Excerpt from The Influence of Crack Length and Thickness in Plane Strain Fracture Toughness Tests The geometric conditions investigated using bend specimens are summarized in table II. The basic test program was confined to specimens tempered at 750 F (672 K). About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.

Results are presented from a systematic investigation of the influence of crack length and specimen thickness on the fracture properties of 4340 steel bend specimens heat treated to yield strength levels between 180 and 213 ksi. It is shown that KIc values determined in accordance with the present ASTM Tenative Method of Test for Plane Strain Fracture Toughness of Metallic Materials (E 399-70T) can vary moderately within the specimen size and geometric limitations imposed by the Test Method. The magnitude of these variations will depend on the material properties and would be increased by relaxation of the size requirements.

A test program has been conducted to determine the influence of geometrical variables on the ability of the notch bend and single-edge-notch tensile tests to measure valid plane strain fracture toughness value. Data were obtained on 2024-T851 aluminum, D6AC steel heat treated to yield strength values of 208 and 247 ksi, and 6A1-4V titanium. The results indicated that in the bend test four-point loading produced more reproducible values than three-point loading. Fracture toughness values were valid when the major span length-to-width ratio was equal to or greater than four and the crack length-to-width ratio was between 0.20 and 0.40. The single-edge-notch produced less variability than the notch bend test and in general, the point at which the onset of slow crack growth occurred was more easily defined. Valid fracture toughness values were obtained using the existing calibration curves in specimens where the crack length-to-specimen width ratio was between 0.20 and 0.40. (Author).