SEDL / STP / STP1329-EB / STP37997S

Developing Fracture Assessment Methods for Fusion Reactor Materials with Small Specimens

Odette, GR
Professor, University of California Santa Barbara, CA

Edsinger, K
Graduate Student or Former Graduate Student, University of California Santa Barbara, CA

Lucas, GE
Professor, University of California Santa Barbara, CA

Donahue, E
Graduate Student or Former Graduate Student, University of California Santa Barbara, CA

Pages: 30    Published: Jan 1998

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Abstract

Design and operation of fusion reactors will require a temperature-dependent effective toughness [K^e(T)] data base. Effective toughness is a function of intrinsic metallurgical/microstructural factors, degraded by irradiation, and extrinsic factors, such as size and geometry. Standard fracture mechanics is inadequate, since the presumption of geometrically independent crack tip stress/strain fields does not apply to either small specimens or in thin-walled structures with shallow cracks. More general approaches to measuring and applying K^e(T) data are described for cleavage initiation in steels and vanadium alloys. The critical stress-critical area (σ*/A*) mechanism of cleavage initiation is demonstrated using a confocal microscopy/fracture reconstruction method that can also directly measure K^e. The σ*/A* model is combined with finite element method (FEM) simulations of crack tip fields to: a) predict K^e(T) for F-82H as a function of size; and b) directly adjust K^e(T) data to a common test geometry. A simpler master curve-(temperature) shift method is also described. Changes in yield stress due to irradiation or strain rates can be related to the shifts. Indeed, tensile properties as a function of temperature, strain rate and alloy condition are required by all assessment methods. Physically-based small specimen methods will reduce enormously what would otherwise be a prohibitive amount of testing.