Use of castor oil as a renewable polyol in the polyurethane foams has been creating an attractive research interest for many researchers since last 5 decades. In this article, we examine the structural stability of flexible polyurethane foam produced using castor oil-glycerol blend by complete replacement of synthetic polyol. Addition of castor oil in the foaming blend as a complete substitute of synthetic polyol results in instability of foam. However, addition of glycerol as a crosslinking agent in the blend helps in overcoming this instability. Cellular morphology, segmented phase morphology and bulk properties of foams were investigated using scanning electron microscope, Fourier transform infrared spectroscopy respectively. Castor oil-glycerol blend significantly improves the foaming process at low concentrations (till 15 wt % glycerol) whereas, at higher concentrations volumetric expanding liquid undergoes faster cross-linking leading to retarded foam growth (above 20 wt % glycerol). Strut thickness shows a sharp decline at 25 wt % glycerol. Polymer phase morphology shows absence of H-bonded urea resulting in discrete hard segmented morphology whereas urea domains undergo agglomeration without glycerol. Foams were also characterized for thermal and bulk mechanical properties.

Helmets are ubiquitously used forms of protective equipment in various industries. A common major drawback in helmets is their poor thermal management. Here, to reduce the dependency on active cooling methods and to conserve same helmet design, a composite thermal liner based passive cooling mechanism is proposed. A multifunctional liner consisting of uniformly distributed graphene oxide nanosheets and icosane is prepared. A helmet liner cast out of a 3D‐printed mold is tested to measure impact energy absorption using a home‐built helmet impact testing setup in accordance with ASTM D7136/D7136M‐20. The liner is expected to deform, thereby absorbing the energy from the impact and eventually reducing the impact experienced by the user. The material (10X‐GOME‐0.75), obtained after careful optimization of the mechanical and thermal properties of different combinations of varying weight fractions of the fillers, exhibits about 300% greater deformation over an unmodified epoxy (UME) liner (0.3% strain) and also shows 98% strain recovery over a fatigue test of >7500 cycles. Thermal characterization shows heat absorption by the material at about 37 °C, which is the average human body temperature. Such materials can have future in developing lightweight next‐generation helmets with better thermal management for use in various fields.

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Laser-to-composite interactions are becoming increasingly common in diverse applications such as diagnostics, fabrication and machining, and directed energy weapon systems. These interactions can induce seemingly imperceptible damage to the material. It is therefore desirable to have a means of sensing laser exposure. Smart or self-sensing materials may be a powerful method of addressing this need. Herein, we present a study on the potential of using changes in the electrical properties of carbon nanofiber (CNF)-modified composites as a way of detecting laser exposure and degradation. To test laser sensing capabilities, CNF composite specimens were exposed to an infra-red laser operating at 1064 nm, 35 kHz, and pulse duration of 8 ns for a total of 20 s. The resistances of the specimens were then measured post-ablation, and it was found that for 1.0 wt.% CNFs, the average resistance increased by approximately 18% thereby demonstrating laser sensing capabilities. In order to expand on this result, electrical impedance tomography (EIT) was employed for spatial localization of laser exposures of 1, 3, 5, 10, and 20 s on a larger, plate-like specimens. EIT was not only successful in detecting and localizing exposures, but it could also find laser damages that were virtually imperceptible to the naked eye. Based on these results, this research could lead to the development of novel carbon-based smart material systems for real-time detection and tracking of laser exposure in the measurement, fabrication, and defense industries.

Laser-to-composite interactions are becoming increasingly common in diverse applications such as diagnostics, fabrication and machining, and weapons systems. Despite a lack of physical contact, lasers can induce seemingly imperceptible structural damage to materials. In safety-critical venues like aerospace, automotive, and civil infrastructure where composites are playing an increasingly prominent role, it is desirable to have means of sensing laser exposure on a composite material. Self-sensing materials may be a powerful method of addressing this need. Herein, we present an initial exploratory study on the potential of using changes in electrical measurements as a way of detecting laser exposure to a carbon nanofiber (CNF)-modified glass fiber/epoxy laminate. CNFs were dispersed in liquid epoxy resin prior to laminate fabrication via hand layup. The dispersed CNFs form a three-dimensional conductive network which allows for electrical measurements to be taken from the traditionally insulating glass fiber/epoxy material system. It is expected that damage to the network will disrupt the electrical pathways, thereby causing the material to exhibit slightly higher resistance. To test laser sensing capabilities, a resistance baseline of the CNF-modified glass fiber/epoxy was first established before laser exposure. The specimens were then exposed to an infra-red laser operating at 1064 nm, 35 kHz, and pulse duration of 8.2 ns. The specimens were irradiated for a total of 20 seconds (4 exposures each at 5 seconds). The resistances of the specimens were then measured again post-ablation. It was found that the average resistance increased by about 18 percent. This established that the laser was indeed causing damage to the specimen sufficient to evoke a change in electrical properties. To expand on this result, electrical impedance tomography (EIT) was employed for localization of 1, 3, and 5-second laser exposure on a larger specimen. EIT was not only successful in detecting damage that was virtually imperceptible to the human-eye, but it also accurately localized the exposure sites. The post-ablation conductivity of the exposure sites decreased in a manner that was comparable to the resistance increases obtained during prior resistance change testing. Based on this preliminary study, this research could lead to the development of a real-time exposure detection and tracking system for the measurement, fabrication, and defense industries.