Papers by Keyword: Ductility

Abstract: The application of high-strength prestressing steel represents a major step forward in the field of concrete structure design and construction. Prestressing steel with a tensile strength exceeding 1860 MPa enables more effective prestressing of structural elements, which in turn results in a substantial reduction in the required amount of reinforcement. At the same time, it allows for the design of more slender, lighter, and structurally optimized members. Due to these characteristics, this type of reinforcement finds wide application particularly in bridge engineering, prefabricated systems, high-rise buildings, and long-span structures. The paper focuses on analysing the principal advantages of employing high-strength prestressing reinforcement with regard to both structural behaviour and construction economy. From the structural design perspective, the main benefits include an increase in load-bearing capacity and a reduction of deformations, even when using smaller cross-sectional dimensions. From the economic viewpoint, advantages are primarily linked to reduced material consumption, lower self-weight of prefabricated elements, and significant cost savings in transport and erection. The concluding part of the paper addresses the anticipated direction of further development in high-strength materials, with particular emphasis on the possibilities of design optimization through nonlinear computational methods. High-strength prestressing reinforcement thus constitutes a promising means of improving the efficiency and sustainability of modern concrete structure design. The study provides a comprehensive summary of the main benefits of this technology, points out practical and design-related limitations, and indicates future development trends consistent with the objectives of sustainable and cost-effective construction.

Abstract: Advanced high-strength steels exhibit sensitivity to diffusible hydrogen content, mainly observed during tensile testing. Although the initial yield stress and ultimate tensile strength are not significantly affected, ductility decreases with increasing hydrogen content. This sensitivity to diffusible hydrogen depends on strain rate and stress concentrations. This study examines the influence of diffusible hydrogen content on the ductile fracture of DP780GI steel, in the form of 1 mm thick sheets. Samples were prepared with specific geometries, with notches and holes, to study different mechanical states, and fracture tests were performed to evaluate ductility as a function of hydrogen content and stress triaxiality. The local strain rate was around 1 × 10−4 s−1, which is lower than the value used in industrial applications, to enhance the hydrogen sensitivity. A hydrogen charging process was used, including zinc coating removal, electrochemical loading, and electrolytic deposition of a zinc layer to prevent hydrogen desorption. The hydrogen content was measured by thermal desorption analysis after the mechanical testing. It is observed that the maximum local elongation decreases with increasing hydrogen content, with a noticeable effect above 0.25 ppm. Cracks form in areas of maximum effective deformation, and their location varies depending on the geometry of the sample and the hydrogen content. The evolution of the maximum effective strain before fracture shows a significant decrease in ductility with increasing hydrogen content, regardless of the mechanical state.

Abstract: The growing use of extruded aluminum components in vehicle structures necessitates both strength and ductility to meet energy absorption requirements. In this study, a new compression calibration method for multi-chamber, hollow sections was developed with the aim of improving dimensional accuracy while enhancing the ductility of AA6061 extruded profiles. The influence of this method on mechanical properties was investigated through uniaxial tensile tests, three-point VDA bending tests, and axial crush tests. The uniaxial tensile test results revealed a reduction in the (logarithmic) strain at necking, while no significant changes were observed in yield and ultimate tensile strengths. On the other hand, the VDA tests showed a systematic increase in the normalized bending angle, indicating improved energy absorption characteristics. Visual inspection and the absorbed energy obtained by axial crush tests supported the findings in the VDA tests, indicating the compression calibration method enhances the crushability of extruded AA6061 profiles, although this improvement is not identified in standard tensile data. Overall, this work introduces a new, industrial calibration method for hollow extrusions that also enhances crushability.

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: Aluminium alloys are widely used in the automotive and aerospace industries, where permanent fastening methods are commonly employed to join aluminium sheets and components. Many aluminium alloys are known for their high strength-to-weight ratio, while others are favoured for their availability and cost-effectiveness. In modern applications, dissimilar aluminium alloys are often joined to achieve enhanced performance. This study explored the effects of artificial aging on the microstructural and mechanical properties of weld joints at varying temperatures. Significant microstructural differences were observed between the heat-affected zone (HAZ) and the weld zone (WZ). Coarse grains in the HAZ enhanced ductility, while the fine-grained structure and increased precipitate formation in the WZ improved strength but reduced ductility. Aging at 165°C induced notable changes, with precipitate formation causing a 30% reduction in elongation and a 3.6% increase in ultimate tensile strength (UTS), attributed to precipitation hardening and improved bonding. At 175°C, mechanical properties further improved, with a 16% increase in yield strength (YS) and up to a 7.7% rise in UTS. The higher temperature facilitated greater precipitate formation, as confirmed by microstructural analysis, enhancing joint strength. However, this improvement came at the cost of ductility, with a 39.3% reduction in elongation due to restricted dislocation movement caused by the precipitates. Thermal conductivity variations in the welded plates influenced heat distribution and precipitate formation during aging. The process also reduced residual stresses from welding, enhancing diffusion and metallic bonding. Overall, artificial aging improved strength and stiffness but significantly decreased ductility, with aging at 175°C yielding optimal mechanical performance despite the trade-off in ductility.

Abstract: Traditionally, reinforced concrete structures are constructed using steel rebars as reinforcement which is more susceptible to reinforcement corrosion in severe exposure conditions. This leads to many disadvantages, like deterioration of concrete, reduction in strength, and increase in maintenance costs, which leads to a decrease in the serviceability of critical infrastructure. Fiber Reinforced Polymer bars are often used as alternative materials for steel bars because they are anti-corrosive, exhibit an excellent strength-to-weight ratio and are easy to handle but the main disadvantage is its brittle nature. Hence, the combination of steel and FRP bars was effectively used to augment both flexural capacity and ductility. As the ductility performance of hybrid Reinforcement is lower than conventional reinforced beams, Polyvinyl Alcohol Fibers in volume fraction were added in this investigation. The present investigation aims to determine the flexural capacity of reinforced concrete beams using Glass Fiber Reinforced Polymer (GFRP) bars and Steel bars. The optimum dosage of PVA fibers while evaluating compressive and split tensile strength is observed at 0.25% in volume fraction. Total six types of concrete beam specimens with and without PVA fibers were experimentally under four-point bending test tested such as beams reinforced with only steel bars, only GFRP bars, GFRP and steel bars. From the experimental results, it is observed that inclusion of PVA fibers in proposed beams with hybrid reinforcement enhanced the crack resistance by 80% and ultimate load capacity by 39% when compared with conventional beam.

Abstract: Tall buildings require slender shear walls as fundamental structural elements since the structure’s performance and safety depend on the walls' capacity to bear lateral loads while retaining their ductility. Concrete that has short fibers, like those made of steel or glass is known as fiber concrete. By increasing the ductility of concrete, these fibers can increase its resistance to brittle shear failure. This work aimed to investigate the effects of fiber concrete on thin shear wall ductility. The ductility of fiber concrete shear walls is significantly higher than that of typical concrete shear walls, according to tests conducted on thin shear walls made of both types of concrete. This occurred because of the fibers in the fiber concrete filling up the cracks and stopping them from getting worse. It has been stated that fiber concrete can be utilized as a building material in a variety of ways after being treated. Its application to cylinder shear walls has not been documented solely, though. Therefore, a thorough assessment of the literature regarding the potential of steel fiber concrete for the prevention of shear cracks. The optimal choice for fiber concrete in this application is characterized by a high fiber aspect ratio and a minimum fiber volume fraction of 1%, with steel fiber concrete being highly recommended. The study's findings imply that slender shear walls' ductility can be increased and their resistance to brittle shear failure increased by using steel fiber concrete.

Abstract: Traditionally, reinforced concrete structures are constructed using steel rebars as reinforcement which is more susceptible to reinforcement corrosion in severe exposure conditions. This leads to many disadvantages, like deterioration of concrete, reduction in strength, and increase in maintenance costs, which leads to a decrease in the serviceability of critical infrastructure. Fiber Reinforced Polymer bars are often used as alternative materials for steel bars because they are anti-corrosive, exhibit an excellent strength-to-weight ratio and are easy to handle but the main disadvantage is its brittle nature. Hence, the combination of steel and FRP bars was effectively used to augment both flexural capacity and ductility. As the ductility performance of hybrid Reinforcement is lower than conventional reinforced beams, Polyvinyl Alcohol Fibers in volume fraction were added in this investigation.The present investigation aims to determine the flexural capacity of reinforced concrete beams using Glass Fiber Reinforced Polymer (GFRP) bars and Steel bars. The optimum dosage of PVA fibers while evaluating compressive and split tensile strength is observed at 0.25% in volume fraction. Total six types of concrete beam specimens with and without PVA fibers were experimentally under four-point bending test tested such as beams reinforced with only steel bars, only GFRP bars, GFRP and steel bars. From the experimental results, it is observed that inclusion of PVA fibers in proposed beams with hybrid reinforcement enhanced the crack resistance by 80% and ultimate load capacity by 39% when compared with conventional beam.

Abstract: In this article, the effect of TiC nanopowder particles on the wear resistance of low-alloy steel 35XGCL (analog is JIS G 5111) is mathematically modeled. First of all, the composition for liquefaction in an electric arc furnace was calculated. 5 and 10% TiC nanopowder particles were added to the alloy as a modifier before pouring liquid metal into the ladle. This process was performed before pouring the liquid metal from the furnace into the ladle. 15% of TiC was added in the furnace as a modifier. Lagrangian interpolation polynomial construction was used in this modeling. The amount of wear resistance was calculated by polynomial expression of the function with determination of unknown coefficients. The results obtained on the basis of the developed model were compared with case studies. The results of the analysis are shown by graphs.

Abstract: Carbon and glass fabric reinforced polymer (C/GFRP) composites are extensively used in aerospace and sports industry because of their exceptional properties. However, during service, static and dynamic bending loads can ensue damage in composites affecting their strength, stiffness and energy absorption. Carbon fiber composites, being inherently brittle, are prone to sudden catastrophic fracture without ductile-like behavior of metals. This study investigates mechanical behavior and damage mechanisms of woven C/GFRP composites in on- and off-axis orientations during bending. Initially, bending tests with quasi-static loading were performed, followed by dynamic ones using an Izod impact testing apparatus. Results showed distinct behavior in on-axis CFRP laminates with brittle fracture. Off-axis CFRP samples and both on- and off-axis GFRP laminates showed signs of damage and non-linear behavior, yet they retained their ability to bear loads. Significantly, off-axis specimens of both types and on-axis GFRP laminates exhibited enhanced energy absorption capabilities without experiencing fracture, undergoing pseudo-ductile deformation. CFRP specimens were analyzed with micro-computed tomography (micro-CT), provided insights into prevalent damage modes such as matrix mircocracking, debonding of tows, delamination and breakage of fabric. While on-axis CFRP laminates experienced brittle fracture, off-axis specimens exhibited a ductile-like response attributed to matrix plasticity, cracking and fiber trellising before eventual failure.