Browse Topic: Polymers
Modern combat helmets improve wearer survivability through preventing ballistic penetration via delamination or deformation of the shell material. However, this deformation may impinge upon the skull and present a risk of behind-helmet blunt trauma (BHBT). While legacy aramid helmets from the late 1970s–1980s inform current NIJ testing standards, the advent of lower areal density ultra-high molecular weight polyethylene (UHMWPE) and modern suspensions may incur unknown changes that present an unknown effect on BHBT risk. This study investigates whether current standards relying on a peak acceleration threshold and residual clay deformation may not reflect changes in deformation geometry seen in newer shell materials and suspension designs. Thirty-eight helmets categorized into three groups, older aramid, newer aramid (with new suspension), and prototype UHMWPE (with old suspension), were mounted on Hybrid III ATD head-necks and impacted on the temporal surface with 9 mm NATO projectiles at velocities between 388 and 482 m/s. Flash x-ray imaging captured deformation geometry. Deformations were digitized to measure maximum depth, volume, and surface area recruited. Multiple linear regression identified the influence of shell material and suspension on geometry. Results indicated that shell material significantly affected deformation volume and area (p < 0.05). Notably, UHMWPE exhibited a qualitatively more “pointed” deformation profile compared to aramid, recruiting material differently as depth increased. In contrast, suspension type and helmet design did not significantly influence deformation geometry. These findings suggest that the BHBT geometry in UHMWPE helmets differs fundamentally from aramid helmets. As UHMWPE helmets encounter higher-energy threats, current acceleration threshold or depth-based standards may not fully capture the risk of skull fracture. To future-proof helmet validation, testing standards should evolve beyond current standards to include area recruitment and other geometric measures.
We present atomistic molecular dynamics simulations of linear and branched fluorinated polymer chains, with and without imidazole functionalization, designed as a model for solvent-free proton-conducting membranes for high-temperature fuel cell applications. Simulations conducted over a temperature range of 300 to 550 K, and diffusion-based relaxation times reveal that glass transition temperatures depend on polymer architecture: the branched and functionalized systems exhibit transitions near 400 K compared to 500 K for the linear chain. Fluorine-fluorine radial distribution functions demonstrate that branching disrupts local packing order, while imidazole substitution creates specific intra-chain interactions. Radius-of-gyration distributions reveal that branching significantly increases chain extension and creates multiple conformational families, whereas imidazole groups stabilize compact conformations at low temperatures that transition to more diverse states upon heating. These findings provide molecular-scale insight into how polymer architecture controls thermal transitions and structural organization in model high-temperature polymer electrolyte membranes.
When policymakers debate defense readiness, the conversation often centers on semiconductors, rare earth magnets, advanced optics, and other headline technologies. What rarely makes the list is the category of engineered technical textiles that equip, protect, and support American warfighters every day. These are not ordinary fabrics. Military technical textiles are engineered systems produced on computer-controlled looms, built from advanced synthetic polymers, and qualified under demanding aerospace and defense standards.
Carbon materials, as typical dielectric loss media, possess the characteristics of low density, stable chemical properties, wide sources, and diverse existing forms, and have been attracting much attention in the microwave absorption field. Based on carbon materials, the rational design and construction of microscopic morphology and microscopic structure is an effective way to improve their microwave absorption performance. Up to now, unique microstructures such as hollow, core-shell, and porous have been widely used in the design of microwave absorption materials, and their performance improvement has also been reliably confirmed. This paper mainly focuses on the research of the preparation and microwave absorption performance of porous carbon foams (CF-x). Firstly, it achieves the fabrication of porous carbon foams by the one-step pyrolysis using readily available glucose and NH4Cl, avoiding the need for polymer templates or magnetic element incorporation. In addition, this paper focuses on investigating the effect of the dosage of NH4Cl on the pore structure and dielectric properties of CF-x, and it reveals the advantages of the foam structure in terms of enhancing microwave absorption performance.
What if there were a fabric that, like Superman, could take a bullet and self-heal? Such a super-dynamic, action-powered polymer might actually help protect real-life flyers in space.
A new prototyping approach leverages thermoplastic composites, swappable cavity inserts and modular tooling to reduce the time required to produce aerospace and defense prototypes by up to 50 percent. Developed by Greene Tweed - the Pennsylvania-based manufacturing and design services provider - the approach is seeing increased demand among advanced air mobility (AAM) and defense companies focused on metal-replacement development projects that require faster testing and validation. Greene Tweed developed its new rapid prototyping process using its Xycomp® DLF™ material, which the company first introduced to commercial aerospace in 2007. Xycomp DLF is a thermoplastic composite that provides a lightweight alternative to complex metallic components for aerospace and defense applications. According to Greene Tweed, Xycomp DLF components can weigh up to 60 percent less than their metal counterparts and are well suited for aircraft, engine and aerostructure applications.
Conveyor belt fault detection is critical for ensuring the safety and efficiency of industrial material transportation. In this study, a screen-printed flexible strain sensor based on a thermoplastic polyurethane (TPU) substrate and graphene conductive ink was fabricated. The sensor exhibited excellent flexibility, mechanical robustness, and stable electromechanical performance. Comprehensive evaluations were conducted, including microstructural analysis, strain sensitivity, hysteresis, dynamic response, and long-term cycling stability. The results demonstrated that a two-layer graphene configuration achieved an optimal balance between sensitivity and structural stability, showing high gauge factor, fast response, and reliable cyclic performance. Furthermore, the sensor was applied to conveyor belt fault monitoring. Experiments validated its ability to detect both halting faults and foreign object intrusions, with distinctive resistance signal features enabling not only fault occurrence detection but also identification of fault location, type, and severity. These findings highlight the potential of the proposed flexible sensor system as a promising solution for intelligent conveyor belt monitoring in harsh industrial environments.
This device belongs to the field of aviation materials technology and discloses a high-efficiency drilling equipment for manufacturing aviation materials, which includes a bottom plate. The top of the bottom plate is provided with a clamping structure and a positioning structure. The clamping structure includes a second moving plate, a third sliding groove, a second bi-directional screw, a fourth screw block, a clamping plate, and a rubber block. This device can hold materials through a clamping structure and effectively and quickly locate and drill holes through a positioning structure. By rotating the first threaded rod, it can drive the first screw block to move the U-shaped column. During the movement of the U-shaped column, it will drive the second threaded rod to move together. By rotating the second threaded rod, it will drive the second screw block to adjust the height of the connecting plate for drilling holes. By rotating the third threaded rod, it will drive the first moving plate to move, which will facilitate the multi-directional movement of the drill bit, improve the efficiency of drilling, avoid multiple position changes, and be beneficial for practical applications and operations.
This research demonstrates a facile method for fabricating an anti-icing coating through spray deposition on a metallic substrate. A dual-layer structure was designed to enhance icephobic properties: a primer layer incorporating fluorocarbon resin, butyl acetate, and rod-shaped micrometer-sized metal oxides to establish a secondary roughness morphology, followed by a topcoat composed of butyl acetate and nano-scaled superhydrophobic particles. Evaluation of the coating performance revealed a maximum water contact angle of 171.9°, indicating exceptional hydrophobicity. Furthermore, the coating exhibited notable abrasion resistance and anti-icing capabilities against overlaying ice.
Noise phenomena in automobiles caused by the stick-slip effect are increasingly among the most frequent reasons for customer complaints and therefore represent a critical vehicle quality attribute. To proactively address such issues, stick-slip testing of contacting material pairs is commonly applied during development. However, the predictive capability of current stick-slip test methods remains limited, particularly when highly flexible materials and realistic, stochastic excitation conditions are involved. The flexibility of sealing systems often allows the actual relative motion at the contact interface to be accommodated through adhesion and elastic deformation, thereby delaying or even preventing sliding. To date, this effect has not been represented by any characteristic parameter in conventional stick-slip testing. Instead, existing evaluations focus exclusively on the analysis of occurring stick-slip oscillations. For the initiation of stick-slip phenomena, however, not only the mean displacement between two stick-slip oscillations during the sliding phase is relevant, but also the relative displacement required to initiate the first slip event of the sealing contact. With the algorithm developed in this work, which reproducibly determines the distance to first slip based on changes in the friction force slope, this methodological gap is now closed. The displacement to first slip depends on numerous influencing factors, including profile geometry, normal load, sliding velocity, excitation profile, and environmental conditions, and was previously inaccessible by both experimental and numerical approaches. In particular, the onset of slip in sealing contacts can now be determined under stochastic excitation of the friction pairing, thereby closely reflecting real operating conditions. As a result, the prevention of noise phenomena can be significantly strengthened at an early stage of vehicle development.
This research investigates the fabrication and evaluation of Delrin (polyoxymethylene, POM) composites reinforcing 5-20 wt.% chopped ramie fiber (RF). The polymer composites were fabricated via the injection moulding technique. Glass transition temperature (Tg), thermal conductivity, Vicat softening temperature (VST), heat deflection temperature (HDT), melt flow index (MFI), and coefficient of linear thermal expansion (CLTE) were the various thermal characteristics of the sustainable composites that were systematically evaluated as per the ASTM standards. The addition of RF drastically altered the Delrin matrix's performance. Among the formulations, the composite with 15 wt.% RF had the best combination of properties: higher VST and HDT values, which provide greater dimensional stability at high temperatures; lower CLTE, resulting in less thermal expansion; comparatively better thermal conductivity; and improved heat dissipation. Eventually, there was a moderate drop in the MFI, indicating more rigid polymer chains that restrict the flowability of the composite, thereby increasing its heat-withstanding capabilities. DSC analysis revealed a slight upward shift in Tg and increased crystallinity, suggesting restricted polymer chain mobility and enhanced load transfer at 20 wt.% RF loadings, agglomeration effects, and weaker interfacial bonding with the matrix led to deterioration in properties. Aircraft cabin components like interior panels, ducting supports, and lightweight non-structural fittings requires dimensional stability, thermal resistance, and mechanical reliability under fluctuating flight conditions.
The future of Moon exploration may be rolling around a non-descript office on the CU Boulder campus. Here, a robot about as wide as a large pizza scoots forward on three wheels. It uses an arm with a claw at one end to pick up a plastic block from the floor, then set it back down.
Aerospace and defense systems demand materials capable of maintaining performance under extreme environmental and operational stressors, including wide thermal cycling ranges, exposure to hydrocarbon fuels, vacuum conditions, and repeated mechanical strain. Silicone-based materials have become essential in these environments because they can retain elasticity, stability, and functionality where many traditional materials fail. Silicones are widely used as coatings, adhesives, sealants, and elastomers in aircraft and spacecraft applications. Their chemical structure enables resistance to both high and low temperatures, while also providing durability against solvents and fuels such as jet fuel. In contrast, many conventional elastomers degrade under prolonged thermal exposure or become brittle at cryogenic temperatures.
Sometimes referred to as “solid smoke,” aerogels are the world’s lightest solid materials, composed of approximately 85 percent air by volume. Polyamide aerogels open up a whole new world of applications due to their unique properties: translucent like silica aerogels; thermoplastic; ultra-low density; superior mechanical properties; low-temperature operating range; and highly flexible (as compared to NASA Glenn’s polyimide aerogels). Polyamide aerogels are further novel because of their tunable glass transition temperatures, meaning that crystallinity, and hence strength, can be controlled via operating temperature. Addressing the key drawbacks of aerogel technology (hydroscopicity, fragility, cost), NASA Glenn’s suite of organic aerogels are cost-competitive with both existing silica aerogels and, with scale-up, high-end foamed polymer insulation.
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