Impact Response of Aramid Fabric-Reinforced Polybenzoxazine/Urethane Composites Containing Multiwalled Carbon Nanotubes Used as Support Panel in Hard Armor

The aim of this research project is to analyze support panels that are based on aramid fabrics which are reinforced with polybenzoxazine/urethane (poly(BA-a/PU)) composites and contain multiwalled carbon nanotubes (MWCNTs). Through the measurement of mechanical properties and a series of ballistic-impact tests that used 7.62 × 51 mm2 projectiles (National Institute of Justice (NIJ), level III), the incorporated MWCNTs were found to enhance the energy-absorption (EAbs) property of the composites, improve ballistic performance, and reduce damage. The perforation process and the ballistic limit (V50) of the composite were also studied via numerical simulation, and the calculated damage patterns were correlated with the experimental results. The result indicated hard armor based on polybenzoxazine nanocomposites could completely protect the perforation of a 7.62 × 51 mm2 projectile at impact velocity range of 847 ± 9.1 m/s. The results revealed the potential for using the poly(BA-a/PU) nanocomposites as energy-absorption panels for hard armor.

Study on the Articulated Finger Based on Pneumatic Soft Joint

This article described a novel pneumatic soft joint used to make articulated soft fingers. This soft joint was designed by improving the basic structure of the fast pneumatic network. The joint was made of high modulus E630 silicon, which can increase the reverse exhaust speed through its high structural elasticity. Aramid fabric was used to restrain the non-working direction of joints to reduce ineffective expansion, thereby reducing air consumption. The kinematics and statics model of the joint was established by the piecewise constant curvature (PCC) method, and the model was proved to be effective. The silicone staging pouring process was used in the manufacture of joints and fingers, which can achieve high-quality product rates. A soft finger actuator composed of three soft joints was designed and manufactured, whose length was 1.3 times the human finger. The finger can nimbly achieve the target motion, and the gripping force of the fingertip can reach 7.1N. The articulated soft finger actuator has applications in soft dextrous hands and soft gripper.

Quasi-static penetration behavior of fiber-reinforced polypropylene and acrylonitrile butadiene styrene matrix composites

The quasi-static punch shear behaviors of thermoplastic composites with different polymer matrices and fiber types were investigated. This study was also focused on how much energy absorption capability can be increased by low fiber fractions. Maleic anhydride grafted polypropylene (MA-g-PP) and acrylonitrile butadiene styrene (MA-g-ABS) were used as the matrix material. One layer of aramid, carbon and glass fiber plain weave fabrics was used as the reinforcement material. Quasi-static punch shear test (QS-PST) was applied to the samples to understand the penetration behavior of the samples. The damaged areas were investigated and related to force-displacement curves. The results showed that the neat form of MA-g-PP exhibited 158% more energy absorption than the neat form of MA-g-ABS. In the samples containing one layer of fabric, the highest improvement was observed in the aramid fabric-reinforced MA-g-ABS matrix composites. Aramid fabric increased the energy absorption at a rate of 142.3% in comparison to the neat MA-g-ABS, while carbon fiber fabric and glass fiber fabric increased it by 40% and 63.52%, respectively. Aramid fiber fabric provided no significant improvement in the energy absorption in the MA-g-PP matrix composites, while carbon and glass fiber fabrics contributed to energy absorption at a rate of 48% and 41%, respectively.

Influence of incident energy on the properties of arc rated para-aramid fabric

To study the protection mechanism of para-aramid fabrics under an electric arc, the structural composition, surface morphology, and thermal properties of an untreated para-aramid fabric and that treated with different incident energy arcs were compared. The intensity of the N-H peak of the para-aramid cellulose amide decreased with increasing exposed arc energy. Moreover, intensities of the C=O peak of the amide bond type I carbonyl and the C-H deformation vibration absorption peak originating from the benzene ring gradually weakened. In contrast, the carbon content of the fabric increased. In the arc deflagration process, the fiber broke and then carbonized and embrittled. With an arc energy of 30.9 cal/cm2, the carbonization degree of the front surface of the fabric increased and was highest at the float line. The initial combustion temperature remained unchanged, and the mass residual quantity gradually increased with increasing arc energy exposed to the fabric. The above results suggest that para-aramid fabric can protect the end user in an arc by carbonization, offering effective assistance in the research and development of personal protective equipment for arc flashes.

Theoretical prediction and experimental characterization of radiative properties and thermal conductivities of fibrous aramid fabrics

Nonwoven aramid fabric is widely used as thermal barrier of fireproofing clothing due to its inherent flame retardancy and light weight. In fire or high temperature scenario, radiative heat transfer becomes the predominant heat transfer mode inside firefighters’ clothing. In this work, Fourier transform infrared spectroscopy (FTIR) was adopted to measure the spectral transmittance and spectral extinction coefficients of four aramid fabrics with different porosity in infrared wavelength range between 2.5 and 25 μm. It was found that the radiative properties of fibrous aramid fabric are strongly dependent on its bulk density or porosity. The spectral extinction coefficient decreases with increasing porosity or decreasing bulk density. The infrared optical properties combined with infrared imaging measurements demonstrate that aramid fabric may be used as infrared semi-transparent textile. A predicted model, combined the effects of conduction-radiation heat transfer, has been developed to calculate the effective thermal conductivity of aramid fiber materials. The model implemented the Rosseland diffusion approximation to evaluate radiative thermal conductivity, and the Parallel-Series structural model to evaluate tortuosity-weighted phonic thermal conductivity. The predicted results were also compared with experimental data obtained from TPS method. This work provides useful information for future studies of heat transfer mathematical modeling of firefighters’ clothing.