Abstract Nomex honeycomb composites are being used more frequently in aerospace, transportation, and defense applications due to their exceptional thermal performance, mechanical strength, and low density. This review comprehensively evaluates the most recent developments in the thermal properties of Nomex honeycomb composites, with a particular focus on their fire performance, thermal stability, and effective thermal conductivity. The effective thermal conductivity (k_eff) of Nomex honeycomb cores typically ranges from 0.03 to 0.06 W/mK, as revealed by a thorough examination of the published literature. This value is primarily determined by the density of the core, the thickness of the wall, the distribution of resin, and the geometry of the cells. The range of near-insulation values to above 13 W/mK has been demonstrated to be extended by structural and material modifications, such as the integration of highly oriented graphite films and phenolic foam infill. This has enabled multifunctional thermal management. Thermogravimetric analysis consistently identifies a two-stage decomposition profile, with phenolic resin degradation occurring between 350 and 450 °C and aramid fiber breakdown between 450 and 600 °C. This results in char residues of 25–35%, which act as protective fire barriers. Cone calorimeter evaluations corroborate adherence to rigorous fire safety standards, including FAR 25.853, by confirming extended ignition times and low heat release rates. The bonding quality, void content, and ensuing thermal-mechanical performance are all significantly influenced by the manufacturing route, which includes hand lay-up, autoclave curing, resin transfer molding, and hot compression molding. This review also underscores a substantial lacuna in the systematic correlation between long-term thermal-mechanical reliability and manufacturing-induced defects under realistic service conditions, and it identifies hybrid core architectures as a design domain that has been largely unexplored. The results offer a comprehensive reference for engineers who are responsible for the development of next-generation sandwich structures that are thermally adaptive and lightweight, with applications in hypersonic, electric mobility, and defense platforms.

Growing environmental concerns have led to a focus on natural fiber-reinforced composites as sustainable alternatives to synthetic materials. Cotton and linen fibers, due to their biodegradability, offer potential for engineering applications. The mechanical performance of cotton and linen fiber-reinforced composites with epoxy and Elium® resins, focusing on tensile and flexural strength were studied. Composites were produced using the vacuum infusion method. Tensile and three-point bending tests, alongside contact angle measurements, X-ray diffraction, and scanning electron microscopy, were performed to assess thee mechanical properties, surface characteristics, and fiber-matrix adhesion. Glass fiber-reinforced epoxy composites achieved the highest tensile strength (85 MPa). Cotton fiber-reinforced epoxy and linen fiber-reinforced epoxy composites reached 60 and 50 MPa, respectively, while Elium® composites showed lower tensile strengths (cotton fiber-reinforced Elium® composite at 45 MPa, linen fiber-reinforced Elium® composite of 40 MPa). Elium® composites were more hydrophilic, especially with cotton, and displayed increased crystallinity with enhanced molecular ordering. Glass fiber-reinforced epoxy composites demonstrated superior mechanical properties; however, natural fiber-reinforced composites, particularly cotton fiber-reinforced epoxy composite, provide a viable, eco-friendly alternative for moderate-strength applications. Improving fiber-matrix interactions could enhance their suitability for broader use.

The performance of current materials remains inadequate in the face of advancing technology and challenging working conditions. Due to the advantages and versatility, they offer, composite materials are utilized in numerous industries. Polyphenylene sulfide (PPS) has attracted significant interest in the aerospace industry due to its lightweight, high strength, high-temperature resistance, availability, and mechanical and physical properties. In this study, PPS was reinforced with multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) to enhance its mechanical properties. Composite materials were produced by mixing PPS matrix material with nanofillers at different weight ratios and then subjected to compression molding. The specified tests were applied to the produced composite materials. When the thermal conductivity properties are examined, it is observed that there is a 490% increase when 10 wt% GNP is added, and a 45% increase when 10 wt% MWCNT is added. When 10 wt% of MWCNT is added to pure PPS, it has been observed that electrical conductivity at mid-frequency measurements increases by 222 % making it a conductive material. Uniform nanofiller distribution is crucial for optimal impact and mechanical performance. Agglomeration reduces properties such as tensile strength, hardness, and impact resistance.

CuCrZr alloy is a widely preferred material in the space, defense, and electronics industries with its high thermal and electrical conductivity properties. There are limited publications on the investigation of the tribological properties of CuCrZr alloys produced via the selective laser melting (SLM) method. In this study, it was aimed to optimize the process parameters and examine the effect of process parameters on density, hardness, microstructure, and tribological properties of domestically produced CuCrZr powder to be produced by the SLM method, which allows the production of complex structured parts. The optimum process parameters of the CuCrZr alloy were determined as laser power of 435 W, scanning speed of 350 mm/s, layer thickness of 0.02 mm, laser diameter of 0.1 mm, hatch distance of 0.1 mm, and energy density of 621.42 J/mm3. The relative density, hardness, COF, and wear values of the samples produced with the optimized SLM process parameters were obtained as 99% and 96 HV, 0.5520 ±0.1648, and 1.17x 10-4 (mm3/N.m), respectively.

Polyetherketoneketone (PEKK) is a highly regarded material in polymer science due to its outstanding thermal stability, mechanical strength, and chemical resistance. Despite substantial research on PEKK composites reinforced with CNTs and GNPs, two primary challenges remain: inconsistent glass transition temperature behavior at varying filler contents, leading to unpredictable shifts in both thermal and mechanical performance, and the absence of direct comparisons under uniform processing conditions that would allow quantitative evaluation of each filler's effect. In this work, PEKK/MWCNT and PEKK/GNP nanocomposites were produced via the same hot-press molding protocol and systematically evaluated for thermal and mechanical performance, electrical conductivity (using S-value analysis) and microstructural morphology. A range of mechanical tests, including tensile, Charpy impact, and hardness tests, were conducted alongside physical analyses such as differential scanning calorimetry (DSC), thermogravimetric analysis, dynamic mechanical analysis (DMA), thermal conductivity, electrical conductivity, and scanning electron microscopy (SEM). The results demonstrated that both MWCNTs and GNPs significantly enhanced PEKK's properties. The incorporation of MWCNTs raised the glass transition temperature (T-g) to 169 degrees C and the crystallization temperature (T-c) to 327 degrees C, whereas GNPs increased the decomposition temperature (T-d) to 572 degrees C. Adding 1 wt.% of either nano-additive notably improved tensile and flexural strength, while an optimal concentration of 0.1 wt.% was determined for Charpy impact performance. Additionally, higher concentrations resulted in exceptional electrical and thermal conductivity.

Various approaches have been proposed to enhance the thermal conductivity of polymers, primarily by incorporating high thermal conductivity nano-additives into the polymer matrix. In this study, graphene nano-platelet (GNP) and titanium diboride (TiB 2 ) were used as nano-additives while polyphenylene sulphide (PPS) was used as polymer matrix. Materials were dry-mixed in predetermined weight ratios and produced using compression molding. Tensile as well as hardness testing, thermal conductivity measurements and scanning electron microscopy analyses were conducted on the produced composite materials. Results show that an improvement in thermal conductivity values was observed. When 0.1 wt% TiB 2 is added, there is a 21% increase in the thermal conductivity compared to pure PPS, whereas the addition of 0.1 wt% GNP results in a 15% increase. Regarding mechanical properties, an increase of 11% in the tensile strength was observed with the addition of 0.1 wt% GNP.

This study is concerned with the optimisation of the processing parameters for the selective laser melting (SLM) of pure copper. The influence of these parameters on the microstructure, density and mechanical properties of copper samples produced by SLM is investigated in detail. Taguchi analysis is used to assess the importance of key building parameters including layer thickness, laser spot size and hatch distance on density. In addition, ANOVA is used to describe the contribution of each parameter to the density. The results reveal that layer thickness is the most effective parameter on density with an impact rate of 88.86%. Contrary to this situation, it appears that the effect of laser spot size and hatch distance on the density is quite limited, with an impact rate of 2.57% and 0.10%, respectively. Optimum results, including a relative density of 95.4% and a hardness of 63 HV, are achieved under specific parameters: a layer thickness of 0.03 mm, a hatch distance of 110 mm and a laser spot size of 70?m. This study provides a valuable insight into SLM processing of pure copper and offers practical recommendations for optimising the parameters used.

Thermoset polymers are cured under natural or synthetic created conditions and retain their solid form when exposed to heat. Unlike thermosets, thermoplastics melt when exposed to heat after production. Thermoplastics are preferred as raw materials because they can be easily shaped after production, have a high shelf life and are recyclable. In this regard, the prominence of high-performance engineering polymers in recent years has led to the preference of alternative polymers to thermosets. High-performance engineering thermoplastics include thermoplastics such as polyphenylene-sulfide (PPS), polyether-ether-ketone (PEEK), polyether-ketone-ketone (PEKK), polyphenylene-ether, polysulfone,polyoxadiazole, polyimide, polyether-amide, polyether-amide-imide, polynaphthalene, and polyamide-imide. These polymers exhibit application potential in aerospace, defense, automotive, marine, energy, and medical sectors. In challenging conditions such as high pressure, temperature, and corrosive environments, they possess high service temperatures, enhanced mechanical and physical properties, preferable chemical resistance as well as out-of-autoclave and rapid processing properties. In this review article, nanomaterial production methods (bottom-up and top-bottom) are mentioned. In the following sections, PPS, PEEK, and PEKK thermoplastics are explained, and carbon- and boron-based nano additives used in constructing nanocomposites are investigated. In the last section, PPS, PEKK, and PEEK polymer nanocomposites are investigated.

High engineering requirements of shock absorbers have increased interest in auxetic materials, which have higher specific energy absorption performance compared to conventional solid absorbers. Last decade, many optimization studies were conducted to improve the energy absorption performance of auxetic tubular structures. Most studies focused on adding inner and outer shells to thin-walled auxetic tubular absorbers with different types of lattice structures to enhance energy absorption of the cylindrical sandwiches. There are limited studies on thicker-walled auxetic tubes and their related shell thicknesses to optimize performance. In this study, the thickness of the thicker-walled auxetic core thickness (1.2 mm, 1.6 mm, 2 mm), shell thickness (16 mm, 20 mm, 24 mm), and auxetic lattice structure (Re-Entrant Circular, SiliComb, and ArrowHead) were optimized to improve the specific energy absorption of cylindrical sandwiches. The Taguchi method was used to determine the optimum parameters for cylindrical sandwiches. In addition, the effect ratio of the parameters on the specific energy absorption was investigated using the ANOVA method. The energy absorption properties of the cylindrical sandwiches were determined using the drop-weight test. The highest specific energy absorption was obtained using a shell thickness of 1.2 mm and a core thickness of 16 mm using an SiliComb lattice. It was determined that the lattice geometry was the most effective parameter on the specific energy absorption of cylindrical sandwiches, with an effect rate of 61.62%.

Bu çalışmada, Reçine Transfer Kalıplama (RTM) yöntemiyle üretilmiş cam fiber takviyeli kompozit plakalarda elyaf ağırlığının ve jelkotun mekanik özelliklere etkisi incelenmiştir. Üç farklı laminasyon planı ve bu planların jelkotlu halleri kullanılmıştır. Numunelerin incelenmesi için çekme testi, üç nokta eğme testi ve Barcol sertlik testleri yapılmıştır. Laminasyon planlarında 300 g/m2, 450 g/m2, 600 g/m2 olmak üzere 3 farklı ağırlıkta elyaf kullanılmıştır. Ayrıca laminasyon arasında 180 g/m2 ve 250 g/m2 polipropilen köpük malzeme kullanılmıştır. Her laminasyon için bir jelkotlu, bir jelkotsuz plaka üretilmiştir. Üretim sonunda kalınlıkları 2.5 – 3.2 mm arasında değişen 6 plaka üretilmiştir. Üç nokta eğme ve çekme testi için 10’ar numune kesilmiştir, Barcol sertlik testi plaka üzerinde 5 noktadan alınmıştır. Testler sonucunda elyaf ağırlığının artmasıyla mukavemet değerlerinin arttığı, uzama değerlerinin azaldığı gözlemlenmiştir. Her laminasyonun jelkotlu hallerinde %5 - 15 aralığında mekanik özellik düşüşü gözlemlenmiştir.

Improving the interface properties of carbon nanotubes increases the mechanical performance of fiber-reinforced polymer matrix composites. Studies on different fiber types and different polymer matrix materials present promising results in literature. The effect of carbon nanotube (CNT) additives on impact performance of fiber reinforced polymer matrix composites produced by vacuum infusion method and drop weight impact test applied. Glass and carbon 1 m2 fiber fabrics were divided into 9 equal square pieces and placed on top of each other to make them multi-layered structure. Fiber reinforcements were produced using vacuum infusion method with epoxy resin. 0.5% of the total composite weight was added to CNT with same production parameters and intraply hybrid composite containing glass, carbon and aramid fibers was also produced. Samples were produced from the composite plates and the drop weight impact test was performed with 50 J impact energy in accordance with ASTM D7136 standard. While this increase could be observed in glass fiber and carbon fiber reinforced composites, the impact energy absorption performance in carbon fiber reinforced composite increased more than 100%. CNT increased the impact performance of multi-layer fiber reinforced polymer matrix composites.

Most of the structures in vehicles used in the automotive, aviation, and marine industries are exposed to different loads. It is seen that these structures are more exposed to flexural stress. Structures can sustain dangerous damage over time under the effects of flexural loads. The resistance of curved glass fiber reinforced polymer composites to flexural force is very important. In this study, the diameters of curved composites of 760 mm, 380 mm, and 304mm are studied. Also, fiber stacking sequences were determined as [0/0/-45/+45/90/90](S) and [90/90/-45/+45/0/0](S) and compared. All specimens were produced by vacuum infusion method. Three-point flexural tests were performed according to the ASTM D7264 standard at 1mm.min(-1) punch speed. Among all composites, 760mm diameter and Type 2 stacking were found to have the highest flexural strength. Hence, it was observed that the flexural strength decreased with the increase in curvature, and Type 2 fiber layer sequencing is more durable than Type 1 sequencing. This is because the 90 degrees fiber direction in the substrate has a damping effect on the applied force.

The purpose of this research article is to show the effect of carbon nanotubes (CNTs) addition on fiber reinforced polymer matrix composites produced by the vacuum infusion method on tensile performance. In this study, glass, carbon, and fiber fabric reinforced polymer matrix composite plates were produced using glass, carbon and aramid fiber fabrics with the same weave type and similar areal density. Using the same production parameters, the composite plates reinforced with different fiber types were produced with CNTs addition by 0.5 wt% of total composite. Additionally, since it is thought that the effect of CNTs on performance in different fiber types may be different, hybrid fiber fabric reinforced composite plate material containing a composition of glass, carbon and fiber fabrics was produced and this material was produced with CNTs additive using the same production parameters as in previous fiber reinforced composite plate productions. In the study, composite plates with and without CNTs were produced in various compositions including glass, carbon, aramid, and hybrid fiber fabrics. As a result, CNTs reinforcement has increased the mechanical performance under tensile stress in glass, carbon, and hybrid reinforced fabric composite structures, but on aramid fiber, CNTs has decreased the performance.

Recently, glass fiber reinforced polymer composites have been increasingly used in applications which are exposed to impact loads due to their high strength, low weight, and corrosion resistance properties. Therefore, the effect of curvature of composite laminate on their impact resistance is important. In this study, the mechanical properties of three curvature diameters and two stacking sequences, which have not been compared before, were examined and compared. The diameter of curved composites is 760 mm, 380 mm, and 304 mm and flat designated as A, B, C, and D, respectively. The fiber stacking orders are [0/0/-45/+45/90/90]S and [90/90/-45/+45/0/0]S designated as Type 1 and Type 2, respectively. The drop-weight impact tests were performed and failure modes of composites were examined. It was observed that the impact resistance decreases with the increase of curvature, where 760 mm diameter and Type 2 composites had the highest strength in all of the composites. In addition, delamination, fiber breakage, and matrix cracking failure modes were observed in the composites after impact. The reason why the strength decreases as the curvature of the composite increases is that the curved areas create an effect that increases the external force applied. The reason why Type 2 stacking order is more durable than Type 1 stacking order is that the 90° fiber direction in the bottom layer has a damping effect on the applied force. According to the results of this study, composite materials with larger diameter and stacking order starting with 0° provides more mechanical strength. [Formula: see text]

The aim of this research article has been to show the effect of Carbon Nanotube (CNT) additive on the performance of composite plate materials with fiber reinforced polymer matrix produced by vacuum infusion method under bending test. In this study, multiple layered composite plates have produced by glass, carbon, and aramid fiber reinforcements with 0.5% CNT addition by mass. In addition, a hybrid composite plate containing glass, carbon and aramid (Kevlar) fiber has produced with CNT addition by using the same production parameters. Three point bending test has performed on the composite plates under 1 mm/min bending with ASTM D7264 standard. As a result, CNT addition has increased the flexural performance but has decreased the elongation of glass and carbon fiber reinforced systems. In aramid reinforced system, both flexural strength and elongation has increased. However, in the hybrid fiber reinforced system, different fiber types have damaged at different elongation distances within the structure under different loads, and gradually more than one failure have observed. When the CNT has added to the hybrid system, the elongation increased but the flexural strength has decreased.

In-service, composite sandwich structures, which consist of fibre-composite skins (also termed face-sheets) adhesively bonded to a polymeric foam core, can encounter extreme quasi-static flexural loading that may cause serious damage to the sandwich structure. The ability to model the flexural behaviour of such structures can lead to improved designs and more efficient maintenance procedures. In the present research, a three-dimensional finite-element analysis (FEA) model is developed to predict the flexural behaviour of such sandwich structures using a commercial software package (i.e. Abaqus/Explicit). The high-fidelity FEA simulation combines an elastic-plastic (E-P) damage model of the composite skins together with a crushable foam-core damage model. The E-P damage model is implemented with a user subroutine to capture the damage, such as plastic deformation of the matrix and matrix cracking, fibre fracture and delamination cracking of the composite skins. The crushable foam model is used to predict (a) the mechanical response of the crushed foam core, (b) the induced damage from ductile fracture due to growth, coalescence and fracture of the cells and (c) the induced damage from shear fracture of the foam due to plastic shear-band localisation. Results from the modelling studies, such as the loading response and the damage mechanisms, are discussed and compared with the experimental results obtained from the sandwich structures manufactured with both uniform- and graded-density foam cores but which all have the same average core density. Good agreement is achieved between the experimental results and the predictions from the numerical modelling simulations.

Plasma electrolytic oxidation (PEO) coatings on commercial pure titanium (Cp-Ti) and hot-dip aluminised Cp-Ti surfaces were prepared in an alkaline electrolyte. The morphological, structural, wear, and corrosion characteristics of the coatings were studied by using SEM, EDS, XRD, electrochemical polarisation, and dry sliding wear tests. The experimental results showed that the main compositions of the PEO coating on Cp-Ti are TiO2 and Al2TiO5 phases, while the PEO coating on hot-dip aluminised (HDA'ed) Cp-Ti mainly consists of the Al2O3 phase. The single PEO coating exhibited more porosity with small diameter micro-pores compared to the PEO coating on the HDA'ed sample. Electrochemical polarisation tests revealed that the PEO coating on the HDA'ed sample exhibited approximately 4.6 times more polarisation resistance than the single PEO coating and 10 times that of the bare Cp-Ti sample. According to the wear test results, the wear resistance of the bare Cp-Ti was doubled by hot-dip aluminising (HDA) and PEO treatments, while the single PEO treatment resulted in better resistance against dry sliding wear.

The effects of a coupling agent on the behavior of flax fiber-reinforced composites have been investigated by testing the specimens under both quasi-static (QS) indentation and high-velocity impact loading. The specimens are manufactured embedding a commercial flax fiber fabric in a polypropylene (PP) matrix, neat and premodified with a maleic anhydride-grafted PP, the latter acting as a coupling agent to enhance the interfacial adhesion. QS compressive tests were performed using a dynamometer testing machine equipped with a high-density polyethylene indenter having the same geometry of the projectile employed in the impact tests. The impact tests were conducted setting three different impact velocities. Digital image correlation maps of out-of-plane displacement were employed to compare the specimens with and without the coupling agent. The QS testing results indicate that the coupling agent has an enhancing influence on the bending stiffness of tested flax composites. The testing results show that the coupling agent improves the mechanical behavior by decreasing the out-of-plane displacement under impact loading. This approach gives rise to new materials potentially useful for applications where impact performance is desired while also providing an opportunity for the incorporation of natural fibers to produce a lightweight composite.

Sandviç kompozitler, farklı malzeme kombinasyonları ile birleştirilerek özel uygulamalar için oluşturulabilen optimum malzeme tasarımlarıdır. Çok sayıda alternatif sandviç kompozit yapı biçimi ile farklı yüzey ve çekirdek malzemeler birleştirilebilir. Bu çalışmada; özellikle otomotiv tampon uygulamalarına yönelik olarak geliştirilen sandviç kompozit malzeme, naylon Poli-amid 12 (PA12) polimer malzemesinden oluşan çekirdek ile cam fiber takviyeli Polipropilen (GFRPP) alt – üst yüzeylerin bir araya getirilmesi ile elde edilmiştir. Malzemelerin önemli bir özelliği olan Poisson oranı; bir malzemenin kuvvet uygulandığı yöndeki şekil değiştirme miktarı ile aksi yöndeki şekil değiştirme miktarı arasındaki bağıntıyı verir. Poisson oranı birçok malzemede pozitif iken bazı malzemelerde ise negatiftir. Poisson oranı negatif olan bu malzemelere "oksetik malzeme" denir. Üretilen sandviç kompozitte negatif Poisson oranına sahip olan oksetik özellikteki çekirdek, üç boyutlu yazıcılardan birisi olan Fused Deposition Modelling (FDM) ile üretilmiştir. Girintili bal peteği geometrisi sayesinde üstün esneme özellikleri beklenmektedir. Bu amaçla; iki farklı kalınlıkta üretilen çekirdek geometrisine sahip olan sandviç kompozit malzemeler üç nokta eğme testlerine tabi tutulmuştur. Bu çalışma kapsamında mukavemet ve darbe absorbsiyonu açısından sandviç yapılarda kullanılan oksetik yapıların arasındaki mesafenin yapının kalınlığından daha önemli bir parametre olduğu ortaya konulmuştur.