Frattura ed Integrità Strutturale https://www.fracturae.com/index.php/fis <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). The Journal is financially supported by Italian Group of Fracture and by crowdfunding and is completely free of charge both for readers and for authors. Neither processing charges nor submission charges will be required.<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.</p> <p>&nbsp;</p> <p><strong>Sister Associations help the journal managing:</strong><br>Australia: Australian Fracture Group - AFG<br>Czech Rep.: Asociace Strojních Inženýrů (Association of Mechanical Engineers)<br>Greece: Greek Society of Experimental Mechanics of Materials - GSEMM<br>India: Indian Structural Integrity Society - InSIS<br>Israel: Israel Structural Integrity Group - ISIG<br>Italy: Associazione Italiana di Metallurgia - AIM<br>Italy: Associazione Italiana di Meccanica Teorica ed Applicata - AIMETA<br>Italy: Società Scientifica Italiana di Progettazione Meccanica e Costruzione di Macchine - AIAS<br>Poland: Group of Fatigue and Fracture Mechanics of Materials and Structures<br>Portugal: Portuguese Structural Integrity Society - APFIE<br>Romania: Romania Association of Fracture Mechanics - ARMR<br>Serbia: Structural Integrity and Life Society "Prof. Stojan Sedmak" - DIVK<br>Spain: Grupo Espanol de Fractura - Sociedad Espanola de Integridad Estructural - GEF<br>Ukraine: Ukrainian Society on Fracture Mechanics of Materials (USFMM)</p> Gruppo Italiano Frattura (IGF) en-US Frattura ed Integrità Strutturale 1971-8993 <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>Frattura ed Integrità Strutturale (Fracture and Structural Integrity, F&amp;SI) 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 BOAI definition of open access. F&amp;SI 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> Critically evaluating mechanics of structure genome-based micromechanics approach https://www.fracturae.com/index.php/fis/article/view/2406 <p>The objective of this paper is to critically evaluate the accuracy and efficiency of a general-purpose micromechanics approach based on the Mechanics of Structure Genome (MSG), when it is applied to the constitutive modeling of 3D&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; structures. The Generalized Method of Cell (GMC) is chosen as a reference method during efficiency evaluation. The predictions by Three-Dimensional Finite Element Analysis (3D FEA) are chosen as benchmarks during accuracy evaluation. Composites such as a continuous fiber-reinforced composite, a&nbsp;&nbsp; particle-reinforced composite, two discontinuous fiber-reinforced composites, and a woven composite are analyzed using MSG, GMC, and 3D FEA.&nbsp; During homogenization, MSG is found to be as accurate but much more efficient than 3D FEA, and despite high efficiency, GMC is found to sacrifice accuracy for&nbsp;&nbsp; efficiency. During dehomogenization, MSG is found to be as accurate as 3D FEA, but GMC is found not to be so accurate. The fidelity of MSG, when it is applied to the modeling of other structures (e.g., beams, plates, and shells), can be similarly evaluated.</p> Hamdi Mawloud Ramdane Zenasni Sidi Mohammed Amine Khiat Copyright (c) 2019 Hamdi Mawloud, Ramdane Zenasni, Sidi Mohammed Amine Khiat http://creativecommons.org/licenses/by/4.0 2019-06-27 2019-06-27 13 49 321 330 10.3221/IGF-ESIS.49.32 Duality of singularities of multiscale damage localization and crack advance: length variety in Theory of Critical Distances https://www.fracturae.com/index.php/fis/article/view/2481 <p>The existence of two singularities related to the stress field at the crack tip and blow-up kinetics of damage localization is considered as the physical basis for the interpretation of the Theory of Critical Distances. The free energy metastability of solid with defects and corresponding free energy release explain the conception of the Finite Fracture Mechanics in the presence of the finite amplitude energy barrier. The variety of crack paths is analyzed as duality of inherently linked two types of singularities related to the singularity of multiscale damage kinetics under crack nucleation and singularity of stress field at the crack tip as the classical framework of fracture mechanics. The singularity of multiscale damage kinetics is a natural precursor of crack nucleation that could provide in some cases the totally independent scenario of fracture from the stress singularity at the crack tips. The influence of two singularities with the nature of intermediate asymptotical solutions for stress at the crack tip and damage localization kinetics over the set of spatial scales represents two attractors, which provides the variety of crack paths for corresponding loading conditions.</p> Oleg Naimark Copyright (c) 2019 Oleg Naimark http://creativecommons.org/licenses/by/4.0 2019-06-27 2019-06-27 13 49 272 281 10.3221/IGF-ESIS.49.27 Characterisation and Evaluation of the Mechanical Behaviour of Endodontic-grade NiTi Wires https://www.fracturae.com/index.php/fis/article/view/2338 <p>With the introduction of new materials and advances in medical science, the endodontic files have changed since the early days of root canal treatments. In the late days, we have seen an increasing use of Nickel-Titanium (NiTi) alloys, to the detriment of more conventional alloys. At body temperature, NiTi alloys present a superelastic behaviour, which allows to be more effective in the removal of the tooth pulp tissue, and in the protection of the tooth structure.</p> <p>Anyhow, these NiTi instruments will eventually fracture, usually without any visual signal of degradation. Thus, there is a need of studying these alloys, as they present a high hysteresis cycle and non-linearities in the Elastic domain.</p> <p>Currently, there is no international standard to test NiTi endodontic files, so various authors have attempted to design systems that can test them under fatigue loads, usually based on empirical setups.</p> <p>Following a systematic approach, this work presents the results of rotary fatigue tests for two Alfa Aesar® Nitinol wires with different diameters (0.58mm and 0.25mm).The formulation is presented, where the material strength reduction can be quantified from the determination of the strain and the number of cycles until failure, as well numerical FEM simulation to verify the analytical model predictions.</p> Samuel Pereira André Rui Dantas Carvalho Luís Reis Manuel Freitas Diogo Montalvão Copyright (c) 2019 Samuel Pereira, André Rui Dantas Carvalho, Luís Reis, Manuel Freitas, Diogo Montalvão http://creativecommons.org/licenses/by/4.0 2019-06-27 2019-06-27 13 49 450 462 10.3221/IGF-ESIS.49.43 Fatigue strength of inner knurled interference fit joined by forming and cutting methods https://www.fracturae.com/index.php/fis/article/view/2309 <p>The joining of machine parts by plastic forming is a common method for transmitting forces and torque. In drive trains, the ‘knurled interference fit’ has a high transmission capacity through the combination of frictional connection and form fit. In the present study, the shaft specimen made of C45 steel material is joined with an inner knurled hub made of 16MnCr5 case hardened steel. The influence of the joining process parameters on the torsional fatigue strength of the shaft-hub connection is investigated by means of experimental studies. The most important parameter is the chamfer angle of the knurled hub, which determines the rate of strain hardening in the material and differs between the cutting and forming joining processes. This study shows that knurled interference fit connections joined by forming achieve a higher fatigue strength and a higher maximum static torque than connections joined by cutting.</p> Lukas Suchy E. Leidich A. Hasse T. Gerstmann B. Awiszus Copyright (c) 2019 Lukas Suchy, E. Leidich, A. Hasse, T. Gerstmann, B. Awiszus http://creativecommons.org/licenses/by/4.0 2019-06-27 2019-06-27 13 49 429 434 10.3221/IGF-ESIS.49.41 Estimation of tensile mechanical parameters of existing masonry through the analysis of the collapse of Volterra’s urban walls https://www.fracturae.com/index.php/fis/article/view/2506 <p>In this work, numerical analyses on the Volterra’s ancient walls are performed to understand the causes of a collapse occurred after an extreme rainfall (2014) and to identify the mechanical parameters that most influenced it. The stretch of collapsed wall is modelled with finite elements by distinguishing the material composing the multi-leaf wall. Non-linear static analyses are carried out with the DIANA software considering different levels of hydraulic head up to reach the collapse of the structure. The impact on the failure modes of the involved parameters, such as tensile strength, fracture energy and shear strength, are discussed. Tensile strength is found as the most relevant parameter in the failure mode. Finally, a 3-dim model is presented, and the results show a very good agreement with the failure mode actually occurred in terms of both failure modes and displacement fields. The safety evaluation is performed in the as-built and the retrofitted configuration, consisting in the wall restrained by tie-rods. The results show a significant increasing of the safety level of the retrofitted configuration showing a considerable improvement not only in terms of limit equilibrium but also in terms of structural capacity of the wall.</p> Mario Lucio Puppio Linda Giresini Copyright (c) 2019 Mario Lucio Puppio, Linda Giresini http://creativecommons.org/licenses/by/4.0 2019-06-27 2019-06-27 13 49 725 738 10.3221/IGF-ESIS.49.65 A 3D analysis of crack-front shape of asymmetric repaired aluminum panels with composite patches https://www.fracturae.com/index.php/fis/article/view/2059 <p>Through this study, a numerical simulation based on 3D in order to investigate the effect of Crack-front shape on the stress intensity factor and fatigue crack growth behavior of center cracked aluminum plate repaired asymmetrically with a bonded composite patch. Consequently, Skew degree is a significant effect on stress intensity factor (SIF) distribution along the crack front in thick panels more than thin panels. Moreover, Fatigue life was calculated using different averages stress intensity factor of patched panel determined from the uniform crack front model and skew crack front model obtained from FEM and when comparing fatigue life values obtained from the finite element model with experimental values were shown a good agreement.</p> Abdelkader Djebli El Hadj Besseghier Mostefa Bendouba Abdelghani Baltach Abdelkrim Aid Copyright (c) 2019 Abdelkader Djebli, El Hadj Besseghier, Mostefa Bendouba, Abdelghani Baltach, Abdelkrim Aid http://creativecommons.org/licenses/by/4.0 2019-06-27 2019-06-27 13 49 547 556 10.3221/IGF-ESIS.49.51 Algorithms for calculation damage processes https://www.fracturae.com/index.php/fis/article/view/2485 <p class="ECF17Reference"><span lang="EN-US">The paper reviews the existing approaches to calculating the destruction of solids. The main attention is paid to algorithms using a unified approach to the calculation of deformation both for nondestructive and for the destroyed states of the material. The thermodynamic derivation of constitutive relations for solids with elastic, viscous and plastic properties accounting possible destruction is presented. Explicit and implicit non-matrix algorithms for calculating the evolution of deformation and fracture development are presented. Implicit schemes are implemented using iterations of the conjugate gradient method, with the calculation of each iteration exactly coinciding with the calculation of the time step for two-layer explicit schemes. Therefore the solution algorithms are very simple.&nbsp;</span><span lang="EN-US">The results of solving typical problems of destruction of solid deformable bodies for slow (quasistatic) and fast (dynamic) deformation processes are presented. Recommendations are given for modeling the processes of destruction and ensuring the reliability of numerical solutions.</span></p> Aleksandr Dmitrievich Nikitin Nikolay G. Burago Ilia S. Nikitin Boris A. Stratula Copyright (c) 2019 Aleksandr Dmitrievich Nikitin, Nikolay G. Burago, Ilia S. Nikitin, Boris A. Stratula http://creativecommons.org/licenses/by/4.0 2019-06-26 2019-06-26 13 49 212 224 10.3221/IGF-ESIS.49.22 Comparative study of Shot creep of single-phase titanium alloys in air and neutral gas environment on the test temperature in range from 673 to 1323 K https://www.fracturae.com/index.php/fis/article/view/2479 <p>The paper presents the results of comparative studies of short-term creep in tensile tests of the VT1-0 commercially pure titanium (analogue Grade 2 according to ASTM A485) and the VT5-1 alloy (analogue Grade 6 according to ASTM B265) in air and argon. Tests by the Dorn’s method were carried out in a gas-tight chamber under constant pressure. The specimens were heated by passing alternating current. Empirical coefficients are determined in power dependences of the creep rate and the conventional creep strength on test temperature in the range from 673 to 1323 K for argon and air environment and nominal stress ranging between 4.45 and 9.36&nbsp;MPa. It is found that heating in argon environment, as compared to heating in air, decreases the rate of short-term creep and increases creep strength at identical nominal stresses in the entire range of test temperatures. Calculations demonstrate that the energy of the activation of short-term creep does not depend on test conditions. This indicates that the deformation mechanism is unchanged.</p> lev Michailovich Zamaraev Sergey Smirnov Copyright (c) 2019 lev Michailovich Zamaraev, Sergey Smirnov http://creativecommons.org/licenses/by/4.0 2019-06-26 2019-06-26 13 49 201 211 10.3221/IGF-ESIS.49.21 Stress intensity factors analyses for external semi-elliptical crack for repaired gas-pipeline by composite overwrap under pressure https://www.fracturae.com/index.php/fis/article/view/2358 <p>The purpose of this article is to present the stress intensity factors (SIF) solutions for semi-elliptic crack in pipelines under internal pressures, the stress intensity factors are calculated by the three-dimensional finite element method (FEM) for cracked pipelines and repaired pipe by composite patch. The distribution of normalized stress intensity factors (K<sub>I</sub>, K<sub>II</sub> and K<sub>III</sub>) along the crack front for different crack lengths, crack depth, crack geometry, lap length and composite thickness was obtained by nodal calculations. Our FE results show that the crack frond is non-regular with respect to the rupture mode and presents three zones where the mixed mode (K<sub>II</sub>) is dominant from the deepest point to the point close to the surface of the pipe not the mode I cited in several studies. When the edge of the crack is close to the outer diameter, the mode III (K<sub>III</sub> ) is dominant and this regardless of the state of the pipelines. it can also be noted that the composite repair reduces the SIF K<sub>I</sub> by 46% and the K<sub>II</sub> by 55% and the K<sub>III</sub> by 72% near the outside diameter of the pipe in each zone of domination. However composite repair is very effective for a rectangular crack as for the semi-elliptical crack. this confirms that the elliptic crack is dominated by the mixed mode II not by mode I.</p> Djamel Eddine Belhadri Mohamed Belhamiani Wahiba Nesrine Bouzitouna Wahid Oudad Copyright (c) 2019 Djamel Eddine Belhadri, Mohamed Belhamiani, Wahiba Nesrine Bouzitouna, Wahid Oudad http://creativecommons.org/licenses/by/4.0 2019-06-26 2019-06-26 13 49 599 613 10.3221/IGF-ESIS.49.55 Analysis of mechanical properties of transition segment of road and bridge based on high-strength foam concrete https://www.fracturae.com/index.php/fis/article/view/2357 <p>The settlement difference in the transition section of road and bridge may lead to traffic accidents, which has many negative effects. Back filling of foam concrete behind abutment is a good method of treatment. In this study, a kind of high-strength foam concrete was designed for back filling of transition section of road and bridge, and the mechanical properties of the transition section of road and bridge were analyzed. It was found that only a large number of micro cracks &nbsp;grew in high-strength concrete under a large number of load cycles, and structural damage did not happen, indicating the high-strength foam concrete had high strength and long service life; the static base pressure was about 40 KPa, indicating a small burden on the structure. Under the vehicle load, the vertical displacement of the transition section of road and bridge with back filling of high-strength foam concrete behind abutment was about 0.7 m and the maximum vertical stress was about -40 KPa, which was significantly lower than that of the ordinary concrete, and the stability was favourable, indicating that the high-strength foam concrete had good vibration absorption effect. The analysis results verifies the value of the high-strength foam concrete as the backfill material of the transition section of road and bridge, providing some theoretical basis for its application and popularization.</p> Hongmei Cao Copyright (c) 2019 Hongmei Cao http://creativecommons.org/licenses/by/4.0 2019-06-26 2019-06-26 13 49 831 839 10.3221/IGF-ESIS.49.73 Numerical model of fracture growth in hydraulic re-fracturing https://www.fracturae.com/index.php/fis/article/view/2454 <p>Simulation of fracture propagation with FEM method generates the need of re-meshing to provide more accurate results. This raises a question of determining the direction and criterion of mesh modification. In the case of general-purpose CAE-packages, we deal with a stationary mesh, and the fracture path is usually represented as a chain of elements with degraded properties. The algorithm proposed in this paper is based on the ANSYS Mechanical APDL language for stepwise geometry reconstruction and mesh modification in accordance with the current configuration of a growing fracture and provides a more accurate description of its shape. The fracture propagation process is divided into stages. Each subsequent stage differs from the previous one by the fracture shape modified due to the crack length increment in the calculated direction. To check the adequacy of the model, an experiment on fracture propagation in glass specimens with an initial notching under uniaxial compression was performed. The laboratory experiments were carried out to determine the fracture toughness of rocks. The developed numerical model has been used to solve the problem of re-fracturing for different stress anisotropy in the oil-bearing rock formation.</p> Oleg Yurievich Smetannikov Yuriy Aleksandrovich Kashnikov Sergey Gennadievich Ashikhmin Artem Eduardovich Kukhtinskiy Copyright (c) 2019 Oleg Yurievich Smetannikov, Yuriy Aleksandrovich Kashnikov, Sergey Gennadievich Ashikhmin, Artem Eduardovich Kukhtinskiy http://creativecommons.org/licenses/by/4.0 2019-06-26 2019-06-26 13 49 140 155 10.3221/IGF-ESIS.49.16 Multi-parameter fracture mechanics https://www.fracturae.com/index.php/fis/article/view/2491 <p>A mixed-mode geometry has been chosen to investigate a crack propagation using the multi-parameter fracture mechanics concept. The so-called Williams’ series expansion is used for the crack-tip stress field approximation. It has been shown that application of the generalized fracture mechanics concept can be crucial for materials with specific fracture behaviour, such as elastic-plastic or quasi-brittle one, when fracture occurs not only in the very vicinity of the crack tip, but also in a more distant surrounding. Then, considering the higher-order terms of the Williams’ expansion in fracture criteria (describing the crack stability and/or crack propagation direction) can bring more precise results. The coefficients of the Williams’ expansion must be calculated numerically (for instance by means of the over-deterministic method in this work) for each cracked configuration, which is very time-consuming, and the analysis is very extensive even for a few basic cracked specimen configurations. On the other hand, a suitable choice of the geometrical configuration of the cracked disc enables performing experiments only on the specimens that could prove the theory about the importance of using the higher-order terms.</p> Lucie Malikova Hana Simonova Barbara Kucharczykova Petr Miarka Copyright (c) 2019 Lucie Malikova, Hana Simonova, Barbara Kucharczykova, Petr Miarka http://creativecommons.org/licenses/by/4.0 2019-06-25 2019-06-25 13 49 65 73 10.3221/IGF-ESIS.49.07 Numerical analysis of a caprock integrity during oil production by steam-assisted gravity drainage method https://www.fracturae.com/index.php/fis/article/view/2460 <p><span lang="EN-US" style="margin: 0px; color: black; font-family: 'Garamond',serif; font-size: 12pt;">The work is devoted to the investigation of a caprock integrity during oil production by steam-assisted gravity drainage method</span><span lang="EN-US" style="margin: 0px; font-family: 'Garamond',serif; font-size: 12pt;">. An originally proposed thermo-hydro-mechanical model was used for the evaluation of mechanical loading acting on the over-burden. The model includes mass conservation laws, the energy conservation law and the linear momentum balance. Filtration of each phase of the three-phase flow (steam, oil and water) is described by Darcy’s law. Inelastic deformations are described by the phenomenological viscoplastic model based on Drucker-Prager yield criterion.<span style="margin: 0px;">&nbsp; </span>The effect of<span style="margin: 0px;">&nbsp; </span>the porosity evolution induced by the propagation of the steam chamber within the reservoir on the oil production rate and the caprock integrity is studied. It has been shown that the oil production rate is strongly depend on the prevailing physical mechanism of the porosity evolution.<span style="margin: 0px;">&nbsp; </span>Reservoirs characterized by the volumetric strain mechanism of the porosity evolution produce slightly higher values of the mechanical loadings acting on the over-burden.</span></p> Anastasiia Kostina Maxim Zhelnin Oleg Plekhov Copyright (c) 2019 Anastasiia Kostina, Maxim Zhelnin, Oleg Plekhov http://creativecommons.org/licenses/by/4.0 2019-06-25 2019-06-25 13 49 302 313 10.3221/IGF-ESIS.49.30 Damage evolution in the AMg6 alloy during high and very high cycle fatigue https://www.fracturae.com/index.php/fis/article/view/2453 <p>Paper presents the “in situ” method for determining of irreversible fatigue damage accumulation, based on the analysis of nonlinear manifestations of the feedback signal in a closed system of an ultrasonic fatigue system. During very high cycle (gigacycle) fatigue, the anomalies of the elastic properties of the material are appear, which leads to a nonlinearity effect in the amplitude of oscillations. This effect increases with the initiation and growth of fatigue cracks. The technology was applied to samples of AMG-6 alloy with preliminary dynamic deformation at various levels of average stress to determine the moment of initiation and growth of the fatigue crack in very high cycle fatigue regime. This method is applicable for the early detection of fatigue cracks both on the surface and inside the material under cyclic loading in the ultrasonic mode. On the basis of wide-range defining relations for a deformable solid body with mesoscopic defects, a mathematical model has been proposed that can adequately describe behavior of the material during fatigue failure. The results of mathematical modeling are in good agreement with the experimental data</p> Mikhail Bannikov Dmitry Bilalov Vladimir Oborin Oleg Naimark Copyright (c) 2019 Mikhail Bannikov, Dmitry Bilalov, Vladimir Oborin, Oleg Naimark http://creativecommons.org/licenses/by/4.0 2019-06-25 2019-06-25 13 49 383 395 10.3221/IGF-ESIS.49.38 Coupled identification of the hardening behavior laws and Gurson–Tvergaard–Needleman damage parameters - Validation on tear test of 12NiCr6 CT specimen https://www.fracturae.com/index.php/fis/article/view/2414 <p>This work is devoted to the application of the micromechanical Gurson-Tvergaard-Needleman (GTN) model to study the ductile tearing of 12NiCr6 steel. GTN model is widely used to describe the three stages of ductile tearing: nucleation, growth and the coalescence of micro-voids. A new approach consists of a coupled identification of the GTN damage model with and without hardening laws using an inverse analysis is proposed. After identification, the obtained results show a good agreement between the experimental curve tensile test of an axisymetric notched bar (AN2) and those numerically obtained for GTN model coupled with the hardening laws. In order to validate the identified GTN parameters, a simulation of tear test is conducted on 12 NiCr6 steel CT specimen. The numerical results are compared with experimental results found in the literature and a good agreement is obtained. This identification procedure is more accurate than when the damage parameters are identified independently of the hardening laws.</p> Mohamed Hadj Miloud Ibrahim Zidane Mohammed Mendas Copyright (c) 2019 Mohamed Hadj Miloud, Ibrahim Zidane, Mohammed Mendas http://creativecommons.org/licenses/by/4.0 2019-06-25 2019-06-25 13 49 630 642 10.3221/IGF-ESIS.49.57 Numerical analysis of application limits of Vyalov’s formula for an ice-soil thickness https://www.fracturae.com/index.php/fis/article/view/2462 <p>Artificial ground freezing is an efficient technique which allows one to sink the mine shafts under complex hydrogeological conditions. The aim of artificial ground freezing is a creation of a temporary wall of frozen soil around the intended excavation. To estimate an optimal thickness of an ice-soil wall, the Vyalov’s formula is widely used by engineers. The article is devoted to analysis of Vyalov’s formula on the basis of the numerical simulation. The numerical simulation has been conducted by the finite element method. For the simulation of a stress-strain state of an ice-soil wall a new computational scheme has been proposed. The scheme is based on Vyalov’s design layout for a vertical shaft sinking and takes into account a soil layer beyond the excavation bottom. A mechanical behavior of frozen soil is described by Vyalov’s constitutive relations. As a result, it has been shown that values of the wall thickness given by Vyalov’s formula do not agree with the ones obtained by the numerical simulation. In order to conform results given by Vyalov’s formula and the numerical simulation, two modifications of the formula have been proposed.</p> Maxim Zhelnin Anastasiia Kostina Oleg Plekhov Ivan Panteleev Lev Levin Copyright (c) 2019 Maxim Zhelnin, Anastasiia Kostina, Oleg Plekhov, Ivan Panteleev, Lev Levin http://creativecommons.org/licenses/by/4.0 2019-06-25 2019-06-25 13 49 156 166 10.3221/IGF-ESIS.49.17 Analysis of the Fatigue Damage Behavior of AW2099-T83 Al-Li Alloy under Strain-Controlled Fatigue https://www.fracturae.com/index.php/fis/article/view/2376 <p>Microstructural characteristics, monotonic and strain-controlled cyclic axial behaviors of AW2099-T83 Aluminum-Lithium alloy were investigated. Grain sizes and structures are not uniform in the different orientations studied. High strength and low ductility characterize the tensile behavior of the alloy under static loading. Strain-controlled fatigue testing was conducted at strain amplitudes ranging from 0.3% to 0.7%. Over this range, macro plastic deformation was only observed at 0.7%.&nbsp; Cyclic stress evolution was found to be dependent on both the applied strain amplitude and the number of cycles. Limited strain hardening was observed at low number of cycles, followed by softening, due probably to damage initiation. With low plastic strain, analytical approach was adopted to profile the damaging mechanism for the different applied strain amplitude. Because of the absence of fatigue ductility parameters due to low plasticity, a three-parameter equation was used to correlate fatigue life. Fractured specimens were studied under SEM to characterize the fracture surface and determine the controlling fracture mechanisms. The fractography analysis revealed that fracture at low strain amplitudes was shear controlled while multiple secondary cracks were observed at high strain amplitude. Intergranular failure was found to be the dominant crack propagation mode.</p> Muhammed Jamiu Adinoyi Nesar Merah, Prof. Jafar Albinmousa, Associate Prof Copyright (c) 2019 Muhammed Jamiu Adinoyi, Nesar Merah, Prof., Jafar Albinmousa, Associate Prof http://creativecommons.org/licenses/by/4.0 2019-06-25 2019-06-25 13 49 487 506 10.3221/IGF-ESIS.49.46 Possibility of tuning shunt circuits for multimodal damping of vibrations of structure with piezoelectric element https://www.fracturae.com/index.php/fis/article/view/2446 <p>In this paper, an approach is proposed that allows for the selecting of the parameters of the shunt circuit that provide multimodal damping of vibrations for the corresponding piezoelectric element location. This technique is based on a solution to the natural vibration problem for an electroelastic structure with an attached piezoelectric element that is shunted with a single external resonant electric circuit. The solution to the problem is complex natural vibration frequencies. The analysis of their behaviour in the space of external circuit parameters (resistance – inductance) allows one to reveal the possibility of natural vibrations control at several frequencies (multimodal vibration damping). The applicability of the proposed approach is demonstrated using a shell structure in the form of a semi-cylinder with a piezoelectric element attached to its surface and shunted with a single-branched resonant electric circuit. Some options are considered that provide multimodal damping at several separated frequencies, which are not from the complete frequency range, and at all the frequencies, which are included in a specified frequency range.</p> Nataliia A. Iurlova Dmitrii A. Oshmarin Maksim A. Iurlov Nataliya V. Sevodina Copyright (c) 2019 Nataliia A. Iurlova, Dmitrii A. Oshmarin, Maksim A. Iurlov, Nataliya V. Sevodina http://creativecommons.org/licenses/by/4.0 2019-06-25 2019-06-25 13 49 800 813 10.3221/IGF-ESIS.49.13 Approximation of the crack-tip field in fatigue cracks in bridge steel specimens: DIC analysis of different constraint levels https://www.fracturae.com/index.php/fis/article/view/2522 <p>A study on the accuracy of the approximation of the displacement field around of crack tip in a sample made from bridge steel (S355) is main objective of contribution. Linear elastic fracture mechanics (LEFM) theory in framework of multi-parameter formulation, i.e. postulated by Williams is used to determine of coefficients of Williams power series terms. Over deterministic method was used to calculate the terms based on the least squares regression technique, applied on data from numerical simulation and experiment on S355 steel grades. Comparison between the stress fields (by principal stress <em>s</em><sub>1</sub> and von Mises stress <em>s</em><sub>HMH</sub>) obtain from experimental measurement DIC, Hybrid method and obtain from reconstruction by using various number of Williams power terms are quantified in order to get key information around the crack tip region on bridge steel specimens.</p> Stanislav Seitl Petr Miarka Vladimir Ruzicka Lucie Malikova Alejandro Cruces Pablo Lopez Crespo Copyright (c) 2019 Stanislav Seitl, Petr Miarka, Vladimir Ruzicka, Lucie Malikova, Alejandro Cruces, Pablo Lopez Crespo http://creativecommons.org/licenses/by/4.0 2019-06-25 2019-06-25 13 49 97 106 10.3221/IGF-ESIS.49.10 Fracture properties of green mortars with recycled sand https://www.fracturae.com/index.php/fis/article/view/2484 <p>Urbanisation is consuming huge amounts of sand, being the basic element of concrete and glass, two of the most popular construction materials. Unfortunately, sand mining is causing environmental damage and drastically reducing the amount of raw resources. The main topic of this research is to investigate the use of Construction and Demolition waste finer fraction - namely recycled sand - to totally replace the standard one into traditional mortars. From the analysis of the mechanical characterization of specimens, it is possible to state that recycled sand could represent a new resource for green and sustainable mortars.</p> Luciana Restuccia Copyright (c) 2019 Luciana Restuccia http://creativecommons.org/licenses/by/4.0 2019-06-25 2019-06-25 13 49 676 689 10.3221/IGF-ESIS.49.61 Post- Impact Fatigue Damage Analysis of Quasi Isotropic CFRP Laminates through Infrared Thermography https://www.fracturae.com/index.php/fis/article/view/2348 <p>Carbon fiber reinforced plastic (CFRP) materials used for lightweight aircraft structures are susceptible to low velocity accidental impacts during manufacture and while in service. In this study the CFRP laminates subjected to low velocity impact conditions of three different energy levels were tested under various fatigue loading conditions till it reached the failure state. The infrared thermography NDT technique was used for the damage analysis of these post-impact fatigue loaded CFRP specimens to understand the damage distribution across the specimen. The cooling response curves obtained from the active thermography of the post impact fatigue specimens under four different combinations (transmission or reflection mode with impacted or un-impacted surface facing camera) for each of the specimens were analyzed. The rate of cooling in the temperature response curves is different for each specimens subjected with various post impact-fatigue loading conditions and it seems to be correlated with the extent of post-impact fatigue damage present in each specimen quantified through X-ray CT image processing. The temperature rise observed in the passive thermography at the fiber/ply breakage during static strength tests were proportional to corresponding load drops and the non-homogeneous spread of damage at the onset of tensile failure was seen from the thermographs.</p> Raghu Vasu Prakash Mathew John Copyright (c) 2019 Raghu Vasu Prakash, Mathew John http://creativecommons.org/licenses/by/4.0 2019-06-24 2019-06-24 13 49 536 546 10.3221/IGF-ESIS.49.50 Structural Integrity Assessment of Weld for Joining Waveguide to Annular Linear Induction Pump Subjected to Vibration https://www.fracturae.com/index.php/fis/article/view/2299 <p>Annular Linear Induction Pump (ALIP) is employed for low flow rate pumping of liquid metals because of its maintenance free operation.&nbsp; In order to monitor pump vibration during operation, a waveguide with accelerometer combination is employed.&nbsp; The waveguide is a SS rod of 300 mm length and 20 mm diameter which is provided with a threaded provision at one end for mounting the accelerometer.&nbsp; The other end of the waveguide is welded to the shell of the ALIP of 3 mm thickness. These waveguides are to be attached to the ALIP in different orientations. The weld connecting the waveguide to the shell of ALIP is subjected to fatigue loading caused due to pump vibration. This paper discusses the analysis carried out to determine the fatigue life of the weld using ASME SECTION VIII DIVISION 2.</p> <p><strong>Keywords</strong><strong>.</strong> ALIP; vibration; waveguide; weld; fatigue.</p> Ashish Kumar Y.V. Nagaraja Bhat B.K. Sreedhar S.I. Sundar Raj V. Prakash P. Selvaraj Copyright (c) 2019 Ashish Kumar, Y.V. Nagaraja Bhat, B.K. Sreedhar, S.I. Sundar Raj, V. Prakash, P. Selvaraj http://creativecommons.org/licenses/by/4.0 2019-06-24 2019-06-24 13 49 515 525 10.3221/IGF-ESIS.49.48 Pipeline repair by composite patch under temperature and Pressure loading https://www.fracturae.com/index.php/fis/article/view/2490 <p>In this study, the three-dimensional finite element method is used to analyze an API 5L X70 steel cylindrical pipeline subjected to an internal pressure load by calculating the stress intensity factors and the integral J at the peak of crack in elastic and elastoplastic behavior. The effectiveness of composite patch repair bonded to the cracked surface is highlighted. The effects of the geometrical and mechanical properties of the composite patch and the adhesive on the effectiveness of the repair were highlighted. The variation of the stress intensity factor at the crack tip is used to evaluate the repair performance. The results obtained show that the residual heat stress significantly increases the stress intensity factor at the bottom of the crack, which reduces the effectiveness of the repair.</p> Elamine Abdelouahed H. Benzaama M. Mokhtari B. Aour Copyright (c) 2019 Elamine Abdelouahed, H. Benzaama, M. Mokhtari, B. Aour http://creativecommons.org/licenses/by/4.0 2019-06-24 2019-06-24 13 49 690 697 10.3221/IGF-ESIS.49.62 Finite Element Analysis of the thermo-Mechanical Behavior of composite Pipe Elbows under Bending and Pressure loading https://www.fracturae.com/index.php/fis/article/view/2492 <p>Elbows under load experience more stress and strain than straight tubes. The strength of the composite tubes plays an important role in their use, the damage under a thermomechanical behavior of a composite tubular structure bent between two linear parts is studied in this work. The HASCHIN criterion model is used through finite element analysis. The main objective is to predict the effect of the main parameters by curves of torque, using the calculation code ABAQUS. These evaluative parameters are addressed to the geometrical conditions of the elbow, in loading mode on the pressurized structures and to the danger of the defect, hence the advantage of using Shell elements as a structure. The numerical results obtained illustrate that the parameters studied condition the level and the mode of failure as well as the response of composite elbows.</p> Elamine Abdelouahed M. Mokhtari H. Benzaama Copyright (c) 2019 Elamine Abdelouahed, M. Mokhtari, H. Benzaama http://creativecommons.org/licenses/by/4.0 2019-06-24 2019-06-24 13 49 698 713 10.3221/IGF-ESIS.49.63 Prediction of thermomechanical behavior of acrylonitrile butadiene styrene using a newly developed nonlinear damage-reliability model https://www.fracturae.com/index.php/fis/article/view/2516 <p>The aim of this work was to evaluate the influence of temperature on the mechanical behavior of an amorphous polymer, namely acrylonitrile butadiene styrene (ABS), based on a series of uniaxial tensile tests on smooth specimens at different temperatures. The results demonstrate that the behavior of the polymers is strongly dependent on the temperature. Its influence on the physical characteristics during the study of polymer behaviors cannot be denied, particularly when the processes of shaping are investigated, which require significant contributions of heat and mechanical effort. For this reason, this study consists of predicting the evolution of ABS damage in two main zones. The first is the industrial zone, in which the configuration of macromolecular chains is largely immobile, and the temperature is below the glass temperature (Tg = 110°C). In this zone, a damage model based on the obtained experimental results allowed us to determine three stages of damage evolution, and then to specify the critical fraction of life, at which the material becomes unstable and defective, for the purpose of predictive maintenance. The second zone is that of thermoforming, in which the temperature is above the glass temperature, Tg. In this zone, the macromolecular chains tend to move more freely as the temperature increases. The same damage model was adopted to follow the flow process according to the fraction of life that represents the critical material parameter. This study also includes a comparison between the static (experimental) damage models and unified theory (theoretical) damage models.</p> Abderrazak En-naji N. Mouhib H. Farid M. El Ghorba Copyright (c) 2019 Abderrazak En-naji, N. Mouhib, H. Farid, M. El Ghorba http://creativecommons.org/licenses/by/4.0 2019-06-24 2019-06-24 13 49 748 762 10.3221/IGF-ESIS.49.67