A novel cement composite containing graphene nanoplatelet (GNP) which can sense its own strain and damage is
introduced in this paper. Piezoresistive strain sensing was investigated for mortar specimens with GNP under both cyclic
and monotonically increasing compressive and tensile strain. Under compression, the electrical resistance decreased with
increasing strain and the normalized resistance can be described by a bilinear curve with a kink at about 400 microstrain.
At low strain, a high gauge factor exceeding 103 in magnitude was obtained and it increased almost linearly with the
GNP content. This can be attributed primarily to the reducing interfacial distance and forming of better contacts between
GNP and cement paste when the composite was initially loaded. At higher compressive strain beyond 400 microstrain,
the gauge factor is consistently about 102 for GNP content exceeding the percolation threshold. A different response was
observed for specimens under tension due to the formation and propagation of microcracks even at low tensile strain due
to the brittleness of the material. The initial gauge factor is of the order 102 for tensile strain up to 100 microstrain and it
increases exponentially beyond that. The damage self-sensing capability of this conductive cement composites is
explored using electric potential method. Closed form expression for the assessment of damage are derived based on the
mathematical analogy between the electrostatic field and the elastostatic field under anti-plane shear loading. The
derived expression provide a quick and accurate assessment of the damage of this conductive material which is
characterized by its change in compliance.
In this work, we demonstrate a monolithic approach to fabricate free-standing LiNbO3 photonic crystal (PhC) slabs. Ion implantation is first applied to form a buried lattice-damage layer at a specified depth in bulk LiNbO3. Photonic crystal slabs are then made with FIB milling followed by wet etching. A high etching rate of 100 nm/min for the implanted layer has been obtained. A vertical PhC profile has been achieved because the bottoms of the milled cones were truncated by an air gap, with a measured slope angle of the hole sidewalls at 89°. Numerical simulation and free-space illumination measurements of the reflectance spectrum over a broadband wavelength were performed to analyse the properties of various PhC slabs. The free-standing LiNbO3 structures make them easily incorporated into MEMS and show potential applications for tunable optical filters, sensors, and quantum optics applications where high quality, single crystal LiNbO3 is needed.