the fracture process of a “pre-cracked” specimen. The objective of the test is similar to the tests outlined above; however the measurement of energy eliminates some of the subjectivity of the other tests. With an actual numerical output from the test, levels of acceptance specified by the end users of the steels in critical applications can be defined.
For this test, we used a Dynatup® Model 8150 Drop Weight Impact System, instrumented with a Model 8340, 1,000 kN tup, 1.0 inch radius (for ASTM E 436 and API 5L) or 0.5 inch radius (for ASTM E 604) tup insert, and Impulse™ Data Acquisition system. Fixtures designed in accordance to the test standards were used to support the specimens. We tested all specimens at room temperature.
Each specimen was centered on the anvils with the point of impact being directly above the cut notch. We maximized the crosshead to ensure sufficient energy to break the specimens with a single impact
The Model 8150 impact testing system is well suited for providing both a simple uninstrumented test, as well as a fully instrumented testing system. The impact resistance information gathered by doing instrumented testing can be used by Research and Development to evaluate the effects of metallurgical variables such as composition, processing, heat treatment can have on the dynamic fracture resistance of new or existing materials. Test results may also be used to indicate particular steel’s suitability for use in a specific application.