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To meet the lightweight requirements of advanced composite materials, the ultralightweight three‐dimensional (3D) braided spacer composites were designed and manufactured by ultra‐high molecular weight polyethylene (UHMWPE). The key structural effects of core column distances and core column heights on the static bending, compression, and low‐velocity impact properties of the composites were further investigated. Results indicated that the mechanical properties of 3D braided spacer composites was closely depended on their structural parameters. The flexure and compression of 3D braided spacer composites decreased with increasing core column distance and core column height. W1/H1 specimen showed the optimal bending and compressive performance. The maximum flexural strength and flexural modulus were approximately 54.77 MPa and 4.95 GPa, respectively. The low‐velocity impact properties were further investigated where the stiffness, energy absorption, and impact resistance of the composite decreased with increasing core column distance. The peak load and energy absorption of the W1 specimen were 2.39 kN and 7.99 J, respectively. While the low‐velocity impact properties increased with increasing core column distance. The H3 specimen exhibited the greatest stiffness, impact resistance and energy absorption with peak loads and energy absorption of 2.81 kN and 8.49 J, respectively. In addition, the macro morphology and scanning electron microscopy (SEM)micrographs were examined to investigate the damage morphology and failure mechanism of the composites. The main failure modes were matrix cracking, interface debonding, fiber buckling, and dislocation, as well as tilting, and failure of the core columns. This work provides guidance for structural design and engineering application of 3D lightweight braided spacer composite. [ABSTRACT FROM AUTHOR]

Although several strain sensors based on carbon nanotubes have been reported, it is still a great challenge to fabricate strain sensors possessed with large workable strain range, high sensitivity and stability. Herein, we developed a highly elastic strain and high sensitivity sensor based on stretchable spandex yarns manufactured by an easy layer-by-layer assembly method. Effects of multi-walled carboxylic carbon nanotubes and chitosan on sensor's properties were investigated. The prepared sensor exhibited fascinating comprehensive sensing performance, including large workable strain range (∼115%), superior sensitivity (gauge factor up to 159 at 0–40% strain and 8175 over 100% strain), In addition, it still exhibited good work stably after 3500 cycles at strain of 50%. The sensor can detect both large and small scale human motions, including joint movement, phonation, swallowing, and drinking. [ABSTRACT FROM AUTHOR]

Vertical flow assay (VFA) is an effective point-of-care (POC) diagnostic tool for widespread application. Nevertheless, the lack of multi-target detection and multi-signal readout capability still remains a challenge. Herein, a brand new VFA scheme for multi-target saliva detection based on electronic tags was proposed, where AlGaN/GaN HEMT sensors modified with different bio-receptors as electronic tags endowed the VFA with multi-target detection capability. In addition, the use of electronic tags instead of optical tags allowed the VFA to simultaneously carry out direct multi-target readouts, which ensure effective POC diagnostics for saliva analysis. Moreover, by integrating a hydrophilically optimized micro-sieve, impurities like sticky filaments, epidermal cells and other large-scale charged particles in saliva were effectively screened, which enabled the direct detection of saliva using AlGaN/GaN HEMT sensors. Glucose, urea, and cortisol were selected to verify the feasibility of the multi-target e-VFA scheme, and the results showed that the limit of detection (LOD) was as low as 100 aM. The linear response was demonstrated in the dynamic range of 100 aM to 100 μM, and the specificity, long-term stability and validity of the actual saliva test were also verified. These results demonstrated that the as-proposed e-VFA has potential for application in saliva detection for simultaneous multi-target detection, and it is expected to achieve the real-time detection of more biological targets in saliva. [ABSTRACT FROM AUTHOR]

An in‐situ regenerative soot particulate matter sensor for automotive exhaust systems based on a discrete AlGaN/GaN high electron mobility transistor (HEMT) was developed and tested, where charge‐sensitive AlGaN/GaN HEMT was utilized to detect the signal variations caused by the presence of soot particulate matters, and the micro‐hotplate serves as soot deposition, while the self‐heating unit was used for sensing and in‐situ regeneration. The two parts were connected for electrical signal transmission. Soot particulate were generated by a laminar diesel flame with an adsorption rate of 23.29 μg cm−2 min−1 on the sensor surface, resulting in 1.32% sensing response after 20 s deposition and reached saturation after a 12 minute deposition of soot. After soot deposition, the sensor was successfully regenerated when a voltage of 2 V was applied to the micro‐hot plate, causing in‐situ heat‐up to reach 600°C for 30 seconds. Moreover, benefiting from the advantage of discrete structure, the sensor exhibited consistent and stable response characteristics even after undergoing more than 10 consecutive regeneration cycles, and the replaceable micro‐hotplate could further extend the service life of the sensor. These results show that the discrete AlGaN/GaN HEMT sensor can be a promising soot particulate sensing platform for automotive exhaust systems. [ABSTRACT FROM AUTHOR]

In this work, the poor fracture toughness of carbon fiber‐reinforced composites (CFRPs) was improved by the introduction of a graphene oxide/nanosilica (GOS) hybrid, and short carbon fibers (SCFs) were investigated through experimental and modeling methods. The effects of the SCF content, number of SCF layers, and introduction position on the mode I fracture toughness (GIC) and mode II fracture toughness (GIIC) of the composites were considered for epoxy resin (EP) modified by GOS. The results showed that GOS and SCF exhibited a synergistic toughening effect on CFRP. The GIC and GIIC of CFRP laminate with GOS content of 0.2 wt% and SCF content of 0.4 wt% reached 0.506 and 2.15 kJ/m2, increased by 72.2% and 53.6% compared to the unmodified composite, respectively. The number of layers and the lamination mode of GC10S5‐B specimens exhibited the optimal improvement of interlaminar fracture toughness. Similarly compared with those of the original. The GIC and GIIC of the CFRP laminates reached 0.662 and 0.506 kJ/m2 (enhanced by 125.9% and 95%, respectively). In addition, the stress propagation path and distribution, and progressive damage of the CFRP composites were obtained to further reveal the toughness mechanism. Highlights: Synergistic toughening of resin modification and short carbon fiber on modes I and II fracture toughness of composites were considered.Content of short carbon fiber and lay‐up methods on toughness performance were investigated thoroughly.Finite element models were established to reveal the stress progress and distribution and toughness mechanism. [ABSTRACT FROM AUTHOR]

A graphene oxide/nano-silica (GOS) hybrid was rapidly and easily synthesized using graphene oxide (GO) and nano-silica (nano-SiO2) as raw materials, and the synthesized GOS was used to improve the mechanical properties of epoxy resin (EP). The modified EP with different mass fractions of GOS (0, 0.1%, 0.2%, 0.3% and 0.4%) were prepared and studied. The structure, thermal stability, mechanical properties, fracture toughness and failure morphology of the modified EP were analyzed. The results showed that the tensile strength of GOS modified EP increased from 40. 6 MPa to 80.2 MPa compared with EP, the critical stress intensity factor of GOS modified EP increased by 65.9% from 0. 82 MPa ⋅ m1/2 to 1.36 MPa ⋅ m1/2, indicating a significant enhancement in fracture toughness. In addition, failure morphology was observed by scanning electron microscopy (SEM) observation. The toughness mechanism of the modified EP was also discussed. Finally, the thermal stability of the modified EP was improved by the addition of GOS. Compared with neat EP, the initial thermal degradation temperature and glass transition temperature of GOS modified EP increased by 4. 5 °C and 10. 3 °C, respectively. [ABSTRACT FROM AUTHOR]

To understand the hybrid fiber enhanced impact‐resistance performance of composite laminates. In particular, the effects of different parameters, such as hybrid fiber ratios and plying modes, were investigated. The effects of UHMWPE short fibers (UHMWPESFs) fiber content and ply angle changes on the impact resistance of Carbon fiber/ultra‐high molecular weight polyethylene short fiber hybrid composite (CUFHRP) laminates were investigated in this article. The impact resistance of the CUFHRP laminate was tested by the drop weight test and residual strength test after impact. The results indicated that the peak load and absorption energy of the specimen with a fiber content of 15 g/m2 were the highest, reaching 6.543 kN and 16.51 J, respectively. Specimens with different ply modes of [0/−45/45/90]2s showed the most obvious effect on the maximum load. Its maximum load was 28.93% higher than that of the original sample. The critical damage threshold load of composite laminates is improved, and the impact resistance is strengthened. Highlights: Study to improve the impact resistance of the composite on the basis of the hybrid structure.Report the optimal parameters of the effects on the impact resistance of the composite, such as: hybrid fiber ratios and plying modes.Reveal the fundamental failure mode of hybrid structure composite laminates under low‐velocity impact. [ABSTRACT FROM AUTHOR]

The fracture toughness of carbon fiber reinforced epoxy composite (CFRP) was investigated through mode I and mode II shaped fracture system in this paper. A novel polyimide with trifluoromethyl groups and grafted nanosilica were used to modify epoxy resin. Effect of modified resin and unmodified resin on fracture toughness of CFRP was compared and discussed. Lay-up angles and thicknesses effects on fracture toughness of composites were also investigated. The fracture toughness of CFRP was obtained through double cantilever beam ( DCB) and end notched flexure(ENF) tests. The results showed that the composites prepared by modified resin exhibited high fracture toughness compared with unmodified composites. The fracture toughness value of mode I increased from 1. 83 kJ/m² to 4. 55 kJ/m². The fracture toughness value of mode II increased from 2. 30 kJ/m² to 6. 47 kJ/m². [ABSTRACT FROM AUTHOR]

Biosensors based on field‐effect transistor (FET) structures have attracted considerable attention because they offer rapid, inexpensive parallel sensing and ultrasensitive label‐free detection. However, long‐term repeatable detection cannot be performed, and Ag/AgCl reference electrode design is complicated, which has hindered FET biosensors from becoming truly wearable health‐monitoring platforms. In this paper, we propose a novel wearable detection platform based on AlGaN/GaN high‐electron‐mobility transistors (HEMTs). In this platform, a sweatband was used to continuously collect sweat, and a pH detecting unit and a potassium ion detecting unit were formed by modifying different sensitive films to realize the long‐term stable and repeatable detection of pH and potassium ions. Experimental data show that the wearable detection platform based on AlGaN/GaN HEMTs has good sensitivity (pH 3–7 sensitivity is 45.72 μA/pH; pH 7.4–9 sensitivity is 51.073 μA/pH; and K+ sensitivity is 4.94 μA/lgαK+), stability (28 days) and repeatability (the relative standard deviation (RSD) of pH 3–7 sensitivity is 2.6 %, the RSD of pH 7.4–9 sensitivity is 2.1 %, and the RSD of K+ sensitivity is 7.3 %). Our newly proposed wearable platform has excellent potential for predictive analytics and personalized medical treatment. [ABSTRACT FROM AUTHOR]