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). 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>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>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> Multiaxial fatigue of in-service aluminium longerons for helicopter rotor-blades Fatigue cracking of longerons manufactured from Al-alloy AVT-1 for helicopter in-service rotor-blades was considered and crack growth period and equivalent of tensile stress for different blade sections were estimated. Complicated case of in-service blades multiaxial cyclically bending-rotating and tension can be considered based on introduced earlier master curve constructed for aluminum alloys in the simple case of uniaxial tension with stress R-ratio near to zero. Calculated equivalent tensile stress was compared for different blade sections and it was shown that in-service blades experienced not principle difference in this value in the crack growth direction by the investigated sections. It is not above the designed equivalent stress level. Crack growth period estimation in longerons based on fatigue striation spacing or meso-beach-marks measurements has shown that monitoring system introduced designer in longerons can be effectively used for in-time crack detecting independently on the failed section when can appeared because of various type of material faults or in-service damages. A. Shanyavskiy A. Toushentsov Copyright (c) 2016 Fracture and Structural Integrity 2018-07-12 2018-07-12 12 45 399 404 10.3221/IGF-ESIS.38.49 S-N curve modeling method of Aluminum alloy welded joints based on the fatigue characteristics domain The scatter degree of the fatigue samples is reduced when the nodal force based structural method is used for steel welded joints, while it is still high for aluminum alloy welded joints. Statistical method and rough set theory is used to fatigue analysis so that fatigue characteristic domains are determined and S-N curves are fitted. Experiment results show that fatigue life of the aluminum alloy welded joints is under the influence of some key factors and the fatigue data with the same characteristics distribute in a relatively independent area. Accordingly, a novel S-N curve modeling method of aluminum alloy welded joints based on the fatigue characteristics domain is proposed. In the proposed method, the nodal force based structural stress method is used for stress calculation and neighborhood rough set theory is used for character extraction to obtain the key factors. Then fatigue characteristics domains are divided and S-N curves are fitted on each fatigue characteristics domain instead of on the whole domain so that a set of S-N curves are obtained. Statistical results show that selection of the S-N curve for the aluminum alloy welded joints according to different fatigue characteristic domain is more accurate. Li Zou Xinhua Yang Jianrong Tan Yibo Sun Copyright (c) 2017 Fracture and Structural Integrity 2018-07-11 2018-07-11 12 45 137 148 10.3221/IGF-ESIS.40.12 Pre-failure indicators detected by Acoustic Emission: Alfas stone, cement-mortar and cement-paste specimens under 3-point bending Acoustic Emission (AE) is the technique most widely used nowadays for Structural Health Monitoring (SHM). Application of this technique for continuous SHM of restored elements of stone monuments is a challenging task. The co-existence of different materials creates interfaces rendering “identification” of the signals recorded very complicated. To overcome this difficulty one should have a clear overview of the nature of AE signals recorded when each one of the constituent materials is loaded mechanically. In this direction, an attempt is here described to enlighten the signals recorded, in case a series of structural materials (natural and artificial), extensively used for restoration projects of classic monuments in Greece, are subjected to 3-point bending. It is hoped that obtaining a clear understanding of the nature of AE signals recorded during these elementary tests will provide a valuable tool permitting “identification” and “classification” of signals emitted in case of structural tests. The results appear encouraging. In addition, it is concluded that for all materials tested (in spite their differences in microstructure and composition) clear prefailure indicators are detected, in good accordance to similar indicators provided by other techniques like the Pressure Stimulated Currents (PSC) one. Stavros K. Kourkoulis Ioanna Dakanali Copyright (c) 2017 Fracture and Structural Integrity 2018-07-11 2018-07-11 12 45 74 84 10.3221/IGF-ESIS.40.07 The discontinuous solutions of Lame’s equations for a conical defect <p>In this article the discontinuous solutions of&nbsp; Lame’s equations are constructed for the case of a conical defect. Under a defect one considers a part of a surface (mathematical cut on the surface) when passing through which function and its normal derivative have discontinuities of continuity of the first kind. A discontinuous solution of a certain differential equation in the partial derivatives is a solution that satisfies this equation throughout the region of determining an unknown function, with the exception of the defect points. To construct such a solution the method of integral transformations is used with a generalized scheme. Here this approach is applied to construct the discontinuous solution of Helmholtz’s equation for a conical defect. On the base of it the discontinuous solutions of Lame’s equations are derived for a case of steady state loading of a medium.</p> Natalya D. Vaysfel'd O. Reut Copyright (c) 2018 Natalya D. Vaysfel'd, O. Reut 2018-07-03 2018-07-03 12 45 183 190 10.3221/IGF-ESIS.45.16 Influence of hydrothermal ageing on single lap bonded CFRP joints <p>Nowadays adhesive are widely used in structural applications, in particular for assembly composite materials. In fact, this technique allows to obtain a more uniform load in the joint, to realise a joint with an higher specific strength and to avoid drilling parts as in the case of bolted joints. However, the mechanical properties of bonded parts over time are not well understood if they are subjected to a more or less aggressive environment. Generally, the main factors of influence regarding the durability of bonded joints are humidity and temperature, but their effects are not always clear if these two factors act simultaneously. In this work the effect of hydrothermal ageing on the mechanical resistance of single lap bonded CFRP joints has been investigated. In particular two types of adhesives (AF 163-2K film and EA 9309NA paste) and three ageing environments (thermal cycles from -28 °C to 85 °C in air, distilled water and salt water) have been chosen for the activity.</p> Costanzo Bellini Gianluca Parodo Wilma Polini Luca Sorrentino Copyright (c) 2018 Costanzo Bellini, Gianluca Parodo, Wilma Polini, Luca Sorrentino 2018-06-25 2018-06-25 12 45 173 182 10.3221/IGF-ESIS.45.15 Forming Process Analysis of an AA6060 Aluminum Vessel <p>This work analyses the results of a simple forming process of an AA6060 aluminium alloy sheet in order to validate the development of a simulation model based on the finite element method (FEM). This work represents the starting point of a broader study aimed at analysing the sheet formability. The FEM based model and the use of both the flow stress curve and the formability limit curve (FLC) were validated through the simulation of a simple forming process that required use of a hemispherical punch. The detailed analysis of the machining process by using FEM allows significant time and cost savings, avoiding "trial-and-error" operations that are normally used in the setup phase of the production process.</p> Gillo Giuliano Costanzo Bellini Luca Sorrentino Sandro Turchetta Copyright (c) 2018 Gillo Giuliano, Costanzo Bellini, Luca Sorrentino, Sandro Turchetta 2018-06-25 2018-06-25 12 45 164 172 10.3221/IGF-ESIS.45.14 Graphene Oxide on the Microstructure and Mechanical Properties of Cement Based Composite Material <p>To investigate the mixing amount of graphene oxide and water cement ratio on the microstructure and mechanical properties of graphene oxide reinforced cement based composite material, graphene oxide suspension was developed using improved Hummers method, and the structure, size and morphology of graphene oxide were represented using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and AFM. The results demonstrated that the bending and compressive strength of graphene oxide reinforced cement based composite material improved firstly and then declined with the increase of the mixing amount of graphene oxide, and moreover the improvement of the bending strength was obvious than that of the compressive strength. When the content of graphene oxide was 0.03%, the bending strength reached the maximum, 13.73 MPa. Under a high water cement ratio, the addition of graphene oxide was more effective in enhancing the strength of cement mortar. The representation of the microstructure of cement based composite material with scanning electron microscope (SEM) suggested that graphene oxide could optimize the microstructure of cement hydration products, improve the pore structure of set cement, reduce the volume of micropore in set cement, and increase the compactness of set cement, i.e. apparently strengthen the toughening effect of set cement. The research achievements are useful to improve the mechanical properties of cement based composite materials.rial.</p> Jinchang Pang Wang Yeming Copyright (c) 2018 Jinchang Pang, Wang Yeming 2018-06-24 2018-06-24 12 45 156 163 10.3221/IGF-ESIS.45.13 Eddy current modelling using multi-layer perceptron neural networks for detecting surface cracks <p>A new method for computing fracture mechanics parameters using computational Eddy Current Modelling by Multi-layer Perceptron Neural Networks for detecting surface cracks. The method is based upon an inverse problem using an Artificial Neural Network (ANN) that simulates mapping between Eddy current signals and crack profiles. Simultaneous use of ANN by MLP can be very helpful for the localization and the shape classification of defects. On the other side, it can be described as the task of reconstructing the cracks and damage in the plate profile of&nbsp; an&nbsp; inspected&nbsp; specimen&nbsp; in&nbsp; order&nbsp; to&nbsp; estimate&nbsp; its&nbsp; material properties. This is accomplished by inverting eddy current probe impedance measurements that are recorded as a function of probe position, excitation frequency or both. In eddy current nondestructive evaluation, this is widely recognized as a complex theoretical problem whose solution is likely to have a significant impact on the detection of cracks in materials</p> Salaheddine Harzallah R. Rebhi M. Chabaat A. Rabehi Copyright (c) 2018 Salaheddine Harzallah, R. Rebhi, M. Chabaat, A. Rabehi 2018-06-21 2018-06-21 12 45 147 155 10.3221/IGF-ESIS.45.12 Influence of limestone dust and natural pozzolan on engineering properties of self-compacting repair mortars <p>The main goal of this work is the formulation of a self-compacting repair mortars (SCRMs) containing limestone dust (LD) and natural pozzolan (NP). For this purpose, a control mortar (SCRM-0) and two different mortars types, one with 10% LD (SCRM-10LD) and the other with 20% NP (SCRM-20NP) as cement replacements were prepared and tested according to EN 1504-3. The results of the experimental study showed that the produced repair materials fulfilled the performances requirements for structural repair products, class R4. In addition, the bond strength between the SCRMs and existing substrate concrete (SUBC), as assessed in this work by slant shear test on composite samples, showed that all tested samples have good bond strength at 28-days and the fractures were only occurred in the SUBC, which means that the substrate is the weakest link in the repair system</p> Mohamed Ghrici Said Choucha Mohamed Ghrici Ahmed Omran Copyright (c) 2018 Mohamed Ghrici, Said Choucha, Mohamed Ghrici, Ahmed Omran 2018-06-21 2018-06-21 12 45 135 146 10.3221/IGF-ESIS.45.11 Fatigue life assessment for a welded detail: advantages of a local energetic approach and experimental validation <p>In modern civil buildings, as well as in mechanical and naval constructions, welding is a widely diffused technological process. The fatigue assessment, as design or verification procedure, of a welded joint to evaluate his endurance with respect to a load spectrum is a challenging but of paramount importance procedure. Several techniques have been proposed in the literature, constantly researching efficient, cost effective and reliable methods to predict the behavior of a complex welded structures. Some of them are part of norms and standards which any design engineer must respect. The aim of the present work is to compare the results provided by some of the principal fatigue life assessment procedures for welded joints, focusing the attention on the stress intensity factor evaluation by the use of numerical methods. Finally the proposed numerical method has been experimentally validated.</p> Luigi Viespoli Filippo Berto Aurelio Somà Copyright (c) 2018 Luigi Viespoli, Filippo Berto, Aurelio Somà 2018-06-20 2018-06-20 12 45 121 134 10.3221/IGF-ESIS.45.10 A New Viscoelastic Mechanics Model for the Creep Behaviour of Fibre Reinforced Asphalt Concrete <p>Based on the Burgers model, by adding a damper unit, this paper proposes a new viscoelastic model with five units and eight parameters to characterize the viscoelastic deformation of fibre reinforced asphalt concrete (FRAC). According to the creep tests of FRAC beams, this paper studies both the parameters in the model and the viscoelastic behaviour of FRAC with different fibre volume fraction and aspect ratio. In this model, this paper establishes the viscoelastic constitutive equation of asphalt concrete, which takes into account the impacts of fibre content characteristic parameter. Both the experimental study and theoretical analysis show that the new model has a high correlation with the results of creep experiment and plays a key role in describing the whole creep process of FRAC. The fibre content characteristic parameter can comprehensively reflect the effects of the fibre volume fraction and aspect ratio on the viscoelastic behaviour of FRAC. Within the range of this test, the optimum fibre volume fraction, fibre aspect ratio and fibre content characteristic parameter are 0.35%, 324 and 1.13, respectively.</p> Chunshui Huang Fangtao Wang Tao Gao Danying Gao Copyright (c) 2018 Chunshui Huang, Fangtao Wang, Tao Gao, Danying Gao 2018-06-20 2018-06-20 12 45 108 120 10.3221/IGF-ESIS.45.09 Seismic Behavior Assessment of a Brazilian Heritage Construction <p>Preservation of historical constructions, and passing it on to future generations, is a major issue in modern societies. Earthquakes are one of the major causes of damages to heritage buildings across the world. The city of Sobral (Ceará State, Brazil) keeps in its historic center a large number of heritage buildings and, since 2008, an intense seismic activity has been observed. This study aims to contribute to the preservation of the Sobral heritage constructions against seismic loads through the assessment of the seismic behavior of one representative building: the Nossa Senhora das Dores Church, a 19th century historical construction. First, a 3D finite element (FE) model was built and tuned according to the results of dynamic tests performed under environmental loads. Next, the FE model was employed to assess the seismic behavior of the church by performing linear time-history analyses employing two real earthquakes. The results showed big displacements and high stresses in many parts of the church, allowing to identify the most critical and most susceptible to damage areas (based on the seismic scenarios considered). These results can be considered as a support for seismic retrofitting measures to be adopted on Sobral heritage constructions.</p> Francisco da Silva Brandão Aldecira Diógenes João Fernandes Esequiel Mesquita Michele Betti Copyright (c) 2018 Francisco da Silva Brandão, Aldecira Diógenes, João Fernandes, Esequiel Mesquita, Michele Betti 2018-06-17 2018-06-17 12 45 14 32 10.3221/IGF-ESIS.45.02 Research on anchor service life base on grey prediction model <p>With the wide application of anchored structures in various engineering, their durability and service life have become an important issue in the development of anchoring technique. According to the corrosion experiment results on different working conditions (close and damp, permanently soaked in water, wet and dry alternately, weak acidity aqueous soaking), and on the basis of determining the loss rate threshold of anchor steel reinforcement bearing capacity, this paper first test the experiment data and then predict the service life of anchor steel on four different working conditions by adopting <em>GM (1,1)</em> model. The results indicate that the grey prediction has a high accuracy.</p> Xinzheng Wang Copyright (c) 2018 Xinzheng Wang 2018-06-17 2018-06-17 12 45 100 107 10.3221/IGF-ESIS.45.08 Effect of corrosion and fatigue on the remaining life of structures and its implication to additive manufacturing <p>This paper investigates the combined effect of corrosion and fatigue on the growth of cracks that arise from natural corrosion in steel bridges. It is shown that if these two effects need to be simultaneously analyzed. If not, then the resulting life is not conservative. Consequently, to enable a better understanding of the remaining life of structures this paper presents a simple methodology for performing this coupled analysis. The implication of this study to additively manufactured Ti-6Al-4V is also discussed.</p> Filippo Berto Javad Razavi Rhys Jones D. Peng Copyright (c) 2018 filippo berto, Javad Razavi, Rhys Jones, D. Peng 2018-06-16 2018-06-16 12 45 33 44 10.3221/IGF-ESIS.45.03 Investigation method of borehole collapse with the multi-field coupled model during drilling in clayey silt hydrate reservoirs <p>The global reserves of natural gas hydrates are extremely abundant, which is attracting more and more scientists’ attention. However, hydrate reservoirs are usually clayey silt hydrate reservoirs with low strength, borehole collapse is a key issue during the drilling operation in these clayey silt hydrate reservoirs in the South China Sea. Therefore, investigation method exploration of borehole collapse simulation for wellbores drilled in hydrate-bearing sediments is of great importance for safely and efficiently developing hydrate in deep water. The finite element model coupled seepage, deformation and heat transfer is developed, and borehole collapse investigation during the overbalanced drilling operation in hydrate-bearing sediment is carried out. The results show that changes in temperature and/or pore pressure do not necessarily lead to the hydrate dissociation. For the investigation case, the temperature front reaches to the position of 35.72 cm from borehole within the near-wellbore area when the drilling operation lasted for 3 hours, but hydrate only dissociates for 17.94cm from the borehole, which is smaller than the temperature disturbance distance. Moreover, the applicability of the investigation method developed herein is verified by comparing the equivalent plastic strains obtained by the coupled model developed in this paper and the simplified model (which neglects the seepage and the heat transfer) respectively. All these results demonstrate that both the investigation method and the finite element model can be used for borehole stability simulation in hydrate-bearing sediments.</p> Qingchao Li Yuanfang Cheng Qiang Li Fuling Wang Chuang Zhang Chuanliang Yan Copyright (c) 2018 Qingchao Li, Yuanfang Cheng, Qiang Li, Fuling Wang, Chuang Zhang, Chuanliang Yan 2018-06-16 2018-06-16 12 45 86 99 10.3221/IGF-ESIS.45.07 Analysis of crack growth problems using the object-oriented program bemcracker2D <p>This paper presents an application of the boundary element method to the analysis of crack growth problems in linear elastic fracture mechanics and the correlation of results with experimental data. The methodology consists of computing stress intensity factors (SIFs), the crack growth path and the estimation of fatigue life, via an incremental analysis of the crack extension, considering two independent boundary integral equations, the displacement and traction integral equations. Moreover, a special purpose educational program for simulating two-dimensional crack growth based on the dual boundary element method (DBEM), named BemCracker2D, written in C++ with a MATLAB graphic user interface, has been developed and used to verify the adopted methodology. The numerical results are compared with those of the finite element method (FEM) and correlated with experimental data of fatigue crack-growth tests for two-dimensional structural components under simple loading, aiming to demonstrate the accuracy and efficiency of the methodology adopted, as well as to evaluate the robustness of the BemCracker2D code.</p> Gilberto Gomes Antonio C O Miranda Copyright (c) 2018 Gilberto Gomes, Antonio C O Miranda 2018-06-16 2018-06-16 12 45 67 85 10.3221/IGF-ESIS.45.06 Fatigue life prediction of 5083 and 5A06 aluminum alloy T-welded joints based on the fatigue characteristics domain <p>Three-point bending fatigue test of 5083 and 5A06 aluminum alloy T-welded joints is carried out, and the fatigue life of the specimens with different influencing factors are obtained. Finite element model of the T-welded joint is established and the nodal force based structural stress is calculated. Neighborhood rough set theory is used for analysis of the factors which influence the fatigue life of the aluminum alloy welded joints. Key influencing factors are studied and the fatigue characteristic domains are determined. The master S-N curve characterized by the nodal force based structural stress range and cycles to failure on semi log coordinate as well as S-N curves corresponding to the fatigue characteristic domain is fitted. A case study of fatigue life prediction of 5A06 aluminum alloy welded joint indicates the effectiveness of the fatigue life prediction method based on the fatigue characteristic domain.</p> li zou Xinhua Yang Jianrong Tan Hongji Xu Yibo Sun Copyright (c) 2018 li zou, Xinhua Yang, Jianrong Tan, Hongji Xu, Yibo Sun 2018-06-16 2018-06-16 12 45 43 66 10.3221/IGF-ESIS.45.05 Effects of weld size on stress concentration factors of CHS-CFSHS joints <p>This paper aims to disclose the effects of weld size on hot spot stress in the calculation of fatigue performance of the joints. For this purpose, the author explored the hot spot stress of CHS-CFSHS T-joints, which consists of circular hollow section (CHS) braces and concrete-filled square hollow section (CFSHS) chords. After reviewing the previous studies and the relevant specifications on weld size, the author probes into the effects of weld size on the stress concentration factor (SCF) of CHS-CFSHS joints via finite-element analysis. The analysis show that the weld size directly affected the hot spot stress in both conditions, and the influence laws were largely the same; with the increase of weld size, the brace-side SCF plunged when the chord-size weld size remained the same, but the chord-side SCF changed slightly when the brace-side weld size was constant; the brace-side and chord-side SCF declined when the brace-side and chord-side weld sizes increased by the same amount. This research successfully determined the weld sizes that are consistent with the relevant specifications, and safe and simple to apply in actual engineering.</p> Delei Yang Lewei Tong Copyright (c) 2018 Delei Yang, Lewei Tong 2018-06-16 2018-06-16 12 45 45 52 10.3221/IGF-ESIS.45.04 Numerical Simulation Analysis of the Dynamic Mechanical Property of Concrete Based on 3D Meso-mechanical Model <p>The dynamic mechanical property of concrete is very complex and is one of the hot spots in academic research. In this paper, concrete is considered as a three-phase composite composed of cement mortar matrix, coarse aggregate and interfacial transition zone (ITZ) at the mesoscopic level. Numerical simulation of the dynamic response of concrete specimen under impact load is carried out using a 3D meso-mechanical model and combining the dynamic constitutive relation of the concrete. The law of influence of the loading velocity, volume content of the aggregate and particle size of coarse aggregate on the dynamic mechanical properties of concrete are analyzed and discussed. The simulation results show that the damage morphology of concrete under impact loadings is in good agreement with the theoretical analysis and that the peak stress of concrete increases with the impact velocity, indicating there is an obvious strain rate enhancement effect in the concrete. In addition, the peak stress of concrete increases with the growth of the volume content of the coarse aggregate. The simulation results also show that for a constant volume fraction and gradation of coarse aggregate, the peak stress of concrete decreases gradually with the increasing of the particle size of the coarse aggregate.</p> Fengyan Qin Jingsong Cheng Heming Wen Hongbo Liu Copyright (c) 2018 Fengyan Qin, Jingsong Cheng, Heming Wen, Hongbo Liu 2018-06-16 2018-06-16 12 45 1 13 10.3221/IGF-ESIS.45.01 A simple model to calculate the microstructure evolution in a NiTi SMA <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 2018-04-01 2018-04-01 12 45 173 182 10.3221/IGF-ESIS.44.14 Development of an optimal process for friction stir welding based on GA-RSM hybrid algorithm <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 2018-03-26 2018-03-26 12 45 106 122 10.3221/IGF-ESIS.44.09 Numerical simulation of self-piercing riveting process (SRP) using continuum damage mechanics modelling <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 2018-03-25 2018-03-25 12 45 161 172 10.3221/IGF-ESIS.44.13 Modification of the Bonora Damage Model for shear failure <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 2018-03-21 2018-03-21 12 45 140 150 10.3221/IGF-ESIS.44.11 An assessment of composite repair system in offshore platform for corroded circumferential welds in super duplex steel pipe <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 2018-03-18 2018-03-18 12 45 151 160 10.3221/IGF-ESIS.44.12 The Effects of Shear on Mode II Delamination <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 2018-03-18 2018-03-18 12 45 123 139 10.3221/IGF-ESIS.44.10