Mechanical Performance Of Materials Research Articles

Lightweight Calcium-Silicate-Hydrate Nacre with High Strength and High Toughness.

Low flexural strength and toughness have posed enduring challenges to cementitious materials. As the main hydration product of cement, calcium silicate hydrate (C-S-H) plays important roles in the mechanical performance of cementitious materials while exhibiting random microstructures with pores and defects, which hinder mechanical enhancement. Inspired by the "brick-and-mortar" microstructure of natural nacre, this paper presents a method combining freeze casting, freeze-drying, in situ polymerization, and hot pressing to fabricate C-S-H nacre with high flexural strength, high toughness, and lightweight. Poly(acrylamide-co-acrylic acid) was used to disperse C-S-H and toughen C-S-H building blocks, which function as "bricks", while poly(methyl methacrylate) was impregnated as "mortar". The flexural strength, toughness, and density of C-S-H nacre reached 124 MPa, 5173 kJ/m3, and 0.98 g/cm3, respectively. The flexural strength and toughness of the C-S-H nacre are 18 and 1230 times higher than those of cement paste, respectively, with a 60% reduction in density, outperforming existing cementitious materials and natural nacre. This research establishes the relationship between material composition, fabrication process, microstructure, and mechanical performance, facilitating the design of high-performance C-S-H-based and cement-based composites for scalable engineering applications.

Fabricating epoxy vitrimer with excellent mechanical and dynamic exchange properties via network topology design

Epoxy vitrimers are a novel type of environmentally friendly materials that possess exceptional properties, including self-healing, recyclability, and reprocessability. They offer a solution to the issue of traditional thermosetting epoxy resins, which are not recyclable. However, the incorporation of dynamic bonds typically results in a decrease in mechanical properties. Therefore, achieving a balance between the mechanical properties and dynamic exchange capability is crucial. In this work, a series of epoxy resin systems with various topological network characteristics were prepared by adjusting the proportions of bisphenol A epoxy resin (E51) and polyethylene glycol diglycidyl ether (EGDGE) epoxy resins in combination with a curing agent containing vinylogous urethane (VU) dynamic bonds. Through further study, we found that with the increase of E51 content, the cross-linking density of the network gradually increased, and the flexibility of the macromolecular chains decreased (favorable for enhancing the material's mechanical performance). Simultaneously, the free volume of the network gradually increased, and the tightness of the macromolecular chains decreased (favorable for improving the material's dynamic exchange ability). These two effects combined to make E51-40 exhibit the lowest activation energy for dynamic covalent bond exchange and the lowest topological transition temperature. Compared to E51-0, the tensile strength and glass transition temperature of E51-40 were improved by 22.23 % and 25.30 %, respectively. After remoulding experiment at 140 °C for 1h, the material exhibited a high tensile strength recovery of 91.34 %. Therefore, starting from the design of molecular structure, adjusting the network topology is an effective means to balance the mechanical and dynamic exchange properties of epoxy vitrimers. This provides experimental guidance and theoretical insights for designing high-performance epoxy vitrimer materials.

A yarn-to-fabric multiscale modeling strategy for auxetic behavior analysis of negative Poisson’s yarn-based fabric

Auxetic behavior is critical to determining the deformation and mechanical performance of materials. Auxetic mechanisms of the woven fabric have previously not been well understood, especially for those containing negative Poisson’s ratio yarn (NPRY). Most theoretical models were developed from the macro geometric structure which lacks analysis of yarn levels. This paper aims to use numeral analysis combined with finite element modeling to investigate the auxetic behavior of the NPRY-based fabric. Firstly, the theoretical model that reveals the relationship between the auxetic behaviors of yarn and NPRY-based fabric was established based on component yarn interweaving rules, deformation, and stress. Following, a strain-dominated deformation simulation was further performed to clarify the micro stress and auxetic mechanism of fabric by calculating the stress–strain response and NPR value. Moreover, the experiments of NPRY-based fabric were also developed to validate the theoretical and simulation results, Results indicate that the model can well predict the auxetic behavior of fabric with an error under 7%. The micro–macro analysis of the auxetic behavior from yarn to fabric provides a fundamental understanding of the auxetic mechanism of NPRY-based fabric. Additionally, the yarn-to-fabric model can used to study the auxetic behavior of NPR fabric with variable parameters thus supplying theoretical guidance for engineering.

Environmental impact evaluation of low-carbon concrete incorporating fly ash and limestone

This work examines the environmental impact of low-carbon concrete that incorporates supplementary cementitious materials (SCMs). After reviewing near-zero carbon SCMs and low-carbon concrete, a life cycle assessment (LCA) was undertaken for concrete mix designs with normal-to-high compressive strengths, incorporating limestone and fly ash as cement replacements. The analysis includes relevant region-specific life cycle inventory parameters for raw materials, energy production, and transportation. A comparative assessment between embodied carbon emissions and the material mechanical performance is then made. The results of this paper indicate that incorporating limestone and fly ash in concrete can reduce carbon emissions, yet at a proportional decrease in mechanical properties compared to conventional cement concrete. The combination of cement and fly ash produced, on average, a higher strength concrete by 20.5% and lower CO2-eq values by 21.1% when compared to limestone cement blends. The CO2-eq emissions associated with transportation of the main constituents for concrete production were on average below 4% of the total CO2-eq per mix. In addition to eco-mechanical quantitative assessments, the study offers insights and recommendations for the development of concrete materials considering global resource availability of near-zero carbon concrete constituents.

Effects of Mo content on the microstructure and mechanical properties of laser cladded FeCoCrNiMox (x = 0.2, 0.5) high-entropy alloy coatings

The laser cladding additive manufacturing technology and high-entropy alloys can serve as ideal techniques and materials for the surface repair of high-speed train axles. Coatings of FeCoCrNiMox (x = 0.2, 0.5) were prepared on EA4T axle steel using laser cladding technology, and their phase, structure, and mechanical properties were analyzed using X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) characterization techniques. Additionally, the mechanical properties of the coatings were tested, and first-principles calculations were used to verify and calculate the material's mechanical performance. The research findings indicate that an increase in Mo content leads to a greater degree of lattice distortion, causing a leftward shift in diffraction peak positions. Significant differences in the microstructure from the substrate to the coating surface were observed, with columnar grain structure at the bottom of the cladding layer and equiaxed dendrites dominating the coating surface. The increase in Mo content promotes the formation of σ phase while also refining the grain size. ECCI results show that both types of coatings consist of a high-density dislocation cell structure and Mo-rich particles. With an increase in Mo content, the peak hardness of the coating increased from 456.5 HV to 469.4 HV, while the impact energy decreased from 56 J to 16 J, attributed to the increase in dislocation density and the greater quantity of σ phase. First principles calculations verified that the comprehensive mechanical properties of FeCoCrNiMo0.2 are superior, providing theoretical guidance for the optimization and design of the coatings.

Construction of silver-epoxy adhesive with suppressed silver migration rate based on thiol-silver interaction

The silver migration limits the application of silver based conductive adhesives in wet environment. The existing methods for inhibiting silver migration in epoxy conductive silver adhesives involve one or more issues such as cost, complexity, and inhibition of conductivity. Moreover, there is currently a lack of strategies that can suppress the silver migration effect while ensuring good dispersion of silver fillers in the matrix and constructing a good filler matrix interface. Herein, a facile method was reported suppressing the silver migration in silver-epoxy conductive adhesive. Tetrafunctional thiopentaerythritol tetramercaptoacetate (PERTMA) was introduced into 1,4-cyclohexanedimethanol diglycidyl ether (CHDMGE) epoxy resin as the curing agent. This method utilized the strong interaction between silver and thiols, including coordination and covalent bonding, to achieve good compatibility between filler and matrix. By tightly combining silver with the resin system, the content of free silver atoms was reduced, capturing and inhibiting the hydrolysis of silver atoms and their migration with current, and the conductivity of the conductive silver adhesive was not greatly degraded due to the silver-thiol interaction. At the same time, the introducing of PERTMA was able to reduce the surface hydrophilicity of epoxy resin, which also helped suppressing the silver migration effect under humid circumstances. The interaction between silver and thiol was characterized, and the influence of silver content on the curing behavior, material mechanical performance, conductivity, resistivity on silver migration and flexibility was explored. The CHDMGE/PERTMA/Ag conductive adhesive based on strong thiol-silver interaction had excellent resistance to silver migration, which occurred after 3500s, which was 10.67 times longer than the control group. In addition, the silver filler enhanced the tensile strength of the matrix resin by this thiol-silver interaction. This study will provide new ideas for the design and development of silver migration resistant conductive adhesives based on matrix filler interaction.

Microstructure and room/high-temperature tensile properties of γ-TiAlNb intermetallic compound subjected to heat treatment

This study aims to investigate the influence of high-temperature heat treatment on the microstructure and mechanical properties of titanium aluminide niobium (γ-TiAlNb) intermetallic compounds. Systematic experiments revealed that heat treatment at 1280 °C resulted in significant changes in various aspects. Firstly, there was a notable reduction in grain size. Secondly, the content of α2-Ti3Al phase increased significantly, leading to a more complex phase distribution. Thirdly, heat treatment induced the formation of a strip structure of β-Ti phase within the grains, providing unique advantages for the material's thermal stability and mechanical performance. Then, the detailed mechanical performance tests indicated a significant improvement in the material properties of TiAlNb intermetallic compounds at both room and high temperatures following heat treatment. The ultimate tensile strength increased significantly, while the elongation also showed a substantial improvement. Finally, these results were closely associated with the evolution of the microstructure, revealing the precise control mechanism of heat treatment on material performance. Further analysis of elemental distribution demonstrated that heat treatment had a minor impact on the elemental content of TiAlNb intermetallic compounds. In conclusion, this study provides profound insights into the mechanisms underlying the improvement of TiAlNb intermetallic compound properties through heat treatment. The findings offer valuable guidance for the engineering optimization and application of such materials in the future.

Product, process, property, and performance (PPPP) relationship of 3D-Printed polymers and polymer composites: Numerical and experimental analysis

Understanding the external and internal factors during an additive manufacturing (AM) process is crucial, as they can significantly affect the final product's performance. Efforts have been made to unwind the product, process, property, and performance (PPPP) relationships. The conventional experimental approaches can lead to boundless runs, resulting in exorbitant costs for research and development. Hence, developing, adapting, and validating numerical models is essential to achieving the desired performance of 3D-printed products with lesser resource utilization. In this study, numerical and experimental techniques were used to perform the PPPP relationship assessment on material extrusion 3D-printed parts. Three infill designs (rectangular, triangular, and hexagonal), with layer heights (0.1 mm, 0.125 mm, and 0.2 mm), and three different materials (carbon fiber-reinforced polyamide-6 (PA6-CF), polyamide-6 (PA6), and acrylonitrile butadiene styrene (ABS)), were selected for the investigation. Taguchi's design of experiments (DOE) method was used to limit the number of numerical simulations and experimental runs. A thermomechanical numerical model was utilized to perform the material extrusion process simulations and mechanical performance prediction of the specimens. Subsequently, the samples were 3D-printed and tested mechanically to validate the numerical simulation results. The dimensional, distortion, and mechanical analysis performed on numerical simulation results agreed well with the experimental observations.

Effect of multistage lamellar microstructure on mechanical properties of Tc18 alloy

In this study, a three-step heat treatment approach, which included annealing, solution treatment at 740–820 °C, and aging at 450–550 °C, was employed to control the precipitation behavior of the α phase in TC18(Ti-5Al-5Mo-5 V-1Cr-1Fe) alloy. The multistage microstructure resulting was found to contain both the primary lamellar structure (α) and the secondary lamellar structure (αs), and the relationship between the spacing of multi-level lamellar microstructure and the mechanical properties of the alloy was effeciently determined. The study demonstrates that lowering the solid solution temperature reduces the interlayer spacing of the primary α phase, and increasing the aging temperature enlarges the interlayer spacing of the secondary αs phase, thereby enhancing the material's mechanical performance. Nevertheless, a substantial discrepancy in yield strength exists between these two interlayer spacings, which impacts the stress-strain coordination and reduces the plastic zone at the crack tip, and also increases the likelihood of formation of microvoids and microcracks at grain boundaries.

Tribological, mechanical, and metallurgical performance of natural fiber-reinforced composites: A comprehensive review

Composite materials have an ever-increasing demand for their application in numerous applications such as aerospace, automobile, petroleum, etc. These materials vary according to their chemical composition, properties, manufacturing techniques, etc. Natural fiber-reinforced composites are the composites where natural fibers such as plant, animal, and mineral fibers are used as reinforcement material. Reinforcement of these fibers yields composite material with extensive properties such as high strength, durability, reliability, etc. These properties lead them to commercial applications in several areas. Therefore, this paper describes various characteristics of the matrix, reinforcement, and resin used for natural fiber composite materials. Also, multiple parameters that affect the growth of these composites are investigated. The tribological behavior of natural fiber composites is focused mainly on friction, wear, and lubrication. Furthermore, the material's mechanical performance and metallurgical behavior are also given significant importance. These materials’ application in various fields is explored separately, and multiple conclusions are drawn.

Mechanical characterisation of Aerosil-polycarbonate-based ceramic nanocomposites: 3D printing versus injection moulding technology

The 3D printing of composite materials especially, nanocomposites, is an essential step in exploring new perspectives for the applications of organic matrix composite materials for industrial applications. In this work, the effect of ceramic nanofillers on the mechanical properties of a thermoplastic matrix is studied using different wt% of nanofillers (AEROSIL). The results showed that the increase in the wt% of AEROSIL resulted in an increase in the mechanical properties in terms of hardness, stiffness, ductility, and tensile strength. Moreover, these samples were 3D printed and were compared with the samples prepared by conventional injection moulding. The comparison characterized the influence of the manufacturing method on the mechanical performance of materials. Although there was very little behavior difference in both samples, the 3D-printed samples showed a weight reduction. This has broadened the possible applications of this material and technique in areas where weight is of utmost significance.

Improvement of Performance of Ultra-high Performance Concrete Based Composite Material Added with Nano Materials

UHPC is a kind of composite material characterized by ultra high strength, high toughness and high durability. It has a wide application prospect in engineering practice. But there are some defects in concrete. How to improve strength and toughness of UHPC remains to be the target of researchers. To obtain UHPC with better performance, this study introduced nano-SiO2 and nano-CaCO3 into UHPC. Moreover, hydration heat analysis, X-Ray Diffraction (XRD), mercury intrusion porosimetry and nanoindentation tests were used to explore hydration process and microstructure. Double-doped nanomaterials can further enhance various mechanical performances of materials. Nano-SiO2 can promote early progress of cement hydration due to its high reaction activity and C-S-H gel generates when it reacts with cement hydration product Ca(OH)2. Nano-CaCO3 mainly plays the role of crystal nucleus effect and filling effect. Under the combined action of the two, the composite structure is more dense, which provides a way to improve the performance of UHPC in practical engineering.

Mechanical properties and micro-mechanism of cement-based materials strengthened by in-situ organic-inorganic polymerization

Ordinary cement-based materials face defects in practical applications, such as poor tensile strength, brittleness, and high cracking risk. Compound modification has great potential to improve cement-based material structural and mechanical performance. In this paper, cement-based materials with a three-dimensional (3D) plug-in network structure are formed by in-situ organic-inorganic polymerization. Partial acrylamide (AM) monomer is inserted into the zirconium phosphate (ZrP) interlayer, and zirconium phosphate-acrylamide (ZrP-AM) composite materials are successfully prepared. During cement hydration, AM undergoes in-situ self-polymerization and co-polymerization with ZrP-AM, forming a complete plug-in network with ZrP distributed on the polymer network. Meanwhile, the plug-in network structure is closely bound to the cement matrix due to the formation of chemical bonds. In the best mix ratio design, the ZrP-PAM-modified sample with 1 wt% ZrP and 3 wt% AM has a 105% higher flexural strength than the cement paste. Moreover, due to the enhancing effect of ZrP on the cement matrix and polymer network, the flexural and compressive strengths of the modified sample increased by 28.5% and 17%, respectively, compared to the single AM modified sample with respect to the same dosage. The formation of the plug-in network structure and chemical bonds greatly enhances the mechanical strength of cement-based materials. This synergistic modification method fully exploits the modifying effects of polymers and nanomaterials and provides a novel strategy to improve the mechanical properties of cement-based materials.

3D-printed metals: Process parameters effects on mechanical properties of 17-4 P H stainless steel

Additive Manufacturing (AM) has spread significantly in recent years, with relevant applications in many fields of research and engineering. Thanks to its distinctive production methods, AM enables the creation of parts with complex shapes that cannot be fabricated easily by employing traditional subtractive processes. 3D printing, which involves overlapping material layer by layer until the designed part is completed, shows several advantages in terms of limiting material waste, reducing production phases and postprocessing/heat treatments needs, leading to an additional benefit in terms of environmental sustainability. However, there are still limited available data on the influence of the 3D printing process on the mechanical properties of the materials that are commonly used and additional investigations are strongly demanded. So, the purpose of the present paper is to provide a useful contribution in the field of metal additive manufacturing, reporting the results of an experimental campaign carried out on 17-4 P H stainless steel, produced using selective laser melting technology. The effects of different printing orientations and scanning times on the tensile behaviour, impact strength and microhardness features of the 3D-printed products are investigated. Furthermore, the influence of an annealing heat treatment on the material mechanical performance is evaluated.

Mechanical Characterisation and Simulation of the Tensile Behaviour of Polymeric Additively Manufactured Lattice Structures

BackgroundThe mechanical properties of lattice structures have been primarily investigated using uniaxial compression loads. Particularly for polymers, tensile properties are rarely considered because of the difficulties of defining a suitable specimen design in which the fracture occurs within the gauge length.ObjectiveThis work proposes a novel formulation to obtain a specimen for the tensile test with a gradation of the lattice density at the interface with the bulk portion, which realises a uniform stress distribution. The aim is to combine a localisation of the fracture in the gauge length with a specimen geometry accomplishing the EN ISO 527 standard and analyse the correlation between the mechanical performance and the defects induced by the process on such thin structures.MethodsThe formulation is experimentally and numerically (FEM) tested by designed specimens with different cell topology, cell size, strut diameter, and number of cells in the sample thickness. Also, results from uniaxial compression tests are used to validate the tensile properties. The specimens are manufactured in different orientations in the building volume by laser powder bed fusion with Polyamide 12. The effects of the pores morphology, distribution, and inherent anisotropy are investigated using X-ray computed tomography analysis. This data is also used to tune a numerical model.ResultsThe numerical analysis showed a uniform stress distribution; experimentally, the fracture is localised inside the gauge length in respect of the ISO standard. Remarkably, among the different strut-based architectures, the elongation at break is, in the best case, 50% of the corresponding bulk material, while the tensile strengths are comparable. Vertical printed specimens exhibited a slight decrease in tensile strength, and the elongation at break was lower than 50% compared to the counterparts built along the horizontal orientation. Modifying the numerical model according to process-related dimensional deviations between the actual and the nominal structures significantly improved the numerical results. The remaining deviation highlighted the incorrectness of modelling the lattice material from the bulk properties.ConclusionDensity gradation is a reliable approach for describing the tensile behaviour of polymeric lattice structures. However, the lower amount of porosity and the different shape in the lattice led to a different material mechanical performance with respect to the corresponding bulk counterpart. Therefore, for polymeric lattice structures, the relationship between process-design-material appears crucial for correctly representing the structure behaviour.

Response of mechanical properties and subsurface damage in β-SiC to temperature and crystal plane during nanoindentation simulation

A series of theoretical calculations based on molecular dynamics (MD) was carried out to investigate the ceramic material mechanical response of β-SiC. Importantly, the effect of temperature and crystal plane on material mechanical performance, correlative mechanisms of subsurface damage behavior, and otherness in the subsurface layer as well as explored and analyzed at nanoindentation process. MD calculation results show that the ambient temperature rises can promote SiC material dislocation generation, nucleation, and propagation, which leads to the degree of damage in the subsurface layer increases and material brittle failure occurs because of the concentration of internal stress in ceramic material. Moreover, it was discovered that dislocation ring was a microscopic phenomenon of the transformation from elastic deformation to plastic deformation of SiC, and the dislocation ring nucleus, dislocation ring growth, dislocation ring propagation, dislocation ring brittle fracture are the main plastic deformation characteristics of SiC during nanoindentation simulation. In addition, with the increase of temperature, the damage degree of subsurface layer is intensified. The direct driving force could induce partial phase transformation occurs for β-SiC material from cubic sphalerite structure to the hexagonal wurtzite structure. Moreover, the majority of amorphous atoms generated at low temperatures would decrease with increasing temperature. The results of this work can be to enrich understand the details information on dynamic microstructure evolution process, and the corresponding subsurface damage behavior at the atomic scale when materials are subjected to external working loads and extreme temperature.

Material characterization and mechanical performance of laser diffusion welded joint between titanium alloy and stainless steel

The new laser diffusion welding method with Monel 400 interlayer was applied to control the Ti-Fe IMCs generated in the welding of titanium (Ti) alloy and stainless steel (SS). The joints produced by the new method have two welding mechanisms: fusion welding and diffusion welding. Fusion welding was used to connect high compatibility SS and Monel 400 interlayer, diffusion welding was used to connect Monel 400 interlayer and Ti alloy which would produce Ti-based IMCs. The effect of new laser welding technology on the microstructure and mechanical properties of SS-Ti alloy butt joint was studied. The joint fractured at Monel 400-Ti alloy interface with a maximum tensile strength of 216 MPa.

Molecular evolution mechanism of flow-induced crystallization in polyphenylene sulfide

Microstructures play a significant role on the mechanical performance of materials. Based on the experimental characterization and molecular modeling techniques, this work assessed the influences on the mechanical properties of semi-crystalline 1-4 polyphenylene sulfide (PPS) from pressure and temperature. It was found that the shear deformation in the flow field is a key factor that induces the transformation from amorphous polymers to precursors. Though, pressure can accelerate the transition of precursors to crystals, proportion of precursors in the PPS is not observed under higher pressure. The understanding established in this work is helpful to identify optimal processing parameters during the manufacturing of PPS for target applications.

Effects of repair techniques and scarf angles on mechanical performance of composite materials

Today, composite materials, which have the advantage of strength and lightness ratio, have gained great importance especially in the aeronautical industry and automotive sector. With widespread use of composites, the repair of damages caused by external factors has also become an important research topic. In this study, the effects of different repair methods and scarf angles on the mechanical performance of the material were investigated. Scarf angles of 20°, 30°, and 45° have been selected in order not to create too many scarf areas and to find a quick repair method. Also, a comparison of single scarf and double scarf repair was made to find a more robust solution. The samples were produced from carbon fiber prepreg and with the [45/0/90/0/45]2s fiber orientation. Tensile, compression, and flexural (3-point bending) tests according to ASTM standards were applied to composite samples prepared with single scarf and double scarf repair configurations at different angles. The stress–strain curves obtained as a result of the tests showed that the specimens repaired at 20° had the highest strength. In addition, it has been determined that the samples repaired with double scarf withstand higher forces compared to the samples repaired with single scarf at the same angle.

Improving the DC Dielectric Properties of XLPE with Appropriate Content of Dicumyl Peroxide for HVDC Cables Insulation

In this research, crosslinked polyethylene (XLPE) is developed with selective content of dicumyl peroxide (DCP), and the influence of microstructural properties and chemical composition on the mechanical and direct current (DC) dielectric properties are investigated. The measurements for the microstructural analysis are taken by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), gel content test and Fourier transform infrared (FTIR). The mechanical properties of XLPE are evaluated by hot-set test. The results of microstructural and chemical composition show that the increase in DCP content increases the crosslinking degree from 74.3% to 81.6%, reduces the crystallinity/lamella thickness from 36.8% to 35.5%/7.6–7.1 nm, reduces the average molecular weight between two crosslinks by 0.01 kg/mol and reduces the oxidation level/carbonyl index. The increase in DCP in XLPE samples decreases the permanent elongation from 2.2% to 0% and elongation rate from 300% to 80% of the cable insulation. The rise in DCP content increases the crosslinking degree due to which the DC resistivity and activation energy is increased. The DC breakdown strength at 30–90 °C is increased due to the increase in crosslinking degree and reduction in carbonyl index/oxidation level. The space charge accumulation is measured at 30 °C under 20–60 kV/mm, resulting in less homo-charges and hetero-charges with the increase in DCP. It is proven that the role of appropriate DCP content is vital in increasing the DC dielectric performance, internal material characteristics and mechanical performance of XLPE.