Frattura ed Integrità Strutturale <p>Frattura ed Integrità Strutturale (Fracture and Structural Integrity) is the International Journal of the Italian Group of Fracture (ISSN 1971-8993). It is an open-access journal published online every three months (January, April, July, October). <br />Frattura ed Integrità Strutturale encompasses the broad topic of structural integrity, which is based on the mechanics of fatigue and fracture and is concerned with the reliability and effectiveness of structural components. The aim of the Journal is to promote works and researches on fracture phenomena, as well as the development of new materials and new standards for structural integrity assessment. The Journal is interdisciplinary and accepts contributions from engineers, metallurgists, materials scientists, physicists, chemists, and mathematicians. The Journal is completely free of charge, both for Readers and for Authors (no APC).</p> <p><strong>More details:</strong></p> <p>- The Journal is financially supported by the <a href="">Italian Group of Fracture (IGF)</a> and by crowdfunding. It is completely free of charge both for readers and for authors. Neither processing charges nor submission charges are required.</p> <p>- Papers can be published only after a preliminary plagiarism/autoplagiarism check and a blind peer-review process (two reviewers, at least). More than one reviewing rounds are possible.</p> <p>- The Journal is well indexed (e.g., Scopus, since 2012, and WoS, since 2015).</p> <p>- All the papers are published with their Visual Abstracts (2 minutes max videos with the "cores" of the papers). All the Visual Abstracts are available both in a dedicated <a href="">YouTube channel</a> and in an "on demand" page (<a href="">LINK</a>). All the issues are also published in a browsable version (<a href="">LINK</a>).</p> en-US <p><strong>Copyright&nbsp;</strong><br>Authors are allowed to retain both the copyright and the publishing rights of their articles without restrictions.&nbsp;&nbsp;</p> <p><strong>Open Access Statement</strong></p> <p><em>Frattura ed Integrità Strutturale</em> <em>(Fracture and Structural Integrity, F&amp;SI</em>) is an open-access journal which means that all content is freely available without charge to the user or his/her institution. Users are allowed to read, download, copy, distribute, print, search, or link to the full texts of the articles in this journal without asking prior permission from the publisher or the author. This is in accordance with the DOAI definition of open access.</p> <p><em>F&amp;SI</em> operates under the Creative Commons Licence Attribution 4.0 International (CC-BY 4.0). This allows to copy and redistribute the material in any medium or format, to remix, transform and build upon the material for any purpose, even commercially, but giving appropriate credit and providing a link to the license and indicating if changes were made.</p> (Francesco Iacoviello) (Support) Sat, 25 Sep 2021 14:17:12 +0000 OJS 60 Sensitivity analysis of the GTN damage parameters at different temperature for dynamic fracture propagation in X70 pipeline steel using neural network <p>In this paper, the initial and maximum load was studied using the Finite Element Modeling (FEM) analysis during impact testing (CVN) of pipeline X70 steel. The Gurson-Tvergaard-Needleman (GTN) constitutive model has been used to simulate the growth of voids during deformation of pipeline steel at different temperatures. FEM simulations results used to study the sensitivity of the initial and maximum load with GTN parameters values proposed and the variation of temperatures.</p> <p>Finally, the applied artificial neural network (ANN) is used to predict the initial and maximum load for a given set of damage parameters X70 steel at different temperatures, based on the results obtained, the neural network is able to provide a satisfactory approximation of the load initiation and load maximum in impact testing of X70 Steel.</p> <p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p> Abdelmoumin Ouladbrahim, Idir Belaidi , Samir Khatir , Erica Magagnini, Roberto Capozucca , Magd Abdel Wahab Copyright (c) 2021 Abdelmoumin Ouladbrahim, Idir Belaidi , Samir Khatir , Erica Magagnini, Roberto Capozucca , Magd Abdel Wahab Sat, 25 Sep 2021 00:00:00 +0000 Analysis of static response of RC beams with NSM CFRP/GFRP rods <div><span lang="EN-US">In this paper experimental results of investigation on reinforced concrete (RC) beams strengthened with the near surface method (NSM) are analyzed considering the response under bending tests on two beams. One of the RC beams was damaged by bending until the yield of reinforcement and successively strengthened with carbon fiber polymer (CFRP) rod, while the second beam was strengthened with glass-FRP rod. Both the beams have been subjected to bending tests until failure. Experimental diagrams and discussion on static response are presented in the paper. It also places a particular emphasis on the non-linear response of RC sections strengthened with CFRP and GFRP rods under bending moment beyond the first elastic behavior. </span></div> Erica Magagnini, Roberto Capozucca, Maria Vittoria Vecchietti Copyright (c) 2021 Erica Magagnini, Roberto Capozucca, Maria Vittoria Vecchietti Sat, 25 Sep 2021 00:00:00 +0000 RC beams damaged by cracking and strengthened with NSM CFRP/GFRP rods <div><span lang="EN-US">The near surface mounted (NSM) method of inserting fiber reinforced polymer (FRP) elements (rods or lamina) into notches has been shown to be a good way for restoring reinforced concrete (RC) elements. The knowledge about the use of Glass-FRP rod following the NSM to reinforce RC beams is limited. This paper deals with the analysis of static and dynamic behaviour of RC beams with and without strengthening. The response of RC beams was assessed at different concrete’s damage level by non-destructive vibration tests. First, a couple of beams have been analysed: one RC beam subjected to bending and under vibration tests; another one beam, damaged by bending and strengthened with NSM Carbon-FRP rods tested again under vibration. Further, one RC beam damage was analysed under bending and vibration tests without strengthening; successively, the beam model with NSM GFRP rod has been tested following the same loading path. Below experimental results are shown and commented; in particular, changes in frequency values are related to the evolution of damage level affected RC beams with NSM CFRP and GFRP rods. </span></div> Roberto Capozucca, Erica Magagnini, Maria Vittoria Vecchietti, Samir Khatir Copyright (c) 2021 Roberto Capozucca, Erica Magagnini, Maria Vittoria Vecchietti, Samir Khatir Sat, 25 Sep 2021 00:00:00 +0000 Influence of 3d-printing parameters on the mechanical properties of 17-4PH stainless steel produced through Selective Laser Melting <p>Additive Manufacturing (AM) is a technological process in which elements are fruitfully built up adding materials layer by layer. AM had a massive development in recent times, thanks to its intrinsic advantages, especially if compared with conventional processes (i.e. subtractive manufacturing methods), in terms of free-form design, high customization of products, a significant reduction in raw materials consumption, low request of postprocessing and heat treatments, use of pure materials and reduced time for final products to be marketed. In order to give an innovative contribution to the knowledge in the field of metal AM materials, this paper reports the main outcomes of an experimental campaign focused on the influence of several specific printing parameters on the mechanical features of the 17-4PH stainless steel, which is one of the most used metal for the Selective Laser Melting (SLM) technology. The influence of different printing directions and sample inclinations on the material mechanical behavior is assessed, with the aim of considering an innovative use in the field of structural engineering. Moreover, the effects due to scanning and recoating times are studied. In addition, the consequences of heat treatment (annealing) on both the residual stresses and the amount of residual austenite are appraised.</p> Francesca Romana Andreacola, Ilaria Capasso, Letizia Pilotti, Giuseppe Brando Copyright (c) 2021 Francesca Romana Andreacola, Ilaria Capasso, Letizia Pilotti, Giuseppe Brando Sat, 25 Sep 2021 00:00:00 +0000 Damage identification in steel plate using FRF and inverse analysis <p>Metaheuristic algorithms have known vast development in recent years. And their applicability in engineering projects is constantly growing; however, their deferent exploration and exploitation techniques cause the engineering problems to favor some algorithms over others. This paper studies damage identification in steel plates using Frequency Response Function (FRF) damage indicator to detect and localize the healthy and damaged structure. The study is formulated as an inverse analysis, investigating the performance of three new metaheuristic algorithms of Wild Horse Optimizer (WHO), Harris Hawks Optimization (HHO), and Arithmetic Optimization Algorithm (AOA).&nbsp; The objective function is based on measured and calculated FRF damage indicators. The results showed that the case of four damages with different damage severity levels presented a good challenge where the HWO algorithm was shown to have the best performance.&nbsp; Both in convergence speed and CPU time.</p> Samir Khatir , Magd Abdel Wahab , Samir Tiachacht, Cuong Le Thanh , Roberto Capozucca, Erica Magagnini, Brahim Benaissa Copyright (c) 2021 Samir Khatir , Magd Abdel Wahab , Samir Tiachacht, Cuong Le Thanh , Roberto Capozucca, Erica Magagnini, Brahim Benaissa Sat, 25 Sep 2021 00:00:00 +0000 Evaluating structural safety of trusses using Machine Learning <p>In this paper, a machine learning-based framework is developed to quickly evaluate the structural safety of trusses. Three numerical examples of a 10-bar truss, a 25-bar truss, and a 47-bar truss are used to illustrate the proposed framework. Firstly, several truss cases with different cross-sectional areas are generated by employing the Latin Hypercube Sampling method. Stresses inside truss members as well as displacements of nodes are determined through finite element analyses and obtained values are compared with design constraints. According to the constraint verification, the safety state is assigned as safe or unsafe. Members’ sectional areas and the safety state are stored as the inputs and outputs of the training dataset, respectively. Three popular machine learning classifiers including Support Vector Machine, Deep Neural Network, and Adaptive Boosting are used for evaluating the safety of structures. The comparison is conducted based on two metrics: the accuracy and the area under the ROC curve. For the two first examples, three classifiers get more than 90% of accuracy. For the 47-bar truss, the accuracies of the Support Vector Machine model and the Deep Neural Network model are lower than 70% but the Adaptive Boosting model still retains the high accuracy of approximately 98%. In terms of the area under the ROC curve, the comparative results are similar. Overall, the Adaptive Boosting model outperforms the remaining models. In addition, an investigation is carried out to show the influence of the parameters on the performance of the Adaptive Boosting model.</p> Tran-Hieu Nguyen, Anh-Tuan Vu Copyright (c) 2021 Tran-Hieu Nguyen, Anh-Tuan Vu Sat, 25 Sep 2021 00:00:00 +0000 Bending cyclic behavior and scatter-band analysis of aluminum alloys under beneficial and detrimental conditions through high-cycle fatigue regime <p>This article presents the bending fatigue behavior and the scatter-band analysis of aluminum alloys under beneficial conditions of nano-clay-particles and heat-treating, compared to detrimental conditions of the mechanical stress and the corrosion. Moreover, the sensitivity analysis was also done on the stress level, the pre-corrosion phenomenon, the addition of nano-particles and applying the heat treatment on the high-cycle bending fatigue lifetime of the aluminum-silicon alloy. For this objective, gravity and stir-casting processes were done for aluminum alloy and nano-clay-composite specimens and then, standard samples were machined from initial casted cylinders. Furthermore, rotary fatigue tests were performed under cyclic bending loadings, through the high-cycle fatigue regime. Some samples were pre-corroded in the sulfuric acid for 200 hours. Based on the sensitivity analysis on experimental data by the Minitab software, the obtained results indicated that the stress level was the effective parameter on the fatigue lifetime. The meaningful regression model was calculated and calibrated on the logarithmic scale of the fatigue lifetime. Then, the second sensitive parameter was demonstrated as the pre-corrosion, which caused a significant degradation of fatigue properties in the material. The last-ranked factor was related to nano-particles for the beneficial effect on the improvement of the high-cycle fatigue lifetime. The scatter-band analysis illustrated that nano-particles and heat-treating changed the scattering behavior of experimental data.</p> Mohammad Azadi, Hanieh Aroo Copyright (c) 2021 Mohammad Azadi, Hanieh Aroo Sat, 25 Sep 2021 00:00:00 +0000 The role of aggregate granulation on testing fracture properties of concrete <p>Concrete is a porous material containing aggregate of different sizes, hardened cement matrix with air pores, microcracks and water. Concrete internal structure is different from that of other engineering materials. Furthermore concrete is described as quazi-brittle material. Fracture processes in it form in a way that does not fit within classical theories. Therefore, to describe failure of concrete structures nonlinear fracture mechanics is often applied with success. Basic concrete parameters, like compressive and tensile strength, and modulus of elasticity, are not enough to analyze fracture processes in concrete structures. Additional fracture properties should be tested, among them fracture energy, complete diagram of stress-deformation under axial tension and the width of fracture process zone. Recognizing and testing fracture parameters is of paramount importance when analysing fracture process in concrete structures. The correct data of material’s properties and the adequate fracture model applied in numerical simulations influence final results. In the paper the findings reported in the professional literature are summarized and obtained results of the own numerical simulation are reported in order to&nbsp; give a deeper knowledge on the role of aggregate on fracture properties of concrete.</p> Marta Słowik Copyright (c) 2021 Marta Słowik Sat, 25 Sep 2021 00:00:00 +0000 Modelling of Low-velocity Impacts on Composite Beams in Large Displacement <p>The paper provides an evaluation of the nonlinear dynamic response of a cantilever beam made of composite material subjected to low-velocity impacts. The structure is assumed to respond in a quasi-static manner and modelled by a continuous beam in large displacement with a lumped mass attached. First, an analytical model was developed to study the free vibrations of a beam, taking into account the nonlinearities due to large displacements and inertia. Then, the analytical findings were compared with experimental test data. The vibration of a real composite beam has been acquired through high-speed imaging technique. The displacements of the beam were extracted by digital image analysis; then, the nonlinear parameters of the analytical model were determined by the Fitting Time History technique. The results obtained by the analytical model and the experimental test are compared with numerical analysis. The validated analytical model was adapted to study a low-velocity impact; the lumped mass was associated with a rigid projectile, whose initial speed represents the impact velocity.</p> Mattia Utzeri, Marco Sasso, Gianluca Chiappini, Stefano Lenci Copyright (c) 2021 Mattia Utzeri, Marco Sasso, Gianluca Chiappini, Stefano Lenci Sat, 25 Sep 2021 00:00:00 +0000 Damage severity for cracked simply supported beams <p>This paper investigated the static and dynamic behaviors of isotropic cracked simply supported beam using finite element analysis (FEA), ANSYS software. Modal and harmonic vibration analysis of intact and damaged beam were performed in order to extract mode shapes of bending vibration, natural frequencies and obtain frequency response diagram. Static finite element analysis of undamaged and damaged simply supported beam was carried out to determine zero frequency deflection, then stiffness of intact and cracked beam was computed using conventional formula. Crack damage severity of damaged beam was calculated and it is noticed that as crack position is increased from left hand support of beam up to central point and crack depth is increased, then crack damage severity increases. The effect of mode shape pattern is investigated and it is found that the amount of decreasing of natural frequency is proportional to the normalized mode shape at position of crack. The exhibited correlation between results for damaged beam revealed that crack damage severity is proportional to zero frequency deflection and inversely proportional to first mode frequency.</p> Ehab Samir Mohamed Mohamed Soliman Copyright (c) 2021 Ehab Samir Mohamed Mohamed Soliman Sat, 25 Sep 2021 00:00:00 +0000 Periodic homogenization and damage evolution in RVE composite material with inclusion <p>This work deals with the coupling between a periodic homogenization procedure and a damage process occurring in a RVE of inclusion composite materials. We mainly seek on the one hand to determine the effective mechanical properties according to the different volume fractions and forms of inclusions for a composite with inclusions at the macroscopic level, and on the other hand to explore the rupture mechanisms that can take place at the microstructure level. To do this; the first step is to propose a periodic homogenization procedure to predict the homogenized mechanical characteristics of an inclusion composite. This homogenization procedure is applied to the theory based on finite element analysis by the Abaqus calculation code. The inclusions are modeled by a random object modeler, and the periodic homogenization method is implemented by python scripts. It is then a matter of introducing the damage into the problem of homogenization, that is to say; once the homogenized characteristics are assessed in the absence of the damage initiated by microcracks and micro cavitations, it is then possible to introduce damage models by a subroutine (Umat) in the Abaqus calculation code. The verifications carried out focused on RVE of composite materials with inclusions.</p> Karim Benyahi, Youcef Bouafia, Mohand Said Kachi, Sarah Benakli, Amel Hamri Copyright (c) 2021 Karim Benyahi, Youcef Bouafia, Mohand Said Kachi, Sarah Benakli, Amel Hamri Sat, 25 Sep 2021 00:00:00 +0000 Determining the endurance limit of AISI 4340 steels in terms of different statistical approaches <p>In engineering applications, fatigue phenomenon is a key issue and needs to be analyzed in the beginning of design phase in case of any component exposed to alternating loading on operation otherwise catastrophic fatigue failure may cause. Component can be designed with safe-life, fail-safe, and damage tolerant approach based on whether redundant load path and damage sensitive. Before starting analyzing the structure, material allowable data needs to be presented in a reliable way to predict fatigue life of components. SN curves with presented confidence levels are the robust approach to make a prediction on safe life of a structure in terms of fatigue. In this point, there are so many approaches to determine fatigue limit of materials and issue shall be handled by statistical manner. In literature, different staircase and curve fitting methods were presented to estimate endurance limit of materials and some reliability manuscript published. In this paper, fatigue limit of AISI 4340 steel will be investigated through most convinced staircase and curve fitting approaches and their reliability will be queried.</p> Salim Çalışkan, Rıza Gürbüz Copyright (c) 2021 Salim Çalışkan, Rıza Gürbüz Sat, 25 Sep 2021 00:00:00 +0000 The effect of using polypropylene fibers on the durability and fire resistance of concrete <p>In order to study the effect of polypropylene fibers on the durability of cementitious composites, several experimental tests have been carried out in the laboratory. The composite was tested with different volume fractions of polypropylene fibers (0.05%, 0.10%, 0.30% and 0.50%). All the results relating to the indicators (porosity accessible to water εb, to the oxygen permeability Kapp.gas and diffusivity Dns) indicate that the addition of polypropylene fibers in a cement matrix represents only a small effect on durability. This panel of general sustainability indicators can be supplemented by indicators more specific to each degradation process identified or envisaged depending on the environmental conditions of the structure. However, the addition of the volume fraction of polypropylene fibers (0.50%) in a cementitious composite, increases fire resistance. Such behavior gives fiber composites interesting properties which favor their use in structures exposed to fire risks.</p> Hassan Suiffi, Anas El Maliki, Fatima Majid, Omar Cherkaoui Copyright (c) 2021 Hassan Suiffi, Anas El Maliki, Fatima Majid, Omar Cherkaoui Sat, 25 Sep 2021 00:00:00 +0000 Supervised Machine Learning Classification Algorithms for Detection of Fracture Location in Dissimilar Friction Stir Welded Joints <p>Machine Learning focuses on the study of algorithms that are mathematical or statistical in nature in order to extract the required information pattern from the available data. Supervised Machine Learning algorithms are further sub-divided into two types i.e. regression algorithms and classification algorithms. In the present study, four supervised machine learning-based classification models i.e. Decision Trees algorithm, K- Nearest Neighbors (KNN) algorithm, Support Vector Machines (SVM) algorithm, and Ada Boost algorithm were subjected to the given dataset for the determination of fracture location in dissimilar Friction Stir Welded AA6061-T651 and AA7075-T651 alloy. In the given dataset, rotational speed (RPM), welding speed (mm/min), pin profile, and axial force (kN) were the input parameters while Fracture location is the output parameter. The obtained results showed that the Support Vector Machine (SVM) algorithm classified the fracture location with a good accuracy score of 0.889 in comparison to the other algorithms.</p> Akshansh Mishra, Apoorv Vats Copyright (c) 2021 Akshansh Mishra, Apoorv Vats Sat, 25 Sep 2021 00:00:00 +0000 Influence of themo-mechanical treatments and microstructural state on the fatigue behaviour of a weald seam: case of API X60 steel <p>The aim of this work is the study of the fatigue behaviour of API X60 steel and the influence of thermal and mechanical treatments. The evaluation of the integrity and safety of welded structures dictates the approach taken in this research. The microstructural observations on the different zones of the weld seam indicates that the variation of heterogeneous structure is a progressive destruction of the strips of lamination which cause a new phase leading to a drop in the mechanical properties requiring treatment after welding. The fatigue cracking rate diverges beyond the threshold of DK, but no deviation of the crack from its propagation axis was noticed, which confirms the correct choice of filler metal over that of the base metal with an overmatching M = 1.1, and the treatments applied to the structure. This fatigue cracking rate transversal to the welding direction initially presents an aspect similar to that of BM but registers a delay as soon as the crack tip enters the second zone (HAZ) then it progresses rapidly. This evolution is characterized by a disturbance due to the repeated change of microstructure.</p> Mohammed Achoui , Fethi Sebaa, Benattou Bouchouicha Copyright (c) 2021 Mohammed Achoui , Fethi Sebaa, Benattou Bouchouicha Sat, 25 Sep 2021 00:00:00 +0000 Influence of Oxidation on Fracture Toughness of Carbon-Carbon Composites for High-Temperature Applications <p>Carbon-Carbon Composites (C-CC), used as composites for their remarkable qualities in the space industry as well as in many other industry sectors. C-CC has proven to be the most efficient material in extreme temperature situations. One of the best high-temperature materials with good thermal quality, such as high-temperature stability, outstanding thermal conductivity and low-temperature expansion coefficients. In aircraft, railways, trucks and even race vehicles, C-CC brake disks are in high demand. In comparison to the favorable thermal and mechanical qualities of C-CC, their great sensitivity to oxidation in an oxidizing environment at temperatures even around 400°C is a major restriction with these composites. In particular, a study of the C-CC oxidation mechanism helps to create protective measures for these composites. The present experimental study explores the influence of oxidation in static air on the fracture toughness of C-CC. At a temperature of around 400°C to 700°C in an increase of 100°C, an oxidation evaluation of the material was carried out in static air. Results show a decrease in fracture toughness to increase in the temperature. We can observe that C-CC fracture toughness is severely affected by oxidation. The variation began at 400°C from 6% and was anticipated at 700°C up to 45%.</p> Sunil Kumar B.V., Neelakantha V. Londe, M. Lokesha, S.N. Vasantha Kumar, A.O. Surendranathan Copyright (c) 2021 Sunil Kumar B.V., Neelakantha V. Londe, M. Lokesha, S.N. Vasantha Kumar, A.O. Surendranathan Sat, 25 Sep 2021 00:00:00 +0000 A new methodology to predict damage tolerance based on compliance via global-local analysis <p>Over the years several design philosophies to fatigue developed in order to combine structural safety and economy to manufacturing and operating aircraft process. The safe-life approach, which consists of designing and manufacturing a safe aeronautical structure throughout its useful life, results in factors that oversize the structural elements, preventing the possibility of failure and evidently leading to high design costs. On the other hand, the approach based on the damage tolerance concept, in which it is assumed that the structure, even whether damaged, is able to withstand the actions for which it was designed until the detection of a crack due to fatigue or other defects during its operation. Here, we propose a new methodology to the damage tolerance problem in which two-dimensional global-local analysis at different levels of external requests will be made by means of compliance, aimed at finding a relationship between fatigue life and the Paris constant. Moreover, the BemCracker2D program for simulating two-dimensional crack growth is used. This methodology has been proved to be an efficient and applied alternative in the damage tolerance analysis.</p> Gilberto Gomes, Thiago Oliveira, Alvaro Martins Copyright (c) 2021 Gilberto Gomes, Thiago Oliveira, Alvaro Martins Sat, 25 Sep 2021 00:00:00 +0000 Study on Micro - Nano Sized Al2O3 Particles on Mechanical, Wear and Fracture Behavior of Al7075 Metal Matrix Composites <p>Having Low density and being Light weight with better mechanical properties, aluminum is the most significant material and is universally used in highly critical applications like navy, aerospace and particularly automotive activities. This research work is aimed to investigate the effect of micro and nano boron Al<sub>2</sub>O<sub>3</sub> (Alumina Oxide) to aluminium (Al) on the mechanical and wear properties of the Al composites. The micro - nano composites with 1, 2, 3 and 4 % of Al<sub>2</sub>O<sub>3</sub> particulates in Al are fabricated using stircasting processes. It was found that an increase of Al<sub>2</sub>O<sub>3</sub> both as micro and nano particulates content resulted in an improved hardness, enhanced tensile strength and high wear resistance. However, nano Al<sub>2</sub>O<sub>3</sub> reinforced MMCs have better hardness, improved tensile strength and higher wear resistance as compared with micro sized Al<sub>2</sub>O<sub>3</sub> reinforced MMCs. Grain refinement of composite and nano composite materials as compared with pure Al were observed from the microscopic images. Analysis of wornout surface and tensile fracture surface were studied by SEM analysis to examine the nature of wear and tensile fracture mode of composite samples.</p> M. Ravikumar, H. N. Reddappa, R. Suresh, E. R. Babu, C. R. Nagaraja Copyright (c) 2021 M. Ravikumar, H. N. Reddappa, R. Suresh, E. R. Babu, C. R. Nagaraja Sat, 25 Sep 2021 00:00:00 +0000 Asymptotic response of friction stir welded joint under cyclic loading <p> Fatigue takes a place more and more important in the design of structures, it remains a key point in the mechanical dimensioning of structures.</p> <p>The Friction Stir Welding (FSW) process is regarded today as the most promising alternative to traditional joining methods. It ranks among the most recent assembly processes and is considered a new technique for the 21st century. Indeed, if the FSW welding process has several advantages, it introduces very strong microstructure heterogeneities in the welded joints.</p> <p>This leads to heterogeneous mechanical behavior in each of the constituent zones. some important efforts have been deployed in industry as well as in research laboratories to understand the behavior of welded joints by the FSW process. There are many questions about the behavior of these areas.</p> <p>This study led to the characterization and understanding of the fatigue behavior of a 2024T351 structure welded by the FSW process. It presente in a numerical work which aims to help determine the asymptotic response of each zone constituting the 2024T351 joint welded by FSW subjected to a cyclic loading and to fully understand the behavior of these zones.</p> <p>To carry out an analysis and a simulation under cyclic loading, our choice fell on the use of the direct cyclic method. Numerical simulation of crack propagation was performed using the extended finite element method XFEM.</p> <p>This research consists in the implementation of the X-FEM in fatigue in a multiscale model X-FEM / direct cyclic.</p> <p>The numerical results consist in highlighting the heterogeneities in the mechanical behavior of the welded joint and in evaluating the impact of the FSW process on the failure of these FSW zones.</p> Imane Elmeguenni Copyright (c) 2021 Imane Elmeguenni Sat, 25 Sep 2021 00:00:00 +0000 Fracture analysis of AA6061-graphite composite for the application of helicopter rotor blade <p>The main objective of the work is to study the fracture behavior of AA6061-graphite material using both experimental technique and finite element simulation by considering helicopter rotor blade as a case study. From the case study, it has been observed that the helicopter rotor blade, made of AA6061, has been failed at the threaded portion of the hole. Experimental fracture toughness is carried out using the compact tension specimens as per ASTM standard testing procedure. Modeling of compact tension specimens and the threaded portion of the bolt hole was utilized to analyze the fracture toughness using a simulation tool. From the results and the comparison, it is recommended to use AA6061-9wt% graphite material as a replacement of AA6061 in the application of main rotor blades of the helicopter.</p> Saleemsab Doddamani, Chao Wang, M. Sheik Mohamed Jinnah, Md. Arefin Kowser Copyright (c) 2021 Saleemsab Doddamani, Chao Wang, M. Sheik Mohamed Jinnah, Md. Arefin Kowser Sat, 25 Sep 2021 00:00:00 +0000 A Simplified ALE model for finite element simulation of ballistic impacts with bullet splash – development and experimental validation <p>An original simplified finite element model is proposed to simulate the effects of non-penetrating ballistic impacts causing the so-called bullet splash phenomenon (complete bullet fragmentation), while no fragmentation is caused to the target. The model is based on the Arbitrary Lagrangian Eulerian formulation (ALE) and it simulates the impact as a fluid-structure interaction. The bullet splash phenomenon has been tested by experimental analyses of AISI 304L plates impacted by 9x21 FMJ (full metal jacket) bullets. The model has been developed with the aim of creating a simplified approach to be used in the industry and forensic sciences to simulate the non-penetrating interaction of soft impactors with hard targets. Comparisons between evidence and simulation results lead to the conclusion that the proposed approach can be used in a conservative way to estimate both local and global effects of bullet-splash phenomena.</p> Riccardo Andreotti, Sergio Abate, Andrea Casaroli, Mauro Quercia, Riccardo Fossati, Marco V. Boniardi Copyright (c) 2021 Riccardo Andreotti, Sergio Abate, Andrea Casaroli, Mauro Quercia, Riccardo Fossati, Marco V. Boniardi Tue, 22 Jun 2021 00:00:00 +0000 Inverse problems with the digital image correlation: approach and applications <p>A viable approach to solve inverse problems in elasticity is proposed. It is based on regression algorithms to estimate materials and/or loading parameters by fitting the experimentally-evaluated displacement field to representative analytical solutions.</p> <p>Displacements are measured by the digital image correlation (DIC) technique and they are used as input for numerical procedures able to minimize the estimation errors of the unknowns and to quantify the unavoidable rigid body motions of the samples/components. In addition, thanks to ad-hoc developed iterative algorithms, non-linear phenomena related to high and localized stress/strain states, can be captured successfully. This latter represents a relevant novelty of the methodology as it allows to investigate plasticity-induced mechanisms in solid mechanics which are impossible to analyze with more traditional DIC-based approaches.</p> <p>Three different case studies are considered: 1) estimation of the stress intensity factor in fracture mechanics problems, 2) estimation of the elastic properties of a material by the Brazilian tests, 3) estimation of the contact pressure generated by thermally activated shape memory alloy (SMA) rings used for pipe coupling.</p> <p>The reliability and the accuracy of the method is demonstrated through systematic comparisons of the results with conventional techniques in experimental mechanics.</p> Emanuele Sgambitterra, Fabrizio Niccoli Copyright (c) 2021 Emanuele Sgambitterra, Fabrizio Niccoli Tue, 22 Jun 2021 00:00:00 +0000 Railway overhead contact wire monitoring system by means of FBG sensors <p>Safety of infrastructures represents one of the most significant concerns for governments and service providers to preserve people's well-being. One of the main ways to keep in safe facilities (buildings, bridges, railways, etc.) involves the use of monitoring sensor systems in charge of measuring critical operating conditions. Those measurements together with periodical maintenance, contribute to minimize potential risks that the infrastructure faces. The paper aims at designing, developing, and testing a monitoring system for mechanical stresses acting on the overhead contact wire (OCW) to ensure the operational safety of the railway network. In this regard, the paper proposes two Fiber Bragg Grating (FBG) sensors-based solutions, relying on the ability of these sensors to allow real-time and continuous data acquisition. The first one consists in a polyimide-coated sensor bonded on an OCW clamp, the second one is a copper-coated sensor hanging between the two separated halves of an OCW clamp. Significant results have been obtained mechanically testing both solutions, trying to simulate the operative conditions.</p> Erwin Ciro Zuleta, Carla Lupi, Ferdinando Felli, Claudio Paris, Cristian Vendittozzi Copyright (c) 2021 Erwin Ciro Zuleta, Carla Lupi, Ferdinando Felli, Claudio Paris, Cristian Vendittozzi Tue, 22 Jun 2021 00:00:00 +0000 Fully implicit numerical integration of the Yoshida-Uemori two-surface plasticity model with isotropic hardening stagnation <p>The paper deals with the numerical investigation and implementation of the two-surface plasticity model (or bounding surface model). This plasticity theory allows to describe the deformation behavior under large strain cyclic plasticity and the material stress-strain responses at small-scale re-yielding after large pre-straining. A novel strategy to model the isotropic hardening stagnation is developed within a fully implicit integration scheme in order to speed up the computation and to improve the material description.</p> Riccardo Fincato, Seiichiro Tsutsumi, Alex Zilio, Gianluca Mazzucco, Valentina Salomoni Copyright (c) 2021 Riccardo Fincato, Seiichiro Tsutsumi, Alex Zilio, Gianluca Mazzucco, Valentina Salomoni Tue, 22 Jun 2021 00:00:00 +0000 Enhancement of circular RC columns using steel mesh as internal or external confinement under the influence of axial compression loading <p>Reinforced concrete (RC) columns cannot get supreme confinement by using the customary steel stirrups reinforcement because of the requirements for the spacing distances between the stirrups in addition to concrete continuance trouble. For this, Steel Mesh (SM) externally wrapped around the outer perimeter of the column as contributory confinement are being widely used due to its features. Limited tests focused on using SM for the internal confinement around the reinforcing cage of RC columns. Moreover, no experimental comparison was presented between RC columns internally and externally confined using SM. This paper investigates experimentally the behavior of circular RC columns confined internally or externally by SM. Six short RC columns have been subjected to axial loading until failure. The main studied parameters were SM schemes, number of SM wraps, SM position (internally or externally), and the steel stirrups existence. Results demonstrated that SM could decrease the crack opening, diminish the concrete spalling, increase the maximum failure load, and enhance the ductility, energy absorption, and column stiffness. Furthermore, the partially internal confinement using two wraps of SM around the steel ties presented the maximum capacity with reasonable ductility. In general, internally confined columns showed better behavior than the externally confined one.</p> Mohamed Emara, Mostafa S. Rizk, Heba A. Mohamed, Mahmoud Zaghlal Copyright (c) 2021 Mohamed Emara, Mostafa S. Rizk, Heba A. Mohamed, Mahmoud Zaghlal Sat, 25 Sep 2021 00:00:00 +0000