Band 38, Heft 5

Stress concentration is an unavoidable phenomenon during the fabrication of composite structures. This research focuses on reducing stress concentration. Circular holes made on the composite structural member induce stress-concentrated regions. These stress-concentrated regions around the circular hole (considered as a weak section) were strengthened by adding synthetic fibre (local hybridization) in the form of fibre stitches (locked loop stitch). Through conducting a single fibre pull-out test, the present study analysed the impact of incorporating synthetic fibres in stitch form and the enhancement of Interfacial Shear Strength (IFSS). The load acting on the broken warp fibres is distributed to the broken weft fibres when the number of concentric stitches increases. The increment of concentric stitches resulted in the increase of IFSS due to localized hybridization. The tensile test results also show a significant improvement with 110 Nmm axial fastening force, from 6.749 MPa (for the natural fibre composite) to 76.91 MPa (for locally hybridized with eight concentric stitches). A simple bolted lap joint with local hybridization around the hole has been evaluated for different clamp-up forces. The best combinations of the clamp-up force and the extent of hybridization have been identified. SEM images illustrate the reduced voids and the reduced fibre pull-out due to the local hybridization around delamination-prone areas.

The environmental awareness and sustainable nature of plant-based fibers have forced material researchers and automakers to use natural fibers instead of petroleum-based fibers for various industrial applications. The need for environmentally and biodegradable fibers has created a demand in the transportation industry. In this study, bio castor seed shell ( C ), glass fiber ( G ), and SiC (SC) fillers in a constant weight fraction (10 %) were reinforced separately with varying weight fractions (5–25 %) of African teff and snake grass fibers to improve the mechanical properties of the hybrid composites. Both African teff and snake grass fibers were subjected to alkaline treatment to remove amorphous elements such as hemicellulose, lignin, and wax, resulting in high surface roughness. The hybrid composites were fabricated by the compression molding technique and their mechanical properties were characterized as per ASTM standards. The fractured surface of the treated fiber was examined by scanning electron microscopy. From the results, it was found that SC10SG20AT showed maximum mechanical properties compared to C10SG20AT and G10SG20AT due to higher load-bearing capacity of SiC filler. Therefore, SC10SG20AT can be recommended for lightweight applications.

The present work investigates the mechanical characteristics of randomly oriented short Sansevieria Trifasciata Fibre Polyester (STFP) composites. The STFP composites are fabricated using compression moulding methods with varying fibre weight percentages (5 %–50 %) and fibre lengths (5 mm–50 mm). It has been observed that the impact, flexural, and tensile strength of STFPs improve as the length of the fibre increases, up to a maximum of 40 mm. After that, these properties start to decrease as the length of the fibre further increases. Further, the analysis revealed that STFPs exhibited an increase in properties when the fibre weight percentage was less than 40 %, followed by a decrease in properties as the fibre percentage increased beyond that point. The impact strength of STFP is around 8.2 J/cm 2 . Similarly, the STFP has a flexural modulus and strength of about 3.4 GPa and 82.6 MPa, respectively. Lastly, the tensile strength of STFP is around 78.26 MPa, the elongation at break is between 6.25 % and 9.36 %, and the Young’s modulus is 11.8 GPa. The matrix and fibre interaction were examined by Scanning Electron Microscopy (SEM). Furthermore, Thermogravimetric (TGA) and Differential Scanning Calorimeter (DSC) analyses are carried out. From these analyses, the thermal stability of STFP is 200 °C and its activation energy is 65.48 kJ/mol. After a thorough comparison with other well-known natural fibres, the proposed properties of STFP demonstrate its superiority as a practical and effective natural fibre composite.

Natural fiber composite materials are able to compete with common synthetic materials in situations where the strength-to-weight ratio is important. In this study, we aim to analyze the mechanical, tribological, and surface morphology of composites fabricated from randomly oriented snake grass natural fiber with java plum seed filler. Different weight ratios of fiber to seed filler are chosen: 30:0, 28:2, 26:4, 24:6, 22:8, and 20:10. A 70 % epoxy resin was kept constant in all compositions. The fabricated hybrid composite samples were subjected to tensile, flexural, shear, Shore D hardness, water absorption, and wear tests as per ASTM standards, and the results were compared with those of snake grass mono fiber composites. The 20:10 composite has the maximum tensile strength, impact resistance, flexural strength, hardness, water absorption, and wear resistance compared to other composites. The fiber/matrix adhesion was explored using a scanning electron microscope (SEM). The 20:10 composite shows predominant mechanical and tribological characteristics, making it easier to utilize in structural and automotive applications.

Rigid polyurethane foams (RPUFs) were synthesized with chicken feather protein using the “one-step method” of all-water foaming. Thermogravimetry, pyrolysis kinetics analysis, Cone calorimetry and smoke density (Ds) were used to investigate the effects of chicken feather protein on thermal stability and combustion performance of RPUFs. The results showed that the modified RPUFs with 2.5 wt% chicken feather protein (RPUF-CF1) had the lowest mass loss, the highest integrated program pyrolysis temperature, the highest activation energy, the lowest Ds (13.3), the highest light transmittance (79.3 %), the lowest heat release rate (22.0 kW/m 2 and 30.6 kW/m 2 ) and total heat release (2.4 MJ/m 2 and 2.8 MJ/m 2 ), which indicated that RPUF-CF1 had better thermal stability and combustion performance. The current research results provide a useful reference for the preparation of RPUFs with good thermal stability by bio-based modification.

The epoxy composite specimens of certain sizes were produced by adding graphite, silicon carbide and boron carbide microparticles separately at the rates of 5, 10 and 15 wt% to the epoxy resin. Free vibrations of these composite samples were investigated experimentally in a simple supported vibration test setup. Frequency spectrums were obtained by modal analysis method in this experimental setup. The damping ratios were calculated using the half power bandwidth method. The mechanical properties of these composite specimens were also determined by applying the tensile test. By controlling the obtained vibration values theoretically, the effects of microparticle contributions to these specimens at certain rates on natural frequency and damping properties were investigated in detail. The maximum reduction in natural frequency was observed at 5 wt% of each reinforcement. Only the first natural frequency of the 15 wt% boron carbide reinforced epoxy composite was slightly increased. The damping ratio was increased at 10 wt% graphite added and 5 wt% boron carbide added epoxy composites compared to pure epoxy, but decreased in other composite specimens.

An in-depth study of polyvinylidene fluoride (PVDF) based nanocomposite systems will be the focus of this research. This polymer being hydrophobic and apolar, it will be unlikely to generate strong interactions with clay leaves called organophilic maghnite. The challenge of this study will therefore be to manage the load/polymer interfaces by using montmorillonite with specific surface treatments by adding a surfactant Cetyltrimethylammonium bromide. Therefore, a significant improvement in mechanical and thermal properties was observed. The properties of PVDFNC nanocomposites were evaluated using various physico-chemical techniques (XRD, FTIR, TGA, DSC, TEM, SEM). The results of the structural and thermal measurements carried out on these products reveal that the structural concept of the surfactant influences both the morphological profile, the thermal and mechanical properties of the nanocomposites obtained. Accelerated crystallization is observed in PVDNC nanocomposites as an effective nucleation agent, the crystals formed are predominantly β shaped and have a small number of polar α crystals. Measurements by X-ray diffraction, as well as transmission and scanning electron microscopy indicated that modified maghnite was perfectly distributed 3 % by weight in the polyvinylidene fluoride matrix. The mechanical properties of the nanocomposites were evaluated according to the filler material used and the polyvinylidene fluoride matrix.