Flash sintering uses a combination of heating and electric fields to rapidly densify ceramics. Previously, it has been shown that a scanning laser can be used to initiate flash sintering in localized regions on an yttria-stabilized zirconia (YSZ) sample in a process known as selective laser flash sintering (SLFS). In this work, we show using a combination of measurements of electric current flowing through the sample and observations of necks formed between powder particles that aluminum nitride (AlN) can also undergo SLFS. Scan conditions required to initiate SLFS are characterized over a range of laser powers and laser scan speeds in a dry nitrogen environment. It is shown that initiation of SLFS in AlN is governed by both the local input energy density per scan and heat dissipation and a numerical model is developed to predict temperatures during SLFS. Assuming the minimum temperature along the conductive path determines the onset of SLFS, the minimum temperature and time required is 450-670 K in 2-0.25 s for the pressed AlN pellets used in this study for laser scan speeds of 33-300 m/s, laser powers of 10-30 W, and an applied electric field of 3000 V/cm.

Fiber Bragg gratings (FBGs) have numerous advantages over traditional foil strain gages, most notably in that they can be embedded in host materials and used to evaluate local deformation. Among the wide variety of grating architectures that have been studied, FBGs inscribed in polarization-maintaining (PM) or other birefringent fibers provide a unique, quantifiable response to strain transverse to the fiber axis. In this work, we show that a PM FBG can accurately predict the asymmetry in transverse strain of a host material in embedded configurations. We do this by diametrically loading an epoxy cylinder that has a uniform PM FBG embedded in the center. We use elasticity and finite element modeling (FEM) to correlate the mechanical response of an embedded fiber with that of the host. An analytical solution of the nominal relationship between Bragg wavelength and strain is included for this loading condition.

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