Search Results (559)

This study examines the flexural behavior of reinforced concrete (RC) beams that utilize steel, glass fiber-reinforced polymer (GFRP), and hybrid steel–GFRP longitudinal bars. It considers variations in stirrup material (steel or GFRP) and stirrup spacing (100 mm or 200 mm). Nine beam specimens were subjected to three-point bending tests until failure. Their performance was assessed based on ultimate load, deflection, stiffness, ductility, energy absorption, and failure mode. The experimental program aimed to isolate the effects of transverse reinforcement detailing and to elucidate the role of stirrup characteristics in governing the transition between flexure and shear-controlled behavior. The findings indicated that both the type of reinforcement and the configuration of stirrups significantly influenced structural performance. Steel-reinforced beams demonstrated stable and ductile flexural behavior, whereas GFRP-reinforced beams supported loads up to 18% higher but experienced abrupt failure in brittle shear with restricted ductility. Hybrid beams effectively integrated the benefits of both materials: The HS100 specimen, which featured closely spaced steel stirrups, achieved the highest ultimate load (162.5 kN), maximum deflection (19.7 mm), and greatest energy absorption (2450 kN·mm). In contrast, beams utilizing GFRP stirrups exhibited early diagonal cracking and abrupt failure, even with closely spaced stirrups. The study indicates that hybrid steel–GFRP reinforcement can enhance the strength, ductility, and toughness of reinforced concrete beams, contingent upon the application of sufficient steel confinement. The findings provide practical recommendations for enhancing hybrid RC design by positioning steel in tension and utilizing steel stirrups for confinement, while effectively employing GFRP in compression zones or in corrosive environments. Full article

Polylactic acid (PLA) is considered as an attractive polymer due to its renewable origin, biodegradability, and promising tensile strength and modulus. However, its inherent brittleness, characterized by a low impact resistance and elongation at break, can significantly restrict its application. This work proposes a new insight to improve the toughness of PLA while keeping its biocompatibility by incorporating two biocompatible ionic liquids (ILs), 1-ethyl-3-methylimidazolium ethyl sulfate ([emim][EtSO₄]), and tris(2-hydroxyethyl) methylammonium methylsulfate ([Tris][MeSO₄]). The modified PLA systems were thoroughly characterized to evaluate their mechanical and thermal behavior. Results demonstrated that the addition of 1 wt% of either IL resulted in significant improvement in modulus. Increasing the amount of IL resulted in an increase in the toughness while maintaining the material’s original stiffness and also the thermal stability. Furthermore, the foaming potential of the modified PLA using supercritical CO₂ was investigated as an environmentally friendly processing method. The ionic liquids contributed positively to the foamability of the material, suggesting improved gas solubility and cell nucleation during the foaming process. The addition of both IL decreased the cell size and resulted in narrower cell size distribution. These findings highlight the potential of ionic liquid-modified PLA systems for the processing of lightweight, and high-performance packaging materials. Full article

Diamond-like carbon (DLC) films exhibit superior tribological properties; however, their widespread adoption in precision manufacturing is hampered by inherent brittleness and a lack of reliable toughness characterization methods at the micrometer scale. This review critically examines existing techniques for evaluating DLC film toughness, highlighting limitations due to film thickness constraints and subjective failure definitions. We focus on two prominent micro-scale methods: impact testing and scratch testing. Impact toughness is assessed through energy absorption analysis based on impact crater morphology, including crack patterns and delamination areas. Scratch toughness is evaluated using critical loads (Lc₁, Lc₂) and the derived Crack Propagation Resistance (CPRS) parameter, complemented by microscopic failure analysis. We argue that neither method alone suffices for comprehensive toughness assessment. Instead, we propose a synergistic strategy integrating both techniques to provide a practical and comprehensive evaluation encompassing energy- and stress-based failure mechanisms under varying loading conditions. This approach offers a practical framework for developing tougher DLC coatings. Full article

Ordinary concrete exhibits inherent brittleness, which restricts its deformation capacity and durability under extreme loading conditions. Engineered cementitious composites (ECC) have been developed to address these limitations; however, conventional ECC often suffers from relatively low compressive strength, limiting its use in demanding structural applications. To overcome this drawback, high-strength ECC (HS-ECC) was prepared by incorporating high-volume mineral admixtures and three types of synthetic fibers-polypropylene (PP), polyethylene (PE), and polyvinyl alcohol (PVA). This study aimed to investigate the influence of fiber type and dosage on the flexural behavior of HS-ECC and to propose a toughness evaluation framework better suited to its strain-hardening characteristics. A comprehensive experimental program, including compressive and four-point bending tests, was conducted to evaluate failure modes, flexural performance, and post-cracking behavior. Results showed that PE fibers significantly enhanced flexural strength and toughness, PP fibers provided superior deformability at higher dosages, while PVA fibers tended to fracture due to strong matrix bonding, limiting their effectiveness in high-strength matrices. Based on the observed load–deflection responses, a physically meaningful flexural toughness evaluation method was developed, which reliably captured elastic, hardening, and softening stages of HS-ECC. The findings not only clarify the role of different fiber types in HS-ECC but also offer a new evaluation approach that can guide fiber selection and mix design for structural applications. Full article

Poly(L-lactide) (PLA) is a promising biopolymer for biomedical applications due to its biodegradability and biocompatibility; however, its brittleness restricts its use in fused deposition modeling (FDM). To overcome this limitation, flexible PLA monofilaments with enhanced mechanical performance and printability were developed. In this study, PLA was melt-blended with acetyl triethyl citrate (ATEC, 1.0–5.0 wt%) as a plasticizer and zinc phenyl phosphonate (TMC-200, 0.3 wt%) as a nucleating agent. It was found that the PLA with 3.0 wt% ATEC (PLA/A) exhibited the greatest flexibility, while the addition of TMC-200 further improved tensile strength and ductility. Specifically, the ternary blend of PLA/TMC-200/ATEC (PLA/T/A) exhibited a synergistic effect, achieving superior mechanical properties (tensile strength: 35.0 MPa, elongation at break: 232.0%, compared to 12.1% for pure PLA) and raising the degree of crystallinity (X_c) from 4.7% to 45.0%. Monofilaments (1.70 ± 0.05 mm) fabricated from PLA/T/A exhibited smooth surfaces, balanced mechanical performance, and excellent cytocompatibility (over 99% cell viability in L929 fibroblasts). Moreover, FDM-printed specimens retained enhanced mechanical and thermal performance, demonstrating material stability after processing. Shelf-life testing further confirmed the structural integrity of PLA/T/A monofilament after 8 weeks at 50 °C. Overall, PLA/T/A provides an effective strategy for producing high-performance, medical-grade PLA monofilaments with improved toughness, printability, and biocompatibility, enabling their application in biomedical 3D printing. Full article

This study explores the comparative evaluation of PLA, carbon fiber-reinforced PLA (PLA-CF), and carbon fiber-reinforced high-temperature polyamide (PAHT-CF) for use in Fused Deposition Modeling (FDM) additive manufacturing. These materials were selected to examine how carbon fiber (CF) reinforcement affects PLA and PAHT, using virgin PLA as the baseline. Mechanical and thermal properties were tested to assess the influence of reinforcement on strength, toughness, and heat transfer. Tensile, impact, and thermal conductivity tests were conducted on all three materials. The results showed that PAHT-CF outperformed both PLA and PLA-CF in all categories, achieving an ultimate tensile strength of 57.5 MPa, an impact strength of 14.30 kJ/m², and thermal conductivity of 0.182 W/m·K. PLA-CF showed moderate improvements in strength over neat PLA but with increased brittleness and slight improvement in thermal conductivity. Notably, this is the first study to investigate the thermal conductivity and resistivity of PAHT-CF in the literature, offering new insights into its heat dissipation capabilities and suitability for high-temperature applications. These findings highlight the critical role of polymer selection and fiber reinforcement in optimizing material performance. The results offer guidance for material selection in additive manufacturing, especially for lightweight, strong, and thermally efficient parts in various industries. Full article

Magnesium phosphate cement (MPC) has gained attention in specialized construction applications due to its rapid setting and high early strength, though its inherent brittleness limits structural performance. This study developed an innovative toughening strategy through synergistic reinforcement using hybrid fibers and carbon fiber-reinforced polymer (CFRP) fabric capable of multi-scale crack control. The experimental program systematically evaluated the hybrid fiber system, dosage, and CFRP positioning effects through mechanical testing of 7-day cured specimens. The results indicated that 3.5% fiber dosage optimized flexural–compressive balance (45% flexural gain with <20% compressive reduction), while CFRP integration at 19 mm displacement enhanced flexural capacity via multi-scale reinforcement. Fracture analysis revealed that the combined system increases post-cracking strength by 60% through coordinated crack bridging at micro (fiber) and macro (CFRP) scales. These findings elucidated the mechanisms by which fiber–CFRP interaction mitigates MPC’s brittleness through hierarchical crack control while maintaining its rapid hardening advantages. The study established quantitative design guidelines, showing the fiber composition of CF/WSF/CPS15 = 1/1/1 with 19 mm CFRP placement achieves optimal toughness–flexural balance (f_f/f_c > 0.38). The developed composite system reduced brittleness through effective crack suppression across scales, confirming its capability to transform fracture behavior from brittle to quasi-ductile. This work advances MPC’s engineering applicability by resolving its mechanical limitations through rationally designed composite systems, with particular relevance to rapid repair scenarios requiring both early strength and damage tolerance, expanding its potential in specialized construction where conventional cement proves inadequate. Full article

Fiber tow-gaps and overlaps formed during the Automated Fiber Placement (AFP) process pose a significant challenge by introducing non-uniform composite morphologies, often characterized by resin-rich regions and fiber waviness. These defects occur as deposited fibers sink into the gap regions during consolidation, with gap geometry determined during path planning. Such morphological inconsistencies can compromise structural reliability by initiating premature failure, particularly through localized out-of-plane waviness and resin accumulation. This study investigates the integration of high melting temperature thermoplastic veils, specifically polyetherimide (PEI), into fiber tow-gaps as a method to prevent ply sinking and reduce fiber waviness on both internal and external surfaces of the laminate. The PEI veils also serve to reinforce resin-rich regions by forming an interpenetrated network of high fracture toughness material within the brittle epoxy matrix. Tensile tests conducted on cross-ply laminates containing staggered gaps demonstrated that the inclusion of PEI veils modified the failure mode. The results suggest that the selective placement of thermoplastic veils within tow-gaps during AFP offers a viable strategy to mitigate manufacturing-induced non-uniform morphologies. Full article

It is known that geopolymer mortar exhibits high compressive strength but relatively low flexural strength, high brittleness, and poor toughness. Engineering practices for cement-based materials have demonstrated that incorporating fibers can effectively prevent the expansion of existing cracks and the formation of new ones in the materials. Adding polypropylene fibers to geopolymer mortar can, on the one hand, improve the crack resistance of the mortar, and on the other hand, enhance the impact resistance of the geopolymer mortar. In this paper, slag, metakaolin, and fly ash are utilized as silico-aluminous raw materials, standard sand is employed as aggregate, and a mixture of water glass and NaOH in a specific proportion is used as the alkali activator to prepare geopolymer mortar. Polypropylene fibers are incorporated to improve its mechanical properties. The effects of fiber length and mixing method on the mechanical properties of geopolymer mortar are studied to determine the optimal fiber length and mixing method. The mechanism of the mechanical properties of fiber-reinforced geopolymer mortar is analyzed by combining SEM. The research results indicate that the geopolymer mortar with 15 mm single-doped fibers exhibits the best flexural strength and toughness. In contrast, the geopolymer mortar with 12 mm single-doped fibers demonstrates the best compressive strength. The geopolymer with 9 mm and 18 mm hybrid-doped fibers has the best mechanical properties and is superior to the geopolymer mortar with single-doped fibers. Full article

In response to the issues of increased brittleness and insufficient toughness in microbially solidified saline sandy soils in cold and arid plateau regions, this study investigated saline sandy soils and indigenous microorganisms from the Qaidam Basin, Qinghai. A dual-reinforcement method combining microbial-induced calcium carbonate precipitation (MICP) with alkali-modified reed fiber (ARF) was proposed to enhance both strength and ductility. The study explored the adsorption characteristics and solidification mechanisms of this approach. Key innovations include: (1) alkali modification significantly improved the interfacial bonding between reed fibers and sand particles, with pull-out tests indicating a 1.24-fold increase in adhesion strength; (2) an orthogonal experimental design identified optimal parameters—fiber length of 15 mm, fiber content of 0.5%, and cementation solution concentration of 3 mol/L—leading to the development of a synergistic “microbial cementation–fiber bridging” enhancement model. Experimental results showed that the proposed method increased the unconfined compressive strength (UCS) of the solidified soil to 2082.85 kPa, 2.99 times higher than that of traditional MICP-treated soil, while it significantly enhanced the ductility of the soil. This approach offers a mechanically robust and environmentally adaptive solution within the ambient temperature range of 0–35 °C for the ecological restoration of saline soils in high-altitude regions. Full article

This study examines how diabetes mellitus and physiological aging influence the nanomechanical behavior of rat rib cortical bone using combined static and dynamic nanoindentation. Ribs from young control, old, and streptozotocin-induced diabetic rats were analyzed to quantify both intrinsic and frequency-dependent mechanical properties. Static nanoindentation revealed markedly higher hardness and elastic modulus in the diabetic group (0.47 ± 0.22 GPa and 9.53 ± 3.03 GPa, respectively) compared to controls (0.11 ± 0.03 GPa and 3.21 ± 0.51 GPa; p < 0.001). The modulus-to-hardness ratio, an indicator of fracture toughness, was reduced from 30.34 in controls to 20.45 in diabetics, suggesting increased stiffness but greater brittleness. Dynamic nanoindentation (0–4.5 Hz) demonstrated significant aging-related changes in the storage and loss moduli (p < 0.001), while the loss factor (tan δ < 1) and viscosity remained similar across groups, indicating predominantly solid-like behavior. These results show that diabetes stiffens bone tissue through matrix-level alterations, whereas aging primarily affects its viscoelastic damping capacity. The combined static–dynamic nanoindentation protocol provides a robust framework for distinguishing disease- and age-related bone degradation at the tissue scale. Translationally, the findings help explain why bones in diabetic or elderly individuals may fracture despite normal mineral density, underscoring the need to assess bone quality beyond conventional densitometry. Full article

Sapphire crystals, owing to their outstanding mechanical and optical properties, which are widely used in advanced optics, microelectronic devices, and medical instruments. The manufacturing precision of sapphire optical components critically affects the performance of advanced optical systems. However, the extremely high hardness and low fracture toughness of sapphire make it a typical hard-to-machine material, prone to brittle surface fractures and subsurface damage during material removal. Improving the machinability of sapphire remains a pressing challenge in advanced manufacturing. In this study, surface modification and enhanced ductility of C-plane sapphire were achieved via ion implantation, and the machinability of the modified sapphire was further improved through laser-assisted diamond machining (LADM). Monte Carlo simulations were employed to investigate the interaction mechanisms between incident ions and the target material. Based on the simulation results, phosphorus ion implantation experiments were conducted, and transmission electron microscopy observation was used to characterize the microstructural evolution of the modified layer, while the optical properties of the samples before and after modification were analyzed. Finally, groove cutting experiments verified the enhancement in ductile machinability of the modified sapphire under LADM. At a laser power of 16 W, the ductile–brittle transition depth of the modified sapphire increased to 450.67 nm, representing a 51.57% improvement over conventional cutting. The findings of this study provide valuable insights for improving the ductile machining performance of hard and brittle materials. Full article

This study investigates the effect of hydrogen embrittlement on the fracture toughness of 9% Ni steel and STS 316L stainless steel under cryogenic conditions ranging from −80 °C to −253 °C. Hydrogen charging was performed using electrochemical methods, and hydrogen uptake was quantitatively analyzed using thermal desorption spectroscopy (TDS). Fracture toughness was evaluated using crack tip opening displacement (CTOD) testing per ISO 12135, both without hydrogen (WO-H) and with hydrogen (W-H). The results showed a gradual decrease in CTOD values with decreasing temperature in both steels under hydrogen-free conditions, with ductile fracture maintained even at −253 °C. In contrast, hydrogen-charged specimens exhibited significant toughness degradation at intermediate subzero temperatures (−80 °C to −130 °C), particularly in 9% Ni steel due to its BCC crystal structure. However, at −160 °C and below, the effect of hydrogen embrittlement was suppressed mainly owing to the reduced hydrogen diffusivity. Scanning electron microscopy (SEM) analysis confirmed the transition from ductile to brittle fracture with decreasing temperature and hydrogen influences. At −253 °C, fully brittle fracture surfaces were observed in all specimens, confirming that at ultra-low temperatures, fracture behavior is dominated by temperature effects rather than hydrogen. These findings identify a practical temperature limit (approximately −160 °C) below which hydrogen embrittlement becomes negligible, providing critical insights for the design and application of structural materials in hydrogen cryogenic environments. Full article

This paper contributes to the knowledge of binderless tungsten carbide (WC), which attracts the attention of many engineers and scientists for its superior properties, but its application is limited due to difficulties with the consolidation of initial powders. In the present study, the microstructure and mechanical properties of binderless WC, sintered with the electroconsolidation technique from the initial powder of a grain size of 100–200 nm, were investigated. The material was compared with nWC sintered with the same method from a nanopowder with particles of size ca. 70 nm. The binderless μWC demonstrated hardness of HV = 30.06 ± 0.09 GPa, which is almost 14% higher than that of nWC, but its fracture toughness was lower (K_IC = 6.59 ± 0.46 MPa·m^1/2 under 1 kg load). These differences can be attributed to the improved homogeneity of the μWC microstructure, where no large agglomerates appeared to be present in nWC. The measured plastic properties, with no signs of brittle fracture, further confirm the applicability of the binderless WC under contact stress conditions. Full article

To address the bottleneck issues of traditional concrete T-beams, such as excessive self-weight, susceptibility to cracking, and insufficient durability, this study investigates the flexural performance of Ultra-High-Performance Concrete (UHPC) T-beams. Through systematic experiments, the combined effects of three UHPC material ratios and three rebar schemes were analyzed. Six UHPC T-beam specimens were designed, and flexural performance tests were conducted using a staged loading approach, focusing on crack propagation, failure modes, and load-deflection curves to reveal their mechanical behavior and failure mechanisms. The results indicate that steel fibers significantly enhance UHPC toughness. At a fiber content of 1.5%, the specimens exhibited a yield load of 395–418 kN, with an ultimate load increase of 93% compared to the fiber-free specimens. The failure mode transitioned from brittle shear to ductile flexural. Increasing the rebar ratio improved load-bearing capacity, with a 4.58% rebar ratio yielding an ultimate load of 543 kN (51% higher than B1-02), but reduced ductility by 36%. Steel fibers restricted crack widths to 0.1 mm via crack-bridging effects, raising the cracking load by 53% and the shear capacity by 2.8 times. UHPC mix ratio adjustments had a limited impact on beam performance at the same fiber content. Overall, UHPC T-beams exhibited a compressive concrete crushing-dominated failure mode, with load-deflection curves showing a 42% gentler slope than conventional concrete. The ductility coefficient ranged from 3.8 to 5.2. For engineering applications, it is recommended to maintain a steel fiber content of at least 1.5% and a rebar ratio of 2.5–4.0% to strike a balance between strength and ductility. Full article