Composites Part C Open Access最新文献

The study aimed to test the hypothesis that biochar's unique properties, such as its microporous structure, can enhance concrete's resilience to high temperatures. Despite expectations of reduced crack formation and enhanced fire resistance, the experimental results revealed a limited impact on concrete's fire behaviour. The investigation involved the use of two biochar types, fine and coarse biochar as replacements for cement and aggregates, respectively. Fine biochar exhibited higher water absorption and Young's modulus than coarse biochar, but both resisted ignition at 35 kW/m² radiative heat flux and had peak heat release rates below 40 kW/m². Incorporating these biochars at varying weight percentages (10, 15, and 20 wt.%) into concrete led to a gradual decline in compressive and tensile strength due to reduced binding ability with increased biochar content. Exposure to 1000 °C compromised mechanical properties across all the samples. However, the biochar concrete maintained compressive strength (compared to the control) with up to 20 wt.% biochar as a fine aggregate substitute after exposure to 600 °C, and as a cement replacement after exposure to 200 °C. This substitution also yielded a significant reduction in CO₂ emissions (50 % reduction as the biochar loading amount doubled) from concrete manufacturing, showcasing biochar's potential for sustainable construction practices. Despite not fully supporting the initial hypothesis, the study demonstrated biochar's viability in reducing carbon footprint while maintaining concrete strength under certain fire conditions.

Recent advancements in additive manufacturing (AM), which includes both three-dimensional (3D) and four-dimensional (4D) printing, have revolutionized manufacturing processes across the board. Fused deposition modeling (FDM) is one of the most widespread 3D printing technique that enables the use of a wide range of virgin polymers and polymer-based composites to meet the demand for high-performance, intelligent, and self-assembling structures. Although polymer-based composites offer a variety of multifunctional properties, it is essential to comprehend the mechanical and microstructural properties of parts printed with virgin polymers to analyze and design the additives and reinforcements required to achieve the optimal desired functionalities. Overall, this review focuses on the adoption and applications of virgin FDM polymers and highlights different virgin polymers and equipment used in 3D and 4D printing. A comparative study on the mechanical and microstructural properties of various FDM polymers is also performed. In addition, this work also covers the state-of-the-art approaches and practices used for 4D printing of polymer-based systems and future directions for this field.

This paper presents the novel development of the dynamic stiffness matrix for a three-layered symmetric pre-twisted sandwich beam (PTSB), aiming to investigate its free vibration characteristics. The outer layers of the beam are modeled using the Euler–Bernoulli theory, while the core is assumed to deform solely in shear. The boundary conditions and governing partial differential equations of motion are derived based on Hamilton's principle. By applying harmonic variations of displacements, the governing equations of motion are expressed as a tenth-order equation, which is solved to obtain the desired dynamic stiffness matrix. To compute the natural frequencies of in-plane and out-of-plane free vibration for both uniform and PTSBs, the Wittrick–Williams algorithm is employed. The computed frequencies are compared with the results obtained by other authors as well as those obtained from ABAQUS simulations. Various vibration modes of uniform and twisted sandwich beams are plotted and thoroughly discussed. Interestingly, contrary to straight symmetric sandwich beams, the results indicate that flexural displacements in pre-twisted symmetric sandwich beams exhibit coupling in two planes. Additionally, although there are minor changes in vibration frequencies, the mode shapes undergo significant transformations as the pre-twist angle is altered.

The use of thermoplastic composites as a sustainable alternative to thermosets is gaining increasing popularity due to their improved recyclability at the end of life. The fatigue performance of glass fibre/acrylic, glass fibre/acrylic- polyphenylene ether, and glass fibre/epoxy specimens, under three distinct upper stress levels (R-ratio = 0.1; f = 5 Hz) was studied. S–N curves were established for these specimens both before and after immersing them for three months in seawater (temperature: 50 °C). The dry thermoplastic composites exhibited similar fatigue performance to the thermoset counterpart at higher stress levels, with thermosets showing greater endurance at lower stress levels. Interestingly, the aged specimens showed comparable fatigue endurance, with a slight advantage in favour of the thermoplastic composites and less variability in their data. This study offers important insights into the fatigue performance of thermoplastic composites, emphasising their potential as sustainable alternatives to conventional thermoset composites for various marine applications.

This research reports the results of implementation of composite materials and the complete redesign of a tipping silo semi-trailer. The conventional semi-trailer, used for comparison, was designed based on a Feldbinder commercial model, while the innovative one has the same overall dimensions but a new geometry, while maintaining the same performance in terms of deflection and safety factor. The research involves sizing and verification of the results obtained using finite element software (Solidworks Simulation®) with different loading conditions. The main result is that the optimised solution has the lowest weight, with a reduction of about 28 % considering the same equipment and accessories mounted on the two solutions. The last part of the research concerns an estimate of economic investment containing the return on the initial investment and the reduction in fuel consumption by comparing the two solutions. Considering that the vehicle always carries the maximum (payload = 27,500 kg) and the overall weight reduction of about 1800 kg, there is a reduction in fuel consumption for the proposed solution. The return on investment for the new solution occurs between three/four years depending on the number of kilometres driven annually. Finally, the purpose of this paper is to create an example of a procedure for reducing the carbon footprint and the fuel consumption of vehicles by replace and redesign entire mechanical components, in this case industrial vehicles, that would be useful to follow and replicate for any specific case study and increase the eco-sustainability of industrial manufacturers.

The quest for light weight hybrid polymer composites (HPC) has resulted into multiple materials and structural configurations for achieving high performance in automotive and aerospace applications. Incidentally, the past reported work has (in general) involved variable GSM while investigating reinforced fiber layers. The variable GSM may lead to a random response of each layer to the applied forces and thermal degradation, due to which attributing the role of various layers to results/properties is difficult to ascertain. This research employs a uniform/consistent approach with high GSM (400) based HPC with multiple stacking sequences of glass (G), carbon (C), and Kevlar (K) to investigate thermo-mechanical properties. The research first focuses on fabrication of eleven stacking sequences of hybrid combinations, followed by identification of an optimal sequence based on mechanical (tensile strength, flexural strength, charpy impact resistance) and thermogravimetric analysis (TGA) characterization. Additionally, scanning electron microscopy (SEM) for fracture mechanisms of hybrid composites showing fiber pull out, matrix crack, and delamination. Results show that the tertiary combination having 2 Glass, 5 Carbon and 5 Kevlar layers (G2C5K5) named H9 herein provides a good balance of tensile, flexural, impact resistance and thermal properties; its deviation from the best of each category is within approximately 5, 13.5, 9.9 and 10.9 % (for tensile, flexural, impact, TGA) respectively. The range of properties evaluated in this study is deemed suitable for lightweight aircraft structures.

A semi-analytical procedure is presented for predicting the complete flexural response of partially interacting steel–concrete composite beams up to failure. The governing equation of the Euler–Bernoulli beam theory is solved wherein concrete, steel and the shear connectors joining the concrete slab to the steel beam are assumed to have nonlinear stress-deformation relationships. The adopted constitutive relationship for the connectors allows for partial or full composite action. The solution is applicable to beams and one-way slabs subjected to concentrated or uniform load and/or their combination. The governing equation is numerically solved by satisfying the equilibrium and compatibility requirements along the member. For the reinforced concrete part of the composite beam, a nonlinear moment–curvature relationship is developed that accounts for concrete nonlinearity in compression and for cracking and tension-stiffening in tension as well as for steel reinforcement nonlinearity. The steel profile is assumed to have a bilinear elasto–plastic strain-hardening moment–curvature relationship. Comparison of the proposed model results with the corresponding experimental load–deflection curves and interfacial shear–slip curves of several beams tested by others shows good agreement. The relative simplicity, efficiency and easy application of the present solution make it possible to accurately predict the failure load, interfacial slip and full nonlinear response of partially interacting composite beams.

Recent earthquakes have highlighted the need to strengthen existing structures with substandard designs. NFRPs provide a sustainable, cost-effective alternative for strengthening, but accurately predicting their performance remains a challenge. This study investigates the use of machine learning algorithms for predicting the compressive strength concrete specimens confined with various NFRPs. Four algorithms were employed: decision tree, random forest, neural network, and gradient boosting regressor. A diverse dataset encompassing various geometries, material properties, and confinement configurations was used to train and evaluate the models. Gradient boosting regressor (GBR) achieved the highest performance, with an average R-squared value of 0.94 and low mean absolute error (MAE) and root mean squared error (RMSE) during training and k-fold cross-validation. Neural network and random forest also demonstrated satisfactory performance, with average R-squared values of 0.88 and 0.86, respectively, during cross-validation. These results suggest that machine learning holds promise for predicting the compressive strength of concrete confined with NFRPs. GBR offers the most accurate predictions, making it a valuable tool for engineers seeking to optimize the design and performance of strengthened structures using sustainable materials.

The purpose of this research was to develop “green” materials by combining poly(lactic acid) (PLA) with two agricultural by-products, namely flax seed meal (FSM) and rapeseed straw (RSS). The natural fillers (0–20 wt.%) were mixed with PLA through extrusion and then injection molded into specimens. The samples were analyzed for their thermal, morphological, mechanical, and physical features and biodegradability. Thermal properties and crystallinity were analyzed using Differential Scanning Calorimetry (DSC), while the morphology was investigated by Scanning Electron Microscopy (SEM). Mechanical properties were characterized through tensile, flexural, and impact measurements, while surface hardness was evaluated by Shore D tests. Water absorption and biodegradability of the samples were also examined. DSC measurements revealed a nucleating effect of both bio-fillers. Based on the tensile tests, major improvement in stiffness was found with the biocomposites having up to ∼16 % higher Young's modulus than neat PLA (2.5 GPa). It came, however, at the cost of tensile strength, which decreased from 56 to 51 MPa even in the presence of the lowest amount (2.5 wt.%) of FSM. Loss in strength was due to the limited adhesion between the components, as also supported by SEM images. The hardness slightly (1–2 %) improved in the presence of even 2.5 wt.% bio-filler and it remained at that level at higher filler loading as well. Laboratory-scale composting revealed that both fillers facilitated biodegradation with FSM being superior. In the presence of 10–20 wt.% FSM, the rate of decomposition was found to be twice as fast compared to neat PLA.

Polymers and their composites are now widely used in several industrial sectors, owing to their flexibility in developing customized products. The significant surge in plastic usage has led to a severe challenge in managing end-of-life plastic waste. Millions of tons of plastic waste produced annually mainly end up in landfills, leaking into the environment and posing severe threats to ecosystems. Innovative solutions to reuse/recycle/repurpose plastic waste are desired to address these global challenges. Therefore, in this study, a sustainable route to converting plastic waste into additive manufacturing (AM) feedstock is presented, where waste plastic bottles (mainly Polyethylene Terephthalate, PET) are recycled using an in-house 3D-printed filament extrusion system to produce filaments for fused filament fabrication (FFF) process. In addition to the recycled PET (rPET), virgin carbon fiber reinforced polyamide-6 (PA6-CF) polymer composites were also used to produce hybrid feedstock filaments. The rPET and rPET/PA6-CF composite filaments were extruded using an in-house filament extruder setup. The produced rPET-based filaments were characterized for their chemical and thermal properties. Subsequently, mechanical characterization was performed on 3D-printed specimens. The mechanical analysis revealed better tensile strength for rPET/PA6-CF than rPET; however, the rPET demonstrated better failure strain and young modulus, demonstrating their potential as viable materials for industrial and consumer applications. The outcomes of this study revealed promising results to promote sustainable production and consumption, complementing the circular economy practices with a straightforward production route to convert plastic waste into AM feedstock.