Strain measurements are essential in structural health monitoring. Traditional strain gages require physical
contact between the sensor and read-out device, perturb the surface being monitored, and allow measurement
only at the specific location and orientation axis of the sensor. We demonstrate a novel non-contact, multi-
point, multi-directional strain sensing approach that overcomes these limitations. In our method, the surface is
coated with a thin film of "smart skin" containing individualized single-walled carbon nanotubes in a polymeric
host. After curing, substrate strains are transmitted through the polymer film to embedded nanotubes. This
induces axial strains in the nanotubes, systematically shifting the wavelengths of their characteristic near-infrared
fluorescence peaks. To measure strain, a visible laser excites nanotubes at points of interest on the surface, and
the near-infrared emission is collected and spectrally analyzed. Observed spectral shifts reveal quantitative strain
values. Laboratory tests show sensitivity down to ~400µm, limited by mechanical properties of the polymeric
host film. We also vary excitation beam polarization to find the axis of substrate strain. Our method provides
spatial resolution down to its gage length of ~100µm. Because the entire substrate is coated with nanoscale
strain sensors, measurements can be made at arbitrary locations to construct a full strain map. We will describe
recent smart skin refinements involving selection of polymer host, nanotube surfactant, nanotube dispersion
method, and preparation protocol. Finally, we characterize the orientational distribution of nanotubes using a
probabilistic model.
In this paper, an approach based on a new damage index-Distributed Force Change(WDFC), for monitoring the structural health of risers used for production in deep-water floating platforms, is presented. Experiments of a scaled pipe are carried out to validate the vibration based damage identification method. The influences of multiple cracks in the WDFC damage index are studied. Futhermore, this paper demonstrates the effectiveness of wave propagation based structural health monitoring (SHM) strategies within the pipe model. This is realized based on the results of numerical investigation obtained by the use of Finite Element Method(FEM) together with application of Time-of-Flight(FoT) damage identification method in which the damage severity is indicated by Root Mean Square(RMS) of the damage-reflected wave. The influence of crack(s) in the riser/pipe on the wave propagation are studied. The results from the experiments and numerical analysis indicate that both the two damage identification methods can provide information about the estimated crack location(s) and the possible extent of crack. Hence the two methods are suitable for globally and locally monitoring the structural health of deepwater risers respectively.
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