Papers by Keyword: Toughness

Abstract: Ultra-high-performance fiber-reinforced concrete (UHPFRC) exhibits outstanding compressive strength but tends to fail in a brittle manner under flexural loading when fibers are absent. This study evaluates the effectiveness of recycled tire steel fibers (RTSF) in improving the flexural strength, ductility, and toughness of UHPFRC beams. Thirty six doubly reinforced beams were cast and tested under three-point bending with reinforcement ratios of 0.009, 0.019, 0.028, and 0.043. The specimens were grouped as non-fiber control, mono RTSF (13 mm, 1.5% by volume), and hybrid RTSF (13 mm at 1.5% + 16 mm at 1.5%). Load deflection and stress strain responses were analyzed to assess structural performance. Beams without fibers failed abruptly, whereas those reinforced with RTSF demonstrated significantly greater ductility and energy absorption. The mono-fiber beams achieved a peak load of 264.46 kN, while the hybrid fiber beams attained a peak stress of 128.66 N/mm², 29% and 23% higher than those of the mono and non-fiber beams, respectively. These results confirm that incorporating RTSF, particularly in hybrid form, effectively mitigates brittle failure in UHPFRC and provides a sustainable, locally sourced solution for achieving superior strength, ductility, and toughness.

Abstract: The utilization of Fiber Reinforced Concrete (FRC) as a structural material is steadily on the rise. Conventional concrete is characterized by its brittleness, displaying a flexural strength that falls within the range of 10-15% of its compressive strength. Incorporation of fibers into concrete enhances various mechanical properties, including tensile strength, flexural strength, and ductility. An advantageous feature of FRC is its capacity to consider cracked concrete below the neutral axis in the cross-section of a beam to some extent. Important factors influencing the flexural strengths of both Plain Concrete (PC) and FRC include the modulus of rupture, corresponding deflection, toughness index, energy absorption, and density. This results in a diminished requirement for additional reinforcement in beams. The modified stress-strain diagram proposed by Bashara proves valuable in integrating the effect of FRC on the tension side, an aspect previously neglected due to the inherent weakness of PC in tension. The ongoing literature review seeks to comprehensively explore the potential of fiber-reinforced concrete in beams situated below the neutral axis, concentrating on articles published in highly reputable journals over the past decade.

Abstract: This study investigated the evolution of microstructure, hardness, and toughness in nodular cast iron following quenching and tempering at 450°C. The research explored how the heat treatment process impacts these mechanical properties, to identify an optimal balance between hardness and toughness. Untreated nodular cast iron displayed a microstructure comprising ferrite, pearlite, and spheroidal graphite, resulting in moderate hardness (24.33 HRC) and toughness (0.082 J/mm²). Quenching at 850°C, followed by rapid cooling in water, induced the formation of martensite, a hard and brittle phase, which significantly increased hardness to 56.73 HRC but decreased toughness to 0.068 J/mm². Tempering at 450°C transformed the martensite into tempered martensite, reducing hardness to 41.37 HRC while improving toughness to 0.11 J/mm². These findings highlighted the importance of tempering in achieving a better balance between hardness and toughness, making the material suitable for industrial applications requiring both wear resistance and impact durability. The results offered valuable insights for optimizing heat treatment procedures to enhance the performance and durability of nodular cast iron components in various industries.

Abstract: 3D printing has been on the rise in recent times and the civil engineering industry has adopted this technology due to its various advantages. However, printing is largely restricted to concrete members while the reinforcement is introduced manually. The current work looks at the possibility of using 3D printed thermoplastics as formwork and reinforcement for concrete beams. Three different polymeric materials, namely PETG, PLA, and TPU were utilized in this research to fabricate formwork-like reinforcement for 150×150×500 mm concrete beams. The reinforcements were 3D-printed using a fused deposition modelling (FDM) printer in the shape of a formwork to serve as moulds and external reinforcement. The reinforcing formwork geometry was designed with trapezoidal corrugations to ensure strong bonding with the concrete. The beams were tested in four-point bending configuration, and their flexural behaviour was characterized and compared with plain and steel reinforced concrete (RC) reference beams. Results indicate that all 3D printed beams reached a load capacity of around 30 kN. The post-peak behaviour of these beams was dependent on the type of polymer used. The PLA and TPU reinforced beams exhibit large post-peak deflection however their load carrying capacity was compromised, while the PETG exhibited a strain hardening behaviour but with much lower deflections. Overall, the results indicate that 3D-printed thermoplastics are a promising economical alternative to the conventional steel reinforcement.

Abstract: The effects of Mo and V on impact toughness in martensitic steels tempered at low temperatures were investigated using three low-alloy medium-C steels. Previous examination of these alloys had identified differences in impact toughness without a clear cause. In this work, the Base alloy with a reduced Mo addition experienced a significant loss in hardenability leading to the formation of small fractions of bainite during quenching even at relatively high quench rates. The use of different quench media to simulate cooling rates throughout a heavy section demonstrated that the variation in previously reported Charpy V-notch impact absorbed energies was readily explained by some regions cooling fast enough to avoid bainite while others formed some small fraction of upper bainite leading to increased cleavage fracture and decreased impact toughness. Small amounts of bainite transformation were not detected by dilatometry or tensile properties. These results emphasize the importance of effective through-hardening and careful microstructure evaluation in alloys that are meant to maintain good toughness and strength in thicker sections.

Abstract: As a new trend in modern structural design, the high-performance steels are increasingly used in steel structures, due to their superior mechanical properties, which could have decisive impact on the resistance and deformation capacity of structural components. High-performance steels include stainless and high-strength steels. The higher proof stress of the high-strength steels allows using thinner sections and material economy for those structural elements that do not experience stability problems. Austenitic stainless steel shows a series of advantages, including low maintenance costs and an excellent toughness at low temperatures. But the main characteristic which matters especially in seismic design, is the higher ductility, larger strain hardening and elongation at fracture in comparison with carbon steels. In this paper, the analysis of the behaviour of 1.4404 austenitic stainless steel and of S690 high-strength steel, in comparison with a reference S235 mild carbon steel is presented. This paper presents the assessment of the monotonic and cyclic performance of these steel grades, as well as the failure pattern, in order to assess the potential use in structural applications.

Abstract: This research work aims to perform a comparative study on the effect of fiber orientation distribution (FOD) on the mechanical properties of composite laminates for aircraft and automobile structure. The objective of this project works is to use an analysis method to study the effect of significant parameters namely, with and without orientation on the glass fibre epoxy composites. The experimental work is used to investigate the mechanical behavior and to examine the properties with respect to fibre orientation on the composite laminates. The glass fibre orientation characteristics for the composite laminates is considered since they affect the strength of the specimen laminates. In this connection, the specimens were fabricated with different orientations and undergone for mechanical testing like tensile, compression and impact tests with Data Acquisition System. The experimental results indicate that the specimens with orientation provide more strength, high stiffness and good toughness than the normal specimens without orientation.

Abstract: API 5L Grade B steel pipe used for the oil and gas industries must meet toughness requirement of higher than 27 Joule and hardness value of lower than 248 HV. The welding process during piping installation sometimes generates lower toughness. Thus additional heat treatment was necessary to recover their superior toughness. Quenching from 900 °C into water or oil medium followed by tempering at 550 °C, 600 °C and 650 °C for 1 hour was selected in this study. Charpy impact test was used to access their toughness data, while the hardness was measured using micro Vickers hardness. It was found that the highest toughness of 168 Joule with a hardness of 166 HV_1.0 was generated in the welding zone after water quenching followed by tempering at 600 °C treatment. The metallographic investigation reveals fully martensite tempered microstructures. These acquired toughness and hardness values were in accordance with API 5L pipe standard requirements.

Abstract: Steel alloys with high Mn and low C, low Cr wt.%, were designed based on the composition system for traditional high toughness, creep resistance, and longevity for high-temperature applications. In terms of energy resource utilization during production and refining, CALPHAD strategical optimization is preferable for all steel alloys. Thermo-Calc software calculates the phase diagrams α-BCC (Ferrite), and M₂₃C₆ (carbide) phases. The vital temperatures which are highlighted in this work are Ac₃ (threshold temperature at which ferrite is fully transformed into austenite (α→γ)), and A₄ (the threshold temperature at which austenite is fully transformed into Delta ferrite (γ→δ)) are essential for phase transformations. JMatPro software is used to predict the mechanical properties of steel alloys. The interfacial energies with regards to alloying elements for M₂₃C₆ are calculated to be between ~0.272 J/m^-2 to ~0.328 J/m^-2 for α-BCC) matrix, while γ-FCC has interfacial energy ranges to be between ~0.132 J/m^-2 to ~0.168 J/m^-2. This paper focuses on investigating the effect of alloying elements on phase transformations, interfacial energy, coarsening rate of carbides, and many other mechanical properties such as toughness at high-temperature applications using CALPHAD strategies.

Abstract: The main objective of this study was to investigate the influence of using magnetized water on the mechanical properties and durability behavior in terms of freeze-thaw resistance of recycled aggregate concrete. In addition to the effect of different numbers of water rounds in the magnetic field, other variables including steel fibers, super-plasticizers and silica-fume were considered in the concrete production in order to achieve the ideal possible performance for recycled aggregate concrete made with 100% coarse aggregates replacements. For this purpose, a total of 11 concrete mixes were prepared and tested. At the first step, the effects of the mentioned variables on the basic properties, including workability, water absorption, compressive strength, splitting tensile strength, flexural strength and freeze-thaw durability test were investigated. Additionally, flexural toughness was evaluated in accordance with the post-crack strength (PCS) method and the microstructure of concrete specimens was also observed by using scanning electron microscope (SEM). The results of most experiments indicated that magnetized water, although highly effective on the mechanical properties of concrete, should not be solely utilized as a compensating factor for the defects caused by recycled coarse aggregates. The optimum toughness and durability results regarding the fiber-reinforced concrete mixes produced with recycled coarse aggregates, were related to samples containing silica-fume and 10-rounds magnetized water. Furthermore, the existence of cement replaced by 10% of silica-fume and 10-rounds magnetized water in the concrete mix MW-SF2, increased the durability of the recycled aggregate concrete by an average of approximately 63%.