Influence of Specimen Design in Plane Strain Fracture Toughness Testing

Abstract

The influence of specimen design on plane strain fracture toughness (KIc) was studied by fracturing 2219-T87 aluminum and 5Al-2.5Sn ELI titanium alloy single-edge notched bend (SENB), single-edge notched tension (SENT), compact tension (CT), and surface flawed (SF) specimens at 72 F (295 K) in laboratory air, at -320 F (78 K) in liquid nitrogen, and at -423 F (20 K) in liquid hydrogen. Specimen thickness for all SENB, SENT, and CT specimens except titanium/room air specimens was approximately 2.5(KIc/σys)2 in. Specimen thickness for SF specimens ranged from 2.5(KIc/σys)2 to 0.25(KIc/σys)2. Relative orientations of crack propagation and rolling directions were identical in all specimens of a given alloy. For aluminum alloy specimens having thicknesses of 2.5(KIc/σys)2, SENB, SENT, and SF specimen tests yielded consistent fracture toughness values at all test temperatures whereas CT specimen tests always yielded lower fracture toughness. For titanium alloy specimens having thicknesses of 2.5(KIc/σys)2, SENB, SENT, CT, and SF specimen tests yielded consistent fracture toughness values at -423 F (20 K); at -320 F (78 K), fracture toughness values from SF specimen tests were significantly greater than those obtained from tests of other specimen types; at 72 F (295 K) no valid fracture toughness data were obtained. Both aluminum alloy SF specimen tests yielded consistent fracture toughness (KIE) values when both flaw depth and distance between flaw tip and back specimen face exceeded 0.5(KIE/σys)2.

Rapid Inexpensive Tests for Determining Fracture Toughness

“…Apparently, onl y one set of tests was conducted to compare K IE and K iṽ alues for a single crack propagation direction (Hall , 1971). Sing le-edge notched bend (SENB), single-edge notched tension (SENT), compact (CT), and surface-flaw specimens were cut from either one 2.…”

“…Tests of each specimen type were conducted at 72° F, -320° F and -423° F in air , liquid nitrogen , and liquid hydrogen , respectively. Results of the aluminum alloy tests are plotted on graphs of fracture toughness versus test temperature in Figure C FIGURE C-19 Test Results for 22 19-T87 Aluminum Alloy (Hall , 1971).…”