Characterization of metal fatigue by optical second harmonic generation

摘要

The optical second harmonic response of a pre-fatigued titanium specimen to picosecond 800 nm pulses has been investigated. Polarization-dependent measurements show that the zxx component of the nonlinear susceptibility tensor χ~((2)) differs markedly when measured in a region of unfatigued polycrystalline titanium compared to the plastic deformation zone ahead of a crack tip and even changes the sign within the plastic wake. This tensor component is sensitive to bulk currents, and we attribute the observed changes to a changed density of states at the Fermi level, caused by the accumulation of dislocations. Second harmonic polarization analysis could thus be useful in non-invasive fatigue analysis.