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The concept of the ductility ratio was introduced by Gerard in 1961, as a quantitative measure of structural ductility useful design. An experimental technique for determining ductility ratio was established which involved the testing to failure of internally notched tension specimens containing a variety of stress concentration values, and this technique was applied in preliminary tests on high-strength aged beta titanium alloy. In the work reported here, more extensive test programs involving the all beta titanium alloy Ti-13V-11Cr-3Al in several thicknesses of sheet are described. The test materials were aged to give the highest strengths prior to testing. The paper presents the technique for performing the tests, the method of reducing the data, as well as giving the experimental results. The results of a literature survey of notch strength data from which ductility ratio values could be derived are also given, and from this survey the effect of decreasing the temperature in increasing the ductility ratio is demonstrated. The value of the ductility ratio varies from zero for a perfectly plastic material to unity for a perfectly brittle material. For the limited ductility alloys tested in the program the ductility ratio was in the range 0.1 to 0.2. There appeared to be a size effect evident with the thinnest sheet displaying the lowest ductility ratio values (highest ductility). The range of thicknesses tested was from 0.040 to 0.093 in. The test results lend additional experimental verification to the relation delineated by Gerard between the strength/weight ratio and the ductility ratio: σtu/ρ = 1.6 × 106 e1/6.
titanium alloys, ductility, structural ductility, elastic stress concentrations, strength, notch strength
Senior scientist, Allied Research Associates, Inc., Concord, Mass.