Sergio Luiz Moni Ribeiro Filho

In the construction industry, PVC pipe off-cuts constitute a significant source of high-quality waste that is frequently disposed of in landfill. This study develops and evaluates the physical and flexural performance of environmentally sustainable aluminium-faced sandwich panels incorporating upcycled PVC pipe off-cuts as a circular honeycomb core. The core is manufactured by arranging PVC rings in cubic and orthotropic configurations, with or without mechanical interlocking joints, and bonding them to structural aluminium face sheets using an epoxy adhesive. A factorial Design of Experiments (DoE), combined with Analysis of Variance (ANOVA) and Student’s t-test, is employed to quantify the effects of ring diameter (20 mm and 32 mm), packing geometry (cubic and orthotropic), and mechanical interlocking on the equivalent density, flexural strength, and flexural modulus of the sandwich panels under three-point bending. The results indicate that the orthotropic packing geometry increases the flexural strength by 3.6% compared with the cubic configuration (p < 0.05). In addition, reducing the ring diameter to 20 mm increases the flexural modulus by 4.7%, while pristine core assemblies (without mechanical interlocking) exhibit a flexural modulus 2.7% higher than that of interlocked cores (p < 0.05). Overall, the proposed sandwich structures demonstrate that upcycled PVC pipe off-cuts provide a technically viable and sustainable alternative to conventional core materials for lightweight structural sandwich applications, contributing to both waste valorisation and circular economy strategies.

Hybrid composites are an advanced solution that offers multifunctional capabilities, including exceptional strength-to-weight ratios, vibrational damping and impact absorption. This work describes the damping capacity and flexural behaviour of a hybrid fibrous-particulate system composed of glass/carbon fabrics and three distinct micro-inclusions: silica particles, carbon waste microfibres, and cement. A statistical methodology based on the full factorial design is applied to identify the effects of fibre stacking sequence, including carbon-C₅, glass-G₅, C₂G₃, G₃C₂, GCGCG and CG₃C, microparticle inclusions and matrix/fibre volume fraction (40/60 and 60/40) on damping and bending responses. A non-linear finite element (FE) analysis is conducted to explore the stress distribution based on the stacking sequence and predict the failure mechanisms of the hybrid laminate. The results indicate significant interaction effects, with hybrid architectures showcasing approximately 33% higher performance compared to glass fibre composites. A greater dependence on the fibre layup sequence is found for the damping factor, flexural modulus and strength. Notably, the incorporation of silica microparticles leads to an increase in flexural strength. Furthermore, a greater volume fraction of the matrix phase enhances the rheological efficiency in terms of the fibre-particle interface. Carbon fibre layers placed symmetrically on both beam sides (CG₃C) and bottom layers (G₃C₂) significantly enhance the bending performance of hybrid composites.

Composite materials are used in a substantial number of products. Environmental concerns highlight the need for the inclusion of recovered waste in their formulation, thus reducing their carbon footprint. These solutions raise the need to confirm the mechanical characteristics of these materials, avoiding unwanted failures. In this work, the authors present an experimental study on the drilling effects on fibrous–particulate hybrid composites made of glass/carbon fabrics and three different micro-inclusions: silica particles, recycled carbon fibre powder and cement. The mechanical features of the plates are confirmed by thrust force monitoring during drilling and by flexural testing. The range of results confirm the mechanical outcomes due to machining. The plates with monolithic carbon fabric or with carbon fabric plies in the outer plies returned higher mechanical characteristics. The plates with micro-inclusions had enhanced the flexural strength by 23% and 10%, in 40% and 60% fabric plates, respectively. The results demonstrate that the use of alternative formulations with micro-inclusions from recovered waste can contribute both to the reduction of the mechanical degradation of drilled hybrid composites and to environmental purposes by avoiding the increase in landfill waste.

This paper investigates the normal hardness, the compressive strength, and the modulus (parallel to the grain) of Pinus caribaea var. hondurensis wood in pristine condition and impregnated with methyl methacrylate (MMA) in autoclave at 0.22 and 0.66 MPa. An artificial weathering over a period of 2,400 h was used to better assess its effect upon the mechanical properties of impregnated wood. The analysis of variance identified that MMA impregnation significantly affected the responses; in contrast, no effect was verified by the artificial aging factor. Treated Pinus wood at 0.66 MPa achieved superior mechanical properties compared with the pristine condition, revealing percent increases in compressive strength, stiffness, and hardness of 84, 36, and 347%, respectively. The scanning electron microscopy (SEM) analysis revealed the MMA polymer was able to fill the wood pores completely. Possibly, impregnated Pinus wood can be used in structural applications in civil construction, in addition to being ...