A cohesive fatigue-crack nucleation and growth model for
ferroelectric materials under electro-mechanical loading is
presented. The central feature of the model is a hysteretic
cohesive law which couples the mechanical and electrical fields.
This law can be used in conjunction with general constitutive
relations of bulk behavior, possibly including domain switching,
in order to predict fatigue crack growth under arbitrary loading
conditions. Another appealing feature of the model is its ability
to predict fatigue-crack nucleation. Despite the scarcity and
uncertainty of the experimental data, comparisons with PZT
fatigue-life data are encouraging.
A model for the Scanning Laser Source (SLS) technique is
presented. The SLS is a novel laser based inspection method for
the ultrasonic detection of small surface-breaking cracks. The
generated ultrasonic signal is monitored as a line-focused laser
is scanned over the defect. Characteristic changes in the
amplitude and the frequency content are observed. The modelling
approach is based on the decomposition of the field generated by
the laser in a cracked two-dimensional half-space, by virtue of
linear superposition, into the incident and the scattered fields.
The incident field is that generated by laser illumination of a
defect-free half-space. A thermoelastic model has been used which
takes account of the effect of thermal diffusion, as well as the
finite width and duration of the laser source. The scattered field
incorporates the interactions of the incident field with the
surface-breaking crack. It has been analyzed numerically by a
direct frequency domain boundary element method. A comparison with
an experiment for a large defect shows that the model captures the
observed phenomena.
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