Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
Not a member yet
2800 research outputs found
Sort by
Effect of Ti addition and cast part size on solidification structure and mechanical properties of medium carbon, low alloy cast steel
Get PDFIn this work, the effect of Ti addition and the cast part size on the solidification structure and mechanical properties of a medium carbon, low alloy cast steel was analyzed. The experimental analysis involved the design of the melts by using Thermo-Calc® software, where different amounts of Ti added to a standard chemical composition of an AISI 13XX steel were simulated. Then, the solidification macrostructure (dendritic pattern and grain size) and microstructure were characterized by using conventional and specific metallographic techniques. Finally, the mechanical behavior in terms of hardness and tensile properties were evaluated.
The results show that the addition of 0.12% of Ti promotes a fine dispersion of Ti nitrides and carbides, but when the Ti concentration raises to 0.2%, the size of the Ti nitrides and carbides increases while its amount decreases. Ti nitrides and carbides particles act as nucleation sites for the precipitation of ferrite from austenite, and it was found that the addition of Ti in the higher concentrations refines the solidification macrostructure (dendritic pattern) for both cast part sizes evaluated.
Regarding mechanical properties, the addition of Ti does not significantly vary the ultimate tensile strength but reduces the total elongation for cast part size
Improvement of mechanical properties of railway track concrete sleepers using ultra high performance concrete (UHPC)
Get PDFIn recent times, the shape of the beams evolved from wooden sleepers and then to steel sleepers until they reached concrete sleepers. These sleepers play a very important role in transferring the loads from the train wheels to the subgrade layers fixed by the railway. This development took place in concrete sleepers until we reached mono-block concrete sleepers. This paper discusses, through laboratory experiments, the effect of ultra-high performance concrete mixtures on the behavior of mono-block concrete sleeper B70. The ability of these new sleepers to resist train loads was also studied, compared to its conventional concrete sleepers. This research aimed to determine through experiment if these sleepers' behavior fulfilled the European requirements standers for prestressed concrete sleepers, and make comparisons between the UHPC sleepers and conventional concrete sleepers. All these sleepers were tested under static load tests at the rail seat and center section and pull-out tests for cast-in fastening components. These initial results suggest that a new generation of Ultra-high performance concrete sleepers can be created; the long-term efficiency of this category of sleeper will need to be confirmed by dynamic and fatigue tests and practical use
Mechanical behaviour of sandy soils embankments treated with cement and reinforced with discrete elements (fibres)
Get PDFIt is well known that the reinforcement of the Soil is considered as a solution to its stability problems. This technique ameliorates the mechanical and physical comportment of the soil. Based on this, this research paper aims at investigating the behaviour of a specific type of dried-cemented-sandy soil reinforced with discrete elements such as polypropylene fiber basically through experimental tests. The latter are a series of consolidated drained triaxial tests which were carried out on samples of sand that are prepared with 0, 3 and 6% of cement, reinforced with 1% of polypropylene fiber (12, 18 mm) randomly distributed. Furthermore, those contents are measured by the volume of dry sand. In addition to these tests, a parametric study has also been conducted on a road embankment using a finite element program such as Plaxis 2D in order to observe the variation of different parameters like safety factor and the displacements (Ut, Ux, Uy). The test results showed that the addition of cement and polypropylene fiber of different accommodations increased both cohesion and friction angle of sands while the numerical results indicated that the presence of these additions improved the safety factor and decreased significantly the displacements
Flexural behavior of delta and bi-delta cold-formed steel beams: experimental investigation and numerical analysis
Get PDFCold-formed steel (CFS) structural members retain their positions in the lightweight construction industry. This is due to the significant advantages of CFS. The optimization of these CFS elements will allow the construction of economical buildings with increased load capacities and solutions for stable and economical construction will be obtained. The main aim of this research was to evaluate the effectiveness of these new CFS sections with the estimation of remarkable instabilities and failure modes. This article deals with an experimental study on the behavior of CFS beams of open delta and bi-delta form stressed by four-point bending loads. These cross section shapes are often used in floors as main and secondary beams. The section properties are based on the effective width method designated by the Eurocode 3 standard. A nonlinear finite element (FE) analysis using the ABAQUS program is performed and the comparison between the experimental, numerical and theoretical results is done.
Finally, the results showed above all that the breaking loads of the delta and bi-delta beams corresponded to the modes of local buckling and crushing of the web
A Simple and Efficient eight node Finite Element for Multilayer Sandwich Composite Plates Bending Behavior Analysis
Get PDFIn this paper, a C0 simple and efficient isoparametric eight-node displacement-model based on higher order shear deformation theory is proposed for the bending behavior study of multilayer composites sandwich plates. Difficult C1-continuity requirement is overcome by extracting the seven degrees of freedom from strain relations for each element node: two displacements for in-plane behavior and five bending unknowns namely: a transverse displacement, two rotations and two shear angles, which results in a kinematic approximation formulation having only first order derivative requirement. The governing equations of the element (constitutive, virtual work and equilibrium equations) are implemented for the prediction of approximate solutions of deflections and stresses of sandwich plates linear elastic problems. Thereby, the formulation element is able to present a cubic in-plane displacement along both core and faces sandwich thickness, as well as, the shear stresses are found to vary as quadratic field without requiring shear correction factors and independent from any transverse shear locking problems. The accuracy and validity of the proposed formulation is verified through the numerical evaluation of displacements and stresses and their comparison with the available analytical 3D elasticity solutions and other published finite element results
Improvement of hydration products for self-compacting concrete by using magnetized water
Get PDFMagnetized water (MW) is one of the most effective and economical ways to improve the properties of self-compacting concrete (SCC). Therefore, the aim of this study is to improve the fresh, mechanical, and microstructural properties of SCC using MW. For this purpose, a total of 12 mixes were produced with silica fume (SF) content (5% and 10% by weight of cement), and the mixing water passed through a permanent magnetic field (with a strength of 1.4 T) for 50, 100, and 150 cycles. Tests were performed for fresh properties (Slump flow, T50cm, V-funnel, and L-box), for mechanical properties (compressive, flexural, and tensile strength), and for microstructure properties (SEM, EDX, and TGA/DTG). The optimum result in compressive strength was achieved in the mix M8 using 5% silica fume and 150 cycles of MW. For fresh properties, the mix M4 using 150 cycles without SF had the workability enhanced by 11% compared to the control mix, and SEM and EDX tests indicated that SCC mixes prepared with MW had more C-S-H, less CH, and were denser. In addition, TGA/DTG analysis showed that the rate of hydration of mix M8 was reached by 61% at 28 days.
Finite Fracture Mechanics and Cohesive Crack Model: Size effects through a unified formulation
Get PDFFinite Fracture Mechanics and Cohesive Crack Model can effectively predict the strength of plain, cracked or notched structural components, overcoming the classical drawbacks of Linear Elastic Fracture Mechanics. Aim of the present work is to investigate size effects by expressing each model as a unified system of two equations, describing a stress requirement and the energy balance, respectively. Brittle crack onset in two different structural configurations is considered: (i) a circular hole in a tensile slab; (ii) an un-notched beam under pure bending. The study is performed through a semi-analytical parametric approach. Finally, theoretical strength predictions are validated with experimental results available in the literature for both geometries, and with estimations by the point criterion in the framework of Theory of Critical Distances
Description of Fatigue Sensitivity Curves and Transition to Critical States of Polymer Composites by Cumulative Distribution Functions
Get PDFIn this paper, a novel model is presented to describe the composite mechanical properties degradation during cyclic loading. The model is based on cumulative distribution functions using. Weibull probability distribution law and beta distribution are considered. The dependences of the fatigue sensitivity coefficient on the preliminary cyclic exposure are derived. The damage value function derivative using is proposed to define damage accumulation stages boundaries. Model parameters are obtained using experimental data. Determination coefficients are calculated. A high descriptive capability is noted. Rationality and expediency of using cumulative distribution functions as the approximation of experimental data on mechanical characteristics reduction after preliminary cyclic exposure is concluded
Effect of beam-column joints flexibility on the seismic response of setback RC buildings designed according to the Algerian seismic code
Get PDFThe Algerian seismic code assumes that the beam-column joints in monolithic reinforced concrete (RC) buildings are fully rigid. However, many experiments have proven the existence of relative rotations in these connections, and then the presence of relative transfer of bending moment. The present work aims to investigate the effect of beam-column joints modelling on the global seismic behaviour of reinforced concrete (RC) moment-resisting frames buildings, designed according to the Algerian seismic code recommendations. To consider the nonlinear deformation of the connections, an analytical model developed recently is used. This model includes two important deformation mechanisms; the first one covers the slippage of the continuous reinforcement within the column, whereas the second involves slippage caused by creating bending cracks at the extremities of the beams. Three multi-storey RC frames with different setback geometry, including a reference frame, are studied considering the connections as rigid/deformable. The nonlinear static procedure or pushover analysis is used to perform a nonlinear analysis of the studied structures and the results in terms of capacity curve, target displacement, storey drift, storey stiffness and the response reduction factor are presented. The results show the necessity of considering the beam-column connection flexibility when modelling this type of building
Impact behaviour of dissimilar AA2024-T351/7075-T651 FSWed butt-joints: effects of Al2O3-SiC particles addition
Get PDFDissimilar friction stir welding joints are widely employed in the industrial field due to the excellent microstructural and mechanical properties of the resulting joints. Nevertheless, to further enhance the weld properties, the addition of reinforcement particles on the joint-line during the process has been proven effective for increasing its mechanical performance. In the present investigation, the microstructure and the impact behaviour of FSWed joints between AA2024-T351 and AA7075-T651 aluminium plates were investigated, considering the effect of different process parameters selected through a full factorial 2k design of experiments: both the rotational and translational speed of the tool, as well as the addition of Al2O3-SiC microparticles, were considered as input parameters. Unnotched 10 x 5 x 55 mm impact specimens were tested through an instrumented 50 J Charpy pendulum: total impact energy, the two complementary initiation and propagation energies as well as the peak force were correlated to the adopted process parameters. From the performed analyses, it was found that joints with reinforcing particles are prone to form wormhole defects across the stir zone that not only affect the microstructural development, but also the impact behaviour since they require less energy at break in comparison with joints fabricated without particles addition