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The present work addresses the optimal design of sandwich panels made of flax fabric (FF)/vinyl ester (VE) composite face sheets and honeycomb VE core. The sandwich structures are first optimized in terms of flammability by obtaining the best combination of ammonium polyphosphate (APP), halloysite nanotube (HNT), and magnesium hydroxide (MH) as three flame retardants (FRs). Using the Taguchi method and horizontal burning test, it is shown that [6, 3, and 3%] and [1, 0.5, and 0%] are the optimal combinations of APP, HNT, and MH for the face sheets and core, respectively. Cone calorimeter test results indicate that the optimal FR combinations significantly decrease the mass lost rate (MLR), heat rate release (HRR), total smoke release (TSR), and maximum average release heat emission (MARHE). The FR sandwich structures are then geometrically optimized under compressive loads based on their weight. Different failure modes are considered as the design constraints of the optimization problem. Imperialist competitive algorithm (ICA), as a powerful meta-heuristic algorithm, is implemented to considerably reduce the computational cost of the optimization process. The results of this study show that proper combinations of FR additives can increase the flame retardancy while decreasing the weight of sandwich panels.

Two main goals are pursued in the present work. First, the global buckling of axially loaded sandwich beams with composite face sheets and aluminum honeycomb cores under humid environments is investigated. An analytical solution with high accuracy is developed based on piecewise low-order shear deformation theory (PLSDT) to estimate the critical buckling loads. A parametric study is carried out to examine the influence of geometric parameters on the buckling loads of simply supported and clamped sandwich beams under different wet conditions. The obtained results indicate that humidity plays a significant role in the buckling behavior of honeycomb sandwich beams. As the second purpose of the present work, the weight minimization of sandwich beams is studied. The optimization variables include the face sheet thickness, core thickness, honeycomb cell size and honeycomb cell wall thickness. Moreover, different failure modes, including global buckling, face sheet dimpling, face sheet wrinkling, core shear instability, and face sheet failure are considered as design constraints. Imperialist competitive algorithm (ICA), a powerful socio-politically motivated global search strategy, is applied to handle the constrained optimization problem. The optimization results show that the presence of humidity in the environment significantly changes the optimal design of sandwich beams and makes them heavier. Furthermore, it is observed that by increasing the length of the structure, the optimal design is more affected by humidity. Moreover, it is found that ICA is a very powerful optimization tool both in obtaining the best values of geometric parameters and in reducing the computational cost. [ABSTRACT FROM AUTHOR]

While the potential of natural fiber (NF) composites for various engineering applications is well‐recognized, a deep understanding of the intricate interactions within these composites remains crucial. This study examines the microstructural characteristics of the polymer matrix and evaluates the impact of reinforcement size, with a particular focus on fire sensitivity. Hybrid‐reinforced polypropylene (PP) composites were introduced using a unique tri‐hybrid system. This system combines long flax fibers (LFF) as primary reinforcement, with short basalt fibers (BF) and micro rice husk powder (RHP) as secondary reinforcements. These composites were fabricated using innovative extrusion, compression, and injection molding techniques. This novel fabrication method and strategic hybrid design bridged gaps in the composite structure, leading to significant enhancements in tensile and flexural strength. Improvements of 57.82%, 67.53%, and 60.02% over LFF/PP composites were observed, respectively. On the thermal front, the char residue surged by an impressive 497.51%. Flame properties, notably pHRR and THR, were reduced by 57.25% and 13.28%, respectively. These enhancements are attributed to the lignin in BF and the silica in RHP. The fire safety index further confirmed these improvements, with FGI and FPI increasing by 27.33% and 111.11%, respectively. [ABSTRACT FROM AUTHOR]

The utilization of plastic waste is another way to protect the ecology and reduce plastic pollution, which researchers and industries have been effectively focusing on for the last decade. Polyethylene terephthalate felt (PETf) is a packaging material abundantly utilized in the automotive sector and is released as waste, and its popularity as an industrial waste necessitates attention to proper disposal. Therefore, the current study utilized waste PETf as a reinforcement (5–15 wt%) for a polypropylene (PP) matrix using various molding approaches, in light of the higher aspect ratio of the fibers. In the first approach, the fibers were extracted from PETf through a mechanical process, and various percentages of PET felt fibers (PETff) were extruded with PP pellets, followed by injection molding. Second, PETf was directly laid on a PP sheet and processed by compression molding. The tensile strength, tensile modulus, and morphological and spectral properties of the fabricated composites were evaluated. Morphological and spectral analyses explain the distribution and interaction of the fibers in the PP matrix. The 10%PETff enhanced the tensile strength and modulus of PP by 37.3% and 52.15%, respectively. Conversely, the 1.5% malic anhydride‐g‐PP (MAPP)‐PP/PETf composites showed similar tensile behavior, with values of approximately 41.53 MPa and 1.6 GPa. In addition, the tensile strength significantly increased by 35.75% with the addition of MAPP. Overall, the current study demonstrates a well‐structured research design that effectively employs waste PETf as reinforcement for PP composites. The mechanical strength of these composites makes them highly versatile and renders them suitable for a wide range of applications, from automotive packaging to the manufacturing of high‐performance automotive components. Highlights: Utilized waste PET as reinforcement for manufacturing of PP composite.PET and PP interacted in a self‐reinforcing manner.Injection and compression molding techniques used for PET/PP composites.Repurposing waste PET by compression molding is eco‐friendly practices.PET fibers significantly improved mechanical properties of PP composites. [ABSTRACT FROM AUTHOR]