Low Mechanical Performance Research Articles

Enhanced transverse strength of 3D printed acrylonitrile butadiene styrene parts by carbon fiber/epoxy pin insertion

Thermoplastic parts fabricated by material extrusion (MEX) 3D printing usually possess weak inter-layer bonding, leading to low mechanical performance in the Z-direction. Here, we develop a simple but effective post-treatment method to improve the Z-strength of MEX-printed acrylonitrile butadiene styrene (ABS) parts. In this method, commercial carbon fiber (CF) tows and epoxy were embedded into internal channels in MEX-printed structures to form high-strength CF/epoxy pins. Due to the mechanical interlock between the CF/epoxy pins and the printed ABS, the Z-strength of the printed parts improved significantly. Specifically, the Z-pinned ABS samples exhibit a strength of up to 71.74 MPa and a Young’s modulus of up to 5.93 GPa in the transverse direction, which were 335 % and 266 % higher than those of the printed neat counterparts, respectively. We find that the mechanical performance of the Z-pinned samples follows a simple rule of mixtures which is able to capture the Z-dependent mechanical strength and Young’s modulus. Also, curved CF/epoxy pins were successfully formed within printed thin-walled curved structures, offering the capability to strengthen MEX printed structures with complex shapes. This work demonstrates that the Z-pin embedding process can be an effective approach to improve the transverse strength of the MEX printed parts for load-bearing structural applications.

An adhesive cellulose nanocrystal-reinforced nanocomposite hydrogel electrolyte for supercapacitor applications

Hydrogel electrolytes were applied in various energy storage devices, including supercapacitors. However, they still suffer from disadvantages such as low mechanical performance and poor adhesion of the interfaces between electrolytes and electrodes. Herein, an adhesive hydrogel electrolyte with promising mechanical strength and electrochemical performance was designed by introducing hydrophobic carbon chains as long-range physical cross-linkers and cellulose nanocrystal (CNC) as biopolymer nano-reinforcement, and soak-loading liquid electrolytes such as KOH into the hydrogel matrix. The hydrogel electrolyte loaded with 1 M KOH demonstrated the best tensile stress of 362.31 kPa and an elongation of 2479 %, and exhibited self-repairability by applying stimuli on the cut interface. The hydrogel electrolyte showed excellent adhesion on various surfaces, including nonconductive and conductive materials such as cardboard, leather, carbon film, and carbon cloth. Regarding electrochemical properties, the hydrogel electrolyte showed the largest conductivity of 0.207 ± 0.005 S/cm when soak-loading in 1 M KOH for 24 h. Moreover, the hydrogel electrolyte exhibited promising electrochemical performance when assembled into coin-cell supercapacitors using free-standing activated carbon sheets as electrodes. A capacitance of 67.31 F/g at 0.05 A/g, and almost 100 % capacitance retention at 0.1 A/g after 2200 cycles was achieved.

Design of a large format printing platform that allows the extrusion of composite materials based on pellets and continuous fibers.

Commonly additive manufacturing (AM) through the technique of extrusion of molten material is used to manufacture prototypes. This is mainly because the materials commonly used in these technologies are thermoplastics of low mechanical performance. That is why this project seeks the development of an extrusion head that uses polymeric matrix composite materials in the form of pellets and reinforcements of natural or synthetic continuous fibers in order to be used in a large format MA system, which allows the manufacture of objects with better functional and mechanical performance than those found conventionally. For this purpose, different stages were carried out for the development of the project, starting with the design and construction of the printing platform; followed by the design of an extrusion head that allows the integration of a polymeric matrix and continuous fibers. As a result, printed traces were obtained using PLA pellets and glass fiber, resulting in a total coating of the fiber on the printed material.

Robot-assisted laser additive manufacturing for high-strength/low-porosity continuous fiber-reinforced thermoplastic composites

Additive manufacturing (AM) of continuous fiber-reinforced thermoplastic composites (CFRTPCs) has become a hot area for both academia and industry. In this paper, a robot-assisted laser additive manufacturing (RLAM) technique is proposed, which involves utilizing a laser beam to heat the filament to a semi-molten state, followed by compacting it with a roller and bonding it layer by layer to create densely structured components. Firstly, an integrated framework of hardware, software, and control systems is presented. Then, the relationship between the processing parameters and the properties of the final specimens was examined. Finally, a process strategy was proposed to improve the forming accuracy. Due to the effective impregnation of continuous carbon fibers, the printed CFRTPCs using the LRAM process exhibit comparatively low porosity and superior mechanical performance. Specifically, the flexural strength, flexural modulus, and interlayer shear strength reached 584 MPa, 43.7 GPa, and 28.0 MPa, respectively. The prepared specimens boast a porosity of 0.19%, approaching levels achieved through autoclave processes. In addition, it was found that the dynamic offset of the yaw axis could be utilized to correct the deviation of the actual forming path due to the pultrusion force, thus making the position of the towpreg under the rollers controllable and improving the accuracy of the parts. This new method combines the advantages of industrial robotics and laser&roller-based continuous fiber additive manufacturing processes to enable high-performance additively manufactured large and complex CFRTPCs, which shows great potential for printing lightweight structures in the rail transit and aerospace industries.

Correlation of Energy Density and Manufacturing Variables of AA6061 through Laser Powder Bed Fusion and Its Effect on the Densification Mechanism

Aluminum alloy processing via additive manufacturing (AM) technologies has increased in usage during the last decade. AM now enables manufacturing complex geometries not previously achieved through traditional manufacturing. Aluminum is usually processed using laser powder bed fusion (LPBF) technologies, which are used to manufacture metallic components of high geometrical complexity and dimensional accuracy and good mechanical, electrical, and chemical properties, which is why this technology is quite popular at industrial levels. To further develop quality control systems and new aluminum alloys using LPBF, there is a need to establish a predictive relationship between the parameters of the material. A study was carried out to investigate the relationship between energy density and process parameters such as laser power, scan speed, hatch spacing, scan pattern, and laser focus and its influence on the densification mechanism in additively manufactured components with aluminum alloys. AA6061 was selected due to its wide usage in different industries, given its low density and high mechanical performance. Relative density was analyzed using the Archimedes principle, and the quality and morphology of the AA6061 powder were analyzed through metallographic analysis. The process parameter selection was performed according to the best results obtained according to the laser power and energy density factors. The best manufactured samples had an energy density between 30 and 40 J/mm3, with relative densities above 99%.

Performance of delaminated CFRP composite under pure bending using two-dimensional digital image correlation

ABSTRACT Delamination is an interlaminar damage which may be pre-existing in multilayered fibre reinforced polymer composite parts due to manufacturing imperfections or generated by out of plane loading during service life. Its existence leads to significant reduction of structural integrity, strength and stiffness of the material. Hence, to study the effect of induced delamination on the performance of a composite under pure bending, a circular polytetrafluoroethylene (PTFE) film was introduced between the second and third plies of a sixteen layered carbon/epoxy laminate during fabrication. The bending tests were conducted in displacement control mode. The displacements and strains were measured through the thickness of the composite using two-dimensional digital image correlation. The damage modes were captured using CCD camera and the causes were explained. The flexural strength and modulus of composite were 329.74 MPa and 104.58 GPa respectively. The delaminated composite behaved as a single member without any crack within the elastic range. The existence of PTFE drastically reduced flexural stiffness of composite beyond the stress at 75.81% of its ultimate strength. The ± 45º plies offered low mechanical performance against the induced off axis loading. Hence, in these plies fibre breakage was higher. In the portion of PTFE, the strains were higher due to larger outward displacements produced by local buckling.

Low strain rate mechanical performance of balsa wood and carbon fibre-epoxy-balsa sandwich structures

The focus of this study is the experimental assessment of the mechanical behaviour of balsa wood and its sandwich structures, where balsa serves as the core, supported by carbon fibre-epoxy skin layers. A comprehensive characterisation is conducted on the mechanical behaviour of balsa wood and carbon fibre-epoxy balsa core sandwich structures subjected to a range of low strain rates. Initially, the study undertakes a consistent procedure for sample preparation. Subsequently, the characterisation of the manufactured composite structures is performed experimentally. A stereo microscope is employed for a detailed visual inspection of the internal structure of the balsa wood and the sandwich structures. Furthermore, the mechanical characterisation is carried out with three-point bending tests at a range of strain rates from 0.1 % to 6 % strain per minute. This research reveals key findings about balsa wood and its sandwich structures, highlighting their performance and their sensitivity even under low strain rates.

Further investigation on fatty acids-based methacrylate monomers: High temperature radical polymerization for obtaining copolymers and their blends with medium-oil alkyd resin for coatings

Fatty acids-based methacrylate monomers have been studied as alternative renewable raw materials for the synthesis of poly(acrylate)s. In this research work, several poly(acrylate)s based on lauric, oleic, linoleic and tall oil fatty acids were obtained by high temperature solution polymerization since it is a process extensively used at industrial scale. The effect of the presence and increase of the aforementioned fatty acids-based methacrylate monomers on the conversion as a function of polymerization time and actual monomer composition in the copolymer were studied, thus inferring that the fatty acid chain length is of paramount importance for the final macromolecular features. The resulting poly(acrylate)s were evaluated as individual and blended with a medium-oil alkyd resin with the aim of balancing the advantages of both, such as low drying, mechanical performance, and chemical resistance, in order to indirectly produce economically viable resins for the industrial coating market.

Mechanical properties and microstructure revolution of vibration assisted wire arc additive manufacturing 2319 aluminum alloy

In this study, a hybrid wire arc additive manufacturing (HWAAM) process that combines low-frequency vibration with cold metal transfer (CMT) arc is proposed to address the problems of porosity, coarse grains, and low mechanical performance encountered in WAAM aluminum alloys. The effects of different vibration frequencies on the microstructure and mechanical properties were investigated. The results indicated that as the vibration frequency increases, the grain size refinement reaches a maximum of 19.1% compared with the non-vibrated specimen. Vibration can enhance the fluidity and the cooling rate of the weld pool. The fatigue fracture of dendrite arms is the main mechanism of microstructure grain refinement caused by vibration. The dynamic bending stress induced by vibration on the dendrite arms and the root remelting phenomenon are the dominant factors for the dendrite fragmentation. Increasing the vibration frequency did not result in an obvious improvement in the tensile strength of the specimens, but did significantly increase the elongation. With the increase in vibration frequency, the maximum transverse and longitudinal elongation reached 22.2% and 23.5% respectively, a raise of 15.6% and 38.2% compared with non-vibrated specimen. Vibration reduced the size and distribution density of pores on the fracture surface, and increased the dimpled microstructure, improving the mechanical performance of the aluminum alloy.

Low defect and high mechanical properties POSS copolymerization phthalonitrile resin prepared by powder hot isostatic pressing

The high melting point of high-temperature resistant phthalonitrile resin is often prone to defects in traditional hot melt manufacturing. And its high cross-linking density leads to poor toughness of the resin. In this work, we report for the first time a novel densifying processing, powder hot isostatic pressing (PHIP), for phthalonitrile resin with low defect and high mechanical performance. The bending strength and impact strength of the pure phthalonitrile resin (PBAPN) by PHIP reached to 108.5 MPa and 9.1 kJ·m−2, respectively, increasing by 186.3% and 405.6% than PBAPN by hot melt method. The epoxycyclohexyl polyhedral oligomeric silsesquioxane (EP-POSS) with excellent heat resistance was used to achieve synchronous improvement of thermal and mechanical properties of phthalonitrile resin. The bending strength and impact strength of the phthalonitrile resin containing 1 wt% POSS (PBAPNPOSS-1) further increased to 120.1 MPa and 13.0 kJ·m−2. In addition, the glass transition temperature of PBAPNPOSS-5 increased by 40 °C compared with PBAPN.

Life cycle assessment applied to a self-healing elastomer filled with ground tire rubber

In this study, we present the first life cycle assessment (LCA) of a self-healing styrene-butadiene rubber (SBR) used in the production of marine fenders. Results show that a rubber with healing capabilities is not environmentally attractive if it cannot last for the same lifetime as a conventional product due to its lower mechanical performance and higher energy consumption. To overcome these constraints, we added a sustainable filler, ground tire rubber, which improved the mechanical properties of the self-healing SBR (x6 increase in tensile strength). Although this addition involved additional sub-processes, the additional environmental impacts were outweighed by the benefits achieved through improved material performance (28% decrease in global warming potential - GWP and 26% in primary energy demand - PED). This study used primary data on experimental healing efficiencies and healing cycles rather than conservative assumptions, which provides a more representative and trustworthy LCA of self-healing rubbers. Our findings have significant implications for the rubber industry, as self-healing rubbers offer a promising avenue for reducing the environmental impact of synthetic materials.

Short Jute Fiber Preform Reinforced Polypropylene Thermoplastic Composite: Experimental Investigation and Its Theoretical Stiffness Prediction.

Natural-based lignocellulose fibrous materials can be used as a sustainable alternative to conventional fossil-based fibers such as glass fibers, in lightweight fiber-reinforced thermoplastic composites for marine, automotive, aerospace, or other advanced applications. However, one of the main challenges in using natural fiber-based thermoplastic composites is the low mechanical performance of composite structures. This can be improved significantly through the development of an optimized novel fiber architecture with enhanced fiber packing properties, following a low-cost production process. In this context, this study demonstrates a less energy-consuming and cheaper manufacturing process, for developing highly individualized short jute fiber-based dry fiber preform architecture, with an improved fiber packing property. Short jute fibers were chemically treated with alkali and PVA sizing treatments in the processing of new fiber preform architectures, and they were used in manufacturing of ultimate short jute fiber/polypropylene (PP) thermoplastic composites. The newly developed short fiber thermoplastic composites showed a significant improvement in mechanical properties (tensile, flexural, and impact) compared to any other natural fiber architecture-based (woven, knitted, nonwoven, unidirectional, etc.) composites found in the literature. Due to the use of new fiber architecture, the developed composites' fiber content was observed to increase. In addition, the compatibility of jute fibers with the polypropylene matrix was strengthened with the application of chemical treatments on highly individualized jute fibers. These reasons were responsible for the enhancement of mechanical properties of developed composites. Micromechanics of the fibers in composites were evaluated using the modified rule of the mixture and Halpin-Tsai equations for stiffness prediction of the composites in order to develop a theoretical understanding of newly developed composites' mechanics. It is thought that the improved mechanical performance of short jute fiber/PP thermoplastic composites can extend the use of these composites in many load-demanding applications, wherein normally synthetic fiber composites are used.

Ultrastretchable, repairable and highly sensitive xanthan collagen nanosilver hydrogel for wide temperature flexible sensing

Conductive hydrogels, lauded for their electrical conductivity, precise information capture, biocompatibility, and extensibility, have gained prominence as ideal candidate materials for flexible wearable sensor applications. Nevertheless, these sensors must surmount numerous challenges such as environmental temperature variations, bacterial growth in high-humidity environments, low signal detection sensitivity, irreversible damage, and mechanical performance stability during use. In response to these challenges, we present a hydrophobic supramolecular and dynamic coordination double-network hydrogel, prepared through a solvent-exchange method, with an accelerated gelation rate. The coordination of dynamic hydrogen bonds and coordination bonds within the hydrophobic supramolecular network imbues the hydrogel with superior mechanical properties (elongation at break around 4900%, tensile strength approximately 506 kPa) and improved self-healing capabilities. This solvent-exchange-mediated hydrogel exhibits broad temperature resilience (−20–60 °C) and reliable repeatability. Additionally, the sensor enables wireless human signal monitoring with a rapid response time (75 ms) and heightened sensitivity (gauge factor = 22.34). The wearable sensor’s antibacterial efficacy effectively suppresses bacterial propagation in high-moisture hydrogels, with a bacterial inhibition rate of 99.9%. The findings from our series of studies reveal the successful fabrication of stable, flexible wearable sensors with self-healing, antibacterial, high sensitivity, and broad temperature tolerance characteristics, showcasing the immense potential for applications in wearable electronics, wireless monitoring, and human–machine interactions.

Hollow glass microspheres/phenolic syntactic foams with excellent mechanical and thermal insulate performance.

Syntactic foams with low density as well as low thermal conduction and proper mechanical performance are vitally important for aerospace, marine, and automotive industries. Here, phenolic-based syntactic foams were fabricated by combining the hollow glass microsphere (GMs) with phenolic resin of in situ synthesis. Benefited from the stirring and hot-pressing treatment, microspheres dispersed homogeneously in the resin matrix and it greatly reduced the density of the composites. Stretching and compression tests were performed to investigate the mechanical behavior of the foams. It is found that both the compressive and tensile strength decreased as the filler loadings increasing. While the elasticity modulus was improved. On the other hand, thermal properties tests revealed superior thermal stability and thermal insulate performance of the composites. The final residue content of the synthetic foam with 40wt% filler was improved by ∼31.5% than that of the neat one at 700°C. And samples with 20wt% microspheres reached a minimum thermal conductivity value of approximately 0.129W (m·K)-1 which is ∼46.7% lower than that of neat resin [0.298W (m·K)-1]. This work provides a feasible strategy to construct syntactic foams with low density and ideal thermal properties.

Construction of High-Strength Flame-Retardant Li-SPEEK-Modified PEG Gel Polymer Electrolytes for Lithium Batteries

The low mechanical performance and high flammability of gel polymer electrolytes limit their application. Here, we prepare a high-strength and nonflammable polymer Li-SPEEK (lithium sulfonated polyetheretherketone) to modify PEG (polyethylene glycol) and construct a PEG-Li-SPEEK cross-linked network as a polymer electrolyte matrix, with an overall improvement in electrochemical performance, mechanical properties, and flame retardancy. The PEG-Li-SPEEK-ls (PEG-Li-SPEEK cross-linked network after gelation of the liquid electrolyte) electrolyte achieves a conductivity of 1.62 × 10–4 S·cm–1 at 30 °C, a wider electrochemical window of 4.5 V vs Li+/Li, and a higher lithium-ion transference number compared to the PEG-ls electrolyte. The excellent mechanical properties allow the symmetric cell-containing PEG-Li-SPEEK-ls electrolyte to exhibit better cycling performance for over 300 h at a current density of 0.2 mA·cm–2. The LFP/PEG-Li-SPEEK-ls/Li cells deliver a maximum discharge capacity of 142.1 mAh·g–1 with a capacity retention of 98.1% after 50 cycles at 0.5 C and the Coulombic efficiency remains above 99.5% throughout the cycling process. In addition, the good carbon formation properties of Li-SPEEK give the electrolyte matrix satisfactory flame-retardant properties. Thus, we validate the excellent performance of Li-SPEEK for modifying conventional polymer electrolytes and improving their mechanical, electrochemical, and flame-retardant properties.

Study on Fibre Reinforced Composites Developed by using Recycled Fibres from Garment Cut Waste

Garment cut wastes from apparel industries are used for various applications in various industries. Normally garment cut wastes and recycled fibres from garment cut wastes are used in textile, furniture, carpet, paper, automobile, construction, and agricultural industries in low mechanical performance applications. In this research, composites are developed by using recycled fibres obtained from garment cut wastes as reinforcement and with different types of matrices. Recycled fibres used as reinforcements are obtained from garment cut wastes of cotton, polyester and cotton/polyester fabrics to develop these composites. These composites are developed by using Epoxy resin, Kaolinite, Polypropylene sheet as matrices. Reinforcements and matrices have used in different compositions and combinations to develop these composites. The main advantages of this type of composites are to combine the different properties of different materials to obtain unique and high-performance material. Technical properties like thickness, mass per unit area, Tensile strength, Flexural strength, Impact strength, Water absorbency and Scanning Electron Microscope of developed composites were tested and analyzed. The outcome of the results demonstrates that many of the composite proportions with different blend, reinforcement and matrcies show superior mechanical performances when compare it with each other, and it can be recommended for many potential applications.

High-performance, low-cost, chemical-free, and reusable bamboo drinking straw: An all-natural substitute for plastic straws

The environmental problems caused by disposable plastic straws have been widely concerned around the world. Developing degradable straws made of eco-friendly materials is an effective solution. Nevertheless, the popular alternatives, for example, polylactic acid (PLA) straw and paper straw are far from satisfactory because of the restrictive degradation conditions, low mechanical performance, poor water stability, and the use of chemicals. As an abundant and sustainable natural resource, bamboo has been widely used in many fields. This study developed a mechanized and industrialized process with high efficiency and automation, including the preparation of bamboo sticks, hydrothermal treatment, and drilling holes in sticks to produce bamboo drinking straws. The production avoided chemicals and bamboo drinking straws retained the natural structure and degradability of bamboo. The performance evaluation shows that bamboo straws had superior mechanical properties (highest compressive strength of 71.65 MPa, bending strength of 123.90 MPa, and ring stiffness of 0.61 MPa), good wetting stability (high appearance quality and wet strength), reusability, high recovery value, and low manufacturing cost (around 17.5–35% of commercial degradable drinking straw costs). Bamboo drinking straws enrich the types of degradable straws and contribute to reducing plastic pollution.

Robust cement composite with low hydration temperature and high mechanical performance achieved by Field's metal and acrylic acid-acrylamide copolymer

Concrete as an artificial stone owns the weakness of high brittleness and poor flexural strength, dramatically restricting its potential. Therefore, it is crucial to reduce the brittleness and increase the flexural strength of concrete to prolong its service life. Herein, we developed a cement composite with low hydration temperature and high mechanical strength (especially in flexural strength) by combining Field’s metal with in situ polymerization of acrylic acid (AA) and acrylamide (AM). A cement composite with compressive and flexural strength increased by 8.2% and 174.2% was achieved by tuning the dosage of Field's metal and AA-AM copolymer. The hydration temperature was significantly reduced with the assistance of Field’s metal and AA-AM copolymer, inhibiting the formation of the thermal crack. In situ polymerization of AA and AM monomers was responsible for improving the intrinsic toughness of cement hydrates by constructing a polymer-cement network, significantly enhancing flexural strength. The in situ polymerized AA-AM copolymer acted as a bridge between Field’s metal and the cement matrix, improving their interface and contributing to the increased mechanical strength. The filling effect of Field’s metal and AA-AM copolymer refined the pore structure of the composite as well. Overall, our findings may offer a promising strategy for developing more robust, resilient, and sustainable cementitious materials.

In Situ Synthesis of Environmentally Friendly Waterborne Polyurethane Extended with Regenerated Cellulose Nanoparticles for Enhanced Mechanical Performances.

The development of waterborne polyurethane (WPU) has been stimulated as an alternative to solvent-based polyurethanes due to low-VOC alternatives and reduced exposure to solvents. However, their relatively low mechanical performance and degradation have presented challenges in their wide application. Here, we developed environmentally-friendly bio polyol-based WPU nanocomposite dispersions and films, and presented the optimal process conditions for their manufacture. Additionally, the condition was established without using harmful catalysts or ethyl methyl ketone (MEK) during the polymerization. Moreover, regenerated cellulose nanoparticles (RCNs) were employed as natural chain-extenders in order to improve the biodegradability and mechanical performances of the nanocomposite films. The RCNs have a lower crystallinity compared to cellulose nanocrystals (CNCs), allowing them to possess high toughness without interfering with the elastomeric properties of polyurethane. The prepared CWPU/RCNs nanocomposite films exhibited high toughness of 58.8 ± 3 kgf∙mm and elongation at break of 240 ± 20%. In addition, depending on the molar ratio of NCO/OH, the polyurethane particle size is variously controlled from 70 to 230 nm, enabling to fabricate their dispersions with various transmittances. We believe that our findings not only open a meaningful path toward green elastomers with biodegradability but provides the design concept for bio-elastomers in order to develop industrial elastomers with mechanical and thermal properties.

Mechanical Properties and Durability of Sustainable Concrete Manufactured Using Ceramic Waste: A Review

Green and sustainable concrete has attracted significant attention from the construction industry and researchers since it was proposed. The ceramic waste materials are often directly buried in the ground or placed in an open dump, and the accumulation of ceramic waste contributes to environmental pollution, which makes the recycling of ceramic waste quite urgent. Owing to the pozzolanic activity, excellent mechanical properties and durability, industrial ceramic waste is considered as a suitable substitute for cement or natural aggregates to fabricate renewable concrete. In this paper, the pozzolanic activity of ceramic waste and the workability, mechanical performance, and durability of ceramic concrete are discussed. In addition, the most recent research results pertaining to ceramic concrete are reviewed. Ground ceramic powder improves the workability, compressive strength, resistance to chloride penetration, and carbonation resistance of concrete to a certain extent. Concrete containing ceramic as the aggregate has a lower mechanical performance than ordinary concrete. However, the resistance to chloride penetration, freeze-thaw resistance, and high-temperature resistance of ceramic concrete are remarkable. Ceramic concrete is environmentally friendly, requires fewer energy resources to manufacture than ordinary concrete, and has excellent engineering properties. However, further research is required for future engineering applications.