High-performance Engineering Materials Research Articles

Simultaneous strengthening and toughening of PLA with full recyclability enabled by resin-microsphere-modified L-lactide oligomers

Various strategies have been developed to improve the brittleness of poly (lactic acid) (PLA), most of which still suffer from the toughness-strength trade-off dilemma. Herein, we prepared phenol–formaldehyde-resin microspheres (PFM) with aliphatic hydroxyl groups to initiate L-lactide polymerization and synthesized a series of PFM-modified L-lactide oligomers (PFM-OLLA) bearing different arm lengths. PFM-OLLA were then physically blended with commercial PLA in different weight ratios to prepare synchronously strengthened and toughened PFM-OLLA/PLA composites. After blending with 4 % PFM2.5-OLLA (PFM content: 2.5 %), the mechanical properties of the PFM2.5-OLLA/PLA composites were best. PFM2.5-OLLA efficiently improved the crystallization behaviors of the PFM2.5-OLLA/PLA composites, thereby significantly enhancing their strength and toughness. The maximum tensile yield strength (40.2 MPa), elongation at break (85.7 %), and impact strength (20.8 kJ/m2) of PFM2.5-OLLA/PLA composites could respectively increase by 44.2 %, 465.7 %, and 100 %, compared to the values of neat PLA. The microscopic strengthening and toughening mechanisms were attributed to the rigidity of PFM, and the heterogeneous nucleating ability as well as larger free volume of PFM2.5-OLLA, whereas the visual toughening effects were attributed to multiple crazing and shear yielding phenomena. After simple alcoholysis and filtration, the polymer components were completely converted into methyl lactate. The recycled PFM, exhibiting excellent chemical stability, were reused to synthesize a new PFM-OLLA for strengthening and toughening PLA. This study provides a sustainable strategy for the development of high-performance PLA engineering materials showing great application potentials in the automotive, electronics and housing fields.

Determination of Kinetic Parameters and Thermal Characteristics of Epoxy Casuarina Bio Composites

By reinforcing casuarina equisetifolia leaf, a flexible bio fibre, in different volume proportions of 4%, 8%, 12%, 16%, and 20% into the epoxy resin, a bio-based composite was produced utilizing the hand layup method. FT IR spectrum was used to verify the production of epoxy casuarina composite. The produced composites have undergone an extensive thermal investigation using Differential Thermal Analysis (DTA), Thermogravimetric Analysis (TGA), Derivative Thermogravimetric (DTG) study and Differential Scanning Calorimetry (DSC) analysis. It has been observed that increasing the percentage of casuarina fibre content enhances the thermal stability of epoxy resin. Horowitz- Metzger (HM), Broido and Coats-Redfern (CR) models were worked and the result revealed that the decomposition of casuarina epoxy composite followed one Dimensional Diffusion Model with coefficient of correlation value close to 1. The thermodynamic parameters including Activation energy (Ea), frequency factor (A), Gibbs free energy (ΔG), entropy (ΔS) and enthalpy (ΔH) of epoxy casuarina composites were found to increase with increase in fibre contents. This makes the composite more suitable for making high performance engineering material for various applications.

Mechanical and Dynamic Mechanical Characterization of Epoxy Composites Reinforced with Casuarina Leaf Bio Fibre

This study investigates the influence of casuarina leaf biofibre on the mechanical and morphological characteristics of epoxy resin composites. Composites were prepared using the hand-layup method, incorporating varying volume fractions of the biofibre (4%, 8%, 12%, 16%, 20% and 24% v/v). Mechanical and dynamic mechanical tests were carried out to assess the impact of the biofibre on the composite material. Mechanical testing revealed significant enhancements in tensile strength of 29.2 MPa, particularly at a biofibre volume fraction of 12% and the composite with the highest impact and flexural strengths measured at 2621 J/m2 and 41.1 MPa, respectively for the 16%v/v fibre loading. Dynamic mechanical analysis (DMA) results demonstrated improved viscoelastic properties attributed to the presence of the biofibre. Scanning electron microscopy (SEM) examination of tensile tested samples provided insights into interfacial bonding and filler dispersion within the composite matrix. Overall, the findings highlight the potential of casuarina leaf biofibre to enhance specific mechanical properties and viscoelastic behaviour of epoxy casuarina composites. Optimizing the biofibre volume fraction offers possibility to tailor composite properties for specific application requirements. This research advances the development of bio-based composite materials, contributing valuable insights for the creation of sustainable and high-performance engineering materials.

Study on the microstructure and impermeability of calcium aluminate cement containing metakaolin for development of high-performance marine engineering materials

To provide a high-performance marine engineering material, the microstructure and impermeability of calcium aluminate cement (CAC) containing metakaolin (MK) were studied. The chloride penetration resistance of the CAC-MK and Portland cement (PC) mortars was assessed based on physical and chemical barrier effects. The results show that the alumina in MK is more easily dissolved than silica, which inhibits the transformation of CAH10 and prevents microstructural deterioration. Adding 7.5% and 15.0% MK reduces the volume of large pores in the 3-day-old CAC paste by 49.8% and 69.1% while increasing the volume of pores smaller than 50 nm by 175.6% and 242.5%, respectively. Moreover, the microstructure of MK-containing CAC pastes becomes denser with age when cured at 40 °C, enhancing the mechanical strength and water penetration resistance. The CAC mortar containing MK exhibits better resistance to chloride attack than PC mortar, due to the stronger chloride binding capacity and migration resistance.

Fracture mechanics model of biological composites reinforced by helical fibers

Many biological materials such as tendons and muscles contain helical fibers. In this paper, the fracture behavior of such chiral composites is investigated through a combination of theoretical analysis and finite element simulations. A mesoscopic fracture mechanics model of helical fiber-reinforced biological composites is presented, with the effects of interfacial damage and fiber breakage. A cohesive law is adopted to characterize the interfacial damage induced by the relative slipping between the fibers and the matrix. The theoretical model agrees well with the numerical results. The optimized fiber radius that can maximize the fracture toughness of the composites is determined. The effects of interfacial (e.g., bonding strength and energy dissipation) and material properties (e.g., strength and elastic modulus) on the resistance to crack propagation are revealed. Our results show that the composites reinforced by helical fibers exhibit comprehensively excellent mechanical properties, e.g., simultaneous high strength, stiffness, and fracture toughness. This work not only helps understand the structure–property interrelations of biological chiral composites, but also provides inspirations for designing high-performance engineering materials.

Grain-selective growth makes Al0.1CoCrFeNi high entropy alloys strong and ultra-ductile

The trade-off between strength and ductility of structural materials has always been a concern, and the pursuit of higher strength often comes with the inevitable sacrifice of ductility, which poses challenges for the design and manufacture of high-performance engineering materials. In this study, we introduce a novel concept called grain-selective growth (GSG) to address the strength-ductility trade-off by effectively triggering the strain hardening capacity of the single-phase FCC HEAs. Specifically, we prepared an Al0.1CoCrFeNi high-entropy alloy with a heterogeneous grain structure using cyclic rolling and annealing. By employing this approach, our GSG HEA achieves an ultra-ductility with ∼53% uniform elongation and an ultimate tensile strength of 1165 MPa. Rapidly accumulating geometrically necessary dislocations in the domain boundary region, as revealed through electron backscatter diffraction analysis, have led to the development of high-level heterogeneous deformation-induced (HDI) stress. In addition, we also observed synergistic strain hardening effects generated by various deformation mechanisms, such as dislocation pile-ups, stacking faults (SFs), deformation twinning, dislocation walls, and SF networks. This study provides valuable insights for the manufacturing of high-performance heterostructure materials, making it possible to develop advanced alloys with higher strength and ductility, suitable for a wide range of engineering applications.

Forming Behavior of Additively Manufactured Al/Ti Material Compounds Produced by Cold Spraying

Cold spraying has great potential for additive manufacturing, especially of oxidation-sensitive metals, because the material is not melted and significantly higher deposition rates can be achieved than with conventional additive manufacturing processes such as selective laser melting or direct metal deposition. Titanium is regarded as a high-performance engineering material due to its unique combination of properties, including good corrosion resistance, biocompatibility and high strength at comparatively low density. However, due to its high price, it appears reasonable for many applications to use material compounds in which titanium is only used on the surface of the workpiece, while less expensive materials such as aluminum are used for the remaining volume. In the present work, cold sprayed pure titanium coatings were deposited on Al substrates and then formed to defined 3-dimensional final contours by die forging and rotary swaging. Different porosities were selectively set in order to evaluate their influence on the coating adhesion and cohesion in the forming process. Pre-consolidation of the coatings and the use of Al/Ti interlayers proved to be promising strategies.

Transforming Wood into a High-Performance Engineering Material via Cellulose Nanocrystal Impregnation

Abstract The demand for wood in construction has led to shortages of strong wood types, causing a shift to costlier alternatives like concrete and nonbiodegradable materials, prompting the investigation of modifying softwoods for better engineering properties. This study investigates the optimization of a multistep impregnation process utilizing functionalized cellulose nanocrystals (f-CNCs) to enhance softwood properties. The process involves alkali delignification, ultrasonication, and vacuum pressure treatment to improve wood porosity and in turn improve CNC impregnation with uniform dispersion. Microstructural analyses through field emission scanning electron microscopy and atomic force microscopy (AFM) offer detailed insights into cell wall morphology and surface topography, whereas Fourier transform infrared spectroscopy highlights compositional shifts resulting from f-CNC impregnation. Mechanical testing demonstrates significant improvements for treated woods, particularly a 67 percent increase in modulus of elasticity for the 2 percent CNC-treated group compared with the control group; a 71 percent increase in modulus of rupture was observed for 2 percent CNC-, 3 percent NaOH-, and 2 percent acetic acid-treated group compared with the control sample. The sample delignified with 3 percent NaOH and impregnated by 2 percent f-CNC emerged as particularly effective. This research sets the stage for potential advancements in strengthening softwood using CNC, including a novel AFM method and alternative impregnation techniques like the Lowry method, inviting further exploration.

Kutu Sementasyon Tekniğiyle GGG70 Küresel Grafitli Dökme Demir Yüzeyine Kaplanan NbC Tabakasının Özelliklerine Kaplama Sıcaklığın Etkisin İncelenmesi

Nodular Graphite Cast Irons stand out with their high castability, high strength, vibration damping and high loading capacity. With today's technologies, the surface properties of materials can be improved by coating them with various methods and high-performance engineering materials can be obtained. Pack Cementation Technique is preferred among coating methods due to its relatively lower cost and applicability. In this study, it was aimed to coat NbC on the surface of GGG70 Nodular Graphite Cast Iron using the Pack Cementation Technique at 900 °C, 1000 °C and 1100 °C for 6 hours. The effect of temperature on the properties of the resulting coating layers was investigated. For this purpose, the surface morphologies of the samples were examined and their fracture toughness and hardness values were obtained. Coating morphologies were examined by XRD, optical microscope and SEM analysis and changes in coating structure and thickness were obtained. When the results were examined, it was determined that the coating thickness increased with the increase in coating temperature. Accordingly, it was observed that the fracture toughness value of the coatings first increased and then decreased slightly. Microhardness values increased approximately 5 times in the coating areas.

Acid‐Assisted Toughening Aramid Aerogel Monoliths with Ultralow Thermal Conductivity and Superior Tensile Toughness

AbstractResisting extreme loading and thermal ablation encountered by aerospace devices demands for high performance engineering materials. Aerogels have achieved satisfactory thermal insulation but the intrinsic brittleness of porous skeletons fail to ensure their normal operation under severe stress fields. Herein, aramid nanofibers (ANFs) are processed into tough 3D aerogel monoliths via a multi‐scale toughening strategy, involving unidirectional freeze‐casting‐enabled microstructure orientation and acid‐assisted nanofiber cross‐linking. Scalable production of ANFs aerogels is realized through fast air‐drying without excessive energy consumption. The aligned sheets in ANFs aerogels enable extreme thermal conductivity of 15.8 mW m−1 K−1, superinsulation from −130 to 300 °C, and durable combustion protection for 20 min. Particularly, highly aggregated nanofibers assemble into dense ANFs skeletons, endowing the tough aerogels with superior specific tensile strength (89 MPa cm3 g−1), ultra‐high toughness (1.3 MJ m−3), and impressive fracture energy (7.36 kJ m−2). Such mechanical properties are highly resistant to harsh environments, including water erosion (7 days) and high temperature baking (30 days). Moreover, ANFs aerogels exhibit two to three times more energy dissipation than commercial foams against ballistic impact at 140 m s−1. This integrated mechanical and thermal robustness may pioneer the potential application in impact‐thermal coupled safeguard for aerogel materials.

Residual Stress Characterization of an Additively Manufactured Titanium Alloy

Additive manufacturing (AM) has emerged as a revolutionary technology for producing complex and customized components, particularly in aerospace and medical industries, using materials like titanium alloys known for their exceptional strength-to-weight ratio. However, the inherent thermal gradients and rapid solidification processes during AM can introduce residual stresses in the manufactured parts, significantly affecting their mechanical properties and structural integrity. This study focuses on the comprehensive characterization of residual stresses in additively manufactured titanium alloy components, particularly on understanding the influence of various AM process parameters, post-processing techniques, and part geometries. We employ state-of-the-art semi-destructive techniques, incremental hole drilling and strain gauging to map and quantify the residual stress distribution within the fabricated parts. We elucidate the factors contributing to residual stress formation through carefully designed experiments and numerical simulations, including thermal history, cooling rates, and build orientation. The findings of this research not only advance our fundamental understanding of residual stress mechanisms in additively manufactured titanium alloys but also provide valuable insights for optimizing the AM process and post-processing steps to minimize residual stress-induced defects and enhance the reliability of components in critical applications. Ultimately, this work contributes to the broader goal of unlocking the full potential of additive manufacturing for high-performance engineering materials like titanium alloys.

LS-DYNA Machine Learning–Based Multiscale Method for Nonlinear Modeling of Short Fiber–Reinforced Composites

Short-fiber-reinforced composites (SFRC) are high-performance engineering materials for lightweight structural applications in the automotive and electronics industries. Typically, SFRC structures are manufactured by injection molding, which induces heterogeneous microstructures, and the resulting nonlinear anisotropic behaviors are challenging to predict by conventional micromechanical analyses. In this work, we present a machine learning-based multiscale method by integrating injection molding-induced microstructures, material homogenization, and Deep Material Network (DMN) in the finite element simulation software LS-DYNA for structural analysis of SFRC. DMN is a physics-embedded machine learning model that learns the microscale material morphologies hidden in representative volume elements of composites through offline training. By coupling DMN with finite elements, we have developed a highly accurate and efficient data-driven approach, which predicts nonlinear behaviors of composite materials and structures at a computational speed orders-of-magnitude faster than the high-fidelity direct numerical simulation. To model industrial-scale SFRC products, transfer learning is utilized to generate a unified DMN database, which effectively captures the effects of injection molding-induced fiber orientations and volume fractions on the overall composite properties. Numerical examples are presented to demonstrate the promising performance of this LS-DYNA machine learning-based multiscale method for SFRC modeling.

Bamboo-inspired strong, tough and stable composites derived from renewable bamboo

Bamboo engineering materials are made from abundant raw material sources and can be easily prepared with minimal processing and low pollution. However, when used as structural materials, they are limited by their weight, strength, and lack of stable designability. The use of laminated structure and a gluing interface are key factors affecting the performance of bamboo engineering materials. Bamboo exhibits excellent toughness and strength when resisting external forces, with a multi-level interlocking reinforced interface with bamboo’s intercellular layer that induces an increase in crack deflection paths (internal toughening) and cell wall energy consumption (external toughening) coupled to microfibril pulling out. Inspired by the functionally graded structure of the lightweight and high-strength bamboo wall layer and the interlocking reinforced interface between vascular bundles and parenchyma cells, we designed a high-performance bamboo engineering material designed to imitate bamboo, Imitation Bamboo Bundle Laminated Veneer Lumber (IBLVL), prepared by uniform lamination and gradient molding. The designed IBLVL is light in weight, with high strength and uniform density. This work demonstrates the feasibility of using resource-rich and sustainable bamboo to manufacture light-weight bamboo engineering materials with high strength and high toughness that can be substituted for non-renewable resources in the fields of construction and transportation.

Remolding and Deconstruction of Industrial Thermosets via Carboxylic Acid-Catalyzed Bifunctional Silyl Ether Exchange

Convenient strategies for the deconstruction and reprocessing of thermosets could improve the circularity of these materials, but most approaches developed to date do not involve established, high-performance engineering materials. Here, we show that bifunctional silyl ether, i.e., R'O-SiR2-OR'', (BSE)-based comonomers generate covalent adaptable network analogues of the industrial thermoset polydicyclopentadiene (pDCPD) through a novel BSE exchange process facilitated by the low-cost food-safe catalyst octanoic acid. Experimental studies and density functional theory calculations suggest an exchange mechanism involving silyl ester intermediates with formation rates that strongly depend on the Si-R2 substituents. As a result, pDCPD thermosets manufactured with BSE comonomers display temperature- and time-dependent stress relaxation as a function of their substituents. Moreover, bulk remolding of pDCPD thermosets is enabled for the first time. Altogether, this work presents a new approach toward the installation of exchangeable bonds into commercial thermosets and establishes acid-catalyzed BSE exchange as a versatile addition to the toolbox of dynamic covalent chemistry.

Room temperature, simple and efficient synthesis and functionalization of aromatic poly(arylene sulfide)s, poly(arylene sulfoxide)s and poly(arylene sulfone)s

Aromatic polysulfides and polysulfones are a large group of sulfur-containing polymers representing an important class of materials with diverse applications, ranging from high performance engineering plastics, gas separation, ultrafiltration, nanofiltration, ion-exchange membranes, and materials for biomedical applications. All these polymers are produced by high temperature nucleophilic substitution reactions of dichlorobenzene with sodium sulfide (PPS) and dichlorodiphenyl sulfone with bis-phenols in the presence of basic catalysts (PAES). In the present work, novel poly(arylene sulfide)s were obtained in nearly quantitative yields, by one-pot, room temperature, metal-free, highly regioselective, non-stoichiometric step-polymerizations of diphenyl sulfide (DPS) with 1,1,1-trifluoroacetone and isatin, in a mixture of trifluoromethanesulfonic acid (TFSA) with CH2Cl2. The polymers obtained were soluble in common solvents. The oxidation of the poly(arylene sulfide)s with H2O2 at room temperature afforded poly(arylene sulfoxide)s and poly(arylene sulfones) with high oxidation selectivity. On heating, sulfoxide groups of the poly(arylene sulfoxide)s are converted into sulfide groups and oxygen, which acts as an expanding agent, is released in the process to form nanofoams with homogeneous pore distribution. Controlled incorporation of hydroxymethyl-, carboxy-, and “click” able allyl- and propargyl- functionalities is carried out by room temperature, post-modification reactions of the polymers bearing reactive oxindole groups.

Spark Plasma Sintering (SPS) of Multi-Principal Element Alloys of Copper-Niobium-Titanium-Di-Boride-Graphite, Investigation of Microstructures, and Properties

A near-equiatomic multi-principal element alloy of Cu40Nb30(TiB2)20C10 with both nano-particle size (14 nm) and micron-particle sizes (−44 µm) of Nb was designed and made via the spark plasma sintering technique at two different sintered temperatures of 650 °C and 700 °C with other SPS parameters being constant. The sintering mode, microstructures, microhardness, density, relative density, wear behavior, and corrosion properties of the alloys were investigated and compared to ascertain the best for aerospace applications. The SPS technique was applied to produce the tested samples in this study. The results showed that the alloys with nano-particles of Nb sintered faster, with the lowest wear rate, and their microstructure shows a dendritic configuration with the existence of graphite-rich and niobium-rich nano-segregations in the inter-dendritic areas with the lowest coefficient of friction, Cu-NbTiB2C with nano-particles of Nb sintered at 650 °C recorded the highest microhardness value (786.03 HV0.2), and CuNbTiB2C with micro-particles of Nb sintered at 700 °C exhibited the best anti-corrosion characteristics in a sulphuric acid environment. The results obtained in this study correspond to the requirements for high-performance engineering materials, which will make the novel materials relevant in the aerospace industry.

Optoelectronic investigation and spectroscopic characteristics of polyamide-66 polymer

Abstract A semi-crystalline designated nylon 66 polymer is a crucial, high-performance engineering material that is used in wide variety of industrial applications including sensors, electrical insulators, electronic devices, and automotive sector. Using modules based on density functional theory and finite-field approaches, this work explores the optoelectronic and spectroscopic characteristics of this polymer. Absorption, dielectric function, refractive index, and optical conductivity are the principle topics of this study. The effects indicated that nylon 66 is a first-rate insulator and the degree of crystallinity estimated is 46.44%. The simulated bandgap vs. the Tauc relation value is greater than 7.0 eV and has a proportional inaccuracy of 2.36%. Absorption coefficient value, however, suggests that while the refractive index and dielectric function remain stable, the optical conductivity is elevated. In order to determine the advantages appropriate for many applications, this research develops a strong basis and perception of the linear and nonlinear optical properties of nylon 66.

Fatigue-Induced Surface Modification of Zr-Based Metallic Glass under Environmental Conditions.

Metallic glass (MG), an intrinsic heterogeneous structure at the atomic scale, is one of the promising engineering materials with intriguing physical properties. MG often suffers from the fatigue issue caused by the repetitive mechanical loading, but it is still elusive how the local heterogeneity evolves and affects the macroscale fatigue and deformation against bulky external stress. In this study, we investigate the fatigue effect in Zr-Cu-Al ribbon using a bending fatigue method. We used scanning probe microscopy (SPM) in parallel with X-ray diffraction and X-ray photoelectron spectroscopy to figure out the loading effect on the local heterogeneities. The spatially resolved SPM images show that there is a local fluctuation of mechanical and electrical properties on the fatigued side along with morphological deformation compared to the unloaded side. Approaching the broken edge where the fatigue failure occurs, the decaying tendency is not only more dominant but also accelerated by surface oxidation of the fatigued regions. Our study provides a useful guideline on how to monitor structural changes of MGs under fatigue conditions in service and will open a door toward commercialization of high-performance structural engineering materials.

High-Strength Collagen-Based Composite Films Regulated by Water-Soluble Recombinant Spider Silk Proteins and Water Annealing.

Spider silk has attracted extensive attention in the development of high-performance tissue engineering materials because of its excellent physical properties, biocompatibility, and biodegradability. Although high-molecular-weight recombinant spider silk proteins can be obtained through metabolic engineering of host bacteria, the solubility of the recombinant protein products is always poor. Strong denaturants and organic solvents have thus had to be exploited for their dissolution, and this seriously limits the applications of recombinant spider silk protein-based composite biomaterials. Herein, through adjusting the temperature, ionic strength, and denaturation time during the refolding process, we successfully prepared water-soluble recombinant spider major ampullate spidroin 1 (sMaSp1) with different repeat modules (24mer, 48mer, 72mer, and 96mer). Then, MaSp1 was introduced into the collagen matrix for fabricating MaSp1-collagen composite films. The introduction of spider silk proteins was demonstrated to clearly alter the internal structure of the composite films and improve the mechanical properties of the collagen-based films and turn the opaque protein films into transparency ones. More interestingly, the composite film prepared with sMaSp1 exhibited better performance in mechanical strength and cell adhesion compared to that prepared with water-insoluble MaSp1 (pMaSp1), which might be attributed to the effect of the initial dissolved state of MaSp1 on the microstructure of composite films. Additionally, the molecular weight of MaSp1 was also shown to significantly influence the mechanical strength (enhanced to 1.1- to 2.3-fold) and cell adhesion of composite films, and 72mer of sMaSp1 showed the best physical properties with good bioactivity. This study provides a method to produce recombinant spider silk protein with excellent water solubility, making it possible to utilize this protein under environmentally benign, mild conditions. This paves the way for the application of recombinant spider silk proteins in the development of diverse composite biomaterials.

High strength and plasticity in Cr-Al-C composite

The microstructure and mechanical behavior of a Cr-Al-C composite rapidly consolidated by spark plasma sintering at a relatively low temperature of 900 °C were investigated. The sintered composite showed a multi-phase microstructure consisting of Cr2AlC and Al4C3 in Cr5Al8 matrix, as confirmed by high intensity X-ray diffraction and transmission electron microscopy (TEM). The multi-phase composite showed high hardness of about 11 GPa, high compressive strength of up to 5.81 GPa and strain-to-failure of 1.76%–10.82% at room temperature. High resolution TEM revealed that the dislocation slip and kink bands within the Cr2AlC MAX phase grains contribute significantly to the plasticity, whereas, the Cr5Al8 and Al4C3 improves the strength and hardness of the overall composite. These results highlight the importance of combining ceramic phases with intermetallic matrix for designing high-performance engineering materials.