J. Compos. Sci., Volume 5, Issue 10 (October 2021) – 32 articles

During LATP (laser automated tape placement), the compaction roller contacts the prepreg and affects the pressure distribution directly. Moreover, the design parameters of the roller are optimized with the aim of improving pressure uniformity. This paper examines the impact of the contact line and surface that depends on the compaction force, the design of the roller, the angle of inclination and the angle of inclination of the strip. These factors significantly affect the expansion of the tape, and it is important to determine it to avoid side effects in the production of composites (formation of gaps or overlaps). Their presence increases the percentage of pores of the final material and thus reduces the mechanical properties. The results show that the pressure uniformity can be improved significantly by design optimization of the roller, which indicates that higher bond quality between layers is achieved. The lower the speed and higher the compact force in this technology give better intimate contact with a lower percentage of voids and good mechanical characteristics. Full article

This paper summarizes recent advances in strain-hardening ultra-high-performance concretes (UHPC) with synthetic fibers, with emphasis on their tensile properties. The composites described here usually contain about 2.0% high-density polyethylene (PE) fibers. Compared to UHPC with steel fibers, strain-hardening UHPC with synthetic fibers generally show a higher tensile ductility, lower modulus in the cracked state, and relatively lower compressive strength. The tensile strain capacity of strain-hardening UHPC with synthetic fibers increases with increasing tensile strength. The f’_cf_tε_t/w index (compressive strength × tensile strength × tensile strain capacity/tensile crack width) is used to compare the overall performance of strain-hardening UHPC. Moreover, a probabilistic approach is applied to model the crack width distributions of strain-hardening UHPC, and estimate the critical tensile strain in practical applications, given a specific crack width limit and cumulative probability. Recent development on strain-hardening UHPC with the use of seawater, sea-sand and PE fibers are also presented. Full article

Resin composite is widely used in the dental field in clinics as a biomaterial. For example, it has been used as a composite material, a type of biomaterial, to repair caries and restore masticatory function, and as a luting agent to adhere the restoration to the tooth substrate. In order to demonstrate its function, we have measured the mechanical strength. From such basic research, we explain the potential of a dental material through the measurement of flexural strength and modulus of elasticity. In this research, we introduce commercial products that are actually used as composite materials suitable for tooth substrate and provide readers with their properties based on flexural strength and modulus of elasticity. In clinical performance, it might be advisable to delay polishing when a composite material is used for a luting material, a filling material and a core build-up material, as the flexural strength and the flexural modulus of elasticity were improved after 1 day of storage, and flexural strength and characteristics are considered as important mechanical properties of oral biomaterials. Full article

The authors report on the manufacturing of mechanically stable β-tricalcium phosphate (β-TCP) structural hybrid scaffolds via the combination of additive manufacturing (CerAM VPP) and Freeze Foaming for engineering a potential bone replacement. In the first step, load bearing support structures were designed via FE simulation and 3D printed by CerAM VPP. In the second step, structures were foamed-in with a porous and degradable calcium phosphate (CaP) ceramic that mimics porous spongiosa. For this purpose, Fraunhofer IKTS used a process known as Freeze Foaming, which allows the foaming of any powdery material and the foaming-in into near-net-shape structures. Using a joint heat treatment, both structural components fused to form a structural hybrid. This bone construct had a 25-fold increased compressive strength compared to the pure CaP Freeze Foam and excellent biocompatibility with human osteoblastic MG-63 cells when compared to a bone grafting Curasan material for benchmark. Full article

Corrosion is one of the leading sources of material failure and deterioration in society. Scholars have proposed different techniques to mitigate corrosion. This research study explores and validates one of these techniques. An Aluminium metal matrix (AMC) was produced using the stir casting method with various weight percentages of AgNp and CaCO₃ reinforcements. Heat treatment was performed on the samples to enhance the metallurgical and corrosion properties of the materials. The corrosion rate of the AMC samples was tested in different corrosive media (neutral and acidic) with different concentrations using the weight loss analysis technique for several days. It was observed that the corrosion rate of the AMC relies on the nature of the electrolyte and the percentage concentration of this electrolyte. The heat treatment improves the corrosion resistance of the AMC samples. In addition, an increase in the % weight composition of the reinforcement (AgNp + CaCO₃) results in a reduction in the corrosion rate of the AMC in both corrosive media. The optimal %weight composition was found to be 4% for the hybrid reinforcement of AgNp + CaCO₃ and 6% for the CaCO₃ reinforcement in both the untreated and heat-treated samples. Full article

The need to develop sustainable concrete in the civil infrastructure industry increases day by day, resulting in new eco-friendly materials such as geopolymer concrete. Geopolymer concrete is one of the eminent alternatives to conventional concrete for sustainable development by reducing the carbon footprint. Ternary blend geopolymer concrete (TGPC) is a sustainable and environmentally friendly concrete produced with three different source materials to form a binder. The main advantage of TGPC is that it possesses densely packed particles of different shapes and sizes, which results in improved properties. This paper deals with the experimental investigations to evaluate the durability properties of plain and hybrid fibre reinforced TGPC. The durability of concrete is defined as the ability to withstand a safe level of serviceability and different environmental exposure conditions without any significant repair and rehabilitation throughout the service life. Conventional concrete is vulnerable to cracking due to its low tensile and durability properties. The TGPC considered in this work consists of fly ash, GGBS and metakaolin as source materials, selected mainly based on the material’s silica and alumina content, shape, size, and availability. The grade of concrete considered was M55. The main variables considered in this study were the proportions of crimped steel fibres (V_f), viz., 0.5% and 1% and proportions of polypropylene fibres (V_p)viz., 0.1%, 0.15%, 0.20% and 0.25%. The durability properties like water absorption, sorptivity, resistance to marine attack, acid attack, sulphate attack, and abrasion were studied in this investigation. The experimental test results were compared with the requirements provided in the standard/literature and found to be well within limits. The study also indicates that the inclusion of fibres in a hybrid form significantly improves the durability parameters of TGPC. The TGPC with 1% steel fibre and 0.15% polypropylene fibre performs better than the other combination of fibres considered in this experimental investigation. Full article

Biomineralization consists of a complex cascade of phenomena generating hybrid nano-structured materials based on organic (e.g., polymer) and inorganic (e.g., hydroxyapatite) components. Biomineralization is a biomimetic process useful to produce highly biomimetic and biocompatible materials resembling natural hard tissues such as bones and teeth. In detail, biomimetic materials, composed of hydroxyapatite nanoparticles (HA) nucleated on an organic matrix, show extremely versatile chemical compositions and physical properties, which can be controlled to address specific challenges. Indeed, different parameters, including (i) the partial substitution of mimetic doping ions within the HA lattice, (ii) the use of different organic matrices, and (iii) the choice of cross-linking processes, can be finely tuned. In the present review, we mainly focused on calcium biomineralization. Besides regenerative medicine, these multifunctional materials have been largely exploited for other applications including 3D printable materials and in vitro three-dimensional (3D) models for cancer studies and for drug testing. Additionally, biomineralized multifunctional nano-particles can be involved in applications ranging from nanomedicine as fully bioresorbable drug delivery systems to the development of innovative and eco-sustainable UV physical filters for skin protection from solar radiations. Full article

Recently, nanofluid application as a heat transfer fluid for a closed-loop solar heat collector is receiving great attention among the scientific community due to better performance. The performance of solar systems can be assessed effectively with the exergy method. The present study deals with the thermodynamic performance of the second law analysis using graphene nanoplatelets nanofluids. Second law analysis is the main tool for explaining the exergy output of thermodynamic and energy systems. The performance of the closed-loop system in terms of energy and exergy was determined by analyzing the outcome of field tests in tropical weather conditions. Moreover, three parameters of entropy generation, pumping power and Bejan number were also determined. The flowrates of 0.5, 1 and 1.5 L/min and GNP mass percentage of 0.025, 0.5, 0.075 and 0.1 wt% were used for these tests. The results showed that in a flow rate of 1.5 L/min and a concentration of 0.1 wt%, exergy and thermal efficiencies were increased to about 85.5 and 90.7%, respectively. It also found that entropy generation reduced when increasing the nanofluid concentration. The Bejan number surges up when increasing the concentration, while this number decreases with the enhancement of the volumetric flow rate. The pumping power of the nanofluid-operated system for a 0.1 wt% particle concentration at 0.5 L/min indicated 5.8% more than when pure water was used as the heat transfer fluid. Finally, this investigation reveals the perfect conditions that operate closest to the reversible limit and helps the system make the best improvement. Full article

Since the finite element analysis of deformations for plates made of functionally graded materials cannot be carried out with the use of commercial FE packages, aconsistent method of analytical analysis is proposed in the paper. The method of the analysis is based on the application of the weighted residuals and the Bubnov–Galerkin method. The 2D formulation of moderately thick plates is adopted herein for classical and transverse shear deformation plate models (first and third order). Plate deformations subjected to uniform normalpressure and free vibrations are considered. The validity of the analytical model was verified by the comparison of results with FE analysis for isotropic plates. Two correction multipliers were proposed in order to take into account the unsymmetric composition of functionally graded porous plate walls. Full article

The outstanding properties of carbon fibre-reinforced polymer composites are affected by the development of its microstructure during processing. This work presents a novel approach to identify microstructural features both along the tape thickness and through the thickness. Voronoi tessellation-based evaluation of the fibre volume content on cross-sectional micrographs, with consideration of the matrix boundary, is performed. The method is shown to be robust and is suitable to be automated. It has the potential to discriminate specific microstructural features and to relate them to processing behaviour removing the need for manufacturing trials. Full article

This study proposes an innovative solution to flame-retard a sandwich composite made of unsaturated polyester resin, glass fibre skins and polyester nonwoven core material. The strategy uses the core material as flame-retardant carrier, while the resin is also flame-retarded with aluminum trihydroxide (ATH). A screening of the fire-retardant performances of the core materials, covered with different types of phosphorous flame-retardant additives (phosphate, phosphinate, phosphonate), was performed using cone calorimetry. The best candidate was selected and evaluated in the sandwich panel. Great performances were obtained with ammonium polyphosphate (AP422) at 262 g/m². The core material, when tested alone, did not ignite, and when used in the laminate, improved the fire behaviour by decreasing the peak of heat release rate (pHRR) and the total heat release (THR): the second peak in HRR observed for the references (full glass monolith and sandwich with the untreated core) was suppressed in this case. This improvement is attributed to the interaction occurring between the two FR additives, which leads to the formation of aluminophosphates, as shown using Electron Probe Micro-Analysis (EPMA), X-ray Diffraction (XRD) and solid-state ³¹P Nuclear Magnetic Resonance (NMR). The influence of the FR add-on on the core, as well as the ATH loading in the matrix, was studied separately to optimize the material performances in terms of smoke and heat release. The best compromise was obtained using AP422 at 182 g/m² and 160 phr of ATH. Full article

Recent studies on zirconia-toughened alumina (ZTA) evidenced that in vivo aged implants display a much higher monoclinic zirconia content than expected from in vitro simulations by autoclaving. At the moment, there is no agreement on the source of this discrepancy: Some research groups ascribe it to the effect of mechanical impact shocks, which are generally not implemented in standard in vitro aging or hip walking simulators. Others invoke the effect of metal transfer, which should trigger an autocatalytic reaction in the body fluid environment, accelerating the kinetics of tetragonal-to-monoclinic transformation in vivo. Extrapolations of the aging kinetics from high (autoclave) to in vivo temperature are also often disputed. Last, Raman spectroscopy is by far the preferred method to quantify the amount of monoclinically transformed zirconia. There are, however, many sources of errors that may negatively affect Raman results, meaning that the final interpretation might be flawed. In this work, we applied Raman spectroscopy to determine the monoclinic content in as-received and in vitro aged ZTA hip joint implants, and in one long-term retrieval study. We calculated the monoclinic content with the most used equations in the literature and compared it with the results of X-ray diffraction obtained on a similar probe depth. Our results show, contrary to many previous studies, that the long-term surface stability of ZTA ceramics is preserved. This suggests that the Raman technique does not offer consistent and unique results for the analysis of surface degradation. Moreover, we discuss here that tetragonal-to-monoclinic transformation is also necessary to limit contact damage and wear stripe extension. Thus, the surface metastability of zirconia-containing ceramics may be a non-issue. Full article

With an aim to develop a good coil winding insulation film, fillers of boehmite alumina in the shape of a roughly rectangular plate were added with ratios of 10 and 20 wt% to polyimide. The filler surface was untreated or treated with a methacrylic or an epoxy silane coupling agent. Such prepared polyimide nanocomposites were subjected to various tests to measure the tensile strength, elastic modulus, complex permittivity, and thermal conductivity. It was found that samples with fillers treated using the methacrylic silane coupling agent have the strongest adhesion at the filler/polyimide interfaces and the lowest dielectric loss factor at high temperatures. A positive relationship between the filler/polyimide adhesion and the thermal conductivity is also indicated. These findings are significant since they indicate that the adhesion status at the filler/polymer interface exerts a strong influence on the thermal and electrical conduction processes in the polymer. Full article

Geopolymer is an eco-friendly material used in civil engineering works. For geopolymer concrete (GPC) preparation, waste fly ash (FA) and calcined clay (CC) together were used with percentage variation from 5, 10, and 15. In the mix design for geopolymers, there is no systematic methodology developed. In this study, the random forest regression method was used to forecast compressive strength and split tensile strength. The input content involved were caustic soda with 12 M, 14 M, and 16 M; sodium silicate; coarse aggregate passing 20 mm and 10 mm sieve; crushed stone dust; superplasticizer; curing temperature; curing time; added water; and retention time. The standard age of 28 days was used, and a total of 35 samples with a target-specified compressive strength of 30 MPa were prepared. In all, 20% of total data were trained, and 80% of data testing was performed. Efficacy in terms of mean absolute error (MAE), root mean square error (RMSE), coefficient of determination (R²), and MSE (mean squared error) is suggested in the model. The results demonstrated that the RFR model is likely to predict GPC compressive strength (MAE = 1.85 MPa, MSE = 0.05 MPa, RMSE = 2.61 MPa, and R² = 0.93) and split tensile strength (MAE = 0.20 MPa, MSE = 6.83 MPa, RMSE = 0.24 MPa, and R² = 0.90) during training. Full article

To evaluate the effects of surface modification with stearic acid on the dispersion of some inorganic fillers in polyethylene (PE) matrix, masterbatches containing 20–40 wt% of stearic acid uncoated and coated inorganic fillers and the linear low-density polyethylene (LLDPE) films containing 3–7% stearic acid uncoated and coated inorganic fillers were prepared. Two types of inorganic fillers used in the masterbatch included bentonite and silica. The structural change of inorganic fillers, whose surface was modified with stearic acid, was studied using IR spectroscopy. The dispersion of inorganic fillers in LLDPE matrix was evaluated using scanning electron microscope (masterbatch samples) and optical microscope (film samples). Changes in the melting temperature of LLDPE in the presence of inorganic fillers were evaluated by using differential scanning calorimeter (DSC). The mechanical properties of the films were evaluated according to ASTM D882. Surface-treated fillers with stearic acid dispersed in the masterbatches and films better than untreated fillers did. Stearic acid did not change the melting temperature of the filler/PE masterbatches. The mechanical properties of the films containing stearic acid coated fillers were higher than those containing unmodified fillers. Full article

The present research investigates the possibility to create a silt-waste reinforced composite through a NaOH-activated, metakaolin-based geopolymerization process. In this regard, we used thermal exo–endo analysis, X-ray diffraction (XRD), and oedometric mechanical tests to characterize the produced composites. In our experimental conditions, the tested material mixtures presented exothermic peaks with maximum temperatures of about 100 °C during the studied geopolymerization process. In general, the XRD analyses showed the formation of amorphous components and new mineral phases of hydrated sodalite, natrite, thermonatrite and trona. From oedometric tests, we observed a different behavior of vertical deformation related to pressure (at RT) for the various produced composites. The present work indicated that the proposed geopolymerization process to recycle silt-waste produced composite materials with various and extended mineralogy and chemical–physical properties, largely depending on both the precursors and the specific alkaline-activating solution. Thermal analysis, XRD, and oedometric mechanical tests proved to be fundamental to characterize and understand the behavior of the newly formed composite material. Full article

Nanofibers of Y- or W-type hexagonal ferrites and core–shell fibers of hexagonal ferrites and ferroelectric lead zirconate titanate (PZT) or barium titanate (BTO) were synthesized by electrospinning. The fibers were found to be free of impurity phases, and the core–shell structure was confirmed by electron and scanning probe microscopy. The values of magnetization of pure hexagonal ferrite fibers compared well with bulk ferrite values. The coaxial fibers showed good ferroelectric polarization, with a maximum value of 0.85 μC/cm² and 2.44 μC/cm² for fibers with BTO core–Co₂W shell and PZT core–Ni₂Y shell structures, respectively. The magnetization, however, was much smaller than that for bulk hexaferrites. Magneto-electric (ME) coupling strength was characterized by measuring the ME voltage coefficient (MEVC) for magnetic field-assembled films of coaxial fibers. Among the fibers with Y-type, films with Zn₂Y showed a higher MEVC than films with Ni₂Y, and fibers with Co₂W had a higher MEVC than that of those with Zn₂W. The highest MEVC of 20.3 mV/cm Oe was measured for Co₂W–PZT fibers. A very large ME response was measured in all of the films, even in the absence of an external magnetic bias field. The fibers studied here have the potential for use in magnetic sensors and high-frequency device applications. Full article

In the 21st century, hybrid nanocomposites were widely used in bioelectronic, biosensing, photocatalytic, and biomedical applications. In the present study, we fabricated a novel Fe₃O₄/PVA/Eggshell hybrid nanocomposite and physicochemically characterized it using powder XRD, EDS, FTIR, VSM, and HR-TEM analysis. The XRD spectrum revealed the crystalline and FCC configuration of Fe₃O₄ NPs with average crystal size of 16.28 nm, and the HRTEM image indicates the prepared hybrid nanocomposite is of spherical shape with less agglomeration. This hybrid nanocomposite showed a significant photodegradation property in degrading organic pollutants such as congo red and crystal violet dyes under the sunlight irradiation. In addition, the hybrid nanocomposite also displayed a potent antibacterial property against different Gram +ve and Gram −ve bacterial pathogens. This study provides a significant example in the overview of fabrication of cost effectively, eco-friendly, and multiple-application hybrid nanocomposites through eggshell membrane fibers. Full article

We prepared six kinds of epoxy resin nanocomposites with silica and an epoxy resin with no silica. The nanocomposites contain silica with different diameters (10, 50, and 100 nm) while their silica contents are 1, 5, 10, and 20 vol%. At 25 and 100 °C, the thermal conductivity has a nearly proportional dependence on the silica content and exhibits an almost reciprocal proportionality to the diameter of the silica. The latter result indicates that the interaction at filler-resin interfaces plays a significant role in heat transfer. However, this view contradicts an easy-to-understand thought that the filler-resin interfaces should work as a barrier for heat transfer. This in turn indicates that the interaction at filler-resin interfaces controls the bulk properties of the resin when the filler is in a nm size. Although the dielectric constant increases with the addition of the silica filler, its increment from the resin with no silica is the smallest in the resin with the 10-nm silica. Therefore, the addition of the 10-nm silica is adequate for electrical insulation purposes. Full article

In this study, we conducted an initial investigation of the post-fire mechanical properties of concrete reinforced with Spanish broom fibers. The mechanical properties were determined at room temperature, and the post-fire mechanical properties were determined at elevated temperature, so that the fire resistance of the concrete could be determined. Five mixtures were considered: three with differently treated Spanish broom fibers, a polypropylene fiber mixture, and a reference concrete mixture. The concrete and reinforced concrete samples were first dried to 100 °C, then heated to 400 °C, and left to cool to room temperature. The samples were tested immediately and 96 h after cooling. The compressive strength, weight loss, ultrasonic pulse velocity, and dynamic modulus of elasticity were determined and compared. The cross-sectional images of the concrete samples captured through an optical microscope were observed and analyzed. The changes in fiber structure were monitored by TG/DTG analysis. The results of the study indicate that even the reference concrete mixture did not have satisfactory residual properties. The reinforced concretes did not improve the residual properties of the reference concrete, but reduced the spalling and explosive failure performance under a compressive load. The concrete reinforced with Spanish broom fibers showed improved residual properties compared with concrete reinforced with polypropylene fibers. Full article

The mechanical and ring stiffness of glass fiber pipes are the most determining factors for their ability to perform their function, especially in a work environment with difficult and harmful conditions. Usually, these pipes serve in rough underground environments of desert and petroleum fields; therefore, they are subjected to multi-type deterioration and damage agents. In polymers and composite materials, corrosion is identified as the degradation in their properties. In this study, tension and compression tests were carried out before and after preconditioning in a corrosive agent for 60 full days to reveal corrosion influences. Moreover, the fracture toughness is measured using a standard single edge notch bending. Ring stiffness of such pipes which, are considered characteristic properties, is numerically evaluated using the extended finite element method before and after preconditioning. The results reported that both tensile and compressive strengths degraded nearly more than 20%. Besides the fracture toughness decrease, the stiffness ring strength is reduced, and the finite element results are in good agreement with the experimental findings. Full article

Polymer photovoltaics (PV) offer the advantage of low-cost, mass-produced, flexible PV films, but they generally suffer from a low-power conversion efficiency (PCE) compared to silicon. This paper studies ITO/PEDOT:PSS/bulk heterojunction/Al PV cells, where two different bulk heterojunction blends are researched: P3HT/PC₆₁BM and PCDTBT/PC₇₀BM. The addition of multiwall carbon nanotubes (CNT) is explored as a conductive network to accelerate the electron transport and extraction to the outer aluminium current collector while reducing the chance of charge recombinations. Several layer deposition techniques are investigated: spin coating and casting, as well as techniques that would induce transverse orientation of polymer grains, including inkjet printing, electrophoresis and the application of a transverse AC field during annealing. Transverse orientation techniques produced architectures that would facilitate charge transport without recombinations, but it is recommended to avoid such techniques for the deposition of conductive PEDOT:PSS and CNT layers as they create a high surface roughness that leads to short circuiting. The best performing PV cell is the ITO/PEDOT:PSS/PCDTBT/PC₇₀BM/CNT/Al structure with a PCE of 11%. Full article

In this paper, the effect of the carbonization temperature on the mechanical properties, density, wear and corrosion resistance of AA 6063 reinforced with eggshells was investigated. The selected fabrication route for this investigation was stir casting while the weight fraction of the eggshells was kept constant at 5 wt.%. The carbonization temperature was varied at 900, 1000, 1100, and 1200 °C. The microstructure revealed that the eggshells were fairly uniformly dispersed on the individual grains and along the grain boundaries of the base metal. It was also shown that the presence of agglomeration increased with increasing carbonization temperature. The densities of the eggshell-reinforced AMCs were lower than that of the base metal. The analysis of the microhardness showed an improvement of 40.79, 22.93, 25.70, and 29.43% for the 900, 1000, 1100, and 1200 °C carbonized eggshell samples, respectively. The compressive strength studies showed that the addition of carbonized eggshells improved the compressive strength of the composites compared to the base metal. The tribology studies showed that the wear resistance improved for the 900 and 1200 °C samples, while the electrochemical studies revealed that the corrosion resistance improved for the 900 and 1000 °C samples only. Full article

This study involves the optimization of the milling parameters of unmodified Calotropis Procera fiber-reinforced PLA composite (UCPFRPC). The material is prepared from the combination of 20% Calotropis-Procera and 80% of PLA by weight. The experiments are designed using the Taguchi methodology, where 16 experiments are obtained using the spindle rotational speed, depth of cut, and feed rate as the parameters. These experiments were conducted while obtaining thermal images using an infrared camera and recording the machining time. The change in mass was then determined and the material removal rate computed. The machined workpieces were then investigated for surface roughness. The study shows that the optimal milling parameters in the machining of UCPFRPC for the lowest surface roughness are 400 rpm, 400 mm/min, and 0.2 mm, for the rotational spindle speed, feed rate, and depth of cut. The parameters were 400 rpm, 100 mm/min, and 1.2 mm for the largest MRR, and 400 rpm, 400 mm/min, and 0.2 mm for the least average milling temperature. In all the responses, the depth of cut is the most significant factor. Full article

The overdependence on fossils as the primary energy source has led to climate change, global warming, and the emission of greenhouse gas. As a result, the United Nations, while setting the goals for the year 2030, has made the provision of a green environment and energy one of the top priorities. In this study, the suitability of corncob for green energy production was investigated. The improvement of corncob’s thermal and combustion properties via the torrefaction process was considered for solid fuel applications. The raw corncob was collected, sorted, and dried for seven days before being used for the torrefaction experiment. Different torrefaction temperatures (200, 240, and 260 °C) and residence times (20, 40, 60 min) were studied. There was no particle reduction—samples were torrefied as collected (whole corncob). The results show that torrefaction temperature and residence time affect the torrefaction products yields along with their properties. Thermal and combustion properties were improved with an increase in torrefaction temperature and residence time. The higher heating value and energy density of the torrefied corncob varied between 17.26 and 18.89 MJ/kg, and 3.23 and 5.66 GJ/m³, respectively. High torrefaction temperature and residence time lead to low solid yield; however, liquid and gas yields increase with torrefaction temperature and residence time. The solid yields varied from 27.57 to 52.23%, while the liquid and gas yields varied from 31.56 to 44.78% and 16.21 to 27.65%, respectively. The properties of corncob improve after torrefaction and are suitable for solid fuel application. Full article

Bioceramics are widely considered as elective materials for the regeneration of bone tissue, due to their compositional mimicry with bone inorganic components. However, they are intrinsically brittle, which limits their capability to sustain multiple biomechanical loads, especially in the case of load-bearing bone districts. In the last decades, intense research has been dedicated to combining processes to enhance both the strength and toughness of bioceramics, leading to bioceramic composite scaffolds. This review summarizes the recent approaches to this purpose, particularly those addressed to limiting the propagation of cracks to prevent the sudden mechanical failure of bioceramic composites. Full article

This study investigated the effects of phosphorus fire retardants (FRs) in matrices from co-cured blends of an unsaturated polyester (UP) with inherently fire-retardant phenolic resoles (PH) on the mechanical and flammability properties of resultant glass fibre-reinforced composites. Three different phenolic resoles with UP have been used: (i) an ethanol soluble (PH-S), (ii) an epoxy-functionalised (PH-Ep), and (iii) an allyl-functionalised resin (PH-Al) with two different phosphorus FRs: resorcinol bis (diphenyl phosphate) (RDP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The flammabilities of the resultant composites were evaluated using cone calorimetry and the UL-94 test. Cone calorimetric results showed reductions in peak heat release rate (PHRR) and total heat released (THR) as expected compared to those of UP and respective UP/PH composite laminates without FRs. UL-94 tests results showed that while all composites had HB rating, FR containing samples self-extinguished after removal of the flame. The mechanical properties of the composites were evaluated using flexural, tensile and impact tests. All FRs reduced the mechanical properties, and the reduction in mechanical properties was more severe in UP/PH-S (least compatible blends) composites with FRs than in UP/PH-Al (most compatible blends) composites with FRs. Amongst the different composites, those from UP/PH-Al with DOPO showed the best fire retardancy with little deterioration of mechanical performance. Full article

Terpenoids are potentially sustainable replacements for petrochemical olefins. Sulfur is a waste product produced in large quantities from fossil fuel refining. Several composites with attractive properties have recently been made from terpenoids and sulfur. This report details the extent to which the ratio of sulfur to terpenoid and the terpenoid olefin content influences the thermal and mechanical properties of such terpenoid-sulfur composites. The terpenoids selected were diunsaturated geraniol and triunsaturated farnesol that, upon their inverse vulcanization with elemental sulfur, yield composites GerS_x and FarS_x, respectively (x = wt % sulfur). The wt % sulfur in the monomer feed was varied from 30–95 for this study, providing twelve materials. Mechanical analysis of these materials was undertaken by compressive and tensile strength techniques. Differential scanning calorimetric analysis revealed both polymeric and orthorhombic sulfur present in the materials with glass transition temperatures (T_g) of −37 °C to −13 °C and melt temperatures (T_m) of 119 to 104 °C. The crystallinity of composites decreases as the weight fraction of sulfur decreases and composites having the highest olefin content exhibit no detectable crystalline microstructures. The compressive strength of the materials showed increasing strength for higher olefin-content materials for both GerS_x (with compressive strength of up to 32 MPa) and FarS_x (with compressive strength of up to 43 MPa). The improved strength with increasing olefin content levels off at around 80–85% of terpenoid, after which point both tensile and compressive strength diminish. Full article

Integrating foil sensors into fibre-reinforced plastics offers the advantage of making manufacturing measurable with spatial resolution and thus simplifies quality control. One challenge here is the possible negative influence of the integrated sensors on the mechanical behaviour of the structure. This article shows how the different parts of a film sensor influence important mechanical strength parameters of fibre composites. A comparison of two thermoplastic carrier films shows that by choosing polyetherimide (PEI) instead of polyimide (PI), a considerably more advantageous failure behaviour of the composite is achieved. While integrated PI films reduce the interlaminar shear strength by 68%, no impairment is noticeable due to PEI films. For the critical energy release rate, PEI-based film sensors even lead to a significant increase, while a significant deterioration of 85% can be observed for PI-based sensors. However, not only the film substrate plays a decisive role for the interlaminar shear strength, but also the sensor structures themselves. In this article, sensor structures made of gold were investigated. The decisive parameter for the impairment seems to be the area share of gold structures in the sensor. For a sensor pattern made of gold lines with an area filling of 50%, a reduction of the interlaminar shear strength of up to 25% was observed depending on the angle between the shear stress and the gold lines. No impairment was observed for sensor structures with less gold area. The results show that PEI substrates can be a superior alternative for sensor integration into fibre composites and suggest that there is a trade-off between sensitivity and degradation of mechanical properties when designing interdigital sensors. Full article

Al-Ce based alloys have gained recent interest and have proven to have excellent strength without heat treatment and high thermal stability. Challenges with the production of Al-Ce samples from elemental powders arise due to the elemental material before alloying being susceptible to rapid oxidation. The methodology for making superconductive wire, powder-in-tube, was used as a consolidate Al and Ce elemental powder, and Al-8 wt % Ce-10 wt % Mg composite powder into bulk nanostructured material. Powder samples are fabricated in an inert controlled atmosphere, then sealed in a tube to avoid oxidation of powders. Therefore, most of the powder is used without much loss. We used 316 stainless-steel tubes as a sheathing material. For Al-xCe wt % (x = 8 to 14) samples of elemental powder, liquid phase sintering was used and for Al-Ce-Mg powder solid-state sintering. Characterization of the bulk consolidated material after sintering, and before and after heat treatment, was made using optical and Scanning Electron Microscope imaging, Energy Dispersive Spectroscopy, Microhardness and Rockwell Hardness test. We demonstrated that microstructure stability in Al-Ce-based specimens can be retained after thermomechanical processing. Densification was achieved and oxidation of powder was avoided in most samples. In addition, we found that Fe and Ni in the sheathing material react with Al in the process, and Ce concentration modifies the reactivity the sheath. Full article