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BALL INDENTATION TESTS AND THE GRAIN STRUCTURE OF LEAD.
BROWN UNIV PROVIDENCE RI DIV OF ENGINEERING
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An investigation of the connection between the appearance of hilling around ball indentations incast lead and the relationship between the ball indentation pressure and the uniaxial stress behavior of lead reveals a strong influence of grain orientation. Both static and dynamic tests were conducted on lead specimens, and a careful correlation was made between Tabors indentation constant C and the microstructure of the metal. Experiments conducted by other investigators had established the value of Tabors constant at approximately 2.8. Such tests, however, were confined to essentially isotropic and homogeneous metal speciemns. Present results indicate substantially higher values of the indentation constant for surfaces of polycrystalline lead of either columnar or oriented grain structure, but significantly lower values for less oriented grain structures. Furthermore, tests of single crystals of lead gave values of Tabors constant ranging from 2.3 to 5.5, depending on the orientation, with the smallest value resulting from indentations of a 111 or principal slip surface. However, static tests of randomly oriented polycrystalline lead gave a value of 2.9, very near the values obtained by other investigators and predicted on a theoretical basis for isotropic homogeneous materials. Author
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