Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Experimental and numerical investigation the effect of concrete strength and area of steel reinforcement on mechanical performance of functionally graded reinforced concrete beams
No full textIn this work, an experimental and numerical program was designed to evaluate the role of compressive strength, Fc, and area of reinforcing steel, As, on the flexural behavior of functionally graded reinforced concrete beams. Eighteen layered sections of reinforced concrete beams were tested with different compressive strengths arrangement and area of main steel. The result showed that the minimum steel reinforcement with higher compressive strength in the compression zone increases load capacity and ductility. The average steel reinforcement with higher strength in the compression zone increases load capacity and decreases ductility. The results also approved that; higher strength in the compression zone can be used in beams with a high tensile steel ratio for decreasing compression steel as an economic side. 3D finite element was executed using ABAQUS to simulate experimental beams. The numerical result showed variation from the experimental but still, the behavior of numerical beams is the same as the experimental
Behavior of Zr–1Nb alloy in coarse- and ultrafine-grain states under laser-induced shock wave loading
Get PDFThe work is devoted to the study of the Zr-1Nb alloy in coarse-grained and ultrafine-grained states under laser-induced shock-wave loading. This material is of interest due to the application for the manufacture of shells for fuel elements of nuclear reactors. The properties of this alloy in the ultrafine-grained state is attracted for the reliability improvement of fuel rods in wide range of load intensity. Shock wave loading was carried out using a Beamtech SGR-Extra-10 high-energy nanosecond laser. The free surface velocity profiles were registered by the VISAR system. Mechanical characteristics are obtained using velocity profiles. It is shown that the spall strength and dynamic elastic limit for the coarse-grained state are higher than for the ultrafine-grained state. In general, the Zr-1Nb alloy in the ultrafine-grained state is more susceptible to spall fracture, including laser shock peening. Numerical simulation of the process under study has been carried out using statistically based nonlinear model of solid with defects and finite element method to describe the deformation behavior and fracture of the material under shock-wave loading. Simulation results are qualitatively consistent with experiments in the prediction of the conditions of spall failure
The effect of beam width and crack-depth ratio on mode I fracture toughness of RCB: an experimental and numerical study
Get PDFIn the present work, the fracture performance of pre-cracked reinforced concrete beams was investigated numerically and experimentally. Experimental and numerical programs were designed to examine the effect of beam width, b, (120 and 250 mm) and crack-to-depth ratio, a/d, (0.1, 0.2 and 0.3) for concrete strength, fc, (40 MPa), on the behavior of stress intensity factor, K1C, and fracture energy, G, for reinforced concrete, RC, beams. The work utilized beams with three-point loading conditions experimentally. Through the use of the ANSYS program, a comprehensive 3-D finite element analysis was conducted with utmost precision to simulate and idealize all experimental specimens. It has been confirmed through numerical and experimental outcomes that the stress intensity factor for RC concrete beams experiences a significant increase as the a/d increases. Furthermore, the fracture toughness values in this study show a slight increase due to the utilization of RC concrete beams with wider width. The validity of the presented concept was demonstrated by comparing the experimentally measured load vs. deflection values to the predicted numerical values and finding them to be acceptable
Experimental work of effect of openings on the post-tensioned flat slab
Get PDFThis study aims to evaluate the effect of various parameters on the behavior of the reinforced concrete flat slabs and the contribution of each design element in the punching shear strength. This research presents experimental results of tested post-tensioned flat slabs with opening under concentric compressive load. The developed post-tensioned flat slabs are to ensure adequate punching shear strength capacity. The experimental work consisted of eight specimens of post-tensioned reinforced concrete flat slabs which classified into groups. All slabs had the same dimension and reinforcement. The slabs had dimensions with a 1750 mm length and 1750 mm width, to study the behavior of post-tensioned flat slab with/out openings under the concentrated load and punching influence
Experimental and numerical investigations of the flexural behaviour of Green - Ultra High Performance Fiber Reinforced Concrete beams under repeated loads
Get PDFThere are various benefits to ultra-high-performance fiber-reinforced concrete (UHPFRC). However, using a lot of cement in this type of concrete has a severe disadvantage since it causes pollution and several environmental concerns. Therefore, another type of concrete that achieves the same superior properties as UHPFRC while using less cement in the mixture should be considered. This research examined replacing cement with fly ash to produce environmentally friendly concrete called Green-UHPFRC. The impact of utilizing G-UHPFRC on the flexural behaviour of thirteen beams was investigated experimentally and numerically under repeated loads. The major parameters of the study were fly ash replacement ratios of 15%, 30%, and 45% and adding steel fiber to mixes with ratios of 1, 2, 3, and 4%. The tested beams were compared to the control beam in their backbone and hysteresis curves, failure load, crack propagation and failure modes, energy dissipation, stiffness degradation, and ductility index. From the results obtained, environmentally friendly concrete (G-UHPFRC) can be produced by replacing cement with fly ash up to 45% and adding 2% steel fiber without affecting the bending performance of beams made of G-UHPFRC compared to those made of UHPFRC
Degradation of the first frequency of an RC frame with damage levels
Get PDFDamage in RC structures causes the degradation of stiffness and frequency parameters. In this study, the relationship between the two coefficients and damage severities is numerically investigated considering a three-dimensional (3D) reinforced concrete (RC) frame in which the concrete damage plasticity model (CDPM) and the elastoplastic model are selected to define concrete and reinforcement materials, respectively. Crack propagation of the frame is obtained utilizing a nonlinear static pushover analysis (NSPA). After the pushing procedure, according to the base shear force versus top displacement curve, the bending stiffness of the RC structure is determined rapidly. Thereafter, the degradation of the first frequency is obtained based directly on the nonlinear curve of stiffness. As a result, it is observed that the degradation of the first frequency of the RC frame is proportional to the severity of damage but not linearly. More significant damage, a more profound decrease in the modal characteristic. Particularly, the fundamental frequency of the RC frame reduces gradually until the base shear force reaches 70% of the ultimate value at which the parameter is about 60% of the counterpart at the intact stage. After that, the reduction gets more significant when the bending capacity approaches the ultimate value
Failure Analysis of Boron Steel Components for Automotive Applications
Get PDFThe automotive industry is continuously looking for an innovative mix of new steels and manufacturing techniques in order to improve process chain efficiency and cost reduction. To this aim, boron steels are becoming increasingly popular thanks to their high hardenability and machinability. Due to their reduced finishing steps, boron steels are commonly processed using fine blanking technologies.
The success of fine blanking on boron steel components is due to heat treatments which must be carefully designed to avoid precipitation of boron-rich compounds that would lower steel hardenability. At high temperature, boron is very reactive with oxygen and nitrogen.
The main focus of this paper is to show some drawbacks that can occur during heat treatments of automotive components. An experimental campaign was performed on two different boron steels, namely EN 34MnB5 and EN 22MnB5. The steel samples were previously spheroidized annealed in a neutral environment (hydrogen/nitrogen atmosphere), and then fine blanked to obtain specific automotive components which were subsequently quenched and tempered. Experimental tests revealed precipitation of nanometric compounds, causing strong grain refinement and localized decrease of steel hardenability. Hardenability problems were brought back to nitrogen pick-up during initial spheroidize annealing treatments
Fatigue assessment of a FSAE car rear upright by a closed form solution of the critical plane method
Get PDFMaterial fatigue is extensively discussed and researched within scientific and industrial communities. Fatigue damage poses a significant challenge for both metallic and non-metallic components, often resulting in unexpected failures of in-service parts. Within multiaxial fatigue assessment, critical plane methods have gained importance due to their ability to characterize a component's critical location and detect early crack propagation. However, the conventional approach to calculate critical plane factors is time-consuming, making it primarily suitable for research purposes or when critical regions are already known. In many real-world scenarios, identifying the critical area of a component is difficult due to complex geometries, varying loads, or time limitations. This challenge becomes particularly crucial after topological optimization of components and in the context of lightweight design. Recently, the authors proposed an efficient method for evaluating critical plane factors in closed form, applicable to all cases that necessitate the maximization of specific parameters based on stress and strain components or their combination. This paper presents and validates the proposed methodology, with reference to a rear upright of a FSAE car, which is characterized by a complex geometry and is subjected to non-proportional loading conditions. The efficient algorithm demonstrated a substantial reduction in computation time compared to the standard plane scanning method, while maintaining solution accuracy
Microstructure Characterization, Mechanical and Wear Behavior of Silicon Carbide and Neem Leaf Powder Reinforced AL7075 Alloy hybrid MMC’s.
Get PDFThe demanding material quality criteria in the automotive and aerospace industries have recently had an impact on the development of lightweight aluminium alloys. The choice and application of metal-matrix composites as structural materials in this context are known to offer a variety of benefits. These benefits include the ability to combine high elastic modulus, toughness, and impact resistance; minimum sensitivity to change in temperature or thermal shock; durability of the surface is good; moisture absorption leads to the potential issue while minimum exposure which leads to environmental degradation; and improved fabricability with conventional metalworking equipment. Aluminium metal matrix composites (AMMCs) are a potential material for advanced structural, aviation, aerospace, marine, and defence applications, as well as for the automotive sector and other related fields, due to their outstanding combination of qualities. The stir casting procedure is used to create an aluminium metal matrix composite (AMMC), which is the most efficient way to do so. In this study, the aluminium alloy 7075 is strengthened using neem leaf powder and SiC. The Vickers hardness examination method is used to govern the hardness of hybrid composites. Eventually, the mechanical and tribological properties of the composites were assessed, and their relationship to the composites' matching microstructure and wear was addressed.
 
Behavior of a Multi-Story Steel Structure with Eccentric X-Brace
Get PDFEccentrically Braced Frames (EBFs) outperform moment-resisting frames in seismically active regions because of their strength, stiffness, energy dissipation, and ductility. Conventional bracing systems, such as X, Y, V, or K types, are utilized to enhance structural integrity. This study employs computational modelling to analyze multi-story steel buildings featuring an eccentric X-brace system. In this investigation, 120 multi-story steel frame buildings were selected. These multi-story structures comprise six-, nine-, and twelve-story geometries. ETABS built a full-scale FE model of multi-story structures. The study's parametric variables are the X-brace eccentricity, steel X-brace section size, and X-braced placement. Steel X-braces may have an eccentricity of 500, 1000, or 1500 millimeters. The ETABS model was validated when its findings matched experimental data. According to the data, the eccentric X-brace increases top-story displacement more for 6-story multi-story structures than for 9- and 12-story ones. Eccentric X-braces reduced lateral stiffness, allowing more significant floor movement. Eccentric and diagonal braces offer less lateral rigidity than concentrically braced frames due to their flexibility. Eccentricity reduces stiffness, even if the X-braced component has a larger cross-section. EBFs may migrate horizontally. Since the EBF absorbs more energy, changing the X-brace section size and eccentricity affects its ductility.