J. Compos. Sci., Volume 8, Issue 4 (April 2024) – 44 articles

Due to their anisotropic behavior, composite structures are weak in transverse direction loading. produces transverse cracks, which for a laminated composite, may lead to delamination and total failure. The transition from transverse crack to delamination failure is important and the subject of recent studies. In this paper, a simulation of transverse crack and its transition to delamination on cross-ply laminate was studied extensively using a cohesive element Finite Element Method (FEM). A pre-cracked [0/90] composite laminate made of bamboo was modeled using ABAQUS/CAE. The specimen was in a three-point bending configuration. Cohesive elements were inserted in the middle of the 90° layer and in the interface between the 0° and 90° layer to simulate transverse crack propagation and its transition to delamination. A load–displacement graph was extracted from the simulation and analyzed. As the loading was given to the specimen, stress occurred in the laminates, concentrating near the pre-cracked region. When the stress reached the tensile transverse strength of the bamboo, transverse crack propagation initiated, indicated by the failure of transverse cohesive elements. The crack then propagated towards the interface of the [0/90] laminates. Soon after the crack reached the interface, delamination propagated along the interface, represented by the failure of the longitudinal cohesive elements. The result of the numerical study in the form of load–displacement graph shows a consistent pattern compared with the data found in the literature. The graph showed a linear path as the load increased and the crack propagated until a point where there was a load-drop in the graph, which showed that the crack was unstable and propagated quickly before it turned into delamination between the 0^o and 90° plies. Full article

This study investigates a sustainable coating method for modified expanded polystyrene (MEPS) beads to improve the thermal insulation of lightweight concrete intended for wall application. The method employed in this study is based on a novel coating technique that represents a significant advancement in modifying Expanded Polystyrene (EPS) beads for enhanced lightweight concrete. This study experimentally assessed the energy-saving capabilities of MEPS concrete in comparison to control groups of uncoated EPS beads and normal concrete by analysing early-stage temperature, thermal conductivity, specific heat capacity, heat flux, and thermal diffusivity. The thermal conductivity of MEPS concrete is approximately 40% lower than that of normal concrete, demonstrating its usefulness in enhancing insulation. The heat flux calculated for MEPS concrete is significantly reduced (approximately 35%), and it has a 20% lower specific heat capacity than ordinary concrete, indicating a reduction in energy transfer through the material and, thus, potential energy-efficiency benefits. Furthermore, the study discovered that all test objects have very low thermal diffusivity values (less than 0.5 × 10⁻⁶ m²/s), indicating a slower heat transport through the material. The sustainable coating method utilized fly ash-enhanced thermal efficiency and employed recycled materials, hence decreasing the environmental impact. MEPS concrete provides a practical option for creating sustainable and comfortable buildings through the promotion of energy-efficient wall construction. Concrete incorporating coated EPS can be a viable option for constructing walls where there is a need to balance structural integrity and adequate insulation. Full article

In polypropylene/polyethylene composite (C-PP/PE) production, stabilizing additives such as Irgafos P-168 are essential as antioxidant agents. In this study, an investigation was carried out that covers different solid–liquid extraction methods (Soxhlet, ultrasound, and microwaves); various variables were evaluated, such as temperature, extraction time, the choice of solvents, and the type of C-PP/PE used, and the gas chromatography coupled to mass spectrometry (GC-MS) technique was used to quantify the presence of Irgafos P-168 in the C-PP/PE samples. The results revealed that microwave extraction was the most effective in recovering Irgafos P-168. A recovery of 96.7% was achieved when using dichloromethane as a solvent, and 92.83% was achieved when using limonene as a solvent. The ultrasound technique recovered 91.74% using dichloromethane and 89.71% using limonene. The Soxhlet extraction method showed the lowest recovery percentages of 57.39% using dichloromethane as a solvent and 55.76% with limonene, especially when the C-PP/PE was in the form of pellets. The degradation products that obtained the highest degradation percentages were Bis (di-test-butyl phenyl) phosphate and Mono (di-test-butyl phenyl) phosphate using the microwave method with dichloromethane as a solvent and PP in film. Finally, the possible mechanisms for forming the degradation compounds of Irgafos P-168 were postulated. Full article

Traditional resistance spot welding (RSW) has been unsuccessful in forming quality composite joints between steel– or aluminum–polymer-based composites. This has led to the development of spot welding variants such as friction stir spot welding (FFSW), ultrasonic spot welding (USW), and laser spot welding (LSW). The paper reviewed the differences in the bonding mechanisms, spot weld characteristics, and challenges involved in using these spot welding variants. Variants of RSW use series electrode arrangement, co-axial electrodes, metallic inserts, interlayers, or external energy to produce composite joints. FFSW and USW use nanoparticles, interlayers, or energy directors to create composite spot welds. Mechanical interlocking is the common composite joint mechanism for all variants. Each spot welding variant has different sets of weld parameters and distinct spot weld morphologies. FFSW is the most expensive variant but is commonly used for composite spot weld joints. USW has a shorter welding cycle compared to RSW and FFSW but can only be used for small components. LSW is faster than the other variants, but limited work was found on its use in composite spot weld joining. The use of interlayers in FFSW and USW to form composite joints is a potential research area recommended in this review. Full article

Hydrogel composites are pivotal in biomedical research, showing promise across various applications. This review aims to thoroughly examine their significance and versatile roles in regenerative medicine, tissue engineering, and drug delivery systems. Key areas of investigation include integrating growth factor delivery systems, overcoming structural limitations in tissue engineering, exploring innovations in clinical applications, and addressing challenges in achieving bioactivity and biomechanical compatibility. Furthermore, the review will discuss controlled release mechanisms for drug delivery, advancements in biocompatibility and mechanical stability, recent progress in tissue regeneration and wound healing, and future prospects such as smart hydrogels, personalized treatments, and integration with wearable technology. Ultimately, the goal is to provide a comprehensive understanding of how hydrogel composites impact biomedical research and clinical practice. Full article

The Resin Transfer Moulding process receives great attention from both academia and industry, owing to its superior manufacturing rate and product quality. Particularly, the progression of its mould filling stage is crucial to ensure a complete reinforcement saturation. Contemporary process simulation methods focus primarily on physics-based approaches to model the complex resin permeation phenomenon, which are computationally expensive to solve. Thus, the application of machine learning and data-driven modelling approaches is of great interest to minimise the cost of process simulation. In this study, a comprehensive dataset consisting of mould filling patterns of the Resin Transfer Moulding process at different injection locations for a composite dashboard panel case study is presented. The problem description and significance of the dataset are outlined. The distribution of this comprehensive dataset aims to lower the barriers to entry for researching machine learning approaches in composite moulding applications, while concurrently providing a standardised baseline for evaluating newly developed algorithms and models in future research works. Full article

Photocatalysis is considered as simple, green, and the best strategy for elimination of hazardous organic contaminants from wastewater. Herein, new broad spectrum photocatalysts based on pure and Sm-doped CuO/ZnO/CuMn₂O₄ ternary composites were simply prepared by co-precipitation approach. The X-ray diffraction results proved the formation of a composite structure. The transmission electron microscope (TEM) images displayed that most particles have a spherical shape with average mean sizes within 26–29 nm. The optical properties of both samples signified that the addition of Sm ions significantly improves the harvesting of the visible light spectrum of CuO/ZnO/CuMn₂O₄ ternary composites. The photocatalytic study confirmed that 97% of norfloxacin and 96% of methyl green pollutants were photo-degraded in the presence of the Sm-doped CuO/ZnO/CuMn₂O₄ catalyst after 50 and 40 min, respectively. The total organic carbon analysis revealed the high mineralization efficiency of the Sm-doped CuO/ZnO/CuMn₂O₄ catalyst to convert the norfloxacin and methyl green to carbon dioxide and water molecules. During three cycles, this catalyst presented a high removal efficiency for norfloxacin and methyl green contaminants. As a dielectric energy storage material, the Sm-doped CuO/ZnO/CuMn₂O₄ ternary composite has large dielectric constant values, mainly at low frequencies, with low dielectric loss compared to a pure CuO/ZnO/CuMn₂O₄ composite. Full article

Injection moulding (IM) is a manufacturing technique used to produce intricately detailed plastic components with various surface finishes, enabling the production of high-tolerance functional parts at scale. Conversely, stereolithography (SLA) three-dimensional (3D) printing offers an alternative method for fabricating moulds with shorter lead times and reduced costs compared to conventional manufacturing. However, fabrication in a layer-by-layer fashion results in anisotropic properties and noticeable layer lines, known as the stair-step effect. This study investigates post-processing techniques for plaques with contrasting stair-step effects fabricated from commercially available SLA high-temperature resin, aiming to assess their suitability for IM applications. The results reveal that annealing significantly enhances part hardness and heat deflection temperature (HDT), albeit with a trade-off involving reduced flexural strength. Experimental findings indicate that the optimal stage for abrasive surface treatment is after UV curing and before annealing. Plaques exhibiting contrasting stair-step effects are characterized and evaluated for weight loss, dimensional accuracy, and surface roughness. The results demonstrate that abrasive blasting effectively removes the stair-step effect without compromising geometry while achieving polished surface finishes with roughness average (RA) values of 0.1 μm through sanding. Overall, a combination of abrasive blasting and sanding proves capable of precisely defining surface roughness without significant geometry loss, offering a viable approach to achieving traditional IM finishes suitable for both functional and aesthetic purposes. Full article

To estimate the possibility of using both low-melting TecaPEI and neat PEI films as energy directors (EDs) for ultrasonic welding (USW) of carbon fiber (CF) fabric–polyetherimide (PEI) laminates, some patterns of structure formation and mechanical properties of their lap joints were investigated by varying the process parameters. The experiment was planned by the Taguchi method with the L9 orthogonal matrix. Based on the obtained results, USW parameters were optimized accounting for maintaining the structural integrity of the joined components and improving their functional characteristics. The use of the low-melting ED_TecaPEI film enabled US-welding the laminates with minimal damage to the fusion zone, and the achieved lap shear strength (LSS) values of ~7.6 MPa were low. The use of ED_SolverPEI excluded thermal degradation of the components as well as damage to the fusion zone, and improved LSS values to 21 MPa. With the use of digital image correlation (DIC) and computed tomography (CT) techniques, the structural factors affecting the deformation behavior of the USW lap joints were justified. A scheme was proposed that established the relationship between structural factors and the deformation response of the USW lap joints under static tension. The TecaPEI film can be used in USW procedures when very high interlayer adhesion properties are not on demand. Full article

Aluminum matrix composites (AMCs) find extensive use across diverse industries such as automotive, aerospace, marine, and electronics, owing to their remarkable strength-to-weight ratio, corrosion resistance, and mechanical properties. However, their limited wear resistance poses a challenge for applications requiring high tribological performance. Abrasive wear emerges as the predominant form of wear encountered by AMCs in various industrial settings, prompting significant research efforts aimed at enhancing their wear resistance. Over the past decades, extensive research has investigated the influence of various reinforcements on the abrasive wear behavior of AMCs. This paper presents a comprehensive review of the impact of different variables on the wear and tribological response of aluminum composites. This review explores possible wear mechanisms across various tribosystems, providing examples drawn from the analysis of existing literature. Through detailed discussions on the effects of each variable, conclusions are drawn to offer insights into optimizing the wear performance of AMCs. Full article

This study addresses the global plastic waste crisis and the urban heat island effect by developing an innovative solution: recycled plastic roof tiles embedded with phase change material (PCM) and coated with hollow-glass-microsphere-based white paint. The samples were fabricated with cow pie fibers, OM37 and OM42 PCM materials with different wt./vol. values, i.e., 15/50, 20/50, 25/50, 30/50 ratios. The fabricated tiles were coated with hollow glass microspheres to provide a reflective layer. The tiles’ effectiveness was evaluated through morphological examination and thermal analysis. The SEM analysis revealed an excellent bonding ability for the PCM blend, i.e., OM37 and OM42 at a 20/50 ratio (wt./vol.) with cow pie fibers. Adding cow pie fibers to the PCM shifted the melting points of OM37 and OM42, indicating an increased heat storage capacity in both blends. The thermal conductivity results revealed decreased thermal conductivity with an increased cow pie fiber percentage. The recycled plastic roof tile of the PCM composite at a 20/50 (wt./vol.) ratio showed good thermal properties. Upon testing in real-time conditions in a physical setup, the roof tiles showed a temperature reduction of 8 °C from outdoors to indoors during the peak of summer. In winter, cozy temperatures were maintained indoors due to the heat regulation from the roof. Full article

In this study, a method for producing nitrogen-modified graphene oxide (NMGO) using hydrothermal synthesis in the presence of triethanolamine is presented. The composition and structure of NMGO are characterized using X-ray phase analysis (XPA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and Raman spectroscopy. Ni-based metal matrix coatings (MMCs) modified with NMGO were obtained from a sulfate-chloride electrolyte in the galvanostatic mode. The process of electrochemical deposition of these coatings was studied using chronovoltammetry. The microstructure of Ni–NMGO MMCs was studied using the XPA and SEM methods. It has been established that the addition of NMGO particles into the Ni matrix results in an increase in the microhardness of the resulting coatings by an average of 1.30 times. This effect is a consequence of the refinement of crystallites and high mechanical properties of NMGO phase. The corrosion-electrochemical behavior of studied electrochemical deposits in 0.5 M sulfuric acid was analyzed. It has been shown that the corrosion rate of Ni–NMGO MMCs in a 3.5% sodium chloride environment decreases by approximately 1.50–1.70 times as compared to unmodified Ni coatings. This is due to NMGO particles that act as a barrier preventing the propagation of the corrosion and form corrosive galvanic microelements with Ni, promoting anodic polarization. Full article

Composite materials represent the evolution of material science and technology, maximizing the properties for high-end industry applications. The fields concerned include aerospace and defense, automotive, or naval industries. Additive manufacturing (AM) technologies are increasingly growing in market shares due to the elimination of shape barriers, a plethora of available materials, and the reduced costs. The AM technologies of composite materials combine the two growing trends in manufacturing, combining the advantages of both, with a specific enhancement being the elimination of the need for mold manufacturing for composites, or even post-curing treatments. The challenge of AM composites is to compete with their conventional counterparts. The aim of the current paper is to present the additive manufacturing process across different spectrums of finite element analyses (FEA). The first outcomes are building definition (support definition) and the optimization of deposition trajectories. In addition, the multi-physics of melting/solidification using computational fluid dynamics (CFD) are performed to predict the fiber orientation and extrusion profiles. The process modelling continues with the displacement/temperature distribution, which influences porosity, warping, and residual stresses that influence characteristics of the component. This leads to the tuning of the technological parameters, thus improving the manufacturing process. Full article

Several design standards have been developed in the last two decades to estimate the punching capacity of two-way reinforced concrete (RC) slabs reinforced with fiber-reinforced polymer (FRP) reinforcement. FRP-RC design standards include the recently published ACI 440.11-22, CSA/S806-12, and JSCE-2007. These models are either based on empirical data or semi-empirical methods and calibrated using different databases. Additionally, these standards do not have provisions for connections with shear reinforcement. Therefore, a reliable worldwide database for developing and assessing the applicability of such provisions with test results is vital. This study presents a worldwide and up-to-date database for punching shear of FRP-RC slabs. The database includes 197 tested connections, comprising interior and edge connections, with and without shear reinforcement, and a wide range of materials and cross-sectional properties. The database was used to evaluate the accuracy of the mentioned standards in predicting the punching shear capacity. For connections without shear reinforcement, it was determined that the three design standards yielded similar performance with different conservatism levels. ACI 440.11-22 yielded the most conservative results, with average V_exp/V_pred ratios of 2.04 compared to 1.28 and 1.3 for other models. For connection with shear reinforcement, specimens with E_vf> 100 GPa resulted in V_exp/V_pred ratios less than 1.0 for ACI and CSA standards. Full article

The vast majority of different waste building units have negative environmental impacts around the world. Crushed building units can be recycled and utilized in the concrete industry to solve these problems and maintain natural resources. This study investigated the feasibility of employing crushed autoclaved aerated concrete (CAAC) and crushed clay brick (CCB) as a lightweight aggregate (LWA) to fabricate environmentally friendly recycled lightweight concrete (LWC). In addition, a lightweight expanded clay aggregate (LECA) was also used as an LWA, namely to study how the high porosity of an LWA can adversely affect the properties of LWC. Through the experimental program, all types of LWAs were pre-treated and strengthened with two cementitious grouts, and then the performance of the produced LWC was assessed by determining the slump of fresh concrete, the dry density, the unconfined compressive strength, and the splitting tensile strength at ages of 3, 7, 28, and 56 days. The laboratory results revealed that both CCB and CAAC can be reused as full substitutions for normal-weight coarse aggregate to manufacture LWC with appropriate properties. The obtained data show that the properties of an LECA, CCB, and CAAC were improved, and the porous structure can be strengthened by pre-treatment and coating with grouts. In the same way, the mechanical performance of produced LWC is also enhanced. Full article

This paper presents a numerical approach for investigating fatigue delamination propagation in composite stiffened panels loaded in compression in the post-buckling field. These components are widely utilized in aerospace structures due to their lightweight and high-strength properties. However, fatigue-induced damage, particularly delamination at the skin–stringer interface, poses a significant challenge. The proposed numerical approach, called the “Min–Max Load Approach”, allows for the calculation of the local stress ratio in a single finite element analysis. It represents the ratio between the minimum and maximum values of the stress along the delamination front, enabling accurate evaluation of the crack growth rate. The methodology is applied here in conjunction with the cohesive zone model technique to evaluate the post-buckling fatigue behavior of a composite single-stringer specimen with an initial delamination. Comparisons with experimental data validate the predictive capabilities of the proposed approach. Full article

This paper reports on the biosynthesis, characterization, as well as the bactericide and cytotoxic properties of silver nanoparticles supported on bovine bone powder (Ag-NPs/BBP). The silver nanoparticles were obtained through the bioreduction of AgNO₃, using an infusion of Heterotheca inuloides leaves and flowers as a reducing agent and bovine bone powder as a support. The ratio of Ag-NPs/bovine bone powder was set as 1:10. The characterization was performed with SEM–EDS, XRD, UV–Vis, and TEM, which showed the formation of nanoparticles with an average size of 22.6 ± 10.8 nm and a quasi-spherical Ag-NPs morphology supported on the BBP surface. The nanocomposite exhibited a band gap of 2.19 eV. The minimal inhibitory concentration and the minimal bactericidal concentration against S. aureus, E. coli, and S. epidermidis were determined for each strain. In addition, the cytotoxic evaluation of the Ag-NPs/BBP on J774.2 mouse macrophage cells was performed. The Ag-NPs/BBP exhibited a bactericide effect on the strains studied, and the cytotoxicity had a dose-dependent behavior on the cells studied. Therefore, it was found that the ecofriendly synthesized Ag-NPs supported on bovine bone powder resulted in an effective bactericidal system against the strains studied, without significant cytotoxicity. Full article

Composite pressure vessels can be exposed to extreme loadings, for instance, impact loading, during manufacturing, maintenance, or their service lifetime. These kinds of loadings may provoke both visible and invisible levels of damage, e.g., fiber breakage matrix cracks and delamination and eventually may lead to catastrophic failures. Thus, the quantification and evaluation of such damages are of great importance. Considering the cost of relevant full-scale experiments, a numerical model can be a powerful tool for such a kind of study. This paper aims to provide a numerical study to investigate the capability of different modeling methods to predict delamination in composite vessels. In this study, various numerical modeling aspects, such as element types (solid and shell elements) and material parameters (such as interface properties), were considered to investigate delamination in a composite pressure vessel under low-velocity impact loading. Specifically, solid elements were used to model each layer of the composite pressure vessel, while, in another model, shell elements with composite layup were considered. Compared with the available experimental data from low-velocity impact tests described in the literature, the capability of these two models to predict both mechanical responses and failure phenomena is shown. Full article

The present investigation reports the synthesis and mechanical properties of a hybrid polymer composite consisting of E-Glass fiber, epoxy and 2 wt.% carbon nanotubes (CNTs) with a varying percentage of natural rubber (NR). The prepared hybrid polymer composites were examined in terms of their surface morphology, thermal properties as well as mechanical properties. The findings from the present study indicate that natural rubber enhances the mechanical properties of the hybrid polymer composites and, in particular, 10 wt.% is the optimum percentage of NR that yields the highest strength of 88 MPa, while the strength is 52 MPa with 5 wt.% NR. In order to evaluate the damping properties, a dynamic mechanical analysis was carried out on the E-Glass/CNT with NR composites at various frequencies along with a thermogravimetric analysis. It was found that the composite reinforced with 10 wt.% natural rubber exhibited a higher glass transition temperature of 376.86 °C and storage modulus of 2468 MPa when compared to the other composites, which indicates the enhanced cross-linking density and higher polymer modulus of the composite. X-ray diffraction analysis was also conducted and the results are reported to improve the general understanding of crystalline phases. Full article

This study investigates the stability of Inconel–Cu Multimetallic Layered Composites (MMLCs) in nuclear reactor applications using Molecular Dynamics simulations. The focus is on understanding the underlying mechanisms governing the properties of MMLCs for advanced nuclear reactors, specifically, the mechanochemistry of the interface between Inconel and copper alloys. The selection of Inconel–Cu MMLCs is primarily due to copper’s superior thermal conductivity, enhancing heat management within reactors by preventing hotspots and ensuring uniform temperature distribution. This research examines Incoloy 800H and two Inconel variants (718 and 625), assessing their stability at 1000 K after exposure to 10 keV collision cascades up to 0.12 dpa. Notable findings include defect clustering on the {1 2 0} family of planes of Inconel and Cu, with Stacking Faults and Lomer–Cottrell locks on the Inconel side. Full article

This paper studies the behavior of S2-glass woven fabric reinforced polymer composite under low-velocity impact at 18–110 J energy. A macro-homogeneous finite element model for the prediction of their response is implemented, considering the non-linear material behavior and intralaminar and interlaminar failure modes for the prediction of impact damage. The model accurately predicted the permanent indentation caused by impact. By applying the Ramberg-Osgood formulation, different initial stiffness values are examined to assess the post-impact unloading response. This approach reveals the significant role of initial stiffness in inelastic strain accumulation and its consequent effect on permanent indentation depth. A higher initial stiffness correlates with increased inelastic strain, influencing the impactor rebound and resulting in greater permanent indentation. By accurately predicting permanent indentation, and damage accumulation for different impact energies, this study contributes to a better understanding of the impact behavior of composite materials, thereby promoting their wider application. Full article

The usage of basalt fiber in the engineering industries has gained significant interest due to its characteristics such as alkali resistance and enhanced mechanical properties. Similarly, E-glass-fiber-reinforced composites have been widely used in the fabrication of electrically resistive industrial components such as switches, circuit panels, and covering cases. In the present study, the tensile, flexural, thermogravimetric, and low-velocity impact characteristics of various percentages of basalt/E-glass-fiber-reinforced polymer composites fabricated via vacuum-assisted resin transfer molding were investigated. The results show that a higher volume percentage of basalt (39%) significantly enhances the impact resistance up to 45% with a moderate improvement in flexural properties. The higher the vol % of E-glass (40%), the more the tensile and flexural properties are increased, i.e., 185 N/mm² and 227.87 N/mm², respectively. It is concluded that by choosing the optimum hybridization method, impact resistance and other mechanical properties can be improved significantly. The thermogravimetric analysis results show that PC313534 (35 vol % basalt and 34 vol % E-glass) possesses the lowest decomposition temperature of 381.10 °C. The results from the present study indicate that the polymer composite fabricated in the present study is suitable for applications where higher structural-load-resistive properties are required. Full article

This paper is the first part of a two-part paper that discusses the development of a novel lightweight and cost-effective hybrid 3D composite material and its and utilization for constructing utility poles. The main objective was to generate a material/pole with a comparable performance to the commercially available poles made of 2D fiber-reinforced polymer (FRP) and examine its feasibility. The novel hybrid composite was configured using a recently developed and marketed 3D E-glass fabric–epoxy composite reinforced with wood dowels, referred to as 3D dowel-reinforced FRPs (3D-drFRPs) hereafter. Firstly, the compressive and flexural properties of the 3D-drFRPs are evaluated. Then, the development of the 3D pole is discussed followed by the fabrication details of two 3D-drFRPs using the standard test method, and their responses are compared. For the second part, robust finite element (FE) models were developed in an LS-DYNA environment and calibrated based on the experimental results. A sophisticated nonlinear FE model was used to simulate the performances of ASTM standard-size compression and three-point bending specimens and tapered 2D and prismatic 3D poles. Moreover, the responses of equivalent 2D and 3D poles were simulated numerically, as the task could not be accommodated experimentally due to our laboratory’s deficiencies. The integrity of the numerical simulation results was validated against experimental results, confirming the accuracy of the developed model. As an example, the stiffness values for the 3-pt bending specimens and the 3D poles obtained through the simulations were very close to the experimentally obtained results, with small margins of errors of 3.2% and 0.89%, respectively. Finally, a simplified analytical calculation method was developed so practicing engineers can determine the stiffnesses of 3D-DrFRP poles very accurately and quickly. Full article

In this study, polyurethane-polystyrene composites (RPURF-EPS) were obtained with the co-expansion method. This method consists of utilizing the heat of the exothermic reaction of polyurethane (PUR) formation to expand polystyrene beads (PSBs). The materials were obtained using polyurethane systems based on the selected blowing agents, such as cyclopentane, a mixture of fluorocarbons and water. The analysis of the foaming process was carried out using a special device called FOAMAT. The characteristic start, rise, gelation and curing times were defined. The rise profile, the reaction temperature, the pressure and the dielectric polarization were measured. The influence of selected blowing agents on the cell structure and physical–mechanical properties of reference rigid polyurethane foam (RPURF) and RPURF-EPS, such as apparent density, compressive strength and thermal conductivity, were evaluated. Based on the research, the blowing agents that have the most beneficial influence on the properties and structure of the composites and that provide the most efficient expansion of PSBs in a light porous composite were found. Full article

Significant interest is devoted to the development of new polymer blends by using concepts of the circular economy. Such materials have predetermined properties, are easy to recycle, ecological, and have a low carbon footprint. This research presents obtaining and characterization of polymer blends based on low-density polyethylene (LDPE) and thermoplastic starch (TPS). In the first stage, TPS was obtained through the gelatinization process, and, in the second stage, mixtures of LDPE and TPS were obtained through a melt mixing process at 150 °C for 7 min. The physical–mechanical characteristics of the samples, like hardness, elongation at break, rebound resilience, and tensile strength, were determined. The sample containing maleic anhydride grafted low-density polyethylene (LDPE-g-MA) as a compatibilizer shows improvements in elongation at break and tensile strength (by 6.59% and 40.47%, respectively) compared to the test sample. The FTIR microscopy maps show that samples containing LDPE-g-MA are more homogeneous. The SEM micrographs indicate that TPS-s is homogeneously dispersed as droplets in the LDPE matrix. From the thermal analysis, it was observed that both the degree of crystallinity and the mass loss at high temperature are influenced by the composition of the samples. The melt flow index has adequate values, indicating good processability of the samples by specific methods (such as extrusion or injection). Full article

The investigation of the in-plane shear behavior of prepreg is crucial for understanding the generation of wrinkles of preforms in advanced composite manufacturing processes, such as automated fiber placement and thermoforming. Despite this significance, there is currently no standardized test method for characterizing uncured unidirectional (UD) prepreg. This paper introduces a ±45° off-axis tensile test designed to assess the in-plane shear behavior of UD carbon fiber-reinforced epoxy prepreg (CF/epoxy). Digital image correlation (DIC) was employed to quantitatively track the strains in three dimensions and the shear angle evolution during the stretching process. The influences of the temperature and stretching rate on the in-plane shear behavior of the prepreg were further investigated. The results reveal that four shear characteristic zones and wrinkling behaviors are clearly distinguished. The actual in-plane shear angle is significantly lower than the theoretical value due to fiber constraints from both the in-plane and out-of-plane aspects. When the off-axis tensile displacement (d) is less than 15.6 mm, the ±45° specimens primarily exhibit macroscale in-plane shear behavior, induced by interlaminar interface shear between the +45° ply and −45° ply at the mesoscale. The shear angle increases linearly with the d. However, when d > 15.6 mm, fiber squeezing and wrinkling begin to occur. When d > 29 mm, the in-plane shear disappears in the completely sheared zone (A). The reduction in the resin viscosity of the CF/epoxy prepreg caused by increased temperature is identified as the primary factor in lowering the in-plane shear force resistance, followed by the effect of the increasing resin curing degree. Higher shear rates can lead to a substantial increase in shear forces, eventually causing cracking failure in the prepreg. The findings demonstrate the feasibility of the test method for predicting and extracting uncured prepreg in-plane shear behaviors and the strain-rate and temperature dependency of the material response. Full article

The present study reports the effective removal of benzene in aqueous phase onto biochar. The adsorption capacity of benzene onto biochars made at different pyrolytic temperatures (e.g., 350, 550, and 750 °C) and from various feedstocks (e.g., grape pomace, rice husk, and Kentucky bluegrass) were investigated. The adsorption capacity of Kentucky bluegrass-derived biochar (KB-BC) prepared at 550 °C for benzene was better than other biochars, owing to the higher surface area and functional groups. The adsorption isotherms and kinetics model for benzene by KB-BC550 fitted the Freundlich and pseudo-first order, respectively. In addition, the results of response surface methodology (RSM) designed with biochar dose, reaction time, and benzene concentration showed the maximum adsorption capacity (ca. 136 mg BZ/g BC) similar to that from kinetic study. KB-BCs obtained as waste grass biomass may be a valuable adsorbent, and RSM may be a useful tool for the investigation of optimal conditions and results. Full article

The choice of material, manufacturing process, and molding tool significantly affects the quality, environmental impact, and cost efficiency of composite components. Producing one-piece hollow profiles with smooth inner surfaces and undercuts presents major challenges for conventional mold concepts. There is yet no thorough review of shape-variable mandrels in composite manufacturing to be found in the literature. This paper provides an overview of research on shape memory polymers and other shape-variable materials used in tooling applications for composite manufacturing. This work covers shape memory, heat shrink, and other deformable tooling concepts that enable the production of one-piece Type V pressure vessels, air intake ducts, or curved struts and tubes. A systematic literature review in combination with a state-of-the-art open-source active learning tool ASReview is conducted. Fifteen relevant studies were identified. Research on shape-variable tooling is mainly conducted by three research groups in the USA and the PRC. The tooling is mostly made of unreinforced thermosets, especially styrene-based ones. Thermoplastic resins are less common, and reinforcements limit the usable elongation in the temporary shape. The shape variability is either a shape memory and/or a softening process, which, in all studies, is activated by heating. Release agents are widely used to ease demolding. No ecological or economical assessment of the manufacturing methods was conducted in the reviewed studies. Three fields for further research that could be identified are as follows: (1) thorough ecological end economical assessment of shape-variable mandrels in comparison with conventional tooling; (2) thermoplastic shape memory polymer mandrels; and (3) further investigation of simulation capabilities for shape memory mandrels. Full article

Finite element analyses of the propagation of damage such as fiber compressive failure and delamination have greatly contributed to the understanding of failure mechanisms of fiber-reinforced plastics owing to extensive studies on methodologies using Continuum Damage Mechanics and Fracture Mechanics. Problems without the need for consideration of inertia, such as Double-Cantilever Beam tests, are usually solved by implicit FE solvers, and explicit FE solvers are appropriate for phenomena that progress with very high velocity such as impact problems. However, quasi-static problems with unstable damage propagation observed in experiments such as Open-Hole Compression tests are still not easy to solve for both types of solvers. We propose a method to enable the static FE solver to solve problems with unstable propagation of damage. In the present method, an additional process of convergence checks on the averaged energy release rate of damaged elements is incorporated in a conventional Newton–Raphson scheme. The feasibility of the present method was validated by two numerical examples consisting of analyses of Open-Hole Compression tests and Double-Cantilever Beam tests. The results of the analyses of OHC tests showed that the present method was applicable to problems with unstable damage propagation. In addition, the results from the analyses of DCB tests with the present method indicated that mesh density and loading history are not significantly influential to the solution. Full article

The relatively low melting point of a traditional Si bonding layer limits the upper servicing temperature of environmental barrier coatings (EBC). To explore suitable high temperature bonding layers and expedite the development of EBC, first-principles calculation was used to evaluate the mechanical properties and thermal conductivity of HfSi₂, HfSi, Hf₅Si₄, Hf₃Si₂, and Hf₂Si with much higher melting points than that of Si. Among them, HfSi₂ has the lowest modulus capable of good modulus matching with SiC substrate. In addition, these Hf-Si compounds have much lower high temperature thermal conductivity with Hf₂Si being the lowest of 0.63 W m⁻¹ K⁻¹, which is only half of Si, capable of improved heat insulation. Full article