FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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ON THE RELATION BETWEEN ULTRASONIC ATTENUATION AND FRACTURE
TOUGHNESS IN TYPE 403 STAINLESS STEEL
F. Nadeau and J.-F. Bui.iie.-xe.
National Reieaicli Council o & Canada, Bouckexv itie, Quebec
G. Van Dianen
Atomic Eneigij oj Canada Limited
Chalk Rive-%] ' Ontaiio
ABSTRACT
Previous studies have indicated the possibility of using ultrasonic
attenuation as a nondestructive tool for predicting the fracture toughness of
metals. In all these studies, however, the fracture toughness was varied by
changing microstructure or composition. In the present paper, ultrasonic
attenuation is measured in a single sample of constant microstructure (type
403 stainless steel) in which fracture toughness is changed by nearly a factor
of three by varying the temperature. Results show that the frequency and
temperature dependence of attenuation are in agreement with conventional grain
scattering theory and do not correlate with the large changes in Kic. It is
concluded that one of the main difficulties of nondestructively characterizing
fracture toughness is that a small variation in one of the material's
properties, such as yield stress, can alter the fracture mechanism, leading to
very rapid changes in Kjc. In most cases, the modest change in yield stress
will be accompanied by similarly modest changes in attenuation, which do not
reflect the rapid changes in Kjc.
INTRODUCTION
As the ability to detect and characterize discrete defects in structures is
improved through the use of better nondestructive methods, more attention is
being focused on novel techniques for the determination of microstructure
'1' and mechanical properties (2). of particular interest is the
possibility of using ultrasonic measurements to determine engineering
mechanical properties such as tensile strength, yield strength, fracture
toughness and the ductile to brittle transition temperature (DBTT). Earlier
attempts in this area have been based on empirical relations between
ultrasonic velocity and yield (or tensile) strength in various steels and
iron-carbon alloys (3-5)t More recently, the bahavior of third-order
elastic constants was shown to correlate with the heat treatment history of
aluminum alloys ("'.
However, most attempts at characterizing microstructure and mechanical
properties ultrasonically have been based on measurements of attenuation.
Attenuation results from the combined effects of scattering, the reorientation
and mode conversion of acoustic energy at microstructural interfaces, and