bluuebunny/crossref_metadata_2025 huggingface dataset:
SOME METHODS OF PARTY-GOVERNMENT MANAGEMENT IN THE USSR IN 1920-1934. (ON THE MATERIALS OF CUBAN)
Authors: Ivantsov I. G.
Published: July 2018

The Article is devoted to the secret correspondence of the CPSU (b), which began its existence in the early period of Soviet power. In the USSR, 1922-1923 were secretly carried out of the party and state reform, in which was installed dictatorship of the ruling party He. The old model of domination of individual Bolshevik leaders were eliminated. All power concentrated in the hands of a few of its leaders at the top. As further development, there is a simple and archaic system of government which is not bound to any laws or control of the company. Whoever was at the top, disposing of everything and governs all. The basis of the Soviet state was the hierarchy of party committees headed by the undersecretaries of 1992. In addition, after the entry of Stalin in the post of Secretary General of the relation of the Supreme party organs to the party apparatus on the ground began to carry secret correspondence between them was classified. Circle functionaries who were sent extracts of the minutes of the Central Committee of the CPSU (b), the party committees and individual orders of the undersecretaries of the Central Committee and party committees, persons carrying out intra-party correspondence was strictly limited.
Sınıf Öğretmenlerinin Birinci Sınıf Yazma Öğretimi Sınıf İçi Uygulamalarına İlişkin Görüşleri
Authors: Özdemir Kemal
Published: July 2018

Bu çalışma, ilkokul birinci sınıfı okutan öğretmenlerin ilk okuma ve yazma öğretiminde sınıf içi uygulamalara yönelik görüşlerini incelemek amacıyla yapılmıştır. Çalışmada, nitel araştırma yöntemlerden temel nitel araştırma yöntemi kullanılmıştır. Temel nitel araştırmalar, bütün alanlarda kullanılmakla birlikte yaygın olarak eğitim bilimleri araştırmalarında kullanılmaktadır. Çalışmanın amacı doğrultusunda öğretmenlerin, okuma ve yazma öğretimi süreci sınıf içi uygulamalarına yönelik görüşleri ele alınmıştır. Araştırmada veriler Kütahya ili merkez ilçe ve köylerinde görevli, birinci sınıfı okutan seksen altı (86) öğretmenden yarı yapılandırılmış görüşme formu kullanılarak toplanmıştır. Araştırmada elde edilen bulgulara göre öğretmenler, okuma ve yazma öğretiminde sınıf içi uygulamalarda sesi tanıtma, hissettirme ve sonrasında yazma çalışmaları yaptıklarını ve yazdırma çalışmalarının sesin öğretimi açısından bir yöntem olmakla birlikte pekiştireç olarak da kullandıklarını ifade etmişlerdir. Ayrıca öğretmenler okuma yazma öğretirken teknoloji kullanımına, sesle ilgili oyun, hikâye ve gösterilere yer verdiklerini, sesi tanıtma, sesi hissettirmek için görsel araçlar kullandıklarını ve sesin sembolünün yazımını göstermede teknolojiden yararlandıklarını da belirtmişlerdir.
Kültürel Kimlik ve Eğitim
Authors: BİLGİN Asude , OKSAL Aynur
Published: July 2018

Bir kişinin kimliği o’nun kendisini nasıl tanımladığı ile ilgilidir. Kimliğimiz insan olarak varlığımızın merkezidir. Kimlik kişisel ve sosyal/kültürel kimlik olarak iki kategoride ele alınabilir. Kültürel ve ulusal/bölgesel kimlik aynı kavramları karşılamaktadır. Kimlik gelişimi sırasında bireyler bu kimlik kategorilerini farklı düzeylerde geliştirebilirler. Kişisel kimlik bireyin kişisel amaçları, değerleri, fikirleri, coşku ve duyguları ile ilgilidir. Kültürel kimlik ise kişinin sosyal dünyaya ait olma biçimidir. Bu aidiyet ırk, din, etnik grup ve toplumsal cinsiyet rolleriyle ilgilidir. İnsanlar genellikle ait oldukları grubun statüsünü abartırlar. Bu nedenle kimlik oluşumunun eğitim sürecindeki etkisi büyüktür. Bu çalışmanın amacı kültürel kimlik ile öğrenme arasındaki ilişkiyi vurgulamaktır. Bu durum eğitimin düzeyini yükseltmek için sınıftaki kültürel kimlik farklılıklarını anlama ihtiyacının gelişmesine yardımcı olacaktır. Çok kültürlü bir öğretme ortamında öğrenciler kendilerini daha rahat hissedeceklerdir. Öte yandan öğretmenler kültürlerini sınıfa sürekli getirirler. Kişilikleri ve öğretme stilleri sosyal ve kültürel etkileşimlerinin eseridir. Tehlike bunun bilincinde olmamaktır. Bu nedenle öğretmen adaylarına pratik ve teorik olarak çok kültürlülük dersi verilmesi bir ihtiyaçtır.
Okul Öncesi Öğretmen Adaylarının Anne Babalarının Kendilerine Göstermiş Oldukları Tutumları ile Gelecekte Çocuklarına Yönelik Göstermek İstedikleri Tutumlar
Authors: BAŞAL Handan Asude , BAĞÇELİ KAHRAMAN Pınar , KOÇ Demet , SARI Burcu
Published: July 2018

Anne baba tutumları ve anne-baba- çocuk arasındaki bu etkileşim çocuğun davranışlarını biçimlendirmekte ve gelecekteki davranışları üzerinde etkili olmaktadır. Yani, anne babaların ve öğretmenlerin gösterdikleri farklı anne baba tutumları, çocukların nasıl bir birey olarak yetişeceği üzerinde belirleyici rol oynamaktadır. Araştırmanın amacı da Okul Öncesi Öğretmenliği öğretmen adaylarının anne-babalarının tutumları ile öğretmen adaylarının gelecekte göstermek istedikleri tutumların çeşitli değişkenler açısından incelenmesidir. Böylece geleceğin öğretmeni olan öğretmen adaylarının sağlıklı bireylerin yetiştirilmesinde nasıl tutum sergileyecekleri de belirlenmiş olacaktır. Araştırmada genel tarama modeli kullanılmıştır. Araştırmanın örneklemi Uludağ Üniversitesi Eğitim Fakültesi Temel Eğitim Bölümüne devam eden, Anne Baba Tutumlarına yönelik bilgilendirmeye katılmış toplam 154 Okul Öncesi Eğitimi öğretmen adaylarından oluşmaktadır. Araştırma kapsamına alınan öğretmen adaylarının dokuzu erkek, 145’i kadındır. Araştırma kapsamına alınan öğretmen adaylarına, anne-babalarının çocukluklarında onlara uyguladıkları anne-baba tutumlarını ve kendilerinin gelecekte göstermek istedikleri anne-baba tutumlarını belirlemeye yönelik olarak açık uçlu sorudan oluşan görüş formu uygulanmıştır. Araştırma kapsamında öğretmen adaylarının kendi anne-baba tutumları ile kendi çocuklarına göstermek istedikleri tutumlar arasında ilişki olup olmadığı korelasyon analizi ile belirlenmeye çalışılmıştır. Ayrıca araştırmada elde edilen veriler sayısallaştırılarak yüzde ve frekans olarak ifade edilmiştir. Yapılan analiz soncunda öğretmen adaylarının anne baba tutumları ile öğretmen adaylarının gelecekte göstermek istedikleri tutumlar arasında pozitif yönlü anlamlı bir ilişki bulunmuştur. Bu kapsamda öğretmen adayları anne baba tutumlarını demokratik, tutarsız, otoriter, aşırı koruyucu, mükemmeliyetçi, hoşgörülü ve güven verici, demokratik-aşırı koruyucu, demokratik-otoriter, baskıcı- otoriter ve kararsız, demokratik- koruyucu-otoriter, otoriter- aşırı koruyucu, demokratik- mükemmeliyetçi gibi çeşitli başlıklar halinde kategorilendirmişlerdir. Okul öncesi öğretmenliği öğretmen adayları anne-baba olduklarında göstermek istedikleri tutumları ise, demokratik, demokratik- hoşgörülü, demokratik- koruyucu, güven verici- demokratik, hoşgörülü- güven verici, demokratik- koruyucu ve demokratik- otoriter olarak belirtmişlerdir.
TWSME of a NiTi strip in free bending conditions: experimental and theoretical approach
Authors: Fortini A. , Merlin M. , Rizzoni R. , Marfia S.
Published: July 2018

This paper deals with the two-way shape memory effect (TWSME) induced on a strip of a nearequiatomic NiTi alloy by means of the shape memory cycling training method. This procedure is based on the deformation in martensite state to reach the desired cold shape followed by cycling the temperature from above Af to below Mf. To this end, the sample was thermally treated to memorise a bent shape, thermomechanical trained as described and thermally cycled in unloaded conditions in order to study the stability of the induced TWSME. Heating to Af was reached by a hot air stream flow whereas cooling to Mf was achieved through natural convection. The evolution of the curvature with the increasing number of cycles was evaluated. The thermomechanical behaviour of the strip undergoing uniform bending was simulated using a one-dimensional phenomenological model based on stress and the temperature as external control variables. Both martensite and austenite volume fractions were chosen as internal parameters and kinetic laws were used in order to describe their evolution during phase transformations. The experimental findings are compared with the model simulation and a numerical prediction based on the approach proposed in [25].
Geometric numerical integrators based on the Magnus expansion in bifurcation problems for non-linear elastic solids
Authors: Castellano A. , Foti P. , Fraddosio A. , Marzano S. , Piccioni M. D.
Published: July 2018

We illustrate a procedure based on the Magnus expansion for studying mechanical problems which lead to non-autonomous systems of linear ODE’s. The effectiveness of the Magnus method is enlighten by the analysis of a bifurcation problem in the framework of three-dimensional non-linear elasticity. In particular, for an isotropic compressible elastic tube subject to an azimuthal shear primary deformation we study the possibility of axially periodic twist-like bifurcations. The approximate matricant of the resulting differential problem and the first singular value of the bifurcating load corresponding to a non-trivial bifurcation are determined by employing a simplified version of the Magnus method, characterized by a truncation of the Magnus series after the second term.
Damage modelling in concrete subject to sulfate attack
Authors: Cefis N. , Comi C.
Published: July 2018

In this paper, we consider the mechanical effect of the sulfate attack on concrete. The durability analysis of concrete structures in contact to external sulfate solutions requires the definition of a proper diffusion-reaction model, for the computation of the varying sulfate concentration and of the consequent ettringite formation, coupled to a mechanical model for the prediction of swelling and material degradation. In this work, we make use of a two-ions formulation of the reactive-diffusion problem and we propose a bi-phase chemo-elastic damage model aimed to simulate the mechanical response of concrete and apt to be used in structural analyses.
A simple beam model to analyse the durability of adhesively bonded tile floorings in presence of shrinkage
Authors: de Miranda S. , Palermo A. , Ubertini F.
Published: July 2018

A simple beam model for the evaluation of tile debonding due to substrate shrinkage is presented. The tile-adhesive-substrate package is modeled as an Euler-Bernoulli beam laying on a two-layer elastic foundation. An effective discrete model for inter-tile grouting is introduced with the aim of modelling workmanship defects due to partial filled groutings. The model is validated using the results of a 2D FE model. Different defect configurations and adhesive typologies are analysed, focusing the attention on the prediction of normal stresses in the adhesive layer under the assumption of Mode I failure of the adhesive.
The research for mechanics stimulation method of nonlinear random vibration based on statistical linear theory
Authors: Guodong Wang
Published: July 2018

Earthquake disasters have brought great harm to people's life safety and economic property. Its effect on fabric mainly focus on random effects currently, the general pseudo excitation method could solve the inefficiency calculation problem of linear random earthquake. However it could not take the nonlinear problem factors into account for calculation. In this paper, we suggest that a nonlinear structural incentive method should be improved based on statistical linearity to calculate and solve absolute displacement value. Through the analysis and research for cases, we calculate the displacement, speed, random vibration spectrum of bridge’s accelerated speed, as well as the influencing situation of axial force. The results indicate that such perfect incentive method could not only perform nonlinear structure analysis, but also to be very accurate and high effective. Such method could reasonably avoid the displacement decomposition and solution of the pseudostatic model?thus it will be widely applied in common software.
Evolution of crack paths and compliance in round bars under cyclic tension and bending
Authors: Toribio J. , Matos J.C. , González B. , Escuadra J.
Published: July 2018

The aim of this paper is to calculate how the surface crack front and the dimensionless compliance evolve in cracked cylindrical bars subjected to cyclic tension or bending with different initial crack geometries (crack depths and aspect ratios). To this end, a computer application (in the Java programming language) that calculates the crack front’s geometric evolution and the dimensionless compliance was made by discretizing the crack front (characterized with elliptical shape) and assuming that every point advances perpendicularly to the crack front according to the Paris law, and using a three-parameter stress intensity factor (SIF). The results show that in fatigue crack propagation, relative crack depth influences more on dimensionless compliance than the aspect ratio, because the crack front tends to converge when the crack propagates from different initial geometries, showing greater values for tension than for bending. Furthermore, during fatigue crack growth, materials with higher values of the exponent of the Paris law produce slightly greater dimensionless compliance and a better convergence between the results for straight-fronted and circular initial cracks.
Definition of the linearity loss of the surface temperature in static tensile tests
Authors: Risitano A. , Fargione G. , Guglielmino E.
Published: July 2018

Static traction tests on material samples for mechanical constructions have pointed out the loss of linearity of the specimen surface temperature with the applied load. This phenomenon is due to the heat generation caused by the local microplasticizations which carry the material to deviate from its behavior, perfectly thermoelastic. The identification of the static load which determines the loss of linearity under the temperature stress becomes extremely important to define an initial dynamic characterization of the material. The temperature variations that can be read during the static loads applications are often very limited (a few tenths of degree for every 100 MPa in steels) and they require the use of special temperature sensors able to measure the temperature variations. The experience acquired in such analysis highlighted that, dealing with highly accurate sensors or with particular materials, the identification of the first loss of linearity can be influenced by the investigator himself mainly for the above mentioned limited temperature variations which can lead to incorrect estimations, sometimes really significant. Checking the validity and the above mentioned observations on the different steels, this work proposes the application of the autocorrelation function to the data collected during the application of a static load in order to make the results of the thermal analysis free from the sensitivity of the operator and also to make the result as objective as possible in order to detect the time of the loss of linearity of the temperature-time function.
Effect of nonlinearity of restrainer and supports on the elasto-plastic seismic response of continuous girder bridge
Authors: Changfeng Wang , Long Zhu , Xingchong Chen
Published: July 2018

During an earthquake, the nonlinearity of the bridge structure mainly occurs at the supports, bridge piers and restrainers. When entering nonlinear stage, members of the bridge structure affect the elasto-plastic seismic response of the whole structure to a certain extent; for multi-span continuous bridges, longitudinal restrainers can be installed on the movable piers to optimise the distribution of seismic force and enable the movable piers to bear a certain amount of seismic effect. In order to evaluate the effect of nonlinearity of restrainer and supports on the elasto-plastic seismic response of continuous girder bridge, analytical models of continuous girder bridge structure considering the nonlinearity of movable supports, restrainers and bridge piers were built and the nonlinear time history analysis was conducted to evaluate the effect of nonlinearity of restraining devices and supports on the elasto-plastic seismic response of continuous girder bridge. Relevant structural measures and recommendation were made to reduce the seismic response of the fixed piers of the continuous girder bridge.
Transverse strength of railway tracks: part 2. Test system for ballast resistance in line measurement
Authors: De Iorio Antonio , Grasso Marzio , Penta Francesco , Pucillo Giovanni Pio , Rosiello Vincenzo
Published: July 2018

In the present paper, testing methods currently adopted to measure the in service ballast resistance are synthetically reviewed to identify the main sources of uncertainty influencing the test loads and to define an experimental methodology allowing the optimal control of the testing parameters without the introduction of spurious or parasitic actions on the track sample. An alternative testing system, which allows applying on a fullscale sample of a railway track testing loads very close the real ones, is presented. Of the new system, both the ways of use for measuring the transversal and axial ballast strength, the general procedure to carry out the experimentation and its application to a real scenario are described, highlighting its main advantages in terms both of modalities for applying the loads and of testing parameter control.
Multi-parameter approximation of stress field in a cracked specimen using purpose-built Java applications
Authors: Veselý V. , Sobek J. , Tesa D. , Frantík P. , Pail T. , Seitl S.
Published: July 2018

A quality of multi-parameter approximation of the stress and displacement fields around a crack tip in a non-brittle material test specimen is studied in the paper. The stress field approximation using Williams power series is intended to be utilized for estimation of the nonlinear zone extent which potentially plays a role within methods for determination of true values of fracture parameters of materials exhibiting nonlinear failure. Considering the fact that in the case of elastic-plastic and especially quasi-brittle materials the size of this zone is substantial in comparison to the specimen dimensions, it is necessary to take a large region around the crack tip into account for this task. An automatic utility created to determine the values of coefficients of the higher order terms of Williams power series by usage of over-deterministic method applied on results of finite element analysis of arbitrary mode I test geometry is one of the tested procedures. The second one provides a backward reconstruction of the crack-tip stress field analytically by means of truncated Williams expansion. The developed procedures are based on the support of Java programming language and considerably simplify analyses of the mechanical fields’ description in a farther distance from the crack-tip. The presented research is focused on optimization of selection of FE nodal results for improvement of accuracy of the approximation.
Microstructural study of multiaxial low cycle fatigue
Authors: Sakane Masao , Itoh Takamoto
Published: July 2018

This paper discusses the relationship between the stress response and the microstructure under tension-torsion multiaxial proportional and nonproportional loadings. Firstly, this paper discusses the material dependency of additional hardening of FCC materials in relation with the stacking fault energy of the materials. The FCC materials studied were Type 304 stainless steel, pure copper, pure nickel, pure aluminum and 6061 aluminum alloy. The material with lower stacking fault energy showed stronger additional hardening, which was discussed in relation with slip morphology and dislocation structures. This paper, next, discusses dislocation structures of Type 304 stainless steel under proportional and nonproportional loadings at high temperature. The relationship between the microstructure and the hardening behavior whether isotropic or anisotropic was discussed. The re-arrangeability of dislocation structure was discussed in loading mode change tests. Microstructures of the steel was discussed in more extensively programmed multiaxial low cycle fatigue tests at room temperature, where three microstructures, dislocation bundle, stacking fault and cells, which were discussed in relation with the stress response. Finally, temperature dependence of the microstructure was discussed under proportional and nonproportional loadings, by comparing the microstructures observed at room and high temperatures.
Estimation of fretting fatigue life using a multiaxial stress-based critical distance methodology
Authors: Castro F. C. , Araújo J. A. , Pires M. S. T. , Susmel L.
Published: July 2018

This work presents a methodology for life estimation of mechanical couplings subjected to fretting fatigue. In this approach, a stress-based multiaxial fatigue parameter is evaluated at a critical distance below the contact surface. The fatigue parameter is based on an improved formulation of the Modified Wöhler Curve Method, in which the shear stress amplitude is measured via the Maximum Rectangular Hull method. To apply the Theory of Critical Distances in the medium-cycle fatigue regime, the critical distance is assumed to depend on the number of cycles to failure. Available fretting fatigue data, conducted on a cylinder-plane contact configuration made of Al alloy 4% Cu, were used to assess the methodology. Most of the life estimates were within an error band given by a factor of 2.
A new micromechanical model of CNT-metal nanocomposites with random clustered distribution of CNTs
Authors: Gao Chongyang , Lu Yu , Zhu Y.T.
Published: July 2018

Uniform dispersion of carbon nanotubes (CNTs) is a key issue for utilization of their reinforcement potential in CNT-reinforced metal matrix nanocomposites (MMNCs). It was reported that CNT clusters often exist in MMNCs prepared by various techniques, which reduces the load transfer efficiency between the matrix and reinforcement. In this paper, a new micromechanical constitutive model of CNT-reinforced MMNCs is developed, which takes into account of the influences of CNT clusters and misorientations. The strength values of a CNT/Al nanocomposite predicted by the new model are compared first with experimental data for validation. Then, the developed model is applied to predict the size effect, temperature effect and strain rate effect of the nanocomposite in its overall elastoplastic response.
Local approaches for the fracture assessment of notched components: the research work developed by Professor Paolo Lazzarin
Authors: Berto F.
Published: July 2018

Brittle failure of components weakened by cracks or sharp and blunt V-notches is a topic of active and continuous research. It is attractive for all researchers who face the problem of fracture of materials under different loading conditions and deals with a large number of applications in different engineering fields, not only with the mechanical one. This topic is significant in all the cases where intrinsic defects of the material or geometrical discontinuities give rise to localized stress concentration which, in brittle materials, may generate a crack leading to catastrophic failure or to a shortening of the assessed structural life. Whereas cracks are viewed as unpleasant entities in most engineering materials, U- and V-notches of different acuities are sometimes deliberately introduced in design and manufacturing of structural components. Dealing with brittle failure of notched components and summarising some recent experimental results reported in the literature, the main aim of the present contribution is to present a review of the research work developed by Professor Paolo Lazzarin. The approach based on the volume strain energy density (SED), which has been recently applied to assess the brittle failure of a large number of materials. The main features of the SED approach are outlined in the paper and its peculiarities and advantages accurately underlined. Some examples of applications are reported, as well. The present contribution is based on the author’s experience over about 15 years and the contents of his personal library. This work is in honor and memory of Prof. Paolo Lazzarin who suddenly passed away in September 2014.
Investigation of Mode I fracture toughness of red Verona marble after thermal treatment
Authors: Scorza Daniela , Carpinteri Andrea , Fortese Giovanni , Vantadori Sabrina , Ferretti Daniele , Brighenti Roberto
Published: July 2018

The present paper aims to assess the effect of freeze/thaw cycles on fracture behaviour of a natural stone: the red Verona marble. A wide variety of specimen types and methods to determine Mode I fracture toughness of natural stones are available in the literature and, in this context, the model originally proposed for plain concrete, i.e. the Two-Parameter Model (TPM), is adopted. Such a method is able to take into account the slow nonlinear crack growth occurring before the peak load, typical of quasi-brittle materials, with the advantage of easy specimen preparation and simple test configuration. In the present paper, the atmospheric ageing is simulated by means of thermal pre-treatments consisting of freeze/thaw cycles. Experimental tests are carried out using three-point bending Single-Edge Notched (SEN) specimens, according to the TPM procedure. The effects of thermal treatment on both mechanical and fracture parameters are examined in terms of elastic modulus and fracture toughness, respectively. KEYWORDS. Mode I Fracture Toughness; Red Verona Marble; Thermal Treatment; Two-Parameter Model.
Effects of microstructure and crystallography on crack path and intrinsic resistance to shear-mode fatigue crack growth
Authors: Pokluda J. , Vojtek T. , Hohenwarter A. , Pippan R.
Published: July 2018

ABSTRACT. The paper focuses on the effective resistance and the near-threshold growth mechanisms in the ferritic-pearlitic and the pure pearlitic steel. The influence of microstructure on the shear-mode fatigue crack growth is divided here into two factors: the crystal lattice type and the presence of different phases. Experiments were done on ferritic-pearlitic steel and pearlitic steel using three different specimens, for which the effective mode II and mode III threshold values were measured and fracture surfaces were reconstructed in three dimensions using stereophotogrammetry in scanning electron microscope. The ferritic-pearlitic and pearlitic steels showed a much different behaviour of modes II and III cracks than that of the ARMCO iron. Both the deflection angle and the mode II threshold were much higher and comparable to the austenitic steel. Mechanism of shear-mode crack behaviour in the ARMCO iron, titanium and nickel were described by the model of emission of dislocations from the crack tip under a dominant mode II loading. In other tested materials the cracks propagated under a dominance of the local mode I. In the ferritic-pearlitic and pearlitic steels, the reason for such behaviour was the presence of the secondary-phase particles (cementite lamellas), unlike in the previously austenitic steel, where the fcc structure and the low stacking fault energy were the main factors. A criterion for mode I deflection from the mode II crack-tip loading, which uses values of the effective mode I and mode II thresholds, was in agreement with fractographical observations.
Crack initiation at V-notch tip subjected to in-plane mixed mode loading: An application of the fictitious notch rounding concept
Authors: Berto F.
Published: July 2018

The fictitious notch rounding concept is applied for the first time to V-notches with root hole subjected to in-plane mixed mode loading. Out-of-bisector crack propagation is taken into account. The fictitious notch radius is determined as a function of the real notch radius?? the microstructural support length and the notch opening angle. Due to the complexity of the problem, a method based on the simple normal stress failure criterion has been used. It is combined with the maximum tangential stress criterion to determine the crack propagation angle. An analytical method based on Neuber's procedure has been developed. The method provides the values of the microstructural support factor as a function of the mode ratio and the notch opening angle. The support factor is considered to be independent of the microstructural support length. Finally, for comparison, the support factor is determined on a purely numerical basis by iterative analysis of FE models.
High temperature fatigue tests and crack growth in 40CrMoV13.9 notched components
Authors: Gallo P. , Berto F.
Published: July 2018

The present paper addresses experimentally the high temperature fatigue of 40CrMoV13.9 steel and the effect of surface roughness on fatigue strength and crack initiation. The 40CrMoV13.9 steel is widely used in different engineering high temperature applications among which hotrolling of metals, where, in order to assure a constant temperature, the rolls are provided with cooling channels. These are the most stressed zone of the rolls where cracks systematically initiate. In order to completely characterize the high temperature behaviour of this steel, firstly uniaxial-tension load controlled fatigue tests have been conducted at different temperatures up to 650°C. Two geometries are considered: plain specimens and plates weakened by symmetric V-notches. Subsequently, with the aim to investigate the influence of the cooling channels roughness on the high temperature behaviour and the cracks initiation, uniaxial-tension load controlled fatigue tests have been conducted on plate with central hole at the service temperature of 650°C varying the surface roughness. After a brief review of the recent literature, the experimental procedure is described in detail and the new data from un-notched and notched specimens are summarized in terms of stress range, at the considered temperatures. Finally, fatigue data from un-notched and notched specimens are re-analysed by means of the mean value of the Strain Energy Density (SED) approach extended at high temperature.
Crack path predictions and experiments in plane structures considering anisotropic properties and material interfaces
Authors: Judt P.O. , Ricoeur A.
Published: July 2018

In many engineering applications special requirements are directed to a material's fracture behavior and the prediction of crack paths. Especially if the material exhibits anisotropic elastic properties or fracture toughnesses, e.g. in textured or composite materials, the simulation of crack paths is challenging. Here, the application of path independent interaction integrals (I-integrals), J-, L- and M-integrals is beneficial for an accurate crack tip loading analysis. Numerical tools for the calculation of loading quantities using these path-invariant integrals are implemented into the commercial finite element (FE)-code ABAQUS. Global approaches of the integrals are convenient considering crack tips approaching other crack faces, internal boundaries or material interfaces. Curved crack faces require special treatment with respect to integration contours. Numerical crack paths are predicted based on FE calculations of the boundary value problem in connection with an intelligent adaptive re-meshing algorithm. Considering fracture toughness anisotropy and accounting for inelastic effects due to small plastic zones in the crack tip region, the numerically predicted crack paths of different types of specimens with material interfaces and internal boundaries are compared to subcritically grown paths obtained from experiments.
Multiple crack propagation by DBEM in a riveted butt-joint: a simplified bidimensional approach
Authors: Citarella R.
Published: July 2018

A Multi-Site Damage (MSD) crack growth simulation is presented, carried out by means of Dual Boundary Element Method (DBEM), in a two-dimensional analysis of a cracked butt-joint made of aluminium 2024 T3. An equivalent crack length is proposed for an approximated 2D analysis of a 3D problem where the crack front assumes a part elliptical shape due to secondary bending effects. The assumptions made to perform such simplified bidimensional analyses are validated by comparing numerical results with experimental data, the latter obtained from a fatigue tested riveted butt-joint.
Analysis of fatigue behaviour of stainless steels under hydrogen influence
Authors: Angelova D. , Yordanova R. , Yankova S.
Published: July 2018

Three stainless steels – ASTM 304, 316 and 316L - used in hydrogen utilization equipment are under investigation at conditions of tension-compression, rotating-bending and fretting fatigue. Fatigue tests are carried out with hydrogen charged and uncharged specimens. Hydrogen charging includes cathodic type of charging and exposure to high pressure hydrogen gas. The experiments under rotating bending and tensioncompression fatigue are conducted under different frequencies in three different laboratories: at The University of Chemical Technology and Metallurgy, Sofia, Bulgaria; at Sandia National Laboratory, California and The University of Tufts, Medford, Massachusetts, USA; The HYDROGENIUS Institute at Kyushu University, Japan. The fretting fatigue tests are presented by The HYDROGENIUS Institute at Kyushu University, Japan. The obtained results are presented in Wöhler curves complemented by plots "Short fatigue crack length– Number of cycles" and “Tangential force coefficient–Stress amplitude”. The found fatigue characteristics are analyzed and compared at different loading conditions, showing the best performance of Steel 316L.
Simulation of accelerated strip cooling on the hot rolling mill run-out roller table
Authors: Muhin U. , Belskij S. , Makarov E. , Koynov T.
Published: July 2018

A mathematical model of the thermal state of the metal in the run-out roller table continuous wide hot strip mill. The mathematical model takes into account heat generation due to the polymorphic ? ? ? transformation of supercooled austenite phase state and the influence of the chemical composition of the steel on the physical properties of the metal. The model allows calculation of modes of accelerated cooling strips on run-out roller table continuous wide hot strip mill. Winding temperature calculation error does not exceed 20°C for 98.5 % of strips of low-carbon and low-alloy steels
Experiment and numerical modeling suspended ceiling with identification of working diagram material
Authors: Flodr J. , Sucharda O. , Mikolasek D.
Published: July 2018

The aim of this topic is to describe creating of working diagrams of structural materials. These will be used as input parameters for nonlinear analysis of real structures. Working diagrams of construction material are derived from experimental tensile tests and numerical analysis. We will use construction steel in this case. Derived working diagrams are used as an input parameter for numerical modelling of real structures. They are also used as a comparison with data from realized physical tests. Numerical modelling is based on 3D model of structure and it takes into account physical and geometrical nonlinearities.
Nonlinear analysis of reinforced and composite columns in fire
Authors: Navrátil Jaroslav , Kabelá Jaromír
Published: July 2018

The paper describes a customer project, the objective of which was to develop a software program for the calculation of reinforced concrete and steel/concrete composite columns subjected to various loadings and exposed to normal temperature or to fire conditions. Such analysis required the use of two Finite Element calculation cores (i) for thermal analysis and (ii) for geometrical and material non-linearity. Calculation cores were connected to graphical user interface via open interface – IDEA Open Model.
Analysis of accuracy of Williams series approximation of stress field in cracked body – influence of area of interest around crack-tip on multi-parameter regression performance
Authors: Sobek J. , Frantík P. , Veselý V.
Published: July 2018

A study on the accuracy of an approximation of the stress field in a cracked body is presented. Crack-tip stress tensor is 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 results from finite element (FE) method computation are usually taken as inputs. Main attention is paid to a detailed analysis of a suitable selection of FE nodes whose results serve as the inputs to the employed method. Two different ways of FE nodal selection are compared – nodes selected from the crack tip vicinity lying at a ring of a certain radius versus nodes selected more or less uniformly from a specified part of the test specimen body. Comparison of these approaches is made with the help of procedures developed by the authors which enable both the determination of the coefficients of terms of the analytical WPS approximation of the stress field based on the FE results and the backward reconstruction of the field (again using WPS) from those determined terms’ coefficients/functions. The wedge-splitting test (WST) specimen with a crack is taken as example for the study.
Numerical study of eddy current by Finite Element Method for cracks detection in structures
Authors: Harzallah S. , Chabaat M. , Chabane K.
Published: July 2018

In this paper, we try to use the finite element method of 2-D axisymmetry to solve problems in eddy current testing problems where the main idea is detecting crack's shape using the NDT-EC. Results are given for a simple eddy current problem using the finite element method as a tool to control cracks and defects in materials and eventually, to study their propagation as well as their shape classification. These latest can be described as the task of reconstructing the cracks and damage in a tube’s profile of an inspected specimen in order to estimate its material properties. This is accomplished by inverting eddy current probe impedance measurements which are recorded as a function of probe position. This approach has been used in the aircraft industry to control cracks. Besides, it makes it possible to highlight the defects of parts while preserving the integrity of the controlled products.
Experimental investigation of the mechanical properties of Alfas stone
Authors: N. Kaklis Kostas , P. Mavrigiannakis Stelios , Agioutantis Zach G. , Steiakakis Emmanouil K. , Stathogianni Foteini K.
Published: July 2018

This paper focuses on the experimental investigation of the mechanical properties of the Alfas natural building stone. Two series of uniaxial compression tests and indirect tensile tests (Brazilian tests) were performed in order to determine the uniaxial compressive strength and the indirect tensile strength respectively. Different sets of cylindrical specimens and circular discs were prepared by varying their geometry in order to examine the size effect on the respective strength values. Also, the size effect was investigated with respect to the calculated intact rock modulus and Poisson’s ratio. All specimens were prepared by following the ISRM suggested methods and the load was applied using a stiff 1600 kN MTS hydraulic testing machine and a 500 kN load cell. Strain was measured using biaxial 0/90 stacked rosettes appropriately attached on each specimen.
Cracking directions in multiaxial low cycle fatigue at high and room temperatures
Authors: Sakane Masao , Itoh Takamoto
Published: July 2018

Cracking direction in multiaxial low cycle fatigue is an important research subject because crack initiation and propagation behavior is a physical background for developing an estimation method of multiaxial low cycle fatigue lives. However, there are a few open questions on cracking direction in multiaxial low cycle fatigue because cracking direction in multiaxial low cycle fatigue is complex and changes depending on stress multiaxiality, strain range, notch and material. This paper overviews cracking directions in tension-torsion low cycle fatigue of low alloy steels and nickel base superalloys. Two types of cracking directions in these materials, maximum shear direction and maximum principal direction, are discussed in relation with strain multiaxiality and an existence of notch and precrack. The two cracking directions in torsion low cycle fatigue of SUS 304 stainless steel are also discussed in relation with strain range. Detailed micro crack observations are finally presented to discuss the two cracking directions in torsion low cycle fatigue of a SUS 304 unnotched specimen.
Evaluation and visualization of multiaxial fatigue behavior under random non-proportional loading condition
Authors: Morishita Takahiro , Ogawa Fumio , Itoh Takamoto
Published: July 2018

In cyclic multiaxial stress/strain condition under nonproportional loading in which principal direction of stress/strain are changed in a cycle, it becomes difficult to analyze stress/strain ranges because of complexity of multiaxial stress/strain states depending on time in cycles. In order to evaluate stress/strain simply and suitably under non-proportional loading, Itoh and Sakane have proposed a method called as IS-method and a strain parameter for life evaluation under non-proportional loading ??NP. In the method, 6-components of stress/strain are converted to an equivalent stress/strain indicating the amplitude and the direction of principal stress/strain as a function of time as well as an intensity of loading nonproportionality fNP. Based on IS-method, the authors also have developed a tool which enables to analyze multiaxial stress/strain condition with the nonproportionality of loading history and evaluate failure life under nonproportional multiaxial loading. The tool indicates the analyzed results on monitor and users can understand visually not only variation of the stress/strain conditions but also non-proportionality during the cycle, which helps the design of material strength.
On the applicability of Miner’s rule for multiaxial fatigue life calculations under non-proportional load histories
Authors: Meggiolaro Marco Antonio , Pinho de Castro Jaime Tupiassú , Ferreira Samuel Elias , Wu Hao
Published: July 2018

Fatigue design routines and computer codes must use some damage accumulation rule to deal with variable amplitude loadings (VAL), usually Palmgren-Miner (or Miner’s) linear rule for lack of a clearly better option. Nevertheless, fatigue lives are intrinsically sensitive to the order of VAL events, which may e.g. induce residual stresses and thus change the critical point stress state, much affecting its subsequent residual life. On the other hand, in general, non-linear damage accumulation rules are not robust, resulting in better predictions than Miner’s rule only for some specific load orders, requiring a case-by-case analysis. Therefore, Miner’s linear damage rule still is the usual choice in practical fatigue calculations and assessments, giving reasonable predictions at least when properly combined with approaches that sequentially consider plasticity-induced effects, following the critical point stress/strain history in a cycle-by-cycle basis. In this work, Miner’s rule is evaluated for non-proportional tension-torsion loadings on annealed tubular 316L stainless steel specimens. Normal-shear strain histories following either cross, diamond, circular or square paths are applied, and their fatigue lives are measured. Then, more complex VAL paths consisting of combinations of these individual path shapes are applied in other specimens, whose associated fatigue lives are predicted based on Miner’s rule.
On the use of length scale parameters to assess the static strength of notched 3D-printed PLA
Authors: Ahmed Adnan A. , Susmel Luca
Published: July 2018

This paper aims to investigate the accuracy of the Theory of Critical Distances (TCD) in estimating static strength of notched additively manufactured PLA as both notch sharpness and infill angle vary. The TCD takes as its starting point the assumption that the extent of damage under static loading can be assessed successfully by using two different material parameters, i.e. (i) a critical distance whose length is closely related to the material microstructural features and an inherent (i.e., a defect free) material strength. Plain and notched specimens of 3D-printed PLA were manufactured horizontally by making the deposition angle vary in the range 0?-90?. Using the TCD in the form of the Point Method, failures were predicted by directly post-processing the linear-elastic stress fields estimated through the well-known analytical solutions due to Glinka and Newport. Independently of the notch sharpness, the estimates being obtained were found to be highly accurate, falling within an error interval of about 20%. This result fully supports the idea that the TCD can successfully be used in situations of practical interest to design against static loading notched components of additively manufactured PLA by directly post-processing the results from simple linear-elastic Finite Element (FE) models.
Application of Leak-Before-Break concept in 316LN austenitic steel pipes welded using 316L
Authors: Giannini de Cunto Gabriel , Paes de Andrade Arnaldo Homobono , Monteiro Waldemar Alfredo
Published: July 2018

The paper presents a study of the application of Leak-Before- Break (LBB) concept in a relatively small-diameter high energy reactor coolant line, where it is proposed type AISI 316LN to be used as base material welded with type AISI 316L coated electrode considering a pipe with diameter of 273 mm. The pipe material was characterized in terms of tensile test with Ramberg-Osgood analyses and fracture toughness tests with J-Resistance curve determination, considering base material, weld joint and heat affected zones. For the mechanical properties found in tensile tests and using the PICEP software, were determined the leak rate curves versus crack sizes, to determine the size of a detectable leakage crack, and the critical crack sizes, considering failure by plastic collapse. For the critical crack sizes found in weld, which presented the lowest toughness, J-Integral analysis was performed considering failure by tearing instability. Results show a well-defined mechanical behavior where base material has a high toughness, weld has a low toughness, and HAZ showed intermediate properties. For the load limit analysis, the lowest critical crack size was found for base material presenting circumferential cracks. For J- Integral analysis, it was demonstrated that failure by tearing instability will not occur.