Material Toughness Research Articles

Evaluation of impact toughness of glass-reinforced composite materials immersed in water

The mechanical and physical properties of glass fiber composite materials can be modified when immersed in water. This change in properties can result from internal instability of the material, interaction with the environment, mechanical stresses, or a combination of these effects. In this study fiber glass reinforced polyester resin plates have been manufactured by the contact molding method with 20% of reinforcement percentage. Prismatic specimens have been cut then notched to evaluate the impact toughness by applying the Charpy impact test. The Williams method based on the principle of linear elastic fracture mechanics was used to deduce the impact toughness of composite. These specimens have been immersed in water for 30 and 90 days to study absorption effect and diffusion on the impact behavior of this material. From the results, it is found that there is a direct correlation between water penetration in the glass-polyester composite and its impact toughness.

Mechanical properties and tensile failure mechanisms of SM400A steel treated by high-power continuous-wave laser

This study systematically investigates the effects of high-power continuous wave laser (CWL) treatment on the mechanical behavior and failure mechanisms of SM400A steel, comparing these outcomes with those of untreated specimens. The findings reveal that while CWL treatment enhances surface hardness, it has minimal impact on the strength of thick structural steel components. However, excessive laser energy density leads to surface defects and softening of the microstructure, adversely affecting the material's toughness. This results in a reduction in elongation at fracture, transitioning the failure mode from ductile to brittle. The study concludes that to ensure the safe use of laser-treated structures, the laser energy density should be carefully controlled not to exceed 3000 J/cm2.

The primitive giant panda Kretzoiarctos beatrix (Carnivora, Ursidae) from the hominid locality of Hammerschmiede: dietary implications

AbstractExtant giant pandas are among the most herbivorous forms of the order Carnivora, feeding mainly on hard plant material. The first steps of their evolutionary lineage are of particular interest for our understanding of the factors that led to this specialized niche. The present work deals with newly discovered dental material of the primitive ailuropodine bear Kretzoiarctos beatrix from the Late Miocene locality of Hammerschmiede (Germany). This is the first report of the genus Kretzoiarctos outside the Iberian Peninsula, expanding its spatial range to Central Europe. All of the currently known localities with K. beatrix, from both Spain and Germany, are very similar in age (c. 11.9–11.4 Ma). The present material has distinct features that enable its taxonomic discrimination from other Miocene ursids of Europe, such as Ballusia, Ursavus, Miomaci, Agriarctos and Indarctos. A thorough comparison is conducted of all of these forms. The new specimens were used in a dental microwear texture analysis in combination with ecomorphological comparisons, to investigate the dietary habits of this primitive ailuropodine. The results suggest that Kretzoiarctos was not an eater of tough plant material like the extant giant panda but was more similar to the extant Tremarctos, exhibiting opportunistic behaviour with occasional consumption of meat.

The formation mechanism of fracture surface separations and their effects on the toughness for ferrite-pearlite steels

The formation mechanism of fracture surface separations for ferrite-pearlite steels is investigated by combining experimental testing and numerical simulation, and the effects of fracture surface separations on the toughness are discussed. The fracture surface of Charpy impact samples for both the as-rolled and the normalized ferrite-pearlite steel were compared. The fracture surface separations occur in the as-rolled plate above the ductile-brittle transition temperature instead of the normalized plate. The fracture surface separations are triggered by transverse tensile stress, which is supported by band-shaped pearlite with poor deformability. It is demonstrated that the formation of fracture surface separations is not only dependent on band-shaped pearlite and temperature but also on the stress state. The normal stress S11 in the X-direction is the largest, and the normal stress S33 distribution concentrates on the plate center, which can explain the location of the fracture surface separations. In contrast to the dispersed distribution of the normal stress S33 for the as-rolled plate, the large normal stress in the normalized plate is in a linear arrangement, resulting in a layered crack. The effects of fracture surface separations on the materials toughness are highly dependent on the number, length, depth and location of the separations.

Low-Hysteresis and Tough Ionogels via Low-Energy-Dissipating Cross-Linking.

Low-hysteresis merits can help polymeric gel materials survive from consecutive loading cycles and promote life span in many burgeoning areas. However, it is a big challenge to design low-hysteresis and tough polymeric gel materials, especially for ionogels. This can be attributed to the fact that higher viscosities of ionic liquids (ILs) would increase chain friction of polymeric gels and eventually dissipate large amounts of energy under deformation. Herein, a chemical design of ionogels is proposed to achieve low-hysteresis characteristics in both mechanical and electric aspects via hierarchical aggregates formed by supramolecular self-assembly of quadruple H-bonds in a soft IL-rich polymeric matrix. These self-assembled nanoaggregates not only can greatly reinforce the polymeric matrix and enhance resilience, but also exhibit low-energy-dissipating features under stress conditions, simultaneously benefiting for low-hysteresis properties. These aggregates can also promote toughness and subsequent anti-fatigue properties in response to external cyclic mechanical stimuli. More importantly, these ionogels are presented as a model system to elucidate the underlying mechanism of the low hysteresis and fatigue resistance. Based on these findings, it is further demonstrated that the supramolecular low-hysteresis strategy is universal.

Effect of multi-pass overlapping friction stir processing on fatigue behavior of Al-Cu alloy

More than half of mechanical breakdowns stem from fatigue failure, often occurring suddenly and without warning. Friction stir processing (FSP) enhances the material's toughness and resilience to fatigue by refining its grain structure. This study investigates how multi-pass overlapping technique impacts the fatigue crack growth rate of FSPed Al-Cu alloy. Microstructural analysis revealed that the stir region exhibited uniformly dispersed and fragmented precipitates and finely recrystallized ultrafine grains. The hardness and strength were reduced, and ductility was enhanced after FSP due to high thermal cycling. Fatigue testing demonstrated a significant increase in fatigue life and reduced fatigue crack growth rate attributable to the combined effects of precipitation and grain refinement during cooling-assisted FSP. SEM examination of fatigue fracture surfaces revealed dimples indicative of ductile failure in the rapid crack propagation zone, while the steady-state propagation region displayed striation markings and secondary fractures.

Mussel-inspired tough ionogel with robust adhesion and mechanical adaptivity for impact resistance

Intrinsic adhesiveness and mechanical adaptivity allowing spontaneous anchoring and impact-stiffening, which facilitate safer impact protection, remain challenges for the design and synthesis of advanced tough impact-resistant materials. Herein, a novel biomimetic mechanically robust impact-resistant ionogel with the mussel-inspired diphasic structure was elaborately developed. The salt-bridge hydrogen bonds between carboxyl and imidazole groups inside rigid clusters serve as reversible crosslinking sites and prime energy-dissipation motifs, leading to strong noncovalent cohesion. Furthermore, the hydrophobic ionic liquid enriches surface interactions, providing extensive adhesive performance for in-situ attachment under external impact. Benefitting from the dynamic nature of the salt-bridge hydrogen bonds, the ionogel possesses impressive energy dissipation, self-healing, and recyclable properties. Notably, the prepared ionogel exhibits rate-dependent mechanical adaptivity and outstanding impact-stiffening performance with extraordinary initial modulus (∼6.3 GPa), impact strength (∼178.5 MPa), and impact toughness (∼89.6 MJ m−3) under high-speed impact (∼5200 s−1). This work offers promising biomimetic design inspirations for the future development of advanced, flexible, sustainable, and protective materials.

High-Strength and High-Toughness Supramolecular Materials for Self-Healing Triboelectric Nanogenerator.

The development of self-healing materials provides a new opportunity and challenge for advancing triboelectric nanogenerators (TENGs). However, the low strength and low toughness of self-healing triboelectric materials often result in the deformation or breakage of TENG under high mechanical loads, thereby limiting their potential applications. Herein, a new strategy for fabricating self-healing triboelectric materials is reported, which introduces cross-linking networks with hydrogen bonds and metal coordination bonds. The desired high performance can be achieved by simply adjusting the molar ratio of the metal to the ligand. When the molar ratio is 1:2, the tensile strength, toughness, and elongation atbreak of the material reached 13.7MPa, 76.9MJ m-3, and 1321%, respectively. Furthermore, its self-healing efficiency can reach 74% at 70°C in 6 h. Working in contact-separation mode, the electrical output can reach 164V, 18.2µA, 57.5 nC, with a maximum power density of 2.54W m-2. Notably, even if it is sheared, the electrical output performances of TENG can be completely recovered to the original state. In addition, the developed TENG exhibits excellent output stability over 10000 contact separation cycles. This study presents a promising approach for the development of stretchable smart generators.

Upcycling of polyethylene/polypropylene mixtures promoted by well-controlled multiblock olefin copolymers

Polyethylene (PE) and isotactic polypropylene (iPP) are two of the most widely used polymer materials, whose huge consumptions urge people to tackle their recycling problem. The incompatibility of PEs and PPs has resulted in their waste streams being recycled into low-value products with poor mechanical properties. Herein, a series of iPP-based olefin block copolymers (OBC) with up to five alternating hard/soft blocks were prepared via coordinative chain transfer polymerization. The facile synthetic strategy of multiblock OBCs not only overcame the inefficiency and diseconomy of living coordination polymerization, but also avoided the critical requirements of complex dual-catalyst systems for chain shuttling polymerization, making it suitable for low-cost and large-scale production of OBCs. These well-designed OBCs provided excellent elastomeric properties combining high strength, high elongation, and high elastic recovery. More importantly, they also demonstrated a strong ability in the upcycling of PE/PP mixtures, transforming brittle blends into tough materials. The PE/PP blends compatibilized with OBCs exhibited greatly improved interfacial adhesion and mechanical properties, with up to 25 times higher elongation at break compared to uncompatibilized blends. It was further demonstrated by the extruding-blow-molded bottles prepared using post-consumer PE/PP products, where recycled bottles containing OBCs exhibited much better mechanical properties than those without OBC. The synthetic strategy of OBCs and the upcycling route of PE/PP blends in this work are not only of great academic value, but also of substantial economic and environmental significance, providing insights into the sustainable development of plastics.

A Relationship between Fracture Toughness Kc and Energy Release Rate Gc According to Fracture Morphology Analysis

This study investigated the relationship between fracture toughness (Kc) and energy release rate (Gc) through fracture morphology analysis, emphasizing the critical role of fractal dimensions in accurately characterizing fracture surfaces. Traditional linear elastic fracture mechanics (LEFM) models relate Gc to Kc by combining energy principles with the nominal area of the fracture surface. However, real materials often exhibit plasticity, and their fracture surfaces are not regular planes. To address these issues, this research applied fractal theory and introduced the concept of ubiquitiform surface area to refine the calculation of fracture surfaces, leading to more accurate estimates of Gc and Kc. The method was validated through standard compact tensile specimen tests on a nickel-based superalloy at 550 °C. Additionally, the analysis of fractal dimension differences and dispersion in various fracture regions provides a novel perspective for evaluating the fracture toughness of materials.

Soybean protein “mechanically interlocked” bonding of polysaccharide and MXene to improve the strength and toughness of biomass adhesive

Simultaneously improving the strength and toughness of soybean protein adhesives is a huge challenge. The multi-scale enhancement strategy proposed in this study introduced MXene nanosheets and oxidized sodium alginate (OSA) to improve mechanical properties. The polymer network framework with high crosslink density dissipates energy by restricting the slip of the SPI molecular chains, and MXene act as stress dispersers in the polymer network in order to solve the challenge of the strength-toughness balance. The prepared biomass-based adhesives with high adhesion (dry/wet shear strength 1.93 MPa/1.33 MPa), high toughness (adhesion work 810.9 mJ), high thermal stability, high residual rate (92.53 %), low moisture absorption rate (11.18 %), and long storage time (12 d). Additionally, the application of SOM-5 adhesive reduces the burden of petrochemical resource extraction for adhesive production and contributes to the sustainable development of the wood industry. Most importantly, it presents an adoptable strategy for resolving the tension between strength and toughness of composite materials.

An Experimental Study on the Thermomechanical Coupling Effects of Carbon-Fiber-Reinforced Polyetheretherketone under Dynamic Impact.

Carbon-fiber-reinforced polyetheretherketone (CF/PEEK) composites are widely utilized in aerospace, medical devices, and automotive industries, renowned for their superior mechanical properties and high-temperature resistance. Despite these advantages, the thermomechanical coupling behavior of CF/PEEK under dynamic loading conditions is not well understood. This study aims to explore the thermomechanical coupling effects of CF/PEEK at elevated strain rates, employing Hopkinson bar impact tests and scanning electron microscopy (SEM) for detailed characterization. Our findings indicate that an increase in temperature led to significant reductions in the yield strength, peak stress, and specific energy absorption of CF/PEEK, while fracture strain had no significant effect. For instance, at 200 °C, the yield strength, peak stress, and specific energy absorption decreased by 39%, 37%, and 38%, respectively, compared to their values at 20 °C. Furthermore, as the strain rate increased, the yield strength, peak stress, specific energy absorption, and fracture strain all exhibited strain-hardening effects. However, as the strain rate further increased, above 4000 s-1, the enhancing effect of the strain rate on the yield strength and peak stress gradually diminished. The interaction of the temperature and strain rate significantly affected the mechanical performance of CF/PEEK under high-speed impact conditions. While the strain rate generally enhanced these properties, the strain-hardening effect on the yield strength weakened as the temperature increased, and both the temperature and strain rate contributed to the increase in specific energy absorption. Microdamage mechanism analysis revealed that interface debonding and sliding between the fibers and the matrix were more pronounced under static compression than under dynamic compression, thereby diminishing the efficiency of stress transfer. Additionally, higher temperatures caused the PEEK matrix to soften and exhibit increased viscoelastic behavior, which in turn affected the material's toughness and the mechanisms of stress transfer. These insights hold substantial engineering significance, particularly for the optimization of CF/PEEK composite design and applications in extreme environments.

Molecular Dynamics Study on the Mechanical Behaviors of Nanotwinned Titanium

Titanium and titanium alloys have been widely applied in the manufacture of aircraft engines and aircraft skins, the mechanical properties of which have a crucial influence on the safety and lifespan of aircrafts. Based on nanotwinned titanium models with different twin boundary spacings, the impacts of different loadings and twin boundary spacings on the plastic deformation of titanium were studied in this paper. It was found that due to the different contained twin boundaries, the different types of nanotwinned titanium possessed different dislocation nucleation abilities on the twin boundaries, different types of dislocation–twin interactions occurred, and significant differences were observed in the mechanical properties and plastic deformation mechanisms. For the {101-2} twin, basal plane dislocations were likely to nucleate on the twin boundary. The plastic deformation mechanism of the material under tensile loading was dominated by partial dislocation slip on the basal plane and face-centered cubic phase transitions, and the yield strength of the titanium increased with decreasing twin boundary spacing. However, under compression loading, the plastic deformation mechanism of the material was dominated by a combination of partial dislocation slip on the basal plane and twin boundary migration. For the {101-1} twin under tensile loading, the plastic deformation mechanism of the material was dominated by partial dislocation slip on the basal plane and crack nucleation and propagation, while under compression loading, the plastic deformation mechanism of the material was dominated by partial dislocation slip on the basal plane and twin boundary migration. For the {1124} twin, the interaction of its twin boundary and dislocation could produce secondary twins. Under tensile loading, the plastic deformation mechanism of the material was dominated by dislocation–twin and twin–twin interactions, while under compression loading, the plastic deformation mechanism of the material was dominated by partial dislocation slip on the basal plane, and the product of the dislocation–twin interactions was basal dislocation. All these results are of guiding value for the optimal design of microstructures in titanium, which should be helpful for achieving strong and tough metallic materials for aircraft manufacturing.

Decolorization of Lignin for High-Resolution 3D Printing of High Lignin-Content Composites.

Lignin, one of the most abundant biomaterials and a large-scale industrial waste product, is a promising filler for polymers as it reduces the amount of fossil resources and is readily available. 3D printing is well-known for producing detailed polymer structures in small sizes at low waste production. Especially light-assisted 3D printing is a powerful technique for production of high-resolution structures. However, lignin acts as a very efficient absorber for UV and visible light limiting the printability of lignin composites, reducing its potential as a high-volume filler. In this work, the decolorization of lignin is presented for high-resolution 3D printing of biocomposites with lignin content up to 40wt.%. Organosolv lignin (OSL) is decolorized by an optimized low-energy process of acetylation and subsequent UV irradiation reducing the UV absorbance by 71%. By integration of decolorized lignin into bio-based tetrahydrofurfuryl acrylate (THFA), a lignin content of 40wt.% and a resolution of 250µm is achieved. Due to the reinforcing properties of lignin, the stiffness and strength of the material is increased by factors of 15 and 2.3, respectively. This work paves the way for the re-use of a large amount of lignin waste for 3D printing of tough materials at high resolution.

Molecular control via dynamic bonding enables material responsiveness in additively manufactured metallo-polyelectrolytes

Metallo-polyelectrolytes are versatile materials for applications like filtration, biomedical devices, and sensors, due to their metal-organic synergy. Their dynamic and reversible electrostatic interactions offer high ionic conductivity, self-healing, and tunable mechanical properties. However, the knowledge gap between molecular-level dynamic bonds and continuum-level material properties persists, largely due to limited fabrication methods and a lack of theoretical design frameworks. To address this critical gap, we present a framework, combining theoretical and experimental insights, highlighting the interplay of molecular parameters in governing material properties. Using stereolithography-based additive manufacturing, we produce durable metallo-polyelectrolytes gels with tunable mechanical properties based on metal ion valency and polymer charge sparsity. Our approach unveils mechanistic insights into how these interactions propagate to macroscale properties, where higher valency ions yield stiffer, tougher materials, and lower charge sparsity alters material phase behavior. This work enhances understanding of metallo-polyelectrolytes behavior, providing a foundation for designing advanced functional materials.

Indoor thermal environment simulation of jade carving design process based on light sensing texture image processing

As a traditional art form, jade carving has gradually combined with modern technology in recent years, introducing new technologies in the design and production process. Indoor thermal environment has an important influence on the creation process of jade carving, especially the influence of temperature and humidity on the physical characteristics of jade carving materials and its processing. In this study, the influence of indoor thermal environment on jade carving design process was simulated by light sensing texture image processing technology, so as to optimize the design scheme and ensure the quality and artistic expression of jade carving works. The temperature, humidity and illumination data of indoor environment are obtained by light sensing technology, and the thermal environment required in jade carving design is simulated by texture image processing method. The thermal environment model was constructed to analyze the performance of jade carving materials under different conditions and evaluate the possible changes in the processing process. The simulation results show that the temperature and humidity of indoor thermal environment have significant effects on the toughness, hardness and detail performance of jade carving materials. At temperatures above 25° C and relatively low humidity, jade carving materials show better cutting results and surface finish. Texture image processing technology can effectively capture and analyze the subtle changes of materials, which provides a reliable basis for design decisions.

A phosphorus/fluorine‐containing block copolymer endows epoxy with multifunctionality

AbstractIn order to achieve flame retardant, hydrophobic, and toughened epoxy resins, phosphorus/fluorine‐containing block copolymer (FBCP) was synthesized by reversible addition‐fragmentation chain transfer polymerization, and then the as‐synthesized PMADOPO‐b‐PHFBA block copolymer was used as additive to modify the epoxy resin, accompanying with a random copolymer (FRCP) serving as control group. It showed that due to the regular arrangement of molecular chains, FBPC formed a fibrous‐like structure at the fracture interface of epoxy/PMADOPO‐b‐PHFBA (EP/FBCP) samples, effectively enhancing the toughness of epoxy composite materials. The fracture energy of EP90/FBCP‐10 was higher than that of EP90/FRCP‐10 and was about twice than that of pure EP. The addition of 3 wt% FBCP could enhance the limited oxygen index (LOI) of EP97/FBCP‐3 to 33.2% and reached a V‐1 UL‐94 rating. As the addition of FBCP increased, the LOI gradually increased. When the addition of FBCP was 10%, the LOI and UL‐94 of EP90/FBCP‐10 was 38.2% and V‐0 grade, respectively. Meanwhile, the presence of fluorine element effectively reduced the surface energy of the composite EP material. Compared with pure EP, the water contact angle of EP90/FBCP‐10 was about 101° with an increasing of 20.8%. Furthermore, the flame‐retardant mechanism of EP/FBCP epoxy composites was discussed.

Effects of alloying element on the interface stability of fcc-Fe/NbC by first principles investigation

Interfacial segregation engineering is widely used as a means of regulating the strength and toughness of materials. In this paper, the effect of alloying elements on the interfacial segregation and interfacial bonding properties of fcc-Fe/NbC is investigated with the precipitated phase NbC in austenitic heat-resistant steel. The results show that there are eighteen interfacial configurations between the fcc-Fe and NbC phase, and the stability of the interface with Nb terminal is better than that of C terminal according to the calculation results of separation work and interface energy. Al atom is easy to segregate on the surface of austenite, while the alloy elements Mo, Nb, Cr, Ti, Mn, Y and Zr tend to segregate in the austenite matrix. The segregation of alloy elements Mo, Nb, Cr and Ti can enhance the hybridization between the d orbits of Fe and Nb atoms at the interface, thus promoting the bonding strength of the interface, while the segregation of Mn, Al, Y and Zr reduces the covalent interaction of the interface atoms, which weakens the bond strength at the interface. The above results have important practical significance for improving and regulating the composition and interfacial properties of heat-resistant steels.

Recycling of LDPE-PVC blends from cable waste: Mechanical characterization and performance optimization

The recycling of polyvinylchloride (PVC) from waste electrical cables in blends with low-density polyethylene (LDPE) is here explored, focusing on the material's mechanical and physical responses. Factors influencing these responses were identified, and reasonable ranges of variability were estimated for each factor. A comprehensive test plan was subsequently devised to develop optimal PVC/LDPE blends. The samples were produced by melt-blending the polymers in a counter-rotating internal mixer followed by compression molding. The effects of suitable coupling additives were also evaluated to enhance phases adhesion. The study investigated the impact of various processing parameters on thermomechanical properties using ANOVA, while a specific focus on optimizing material toughness was pursued. This optimization aimed to maximize both elastic modulus and elongation at break, through the application of genetic algorithms. Introducing a 5 % compatibilizer significantly enhances the interface, resulting in a complex fracture surface facilitated by its presence. Higher mixing temperatures promote better dispersion and distribution of PVC and the compatibilizer within the LDPE matrix, yielding a more uniform and interconnected structure. Increased PVC content correlates with reduced elastic modulus in the blend. The inclusion of a compatibilizer plays a vital role in counteracting the negative effects of PVC particles on stiffness, acting as a bridge to enhance interactions with the matrix and thereby improving interfacial adhesion and overall structure. The study offers insights into enhancing the recyclability of PVC from waste cables and optimizing the mechanical performance of the resultant materials.

Polymeric Fibers with High Strength and High Toughness at Extreme Temperatures.

Developing strong and simultaneously tough polymeric materials with excellent thermal stability and mechanical performance even under extreme temperatures is truly a challenge. In a disruptive progress, continuous polymeric yarns are developed with a combination of high tensile strength of (1145 ± 44) MPa and ultrahigh toughness of (350 ± 24) J g-1 and high thermomechanical properties from -196 to 200°C. The comprehensive thermomechanical performance of this yarn surpasses that of previously developed polymeric materials and dragline spider silks. The results demonstrate that the molecular structure of polyimide (PI) with the incorporation of flexible-rigid macromolecular, hierarchically spiral-oriented fibers, and high glass transition temperature (248°C) are keys for the yarn's notable comprehensive performance in thermomechanical properties. The materials are ideal for technical components exposed to high thermomechanical loadings, such as those encountered in spacecraft or automotive engineering for safety-critical applications.