PLANE STRAIN FRACTURE TOUGHNESS AND MECHANICAL PROPERTIES OF 5A1-2.5SN ELI TITANIUM AT ROOM AND CRYOGENIC TEMPERATURES

The suitability of 5Al-2.5Sn ELI titanium alloy for cryogenic tankage applications was studied by determining the mechanical and fracture properties of the material at testing temperatures ranging from room temperature to -423F. Small round tensile specimens were developed to measure the tensile properties over the range of testing temperatures. Plane strain fracture toughness measurements were also made at these temperatures using the 'pop-in' technique with a small notched bend specimen. Special laboratory techniques were developed to test the specimens at -423F, utilizing the specific heat of vaporization of liquid helium. The degree of preferred orientation in this alloy was qualitatively studied by determining the ratio of the width strain to the thickness strain. The fracture toughness values were interpreted in terms of the crystallography and mechanism of deformation of titanium. The data are summarized in terms of a part-through defect which will be stable at various operating temperatures and stress levels. It has been shown that texture hardening may be used to obtain high burst stresses under biaxial stress conditions. (Author)