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Fatigue-induced cracking in steel components and other brittle materials of civil structures is one of the primary mechanisms of degrading structural integrity and can lead to sudden failures. However, these cracks are often difficult to detect during visual inspections, and off-the-shelf sensing technologies can generally only be used to monitor already identified cracks because of their spatial localization. A solution is to leverage advances in large area electronics to cover large surfaces with skin-type sensors. Here, the authors propose an elastic and stretchable multifunctional skin sensor that combines optical and capacitive sensing properties. The multifunctional sensor consists of a soft stretchable structural color film sandwiched between transparent carbon nanotube electrodes to form a parallel plate capacitor. The resulting device exhibits a reversible and repeatable structural color change from light blue to deep blue with an angle-independent property, as well as a measurable change in capacitance, under external mechanical strain. The optical function is passive and engineered to visually assist in localizing fatigue cracks, and the electrical function is added to send timely warnings to infrastructure operators. The performance of the device is characterized in a free-standing configuration and further extended to a fatigue crack monitoring application. A correlation coefficient-based image processing method is developed to quantify the strain measured by the optical color response. Results show that the sensor performs well in detecting and quantifying fatigue cracks using both the color and capacitive signals. In particular, the color signal can be measured with inexpensive cameras, and the electrical signal yields good linearity, resolution, and accuracy. Tests conducted on two steel specimens demonstrate a minimum detectable crack length of 0.84 mm.

Combining dielectric elastomers with photonic glasses enables homogeneous structural colors that can be rapidly tuned using voltage-triggered shape instabilities.

Multilayer dielectric elastomer actuators  have a wide range of potential applications, but their development and commercial implementation have been hindered by existing manufacturing processes. Existing processes are low‐throughput, limited in area, and/or can only process a narrow range of elastomers. This study presents a novel fabrication paradigm that overcomes these challenges: instead of sequentially patterning electrodes directly onto successive elastomer layers, electrode stamps are patterned onto a carrier film in an independent batch‐spray process and the electrodes are then stamp‐transferred onto each elastomer layer. By modularizing the production and assembly of electrodes, a laboratory‐scale implementation of the process achieves a throughput of 15 layers h⁻¹, a maximum electrode size of 300×300 mm, and tuning‐free compatibility with a wide range of elastomers. The batch‐spraying paradigm also provides the unique capability to evaluate and modify electrodes before they are assembled into a multilayer; a method of mechanically treating the electrodes is employed to increase the breakdown strength of Elastosil P7670 devices from 15.7 to 33.5 V µm⁻¹. The electrodes are conductive up to a strain of more than 200% and add negligible stiffness to the multilayer structure. The capabilities of this process to produce useful devices are demonstrated with a large‐area loudspeaker and an actuator with 60 active layers.