Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Numerical analysis of repaired wall loss defect pipelines for optimum composite wrap thickness
Get PDFThe paper presents the numerical analysis of failure pressure of wall loss defect metallic pipelines and validate it with experimental results. An optimization of composite thickness for repair of wall loss defect pipeline is also carried out using numerical analysis. A nonlinear explicit FE code with constitutive models for metallic steel and composite material to failure modelling was used. Three different cases: non-defective pipe, wall loss defective pipe and composite repaired of defective pipe are considered. It was found that the numerical results are in good agreement with the analytical results in all the three cases. The theoretical failure pressure determined by ISO/TS 24817 standard for wall loss defect pipe is highly conservative compared to the numerical failure pressure for the given composite repair thickness. Additionally, the numerical study on optimization of repair thickness revealed that lower composite repair thickness can also sustain the designed failure pressure (composite repair thickness of 8.4 mm can sustain the same designed pressure instead of 16.1 mm thickness), which implies there is scope to further reduce the composite thickness, which ultimately reduce the repair cost
Numerical analysis of isolated end-flattened steel bars under compression in space trusses
Get PDFThis research aims to characterize the behavior of isolated end-flattened steel bars under compressive loading, in which global instabilities or excessive local deformations represent a significant part of the causes of structural collapse. The association of numerical analyses using the finite element method (FEM) with previously collected experimental data is performed, and their respective results are the core object of critical analysis in this work. Numerical simulations are based on the modified Riks method, complemented in part by modal analysis, whose results demonstrate the occurrence of the aforementioned failure modes in prototypes with slenderness ratios varying in the spectrum from 20 to 200. Finally, the analytical formulations that describe the phenomenon from the approach of global and local instabilities incorporated into current normative expressions are applied in a comparison with the results gathered in the numerical approach
Numerical nonlinear analysis of RC beans with un-strengthened and CFRP-strengthened opening drilled under service loads within shear zones
Get PDFCurrent research paper deals with reinforced concrete (R.C.) beams numerical modeling and suggested strengthening procedure if it is required to create an opening within their shear zones. Strengthening is assumed to be achieved during different service load application conditions. Reinforced Concrete beams with rectangular or circular opening in shear zone; as critical regions; sustain two concentrated system of loads are tested till failure before and after performing suggested opening assessing technique by means of Carbon Fibers Reinforced Polymer sheets (CFRP). The main aim of this research is simulating real practice situation where the beam is subjected to service loads, supported temporary by means of hydraulic jacks, opening is created and strengthening is performed then jacking supports are released. Results of achieved numerical nonlinear modeling are introduced and influence of strengthening achieving on improving assessed beams almost structural behavior such as initial cracking loads, load deflection curves, cracking patterns, failure loads & modes for reference (without opening), main un-strengthened control beams, and CFRP strengthened opening beams are introduced and analyzed in details. Some important conclusions & recommendations for designer and executive engineers are stated
Mechanical, Wear, and Fracture Behavior of Titanium Diboride (TiB2) - Cerium Oxide (CeO2) Reinforced Al-6061 Hot-rolled Hybrid Composites
Get PDFDevelopment of aluminium composites by stircasting technique is an effective method for fabrication of better quality of MMCs. Stircasting technique is one of the most commonly accepted techniques. In this research work, Al6061 / TiB2+CeO2 hybrid MMCs have been fabricated with varying wt. % of TiB2 (2.5%, 5%, 7.5% and 10%) particulates and constant 5% of CeO2 particulates. The monolithic alloy and hybrid composite were hot-rolled at a temperature of 515°C. Whereas, both the monolithic and hot-rolled hybrid composite was subjected to micro-structural study, hardness and tensile test. Optical microscope analysis revealed uniform dispersal of hard particles with in the base matrix in case of both of ascast and hot-rolled composites. Both ascast and hotrolled hybrid composites have shown extensive enhanced mechanical behavior and high wear resistance when compared with monolithic alloy. Though, ductility of the hybrid MMCs decreased with increasing TiB2 and CeO2 content. A tensile and wear fractography outcome shows the internal fractured structure of a tensile and wear specimen which was analysed using a SEM analysis
The earth-fill dam state express investigation using mechanical vibrations produced by HPP
Get PDFThe usage of mechanical vibrations produced by the hydropower plant (HPP) turbine may be used for seismic sounding of large-scale constructions as the earth-fill dam and its abutment contacts. Such vibrations are monochromatic oscillations on main frequencies and their harmonics produced by turbine. Seismic sensors installed on the dam's crest and inside it, if it possible, and in the area of abutment contacts register microseisms include HPP turbine operation vibrations which may be extracted by seismic data processing, i.e., filtering. We discuss two data processing possibilities: symphonious filter as the hardware one and power spectrum calculation as digital one. We consider the two case of earth-fill dams state investigations. There are the Chiryurt HPP dam (Republic of Dagestan, Russia, 9.5 m high) and the Nurek HPP dam (Tajikistan, 300 m high). We show the possibilities of seismic express investigations using signals of main frequencies produced by HPP turbine for dam sounding. For Chiryurt dam the extra fluid filtering in the central part of the dam was revealed. Nurek dam abutment contact monitoring showed the temporal variation of its stress-strain state associated with deformation variation 10-5-10-6 presumably due to regional seismicity
Experimental and computational study on dynamic analysis of cracked simply supported structures under moving mass
Get PDFIn this study, the influences of crack parameters like crack location from the left end, crack height, number of cracks and the magnitude of mass and the velocity of the transit load on the vertical displacements of the cracked simply supported beams subjected to transit mass are investigated. The transverse open cracks with numerous damage scenerios are considered for the mathematical modelling of the system. The governing equations of motion for the system have been obtained and the equations have been solved by the help of Duhamel integral technique. The theoretical formulation has been exemplified with numerical studies. By utilizing ANSYS Workbench 2020, transient structural analysis has been carried out. The mode shapes and the frequency ratios of damaged simply supported beam have also been determined. To validate the numerical and FEM models, the experiments with damaged beams have been carried out in the laboratory. It has been proven that the results of the theoretical and FEM models are well convergent with the experimental data. The results gathered from the numerical analysis, FEA as well as experimental study have been presented with comparative graphs and tables. The outcomes of the examinations have been interpreted in the conclusions part. It has been observed that subject parameters are of considerable significance on the time dependent response of the cracked beams
Synthesis and Characterization of Fe2O3 Nanoparticles Reinforced to Recycled Industrial Aluminium Scrap & Waste Aluminium Beverage Cans for Preparing Metal Matrix Nanocomposites
Get PDFIncreased material demand in all sectors is primarily due to exponential growth in population to fulfill human needs and comforts. Recycling of collected aluminium beverage cans and Al 6061 alloy scraps from industries ensures energy savings with reduced environmental problems in fabricating composite parts economically. The iron oxide (α-Fe2O3) nanoparticles were prepared by precipitation method using ferric chloride and ammonia as a precursor. The prepared nanoparticles were characterized by using Transmission Electron Microscope (TEM), X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR). Stir cast processing route ensures uniform mix of reinforcement nanoparticles in matrix material. The prepared nanocomposites (matrix: Al Scrap (90% Scrap Al 6061 alloy + 10% Waste Al can); reinforcement: 2%, 4% and 6% wt. of Al matrix) were mechanically characterized for hardness and tensile strengths. It was observed that, increased percent of Fe2O3 nanoparticles in the metal matrix nanocomposite (MMCs) resulted in significant increase in hardness and tensile strength values. Fractography analysis examined viz. scanning electron microscope (SEM) revealed a ductile failure for as-cast Al scrap followed by brittle failure in Al MMC's
Structural and seismic vulnerability assessment of the Santa Maria Assunta Cathedral in Catanzaro (Italy): classical and advanced approaches for the analysis of local and global failure mechanisms
Get PDFThe evaluation of the seismic vulnerability of existing buildings is becoming very significant nowadays, especially for ancient masonry structures, that represent the cultural and historical heritage of our countries. In this research, the Cathedral of Santa Maria Assunta in Catanzaro (Italy) is analyzed to evaluate its structural response. The main physical properties of the constituent materials were deduced from an extensive diagnostic campaign, while the structural geometry and the construction details were derived from an accurate 3D laser scanner survey. A global dynamic analysis, based on the design response spectrum, is performed on a finite element model for studying the seismic response of the structure. Moreover, a local analysis is conducted to evaluate the safety factors corresponding to potential failure mechanisms along preassigned failure surfaces. Furthermore, pushover analyses are performed on macro-elements, properly extracted from the whole structure and with an independent behavior with regard to seismic actions. A novel model based on inter-element fracture approach is used for the material nonlinearity and its results are compared with a well-known classical damage model in order to point out the capability of the method. Finally, the results obtained with the three different models are compared in terms of seismic vulnerability indicators
Composite lay-up configuration effect on double and single sided bonded patch repairs
Get PDFUnderstanding the failure modes of damaged or cracked structures and repaired by bonding a composite patch is an essential point to improve its resistance to failure and subsequently extend its service life. In the present study, a 3D finite element analysis using ANSYS software was performed to elucidate the failure modes of the repaired structures by double and single sided bonded composite. The plate is represented by an aluminum plate (Al2024 T3), cracked at the edge and repaired by three types of laminates, with different fiber orientation in order to determine its effect on the repair. The contact interfaces patch-adhesive and aluminum-adhesive were modeled by cohesive zone modeling (CZM) using bilinear interface of delamination (BID) method to determine the failure at the adhesive layer. The obtained results show the importance of the impact of the composite patch fiber orientation on the structure design for suitable repair.  
A Study on microstructure, mechanical and fracture behavior of Al2O3 - MoS2 reinforced Al6061 hybrid composite
No full textAl composites usage is growing and is gaining importance in aerospace, automotive and marine industries due to their excellent characteristics. Aluminum composites exhibit high resistance to wear and corrosion, possess high strength, offer durability and more such properties. In this study, Al 6061 alloy, reinforced with Al2O3 - MoS2 was produced by a stir casting technique and its microstructure and mechanical behavior were evaluated. Reinforcements were added in the range of 0 - 9 wt. %. The microstructure analysis, tensile and compressive strength of the hybrid MMCs (Metal Matrix Composites) have been analyzed and examined. From the investigational study, it was found that the reinforcing particulates are evenly dispersed in the base matrix. The porosity and density of the hybrid composites were found to be enhanced. The ultimate tensile and compressive strength of the hybrid MMCs could be improved by addition of ceramic (Al2O3) particulates compared to monolithic. Further, the strength of hybrid composites was decreased by adding of MoS2 (solid lubricant) along with hard ceramic particulates. Finally, fractured surface of the UTS test specimens were analysed using a SEM analysis