Increase In Toughness Research Articles

Full bio-based flame retardant towards multifunctional polylactic acid: Crystallization, flame retardant, antibacterial and enhanced mechanical properties

The preparation of flame-retardant high-performance polylactic acid (PLA) composites by adding green flame retardants have always been a challenge. In this work, an intumescent flame-retardant PCR based on phytic acid, chitosan, and resveratrol was successfully designed. Adding 4 wt% of PCR, the PLA-PCR composite was classified as UL-94 V-0 grade, with a LOI value increasing from 19.7 % (pure PLA) to 26.0 %, a peak heat release rate decreasing from 433 to 344 kW/m2. Owing to excellent compatibility of PCR, the mechanical strength and toughness of PLA-PCR composites have been improved, as reflected by a ~ 16 % increase in tensile strength, a ~ 73 % increase in impact strength and a ~ 57 % increase in toughness. In addition, PCR also presented plasticization effect on PLA, making it easier to process. This work provided a highly efficient and environmental-friendly modification approach for the development of multifunctional polymers.

Constructing a multifunctional reactive MXene-based additive for micro-crosslinking polyurea elastomer to achieve superior mechanical properties and enhanced fire safety

The widespread application of polyurea (PUA) in protective coatings typically requires excellent flame retardancy due to real-world usage scenarios. However, the addition of flame retardant additives often compromises the material’s mechanical properties. In this study, a multifunctional reactive additive, MX-SP-NH2, was creatively prepared by covalently grafting spirocyclic pentaerythritol bisphosphorate disphosphoryl chloride (SPDPC) onto MXene (Ti3C2Tx) surfaces, followed by the introduction of 1,3-propanediamine (PDA) by the reaction with SPDPC. MX-SP-NH2 was then incorporated into PUA, participating in its crosslinking process and significantly enhancing both its mechanical strength and flame retardancy. Compared to the control PUA sample, the micro-crosslinked PUA sample with just 1.0 wt% MX-SP-NH2 demonstrated a 184.3% increase in tensile strength, a 126.1% increase in elongation at break, and a 436.3% increase in toughness. The flammability characterization revealed that the peak heat release rate, peak smoke production rate, and peak CO production rate were reduced by 31.7%, 28.9%, and 61.5%, respectively, indicating a substantial improvement in fire safety. Additionally, the flame retardant PUA-based flexible strain sensors demonstrated stable electrical signal responsiveness. This work has opened up new potential applications of PUA in flexible electronics.

End anchorage‐reinforcement CFRP systems for heat‐damaged beams with side NSM CFRP rope

AbstractThe efficiency of retrofitting systems with side near surface mounted (SNSM) CFRP ropes in boosting the flexural performance of intact/heat‐damaged reinforced concrete (RC) beams was investigated using a total of 14 RC beams (250 × 150 × 1450 mm) in two groups. In the first group, the beams were strengthened using SNSM CFRP ropes of a parabolic profile without and with end fan or hock anchorages, coupled with the implantation of lateral and/or vertical CFRP dowels in the high‐shear zone. The beams of the second group were repaired using similar configurations after being heated to 400°C in an electrical furnace for 2 h. A control beam in each group was designated as a reference. The mechanical performance and cracking sequence in all beams was evaluated under four‐point loading test setup. Heat‐damage resulted in reductions in load capacity and stiffness at 11% and 10%, yet an increase in toughness and displacement ductility by 18% and 20%, respectively. Implementing end hocks with end vertical and lateral dowels prevented concrete‐cover separation; imparting the best enhancement in structural performance for the repaired and post‐heated beams. All beams experienced flexural failure mode except for the heat‐damaged one, repaired with end‐hock anchorage without lateral doweling.

Experimental and Numerical Research on Fracture Properties of Mass Concrete Under Quasi-Static and Dynamic Loading

The dynamic fracture behavior of mass concrete is crucial to the dynamic analysis and safety evaluation of concrete dams subjected to strong earthquake shocks in the framework of fracture mechanics. In the presented research, cylindrical specimens with a ring of preset cracks were cast by three-graded mass concrete, and direct tension tests were performed with two loading rates considered, i.e., 10−6/s for quasi-static loading and 10−3/s for dynamic loading. The load–crack mouth opening displacement (P-CMOD) curves were obtained, from which the fracture toughness, fracture energy, and characteristic length of the mass concrete were obtained. In this process, the influence of the eccentricity in the tests was compensated by the numerical modeling of the tests. Next, the crack propagation process of the mass concrete was modeled using the extended finite element method. From the test results, it is found that, under quasi-static loading, the crack generally propagates along the interface between the aggregates and the matrix, while, under dynamic loading, more aggregates are fractured. As compared to the case of quasi-static loading, the energy absorption capacity, fracture energy, and fracture toughness increase for dynamic loading, while the characteristic length decreases. Moreover, the numerically predicted P-CMOD curves agree reasonably well with the experimental measurements.

Boosting the Strength and Toughness of Polymer Blends via Ligand-Modulated MOFs.

Mechanically robust and tough polymeric materials are in high demand for applications ranging from flexible electronics to aerospace. However, achieving both high toughness and strength in polymers remains a significant challenge due to their inherently contradictory nature. Here, a universal strategy for enhancing the toughness and strength of polymer blends using ligand-modulated metal-organic framework (MOF) nanoparticles is presented, which are engineered to have adjustable hydrophilicity and lipophilicity by varying the types and ratios of ligands. Molecular dynamics (MD) simulations demonstrate that these nanoparticles can effectively regulate the interfaces between chemically distinct polymers based on their amphiphilicity. Remarkably, a mere 0.1wt.% of MOF nanoparticles with optimized amphiphilicity (ML-MOF(5:5)) delivered ≈3.4- and ≈34.1-fold increase in strength and toughness of poly (lactic acid) (PLA)/poly (butylene succinate) (PBS) blend, respectively. Moreover, these amphiphilicity-tailorable MOF nanoparticles universally enhance the mechanical properties of various polymer blends, such as polypropylene (PP)/polyethylene (PE), PP/polystyrene (PS), PLA/poly (butylene adipate-co-terephthalate) (PBAT), and PLA/polycaprolactone (PCL)/PBS. This simple universal method offers significant potential for strengthening and toughening various polymer blends.

Energy Dissipation and Toughening of Covalent Networks via a Sacrificial Conformation Approach.

Covalent polymer networks find wide utility in diverse engineering applications owing to their desirable stiffness and resilience. However, the rigid covalent chemical structure between crosslinking points imposes limitations on enhancing their toughness. Although the incorporation of sacrificial chemical bonds has shown promise in improving toughness through energy dissipation, composite networks struggle to maintain both rapid recovery and stiffness. Consequently, a significant challenge persists in achieving a covalent network that combines high strength, stiffness, toughness, and fast recovery performance. To address this challenge, we propose a novel sacrificial structure termed "sacrificial conformation." In this approach, β-cyclodextrin is covalently embedded into the network skeleton as the sacrificial conformation element. Compared to traditional covalent networks (LCN), well-designed cyclodextrin-embedded covalent network (CCN) exhibit a 100-fold increase in Young's modulus and a 60-fold increase in toughness. Importantly, CCN maintains excellent elasticity, ensuring swift recovery after deformation. This sacrificial conformational strategy enables efficient energy dissipation without necessitating the rupture of chemical bonds, thereby overcoming the limitations of traditional approaches. This advancement holds great promise for the design and fabrication of advanced elastomers and hydrogels with superior mechanical properties and dynamic behavior.

Energy Dissipation and Toughening of Covalent Networks via a Sacrificial Conformation Approach

Covalent polymer networks find wide utility in diverse engineering applications owing to their desirable stiffness and resilience. However, the rigid covalent chemical structure between crosslinking points imposes limitations on enhancing their toughness. Although the incorporation of sacrificial chemical bonds has shown promise in improving toughness through energy dissipation, composite networks struggle to maintain both rapid recovery and stiffness. Consequently, a significant challenge persists in achieving a covalent network that combines high strength, stiffness, toughness, and fast recovery performance. To address this challenge, we propose a novel sacrificial structure termed "sacrificial conformation." In this approach, β‐cyclodextrin is covalently embedded into the network skeleton as the sacrificial conformation element. Compared to traditional covalent networks (LCN), well‐designed cyclodextrin‐embedded covalent network (CCN) exhibit a 100‐fold increase in Young's modulus and a 60‐fold increase in toughness. Importantly, CCN maintains excellent elasticity, ensuring swift recovery after deformation. This sacrificial conformational strategy enables efficient energy dissipation without necessitating the rupture of chemical bonds, thereby overcoming the limitations of traditional approaches. This advancement holds great promise for the design and fabrication of advanced elastomers and hydrogels with superior mechanical properties and dynamic behavior.

Reinforcement and Controlling the Stability of Poly(ε-caprolactone)-Based Polymeric Materials via Reversible and Movable Cross-Links Employing Cyclic Polyphenylene Sulfide.

Due to its biodegradation ability, poly(ε-caprolactone) (PCL) is a suitable alternative for packaging materials; however, its biodegradation can also lead to instability in its usage. Cyclic polyphenylene sulfide (7U) has been shown to form rotaxane structures with PCL by simple blending to generate the π-π stacking effect and movable cross-link. A 2-fold increase in toughness and no decrease in Young's modulus for the PCL-based polyurethane with 7U are observed. The rotaxane structures mainly exist in the amorphous regions and have no impact on the crystallinity of PCL. Under the catalysis of lipase in aqueous solution, the stability of PCL is improved due to the 7U's suppression of the attack from the enzymes on PCL. After dissolution of the PCL films in the organic solvent, the dispersion of 7U and the breakage of the cross-links lead to little suppression on degradation during the catalysis of lipase. Thus, the controlled stability of PCL using 7U can prolong the life span of the biodegraded PCL materials.

Development of a Composite Filament Based on Polypropylene and Garlic Husk Particles for 3D Printing Applications

Lignocellulosic waste materials are among the most abundant raw materials on Earth, and they have been widely studied as natural additives in materials, especially for polymer composites, with interesting results when it comes to improving physiochemical properties. The main components of these materials are cellulose, hemicellulose, and lignin, as well as small amounts of other polysaccharides, proteins, and other extractives. Several kinds of lignocellulosic materials, mainly fibers, have been evaluated in polymer matrices, and recently, the use of particles has increased due to their high surface area. Garlic is a spice seed that generates a waste husk that does not have applications, and there are no reports of industrial use of this kind of lignocellulosic material. Additive manufacturing, also known as 3D printing, is a polymer processing technique that allows for obtaining complex shapes that are hard to obtain with ordinary techniques. The use of composites based on synthetic polymers and lignocellulosic materials is a growing field of research. In the present work, the elaboration and evaluation of 3D-printed polypropylene–garlic husk particle (PP-GHP) composites are reported. First, the process of obtaining a filament by means of a single extrusion was carried out, using different GHP contents in the composites. Once the filament was obtained, it was taken to a 3D printer to obtain probes that were characterized using differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) was performed with the aim of evaluating the thermal behavior of the 3D-printed PP-GHP composites. According to the obtained results, the crystallization process and thermal stability of the PP-GHP composites were modified with the presence of GHP compared with pristine PP. Dynamic mechanical analysis (DMA) showed that the addition of GHP decreased the storage modulus of the printed composites and that the Tan δ peak width increased, which was associated with an increase in toughness and a more complex structure of the 3D-printed composites. X-ray diffraction (XRD) showed that the addition of GHP favored the presence of the β-phase of PP in the printed composites.

Bamboo fiber-enhanced UHPC: Early hydration and microstructural/mesoscale analysis

This study investigates the impact of incorporating bamboo fibers, a natural and renewable material, into ultra-high performance concrete (UHPC) on its early hydration, mechanical properties, internal relative humidity, autogenous shrinkage, and microstructure. The results show that adding bamboo fibers significantly improves various UHPC properties. Bamboo fibers regulate hydration and prolong the hydration process through their water absorption and retention abilities. With a fiber content of 1.0 vol percent (vol%), the compressive strength increases by 10.2 %, reaching 97.1 MPa, and at 2.0 vol%, flexural strength and toughness increase by 37.9 % and 739.5 %, respectively. Additionally, bamboo fibers help maintain internal relative humidity above 98 % during the first 7 days of curing and reduce autogenous shrinkage by up to 55.9 %. The fibers also optimize the microstructure by minimizing voids, with a 1.0 % fiber content reducing the void ratio to 1.64 %. This reduces large voids and improves the material's density. Overall, bamboo fibers show great promise in enhancing UHPC's structural performance and environmental adaptability while being a sustainable and cost-effective material.

Effect of short-time high-temperature stabilization on the microstructure and tensile property of severely deformed Al-Mg-Sc alloy

In this paper, the effect of short-time high-temperature stabilization on the microstructure and tensile property of the Al-Mg-Sc alloy deformed by equal channel angular pressing (ECAP) has been investigated. The results show that the 2-pass ECAP cannot completely refine the grain, and the distribution of the deformed structure is inhomogeneous. After short-time stabilization, the grain of the material is refined, the shear zone becomes small grains with a size of about 1 μm, and the non-uniform deformation structure is alleviated. This change results in a small reduction in strength but a large increase in toughness. Short-time stabilization also improves the workability of the material. Re-deforming the material by another 2 pass ECAP, the sample with short-time stabilization demonstrates fewer internal defects, a more uniform structure, and finer grains.

Aerated Concrete, Based on the Ash of Thermal Power Plants, Nanostructured with Water-Soluble Fullerenols

This study is devoted to the synthesis of aerated concrete by a non-autoclave method using ash from thermal power plants and a nanopreparation. Fullerenol-m was used as a nanopreparation. The fullerenol-m content in the sealing water of aerated concrete changed in the range of 0.00 ÷ 0.03 mas.%. The main performance characteristics of the nanostructured aerated concrete were studied, namely the compressive strength, impact toughness, thermal conductivity, density and moisture content. A significant improvement in the performance characteristics of the nanomodified aerated concrete compared to unmodified samples was demonstrated, which was most clearly manifested as an increase in impact toughness by several (three to five) times. The best performance characteristics of the modified aerated concrete were observed at a fullerenol-m concentration relative to the added cement within 0.022–0.028 wt.%. The authors attribute such a strong change and improvement in the physical, chemical and operational properties of aerated concrete when modified with fullerenol-m to the fact that fullerenol-m (a few thousandths of wt.%) has a very strong structuring effect on the sealing water and, as a consequence, on the resulting aerated concrete.

Influence of Y2O3 doping on the aging behavior and mechanical properties of ATZ ceramics

The aim of this study was to investigate the influence of the Y2O3 content on the mechanical properties and aging behavior of ATZ ceramic. For this purpose, an ATZ ceramic consisting of 80 wt% stabilized ZrO2 and 20 wt% Al2O3 with varying Y2O3 stabilizer content between 2 and 3 mol% was prepared. The samples were analyzed regarding their sintered density, grain size, hardness and fracture toughness. The results show an increase in fracture toughness and a decrease in hardness with decreasing Y2O3 content. In addition, the aging stability was assessed by analyzing the phase composition determined by X-ray diffraction after aging the samples for up to 150 hours in steam atmosphere at 134 °C and 2 bar. The aging stability decreases with decreasing stabilizer content. Nevertheless, by producing a very fine-grained material, high aging stability can be achieved despite reduced Y2O3 content.

Effects of binary sintering additives (SmF3-Sm2O3) and sintering temperature on β-SiAlON ceramic tool materials

β-SiAlON ceramic tool materials were fabricated via spark plasma sintering using binary sintering additives (SmF3-Sm2O3). The effects of SmF3 addition and sintering temperature on the densification, phase composition, microstructure and mechanical properties were studied. Furthermore, the corrosion behavior of β-SiAlON ceramic tool materials due to excessive SmF3 at high sintering temperatures (≥1700 °C) was revealed. The results indicated that SmF3 could promote the densification and generation of β-SiAlON. Higher SmF3 content and sintering temperature increased the aspect ratio and average grain size of β-SiAlON, which made fracture toughness increase and Vickers hardness decrease. The best density, fracture toughness and hardness of β-SiAlON ceramic tool materials were 3.204 g/cm3, 6.45 ± 0.07 MPa m1/2 and 16.72 ± 0.09 GPa. However, β-SiAlON was corroded by excessive SmF3 during high temperature sintering, resulting in deterioration in densification and properties.

PREDICTION OF STRENGTH DEPENDING ON THE INFLUENCE OF THE CHEMICAL COMPOSITION IN THE 40КХНМ ALLOY

Introduction. The study is devoted to the analysis of the influence of the chemical composition of the 40КХНМ alloy on its hardness. The relevance of the work lies in the fact that mechanical tests require significant material and time costs. For the operational assessment of metal quality criteria, it is proposed to apply mathematical modeling in the work. Materials and methods. A study of the effect of the chemical composition on the hardness of the 40KHNM alloy, which meets the requirements of the state standard 51397, was carried out. The results of the experiment. In the course of research, it was found that changes in the chemical composition of the 40КХНМ alloy significantly affect its mechanical properties, including hardness and resistance to shock loads. An increase in the content of carbon, molybdenum and chromium in the alloy leads to an increase in its hardness. This is with the formation of stronger carbide and molybdenum phases in the structure of the alloy, which leads to an improvement in its mechanical properties. Increased hardness makes the alloy more resistant to wear and increases its durability in operating conditions. An increase in the nickel content in the alloy leads to an increase in its resistance to shock loads. This is caused by an increase in plasticity and impact toughness of the alloy with an increased nickel content. Higher resistance to shock loads makes the alloy suitable for use in conditions that require high resistance to shocks, for example, in the production of machine parts and equipment. A mathematical model of the dependence of the strength of the alloy on the percentage content of the components of the chemical composition was built, which allows to control the indicators of the strength of the alloy in the process of its manufacture. Conclusions. The research results confirm that changes in the chemical composition of the 40КХНМ alloy have a significant impact on its mechanical properties. As a result of the experiments, it was established that the chemical composition of the metal significantly affects the hardness of the material. By changing the composition of the metal, it was possible to achieve a significant increase in hardness to levels that meet the requirements of quality standards. These results are an important step in optimizing the production processes and improving the properties of the final products from the 40КХНМ alloy.

On the interlaminar mode II fracture toughness evaluation of glass Fiber/Epoxy composites with cotton and kenaf natural fibers utilizing acoustic emission features

Considering the widespread use of polymer composites due to their diverse engineering properties, the incorporation of natural fibers is a novel approach to enhance their environmental properties and acquire additional engineering benefits. Applying natural fibers in composites can offer a biocompatible solution to plastic and polymer composite waste issues. Studying the overall properties of composites made with these fibers is a novel area of research. Investigating effective methods for detecting defects and measuring mechanical properties, such as integrity, resilience to failure, and fracture toughness, is particularly crucial. In the current study, the effect of adding cotton and kenaf natural fibers on the resistance to delamination, which is the most common type of failure in laminated composites, is investigated in mode Ⅱ of loading. Specimens of woven glass/epoxy composites with natural fibers were fabricated using the hand lay-up method and end notched three-point bending test was performed. Using the methods provided in the JIS K 7086 standard, the moment of initiation of delamination is determined in the samples. The results demonstrate that only using the mechanical methods provided in the mentioned standard is not sufficient to determine the initiation of delamination. Hence, the acoustic emission can be employed for an easier and more accurate determination of the initiation of delamination. According to the obtained results, cotton and kenaf fibers show a significant increase in the interlaminar fracture toughness of woven glass/epoxy composites. Using cotton fibers shows 212% − 249% and employing kenaf fibers shows 144% − 281% increase in interlaminar fracture toughness respectively. Among the different acoustic emission data analytics, the cumulative energy method shows the lowest mean percentage deviation error of %2.59 among other examined diagnosing techniques.

Bio-based liquid crystal epoxy resins: Toughening and strengthening of conventional epoxy resins with strategically extended spacer layers

Liquid crystal epoxy resin, as an ideal toughening agent, combines the features of liquid crystal ordering and network cross-linking, which can effectively optimize the comprehensive performance of blended epoxy resins and achieve an ideal balance of rigidity and toughness. Here we successfully synthesized rigid and flexible bio-based liquid crystal epoxy resin (THBR-EP) by finely tuning the length of alkyl side chains. Using aromatic diamine as curing agent, a homogeneous network without phase separation was constructed by taking advantage of the different activity but good compatibility with ordinary epoxy resins, which significantly improved the toughness of the blended system. Specifically, only a small amount of THBR-EP(2.5 wt%) was required to exhibit a maximum impact strength of 48.8 kJ/m2. Moreover, the increase in system toughness was accompanied by a benign improvement in flexural strength, modulus and thermal stability. The ordered structure of the liquid crystals and their good compatibility with the resin matrix enhanced the ability to inhibit crack extension and energy dissipation. The feasibility to simultaneously achieve effective toughening and other property improvements of common resins broadens the application of resins under various demanding scenarios.

New insights from crystallography into the effect of Ni content on ductile-brittle transition temperature of 1000 MPa grade high-strength low-alloy steel

The significant effect of Ni content (0.92, 1.94 and 2.94 wt%) on ductile-brittle transition temperature (DBTT) and microstructure in a 1000 MPa grade high-strength low-alloy (HSLA) steel was studied. Using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), Charpy impact test and low-temperature tensile test to study the fundamental reasons for the effect of Ni content on toughness. The results indicated that increasing the Ni content can reduce the DBTT of HSLA steel and improve the impact toughness at low temperatures. EBSD data post-processing analysis revealed that the key reason for the increase in low-temperature toughness is the refinement of the microstructural crystallographic structure, specifically the significant increase in the boundary density of the block and packet. With the increase of Ni content, the density of grain boundary with an orientation difference greater than 5° between two adjacent {110} crystal planes was higher, which can form a higher density of dislocation pile-up group, thus better reducing local stress concentration. Meanwhile, the stacking fault energy (SFE) increases with the increase of Ni content, which made the screw dislocation more prone to cross slip at low temperature, resulting in an increase in plasticity at low temperatures. These observed phenomena and reasons provided a theoretical explanation for the role of Ni content in reducing DBTT and enhancing the toughness of the core in heavy gauge plates.

Synthesis and evaluation of novel urethane macromonomers for the formulation of fracture tough 3D printable dental materials

3D printing of materials which combine fracture toughness, high modulus and high strength is quite challenging. Most commercially available 3D printing resins contain a mixture of multifunctional (meth)acrylates. The resulting 3D printed materials are therefore brittle and not adapted for the preparation of denture bases. For this reason, this article focuses on toughening by incorporation of triblock copolymers in methacrylate-based materials. In a first step, three urethane dimethacrylates with various alkyl spacer length were synthesized in a one-pot two-step synthesis. Each monomer was combined with 2-phenoxyethyl methacrylate as a monofunctional monomer and a polycaprolactone-polydimethylsiloxane-polycaprolactone triblock copolymer was added as toughener. The formation of nanostructures via self-assembly was proven by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The addition of the triblock copolymer resulted in a strong increase in fracture toughness for all mixtures. The nature of the urethane dimethacrylate had a significant impact on fracture toughness and flexural strength and modulus of the cured materials. Most promising systems were also investigated via dynamic fatigue propagation da/dN measurements, confirming that the toughening also works under dynamic load. By carefully selecting the length of the urethane dimethacrylate spacer and the amount of block copolymer, materials with the desired physical properties could be efficiently formulated. Especially the formulation containing the medium alkyl spacer length (DMA2/PEMA) and 5 wt% BCP1 (block copolymer), exhibits excellent mechanical properties and high fracture toughness.

Tough double-bouligand architected concrete enabled by robotic additive manufacturing

Nature has developed numerous design motifs by arranging modest materials into complex architectures. The damage-tolerant, double-bouligand architecture found in the coelacanth fish scale is comprised of collagen fibrils helically arranged in a bilayer manner. Here, we exploit the toughening mechanisms of double-bouligand designs by engineering architected concrete using a large-scale two-component robotic additive manufacturing process. The process enables intricate fabrication of the architected concrete components at large-scale. The double-bouligand designs are benchmarked against bouligand and conventional rectilinear counterparts and monolithic casts. In contrast to cast concrete, double-bouligand design demonstrates a non-brittle response and a rising R-curve, due to a hypothesized bilayer crack shielding mechanism. In addition, interlocking behind and crack deflection ahead of the crack tip in bilayer double-bouligand architected concrete elicits a 63% increase in fracture toughness compared to cast counterparts.