Effect of Impact Position on Repaired Composite Laminates Subjected to Multi-Impacts.

Because the certification of aircraft structures requires significant costs and time-consuming experimental tests, all the studies carried out are strong contributions to the applicability of repairs based on adhesively bonded fibre composite patches. In this context, the main goal of this study aims to analyse the effect of the impact position on the multi-impact response of repaired composites. The results will be compared with those obtained in composites containing holes. Therefore, experimental tests will be carried out using an energy of 8 J and centrally supported samples. It was noted that the patch region proved to be very sensitive to impact due to its thickness. Full perforation occurred after two to three impacts, and to obtain higher strength it would be necessary to increase the thickness of the patch. However, depending on the location of the repair, this could bring aerodynamic problems. For the distance of 15 mm from the centre, an overlap region, the repaired laminate shows 494.7% higher impact strength than a laminate with a hole. In this case, the effect of the stress concentration is determinant in the impact fatigue life. Finally, for the 35 mm distances that are close to the border, no significant changes in impact fatigue life were observed for both the repaired laminates and those containing the hole. This leads to the conclusion that the border effect is much more significant than the presence of the hole for this distance.

Abnormal stiffness behaviour in artificial cactus-inspired reinforcement materials.

Cactus fibres have previously shown unusual mechanical properties in terms of bending and axial stiffness due to their hierarchical structural morphology. Bioinspiration from those cactus fibres could potentially generate architected materials with exciting properties. To that end we have built bioinspired artificial analogues of cactus fibres to evaluate their mechanical properties. We have generated 3D printed specimens from rendered models of the cactus structure using two different printing techniques to assess the reproducibility of the structural topology. Bioinspired additive manufactured materials with unusual mechanical properties constitute an ever-evolving field for applications ranging from novel wing designs to lightweight plant-inspired analogues. The cactus-inspired 3D printed specimens developed here demonstrate an unusually high bending to axial stiffness ratios regardless of the manufacturing method used. Moreover, when compared to their equivalent beam analogues the cactus specimens demonstrate a significant potential in terms of specific (weight averaged) flexural modulus. Imaging of the artificial cactus reinforcements has enabled the generation of a one-dimensional reduced order finite element model of the cactus structure, with a distribution of cross sections along the length that simulate the inertia and mechanical behaviour of the cactus topology. The novel bioinspired material structure shows an excellent reproducibility across different manufacturing methods and suggest that the tree-like topology of the cactus fibre could be very suited to applications where high bending to axial stiffness ratios are critical.

Extraction and characterization of vascular bundle and fiber strand from date palm rachis as potential bio-reinforcement in composite.

Date palm rachis fibers are rich in cellulose, relatively inexpensive, and readily available in Algeria. The aim of this study is to investigate the morphology, structure, mechanical and physicochemical characteristics of both vascular bundles and fiber strands extracted from date palm rachis. The difficulties encountered are associated to the extraction of the fibers without damaging them. The study focuses on the morphological and surface roughness analysis using optical and scanning electron microscopies (SEM), and a non-contact 3D profiler. The chemical, physical and thermal properties have been studied using Fourier-transform infrared (FTIR) spectroscopy, energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The mechanical properties were accessed by tensile tests and they were analyzed using two-parameter Weibull distribution.

Characterization of a novel natural cellulosic fiber from Juncus effusus L.

This study aims to assess the morphology and properties of fibers extracted from a wild natural plant largely available in Algeria known as Juncus effusus L. (JE). The morphology and diameter of the fiber bundles extracted from the stem of the JE plant were characterized by optical and scanning electron microscopy. The functional groups of the extracted lignocellulosic JE fibers were studied by FTIR, their thermal degradation behavior was investigated by TGA and their crystallinity was determined using X-ray diffraction technique. In addition, mechanical characterization was carried out using tensile tests on the lignocellulosic fiber in order to evaluate their strength, strain at break and Young's modulus. In view of the dispersion in the obtained experimental results, the latter were analyzed using the Weibull statistical laws with two and three parameters.