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>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> en-US <p><strong>Copyright&nbsp;</strong><br>Authors are allowed to retain both the copyright and the publishing rights of their articles without restrictions.&nbsp;&nbsp;</p> <p><strong>Open Access Statement</strong></p> <p>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> (Francesco Iacoviello) (Support) Wed, 19 Dec 2018 00:00:00 +0000 OJS 60 Influence of material inhomogeneity and non-linear mechanical behavior of the material on delamination in multilayered beams <p>The delamination fracture in four-point bending beams made of adhesively bonded lengthwise vertical layers is studied assuming that each layer exhibits smooth material inhomogeneity along the width and length of the layer. The study aims at determining the strain energy release rate with applying the Ramberg-Osgood equation for modeling the non-linear mechanical behavior of the material in each layer. Cosine laws are used to describe the continuous variation of the modulus of elasticity in width and length directions of layers. Beams made of an arbitrary number of vertical layers which have individual widths and material properties are considered. Besides, the delamination crack is located arbitrary between layers, i.e. the two crack arms have different widths. The <em>J</em>-integral is applied for verification of the non-linear solution to the strain energy release rate derived in the present paper. The solution is used to investigate the influence of material inhomogeneity in width and length directions of layers, the crack location along the beam width, the non-linear mechanical behavior of the material and the crack length on the delamination fracture behavior. The approach developed is expected to be useful in structural design of multilayered inhomogeneous beams with considering the delamination fracture behavior.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p> Victor Rizov Copyright (c) 2019 Victor Rizov Tue, 18 Dec 2018 19:48:41 +0000 Mechanical Behavior Analysis of a Friction Stir Welding (FSW) for Welded Joint Applied to Polymer Materials <p>Welding is a technique of fusion joining the material involving a process of inter-molecular diffusion adhesion. Polymer welding is an assembly method among several known assembly techniques such as gluing. This welding process applies to thermoplastics; they have the rheological or softening characteristics during melting. This process is fast and controlled in order to obtain a solid and durable mechanical connection on the series parts. This study focuses on the weldability of high density polyethylene (HDPE) using the friction stir welding technique. A parametric choice was made to optimize the operating parameters namely the shape of the welding tool, the speed of rotation and the speed of advance of the tool.&nbsp; Monotonic tensile tests were used to compare the mechanical characteristics between a HDPE test specimen and a specimen taken from an FSW weldment.</p> <p>It emerges from this study that the FSW welding introduces a weakening of the joints characterized by a clear decrease of the deformation at break.</p> Hachellaf kaddour, Meddah Hadj Miloud, Ould Chikh El Bahri, Lounis Abdallah Copyright (c) 2019 Hachellaf kaddour, Meddah Hadj Miloud, Ould Chikh El Bahri, Lounis Abdallah Mon, 17 Dec 2018 06:19:26 +0000 Timber beam seismic design – A numerical simulation <p style="margin: 16px 0px; text-align: justify;"><span style="margin: 0px; color: black; font-family: 'Garamond',serif;">To seismic design of timber beam, effect of <span style="margin: 0px; letter-spacing: -0.15pt;">near-fault ground motion on </span>timber beam has numerically been investigated, with refer to </span><span style="margin: 0px; color: black; font-family: 'Garamond',serif;">small displacement theory</span><span style="margin: 0px; color: black; font-family: 'Garamond',serif;">. <span style="margin: 0px; letter-spacing: -0.15pt;">The simulated near-fault ground motion is applied on the fixed base of timber frame model. </span>The beam is located in single span of a timber frame. The beam has two different size of 1.8 and 3.3 meter length. The </span><span style="margin: 0px; color: black; font-family: 'Garamond',serif;">seismic load-displacement seismic load-strain and </span><span style="margin: 0px; color: black; font-family: 'Garamond',serif;">strain-displacement </span><span style="margin: 0px; color: black; font-family: 'Garamond',serif;">have been calculated for all models and graphically depicted. The beam is designed with nonlinear analysis method and same mechanical properties for all models have been used, in numerical analysis. The numerical analysis results indicate that, the inertial interaction, energy dissipation and nonlinear deformation of beam in timber frame have direct relationship with frame span. In beam with smaller length, higher seismic loading is caused lower displacement. The displacement is reduced with reduction length of the beam. The inertial interaction, energy dissipation and nonlinear deformation are changed in respect to length of beam. The novelty of this paper is developing cycling graphs by using ABAQUS, for improve design of timber frame, and adequate explanation of seismic behavior of timber beam.</span></p> Abdoullah Namdar, Yun Dong, Yuyi Liu Copyright (c) 2019 Abdoullah Namdar, Yun Dong, Yuyi Liu Sat, 15 Dec 2018 04:27:06 +0000 A quick-assessment procedure to evaluate the degree of conservation of rockfall drapery meshes <p>Drapery meshes are protection devices installed on a cliff for mitigating rockfall hazard. They can prevent the detachment of rock fragments and control the dynamics of the falling blocks. During their design working life, drapery meshes are subjected to ageing phenomena, corrosion and impact, which can invalidate the purposes of the protection devices. A novel procedure based on a multi-hierarchical assessment of the damages is proposed. The approach is tailored for two technologies well diffused in the Alps. The main components of the system are identified and the effects of each potential damage on the overall behaviour are taken into account through risk analysis approached. A site campaign serving to test the procedure is described. The proposed approach can be modified to consider other drapery mesh installation types.</p> Maddalena Marchelli, Valerio De Biagi, Daniele Peila Copyright (c) 2019 Maddalena Marchelli, Valerio De Biagi, Daniele Peila Fri, 14 Dec 2018 05:51:37 +0000 Comparison of tensile strength and fracture toughness under mode I and II loading of co-cured and co-bonded CFRP joints <p><span lang="EN-US" style="margin: 0px; font-family: 'Garamond',serif; font-size: 12pt;">Adhesive bonding is the elective joining system between Carbon-Fiber Reinforced Polymer (CFRP) parts because, with respect to fastening, it allows a large connection area, no additional parts (hence weight saving) and no need to drill holes into the composite, that is always detrimental for the strength due to the possibility of developing damage. However, the choice of bonding CFRP should be evaluated as alternative to direct curing in terms of strength and durability, compared to cost and manufacturing time and complexity. In this work, a comparison between co-cured and co-bonded CFRP is done with respect to tensile strength and mode I and mode II fracture toughness, in order to understand whether co-bonding guarantees the same performance of a co-cured composite part.</span><span lang="EN-US" style="margin: 0px; font-family: 'Garamond',serif; font-size: 12pt;">Adhesive bonding is the elective joining system between Carbon-Fiber Reinforced Polymer (CFRP) parts because, with respect to fastening, it allows a large connection area, no additional parts (hence weight saving) and no need to drill holes into the composite, that is always detrimental for the strength due to the possibility of developing damage. However, the choice of bonding CFRP should be evaluated as alternative to direct curing in terms of strength and durability, compared to cost and manufacturing time and complexity. In this work, a comparison between co-cured and co-bonded CFRP is done with respect to tensile strength and mode I and mode II fracture toughness, in order to understand whether co-bonding guarantees the same performance of a co-cured composite part.</span></p> Alessandro Pirondi, Fabrizio Moroni, Chiara Pernechele, Arturo Gaita, Luca Vescovi Copyright (c) 2019 Alessandro Pirondi, Fabrizio Moroni, Chiara Pernechele, Arturo Gaita, Luca Vescovi Wed, 12 Dec 2018 14:09:18 +0000 Analysis of dissipated energy and temperature fields at severe notches of AISI 304L stainless steel specimens <p>In the last years, a large amount of fatigue test results from plain and bluntly notched specimens made of AISI 304L stainless steel were synthetized in a single scatter band by adopting the specific heat loss per cycle (Q) as a damage parameter. During a fatigue test, the Q parameter can be evaluated measuring the cooling gradient at a point of the specimens after having suddenly stopped the fatigue test. This measurement can be done by using thermocouples; however, due to the high stress concentration at the tip of severely notched components analysed in the present paper, an infrared camera achieving a much improved spatial resolution was adopted. A data processing technique is presented to investigate the heat energy distribution close to the notch tip of hot-rolled AISI 304L stainless steel specimens, having notch tip radii equal to 3, 1 and 0.5 mm and subjected to constant amplitude cyclic loads. A thermal finite element analysis was also performed by assigning heat generation in the appropriate region close to the notch tip. Then the numerical temperature values were compared with the experimental measurement.</p> Daniele Rigon, Mauro Ricotta, Giovanni Meneghetti Copyright (c) 2019 Daniele Rigon, Mauro Ricotta, Giovanni Meneghetti Thu, 06 Dec 2018 04:45:20 +0000 Composite sandwich impact response: experimental and numerical analysis <p>The use of composite materials allows to have a great flexibility in terms of mechanical and physical characteristics. One of the most used composite structure in naval field, is the sandwich, which is composed by a stacking sequence of different plies. The designer, in preliminary phase, must handle a great quantity of degree of freedom (types of materials, orientation of the fibres, position along the stack, thickness, etc.) in order to reach the best compromise between mechanical behaviour, environmental impacts and production costs. Finite Element analysis represents a useful tool in order to optimize all these parameters and to estimate the outcome of experimental tests at design stage. The main goal of this work is to develop and to validate a FE model for the simulation of a particular family of composites, widely used in naval field and, in particular, in High Speed Crafts and powerboats. The first part of the paper concerns the experimental tests on two different types of sandwich specimens. Two families of tests were conducted: four-point bending tests and impact drop tests. The second part of the paper focuses on the validation of a FE model for both experimental setups.</p> Filippo Cucinotta, Paolo Neri, Felice Sfravara, Armando Razionale Copyright (c) 2019 Filippo Cucinotta, Paolo Neri, Felice Sfravara, Armando Razionale Wed, 05 Dec 2018 17:17:12 +0000 Structural Form of Bridges Reflecting the Construction Processes <p>The structural form of a completed bridge is strongly affected by its structural form during construction. It follows that innovative construction processes sometimes produce innovative bridge designs. It is important to consider the construction process in conjunction with bridge design methods. This approach could be applied not only to new construction but also to replacements, reconstructions, or reinforcements. One of the authors has systematized the structural forms of bridges and clarified the principles underlying them. This paper aims to extend these principles to construction systems. In other words, changes in the structural systems of the construction processes and systematization of the relationship between a completed bridge and construction process in a design are illustrated. This systematization enables the application of a variety of conventional construction methods in a system. This would be helpful in developing new construction methods and designs for bridges.</p> Yusuke Mizuno, Yoshiaki Kubota Copyright (c) 2019 Yusuke Mizuno, Yoshiaki Kubota Wed, 05 Dec 2018 16:58:32 +0000 The effect of low-cycle fatigue on evolution of fracture mechanics parameters in residual stress field caused by cold hole expansion <p>Localized displacement measurements based on electronic speckle-pattern interferometry are used to obtain crack mouth opening displacement (CMOD), stress intensity factor (SIF) and T-stress values during crack growth around cold-expanded holes. The specimens with a central open hole are made from 2024 aluminium alloy. The expansion level is 5% of nominal interference. The results are obtained for the same stress range&nbsp; &nbsp;= 350 MPa, but different stress ratio<em> R</em> = –0.4 and <em>R</em> = –1.0. A sequence of narrow notches, inserted under the constant external load, serves for crack modelling at different stages of cyclic loading. Initial experimental data represent in-plane displacement component values measured in the vicinity of the crack tip. The transition from in-plane displacement components to SIF and T-stress values follows from the relationships of modified version of the crack compliance method. The crack length curves of CMOD, SIF and T-stress profiles are obtained for different stages of cyclic loading. These data provide the construction of dependencies of fracture mechanics parameters for cracks of fixed lengths from the loading cycle number.</p> Yury Matvienko, Vladimir Pisarev, Svyatoslav Eleonsky Copyright (c) 2019 Yury Matvienko, Vladimir Pisarev, Svyatoslav Eleonsky Wed, 05 Dec 2018 16:44:22 +0000 The “Projection-by-Projection” (PbP) criterion for multiaxial random fatigue loadings <p>This work is motivated by the increasing interest towards the application of the “Projection-by-Projection” (PbP) spectral method in finite element (FE) analysis of components under multiaxial random loadings. To help users and engineers in developing their software routines, this paper presents a set of numerical case studies to be used as a guideline to implement the PbP method. The sequence of analysis steps in the method are first summarized and explained. A first numerical example is then illustrated, in which various types of biaxial random stress are applied to three materials with different tension/torsion fatigue properties. Results of each analysis step are displayed explicitly to allow a plain understanding of how the PbP method works. The examples are chosen with the purpose to show the capability of the method to take into account the effect of correlation degree among stress components, and the relationship between material and multiaxial stress in relation to the tension/torsion fatigue properties. A case study is finally discussed, in which the method is applied to a FE structural durability analysis of a simple structure subjected to random excitations. The example describes the flowchart and the program by which to implement the method through Ansys APDL software. This final example illustrates how the PbP method is an efficient tool to analyze multiaxial random stresses in complex structures.</p> Denis Benasciutti, Davide Zanellati, Alessandro Cristofori Copyright (c) 2019 Denis Benasciutti, Davide Zanellati, Alessandro Cristofori Wed, 05 Dec 2018 16:14:14 +0000 The Strain energy density to estimate lifetime of notched components subjected to variable amplitude fatigue loading <p>In the present paper, the approach based on the strain energy density (SED) averaged over a structural volume is reformulated to estimate the lifetime of notched components subjected to variable amplitude (VA) uniaxial fatigue loading. The accuracy and reliability of the proposed reformulation of the SED approach was checked against a large number of data taken from the literature and generated, under two different load spectra, by testing specimens of carbon steel C40 containing notches of different sharpness. Such a validation exercise allowed us to demonstrate that the extension of the SED approach as proposed in the present paper is capable of accurately estimating fatigue damage in notched components subjected to in-service VA fatigue loading.</p> Luca Susmel, Filippo Berto, Zheng Hu Copyright (c) 2019 Luca Susmel, Filippo Berto, Zheng Hu Wed, 05 Dec 2018 14:58:18 +0000 Assessment of tensile and fatigue behavior of PEEK in a physiologically relevant environment <p>In the last decades the necessity of implant devices is continuously increasing. The researchers have thus focused their attentions on the development of new biocompatible materials, in particular polymers. Among them, polyetheretherketone (PEEK) has gained wide interest in load-bearing applications such as spinal cages due to its yielding behavior and its superior corrosion resistance. Since such applications are characterized by notches and other stress concentrators weakening the implant resistance, a design tool for assessing their tensile and fatigue behavior in the presence of such discontinuities is highly claimed. To this aim, tensile and fatigue data available in literature of neat and differently notched PEEK samples (circumferentially cracked and U-notched specimens with different notch radii) experimentally tested in a phosphate-buffered saline (PBS) at 37 °C have been analyzed using the strain energy density (SED) approach. The method is shown to provide accurate results regardless of the different notch geometries, both for tensile and fatigue data. Concerning the former, the tensile strength was in fact estimated with an error lower than ±10%, regardless of the strain rate, while for the latter the SED approach was able to summarize the fatigue data with a single narrow scatter band independently from the notch geometry</p> Mirco Peron, Jan Torgersen, Filippo Berto Copyright (c) 2019 Mirco Peron, Jan Torgersen, Filippo Berto Wed, 05 Dec 2018 05:52:53 +0000 Brittle crack propagation acceleration in a single crystal of a 3% silicon-Fe alloy <p>Brittle fracture in carbon steel has a serious impact on the safety of steel structures. Thus, technology that arrests crack propagation is the final line of protection for such structures. It is such an important issue that conditions that can reliably stop crack propagation should be thoroughly clarified. Due to the social importance of the problem, many experimental and theoretical studies have been conducted from both the mechanical and microstructural viewpoints.</p> <p>Though it has been reported that the upper limit of the speed of brittle crack propagation is theoretically the Rayleigh wave speed, which is approximately 2,900 m/s in steels, the actual speed of brittle crack propagation in steels is approximately 1,000 m/s and lower. The reason for this difference is due to braking effects during crack propagation, for example, unevenness in the faceting, tear ridges, microcracking, twin deformation and side ligaments, which are the elements that dominate the arresting toughness. To evaluate the most fundamental element of the arresting toughness, the authors have studied the crack propagation resistance inside a single crystal and across a grain boundary by using a 3% silicon steel with a microstructure of single phase ferrite and a very large grain size of 4-5 mm. The crack propagation rate inside a single crystal is relatively large, but only half of the Rayleigh wave speed even under the highest stress intensity factor conditions.</p> <p>In this study, the change in the crack propagation rate was measured using small sized multiple-strain gauges that were pasted inside a single crystal along the crack line. From these measurements, crack propagation resistance and the role of grain boundaries are quantitatively discussed in this article.</p> Tomoya Kawbata, Noritaka Nakamura, Shuji Aihara Copyright (c) 2019 Tomoya Kawbata, Noritaka Nakamura, Shuji Aihara Tue, 04 Dec 2018 18:02:17 +0000 Size effect on the fracture resistance of rough and frictional cracks <p>Elastic fracture mechanics commonly defines the fracture<br>resistance of brittle materials within an idealised picture of planar and tractionfree<br>cracks. An efficient approach to describe the interface conditions in real<br>cracks, such as those occurring in concrete, ceramics or stones, is to include<br>the effect of both roughness and friction by means of a constitutive<br>relationship between opposite points on the interface. In the present paper,<br>we use a numerical technique, based on the solution of singular integral<br>equations, to derive the near-tip stress field with various interface conditions.<br>Then, the technique is applied to investigate the size effect of the interface<br>roughness, where such an effect is related to the ratio between the<br>characteristic length of the roughness and the nominal length of the crack. It<br>is found that the resulting near-tip stresses can be profoundly influenced by<br>the crack path, particularly for short cracks.</p> Andrea Spagnoli, Andrea Carpinteri, Michele Terzano Copyright (c) 2019 Andrea Spagnoli, Andrea Carpinteri, Michele Terzano Tue, 04 Dec 2018 17:14:28 +0000 Experimental Investigation on the Fracture Behaviour of Natural Stones Exposed to Monotonic and Cyclic Loading <p>The present paper is devoted to an experimental study on the fracture behaviour of natural stones, commonly used as elements for building cladding, under both monotonic and cyclic loading, with particular emphasis to white Carrara marble. The effect of progressive damage produced by in-service thermal fluctuations can be investigated through the application of appropriate cyclic mechanical loads. In the experimental tests conducted, some static mechanical properties of marble are characterized by means of three-point bending tests on edge-cracked prismatic specimens for the determination of Young's modulus, tensile strength and fracture energy. Moreover, cyclic three-point bending tests are conducted to determine the propagation rate of nominally Mode-I fatigue cracks. Finally, the fatigue behaviour of the marble is studied through a cohesive crack model, in which the direct tensile strength of the material is determined by a Brazilian test, and the behaviour is calibrated by means of a suitable FE model. The effect of crack path on the fracture resistance of marble is discussed.</p> Andrea Spagnoli, David Cendon Franco, Antonio D’Angelo Copyright (c) 2019 Andrea Spagnoli, David Cendon Franco, Antonio D’Angelo Tue, 04 Dec 2018 17:01:33 +0000 Numerical simulation of the de-bonding phenomenon of FRCM strengthening systems <p>Aim of the paper is to present a one dimensional simple model for the study of the bond behavior of Fabric Reinforced Cementitious Matrix (FRCM) strengthening systems externally applied to structural substrates. The equilibrium of an infinitesimal portion of the reinforcement and the mortar layers composing the strengthening systems allows to derive the governing equations. An analytical solution is determined solving the system of differential equations. In particular, in the first part of the paper a nonlinear shear-stress slip law characterized by a brittle post-peak behavior with a residual shear strength in the post peak phase is introduced for either the lower reinforcement-mortar interface (approach 1) or both the lower and the upper interface (approach 2). In the latter approach, a calibration of the shear strength of the upper interface is proposed in order to implicitly account for the effect of the damage of the mortar on the bond behavior. In the second part of the paper it is presented the solution of the problem in the case of softening behavior by approximating the shear-stress slip law throughout a step function. Comparisons with experimental data, available in literature, are presented in order to assess the reliability of the proposed approach.</p> Ernesto Grande, Maura Imbimbo, Sonia Marfia, Elio Sacco Copyright (c) 2019 Ernesto Grande, Maura Imbimbo, Sonia Marfia, Elio Sacco Tue, 04 Dec 2018 05:51:40 +0000 Experimental characterization at nanoscale of single crystal silicon fracture toughness <p>The work reviews some preliminary recent micromechanical tests aimed at the evaluation of the fracture toughness of silicon. Pre-cracked nano specimens and alternatively notched nano specimens combined with the theory of critical distances (TCD) are compared. The results show that the fracture toughness of silicon is approximately 1 MPa·m<sup>0.5</sup>, regardless of the procedure involved (i.e., pre-cracked samples or TCD). This value agrees with macro counterpart, i.e., 0.75-1.08 MPa·m<sup>0.5</sup>, and therefore the <em>K</em><sub>IC</sub> is independent of the size and crystal orientation. However, by employing the TCD, the accurate control of the final crack tip which is currently very challenging, is overcome by using notched specimens. Additionally, the results give information about the crack propagation at the nanoscale. It seems that although the specimen axis deviates from the (011), the crack propagates along the cleavage plane (011) and the process develops very fast by breaking covalent bond at the crack tip. A brief discussion on beyond the breakdown of continuum theory and challenges toward nanometer scale fracture mechanics concludes the paper.</p> Pasquale Gallo, Takashi Sumigawa, Takayuki Kitamura Copyright (c) 2019 Pasquale Gallo, Takashi Sumigawa, Takayuki Kitamura Tue, 04 Dec 2018 00:00:00 +0000 A numerical model based on ALE formulation to predict crack propagation in sandwich structures <p>A numerical model to predict crack propagation phenomena in sandwich structures is proposed. The model incorporates shear deformable beams to simulate high performance external skins and a 2D elastic domain to model the internal core. Crack propagation is predicted in both core and external skin-to-core interfaces by means of a numerical strategy based on an Arbitrary Lagrangian–Eulerian (ALE) formulation. Debonding phenomena are simulated by weak based connections, in which moving interfacial elements with damage constitutive laws are able to reproduce the crack evolution. Crack growth in the core is analyzed through a moving mesh approach, where a proper fracture criterion and mesh refitting procedure are introduced to predict crack tip front direction and displacement. The moving mesh technique, combined with a multilayer formulation, ensures a significant reduction of the computational costs. The accuracy of the proposed approach is verified through comparisons with experimental and numerical results. Simulations in a dynamic framework are developed to identify the influence of inertial effects on debonding phenomena arising when different core typologies are employed. Crack propagation in the core of sandwich structures is also analyzed on the basis of fracture parameters experimentally determined on commercially available foams.</p> Marco Francesco Funari, Fabrizio Greco, Paolo Lonetti, Saverio Spadea Copyright (c) 2019 Marco F Funari, Fabrizio Greco, Paolo Lonetti, Saverio Spadea Mon, 03 Dec 2018 16:01:30 +0000 Analytical and numerical study of the stress field in a circular semi- ring under combined diametral compression and bending <p>The stress field developed in a circular semi-ring under the com­bined action of diametral compression and bending is explored both analytically and num­erically. The analytic solution is implemented by means of the complex potentials technique as it was formulated by Muskhe­lishvili, while for the nu­m­eri­cal study a finite element model, properly validated based on expe­ri­mental data, is used. The ana­lytic solution provided closed formulae for the stress field along strategic loci of the specimen, while the nu­m­eri­cal model permitted thor­ough parametric investigation of the de­pend­ence of critical quantities on geometrical and loading factors. The idea behind the study is to assess the potentialities of the circular semi-ring as a possible substitute of the familiar Brazilian disc, in the direction of curing drawbacks of the latter. It was concluded that a circular semi-ring subjected to eccentric diametral com­pression provides reliable data for the tensile strength of very brittle materials, relieved from ambiguities char­acterizing the standardized Brazilian-disc test.</p> Stavros K Kourkoulis, Ermioni D. Pasiou, Christos F. Markides Copyright (c) 2019 Stavros K Kourkoulis, Ermioni D. Pasiou, Christos F. Markides Mon, 03 Dec 2018 14:31:00 +0000 Ductile damage evolution law for proportional and non-proportional loading conditions <p>The characterization of ductile damage evolution, and its description, have been the object of extensive research in the continuum damage mechanic field. Many different models have been developed since the pioneering works carried out a few decades ago. In detail, the stress triaxiality and the Lode angle parameters have been identified as the two main variables that affect the material ductility. The literature offers a great number of investigations under monotonic loading conditions, however, a proper characterization of the damage evolution under cyclic loading or non-proportional loading is still missing.</p> <p>In this paper, an unconventional coupled elastoplastic and damage constitutive model with a Mohr-Coulomb failure criterion is presented. The novelty of this study is represented by the modification of the ductile damage law in order to consider the damage evolution under non-proportional loading conditions. Therefore, the idea is to investigate the structural response of a steel bridge column subjected to a cyclic non-proportional loading, showing how, a different approach in the description of the ductile damage evolution, is necessary for a realistic description of the pier behavior.</p> Riccardo Fincato, Seiichiro Tsutsumi, Hideto Momii Copyright (c) 2019 Riccardo Fincato, Seiichiro Tsutsumi, Hideto Momii Mon, 03 Dec 2018 05:25:43 +0000 Numerical modelling of residual stress redistribution induced by TIG-dressing <p>TIG-dressing is a technique used to improve the fatigue strength of welded joints by a remelting of the weld toe region that promotes both a smoother transition between the plate and the weld crown and a residual stress redistribution. These effects are very hard to be quantified by numerical simulation since a highly coupled thermo-fluid-mechanical analysis is required. However, if the final weld toe geometry is supposed to be known or a-posteriori measured, a simplified numerical method can be used to simulate the residual tress redistribution that uses the activation-deactivation function of elements. This technique is applied to a real steel weldment and results, in terms of phases proportions and residual stress redistribution, were found in good agreement both with data coming from metallurgical analysis and the improved fatigue strength observed on welded joints after the TIG-dressing operation.</p> Paolo Ferro, Filippo Berto, Franco Bonollo, Roberto Montanari Copyright (c) 2019 Paolo Ferro, Filippo Berto, Franco Bonollo, Roberto Montanari Mon, 03 Dec 2018 05:11:16 +0000 Mechanical and fracture properties of particleboard <p>Particleboard (PB) are wood-based composites with fine wood fibers bound together by a small amount of polymeric adhesive, widely used in furniture industry and civil engineering. PB plates can be painted, laminated or veneered, and have good dimensional stability and load bearing capacity when properly designed. However, the deformation and fracture of such elements create malfunctions of structures mad of MDF. This paper presents experimental results obtained for three point bending (TPB) tests, mode I and mode II fracture toughness. The bending tests were carried on rectangular specimens, while the fracture toughness tests were performed on Single Edge Notched Bend (SENB) specimen for mode I, respectively on Compact Shear (CS) specimens for mode II loading. Digital Image Correlation techique allow the determination of Crack Relative Displacement Factor and estimation of Energy Release Rate.</p> Liviu Marsavina, Ion Octavian POP, Emanoil LINUL Copyright (c) 2019 Liviu Marsavina, Ion Octavian POP, Emanoil LINUL Mon, 03 Dec 2018 00:00:00 +0000 Hexagrid-Voronoi transition in structural patterns for tall buildings <p>In this paper, a first insight into the role that non-conventional structural patterns might play in the design of tall buildings is presented. The idea is to explore the mechanical properties of selected non-conventional structural patterns, in the form of both regular (Hexagrid) and irregular (Voronoi tessellation inspired) arrays, in order to assess their actual applicability in tall building design. For this aim, the concept of Representative Volume Element (RVE) and a classical homogenization-based micromechanical approach are employed for identifying the pattern units and deriving the relevant generalized stress-strain relationships. In the case of irregular patterns based on Voronoi diagrams, obtained by perturbing prescribed key geometrical features of hexagrids, a statistically significant sample of RVEs is defined on the basis of sensitivity analyses, and the related mechanical characterization is developed in statistical terms. Finally, a preliminary stiffness-based design procedure is proposed and applied to a tall building model with Voronoi exoskeleton. In conclusion, a discussion on the effectiveness of the design procedure and on the structural efficiency of the Voronoi patterns for tall buildings is presented</p> elena mele, massimiliano fraldi, Gian Maria Montuori, gianpaolo perrella, vincenzo della vista Copyright (c) 2019 elena mele, massimiliano fraldi, Gian Maria Montuori, gianpaolo perrella, vincenzo della vista Sun, 02 Dec 2018 16:37:31 +0000 The impacts of type and proportion of five different asphalt modifiers on the low temperature fracture toughness and fracture energy of modified HMA <p>Low temperature fracture toughness and fracture energy are two important measures that could be used to investigate the impacts of using asphalt modifiers on the performance of asphalt pavements in cold regions. The aim of this research was to identify the impacts of using various proportions of five different asphalt modifiers on the fracture toughness and the fracture energy of Hot Mix Asphalts (HMA) under mode I loading and at low environmental temperatures. The asphalt modifiers used for this purpose were: Elastoplastomer Polymer Strings (EPS), Parafiber, Sulfur Polymer, Polyolefin-Aramid Compound Structural Fibers (PACSF) and Sasobit. These modifiers were individually used at three different proportions to produce Semi-circular Bend Specimens containing vertical edge crack. Each specimen was then tested under symmetric monotonic three-point bend loading at -15°C. The results indicated that, except for the EPS, both measures were increased with an increase in the modifier proportion. The most increase in the both measures was observed in the specimens modified with the PACSF, closely followed by specimens modified with the Parafibers. The least increase in these two measures were observed in the specimens modified with the Sulfur Polymer. The results indicated the applicability of examined modifiers to improve the resistance of HMA to crack initiation and crack growth at low temperatures.</p> Mehdi Fallah Tafti, Seyyed Abuzar Hoseini Aqda, Hamed Motamedi Copyright (c) 2019 Mehdi Fallah Tafti, Seyyed Abuzar Hoseini Aqda, Hamed Motamedi Sun, 02 Dec 2018 16:17:55 +0000 Building irregularity issues and architectural design in seismic areas <p>When designing buildings in seismic areas, choices of the architectural designer heavily influences seismic structural performances. Namely, building morphology may lead to complex seismic responses as it occurs when building plan and elevation become irregular. Typical irregularities are due to architectural, functional and distribution constraints, thus leading to plan or vertical or combined plan/vertical irregularities. A frequent plan-wise irregularity arises when earthquake resistant structures, such as cores and shear walls, are concentrated on one side of the building plan, while vertical irregularity often arises from the presence of soft stories especially located at the ground level or, less frequently, at an intermediate level.<br>In the last decades, some trends in architectural design, such as Deconstructivism and other contemporary theories, worked in pursuing architectural solutions based on the concept of “deconstruction” in place of “construction”, favoring non-rigid schemes, non-regular shapes and, more generally, avoiding geometric rules and classical canons of symmetry and regularity. <br>In this paper the above issues are investigated with the goal of assessing effects of irregularity conditions, introduced by the architectural design, on the building seismic performances with the aim at not forbidding the designer ambitions but at making him aware of the effects of his architectural choices</p> Valerio Alecci, Mario De Stefano Copyright (c) 2019 Valerio Alecci, Mario De Stefano Sun, 02 Dec 2018 14:27:03 +0000