鉛フリーはんだにおけるモードIおよびII荷重条件下での疲労き裂進展

概要

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Crack propagation tests of lead-free solder were conducted using center-cracked plates (CCP) for tension-compression loading (mode I loading) and thin-walled tubular specimens for torsional loading (mode II loading). Both specimens have an initial slit as a crack starter. The path of crack propagation under mode I loading was macroscopically straight, and perpendicular to the maximum principal stress direction. In tubular specimens under mode II loading, at the high strain amplitude, the crack propagate in shear mode along the maximum shear direction. At low strain amplitude, four cracks are formed from the initial silt and propagate showing macroscopically tensile-mode propagation. The crack propagation rate is expressed as a power function of the J-integral range for both mode I and II loadings. The relation was not much different between mode I and II loadings. Fatigue crack propagation takes place by joining microcracks formed along the maximum shear planes ahead of the crack tip. At high strain ranges of mode II loading, microcracks ahead of the main crack tip were long and abundant, and their connection with the main crack gave rise shear-mode crack propagation.
2009-12-25