Examination of the size effects and data scatter observed in small-specimen cleavage fracture toughness testing

Technical Report · Sun Apr 01 04:00:00 EST 1984

OSTI ID:5133079

Merkle, J G

In the transition range of temperature, the cleavage fracture toughness of steel rises steeply with temperature, often necessitating the use of elastic-plastic methods for calculating toughness values with small specimens. This usually leads to size effects, whereby measured toughness values increase with decreasing specimen size and data scatter becomes large. Existing literature pertaining to the physical aspects of the onset of cleavage fracture and the occurrence of size effects is examined, and it is concluded that the primary cause of size effects is loss of triaxial constraint due to crack-tip yielding and transverse contraction along the crack front. The implications of an existing semiempirical equation, known as the Irwin ..beta../sub Ic/ equation, for removing size effects from small-specimen cleavage fracture toughness data are examined by developing the equation based on reasonable assumptions, including the conditions specified by American Society for Testing and Materials (ASTM) Standard E399 for valid K/sub Ic/ testing. The applicability of the Irwin ..beta../sub Ic/ adjustment equation to pressure vessel steels is evaluated by applying it to several sets of small-specimen fracture toughness data, and it is found that the equation consistently eliminates apparent size effects and significantly reduces data scatter. The ..beta../sub Ic/ adjustment appears to be applicable to dynamic as well as to static initiation toughness data, but only to the cleavage fracture toughness and not to the ductile tearing resistance.

• Research Organization: Oak Ridge National Lab., TN (USA)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5133079
• Report Number(s): NUREG/CR-3672; ORNL/TM-9088; ON: DE84009697
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103 -- Metals & Alloys-- Mechanical Properties
42 ENGINEERING
420500* -- Engineering-- Materials Testing
ALLOYS
CONTAINERS
CRACKS
FRACTURE PROPERTIES
IRON ALLOYS
IRON BASE ALLOYS
MATERIALS TESTING
MECHANICAL PROPERTIES
PRESSURE VESSELS
SIZE
STEELS
TESTING