Location

La Jolla, CA

Start Date

1-1-1998 12:00 AM

Description

There are numerous nondestructive inspection methods which can be used to detect and quantitatively characterize advanced fatigue damage following crack initiation. However, crack nucleation occurs at a much smaller microstructural scale following a more or less extended period of gradual material degradation which remains beyond the reach of known eddy current, ultrasonic, and other inspection methods. Before crack initiation, fatigue degradation remains an elusive process leading to distributed crystal defects on the scale of individual grains and grain boundary imperfections. This gradual evolution of early fatigue damage first results in increasing dislocation density, formation of slip bands, microplasticity, cold work, etc., then leads to crack nucleation at multiple sites. Following crack nucleation the growing microcracks ultimately coalesce into larger detectable fatigue cracks, but current NDE methods cannot detect the often quite serious preexisting fatigue damage in the material before this point.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

17B

Chapter

Chapter 6: Materials Characterization

Section

Fracture and Cracks

Pages

1573-1580

DOI

10.1007/978-1-4615-5339-7_204

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Thermo-Electric Detection of Early Fatigue Damage in Metals

La Jolla, CA

There are numerous nondestructive inspection methods which can be used to detect and quantitatively characterize advanced fatigue damage following crack initiation. However, crack nucleation occurs at a much smaller microstructural scale following a more or less extended period of gradual material degradation which remains beyond the reach of known eddy current, ultrasonic, and other inspection methods. Before crack initiation, fatigue degradation remains an elusive process leading to distributed crystal defects on the scale of individual grains and grain boundary imperfections. This gradual evolution of early fatigue damage first results in increasing dislocation density, formation of slip bands, microplasticity, cold work, etc., then leads to crack nucleation at multiple sites. Following crack nucleation the growing microcracks ultimately coalesce into larger detectable fatigue cracks, but current NDE methods cannot detect the often quite serious preexisting fatigue damage in the material before this point.