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) Fri, 22 Mar 2019 10:31:40 +0000 OJS 60 Response of fabric insert injection overmolding PP based composites subjected to single and muti-impact <p>This paper presents the results of a current study on the development and impact response of composite plates manufactured by injection overmolding on the two sides of a single reinforcement fibre mat. The injection polymer is a talc-filled polypropylene, nowadays used for structural purposes. Three configurations with different insert fibre mats were used: Kevlar, biaxial and multiaxial glass fibre mats. The parameters studied were the fibre mat type and the impact energy. For single impact tests, it was concluded that the highest impact energy required to achieve impactor perforation is obtained with Kevlar insert, while the highest percentage of energy recovered is achieved with biaxial glass fibre netting. Kevlar insert also allows for the maximum impact stiffness. For the multi-impact tests, the recovered energy and the dynamic stiffness show the same tendencies of the single impact tests. On low energy impacts, the effect of the insert fibre and of the previous impact are quite reduced, while for impact energies above 6J, previous impacts reduce significantly the recovered energy and the impact energy for which the perforation was achieved.</p> José António Martins Ferreira, Tiago Febra, José Costa, Carlos Capela Copyright (c) 2019 José António Martins Ferreira, Tiago Febra, José Costa, Carlos Capela Fri, 22 Mar 2019 05:20:21 +0000 Fatigue reliability assessment of small sample excavator working devices based on Bootstrap method <p>To evaluate the fatigue reliability of the excavator working device, the fatigue tests of 2 sets of moving arm and bucket rod of medium-sized excavators with self-weight of 26000 kg were carried out. The virtual augmented sample method (VASM) combined with Bootstrap method was used to analyze the reliability of the excavator working device under extreme&nbsp;small&nbsp;samples, and the interval and point estimations of life parameters were obtained. Based on the lognormal distribution of the excavator working device, the reliability evaluation model of the excavator working device was esTablelished, and reliability indexes, such as reliability function, failure distribution function, inefficiency function, reliable life and so on, were obtained. And the results of fatigue safety life under different confidence and reliability were calculated. The evaluation results show that the average failure time of the excavator working device is 5885 hours under the confidence of 75%, which provides an important reference for the design, the safety inspection and maintenance decision of the excavator working device.</p> Yuhong Shao, Pengmin Lu, Binhua Wang, Qingyi Xiang Copyright (c) 2019 Yuhong Shao, Pengmin Lu, Binhua Wang, Qingyi Xiang Fri, 22 Mar 2019 04:58:48 +0000 An uncoupled thermoelasticity problem for a semi-infinite layer with regard of its proper weight <p>The exact solution of the uncoupled thermoelasticity problem for a semi-infinite elastic layer with regard of its proper weight was constructed. The solving method is differ from the known previous and is based on reducing of Lame equations to two jointly and one separately solvable equation. It allows application of integral transformations directly to the transformed equations of equilibrium and makes it possible to reduce the initial problem to a one-dimensional vector boundary problem. A special technique is given to calculate multiple integrals containing oscillating functions that appear during the inversion of the transformations. The character of the temperature and proper weight influence on the value of normal stresses on the lateral face of the semi-infinite layer, the zone of tensile stresses depending on the shapes of the distributed load section and the temperature and Poisson's ratio is established. The parameters of dimensionless mechanical load and temperature, when the separation of the side wall of the semi-infinite layer can be eliminated, were established. A study of the influence of the layer’s proper weight on the stress emerging on the layer’s edge is conducted. The constructed exact solution can be used as a model for solving a similar class of problems by numerical methods.</p> Anna Fesenko, Nataly Vaysfeld Copyright (c) 2019 Anna Fesenko, Nataly Vaysfeld Thu, 21 Mar 2019 19:02:23 +0000 Effect of protective coatings on the water absorption and mechanical properties of 3D printed PLA <p>This work aims to study the influence of protective coatings on the water absorption and mechanical properties of 3D printed poly–lactic acid (PLA) parts. The PLA parts were fabricated with different levels of the 3D printing process parameters, aiming to define samples with distinct strength and ductility/toughness characteristics. Water absorption tests following the standard ASTM D570–98 were performed on uncoated and coated PLA specimens. The effectiveness of two protective coatings based on acrylic and polyurethane varnish on reducing water absorption was evaluated. Both protective coatings have shown being effective on preventing water absorption by the PLA, with polyurethane presenting the best performance reducing water absorption by 38%. Tensile tests were carried out to determine the ultimate tensile strength, elastic modulus, yield tensile strength, fracture strain and toughness of specimens, before and after the application of protective coatings. The polyurethane protective coating also benefits the tensile properties of PLA parts, increasing the strength and ductility/toughness characteristics of specimens up to 24%.</p> Carlos Vicente, João Fernandes, Augusto Deus, Maria Vaz, Marco Leite, Luis Reis Copyright (c) 2019 Carlos Vicente, João Fernandes, Augusto Deus, Maria Vaz, Marco Leite, Luis Reis Fri, 15 Mar 2019 19:19:09 +0000 Intermetallic phase kinetic formation and thermal crack development in galvanized DCI <p>A new class of material characterized by mechanical properties close to the traditional low and medium carbon steel is the Ductile Cast Irons (DCIs). High castability and low production costs allow them to be used in many fields, ranging from automotive to piping. In this class of iron-based alloy the content of carbon is mainly localized in the graphite nodules, which are dispersed in a metallic matrix characterized by different phases: ferrite, austenite, pearlite, martensite or their mix, depending on the chemical composition and the heat treatment. Metallic matrix is subjected to the corrosion phenomenon, and, for this reason, the study and the development of traditional and innovative protection techniques are important, mainly in critical applications. Hot dip galvanizing is one of the investigated protections because the zinc is able to protect the iron-based alloys thanks to the reduction potential that is lower than the iron one.</p> <p>In this work, a ferritic-pearlitic DCI (GS500) is galvanized by using a pure Zn bath at 440°C in order to generate a zinc coating at different dipping time. The presence of thermal cracks is observed by means of a Scanning Electron Microscope (SEM).</p> Costanzo Bellini, Francesco Carlino Copyright (c) 2019 Costanzo Bellini, Francesco Carlino Fri, 15 Mar 2019 19:05:29 +0000 Parametric analysis on external dissipative link system for seismic protection of low rise r.c. buildings <p>&nbsp;</p> <p>The seismic rehabilitation of existing r.c. and masonry buildings is a topical issue in Civil Engineering. A useful technique consists in the introduction of external bracing system. This kind of intervention can be improved throughout the introduction of dissipative links, here investigated with the help of some examples.. The links are made of common steel profiles: length, geometry and its disposition are considered as design parameters. A general procedure of link-bracing optimization is proposed applying a set of identical external restraints . The adopted dissipative links consent a cheaper and effective design both in terms of ULS than in DLS: the damages are addressed in a small area permitting an easy replacement of the links in case of earthquake. &nbsp;&nbsp;</p> Mario Lucio Puppio, Martina Ferrini Copyright (c) 2019 Mario Lucio Puppio, Martina Ferrini Wed, 13 Mar 2019 15:35:52 +0000 Damage detection in a reinforced concrete bridge applying wavelet transform in experimental and numerical data <p>In recent years, one can observe a constant worry of the scientific community on the search for demage detection techniques in structures. Such worry contributed to the progressive development of Structural Health Monitoring. This paper purpose a methodology using Continuous Wavelet Transform associated with interpolation and regularization techniques applied in the experimental and numerical mode shapes of the Dogna Bridge using only the demaged responses. The results of the analyses are presented and discussed in this paper.</p> ramon saleno yure rubim costa silva, Erwin U. L. Palechor, Luciano M. Bezerra, Marcus V. G. de Morais, Welington V. da Silva Copyright (c) 2019 ramon saleno yure rubim costa silva, Erwin U. L. Palechor, Luciano M. Bezerra, Marcus V. G. de Morais, Welington V. da Silva Mon, 11 Mar 2019 06:11:34 +0000 Stress Intensity Factor Solutions for CTS Mixed Mode Specimen <p>The Compact Tension Shear (CTS) specimen is used to study fracture and fatigue under mixed mode I/II loading conditions. Existing K solution was developed for fracture studies and it does not consider the effect of crack deflection. The aim of present work is to develop K<sub>I</sub> and K<sub>II</sub> empirical solutions for cracks with different crack length, loading angle and crack orientation. A total number of 1120 cracked geometries were studied numerically by the finite element method and solutions were fitted to numerical predictions. An average difference of 0.53 % was found between numerical predictions and the solution proposed for K<sub>I. </sub>For K<sub>II</sub> the difference is higher, but the equivalent stress intensity factor showed a difference of only &nbsp;1% because K<sub>II</sub> is lower than K<sub>I</sub>. Experimental work was developed to study fatigue crack growth in CTS specimens. The cracks always adopted a direction approximately normal to loading direction, i.e., tend to propagate under mode I.</p> Fernando Ventura Antunes, Ricardo Branco, José António Martins Ferreira, Luís Borrego Copyright (c) 2019 Fernando Ventura Antunes, Ricardo Branco, José António Martins Ferreira, Luís Borrego Sun, 10 Mar 2019 08:36:33 +0000 Fatigue crack growth in notched specimens: a numerical analysis <p>Fatigue crack growth (FCG) is linked to irreversible and non-linear processes happening at the crack tip, which explains different problems observed in the use of da/dN-DK curves. The replacement of DK by non-linear crack tip parameters, namely the crack tip opening displacement (CTOD) is an interesting alternative. The objective in here is to study the effect of notches on FCG using the plastic CTOD range, d<sub>p</sub>. M(T) specimens with lateral notches of different radius (1, 2 4 and 8 mm were analysed numerically, keeping the total depth constant (8 mm). The increase of crack length increases d<sub>p</sub> and therefore FCG rate. For plane stress state, the formation of the residual plastic wake with crack propagation produces crack closure which compensates the effect of crack length and there is a stabilization of d<sub>p</sub>. The reduction of notch radius increases d<sub>p</sub> for all crack lengths, particularly for the shortest ones. For plane strain state there is almost no crack closure therefore d<sub>p</sub> is higher than for plane stress state, and the effect of crack length produces a relatively fast increase of d<sub>p</sub></p> Fernando Ventura Antunes, Ricardo Branco, Pedro Prates, José Domingos Costa Copyright (c) 2019 Fernando Ventura Antunes, Ricardo Branco, Pedro Prates, José Domingos Costa Sat, 09 Mar 2019 04:35:07 +0000 Localized wrinkling of metal films on elastic and liquid substrates <p>Global and localized wrinkling phenomena in films/substrates have been widely studied by means of experiment and theoretical analyses in the past two decades. They have shown broad application prospect in microstructure manufacture. The global wrinkling patterns with well-defined wavelengths can be readily fabricated in the polymer films, the metal films and the surface of modified elastic substrates by O<sub>2</sub> plasma or UVO, and they have attracted much attention. For the localized wrinkling patterns, however, most previous studies were limited to polymer films, which while metal films were not properly considered. Recent studies have shown that wrinkles can be localized by constrained edges and cracks in metal films deposited on the elastic and liquid substrates. In this review, we focus on the formation and evolution mechanisms of these localized wrinkle patterns, and we aim to provide some useful guidance for future studies on designing the localized wrinkling patterns with real-time controllable dimension, orientation and morphology in the films/substrates.</p> Yi Sun, Liping Yan, Benyong Chen, Wei Song, Filippo Berto Copyright (c) 2019 Yi Sun, Liping Yan, Benyong Chen, Wei Song, Filippo Berto Fri, 08 Mar 2019 17:43:00 +0000 Multi-axial fatigue numerical crack propagation in cruciform specimens <p>Two cracks, initiated from the opposite tips of a central notch inclined by 45°, were considered in cruciform specimens made of Ti6246. A static load was applied to a cruciform arm while a cyclic load was applied along the other arm.</p> <p>Fatigue propagation of cracked specimens was performed by means of Dual Boundary Element Method (DBEM) and Finite Element Method (FEM) codes. For crack path assessment, the Minimum Strain Energy Density (MSED) and the Maximum Tensile Stress (MTS) criteria were adopted in DBEM and FEM approaches, respectively. Moreover, the J and M integrals’ formulations were used to evaluate the SIFs along the crack fronts for DBEM and FEM codes, respectively. Crack-growth rates were predicted by using a Walker law, calibrated on mode I fracture experimental data.</p> <p>A good agreement between numerical and experimental crack paths was obtained.</p> Venanzio Giannella, Michele Perrella Copyright (c) 2019 Venanzio Giannella, Michele Perrella Fri, 08 Mar 2019 14:14:19 +0000 Effect of Contact Geometry on the Contact Stresses in a Flat with Round Edge Contact <p>The blade-disc dovetail interface in an aero-engine compressor is characterized by a non-uniform pressure distribution which can be obtained by an equivalent flat with round edge-on-plate configuration. The contact tractions for a mating pair are affected by many parameters which include, contact geometry, loading conditions, and material properties; with contact geometry being one of the prominent factors. In the present work, a 2-D elastic and elasto-plastic finite element analysis has been carried out for a rounded contact geometry to study the influence of the radius of the corners ‘R’ and length of the flat region ‘2a’. It is observed that the peak tensile stress in the fretting direction was found to decrease with increasing ‘a’ (for constant ‘R’) which is likely to delay the crack initiation. Also, as compared to elasto-plastic analysis, elastic analysis overestimates peak tensile stress and possibly give a conservative estimate for the fretting fatigue life. Further, the effect of modelling elastic-plastic behaviour is significant for low a/R ratio (for constant ‘R’). However, opposite trend was observed when ‘R’ was varied keeping ‘a’ constant. Also, it is found that the effect of contact geometry cannot be characterized using a single parameter like a/R ratio or contact area.</p> Pankaj Dhaka, Mr, Raghu Vasu Prakash Copyright (c) 2019 Pankaj Dhaka, Mr, Raghu Vasu Prakash Fri, 08 Mar 2019 13:57:50 +0000 Stress Intensity Factor Equations for the Evolution of Surface and Corner Cracks to Through Cracks <p>Part-through surface or corner 2D cracks are commonly found in structural components, even because practically all fatigue cracks tend to start this way. It is a reasonable hypothesis to model them assuming the shape of their fronts is approximately an elliptic arc, as supported by many fractographic observations. But their transition to a 1D through-crack, an important issue in many practical applications, is normally not properly addressed in fatigue life predictions. Although experimental results reveal that the frontier of surface cracks essentially retain their elliptical shape as they gradually grow into a through-crack, it is usual to assume they are immediately transformed into a through-crack when their depth reaches the cracked component thickness. This crude approximation may create a large jump in stress intensity values, leading to excessively conservative fatigue crack growth predictions, or else the crude shape jump hypothesis may induce false overload events that can much affect fatigue crack growth retardation models, leading to inadmissible non-conservative life predictions. To minimize such problems, an improved model to describe the transition of 2D surface cracks to 1D through-cracks is proposed and verified by crack propagation tests in two different materials, 4340 steel and polycarbonate (PC). Moreover, fatigue life predictions based on this improved model are compared with experimental results.</p> Antonio Miranda, Rafael Marques, Marco Antonio Meggiolaro, Jaime Tupiassú Pinho de Castro Copyright (c) 2019 Antonio Miranda, Rafael Marques, Marco Antonio Meggiolaro, Jaime Tupiassú Pinho de Castro Fri, 08 Mar 2019 06:10:10 +0000 Evaluation of mixed mode (I/II) notch stress intensity factors of sharp V-notches using point substitution displacement technique <p>In this paper, determination of the accurate notch stress intensity<br>factors (NSIFs) have been demonstrated using a recently proposed technique:<br>The point substitution displacement technique (PSDT) for the sharp Vnotched<br>configurations. In this technique, certain optimal point(s) on the<br>notch flanks are obtained where the displacements are found to be highly<br>accurate. Using the PSDT, the NSIFs are determined from the finite element<br>(FE) displacements at these optimal point(s). The NSIFs of one pure mode I<br>and two mixed mode (I/II) examples have been determined and excellent<br>agreement of the present results with the published results is observed. The<br>PSDT is efficient, robust and easy to be implemented in the available FE<br>code.</p> Mirzaul Karim Hussain, K.S.R.K. Murthy Copyright (c) 2019 Mirzaul Karim Hussain, K.S.R.K. Murthy Fri, 08 Mar 2019 05:02:53 +0000 In-plane anisotropy in deformation micro-mechanism of commercially pure titanium during monotonic tension and cyclic loading <p>In the present investigation in-plane anisotropy in tensile and ratcheting behavior of cold rolled and annealed commercially pure titanium plate has been studied. Flat tensile and fatigue test specimen oriented at 0, 45, and 90 degree to the rolling direction in the rolling direction–transverse direction (RD–TD) plane of the plate has been machined out. Specimens with loading axis at 0, 45 and 90 degree to RD have been designated as 0T, 45T and 90T for tensile and 0R, 45R and 90R for fatigue. Owing to initial TD split basal texture of as received plate, 0T sample has crystallographic direction &nbsp;&nbsp;aligned with loading axis. It shows lowest yield strength but highest ductility in monotonic tension. Although ultimate tensile strength (UTS) and strain to failure of samples 45T and 90T are similar, the former has significantly lower yield strength than the latter, indicating different strain-hardening behavior due to different slip/twin activity. On the other hand, 0R sample exhibits longer ratcheting life while 90R sample accumulates highest ratcheting strain. This is attributed to higher propensity for twinning with the formation of intersecting multiple variant twins during cyclic deformation of 0R sample. Viscoplastic self-consistent (VPSC) simulations of one-cycle tension-compression-reload tension indicate that there is alternate activity of pyramidal &lt;c+a&gt; slip and extension twinning during cyclic loading. This induces cross slip activity and detwinning of extension twins in 90R which causes rapid accumulation of strain leading to early failure.</p> Atasi Ghosh Copyright (c) 2019 Atasi Ghosh Fri, 08 Mar 2019 04:45:19 +0000 Interfacial shear strength of carbon nanotubes based hybrid composites: effect of loading rate <p>Interfacial interaction is investigated between the two basic constituents in carbon fiber reinforced plastics (CFRPs). Efforts have been made to quantify the interfacial shear strength (IFSS) between individual carbon fiber (CF) and epoxy matrix in CFRPs by performing single fiber micro-droplet debond test. Initially, IFSS of the epoxy composites reinforced with unsized carbon fiber (HCF) is assessed. Study is then extended to assess the IFSS of carbon nanotubes (CNTs) based CFRP hybrid composites. The hybrid composites are prepared by reinforcing epoxy matrix with CNT grafted carbon fibers (CNTCF). The versatile, simple and time effective method of chemical vapor deposition is used to synthesize CNTs directly on the surface of CF. IFSS is found to enhance after the inclusion of grafted CNTs in CFRP composites. Keeping in mind the application view point of CFRPs to put up with varying loads, effect of loading rate on the IFSS of CFRPs is also examined. To this end, both HCF/epoxy and CNTCF/epoxy composites are debonded at cross-head rates varying by two orders of magnitude and IFSS is compared. Finally, scanning electron microscopy of debonded fibers is carried out to understand the interfacial failure mechanism in various composites.</p> Harpreet Singh Singh Bedi, Beant Kaur Billing, Prabhat K Agnihotri Copyright (c) 2019 Harpreet Singh Singh Bedi, Beant Kaur Billing, Prabhat K Agnihotri Thu, 07 Mar 2019 17:55:21 +0000 Determination of dissipated Energy in Fatigue Crack Propagation Experiments with Lock-In Thermography <p>Lock-In thermography can be used to investigate elastic stresses and dissipative effects in dynamic processes like crack propagation. The evaluation normally is performed with a Discrete Fourier Transformation resulting in E- and D-Amplitude and phase images. The E-Amplitude images give information about the stress distribution, the D-Amplitude is connected with dissipated energies. The observed changes in the E-amplitude values can be contributed to a change in the stress state at the crack tip due to bending of the specimen caused by the propagating crack. In the crack propagation experiments the maximum value of the D-Mode in the area in front of the crack tip was found to be constant. The appearance of higher harmonic modes in the evaluation raises the question if the Discrete Fourier Transformation is the appropriate method for a quantitative evaluation of dissipative effects. Experiments performed on flat specimens show that a description of the temperature change due to dissipative effects could not be described with a sine wave with the double loading frequency. Therefore, a quantitative determination of dissipated energies using the Discrete Fourier Transformation is impossible. For a quantitative determination of dissipated energies a new evaluation method has to be developed.</p> Jürgen Bär, Ralf Urbanek Copyright (c) 2019 Jürgen Bär, Ralf Urbanek Thu, 07 Mar 2019 17:03:35 +0000 Comparative evaluation of two physically based models for the description of stress-relaxation behaviour of 9% chromium containing steel <p>An attempt has been made to evaluate the applicability of two constitutive models related to the dislocation-obstacle interactions for the description of stress-relaxation behaviour of E911 tempered martensitic steel. The first one is Feltham model (Model-I) and the Model-II proposed by Christopher and Choudhary is based on the sine hyperbolic kinetic rate formulation coupled with the evolution of internal stress. The physical constants associated with these models have been determined by the minimization of errors between experimental and predicted relaxation stress vs. hold time data for two different strain hold levels of 1.3 and 2.5% at 873 K for E911 steel. Model-II provides better prediction of stress-relaxation behaviour of the steel as compared to Model-I. In addition to prediction of relaxation stress vs. hold time data, Model-II can able to capture the evolution of internal stress, inter-barrier spacing and activation volume with the hold time. The predicted increase in inter-barrier spacing and activation volume with hold time indicated that substructural coarsening remains dominant in E911 steel under stress-relaxation conditions.</p> J. Christopher, C. Praveen, B.K. Choudhary Copyright (c) 2019 J. Christopher, C. Praveen, B.K. Choudhary Thu, 07 Mar 2019 14:18:30 +0000 Evaluation of Fatigue Properties under Four-point Bending and Fatigue Crack Propagation in Austenitic Stainless Steel with a Bimodal Harmonic Structure <p>Austenitic stainless steel (JIS-SUS304L) with a bimodal harmonic structure, which is defined as a coarse-grained structure surrounded by a network of fine grains, was fabricated using powder metallurgy to improve both the strength and ductility. Four-point bending fatigue tests and <em>K</em>-decreasing tests were conducted in air at room temperature under a stress ratio <em>R</em> of 0.1 to investigate fatigue crack propagation in SUS304L. The fatigue limit of this harmonic-structured material was higher than that of the material with a homogeneous coarse-grained structure. This is attributable to the formation of fine grains by mechanical milling and to the suppression of pore formation. In contrast, the threshold stress intensity range, D<em>K</em><sub>th</sub>, for the harmonic-structured material was lower than that for the homogeneous coarse-grained material, while the crack growth rates, d<em>a</em>/d<em>N</em>, were higher at comparable D<em>K</em>. These results can be attributed to a reduction in the effective threshold stress intensity range, D<em>K</em><sub>eff,th</sub>, due to the presence of fine grains in the harmonic structure.</p> Shoichi Kikuchi, Yuta Nakatsuka, Yoshikazu Nakai, Masashi Nakatani, Mie Ota Kawabata, Kei Ameyama Copyright (c) 2019 Shoichi Kikuchi, Yuta Nakatsuka, Yoshikazu Nakai, Masashi Nakatani, Mie Ota Kawabata, Kei Ameyama Thu, 07 Mar 2019 13:51:59 +0000 Experimental investigation of surface roughness effect on fatigue performance of AISI 1045 carbon steel and fatigue limit prediction <p>In fatigue life, surface integrity perform a major role to determine the fatigue lifetime. It could differ greatly among specific cases even for the same solicitations. Indeed, the manufacturing process carries modifications on surface state, residual stresses and the microstructure which affects the fatigue behavior of mechanical parts.<br>This article investigate the effect of surface roughness on the fatigue strength of AISI 1045 carbon steel obtained by the turning process. <br>The work carried out consists in testing in uniaxial fatigue different batches of specimens which have a controlled surface state. The S-N curves obtained present a strong dependence between fatigue performance and surface state. Based on the surface topography, a model for predicting fatigue limit will be adopted.</p> Khadija Kimakh, Abdelkerim Chouaf, Amal Saoud, El Hassan Mallil, Samir Aghzer Copyright (c) 2019 Khadija Kimakh, Abdelkerim Chouaf, Amal Saoud, El Hassan Mallil, Samir Aghzer Thu, 07 Mar 2019 05:45:20 +0000 Low cycle fatigue and creep-fatigue response of the 316Ti stainless steel <p>SS 316Ti is widely used in bellows industry and is a good candidate material for high temperature bellows in sodium cooled fast reactor (SFR) systems. Typical operating temperature experienced by SFR systems is around 823K. Design of bellows for nuclear applications need to be in compliance with the standard design codes such as ASME section-III and RCC-MR. The fatigue data and cyclic stress strain curve of SS316Ti are not available in design codes such as RCC-MR or ASME section-III/NH. Hence, the material data required for high temperature design of bellows are generated experimentally. Initially, the basic tensile data such as yield strength, ultimate tensile strength and % elongation of the material were obtained from tensile testing at 823K. Low cycle fatigue tests were carried out in strain controlled mode on SS316Ti at 823K different strain ranges in air and variation of number of cycles with strain range was obtained. Creep-fatigue interaction (CFI) experiment was also conducted at 823K and strain amplitude of ± 0.4% with 1 minute hold time in peak tensile strain. The stress response (peak stress variation with number of cycles) of the material showed continuous hardening up to saturation followed by crack nucleation and final failure. The fatigue life was found to decrease with increase in strain range. The fatigue life decreased in presence of hold period in tension. The design fatigue curve for SS316Ti at 823K has been generated using the LCF data by incorporating factors of safety on strain and number of cycles. Cyclic stress strain curve was generated for the material at 823K. The tensile, LCF and CFI data generated will be useful in design of SS316Ti bellows for SFR systems.</p> S C S P Kumar Krovvidi, Sunil Goyal, A K Bhaduri Copyright (c) 2019 S C S P Kumar Krovvidi, Sunil Goyal, A K Bhaduri Thu, 07 Mar 2019 00:00:00 +0000 Fatigue strength evaluation and fracture behavior of joined dual phase steel/AA6061-T6 aluminum alloy <p>The fatigue strength evaluation and fracture behavior for a dual phase steel-AA6061-T6 bonded joints with three different adhesives (DC-80, Betamate 120 and MP55420) are presented in this paper. Single lap shear tests were used to determine maximum shear loads, for the single lap shear testing for 5.0 mm overlap length were 2 to 3.5 times higher in comparison to the 12.7 mm overlap length specimens. The results for the strain measurement revealed that higher strain-stress were developed in the 6061-T6 aluminum alloy adherend and in all cases they were lower than the adherends yield strength. Fatigue testing was carried out at 30, 50 and 70 % of the maximum shear load, 0.1 of reversibility load ratio (R) and 30 Hz of frequency. After testing, Basquin and Wholer graphs were built for each adhesive at 12.7 and 50.0 mm of overlap length. The results suggested that at higher overlapping, the cyclic maximum load increased. Additionally, the maximum fatigue loading at 10^6 cycles for MP55420 adhesive was 1.3 kN for an overlapping of 12.7 mm and 2.9 kN for 50 mm. For DC80 adhesive was 1.75 kN for overlapping 12.7 mm and 4.8 kN for 50 mm. Finally, for the Betamate 120 adhesive was 1.8 kN for 12.7 mm of overlapping and 6 kN for 50 mm. The post-fracture visual inspection revealed that MP55420 and Betamate 120 adhesives had a cohesive failure, while the DC-80 showed cohesive-adhesive failure. Additionally, the scanning electron microscopy evaluation on the spew fillet revealed resolved striations and a network of small micro-dimples for the Betamate 120 and MP55420 adhesives. On the other hand, DC-80 adhesive exhibited notable facet fragile failure that was confirmed by the shape of stress-strain plot with straight line from the origin to the point of fracture.</p> Ruben Perez Mora, Celso Eduardo Cruz Gonzalez, Saul Daniel Santillan Gutierrez, Jose Jaime Taha Tijerina, Benjamin Vargas Arista, Arturo Barba Pingarron Copyright (c) 2019 Ruben Perez Mora, Celso Eduardo Cruz Gonzalez, Saul Daniel Santillan Gutierrez, Jose Jaime Taha Tijerina, Benjamin Vargas Arista, Arturo Barba Pingarron Wed, 06 Mar 2019 05:42:55 +0000 Mechanical Stability Investigation of Advanced Composite Plates Resting on Elastic Foundations Using a New Four-Unknown Refined Theory <p>A refined and simple shear deformation theory for mechanical buckling of composite plate resting on two-parameter Pasternak’s foundations is developed. The displacement field is chosen based on assumptions that the in-plane and transverse displacements consist of bending and shear components, and the shear components of in-plane displacements give rise to the parabolic variation of shear strain through the thickness in such a way that shear stresses vanish on the plate surfaces.Therefore, there is no need to use shear correction factor. The number of independent unknowns of present theory is four, as against five in other shear deformation theories.It is assumed that the warping of the cross sections generated by transverse shear is presented by a hyperbolic function. The stability equations are determined using the present theory and based on the existence of material symmetry with respect to the median plane.The nonlinear strain-displacement of Von Karman relations are also taken into consideration. .The boundary conditions for the plate are assumed to be simply supported in all edges. Closed-form solutions are presented to calculate the critical load of mecanical buckling, which are useful for engineers in design. The effects of the foundation parameters,side-to-thickness ratio and modulus ratio, the isotropic and orthotropic square plates are considered in this analysis.are presented comprehensively for the mechanical buckling of rectangular composite plates.</p> Yassine khalfi; Aboubakar Seddik BOUCHIKHI; Yassine BELLEBNA Copyright (c) 2019 Yassine khalfi; Aboubakar Seddik BOUCHIKHI; Yassine BELLEBNA Tue, 05 Mar 2019 17:55:46 +0000 Prediction and optimizing residual stress profile induced by cold expansion in aluminum alloys using experimental design <p>Cold expansion by hardening is a common process used in the aerospace industry to extend the fatigue lifetime of assembly holes, through a field of high compressive tangential residual stresses. The understanding and the control of the residual stresses are thus important, since it can be beneficial to improve lifetime of the structures. The main objective of this work is to establish and validate a predictive model of residual stresses generated by cold hardening. This technique can be an effective ways for industrials allowing an estimation of the fatigue lifetime of parts according to the process parameters or to determine the optimal parameters to maximize fatigue lifetime. An experimental setup was used to highlight the effect of expansion degree, thickness of the part and yield strength on the residual stresses profiles. Moreover, the proposed mathematical models were used to determine the optimal values of the various factors for the residual stress profiles prediction at any factor values, in order to achieve maximum service life after repair of a cracked structure or to delay crack initiation and growth in riveted or bolted structures. Besides, the modelling permits us to highlight the effect of interaction of these factors on the residual stresses profiles.</p> Abdelkader Miloudi, M. Laredj, A. Lousdad, B. Benguediab Copyright (c) 2019 Abdelkader Miloudi, M. Laredj, A. Lousdad, B. Benguediab Tue, 05 Mar 2019 17:50:35 +0000 Development of hybrid friction stir welding and adhesive bonding single lap joints in aluminium alloys <p>Aircraft have been manufactured for decades using a wide variety of welding and joining techniques. There have been significant developments in techniques over the last 15–20 years.</p> <p>In civil aeronautical industry the main materials used for the fuselage and structural parts are aluminium alloys. In order to reduce weight, leading to a better fuel and economic efficiency, there is the need to find innovative solutions to join aluminium components in a single lap joint (SLJ) configuration with higher strength to weight ratio than riveting and fastening. In this work, a combination of the friction stir welding (FSW) and adhesive bonding (AB) processes is presented. Quasi-static mechanical properties, fatigue behaviour and other properties of the friction stir weld-bonding joints were assessed and compared with adhesive only and friction stir welded only joints.</p> <p>The development of this new joining technology, the combination of FSW with AB, forming friction stir weld-bonding, aims to incorporate properties and characteristics of both joining technologies, as well as improving damage tolerance.</p> <p>The present research involved the production of two types of overlap joints - FSW and hybrid friction stir weld-bonding. The main objective of this study is to compare the different joining technologies in lap joint configuration and evaluate the influence of different parameters on the mechanical behavior of the joints. &nbsp;</p> <p>The hybrid joints present better overall results, and the best joint was efficiency achieved with the hybrid joint produced with 450 kgf. The average efficiency value in this case was 73.75%, however in a particular specimen it reached the value of 85.21%. From the results it is possible to affirm that the hybridization process confers an improvement between 20-30 % in most cases.</p> Ricardo Leite Maciel, Virginia Infante, Daniel Braga, Pedro Moreira, Tiago Bento, Lucas da Silva Copyright (c) 2019 Ricardo Leite Maciel, Virginia Infante, Daniel Braga, Pedro Moreira, Tiago Bento, Lucas da Silva Tue, 05 Mar 2019 17:42:13 +0000