bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of stress intensity factor for internal cracks in FG cylinders under static and dynamic loading
Authors: Shariati Mahmoud , Mahdizadeh Rokhi Masoud , Rayegan Hassan
Published: July 2018

This paper investigates the variations of mode I stress intensity factor (KI) for inner penny-shaped and circumferential cracks in functionally graded solid and hollow thick walled cylinders, respectively with the changes of crack geometry, material gradation and loading conditions. The functionally graded material of cylinders consists of epoxy and glass. It is assumed that the mechanical properties vary with a power law in the radial direction of cylinders. Micromechanical models for conventional composites are used to estimate the material properties of functionally graded cylinders. The equations of motion obtained from the extended finite element discretization are solved by the Newmark method in the time domain. The interaction integral method is employed to calculate the mode I stress intensity factor (KI). The MATLAB programming environment was implemented to solve the problem.
From test data to FE code: a straightforward strategy for modelling the structural bonding interface
Authors: Lepore M. A. , Perrella M.
Published: July 2018

A straightforward methodology for modelling the cohesive zone (CZM) of an adhesively bonded joint is developed, by using a commercial finite element code and experimental outcomes from standard fracture tests, without defining a damage law explicitly. The in-house developed algorithm implements a linear interpolated cohesive relationship, obtained from literature data, and calculates the damage at each step increment. The algorithm is applicable both to dominant mode I or dominant mode II debonding simulations. The hypothesis of unloading stages occurrence is also considered employing an irreversible behaviour with elastic damaged reloading. A case study for validation is presented, implementing the algorithm in the commercial finite element method (FEM) software Abaqus®. Numerical simulation of dominant mode I fracture loading provides with satisfactory results.
Experimental and numerical study on mechanical properties of aluminum alloy under uniaxial tensile test
Authors: Daghfas O. , Znaidi A. , Ben Mohamed A. , Nasri R.
Published: July 2018

The main objective is to model the behavior of 7075 aluminum alloy and built an experimental database to identify the model parameters. The first part of the paper presents an experimental database on 7075 aluminum alloy. Thus, uniaxial tensile tests are carried in three loading directions relative to the rolling direction, knowing that the fatigue of aircraft structures is traditionally managed based on the assumption of uniaxial loads. From experimental database, the mechanical properties are extracted, particularly the various fractures owing to pronounced anisotropy relating to material. In second part, plastic anisotropy is then modeled using the identification strategy which depends on yield criteria, hardening law and evolution law. In third part, a comparison with experimental data shows that behavior model can successfully describe the anisotropy of the Lankford coefficient.
Strain monitoring of cement-based materials with embedded polyvinyl alcohol - carbon nanotube (PVA-CNT) fibers
Authors: Metaxa Zoi S. , Neri Wilfrid , Poulin Philippe , Alexopoulos Nikolaos D.
Published: July 2018

This article investigates the possibility of exploiting innovative polyvinyl alcohol fibers reinforced with carbon nanotubes (PVA-CNT fiber) as a strain sensor in cement mortars used in the restoration of Cultural Heritage Monuments. Two types of PVA-CNT fibers were embedded in the matrix at a short distance from the bottom of the beam and their readings were correlated with traditional sensors, e.g. strain gauges and Fiber Optic Bragg Gratings. The Electrical Resistance Change (ERC) of the embedded PVACNT fiber was in-situ monitored during four-point bending mechanical tests. For the case of coated PVA-CNT fiber, a linear correlation of the applied strain at the bottom surface of the specimen along with ERC values of the fiber was noticed for the low strain regime. For the case of incremental increasing loading – unloading loops, the coated and annealed PVA-CNT fiber gave the best results either as embedded or as ‘surface attached’ sensor that exhibited linear correlation of ERC with applied strain for the low applied strain regime as well as hysteresis loops during unloading. The article discusses their high potential to be exploited as strain/damage sensor in applications of civil engineering as well as in restoration of Monuments of Cultural Heritage.
Exercise as a mean to reverse the detrimental effect of high-fat diet on bone’s fracture characteristics
Authors: Doulamis Ilias , Perrea Despina N. , Chatzistergos Panagiotis E. , Mitousoudis Athanasios S. , Kourkoulis Stavros K.
Published: July 2018

The aim of this study is to investigate whether exercise can reverse some of the adverse effects of high-fat-diet-induced obesity on lipid metabolism and bone biomechanical properties. A total of 26 adult male C57bl/6J mice were randomly assigned into three groups: (A) Control group (n=6), (B) High-fat diet group (n=10), (C) High-fat diet and exercise group (n=10). Body mass and relevant biochemical parameters were measured for the duration of the experimental protocol (37 weeks). Mechanical strength of both femurs of each animal was assessed in-vitro based on three point bending tests. It was revealed that exposure to high-fat diet led to significant increase of body mass and cholesterol levels and also to substantial changes in bone morphology and strength. Ultimate stress for the animals exposed to high-fat diet and those exposed to high-fat-diet and exercise was 25% and 24% lower compared to control, respectively. Exercise increased bone thickness by 15% compared to animals that were not exposed to exercise. It was concluded that high-fat-diet appears to have a detrimental effect on bone biomechanics and strength. Exercise reversed the reduction in bone thickness that appears to be induced by high-fat diet. However no statistically significant increase in bone strength was observed.
Structural interventions on the drums of the Parthenon’s north colonnade
Authors: Mentzini Marilena
Published: July 2018

The Acropolis monuments are globally recognized as a cultural heritage and a value belonging not only to Greece but also to Humanity. From 2000 the most recent phase of restoration in their history began by the “Acropolis Restoration Service” (YSMA), introducing new, pioneering methods, recognized now worldwide. Especially the restoration of the Parthenon’s North Colonnade is an enormous work-plan to be carried out (extended area of intervention, great number of members to be restored and high degree of damages). Moreover, the structural stability of the Parthenon’s north colonnade is among the most important challenges confronted by experts working in this sector. The complexity of this effort (a combination of scientific research and direct field application) makes the implementation of the restoration project difficult, rendering its division into smaller projects (for similar structural members) a necessity. In this direction, characteristic examples of the procedure followed for the structural intervention on the drums are presented in this paper. Each member’s report includes a short history of its restoration, the intervention steps, pictures/sketches and the methodology chosen for its structural study, focusing on the particularities of the member and the in-field realization.
Multiaxial elastoplastic cyclic loading of austenitic 316L steel
Authors: Mazánová V. , Polák J. , Škorík V. , Kruml T.
Published: July 2018

Cyclic stress-strain response and fatigue damage character has been investigated in austenitic stainless steel 316L. Hollow cylindrical specimens have been cyclically deformed in combined tension-compression and torsion under constant strain rate condition and different constant strain and shear strain amplitudes. In-phase and 90° out-of-phase cyclic straining was applied and the stress response has been monitored. Cyclic hardening/softening curves were assessed in both channels. Cyclic softening followed for higher strain amplitudes by long-term cyclic hardening was observed. Cyclic stress-strain curves were determined. Study of the surface damage in fractured specimens revealed the types and directions of principal cracks and the sources of fatigue crack initiation in slip bands.
A two-step multiaxial racetrack filter algorithm for non-proportional load histories
Authors: Meggiolaro Marco Antonio , Pinho de Castro Jaime Tupiassú , Wu Hao
Published: July 2018

The recently proposed multiaxial racetrack filter (MRF) is able to deal with general non-proportional multiaxial load histories. While only requiring a single user-defined scalar filter amplitude, the MRF is able to synchronously eliminate non-damaging events from any noisy multiaxial load history without changing the overall shape of its original path, a necessary condition to avoid introducing errors in fatigue damage assessments. The MRF procedures are optimized here by the introduction of a pre-processing “partitioning” step on the load history data, which selects candidates for the reversal points in a robust partitioning process, highly increasing the filter efficiency and decreasing its computational time. The improved MRF is evaluated through the fatigue analyses of over-sampled tension-torsion data measured in 316L stainless steel tubular specimens under non-proportional load paths.
Crack initiation life in notched Ti-6Al-4V titanium bars under uniaxial and multiaxial fatigue: synthesis based on the averaged strain energy density approach
Authors: Meneghetti Giovanni , Campagnolo Alberto , Berto Filippo , Tanaka Keisuke
Published: July 2018

The fatigue behaviour of circumferentially notched specimens made of titanium alloy, Ti-6Al-4V, has been analysed. To investigate the notch effect on the fatigue strength, pure bending, pure torsion and multiaxial bending-torsion fatigue tests have been carried out on specimens characterized by two different root radii, namely 0.1 and 4 mm. Crack nucleation and subsequent propagation have been accurately monitored by using the direct current potential drop (DCPD) technique. Based on the results obtained from the potential drop technique, the crack initiation life has been defined in correspondence of a relative potential drop increase ?V/?V0 equal to 1%, and it has been used as failure criterion. Doing so, the effect of extrinsic mechanisms operating during crack propagation phase, such as sliding contact, friction and meshing between fracture surfaces, is expected to be reduced. The experimental fatigue test results have been re-analysed by using the local strain energy density (SED) averaged over a structural volume having radius R0 and surrounding the notch tip. Finally, the use of the local strain energy density parameter allowed us to properly correlate the crack initiation life of Ti-6Al-4V notched specimens, despite the different notch geometries and loading conditions involved in the tests.
Effect of spectral cross-correlation on multiaxial fatigue damage: simulations using the critical plane approach
Authors: Carpinteri Andrea , Spagnoli Andrea , Vantadori Sabrina
Published: July 2018

The present paper aims to discuss a frequency-domain multiaxial fatigue criterion based on the critical plane approach, suitable for fatigue life estimations in the presence of proportional and non-proportional random loading. The criterion consists of the following three steps: definition of the critical plane, Power Spectral Density (PSD) evaluation of an equivalent normal stress, and estimation of fatigue damage. Such a frequency-domain criterion has recently been validated by using experimental data available in the literature, related to combined proportional and non-proportional bending and torsion random loading. The comparison with such experimental data has been quite satisfactory. In order to further validate the above criterion, numerical simulations are herein performed by employing a wide group of combined bending and torsion signals. Each of such signals is described by an ergodic, stationary and Gaussian stochastic process, with zero mean value. The spectrum of each signal is assumed to be represented by a PSD function with rectangular shape. Different values of correlation degree, variance and spectral content are examined.
Evaluation of new multiaxial damage parameters on low carbon steel
Authors: Cruces A. S. , Lopez-Crespo P. , Moreno B. , Lopez-Moreno A. , Suman S.
Published: July 2018

Most mechanical components are subjected to the complex fatigue loading conditions, where both amplitude and direction of loading cycles change over the time. The estimation of damage caused by these complex loading scenarios are often done by simplified uniaxial fatigue theories, which ultimately leads to higher factor of safety during the final design considerations. Critical plane-based fatigue theories have been considered more accurate for computing the fatigue damage for multiaxial loading conditions in comparison to energy-based and equivalent stress-based theories. Two recently developed fatigue theories have been evaluated in this work for the available test data. Test data includes significant amount of biaxial load paths.
Influence of crack micro-roughness on the plasticity-induced fatigue propagation in high strength steel
Authors: Toribio J. , Matos J.C. , González B.
Published: July 2018

This article deals with the locally multiaxial fatigue behaviour of high strength steel. To this end, the influence of the cracking path deflections (at the micro level) on the plasticity-induced fatigue crack growth is analyzed. With regard to this, a modelling by means of the finite element method was performed for a given stress intensity factor in the Paris regime, considering the existence of micro-roughness in the crack path (local micro-deflections with distinct micro-angles as a function of the microstructure of the material). The numerical results allow one to obtain the fatigue crack propagation rate and compare it with that for the same material in the absence of micro-roughness (with no micro-crack deflections, i.e., uniaxial fatigue behaviour).
Prediction of fatigue crack initiation under biaxial loading
Authors: Sahadi J.V. , Nowell D. , Paynter R.J.H.
Published: July 2018

This investigation revisits biaxial fatigue experiments carried out with the nickel-based superalloy termed Waspaloy. Recently, yield criteria extended to multiaxial fatigue and stress based approaches were analysed and their performance to correlate the biaxial test data was evaluated. It was concluded that despite their reliable results, the parameters did not properly represent the physical behaviour of the material. In this context, an extension of this study was executed considering the strain based critical plane approaches proposed by Fatemi-Socie (FS) and Smith- Watson-Topper (SWT). The first parameter presented overly conservative predictions with large scatter of results. In contrast, more accurate predictions were obtained with the SWT parameter.
Sharp three-dimensional notches under combined nominal normal and shear fatigue loading
Authors: Vormwald M. , Shams E.
Published: July 2018

Many engineering structures are exposed to non-proportional fatigue loading. However, at the critical location of crack initiation, often only one of the load sequences dominates – the individual load cases result in different crack initiation sites. Based on engineering judgment a simplified local uniaxial or proportional loading situation may be assessed. In general, the critical location must be identified by calculating fatigue lives for a variety of locations. The position of the critical location depends on the hypothesis applied for life calculation – besides loading, geometry, material and many other influence factors. For sharp three-dimensional notches the region for the search of the critical location may be restricted considerably. Weld start and stop points are an industrial example for such sharp notches. They are the object of the present investigation. They are exposed to nominal normal and shear loading. The individual hot spots for crack initiation lie necessarily close together. A strong interaction of the loading cases for both proportional and non-proportional loading was experimentally observed. In the numerical investigation notch stresses were calculated using an idealised weld end model. Based on the critical plane approach according to Findley, numerical interaction lines were produced.
Crack tip field in circumferentially-cracked round bar (CCRB) in tension affected by loss of axial symmetry
Authors: Toribio J. , González B. , Matos J.C.
Published: July 2018

In this paper, the stress intensity factor (SIF) is computed in a circumferentially-cracked round bar (CCRB) subjected to tensile loading, considering that the resistant ligament is circular and exhibits certain eccentricity in relation to the cylinder axis. The computation was performed by means of the finite element method (FEM) using a three dimensional (3D) model and the J-integral, the analyzed variable being the eccentricity of the circular ligament. Results show that the SIF is higher at the deepest point of the crack and that an increase of eccentricity (in relation to the bar axis) raises the difference between the SIF values along the crack front. From a certain value of the misalignment a bending effect appears, so that the crack remains closed in the area near the point of lower depth.
Fracture toughness of rough and frictional cracks emanating from a re-entrant corner
Authors: Carpinteri Andrea , Spagnoli Andrea , Terzano Michele , Vantadori Sabrina
Published: July 2018

In mixed-mode conditions, the competing contribution of the different stress intensity factors predicts fracture initiation load as well as crack propagation direction. Commonly, mixed-mode fracture resistance is based on the assumption of smooth and frictionless cracks. However, the effect of friction and roughness cannot be neglected when mixed mode loading occurs, as in the case of a crack emanating from a re-entrant corner. In this paper, the effect of friction and roughness is evaluated through a simple saw-tooth model in a three-quarter-infinite plane (corresponding to a 90 degree re-entrant corner). The crack surfaces are assumed to be globally smooth, and roughness and friction are incorporated through a constitutive law between opposite crack surfaces. The solution is found using the distributed dislocation method, and an iterative algorithm is needed due to the non-linearity of the model. The effect of friction and roughness angle is discussed for a simple case.
Measurement and analysis of fatigue crack deformation at the micro-scale
Authors: Nowell D. , Dragnevski K.I. , O’Connor S.J.
Published: July 2018

This paper introduces the use of digital image correlation for the measurement of surface displacements in the neighbourhood of a crack tip, both at the macro- and micro- scale. Various methods of interpreting the measured data and producing a crack driving force are then discussed, including the use of the full CJP model. A reduced set of parameters are then proposed, corresponding to the three principal interaction forces between the plastic enclave and the surrounding elastic material. Our own results, and those of Vasco Olmo, previously reported in the literature are then reanalysed using this new framework, and excellent agreement between two independent experiments is obtained. Implications for the analysis of further data sets are then discussed.
Mid-thickness studies of the stress intensity factor in the bulk of bainitic steel
Authors: Lopez-Crespo P. , Vazquez-Peralta J. , Simpson C. , Buslaps T. , Withers P. J.
Published: July 2018

The current work aims at estimating the stress intensity factor deep inside the bulk from elastic strain data measured by synchrotron X-ray diffraction. Key features affecting the evaluation of the stress intensity factor are the number of terms in the analytical model describing the crack tip field, the extension and position of the area of interest of the experimental data, the effect of the experimental data collected within the plastic zone and the number of elastic strain data points used. Here a parametric study of these features is presented in terms of their influence for the stress intensity factor determination. It was found that 3 or 4 terms in Williams’ expansion is often sufficient; the data should be collected from across the full range of angles around the crack tip; and the number of points/number of terms should be greater than 40.
On the connection between mode II and mode III effective thresholds in metals
Authors: Vojtek Tomas , Zak Stanislav , Pokluda Jaroslav
Published: July 2018

Closure-free long cracks under the remote mode III loading grow in a more complicated way than those under the remote mode II. For bcc metals, a coplanar in-plane spreading of tongues driven by the local mode II loading components at crack-front asperities prevails while twisting of crack-front segments to mode I, often leading to factory-roof morphology, is typical for other materials. In bcc metals, therefore, the formulation of a quantitative relationship connecting effective thresholds in modes II and III demands to calculate the local mode II components of stress intensity factors at typical asperities of a crack front loaded in the remote mode III. Therefore, a numerical model of a serrated crack front was created and the results were compared with experimentally determined ratio of mode II and III effective thresholds for the ARMCO iron. Although the calculated crack-front roughness needs an experimental verification, the preliminary results indicate that the model can provide a quantitative explanation of the experimentally observed ratio of mode II and mode III effective thresholds in bcc metals.
Study of strain localizations in a polycrystalline medium in presence of a quasi-static crack
Authors: Patriarca L. , Luccarelli P.G. , Foletti S.
Published: July 2018

Numerical techniques have been widely applied in many recent works to investigate micro-scale behavior of materials. This work focuses on the analysis of strain localizations in a Nickel-based alloy, Haynes 230. Numerical models and experiments concern the study of the strain field generated around the crack tip inside a polycrystalline medium when the crack is quasi-static (not propagating). Experimentally, the tests were conducted in load control; one face of the specimens was monitored by high-resolution Digital Image Correlation (DIC) technique to evaluate the strain field ahead of the crack tip. The simulations were conducted adopting an open source finite element code, Warp3D, which implements a state of art Crystal Plasticity (CP) model. The models of the polycrystalline matrix were created considering the data obtained inspecting the specimen surface by the Electron Back-Scatter Diffraction (EBSD) technique, which allowed defining grains size and orientations. Experimental and numerical results were then compared in terms of strain localizations to evaluate the prediction capabilities of the models. The comparison focused on strain field extension and active grains.
The effect of residual stress on the nonsingular T-stresses
Authors: Chernyatin A.S. , Matvienko Yu.G. , Razumovsky I.A.
Published: July 2018

The effect of residual stresses on surface fatigue crack propagation and fracture mechanics parameters of intersecting orthogonal cracks is discussed. Mutual influence of intersecting cracks and biaxiality affects the nonsingular parameters Txx and Tzz. At the same time, the effect on the stress intensity factor is negligible. Two-parameter fracture mechanics is employed for an analysis of fatigue crack propagation taking into account residual stresses. The final configuration of the crack front is close to the semi-elliptical configuration.
The heat energy dissipated in a control volume to correlate the crack propagation rate in stainless steel specimens
Authors: Meneghetti G. , Ricotta M.
Published: July 2018

Metallic materials dissipate thermal energy when subjected to fatigue. Some of them, due a favorable combination of thermo-physical material properties, exhibit a significant temperature rise, which can be easily measured in-situ by means of thermocouples or infrared cameras. The heat energy dissipated in a unit volume of material per cycle (the Q parameter) has proven to be effective as a fatigue damage index in case of AISI 304L plain and notched specimens. Originally conceived and applied as a point-related quantity, recently Q has been averaged at the tip of propagating fatigue cracks (the Q* parameter) in order to correlate crack growth data gathered from fracture mechanics tests. The use of Q* seems interesting because (i) it can be evaluated in-situ from infrared temperature maps and (ii) crack acceleration due to excessive plasticity is likely to be accounted for.
Williams expansion-based approximation of the stress field in an Al 2024 body with a crack from optical measurements
Authors: Seitl S. , Malíkova L. , Sobek J. , Frantík P. , Lopez-Crespo P.
Published: July 2018

A study on the approximation of the stress field in the vicinity of crack tip in a compact tension specimen made from Al 2024-T351 is presented. Crack tip stress tensor components are expressed using the linear elastic fracture mechanics (LEFM) theory in this work, more precisely via its multi-parameter formulation, i.e. by Williams power series (WPS). Determination of coefficients of terms of this series is performed using a least squares-based regression technique known as over deterministic method (ODM) for which displacements data obtained experimentally via optical measurements are taken as inputs. The stress fields reconstructed based on the displacement data obtained experimentally by means of optical measurements are verified by means of the stress field approximations derived for the normalized CT specimen via hybrid elements.
An original method of direct calculation for the identification of the last hinge and the definition of the deformative state at collapse
Authors: De Salvo Roberto Maria
Published: July 2018

The subject matter of these notes refers to the Ultimate Strength Design of 2-D steel framed structures and in particular to the analysis of the deformation state at collapse. The idea is based on the consideration that, if the structure at its collapse condition is subjected to an articulated movement, similar and concordant to the crisis motion, this will not change the stress state of the system. This motion is known once a single parameter is fixed, namely the displacement of a point or the rotation of a beam. When the collapse mechanism of the structure is already determined through any instrument of the Limit Analysis, a subsequent (k+1) plastic hinge can be arbitrarily fixed and assumed as the last developed one. It is therefore possible to solve the modified scheme through the rotation method and make a comparison in the verses between the known plastic moments and the rotations at the corresponding hinges. If the comparison is successful, in the sense that the checked verses are concordant, the selected hinge is actually the one formed as the last. On the contrary, the rotations resulting from an imprinted motion in the verse of collapse movement are algebraically added. If, for each hinge, the product between the plastic moment and the correspondent algebraic sum is made, this product has to be surely positive, due to the verses concordance. This can be translated in k+1 inequalities, with each one furnishing a lower limit for the parameter from which the articulated motion depends. Among these, the highest value is that one which makes all the inequalities to be simultaneously verified. The substitution of this value into the expressions for rotations permits to arrive to the simultaneous identifying of the last hinge and of the complete picture of deformations.
Residual welding stress of I-section members beyond the limits of width-thickness ratio
Authors: Li Zhiyuan , Zhao Zhiyun
Published: July 2018

Despite the extensive studies on the effect of width-thickness ratio and residual stress on member behavior, few scholars have probed into the residual stress distribution on the I-section members. Based on the principle of blind hole drilling, this paper conducts an experimental study of the residual welding stresses of eight welded I-shaped members. Through the analysis of the test results, the author draws the following conclusion: it is safe to use I-section members beyond the limits of width-thickness ratio because the residual stress distribution is not severely affected by width-thickness ratio.
Influence of the stress gradient on the fatigue life calculation of a martensitic high strength steel
Authors: Miloševic Igor , Winter Gerhard , Grün Florian , Kober Martin
Published: July 2018

Nowadays lifetime calculation in the high cycle fatigue region is commonly based on S/N curves which are modified by different influences to ensure accurate results. Especially the application of these models is important when small components with complex stress distributions are used. The influence of the stress distribution was considered by the stress gradient approach which is implemented in the lifetime tool FEMFAT. Specimens with diameters of D4mm and D7.5mm were used to examine the effect of the calculation modified by the stress gradient. On the one hand regarding different types of this approach it can be shown that the results fit very well compared to the testing results but on the other hand a big difference was observed when the gradient increases by smaller specimen sizes.
Fatigue crack growth in 2017A-T4 alloy subjected to proportional bending with torsion
Authors: Rozumek D. , Faszynka S.
Published: July 2018

The paper presents the results of tests on the fatigue crack growth for a constant moment amplitude under combined bending with torsion in the aluminium alloy AW-2017A-T4. The tests were performed under different values of the load ratio R. Plane specimens with stress concentrators in form of the external one-sided sharp notch were tested. A non-uniform fatigue cracks growth on both lateral surfaces of specimens was observed during experimental tests. Fatigue cracks were developing in the specimens in two stages; quarter-elliptic edge cracks were observed at the beginning, then evolving into through cracks.
Modeling of the stress-strain relationship for specimens made of S355J0 steel subjected to bending block loading with mean load
Authors: Pawliczek R. , Lachowicz C.T
Published: July 2018

The paper presents results of calculation for modelling of the stressstrain relationship in the case of block loads with mean load value. A model, based on the stable hysteresis loops, was assumed and modified to use for block loading analysis. For stress history calculation, the proposed model and two other constitutive models were used. Results of fatigue test of specimens made of S355J0 steel subjected to bending block loading with mean load value are presented and used to verify the proposed model. In the tests, the mean load was increased and decreased in subsequent blocks. The changes of strain recorded during the tests shown in the paper indicate a different behavior of the material. Damage accumulation degree for block sequence was used to compare the results of calculations. It was shown, that stress history parameters (stress amplitude and mean stress value in this case) are similar for all investigated models.
Fragmentation of Mansurov granite under quasi-static compression
Authors: Davydova Marina , Panteleev Ivan , Naimark Oleg
Published: July 2018

The fragmentation statistics was studied in the quasi-static compression experiments conducted on prismatic specimens of Mansurov granite. The statistical analysis showed that the cumulative fragment mass distribution for granite specimens is well described by a power law function, but the fragment number-sieve size distribution deviates from the power law in the range of are equal to about 1 mm. In order to explain this fact, we investigated the structure of fractured material (Computed Tomography and microstructures study in thin sections). A sharp increase the number of grains in the range of size from to 0.5 mm to 1 mm and a change in the fragment shape (from splinter to oval) allow us to suppose that there is an addition fracture mechanism associated with disintegration of feldspar and amphiboles grains.
Local strain energy density for the fatigue assessment of hot dip galvanized welded joints: some recent outcomes
Authors: Peron M. , Razavi S.M.J. , Berto F. , Torgersen J. , Mutignani F.
Published: July 2018

Since in literature only data about the effect of the hot-dip galvanizing coating on fatigue behavior of unnotched specimens are available, whereas very few for notched components and none for welded joints, the aim of this paper is to partially fill this lack of knowledge comparing fatigue strength of uncoated and hot-dip galvanized fillet welded cruciform joints made of structural steel S355 welded joints, subjected to a load cycle R = 0. 34. The results are shown in terms of stress range ?? and of the averaged strain energy density range DeltaW in a control volume of radius R0 = 0.28 mm
Study on the abrasion property of the anvil inside a hydraulic DTH hammer fitted with horizontal oriented sliders
Authors: He Jiang-fu , Yin Qi-lei , Yin Kun
Published: July 2018

Hydraulic hammers have been extensively applied to horizontal directional well drilling in hard rock formations. However, the service life of a hydraulic hammer is still unsatisfactory due to the heavy wear or abrasion of the horizontal anvil, which leads to the failure and the reduction of service life in directional well drilling. In order to improve the performance life of a hydraulic hammer, the new type of anvil with a horizontal oriented slider has been designed. The abrasion property of the horizontal oriented slider have been numerically simulated and analyzed by Finite Element Analysis. Simulation and experimental results have shown that the abrasion rate exponentially varies with the mass of the anvil and the friction coefficient of horizontal oriented slider, nevertheless the abrasion rate of horizontal anvil is almost logarithmically varies with moving velocity of oriented slider. The maximum abrasion rate of horizontal oriented sliders will exceed 4% while moving velocity of the horizontal anvil is larger than 3m/s. While the mass of the anvil is 100kg, the maximum abrasion rate of horizontal oriented slider is 7.5?. However, the maximum abrasion rate of a horizontal oriented slider will be up to 16.5% while the friction coefficient is more than 0.2.
Investigation on some factors affecting crack formation in high resistance aluminum alloys
Authors: Brotzu A. , Felli F. , Pilone D.
Published: July 2018

Aluminum alloys having good mechanical properties are Al-Zn- Mg alloys (7xxx) and Al-Cu-Li alloys (Weldalite®). These alloys may be subjected to stress corrosion cracking. In order to overcome this problem the Al 7050 alloy has been developed and it is widely used for aerospace applications. Despite that, some components made of this alloy cracked during the manufacturing process including machining and chemical anodization. In a previous work cracked Al 7050 components have been analyzed in order to identify possible causes of crack formation. In this work the susceptibility of this alloy to intergranular corrosion has been analysed and compared with that of other high resistance aluminum alloys.
Macroscopic criteria for the deformation and fracture of iron based alloys
Authors: Orlova Dina V. , Lunev Alexey G. , Danilova Lidiya V. , Zuev Lev B.
Published: July 2018

In the article the deformation of different steels is analyzed using the autowave theory of plasticity. The article considers the possible use of an autowave model to formulate criteria for the structural strength of materials and elastic-plastic transition. The time and place of future fracture for steel samples are shown can be predicted before visible necking takes place by using the kinetic dependencies of localized plasticity domains at the prefracture stage. The results show that during elastic-plastic transition in lowcarbon steel, there is the break of the curve for the ultrasound velocity versus deformation, which can serve as an acoustic criterion of irreversible deformation for the pressure treatment of metals, the operation and nondestructive testing of products and structures.
Failure analysis of thin metal foils
Authors: Bolzon G. , Shahmardani M. , Liu R. , Zappa E.
Published: July 2018

The mechanical response and the failure mode of thin metal foils under tensile load has been analyzed supplementing the usual test records with full-field measurements performed by three-dimensional digital image correlation (3D DIC) techniques. The experiments have been simulated by finite element models formulated within a non-linear continuum framework. The study presented in this contribution concerns symmetrically pre-cracked aluminum samples. The wrinkling of the specimens during the test and the possible and alternative failure mechanisms are evidenced and discussed.
15-15Ti(Si) austenitic steel: creep behaviour in hostile environment
Authors: Strafella Alessandra , Coglitore Antonino , Fabbri Paride , Salernitano Elena
Published: July 2018

This work aims at studying the creep behaviour of 15-15Ti(Si) austenitic steel, under uniaxial stress (range of 300-560 MPa), and its interaction with liquid lead. The steel was tested to verify its sensitivity to Liquid Metal Embrittlement (LME) and to simulate its behaviour in operating thermal and mechanical stress conditions of the IV generation Lead-cooled fast reactor. The experimental results permitted to plot the time-strain creep curve and the characteristic Norton-based curve, simulating the creep behaviour at all stress values. The comparison between the creep curves in air and in lead showed that the LME produces a decrease of creep-rupture time, a reduction of creep strain and then the loss of steel ductility. Moreover, the raw material and fracture surfaces were analyzed by Optical Microscope and Scanning Electron Microscope (SEM). SEM micrographs highlighted that lead changes both the mode and the type of specimen fracture. In addition, it was analyzed the lead action time, as the time after which the corrosion appears with macroscopic effects. Although some tests are still ongoing, it can be assumed that at high stresses, LME takes place after a long time of steel/lead contact while at low stresses, LME tends to prevail on creep effect.
A Description of Laying Hen Husbandry and Management Practices in Canada
Authors: Van Staaveren Nienke , Decina Caitlin , Baes Christine , Widowski Tina , Berke Olaf , Harlander-Matauschek Alexandra
Published: July 2018

Canadian laying hen farms are transitioning from conventional cage housing to furnished cage and non-cage housing systems to improve laying hen welfare. However, little is known about the current housing and management systems in Canada. This study addresses this knowledge gap by describing different housing and management practices used on farms where laying hens were housed in furnished cages or non-cage housing systems. A questionnaire covering farm and housing conditions, litter management, nutrition and feeding, environmental control, flock characteristics, rearing and placement, health, egg production and performance were distributed through provincial egg boards to 122 producers across Canada. Data were collected from 65 laying hen flocks (52.5% response rate) in 26 furnished cage, 17 single-tier and 22 multi-tier systems. Flocks were on average 45.1 ± 14.59 weeks old (range: 19–69 weeks). Frequencies of different management practices were calculated according to housing system. Most flocks were reared in the same housing system as they were housed in during lay, with the exception of furnished cage layers which were reared in conventional cage systems. Results indicated that a large proportion of non-cage systems were either fully slatted or had manure as a litter substrate, which could have implications for consumer perspectives on these systems. Further research is needed to develop clear recommendations on proper litter management for farmers. In general, flock health was managed through daily inspections and vaccination schemes, whereas veterinarian involvement on-farm was less common. Vaccination, hygiene, and effective biosecurity should be maintained to ensure good health in laying hens in furnished cage and non-cage systems during the transition to these systems.
Changes in Earth’s Energy Budget during and after the “Pause” in Global Warming: An Observational Perspective
Authors: Loeb Norman G. , Thorsen Tyler J. , Norris Joel R. , Wang Hailan , Su Wenying
Published: July 2018

This study examines changes in Earth’s energy budget during and after the global warming “pause” (or “hiatus”) using observations from the Clouds and the Earth’s Radiant Energy System. We find a marked 0.83 ± 0.41 Wm−2 reduction in global mean reflected shortwave (SW) top-of-atmosphere (TOA) flux during the three years following the hiatus that results in an increase in net energy into the climate system. A partial radiative perturbation analysis reveals that decreases in low cloud cover are the primary driver of the decrease in SW TOA flux. The regional distribution of the SW TOA flux changes associated with the decreases in low cloud cover closely matches that of sea-surface temperature warming, which shows a pattern typical of the positive phase of the Pacific Decadal Oscillation. Large reductions in clear-sky SW TOA flux are also found over much of the Pacific and Atlantic Oceans in the northern hemisphere. These are associated with a reduction in aerosol optical depth consistent with stricter pollution controls in China and North America. A simple energy budget framework is used to show that TOA radiation (particularly in the SW) likely played a dominant role in driving the marked increase in temperature tendency during the post-hiatus period.
Effect of Electrode Coating with Graphene Suspension on Power Generation of Microbial Fuel Cells
Authors: Tsai Hung-Yin , Hsu Wei-Hsuan , Liao Yi-Jhu
Published: July 2018

Microbial fuel cells (MFCs), which can generate low-pollution power through microbial decomposition, are a potentially vital technology with applications in environmental protection and energy recovery. The electrode materials used in MFCs are crucial determinants of their capacity to generate electricity. In this study, we proposed an electrode surface modification method to enhance the bacterial adhesion and increase the power generation in MFCs. Graphene suspension (GS) is selected as modifying reagent, and thin films of graphene are fabricated on an electrode substrate by spin-coating. Application of this method makes it easy to control the thickness of graphene film. Moreover, the method has the advantage of low cost and large-area fabrication. To understand the practicality of the method, the effects of the number of coating layers and drying temperature of the graphene films on the MFCs’ performance levels are investigated. The results indicate that when the baking temperature is increased from 150 to 325 °C, MFC power generation can increase approximately 4.5 times. Besides, the maximum power density of MFCs equipped with a four-layer graphene anode is approximately four times that of MFCs equipped with a two-layer graphene anode. An increase in baking temperature or number of coating layers of graphene films enhances the performance of MFC power generation. The reason can be attributed to the graphene purity and amount of graphene adhering to the surface of electrode.
Thin Film Thermoelectric Materials: Classification, Characterization, and Potential for Wearable Applications
Authors: Chen Xinqi , Dai Wei , Wu Tian , Luo Wei , Yang Jianping , Jiang Wan , Wang Lianjun
Published: July 2018

Thermoelectric technology has the ability to convert heat directly into electricity and vice versa. With the rapid growth of portable and wearable electronics and miniature devices, the self-powered and maintenance of free thermoelectric energy harvester is highly desired as a potential power supply. Thin film thermoelectric materials are lightweight, mechanically flexible, and they can be synthesized from abundant resources and processed with a low-cost procedure, which offers the potential to develop the novel thermoelectric devices and hold unique promise for future electronics and miniature accessories. Here, a general classification for thin film thermoelectric materials varied by material compositions, and thermoelectric properties depended on different measurement technique. Several new flexible thermoelectric strategies are summarized with the hope that they can inspire further development of novel thermoelectric applications.
Challenges of Participatory Community Monitoring of Biodiversity in Protected Areas in Brazilian Amazon
Authors: C. Costa Daniel , S. Pereira Henrique , A. E. L. Marchand Guillaume , C. P. Silva Suzy
Published: July 2018

Participatory community monitoring programs (PCM) have become an important methodological innovation for the management of biodiversity conservation in protected areas. Based on the participation of the local communities, they are presented as less costly programs than conventional ones. However, in practical terms, such programs pose serious implementation challenges. In this article, we identify the achievements, obstacles, and perspectives of four PCM implemented in the state of Amazonas, Brazil. Based on bibliographical and documentary research, direct observations and in-person interviews with program managers and specialists, we qualitatively evaluated these programs with respect to participation, data production and retrieval, and financing. We found that the performances of these programs were not yet adequate to their protected areas management priorities and that they had not yet generated perceptible benefits enough to enhance community trust and full appropriation of the programs’ outcomes by resource users and by conservation unit management teams.