Application of fracture mechanics principles to fatigue crack growth in a powder metallurgy Ni-base superalloy

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1985

OSTI ID:5774679

Vecchio, R S

The fatigue-crack propagation response of hot isostatically pressed (HIP) L.C. Astroloy was examined as a function of grain size, various loading parameters, crack configurations, and temperature. Results for material with average grain sizes ranging from 5 to 50 ..mu..m are presented. Long crack near threshold FCP behavior obtained using disc compact tension (DC(T)) specimens was found to be relatively insensitive to changes in grain size at a stress ratio of 0.1. Increasing the stress ratio to 0.5 revealed an increase in FCP rates with increasing grain size. Of greater significance, however, was the observation that crack growth rates in region I were highly sensitive to variations in specimen geometry. At a given stress intensity range, fatigue crack growth rates were observed to increase as the loading of a given geometry became more symmetric with respect to the crack plane. It is suggested that this phenomenon is related to differing near field crack tip stress distributions between specimen geometries and their interaction with the material's microstructure. Fatigue-crack-propagation rates at high cyclic frequency (30 Hz) were observed to increase at elevated temperatures. This increase is attributed primarily to reduced component stiffness associated with elevated-temperature exposure as well as changes in environmental sensitivity and variations in deformation mechanisms.

• Research Organization: Lehigh Univ., Bethlehem, PA (USA)
• OSTI ID: 5774679
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
ALUMINIUM ALLOYS
ASTROLOY
BORON ADDITIONS
BORON ALLOYS
CARBON ADDITIONS
CHROMIUM ALLOYS
COBALT ALLOYS
CRACK PROPAGATION
CRYSTAL STRUCTURE
FATIGUE
FRACTURE MECHANICS
GRAIN SIZE
HEAT RESISTANT MATERIALS
HEAT RESISTING ALLOYS
MATERIALS
MECHANICAL PROPERTIES
MECHANICS
MICROSTRUCTURE
MOLYBDENUM ALLOYS
NICKEL ALLOYS
NICKEL BASE ALLOYS
SIZE
TITANIUM ALLOYS