DOE OSTI2013
When considering alternate test methods for assessing the tensile performance of insensitive plastic bonded explosive (PBX) materials, Brazil disc tensile testing is attractive from several standpoints. First, compared to the traditional dog-bone shaped specimen normally used in the direct tensile test, the Brazil test specimen is considerably easier to produce. Second, the Brazil specimen is compact, with a low aspect ratio that allows it to be machined from a wide variety of pressed geometries. Assuming test results are consistent and interpretable, the method could open up possibilities for rapid assessment of ultimate tensile strengths, and might be especially attractive when a large number of samples are to be tested. The trade-off for specimen simplicity is, however, that interpretation of the results from Brazil tests is inherently far less intuitive, and more difficult, than is the case with traditional tensile testing, since the method involves complex stress loading. As a result, the derivation of what one hopes are equivalent tensile failure stresses from Brazil testing necessitates some fairly involved calculations, requiring parameters that are not always readily obtained. In addition to some significant uncertainties, the specimen geometry does not lend itself easily to the accommodation of traditional strain measurement devices such as extensometers. As a consequence, optical techniques such as digital image correlation (DIC) are preferred when stress-strain curves are needed. In this test series we performed a sequence of experiments using Brazil discs made from LX-17-1. Tests were performed on samples at two different scaled sizes: discs that were 0.5 inches in diameter and 0.25 inch thick, and discs that were 1 inch in diameter and a 0.5 inch thick. Each of the specimen sets was tested using matching, equivalently scaled test fixtures, each with anvils whose radii were 0.25% greater than their respective specimen radii. All specimens tested were machined from billet pressed material made from Holston #851009 (LLNL tag #C-329) LX-17-1 molding powder. Tests were performed at two temperatures, +23 °C and +50 °C, with three each test redundancies at each condition. Based on data from this set of experiments we hoped to provide preliminary answers to a number of questions, including: 1) Roughly, what is the level of scatter in the data? 2) Are results scale independent, at least within the limited range of specimen sizes tested? 3) Using a consistent set of parameters, can we use the equations given by Sato and Awaji1 to calculate peak tensile stresses that are nearly equivalent to those measured using traditional dog-bone tensile testing methods.
45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗