Crack Toughness Evaluation of Hot Pressed and Forged Beryllium

Abstract

AbstractFracture toughness tests at room temperature were made on three-point loaded beryllium bend specimens cut from hot pressed block and a forged disk. These specimens had plane proportions conforming to ASTM E 399 and covered a thickness range of from 1∕32 to ½-in. Two sets of bend specimens were tested, one having fatigue cracks and the other 0.5 mil radius notches. During each test, records were made of crack (or notch) mouth displacement and electric potential vs applied load. One objective of the investigation was the development of techniques to produce fatigue cracks in accordance with the procedures specified in ASTM E 399. This objective was achieved for the hot pressed material. In plane cracks were not consistently produced in the specimens cut from forged stock.Results of the fracture toughness tests showed that specimens with fatigue cracks had considerably lower values of Kmax than those with sharp machined notches. Various anomalies were observed in the behavior of the beryllium specimens from hot pressed stock. Among these were nonlinearities in the load-displacement records in what was expected to be the elastic range, negative crack mouth displacements on unloading from this range, and a decrease in electrical potential with increasing load which was recoverable on unloading. While valid KIc values could not be established, the data indicate that for practical purposes a value of about 10 ksi-in.½ would characterize both the hot pressed and the forged stock.