Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Characterization of the mechanical properties and microstructural evolution of martensitic steel in repeated tempering cycles
Get PDFThe purpose of this study was to understand the behavior of martensitic H13 steel in accordance with the microstructural evolution, mechanical properties and wear in repeated tempering cycles. The microstructures were characterized by axio image observer microscope, scanning electron microscope (SEM), x-ray diffraction (XRD). Uniaxial tensile test, charpy v-notch impact test, rockwell hardness test and wear test were conducted to analyze the changes in mechanical properties, impact properties, hardness and wear in repeated tempering cycles. The specimen prepared were subjected to the hardening at 1030 °C for 20 minutes, oil quenched and subjected to repeated tempering cycles at 570 °C for 2hrs holding time each. The mechanical properties recorded indicates that the maximum ultimate tensile strength obtained was at double tempering due to secondary hardening effect i.e., alloy carbides precipitation offering strength to the matrix and corresponding wear was found to be minimum. The annealed specimen revealed bainitic microstructure and with hardening and repeated tempering cycles, fine needle like structure and carbides was observed in microstructure and retained austenite was converted into martensite and martensite was converted into tempered martensite. Carbide size and martensite lath distribution controls the strength and fracture rate
Crack identification in plates-type structures using natural frequencies coupled with successful history-based adaptive differential evolution algorithm
Get PDFIn this study, a new approach, for identification and characterization of straight cracks in plates-like structures, is presented. The finite element method using a commercial software (Abaqus)is coupled with successful history-based adaptive differential evolution algorithm (SHADE) which, ensures the minimization of the objective function based on the mean relative error, that is defined as the difference between the measured (experimental) frequencies of a plate with an unknown crack identity and numerical frequencies of a cracked plate given by the approach Shade/FEM. This method will be applied on a steel thin plate to find the identity of the crack given by length, orientation and centre coordinates. Two strategies are applied to validate the effectiveness of the proposed approach. The first one, is based on the inverse problem using natural frequencies of a plate withknown crack identity obtained by a modal simulation on Abaqus. In the second, the experimental frequencies of a cracked plate were used. With just a population size of 25 and 150 iterations, the results show a good accuracy of the proposed approach with a relative error of the objective function less than 0.8%
Estimating degradation of strength of neat PEEK and PEEK-CF laminates under cyclic loading by mechanical hysteresis loops
Get PDFA method for assessing the degradation of mechanical properties of neat polyetheretherketone and its laminated composite reinforced with unidirectional carbon fibers is proposed. It is based on the calculation of the maximum and minimum strains in a cycle, as well as both dynamic and secant moduli estimated from mechanical hysteresis loops. These parameters reflect the material damage degree, enabling to predict its current mechanical state
Optimization of S-N curve fitting based on neighborhood rough set reduction with improved firefly algorithm
Get PDFS-N curve fatigue samples of titanium alloy welded joints have such a comparatively significant scatter, that results in the issue that the fatigue life prediction accuracy is not optimal. In this work, the titanium alloy welded joints' fatigue data is used as analysis data, and the neighborhood rough set reduction with improved firefly algorithm efficient method of fitting stress-life curves is set forth. The welded joint's fatigue decision system is built with fatigue data. The continuous iteration of the firefly algorithm is used as the search strategy, the neighborhood rough set is adopted to decrease attributes, and the major deciding elements of welded joints' fatigue life is identified. The fatigue characteristic domains are divided based on the neighborhood rough set reduction with improved firefly algorithm's key factor set, and the S-N curves can then be fitted to each domain individually. According to the goodness-of-fit analysis, the proposed approach can improve fatigue life accuracy and reduce sample scattering from fatigue
Fault detection in beam structure using adaptive immune based approach
Get PDFDifferent structural and machine elements are used over the ages. These are subjected to various loads like static and dynamic load, temperature, corrosion etc. Due to the above-mentioned reasons, ageing of the structural elements occur. So, to enhance the designed lifetime of any structure continuous maintenance is required. One such method has been proposed in this research work and the proposed method can be employed as an online tool for the fault identification. Here dynamic analysis of structure has been conducted as the forward method to find out the modal natural frequencies related with the damage. Recently with the application of machine learning approaches and the soft computing, the damage can be detected easily. In this methodology, Clonal Section Algorithm (CSA) has been applied to find out the faults (crack locations and depth) in the structure initially. Later one such method has been developed in the concepts of adaptive immune based technique (Adaptive Clonal Section Algorithm-ACSA) which is the combination of an artificial immune (Clonal Selection Algorithm) and Regression Analysis (RA). The use of regression analysis makes the proposed method more adaptive and the residual error in the collection of vibration data is reduced. The mechanism and various steps involved in CSA, RA and ACSA are analyzed here in a precise manner. The key endeavor of this study is the development of ACSA and its implementation to condition monitoring of structure. To authenticate and check the accuracy of both the methods (CSA and ACSA), laboratory tests are carried out. The results obtained from each method are corroborated with other and found to be convergent.
Optimization of damage repair with piezoelectric actuators using the Taguchi method
Get PDFOver the last two decades, piezoelectric actuators have emerged as a promising solution for structural repair. In this work, initially the stress intensity factor (SIF) estimation using the finite element (FE) approach at crack tips in aluminium 2024-T3 plates. Based on Taguchi’s L9 orthogonal array the FE simulation has been conducted. Later, this study uses the optimization method via the design of experiments to systematically evaluate the effect of various dimensions and material qualities, especially under the conditions of Mode-I crack propagation. It also investigated the complex interaction of factors impacting adhesive bonds, piezoelectric actuators, and aluminium plates, The study not only analyses the parameter relationships but also examines their controls, identifying those best aligned with primary objectives. This sensitivity enhances the piezoelectric actuator's efficacy and quality. The research determines an optimal parameter combination, developing active repair performance and establishing an essential SIF benchmark. This research explores the complex world of piezoelectric actuator-assisted repairs, providing a road map for better structural rehabilitation
Investigations on tool wear behavior in turning AISI 304 stainless steel: An empirical and neural network modeling approach
Get PDFMachining with a cutting edge with extensive damage or a fractured cutting edge significantly influences the machining performance. Therefore, investigations on tool wear behavior, their forms, and wear mechanisms will be very helpful in the current environment of sustainable manufacturing. On the other hand, the machining economy is negatively impacted by replacing the tool well before its useful life. This proactive maintenance planning reduces the risk of sudden tool failure and potential workpiece damage. Accordingly, the current work creates empirical and ANN models to predict flank wear growth for turning AISI 304 stainless steel using a MTCVD-TiCN/Al2O3 coated carbide tool. The experiments were designed to cover a broad range of operating conditions to ensure the model's accuracy and applicability in practical machining scenarios. An ANN was modeled using a feedforward backpropagation machine learning technique. In this study, a higher prediction accuracy of 0.9975 was achieved with ANN model as compared to the empirical model. The most common wear mechanism observed is metal adhesion, followed by fracture due to the pulling away of adhered material. The developed models have been found to be valuable for optimizing cutting parameters and enhancing tool life in machining. 
Investigation on Microstructure and Tensile Fractography of RE Oxides (CeO2/Y2O3) Reinforced AZ91D Magnesium Matrix Composites
Get PDFThe current work aims to investigate the mechanical properties of rare oxide reinforced Mg alloy based MMCs. Magnesium matrix considered in the study is AZ91D alloy, whereas rare earth oxides reinforced were CeO2 and Y2O3. The Y2O3 particulate reinforcement percentage was varied from 1 to 3% in the steps of 1% to study its influence on mechanical properties of MMCs. Stir casting route was adopted to fabricate sample for study. Microstructure analysis illustrated the uniform distribution of particulate in matrix alloys. The obtained results revealed the enhanced mechanical properties such as tensile strength, yield strength, elongation and hardness of MMCs due to increased percentage of reinforcement. Fractography analysis of fracture surfaces demonstrated the microcracks and cleavage were dominant in pure alloy. While particle debonding, extensive plastics deformation were prominent in-addition to microcracks in MMCs
Influence of Pr6O11 addition on structural and magnetic properties of mechanically alloyed Fe65Co35 nanoparticles
Get PDFThis work focuses on the synthesize of nanostructured (Fe65Co35)100-x (Pr6O11)x (x = 0, 5) powders using high energy ball milling. The influence of Pr6O11 on structural, morphological and magnetic properties of Fe65Co35 nanoparticles were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) with a dispersive energy analyzer (EDS), vibratory sample magnetometer (VSM) and differential scanning calorimetry (DSC). Results show that the praseodymium oxide addition increased the decrement rate of the crystallite size with milling time of about 27 % and decreased the increment rate of the internal micro-strain of 50 %. Moreover, because of its high grain fragmentation tendency, Pr6O11 increases the hardness and brittleness of Fe-Co powders. Moreover, it minimized the cold welding between Fe-Co ductile particles leading to a significant decrease in the average particle size (~1µm). The magnetic measurements conducted at room temperature show that the saturation magnetisation (Ms) and the coercivity (Hc) increased with milling time in both compositions. A low Ms and high Hc values were detected in (Fe65Co35)95 (Pr6O11)5 nanoparticles. The results demonstrated a soft ferromagnetic nature in all of the synthesized nanoparticles with Ms in the range 207 – 216 emu/g and Hc is found to be 113 Oe
THM-coupled numerical analysis of temperature and groundwater level in-situ measurements in artificial ground freezing
Get PDFBelarusian Potash salt deposits are bedded under aquifers and unstable soil stratums. Therefore, to develop the deposits a vertical mine shaft sinking is performed using the artificial ground freezing technology. Nowadays, real time observations of ground temperature and groundwater level is applied to control the ground freezing process. Numerical simulation can be used for a comprehensive analysis of measurements results. In this paper a thermo-hydro-mechanical model of freezing of water saturated soil is proposed. The governing equations of the model are based on balance laws for mass, energy and momentum for a fully saturated porous media. Clausius-Clayperon equation and poroelastic constitutive relations are adopted for description of a coupled change in water and ice pore pressure, porosity and a stress-strain state of freezing soil. The proposed model enables us to describe evolution of equivalent water content measured in Mizoguchi’s test and predict frost heave strain in one-sided freezing test. Numerical simulation of ground freezing in the Petrikov mining complex located in Belarus has shown that the model is able to describe field measurements of pore pressure inside a forming frozen wall. Furthermore, the mismatch between hydro- and thermo-monitoring data obtained during the artificial freezing is analyzed