Key Engineering Materials Vol. 812

Abstract: The aim of this research was to develop fibrous structures using flax, functionalized with calcium oxide nanoparticles, with degradation properties and antibacterial activity. Flax samples were successfully functionalized with CaO nanoparticles (CaO NPs) and characterized by ATR-FTIR, FESEM, EDX and TGA techniques. ATR-FTIR and FESEM results clearly indicated the presence of CaO NPs in the flax fabrics’ surface. The influence of surface pre-treatments on the effectiveness of the nanoparticles’ deposition was also studied. Three different treatments were used: Alkali, Acetylation and Potassium Permanganate. The alkali treatment presented the best results, therefore, only alkali flax samples were used in UV degradation experiments, as well as antibacterial activity analysis. In order to evaluate the efficiency of the developed systems as agents against chemical and biological warfare, the samples’ organophosphate degradation ability (using DMMP as a GB mimic) was tested, under UV irradiation. ATR-FTIR results indicated that DMMP was successfully degraded by CaO Flax samples. Antibacterial tests were also performed, using the Halo method, which did not yield the expected results, in the range of tested conditions.

Abstract: Landmines and Improvised Explosive Devices are known to be major threats for the coalition armies in operation. In order to protect the soldiers from their effects, armored vehicle manufacturers developed some blast protective solutions. However, these solutions often reduce the vehicles’ mobility and payload capacity because of their shape or weight. Fiber Metal Laminates (FML) look like promising light weight blast protective solutions as they associate low areal densities with good bending rigidity and a high number of impedance mismatches which tend to attenuate the shock wave propagation. In this paper, three FML composed of a back plate of armored steel, a middle composite panel named A, B or C and a thin front plate made of mild steel were subjected to a blast loading. The maximum dynamic deformation of each target was recorded during the blast test. A macroscopic post-mortem analysis exhibits three similar behaviors of the back plates but very different permanent deformation patterns of the composite panels. A CT-scan of each panel was then realized to explain these three patterns and, based on these analysis, some hypothesis were made to improve the blast resistance of the B and C panels.

Abstract: The response of the bulkhead type of blast wall under deflagration blast pulse was studied using finite element modelling software. The behavior of unstiffened and stiffened panels was analyzed. The study aimed at determining the effect of plate and stiffener thicknesses on energy dissipation and distribution of reaction forces. This was carried out in order to optimize the response of the primary steelwork through typological and geometrical modifications of the local element. Furthermore, novel strategies for the improvement of the blast response were introduced with a focus to use alternative materials and innovative connections. The latter was assessed numerically using a simplified model and its benefits were analyzed by comparing with the traditional approach.

Abstract: In this work, a weft-knitted fabric produced from 100% meta-aramid (MA) fibre was functionalized by using polyelectrolyte, Poly (diallyldimethylammonium chloride) (PDDA), in order to modify its surface for dyeing with an uncommon dye class for MA fibres. Contact angle, dye solution drop adsorption, Scanning Electron Microscopy (SEM), reflectance spectrophotometry, washing and rubbing fastness tests were performed to study the effects caused by the interaction between PDDA and MA fabric. Good results of dyebath exhaustion with excellent values of colour strength were obtained for the samples previously treated with PDDA. These results showed the possibility of obtaining distinct and deep colours besides generating a lower energetic cost using shorter time and lower dyeing temperature as compared to those normally used in the MA dyeing process.

Abstract: Lightweight and strong composite material beams are increasingly sought to quickly, easily, and cost-effectively transport and setup a variety of constructions such as bridges, cabins/ stores/shelters, vehicles etc. For structural beams produced as conventional laminated composite materials, their weak areas tend to occur at intersections such as web-flange junctions due to absence of fibres bridging the interconnections. This drawback can however be overcome with development of profiled 3D textile reinforcements having combination architectures and constituent web-flange parts inherently mutually interconnected through fibre interlacement. In addition to general strength improvement, beams containing such novel reinforcement architectures also show increased energy absorption capability due to the mutual web-flange integration at the junctions. An ‘I’ and a ‘flanged-triangle’ cross-section beams were produced by a novel non-conventional weaving method, using carbon fibres as reinforcement, and their energy absorption capabilities were tested. These beams respectively absorbed over 50% and 300% more energy per weight in bending, compared to metal counterparts. This paper presents some relevant aspects of these innovative beams.

Abstract: Textiles for military clothing face a complex set of challenges. They must provide protection, durability and comfort in a wide range of hostile environments. The general requirements of military textiles include damage resistance, comfort, sweat management, cold-weather conditions and the integration of high-tech materials into uniforms. This paper discusses the main concepts regarding the application of textiles in military uses, where the surrounding environments such as desert, jungle or extremely cold areas as well as the nature of the situations involved pose a threat to the soldier’s safety. Therefore, the improvement and development of fibrous materials, textile structures and finishing processes can bring new perspectives for saving lives.

Abstract: This work compares thermal colour and emissivity of different pigments printed on to two types of jersey knitted fabrics (cotton and polyester). In order to analyze and differentiate the thermal colours of the knitted fabrics samples, diurnal and nocturnal thermal images of a female body were captured in an outdoor environment using a thermal imaging camera. Five pigments (white, black, yellow, magenta and cyan blue) were analyzed in a conditioned environment, simulating atmospheric (diurnal/nocturnal) and skin temperature, using a climatic chamber, a thermal manikin and a thermal imaging camera. The thermal tests allowed identifying the thermal colour of the printed pigments for application in the diurnal thermal camouflage garments.

Abstract: The understanding of textile yarns behavior is of paramount relevance for the textile industry, mainly for technical applications. This describes the research work to introduce an alternative method for both yarns diameter and volumetric measurement using image analysis. Its main goal is to better describe the transverse dynamic behavior of multifilament yarns when submitted to tensile loads. Methods for measuring yarns diameter found in the literature are described and discussed. The proposed method presents significant advantages allowing the possibility to perform tests without interruption, as well as the ability to generate a greater amount of data, providing more accurate results. Longitudinal tensile tests using two types of multifilament polyamide yarns were performed and their actual dynamic behavior is analyzed using the experimental results.