Small punch testing for fracture toughness measurement. Final report

Technical Report · Thu Jun 01 04:00:00 EDT 1995

OSTI ID:108135

Foulds, J R; Woytowitz, P J; Parnell, T K ^[1]

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1. Failure Analysis Associates, Inc., Menlo Park, CA (United States); and others

The fracture toughness of the material of an operating power plant structural component affects the flaw tolerance of the component. A lower toughness implies a lower flaw tolerance, and generally results in an increased concern for component integrity and higher operation and maintenance costs. Often, the material fracture toughness is unknown because it was never specified or measured, or because service conditions have resulted in its degradation to an unknown extent. Examples of in- service degradation include temper embrittlement of steam turbine rotor low alloy steels exposed to elevated temperatures and neutron irradiation embrittlement of nuclear reactor pressure vessel steels. Conventional test methods for measuring toughness require the removal of large material samples from the in-service component, which is generally impractical. However, the recent development of miniature sample removal systems and the small punch test technique (which utilizes non-standard, miniature specimens of 0.5 mm or 0.020 in. thickness) now provides a convenient, practical, and virtually nondestructive means of evaluating the material of an in-service component for toughness and related mechanical properties. The small punch test method follows an approach that is based on the continuum material toughness concept wherein the criterion for fracture is defined and measured via the continuum stress-strain deformation properties of the material. The procedure specifically involves computing the {open_quotes}local{close_quotes} strain energy density accumulated at the location and time of crack initiation in the small punch test specimen using large-strain finite element analysis. Since the procedure also includes estimation of the material uniaxial tensile stress-strain behavior from the small punch load-displacement curve, both the fracture toughness and the uniaxial tensile behavior are determined from a single small punch test.

• Research Organization: Electric Power Research Inst., Palo Alto, CA (United States); Failure Analysis Associates, Inc., Menlo Park, CA (United States)
• Sponsoring Organization: Electric Power Research Inst., Palo Alto, CA (United States)
• OSTI ID: 108135
• Report Number(s): EPRI-TR--105130
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
44 INSTRUMENTATION
INCLUDING NUCLEAR AND PARTICLE DETECTORS
DEFORMATION
DESIGN
EMBRITTLEMENT
FRACTURE PROPERTIES
IRRADIATION
LOW ALLOY STEELS
MATERIALS TESTING
MECHANICAL PROPERTIES
PRESSURE VESSELS
PROGRESS REPORT
SAMPLERS
SAMPLING
STEAM TURBINES
STEELS
TEMPERATURE DEPENDENCE
TENSILE PROPERTIES
TRANSITION TEMPERATURE