Laminate composites are increasingly being used in the transport sector due to their lightweight structures, resulting in fuel savings. However, waste is generated in the form of post-industrial or post-consumer goods that end up in landfill or incineration. One way to minimize the impact of these disposals is through recycling or reuse, but introducing reused fibers with reduced length has been a challenge to keep the mechanical properties. In this context, this research aims to evaluate the influence of the fabric (satin weave) length on the tensile properties of discontinuous laminate and investigate the failure process of such composites manufactured with carbon fabric waste generated at the cutting process. For this purpose, two types of laminates were manufactured, each comprised of five plies (i) three continuous plies and two discontinuous plies; and (ii) one continuous ply and four discontinuous plies with varied fiber length. The laminates were tested by tensile loading, and the strain field was monitored by a non-contact technique called digital image correlation (DIC), which allowed the investigation of the local strain variation due to the interrupted section. It was possible to observe a sharp stress range in which the joint failure was evidenced by strain field variation over the joint. For both laminates, it was possible to depict the events that constrain the tensile strength of the discontinuous laminates, which is severe in laminates with surface discontinuity, and it shows to be advantageous to employ a continuous ply on both surfaces, improving loading transfer between plies. Highlights: Environmental problem related to carbon fiber waste from the cutting process. Take advantage of using small pieces of carbon fiber fabric in laminate architecture. Investigation of the influence of fabric disposition and fabric length on in-plane mechanical properties. Analysis of failure events using strain field measurements via DIC.

The design of damage-tolerant aeronautical composite structures often involves thin-walled components that are susceptible to in-plane mixed-mode fracture. Unlike with metals, this process is complicated by the composites anisotropy and the lack of standardized procedures for predicting failure in notched, holed or cracked composites under mixed-mode loading. This study introduces a novel Modified Arcan Fixture (MAF) for testing Compact Tension Shear (CTS) specimens of carbon fibre woven reinforced polymer composite. Digital Image Correlation (DIC) was used to capture strain fields and calculate Stress Intensity Factors (SIFs), which were then compared to analytical predictions for different mode combinations and notch lengths. R-curves were generated for specimens exhibiting self-similar crack propagation. The results revealed that failure modes were dominated by tensile cracking in Mode I and compressive cracking in Mode II, indicating that a single-parameter fracture criterion inadequate for the failure description. A theoretical model that incorporates both tensile and compressive cracking is proposed, which can accurately predict the complete mixed-mode fracture envelope. Furthermore, Scanning Electron Microscopy (SEM) and X-ray micro-tomography were used to elucidate the mechanisms of surface failure and the morphology of internal damage.

Three-phase composites, especially those composed of high performance thermoplastics, have not been properly investigated with respect to their interlaminar fracture toughness. Therefore, this study investigates effect on the interlaminar fracture toughness by adding carbon nanotube buckypaper (BP), tested under cyclic loading in mode I and II. BP weakened the interlaminar fracture toughness in mode I, creating an easy path for crack growth and reducing the strain energy release (SERR) values in the Paris curves. Conversely, under mode II BPs presented no significant influence to the interlaminar fracture toughness and fatigue life; however, a slight improvement was observed due to the bridging effect. The energy balance principle model for opening delamination showed that BP composites require less energy per unit of area to crack growth, resulting in a smoother fracture surface with fewer failure mechanisms. In contrast, BP slightly increased the energy per unit of area for crack growth, leading to a rougher fracture surface with a higher prevalence of failure mechanisms under mode II. This work underscores the importance of examining the individual effects of mode I and II loadings on BP laminates since these interleaves affect the interlaminar toughness and fatigue life differently.

Discharging oil-contaminated wastewater into the environment without adequate treatment can have a negative impact on water resources, public water and wastewater treatment systems, and even human health. In this sense, it is essential to develop compact, easily automated, low-cost, and highly efficient unitary treatment processes in order to comply with legal requirements regarding effluent emission standards for water bodies. Therefore, the present study consisted of the development of two treatment processes aimed at the separation of oil emulsions stabilised by anionic surfactants: a sorption column using polyurethane/graphene foam composites as sorbent material and a continuous flow AC electroflotation reactor. Initially, composites with 0.5% and 1% w/w graphene (based on polyol mass) were developed using a dispersing agent (1-methyl-2-pyrrolidone). The foams were characterised in terms of morphology and mechanical and sorption properties. In the fixed bed column, the foams retained up to 77.15% of the emulsified oil and 52.36% of the anionic surfactants. In the continuous flow electroflotation reactor, emulsified oil removal efficiencies above 90% were achieved at all electrical currents tested, and up to 88.6% of anionic surfactants were removed at an electrical current of 150 A. Given the advantages and disadvantages of the two oily effluent treatment processes, their combined use in the same system proved promising.

Delamination fatigue propagation is known to cause a progressive degradation of stiffness and strength in composite laminates. Since delamination tends to follow a preferential plane, fracture resistance is conveniently analysed in terms of dominant loading modes at the crack tip: mode I (opening) and mode II (shearing). To this end, coupon tests can be performed to determine the growth rates under these particular stress states. Paris parameters from such tests are then often used in numerical implementations adopting mesoscale modelling, like in the case of cohesive element traction-separation laws. The majority of coupon tests available in the literature focus on interfaces where the fibres of the upper and lower plies have the same orientation, typically aligned with the direction of delamination growth. However, most practical applications involve multidirectional laminates, where delamination tends to develop at interfaces where the upper and lower plies have mismatching angles. Studying angled interfaces may lead to different results since some fracture phenomena, like fibre bridging and crack migration, are highly dependent on fibre orientations of plies adjacent to the delaminated interface [1].
The present work experimentally explored the various effects of fibre orientation on fatigue delamination growth in the different fracture modes. IM7/8552 carbon fibre epoxy prepreg (Hexcel), a material system commonly adopted in aerospace field, was tested under mode I Double Cantilever Beam (DCB), mode II End-Loaded Split (ELS), and Mixed-Mode Bending (MMB) tests. For all cases a combination of different interfacial fibre orientations were tested and the crack growth rate curves were compared in relation to the observed fracture behaviour.

Cellulose-derived battery separators have emerged as a viable sustainable alternative to conventional synthetic materials like polypropylene and polyethylene. Sourced from renewable and biodegradable materials, cellulose derivatives—such as nanofibers, nanocrystals, cellulose acetate, bacterial cellulose, and regenerated cellulose—exhibit a reduced environmental footprint while enhancing battery safety and performance. One of the key advantages of cellulose is its ability to act as a hybrid separator, using its unique properties to improve the performance and durability of battery systems. These separators can consist of cellulose particles combined with supporting polymers, or even a pure cellulose membrane enhanced by the incorporation of additives. Nevertheless, the manufacturing of cellulose separators encounters obstacles due to the constraints of existing production techniques, including electrospinning, vacuum filtration, and phase inversion. Although these methods are effective, they pose challenges for large-scale industrial application. This review examines the characteristics of cellulose and its derivatives, alongside various processing techniques for fabricating separators and assessing their efficacy in battery applications. Additionally, it will consider the environmental implications and the primary challenges and opportunities associated with the use of cellulose separators in energy storage systems. Ultimately, the review underscores the significance of cellulose-based battery separators as a promising approach that aligns with the increasing demand for sustainable technologies in the energy storage domain.

Impact damage to composite structures results in multiple, complex failure modes, often requiring the replacement of entire components and thereby escalating aircraft maintenance costs. To address this issue, the present study investigates the damage propagation behaviour with particular emphasis on intra- and interlaminar failure modes. Carbon fibre/epoxy composites were subjected to tensile after impact (TAI) fatigue tests at different energy levels to induce different damage modes and extents within the specimens. A non-destructive testing technique (C-scan) was used to assess the interlaminar damage propagation, while the intralaminar fracture toughness of the post-impact specimens was characterised using a finite fracture mechanics model. The results show that the crack propagation behaviour is strongly influenced by the initial impact damage characteristics, in particular the impact energy level. Lower impact energies tend to promote interlaminar failure modes leading to fatigue crack propagation by delamination. Conversely, higher impact energy levels induce fibre fracture, resulting in a self-similar relationship between intra- and interlaminar propagation.

Characterisation of the effect of lay-up on the delamination growth revealed a complex set of damage characteristics. Tortuous propagation resulted in higher fibre bridge densification in the off-axis laminates, requiring an increased number of experimental tests to validate the characterisation of fibre bridge saturation effects. The main objective of this research is to apply a modified Sørensen model [1] to measure the fibre bridge (FB) stress curve. In addition, the research aims to estimate the full saturation curve. These objectives will contribute to a more efficient and accurate characterisation of fatigue delamination behaviour in composite materials. The procedure was carried out using a model proposed in the literature [2] for unidirectional composites, to estimate positions of the sull-saturated and fibre bridge Paris curves. The proposed model, based on physical considerations of FB stress formation, was applied to a quasi-static curve and a fatigue curve for each lay-up: 0//0, 0//45 and 0//90. Based on the resulting R-curve, the FB stress curve is derived for each case. This approach accurately models the fatigue behaviour and bridging effects in composites by providing the zero bridging curve (Fig. 1). Following a similar procedure, but now adding the full saturation stress integrated along the end opening delamination, provides the additional strain energy in the steady state region (Fig. 1). This approach allows a more efficient and cost-effective characterisation of fatigue delamination behaviour with a reduced number of experiments, and evaluates the feasibility of applying the proposed model to a single quasi-static and fatigue curve. In addition, the proposed method addresses a comprehensive understanding of fatigue behaviour considering the effect of fibre orientation, thereby contributing to a more comprehensive understanding of fatigue behaviour.

Studies have shown that temperature and moisture play a critical role in altering material properties, with both factors contributing to the overall degradation of structural components. This research aims to provide a deeper insight into the complex interplay between environmental factors and fatigue delamination behaviour in composite materials. To this end, the effect of hygrothermal aging and in-service temperature conditions on mode I fatigue delamination was investigated considering the relationship between fracture surface patterns and fatigue propagation behaviour. To investigate the effects of in-service temperature, Mode I delamination tests followed standardised protocols with pristine (unaged) samples tested at -40, 22, and 80ºC. Hygrothermal ageing (HA) was performed in a climatic chamber at 90ºC and 90% relative humidity for 60 days. After reaching an equilibrium moisture content of 1.2%, the samples were tested at in-service temperature levels of -40, 22, and 80ºC. The in-service humidity was set at 50% in all cases to ensure control of the absorbed moisture under the previous HA conditions. The fatigue curves were remarkbly affected by hygrothermal ageing, as a consequence of the change in the material properties. The individual effect of in-service temperature leads to a temperature-dependent variation in the slope of the da/dN versus dU/dN curves. On the other hand, hygrothermal ageing consistently reduced the slope of all curves, compared to pristine samples (Fig. 1a). The results confirm that temperature inversely affects the slope of the fatigue propagation curve, while hygrothermal ageing promotes a tougher fracture behaviour. The fractography investigation reveals that the surface roughness (Fig. 1b) follows the same trend as the dU/dN slope: higher slopes (lower temperature) correspond to less damage (lower tortuosity), while lower slopes (higher temperature) indicate more damage represented by higher surface roughness.

This research investigated the combination of acid functionalization and metal deposition on commercial activated carbon (AC) for the synthesis of electrodes for applications in supercapacitors. The effect of acid treatment and the deposition of metals, including nickel, copper, and cobalt on the electrochemical characteristics of the carbon material were assessed. The AC treatment with sulfuric acid resulted in a nearly twofold increase in surface area compared to the untreated AC, enhancing porosity and creating irregularities that improved the motion of ions and electrons, increasing the specific capacitance and energy density. Notably, we demonstrate that nickel deposition at only 2 wt% significantly improved specific capacitance (up to 59.58 F·g⁻¹), while preserving porosity and enhancing surface wettability. The adoption of a scalable, solvent-free, and low-energy technique for metal deposition on carbon structures presents promising opportunities for developing sustainable alternatives in energy storage technologies.

Fibre bridging is an important phenomenon influencing the mode I delamination growth behaviour in composite materials. Accurate modelling of this phenomenon is required in order to be able to account for its effects in damage tolerance evaluation of composite structures. Therefore, this study introduces a novel physical model to isolate and quantify the contribution of fibre bridging to Mode I fatigue delamination. The model distinguishes between monotonic and cyclic components of fibre bridging stress, capturing their individual effects on the strain energy release rate (SERR) in the Paris curve. The monotonic component, based on the Sørensen model, accounts for pre-cracking effects, while the cyclic component is derived by integrating a bridging stress function over the end-opening displacement, with both components modelled by empirical exponential relationships. The model has been validated against established methods such as the Yao model and specific extrapolation techniques, demonstrating improved accuracy in fitting the Paris curve, particularly in accounting for the monotonic influence in the shift of the SERR and the cyclic contribution to the curve slope. Importantly, the model requires only one quasi-static and one fatigue test, reducing the experimental workload. In conclusion, this method provides a more accurate characterisation of fibre bridging effects, making it a robust tool for fatigue delamination analysis.

The aim of this research is to evaluate the physical, chemical, thermal, and mechanical properties of Itauba (Mezilaurus itauba) wood fiber and Itauba wooden board. The chemical composition presented 33, 29, and 10% lignin, cellulose, and hemicellulose, respectively. The thermal stability was found to be 250 °C for both atmospheres (air and nitrogen), and the simulated TG curve was similar to the one performed on a nitrogen atmosphere. Cone calorimetric results showed a higher steady state when compared to other wood fibers found in the literature with peak heat release rates of 281.762, 424.029, and 482.335 kW/m²when exposed to constant levels of radiant heat flux of 25, 50, and 75 kW/m²at similar weights and densities. Furthermore, X-ray diffraction (13.5% crystallinity) and mechanical tests (flexural and tensile Young’s modulus of 12010 and 969.9 MPa, respectively) were performed on the Itauba wooden board. The tensile results showed to be higher than propylene composites reinforced with 40% wood fiber found in the literature while the storage modulus obtained in the dynamic mechanical thermal analysis found to be higher (11.5 GPa at −130 °C) than most of the commercial thermoplastics used in the industry (polypropylene (9 × 10²MPa), high-density polyethylene (2 × 10³MPa), and polyvinyl chloride (3000 MPa)). This study showed the potential in using Itauba wooden boards in replacing many commercial products, mainly when an adequate mechanical performance is required.

The present study aims to evaluate thin plate-injected polypropylene (PP) composites containing short aramid fibers (AF) and graphene nanoplatelets (GNPs). The aramid fibers were manually cut to a length of 10 mm and added to the polypropylene matrix at a concentration of 10 wt.%. Additionally, GNPs were incorporated at concentrations of 0.1, 0.25, and 0.5 wt.%. Maleic anhydride grafted polypropylene (MAPP) was used at a concentration of 2 wt.% to improve the adhesion and compatibility between the polymer matrix and the fillers. Thermal analyses, tensile and flexural tests, and dynamic mechanical thermal analysis were performed, followed by statistical analysis using ANOVA and Tukey’s test. The composites demonstrated significant improvements in storage and loss moduli compared to neat polypropylene. With the addition of AF and GNPs, tensile strength increased to 46.8 MPa, which represents a 265% enhancement compared to PP. Similarly, flexural strength reached 62.4 MPa, significantly higher than the 36.73 MPa for PP, particularly for the composite containing AF and 0.25 wt.% GNPs. The results presented in this study highlight the synergistic effect of aramid fibers and GNPs on PP. These improvements make the proposed composites highly promising for a range of applications, including ballistic interlayered aramid/thin-plate laminates.

Laminated pultruded composite plates are gaining interest for use in wind turbine blades due to their excellent structural performance with affordable cost. However, there is limited understanding of their fracture properties. The present work explores the interlaminar fracture behaviour of pultruded composite plates, bonded through resin infusion, to form thick CFRP structures. Mode-I, −II, and mixed-mode (I/II) tests were performed to obtain fracture properties at different mixed-mode ratios. Mode I crack propagation exhibits stick–slip behaviour, resulting in brittle failure in a few steps, while mode II provides more stable crack propagation along with cohesive failure. The mixed-mode fracture patterns follow the trend of the mode-mix ratios, in which higher mode-mix ratios (more mode II) induce more stable crack propagation. Benzeggagh-Kenane and power law criteria were compared regarding their prediction of crack initiation toughness given a mode mix ratio, and a linear relation between the mixed mode I/II fracture toughness components could exist at interfaces of laminated pultruded plates. Meanwhile, applicability of testing standards and the effect of manufacturing-induced defects on fracture properties are thoroughly discussed. The results show that existing standards provide sufficient support for characterising fracture properties of bonded pultruded plates; and that manufacturing-induced defects can be detrimental to crack propagation and cause more brittle behaviour in mode I dominant cases, while beneficial effect of defects by toughening the interface was exhibited in mode II dominant cases.

Wood is a versatile material extensively utilized across industries due to its low density, favorable mechanical properties, and environmental benefits. However, despite considerable research, the diversity in species with varying compositions and properties remains insufficiently explored, particularly for native woods. A deeper understanding of these differences is crucial for optimizing their industrial applications. This study investigated the composition, tensile strength, flexural strength, Young’s modulus, bending stiffness and elongation at break, thermal behavior, and viscoelastic properties of three Brazilian native wood species: Araucaria angustifolia (ARA), Dipterix odorata (DOD), and Tabeuia ochracea (TOC). The density of these woods showed a linear correlation with mechanical properties such as Young’s modulus (0.9) and flexural modulus (0.9). The research revealed a linear correlation between the woods’ density and mechanical properties, with lignin content emerging as a key determinant of thermal stability. This study highlights the importance of understanding wood species’ composition and physical properties, and provides valuable insights into their behavior.

Driven by the energy transition and the reduction of carbon emissions, pultruded CFRP plates have emerged as an affordable high performance material for designing wind turbines with larger rotors. To enable the creation of thicker laminates, pre-cured plates are bonded together using an epoxy resin. The present study focuses on characterizing the fracture behaviours of these laminated bonded plates under different modes, and to generate fracture criteria for numerical simulations establishing design allowables and service life. Double cantilever beam tests, end-loaded split tests, and mixed-mode bending tests were conducted under quasi static loading for such plates. Mode I crack propagation showed brittle failure while mode II fracture tests on the other hand, presented a more stable crack growth. Finally, power law and Benzeggagh-Kenane law criteria were established to numerically describe the fracture behaviours. Overall, the results show that the available standards for fracture toughness testing are also suitable for these laminated-pultruded composite plate structures, enabling the material characterization needed for design.

This paper investigates the fatigue-induced delamination growth in carbon fibre-reinforced polymer (CFRP), considering different fibre orientation combinations. The study explores the application of Artificial Neural Networks (ANN) in the simulation of fatigue delamination behaviour to reduce the number of experimental tests required for fatigue evaluation and eventual certification. The research aims to evaluate the effectiveness of ANN at different stages of data processing, including raw data simulation and final curve estimation. The results show that applying ANN at the raw data stage provides flexibility in modelling, with error < 10%. In addition, when ANN is applied directly to the final Paris curve, it minimises errors and increases reliability, allowing for a more cost-effective fatigue evaluation process. The study highlights the importance of the data processing stages in determining the accuracy of fatigue delamination predictions with AI modelling, thus informing strategies for efficient fatigue evaluation of CFRP components in structural applications. 

The demand to capture translaminar crack growth under fatigue loading scenarios led this work contribution to carry out the Finite Fracture Mechanics (FFM) method in fatigue damage growth and the application of the Paris model to generate the translaminar damage propagation prediction. The purpose of this study is to analyse the effect of fibre orientation on translaminar crack propagation rate using the FFM model, which includes cycle damage increment estimation and fractographic analysis. The results confirm the feasibility of FFM in predicting crack growth and estimating life under cyclic loading. However, C-scan analysis and the revised crack propagation direction are critical in determining the realistic crack length, considering adhesive failure along the fibre direction. Additionally, this work contribution is also related to the application of the Paris model (based on dL/dN vs ΔK) to generate the translaminar damage propagation prediction model. The most dominant damage mechanism was the splitting pattern, which changed the aspect of failure for each laminate architecture as a function of fibre orientation. The laminate with multidirectional fibre orientation exhibited higher resistance to translaminar crack propagation due to the growth of splitting and delamination in multiple directions. The fibre orientation changed the propagation path, which influenced the fracture toughness and crack propagation rate behaviour.

Different amounts of graphene quantum dots (CQDs) (0, 1, 2.5, and 5 wt%) were incorporated into an epoxy matrix. The thermal conductivity, density, morphology, and dynamic mechanical thermal (DMTA) properties were reused from the study of Seibert et al.. The Pearson plot showed a high correlation between mass loading, thermal conductivity, and thermal diffusivity. A poorer correlation with density and heat capacity was observed. At lower CQD concentrations (0.1 wt%), the fracture surface showed to be more heterogeneous, while at higher amounts (2.5 and 5 wt%), a more homogeneous surface was observed. The storage modulus values did not change with the CQD amount. But the extension of the glassy plateau increased with higher CQD contents, with an increase of ~40 °C for the 5 wt% compared to the 2.5 wt% and almost twice compared to the neat epoxy. This result is attributed to the intrinsic characteristics of the filler. Additionally, lower energy dissipation and a higher glass transition temperature were observed with the CQD amount. The novelty and importance are related to the fact that for more rigid matrices (corroborated with the literature), the mechanical properties did not change, because the polymer bridging mechanism was not present, in spite of the excellent CQD dispersion as well as the filler amount. On the other hand, thermal conductivity is directly related to particle size and dispersion.

Carbon fiber reinforced polymer (CFRP) composites are widely used to produce structural components. However, their low interlaminar strength makes them susceptible to delamination, limiting structural applications. Aiming to solve this problem, this work proposes adding carbon nanotubes buckypaper (BP) into CFR thermoplastic composites as an interlayer to enhance the interlaminar strength through the BP bridging effect. Despite this objective, the carbon nanotube BP changed the delamination behavior in mode-I, creating an easy pathway for crack growth (smooth fracture surface) and reducing the interlaminar strength. An opposite behavior was observed for mode-II, in which BP acted as an obstacle for crack growth through the shear direction due BP bridging effect, which slightly improved interlaminar strength, resulting in a rougher surface. The experiments demonstrated through the energy involved in crack growth, the roughness of the fracture surface, and the amount of fracture mechanisms when BP was incorporated that in mode-I the delamination strength decreased, while it increased under the shear mode. This evidences that the BP bridging effect is influenced by the loading mode. Finally, this work highlights the need to study individual modes I and II in composites with buckypaper as an interlayer, since it influences the interlaminar toughness differently.