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>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>Portugal: Portuguese Structural Integrity Society - APFIE<br>Serbia: Structural Integrity and Life Society "Prof. Stojan Sedmak" - DIVK<br>Spain: Grupo Espanol de Fractura - Sociedad Espanola de Integridad Estructural - GEF</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> A simple model to calculate the microstructure evolution in a NiTi SMA https://www.fracturae.com/index.php/fis/article/view/2055 <p>Shape memory alloys (SMAs) are a wide class of materials characterized by the property to recover the initial shape. This property is due to ability of alloys to change the microstructure from a “parent” microstructure (usually called “Austenite”) to a “product” microstructure (usually called “Martensite”). Considering the tensile resistance, SMAs stress strain curves are characterized by a sort of plateau were the transformations from Austenite to Martensite (in loading condition) and from Martensite to Austenite (in unloading condition) take place. In this work a simple model to predict the microstructure modification has been proposed and verified with an equiatomic NiTi alloy characterized by a pseudo-elastic behavior.</p> Vittorio Di Cocco Stefano Natali Copyright (c) 2018 Vittorio Di Cocco, Stefano Natali http://creativecommons.org/licenses/by/4.0 2018-04-01 2018-04-01 12 44 173 182 10.3221/IGF-ESIS.44.14 Development of an optimal process for friction stir welding based on GA-RSM hybrid algorithm https://www.fracturae.com/index.php/fis/article/view/2026 <p>Performance of Friction Stir Welding (FSW) as a solid-state process is approved in several engineering applications, especially aluminum industries. Identification of mechanical behavior of the associated welded zone is necessary due to these extensive applications of FSW. In this study, considering the effect of rotational and forward speed of welding tool on the mechanical properties of welded region, a hybrid optimization method based on combination of Genetic Algorithm (GA) and Response Surface Method (RSM) named here as GA-RSM is proposed to achieve maximum tensile and ultimate strength. The results of GA-RSM are validated by per-forming necessary experimental tests on two wide-used 2024 and 5050 aluminum alloys. The results show that GA-RSM could be an effective approach to achieve optimized process for FSW with minimum cost.</p> Nabi Mehri Khansari Filippo Berto Namdar Karimi S.M.N Ghoreishi Mahdi Fakoor Mozhgan Mokari Copyright (c) 2018 Nabi Mehri Khansari, Filippo Berto, Namdar Karimi, S.M.N Ghoreishi, Mozhgan Mokari http://creativecommons.org/licenses/by/4.0 2018-03-26 2018-03-26 12 44 106 122 10.3221/IGF-ESIS.44.09 Numerical simulation of self-piercing riveting process (SRP) using continuum damage mechanics modelling https://www.fracturae.com/index.php/fis/article/view/2051 <p><span lang="EN-US" style="margin: 0px; font-family: 'Garamond',serif; font-size: 11pt;">The extended Bonora damage model was used to investigate joinability of materials in self-piercing riveting process. This updated model formulation accounts for void nucleation and growth process and shear-controlled damage which is critical for shear fracture sensitive materials. Potential joint configurations with dissimilar materials have been investigated computationally. In particular the possible combination of DP600 steel, which is widely used in the automotive industry, with AL2024-T351, which is known to show shear fracture sensitivity, and oxygen-free pure copper, which is known to fail by void nucleation and growth, have been investigated. Preliminary numerical simulation results indicate that the damage modelling is capable to discriminate potential criticalities occurring in the SPR joining process opening the possibility for process parameters optimization and screening of candidate materials for optimum joint. </span></p> Nicola Bonora Gabriel Testa Gianluca Iannitti Andrew Ruggiero Domenico Gentile Copyright (c) 2018 Nicola Bonora, Gabriel Testa, Gianluca Iannitti, Andrew Ruggiero, Domenico Gentile http://creativecommons.org/licenses/by/4.0 2018-03-25 2018-03-25 12 44 161 172 10.3221/IGF-ESIS.44.13 Modification of the Bonora Damage Model for shear failure https://www.fracturae.com/index.php/fis/article/view/2046 <p>The Bonora damage model was extended to account for shear-controlled damage. To this purpose, a new definition for the damage dissipation potential in which an explicit dependence on the third invariant of deviatoric stress was proposed. This expression leads to damage rate equation in which two contributions, the first for void nucleation and growth damage process the latter for shear fracture, can be recognized. For the <em>J<sub>III</sub></em> controlled damage contribution, only two additional material parameters are necessary of easy experimental identification The extended model formulation was verified predicting the failure locus for AL 2024-T351 alloy. Finally, the failure locus for stress state combinations, where the minimum material ductility is expected, was determined.</p> Nicola Bonora Gabriel Testa Andrew Ruggiero Gianluca Iannitti Domenico Gentile Copyright (c) 2018 Nicola Bonora, Gabriel Testa, Andrew Ruggiero, Gianluca Iannitti, Domenico Gentile http://creativecommons.org/licenses/by/4.0 2018-03-21 2018-03-21 12 44 140 150 10.3221/IGF-ESIS.44.11 An assessment of composite repair system in offshore platform for corroded circumferential welds in super duplex steel pipe https://www.fracturae.com/index.php/fis/article/view/2043 <p>The main aim of this study is to assess the effectiveness of a composite repair system in severely corroded circumferential welds in super duplex stainless steel pipes as a preventive measure against the premature corrosion damage at the welds. Artificial defects were fabricated on the super duplex steel tube in order to reproduce the localized corrosion damage defects found in real welded joints. Three kinds of through thickness defects were considered: 25%, 50% and 96% of the perimeter of the pipe. The performance of the repaired pipe was assessed by hydrostatic tests as per ISO 24817 standard. The results showed that the composite repair system can sustain the designed failure pressure even for the pipe damaged with through-wall defect up to 96% of the perimeter of the pipe. Hence, the composite repair system can be used as a preliminary tool to protect the unexpected or premature failure at the welds and maintain an adequate level of mechanical strength for a given operating pressure. This composite repair system can assure that the pipe will not leak until a planned maintenance of the line. Nevertheless, further work is still desirable to improve the confidence in the long-term performance of bonded composite.</p> Silvio de Barros Sandip Budhe Mariana D. Banea Ney R.F. Rohen Eduardo M. Sampaio Valber A. Perrut Luiz D.M. Lana Copyright (c) 2018 Silvio de Barros, Sandip Budhe, Mariana D. Banea, Ney R.F. Rohen, Eduardo M. Sampaio, Valber A. Perrut, Luiz D.M. Lana http://creativecommons.org/licenses/by/4.0 2018-03-18 2018-03-18 12 44 151 160 10.3221/IGF-ESIS.44.12 The Effects of Shear on Mode II Delamination https://www.fracturae.com/index.php/fis/article/view/2022 <p>The paper focuses on the effects of shear deformation and shear forces on the mode II contribution to the energy release rate in delaminated beams. A critical review of the relevant literature is presented, starting from the end-notched flexure test as the prototype of delaminated laminates subjected to pure mode II fracture. Several models of the literature are recalled from simple beam theory to more refined models. The role of first-order shear deformation in line with the Timoshenko beam theory is investigated as distinct from the local crack-tip deformation related to the shear modulus of the material. Then, attention is moved on to a general delaminated beam with an arbitrarily located through-the-width delamination, subjected to mixed-mode fracture. Several fracture mode partition methods of the literature are reviewed with specific attention on the effects of shear forces and shear deformation on the mode II contribution to the energy release rate.</p> Paolo Sebastiano Valvo Copyright (c) 2018 Paolo Sebastiano Valvo http://creativecommons.org/licenses/by/4.0 2018-03-18 2018-03-18 12 44 123 139 10.3221/IGF-ESIS.44.10 Experimental characterization and numerical modelling analyses of nano-adhesive-bonded joints https://www.fracturae.com/index.php/fis/article/view/2008 <p>This paper presents an experimental and numerical characterization, typical for adhesive aerospace applications. The task is carrying two steps. The first consists on the analysis of a single lap joint produced by a carbon fiber fabric reinforced composite with five samples joined by injecting a nanostructure epoxy resin (Graphene 2% by weight) while five others are not. The shear tests have been carried out on the specimens with the purpose of measuring the resistance of the bonded joint, to look forward the resulting differences of structural performances. The second deals with numerical models which have been developed based on the experimental tests for adhesive joints using the finite element techniques. The numerical simulation has been expressed using the ANSYS software in order to analyze the adhesive lap joint model. It has been noted that two options have been retained in attention which deals with and without nano-adhesive. In the two alternatives, we focused on the cooling process where the adhesive single-lap joints are mainly generated. Roughly speaking, the experimental tests and the numerical model show a good agreement. Moreover, the Graphene increases the stiffness of the lap joints under rational loads charges. On the other side, the nanostructure injection in the adhesive has increased the failure as the load increase. However, this increase of failure depends on parameters such as adhesive structural features and nanostructure’s structure. Finally, we were fortunate to observe that, the reinforced adhesive nanostructure has decreased the weight.</p> Fayssal Hadjez Brahim Necib Copyright (c) 2018 fayssal hadjez, Brahim Necib http://creativecommons.org/licenses/by/4.0 2018-03-18 2018-03-18 12 44 94 105 10.3221/IGF-ESIS.44.08 Elastic crack-tip stress field in a semi-strip https://www.fracturae.com/index.php/fis/article/view/2013 <p>In this &nbsp;article the plain elasticity problem for a semi-strip with a transverse crack is investigated in the different cases of the boundary conditions at the semi-strip’s end. Unlike many works dedicated to this subject, the fixed singularities in the singular integral equation’s kernel are considered. The integral transformations’ method is applied by the generalized scheme to reduce the initial problem to a one-dimensional problem. The one-dimensional problem is formulated as the vector boundary value problem which is solved with the help of matrix differential calculations and Green’s matrix apparatus. The solution of the problem is reduced to the solving of the system of three singular integral equations. Depending on the conditions given on the short edge of the semi-strip, the constructed singular integral equation can have one, or two fixed singularities. A special method is applied to solve this equation in regard of the singularities existence. Hence the system of the singular integral equations (SSIE) is solved with the help of the generalized method. The stress intensity factors (SIF) are investigated for different&nbsp; lengths of crack. The novelty of this work is in the application of new approach allowing the consideration of the fixed singularities in the problem about a transverse crack in the elastic semi-strip. The comparison of the numerical results’ accuracy during the usage of the different approaches to the solving of SSIE is worked out.</p> Victor Reut Natalya Vaysfeld Zinaida Zhuravlova Copyright (c) 2018 Victor Reut, Natalya Vaysfeld, Zinaida Zhuravlova http://creativecommons.org/licenses/by/4.0 2018-03-18 2018-03-18 12 44 82 93 10.3221/IGF-ESIS.44.07 An innovative micromechanics-based three-dimensional long-term strength criterion for fracture assessment of rock materials https://www.fracturae.com/index.php/fis/article/view/2015 <p>Rocks may exhibit time-dependent behaviors. Long-term strength criterion significantly dominates creep failure of rocks. Rocks contain many microcracks, which lead to degrade of long-term strength. In this paper, it is assumed that there exist three-dimensional penny-shaped microcracks in rocks. The mode II stress intensity factors at tips of three-dimensional penny-shaped microcracks in Burgers viscoelastic rock matrix is derived. A novel micromechanics-based three-dimensional long-term strength criterion is established to consider the effects of time and the intermediate principal stress on creep failure of rocks. By comparison with the previous experimental data, it is found that the novel micromechanics-based three-dimensional long-term strength criterion is in good agreement with the experimental data.</p> xiaoping zhou Xiaocheng Huang Filippo Berto Copyright (c) 2018 xiaoping zhou, Xiaocheng Huang, Filippo Berto http://creativecommons.org/licenses/by/4.0 2018-03-18 2018-03-18 12 44 64 81 10.3221/IGF-ESIS.44.06 On notch and crack size effects in fatigue, Paris’ law and implications for Wöhler curves https://www.fracturae.com/index.php/fis/article/view/2009 <p>As often done in design practice, the Wöhler curve of a specimen, in the absence of more direct information, can be crudely retrieved by interpolating with a power-law curve between static strength at a given conventional low number of cycles N<sub>0</sub> (of the order of 10-10<sup>3</sup>), and the fatigue limit at a “infinite life”, also conventional, typically N<sub>∞</sub>=2·10<sup>6</sup> or N<sub>∞</sub>=10<sup>7</sup> cycles. These assumptions introduce some uncertainty, but otherwise both the static regime and the infinite life are relatively well known. Specifically, by elaborating on recent unified treatments of notch and crack effects on infinite life, and using similar concepts to the static failure cases, an interpolation procedure is suggested for the finite life region. Considering two ratios, i.e. toughness to fatigue threshold <em>F<sub>K</sub>=K<sub>Ic</sub>/</em><em>D</em><em>K<sub>th</sub></em>, and static strength to endurance limit, <em>F<sub>R</sub></em><em> =s</em><em><sub>R</sub></em><em> /Ds</em><em><sub>0</sub></em>, qualitative trends are obtained for the finite life region. Paris’ and Wöhler’s coefficients fundamentally depend on these two ratios, which can be also defined “sensitivities” of materials to fatigue when cracked and uncracked, respectively: higher sensitivity means stringent need for design for fatigue. A <em>generalized Wöhler coefficient</em>, <em>k’</em>, is found as a function of the intrinsic Wöhler coefficient <em>k</em> of the material and the size of the crack or notch. We find that for a notched structure, <em>k&lt;k’&lt;m</em>, as a function of size of the notch: in particular, <em>k’=k</em> holds for small notches, then <em>k’</em> decreases up to a limiting value (which depends upon <em>K<sub>t</sub></em> for mildly notched structures, or on<em> F<sub>K</sub></em> and <em>F<sub>R</sub></em> only for severe notch or crack). A perhaps surprising return to the original slope <em>k</em> is found for very large blunt notches. Finally, Paris’ law should hold for a distinctly cracked structure, i.e. having a long-crack; indeed, Paris’ coefficient <em>m</em> is coincident with the limiting value of <em>k’<sub>lim</sub></em>. The scope of this note is only qualitative and aims at a discussion over unified treatments in fatigue.</p> Michele Ciavarella A. Papangelo Copyright (c) 2018 MIchele Ciavarella http://creativecommons.org/licenses/by/4.0 2018-03-18 2018-03-18 12 44 49 63 10.3221/IGF-ESIS.44.05 Effect of inter-cluster interference on fracture morphology in multi-cluster staged fracturing for shale reservoir https://www.fracturae.com/index.php/fis/article/view/2016 <p>Multi-cluster staged fracturing technology is an effective measure to stimulate the reservoir properties. However, the inter-cluster interference effect is obvious when the cluster spacing is very narrow, which seriously affects the effect of fracturing. In order to understand the interference among fracturing clusters within the single fracturing section of the shale horizontal wells during multi-cluster staged fracturing, a finite element model is developed by using ABAQUS finite element simulation software. On this basis, the influences of factors on the fracture morphology are studied. The simulation results have shown that the cluster spacing is the most important factor affecting inter-cluster interference. With the increase in the distance between adjacent clusters, the interference among the fracturing fractures decreases and the propagation of different fractures become homogeneous or similar. Moreover, the increase in the elastic modulus of the shale formation promotes the propagation of the fractures longitudinally, but it hinders the crack opening of the fracture laterally. In addition, properly increasing the injection rate of fracturing fluid during fracturing is more advantageous for obtaining long and wide fractures. Besides, the effect of the fracturing fluid viscosity on fracture width is greater than that on the fracture half-length. The simulation results show the existence of inter-cluster interference comprehensively, which can provide a reference for the design and optimization of multi-cluster staged fracturing to some extent.</p> Qingchao Li Yuanfang Cheng Dongxian Zhou Qiang Li Ubedullah Ansari Copyright (c) 2018 Qingchao Li, Yuanfang Cheng, Dongxian Zhou, Qiang Li, Ubedullah Ansari http://creativecommons.org/licenses/by/4.0 2018-03-18 2018-03-18 12 44 35 48 10.3221/IGF-ESIS.44.04 Mechanical behavior of wood subjected to mode II fracture, using an energetic criterion: Application on THUJA of Morocco https://www.fracturae.com/index.php/fis/article/view/2024 <p>Shear strength is one of the properties often used to qualify a wood species for use in industry. But until now there is no standardized test which allows understanding this phenomenon. This paper constitutes a new approach to study the behavior of the wood material subjected to the mode II fracture. For that we designed and realized a new prototype of a wooden specimen that we tested in our laboratory which gives rise to an evaluation of the fracture until separation by pure shear of the specimen in the TL plane. The experimental data from a first series of tests on Thuja wood (Tetraclinis Articulata (Vahl) Masters) as a test material as well as the calculation of mode II initiation fracture toughness and the critical stress intensity factor are presented in this paper.</p> Amal Saoud Abdelhamid Elamri Khadija Kimakh Mohsine Ziani Moussa Elmatar Copyright (c) 2018 Amal Saoud, Abdelhamid Elamri, Khadija Kimakh, Mohsine Ziani, Moussa Elmatar http://creativecommons.org/licenses/by/4.0 2018-03-18 2018-03-18 12 44 25 34 10.3221/IGF-ESIS.44.03 Experimental study of the effect of water-cement ratio on compressive strength, abrasion resistance, porosity and permeability of Nano silica concrete https://www.fracturae.com/index.php/fis/article/view/1997 <p>The effect of water-cement ratio on abrasion resistance, porosity and hydraulic conductivity coefficient of Nano silica concrete have been studied in this research (paper). The compressive strength of concrete in a particular temperature is related to two factors: water-cement ratio and density. Decreasing the water-cement ratio from 0.46 to 0.30 improves the abrasion resistance of Nano silica concrete by 42%, the hydraulic conductivity coefficient of concrete decreases from 28.5⤬10<sup>-15</sup> to 1.7⤬10<sup>-15</sup> m/s and the porosity of concrete decreases to 13.1%. The abrasion depth increases gradually by increasing the water-cement ratio from 0.30 to 0.46.</p> Kamal Rahmani Belal Rahmanzadeh Saber Piroti Copyright (c) 2018 Kamal Rahmani, Belal Rahmanzadeh, Saber Piroti http://creativecommons.org/licenses/by/4.0 2018-03-18 2018-03-18 12 44 16 24 10.3221/IGF-ESIS.44.02 Design of Experiment as a powerful tool when applying Finite Element Method: a case study on prediction of hot rolling process parameters https://www.fracturae.com/index.php/fis/article/view/1998 <p>The ultimate goal in hot roll pass design is to manufacture a rolled product with the required dimensional accuracy, defect free surface, and mechanical properties. The proper selection of process parameters is crucial to meet increasing requirements for desired quality and geometrical properties of rolled products. Due to the complex behavior of the metal flow at high temperatures and the severe plastic deformations in shape rolling, most efforts that have been made so far only rely upon the practical experience gained by operators. The large number of variables involved and the difficulty in investigating the process characteristics, make the use of finite element (FE) tools an effective and attractive opportunity towards a thorough understanding of the rolling process.</p> <p>In this work, Design of Experiment (DOE) is proposed as a powerful and viable method for the prediction of rolling process parameters while reducing the computational effort. Nonlinear 3D FE models of the hot rolling process are developed for a large set of complex cross-section shapes and validated against experimental evidences provided by real plant products at each stage of the deformation sequence. Based on the accuracy of the validated FE models, DOE is applied to investigate the flat rolling process under a series of many parameters and scenarios. Effects of main roll forming variables are analyzed on material flow behavior and geometrical features of a rolled product. The selected DOE factors are the workpiece temperature, diameter size, diameter reduction (draught), and rolls angular velocity. The selected DOE responses are workpiece spread, effective stresses, contact stresses, and rolls reaction loads. Eventually, the application of Pareto optimality (a Multi-Criteria Decision Making method) allows to detect an optimal combination of design factors which respect desired target requirements for the responses.</p> Giancarlo Giuseppe Bordonaro Riccardo Leardi Luca Diviani Filippo Berto Copyright (c) 2018 Giancarlo Giuseppe Bordonaro, Riccardo Leardi, Filippo Berto http://creativecommons.org/licenses/by/4.0 2018-03-18 2018-03-18 12 44 1 15 10.3221/IGF-ESIS.44.01 Fatigue strength of corroded bolted connection https://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.43.06 <p>This note summarizes some recent investigation results on the behavior of corroded steel bolted joints under uniaxial fatigue loading. Fatigue test specimens, were made up using S355 structural steel plates joined together with preloaded M12 bolts of class 10.9 with a geometry that corresponds to the Δσ = 112 MPa EC3 detail category. The accelerated corrosion process was accomplished using an electrolyte consisting of an aqueous 5% NaCl solution whereby the specimens were treated. In particular, during the corrosion process specimens were repeatedly immersed for 2 minutes in the electrolyte and then removed keeping them 60 minutes long in free air at 35 °C. An atmospheric corrosion in marine-industrial environment is wellrepresented through corrosion test. Fatigue loading tests and surface morphology measurement of uncorroded and corroded specimens were performed and the results were compared.</p> Paolo Zampieri Andrea Curtarello Carlo Pellegrino Emanuele Maiorana Copyright (c) 2017-12-29 2017-12-29 12 44 90 96 10.3221/IGF-ESIS.43.06 Residual life prediction of defected Polypropylene Random copolymer pipes (PPR) https://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.43.07 <p>The polypropylene random copolymer (PPR) is a thermoplastic material generally used for the transport of water under pressure, especially hot water. PPR pipes are exposed to severe conditions in terms of pressure and temperature, hence the need to characterize their fracture behavior in order to avoid the design risks. Sudden overpressure is one of the most common problems in piping. It can affect the security of goods and the safety of people. In this context, we have performed tests of overpressures at the laboratory scale according to ASTM D1599 standard, on virgin and notched pipes, to characterize mechanically the fracture behavior of PPR pipes. Afterwards, we identify experimentally the evolution of their damage. The calculation of the damage, by experimental damage models, have led to determine the three stages of evolution of the damage, which are the initiation, the progression and the acceleration of it. Therefore, the concept of reliability is used to specify the critical life fraction relative to the notch depth (βc) of a defect modeled as an external longitudinal groove on the PPR pipe. A comparison of PPR and HDPE pipes damage and reliability has been done. Moreover, a theoretical reassessment of the damage level was done through a judicious adaptation of the theoretical model proposed by the unified theory. From the latter, we proved that theoretical and experimental results show good agreement and correlations.</p> Abderazzak Ouardi Fatima Majid Nadia Mouhib Mohamed Elghorba Copyright (c) 2017-12-29 2017-12-29 12 44 97 105 10.3221/IGF-ESIS.43.07 The effect of porosity on fragmentation statistics of dynamically loaded ZrO2 ceramics https://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.43.08 <p>The effect of load intensity and porous material structure on the fragmentation statistics of ZrO2(MgO)-based ceramics is studied. Cylindrical samples were fragmented under dynamic compression. Experimental data processing showed that the shape of stress-strain curves, the fragment size distribution and distribution of time intervals between the fractoluminiscense impulses depend on the sample porosity and load intensity. The X-ray Computed Tomography (CT) study of porous material structures allowed us to link the fragmentation statistics with pronounced porosity clustering (about 97% of the total pore volume) formed due to sintering.</p> Marina Davydova Sergei Uvarov Oleg Naimark Copyright (c) 2017-12-29 2017-12-29 12 44 106 112 10.3221/IGF-ESIS.43.08 The effect of loading rate on fracture energy of asphalt mixture at intermediate temperatures and under different loading modes https://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.43.09 <p>At intermediate service temperatures hot mix asphalt (HMA) concretely are subjected to different loading rates due to movement of vehicles which can significantly affect their mechanical characteristics and final service load. Hence, in this paper the effect of loading rate on intermediate temperature fracture resistance of HMA materials is investigated experimentally in different modes of cracking. Different hot mix asphalt mixtures made of various compositions were subjected to asymmetric threepoint bend loading in the form of edge cracked semi-circular bend (SCB) specimens. The effect of aggregate type and air void were studied on the fracture energy values for three mode mixities (including pure mode I, mixed mode I/II and pure mode II) and at different temperatures of 5°C, 15°C and 25°C. Trends of change in fracture energy values revealed noticeable influence of loading rate on the low and intermediate temperature cracking behavior of tested asphalt mixtures with different air void contents and aggregate types subjected to mixed mode I/II loading. Also, a change observed in fracture resistance of asphalt mixtures at nearly zero (5°C) and intermediate temperatures (25°C) that was due to change in the behavior of bitumen from elastic to viscoelastic.</p> M.R.M. Aliha M. Fakhri E. Haghighat Kharrazi F. Berto Copyright (c) 2017-12-29 2017-12-29 12 44 113 132 10.3221/IGF-ESIS.43.09 Characterization of uniaxial fatigue behavior of precipitate strengthened Cu-Ni-Si alloy (SICLANIC(TM)) https://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.43.10 <p>Fatigue tests were conducted on cylindrical bars specimens to understand the fatigue behavior of SICLANIC®. Although it displays good resistance in monotonic tension, this material weakens and shows a softening in repeated solicitation. This has been verified through a SEM observation, the Cu-Ni-Si alloy presents transgranular failure by cleavage. The MansonCoffin diagram exhibited the plastic deformation accommodation. The plastic deformation becomes periodic and decreases progressively as the cycle number increases. The approximations of Manson Coffin give fatigue parameters values which are in good agreement with the experience.</p> B. Saadouki M. Elghorba PH. Pelca T. Sapanathan M. Rachik Copyright (c) 2017-12-29 2017-12-29 12 44 133 145 10.3221/IGF-ESIS.43.10 Regularities of mechanical behavior of steel 40Cr during the postcritical deformation of specimens in condition of necking effect at tension https://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.43.11 <p>The work is devoted to the experimental study of mechanical behavior regularities of the structural steel 40Cr under postcritical deformation of specimens in conditions of strain localization formation in the form of neck during extension. The results of testing specimens cut from the initial samples with a neck are given. Various levels of preliminary postcritical deformation of initial samples are implemented. Using a noncontact 3D video system for recording displacement and strain fields of Vic 3D Correlated Solutions, based on the digital images correlation technique, the displacement and strain fields in the gauge length of both the original specimens with the neck and after the groove were recorded in two different schemes to eliminate geometrical heterogeneity. On the base of obtained results, the stiffness and strength of 40Cr steel were evaluated in a necked specimen at various stages of postcritical deformation. It is shown that the material in the peripheral areas of the gauge length of the sample is in a strengthened state, which does not depend on the degree of previously achieved postcritical deformation, and the strength of the material in the neck-forming zone on the initial specimens is thereby increased.</p> M.P. Tretyakov T.V. Tretyakova V.E. Wildemann Copyright (c) 2017 2017-12-29 2017-12-29 12 44 146 154 10.3221/IGF-ESIS.43.11 Experimental characterization of interlaminar fracture toughness of composite laminates assembled with three different carbon fiber lamina https://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.43.12 <p>In the present work, the fracture resistance of a carbon fiber composite under mode I and mode II loading have been experimentally determined. For the mode I and II, the energy release rate G has been determinate for each material. In some cases, only a single estimation of G was possible due to problems in the propagation such as extensive fiber bridging and loss of planarity of the running crack. The experimental results relative to DCB tests have been analyzed in order to derive statistical trends. Only the samples for which more than three crack advance data points have been collected are considered in the analysis. The G values are those obtained with the compliance calibration method (CC). For ENF test, determination of critical GII, in addition to the value calculated with the relationship given in the prescription EN6034, other two values, the non linear and visual non linear, are also given. The crack propagation resulted to be unstable for all specimens tested and only a single value of GII could be determined.</p> Domenico Gentile Copyright (c) 2017-12-29 2017-12-29 12 44 155 170 10.3221/IGF-ESIS.43.12 Fatigue assessment of Ti-6Al-4V titanium alloy laser welded joints in absence of filler material by means of full-field techniques https://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.43.13 <p>The aim of this research activity was to study the fatigue behavior of laser welded joints of titanium alloy, in which the welding was performed using a laser source and in the absence of filler material, by means of unconventional full field techniques: Digital Image Correlation (DIC), and Infrared Thermography (IRT). The DIC technique allowed evaluating the strain gradients around the welded zone. The IRT technique allowed analyzing the thermal evolution of the welded surface during all the fatigue tests. The fatigue limit estimated using the Thermographic Method corresponds with good approximation to the value obtained from the experimental fatigue tests. The obtained results provided useful information for the development of methods and models to predict the fatigue behavior of welded T-joints in titanium alloy.</p> Pasqualino Corigliano Vincenzo Crupi Eugenio Guglielmino Carmine Maletta Emanuele Sgambitterra Giuseppe Barbieri Fabrizia Caiazzo Copyright (c) 2017-12-29 2017-12-29 12 44 171 181 10.3221/IGF-ESIS.43.13 Structural behaviour of masonry arch with no-horizontal springing settlement https://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.43.14 <p>This paper presents a calculation procedure for assessing the structural integrity of a masonry arch with non-horizontal springing settlement. By applying the Principle of Virtual Work (PVW) to the deformed arch system, the procedure proposed herein details the reaction forces and thrust lines for each step of imposed settlement of the support. The procedure can also be used estimate the final displacement that causes complete failure of arch structural capacity. The results of the analysis procedure were compared against those obtained by experimental testing so as to validate the proposed calculation method.</p> P. Zampieri N. Simoncello C. Pellegrino Copyright (c) 2017-12-29 2017-12-29 12 44 182 190 10.3221/IGF-ESIS.43.14 Investigation on the static and dynamic structural behaviors of a regional aircraft main landing gear by a new numerical methodology https://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.43.15 <p>In this paper, a new methodology supporting the design of landing gears is proposed. Generally, a preliminary step is performed with simplified FE model, usually one-dimensional, to achieve the reaction forces involving each component during all aforementioned aircraft operations. Though this approach gives a valid support to the designer, it is characterized by several problems, such as the related approximations. So, it is important, by a numerical point of view, to develop an isostatic FE model equivalent to the real one. In fact, if the landing gear is modelled as hyperstatic, the static equilibrium equations are insufficient for determining the internal forces and reactions on each sub-component; so, the modelled material properties and geometries assume an increasing importance, which gets the model too approximating. The proposed methodology consists of achieving the reaction forces by means of multibody simulations, by overcoming such problems, since each component is modelled as rigid. In this paper, also a FE model for the investigation of the structural response is proposed. Aimed to Certification by Analysis purposes, the developed multibody and the FE models have been assessed against an experimental landing gear drop test carried out by Magnaghi Aeronautica S.p.A., according to the EASA CS 25 regulations.</p> F. Caputo A. De Luca A. Greco S. Maietta A. Marro A. Apicella Copyright (c) 2017-12-29 2017-12-29 12 44 191 204 10.3221/IGF-ESIS.43.15 Experimental tests on slip factor in friction joints: comparison between European and American Standards https://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.43.16 <p>Friction joints are used in steel structures submitted to cyclic loading such as, for example, in steel and composite bridges, in overhead cranes, and in equipment subjected to fatigue. Slip-critical steel joints with preloaded bolts are characterized by high rigidity and good performance against fatigue and vibrational phenomena. The most important parameter for the calculation of the bolt number in a friction connection is the slip factor, depending on the treatment of the plane surfaces inside the joint package. The paper focuses on the slip factor values reported in European and North American Specifications, and in literature references. The differences in experimental methods of slip test and evaluation of them for the mentioned standards are discussed. The results from laboratory tests regarding the assessment of the slip factor related to only sandblasted and sandblasted and coated surfaces are reported. Experimental data are compared with other results from the literature review to find the most influent parameters that control the slip factor in friction joint and differences between the slip tests procedures.</p> Emanuele Maiorana Paolo Zampieri Carlo Pellegrino Copyright (c) 2017-12-29 2017-12-29 12 44 10.3221/IGF-ESIS.43.16