Investigation of surface textured sensing skin for fatigue crack localization and quantification

Abstract

The timely discovery and monitoring of fatigue cracks in steel structures is an important task in order to ensure structural integrity. However, off-the-shelf strain sensors are small and their deployment is too spatially localized to successfully locate new crack formation or growth within acceptable confidence. A solution is the use of large-area electronics capable of covering large surfaces. The authors have previously developed a sensing skin technology based on a soft elastomeric capacitor (SEC) that consists of a highly compliant, low-cost, and scalable strain gauge that transduces surface strain into a measurable change in capacitance. In prior work, the SEC was fabricated using three flat layers that formed a parallel plate capacitor. An improvement to that design has recently been proposed, in which the dielectric layer is textured using a corrugated pattern, and preliminary work showed a substantial improvement in sensing performance due to the added in-plane stiffness and decrease in the sensor's transverse Poisson's ratio. This paper extends preliminary work by studying the textured sensor's capability to quantify and discover a fatigue crack, and to study the general sensing performance in terms of linearity, sensitivity, resolution, and accuracy. Four specific corrugation patterns are investigated: a symmetric grid, a diagonal diagrid, a reinforced diagrid, and a non-symmetric re-entrant hexagonal honeycomb (auxetic) pattern. Experimental results show that the use of a texture results in a significant increase in sensing performance, with auxetic and reinforced diagrid patterns outperforming the other patterns. In particular, the auxetic and reinforced diagrid patterns allowed the discovery of a 0.28 mm and 0.31 mm fatigue crack, compared to a 0.53 mm crack for the untextured SEC, and resulted in up to 106% increase in sensitivity, 113% in linearity, 319% in resolution, and 582% in accuracy, compared to untextured SECs.

Investigation of electrically isolated capacitive sensing skins on concrete to reduce structure/sensor capacitive coupling

“…where ν 0 is Poisson's ratio for the SEC, and λ 0 is the SEC's gauge factor In this paper, a gauge factor of 1.7 was used, experimentally validated in Liu et al [20]. If ε m is the strain on the monitored surface:…”

Multifunctional soft stretchable strain sensor for complementary optical and electrical sensing of fatigue cracks

“…The performance of the sensor at detecting and quantifying fatigue cracks was examined on C(T) specimens. The experimental test was conducted by following the same procedure as in prior work [31]. Figure 2(d) shows the overall experimental setup.…”

Investigation of textured sensing skin for monitoring fatigue cracks on fillet welds

“…Figure 4(d) shows the simulated maximum principal stress distributed on the welded specimen, where it can be observed that high stress is concentrated along the edge of the welds consistent with the crack propagation path. The fatigue behavior in the numerical simulation is dominated by Paris' law, and the simulation of the fatigue crack growth behavior on the welded specimen was conducted by following the same procedure used in prior work [30], where the separating morphing and adaptive re-meshing technology crack growth simulation tool was used, and 40 face nodes were uniformly assigned on the top and bottom crack faces, as presented in the onset Figure 4(e) presents the normal elastic strain distribution on the cSEC installed at the bottom corner, while figures 4(f) and (g) are the front section views of the sensor installed in the top and bottom corners showing the deformation of the sensors under angular motion. The cSEC's signal can be simulated by extracting the initial area A p,q 0 and the area after deformation A p,q of each mesh element from the FEM to compute the deformed area ∆A p,q , and substituting them into the FE based algorithm (equation ( 17)) to obtained the numerical capacitance response.…”

“…It is fabricated by infilling titania (TiO 2 ) and carbon black (CB) particles into a styrene-ethylene-butylene-styrene (SEBS) block copolymer matrix to form the dielectric layer and conductive plates, respectively, and layering them into a sandwiched structure. Notably, the cSEC technology has been characterized and demonstrated for in-plane fatigue crack monitoring and out-of-plane angular motion sensing [30,31]. Compared to conventional strain sensors such as foil gauges, the cSEC covers and senses over large areas and can thus be used to discover new cracks instead of being exclusively used to monitor existing damage.…”