ISSN: 0090-3973
Page Count: 8

A Method for Generating Fatigue Marker Bands Using a Constant K^max Test Procedure

Ragazzo, C
Research Assistant and New Jersey Zinc Professor,Lehigh University,PA,

Hertzberg, RW
Research Assistant and New Jersey Zinc Professor,Lehigh University,PA,

Jaccard, R
Head of Consulting and Supervision,Alusuisse, Lonza Services Ltd.,

(Received 18 April 1994; accepted 7 July 1994)

Abstract

Marker bands were introduced onto fatigue fracture surfaces by a block loading technique wherein K^max was held constant while K^min was varied. Materials examined included Astroloy nickelbase superalloy, 1020 hot-rolled steel. AC112-TL aluminum, and 2024-T3 aluminum. The use of a constant K^max test procedure allowed ΔK to be varied without affecting crack growth rates, thereby providing a convenient method for documenting the shape of a progressing flaw. The nature of contrast differences between marker bands generated at different ΔK levels were examined in terms of changes in fracture micromechanisms as well as changes in fracture surface roughness. Results indicate that a micromechanism transition from cleavage-like faceted growth at low ΔK to striated growth at intermediate ΔK was responsible for the major difference in fracture surface appearance.

Keywords:
constant Kmax, fatigue marker bands, micromechanism changes, contrast differences

Paper ID: JTE10394J
DOI: 10.1520/JTE10394J
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