bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent Developments in Brittle and Quasi-Brittle Failure Assessment of Graphite by Means of SED
Authors: Berto Filippo , Lazzarin Paolo , Ayatollahi Majid R.
Published: September 2013

Brittle fracture of polycrystalline graphite under tension, in-plane shear and torsion loading is studied experimentally and theoretically using prismatic and axisymmetric specimens weakened by sharp and rounded-tip V-notches. The main purpose is twofold. First, to provide a new set of experimental data from notched samples made of isostatic polycrystalline graphite with different values of notch opening angles and root radii, which should be useful to engineers engaged with static strength analysis of graphite components. At the best of authors' knowledge, data from notch specimens are very scarce in the literature for this material. Second, to apply a fracture criterion based on the strain energy density (SED) averaged over a well-defined control volume surrounding the notch tip, extending what was made by the present authors for in-plane tension-shear loading conditions in notched specimens made of other materials. Good agreement is found between the experimental data related to the critical loads to failure and the theoretical assessments based on the constancy of the mean SED over the material-dependent control volume.
Investigation of Fracture and Electrical Resistivity Parameters of Cementitious Composite for their Utilization in Deterioration Models
Authors: Veselý Václav , Konečný Petr , Lehner Petr , Pařenica Přemysl , Hurta Jan , Žídek Libor
Published: September 2013

The paper is focusing on the investigation of the effective crack length obtained from bending test on concrete notched beams with the complementary measurements of electrical resistivity of the tested concrete. The electrical resistivity measurements are performed on several stages of the fracture process along the specimen ligament for each tested notched beam. Gained results of the concrete resistivity during the fracture process, i.e. its dependence on the crack length or opening, provide information which should be taken into account in structural durability analyses. The fracture tests are conducted for a set of specimens differing in the notch length. Changes of the concrete resistivity with increasing effective crack length are observed and discussed.
Influence of Dissipative Structures Formed by Impulsed Loads on the Processes of Deformation and Fracture
Authors: Hutsaylyuk Volodymyr , Czausow Mykola , Berezin Valentin , Pylypenko Andriy , Volyanska Katerina
Published: September 2013

By applying original experimental methodology and software system for non-contact research of deformation field investigated conditions of DNP in the test setup of given stiffness. Established that at the speed of additional impulse loading within 300-500 MN / s, specimens of aluminum alloy 2024 - T3 and D16 exposed low cycle, high-frequency oscillations with a frequency of 1.5 ... 2 KHz. This process of load with deformations speeds of the material 2 ... 60s-1 promotes plasticizing of aluminum alloys and delays in "neck forming.".
Numerical Modelling and Bearing Capacity of Reinforced Concrete Beams
Authors: Sucharda Oldrich , Brozovsky Jiri , Mikolášek David
Published: September 2013

This paper discusses the fracture-plastic material models for reinforced concrete and use of this model for modelling of reinforced concrete beams. Load-displacement relations and bearing capacity of reinforced concrete beams will be evaluated. A series of original (own) experiments - the beam and data from completed experiments - have been chosen for the numerical modelling. In case of the original experiments - reinforced concrete beams, stochastic modelling based on LHS (Latin Hypercube Sampling) will be carried out in order to estimate the total bearing capacity. The software used for the fracture-plastic model for reinforced concrete is ATENA.
Determination of Stress Intensity Factor for Cracked Brazilian Disc Using Weight Function
Authors: Zhao Yan Hua , Liu Jin , Gao Hong Bo , He Huan An , Zhang Tao
Published: September 2013

To reduce stress concentration near the loading point, Brazilian test, normally used for the indirect determination of tensile strength for rock or concrete quasi-brittle materials, is usually subjected to uniformly distributed pressure over finite width (or arc) of the Brazilian disc. As an extension, the same geometry, in which a central notch is introduced in the symmetrical plane of applied forces, can be used to determine fracture toughness of the materials. For this purpose, accurate expression for stress intensity factor (SIF) for central cracked Brazilian disc should be provided first. To this end, weight function method is used in this paper where weight function for central cracked disc is available in general SIF handbooks. Meanwhile, the exact stress solution in the intact Brazilian disc subjected to uniformly distributed pressure is derived by use of numerical method. In the end, some finite element analysis is carried out using the program package ABAQUS on the Brazilian disc, and the comparison results regarding the SIF between the weight function method and numerical method prove the validity of the proposed method.
Torsion Characteristics on Drive Shaft of Independent Wheel Drive for Articulated Vehicle
Authors: Kim Yeon Su , Park Sung Hyuk , Yoon Sung Cheol , Mok Jai Kyun
Published: September 2013

The drive shaft of the bi-modal tram has been designed and built into independent wheel drive; all driving wheels are driven by electric motor-gearbox sets independently, in order to make low floor to provide the old and the handicapped with easy access, and to remove differential gears to reduce turning radius. This paper was aimed to evaluate torques on drive shafts while the bi-modal tram was running on slope way in the test track, and at maximum speed in public roadway. On the basis of the torques measured on the drive shafts, torsion characteristics of the independent wheel drive were discussed in this paper.
Cracks Interaction due to Sequential Indentation in Curved Brittle Coating: Effect of Relative Orientation
Authors: Qasim Tarek , Al-Khateeb Susan
Published: September 2013

This study investigates the influences of pre-existing cracks to simulate defects in structures using curved bi-layer system consisting of glass coating on a polymeric support layer, to illustrate the role of defects on the evolution of failure of hard coating bi-layer system under loading. The densities of pre-existing cracks were initiated near the margins and the relative orientations were varied. The pre-existing cracks were induced by using hard spherical indenter. The failure of these samples was investigated under single-cycle axial loading tests using soft indenter of low elastic modulus. The onset of fracture was observed in situ using a video camera. Margin cracks were observed to propagate from pre-existing cracks near the margins, while the pre-existing cracks in the compression zone under the soft indenter were arrested. Experimental trends suggested that critical loads were increased with specimens having no defects (pre-existing cracks). Finite element modeling was used to evaluate the stress distribution in the brittle coating and compared with the experimental trend. It is concluded that radial cracks can initiate and propagate anywhere in the tensile region. The larger the flaws the smaller the loads required for defects pre-existing cracks to propagate radials to failure.
Evaluation of Fatigue Crack Growth Rates and Threshold Conditions in an Al 2124-T851 Alloy at Different Load Asymmetry Considering Microstructure Orientation
Authors: Černý Ivo
Published: September 2013

Results of a fairly comprehensive experimental programme aimed at evaluation of fatigue crack growth (FCG) rates in an aircraft Al 2124 alloy in T851 state, after hot rolling, solution annealing, small plastic strain and artificial ageing are presented and discussed. Measurement was performed not only in the region of stable crack growth, but also in the threshold region enabling to estimate threshold values of stress intensity factor range using method of regression analyses. FCG rates were evaluated in both L-T and T-S directions to evaluate sensitivity of FCG resistance on different microstructure orientation. Different load asymmetry conditions R = Fmin / Fmax were used, namely R = 0.1 and 0.6. Repeated measurements in more than one specimen at each condition enabled to evaluate reproducibility, scatter of measurement and to perform eventually probabilistic assessment. The reproducibility of measurement was particularly good for L-T orientation. In this case, threshold values were somewhat higher and FCG rates lower in comparison with the T-S orientation. In the contrary, cyclic fracture toughness in T-S orientation was slightly higher. The results are discussed form the viewpoint of residual fatigue life in aircraft components considering probabilistic aspects.
Effects of the Interference Level on the Residual Stresses in a Cold-Working Expansion Method
Authors: Giglio Marco , Lodi M. , Giudici L.
Published: September 2013

The cold-working expansion methods are extensively used in the aerospace and mechanical industry to obtain forced couplings of steel bushings into holes made on mechanical components, by means of the passage of an oversized mandrel. This work describes a calculation algorithm, able to correlate the selected interference level, as the difference between the maximum radius of the mandrel and the inner radius of the bushing, to the residual stresses expected on the hole surface. The designer, taking into account the different design choices already made, can choose the optimal interference, estimating the uncoupling resistance and the fatigue strength of forced components. Two original and different systems bushing-mandrel, in low and high interference, have been tested for determining the characteristics of fatigue resistance in the finite life part of the Wohlers diagram.The results have been compared with previously estimated data, getting a good agreement of the series. The increase of the adopted interference value determine a corresponding increase of residual stresses on the hole, both in the radial than in the circumferential direction, and an appreciable and predictable improvement of the fatigue strength of components.
Experimental Soil - Concrete Plate Interaction Test and Numerical Models
Authors: Čajka Radim , Burkovič Kamil , Buchta Vojtech , Fojtík Roman
Published: September 2013

State of stress in foundation structure is structure is significantly influenced by the contact stress course in the subsoil. At the Faculty of Civil Engineering VSB TU Ostrava testing device was constructed so that the phenomena could be experimentally investigated and compared with numerical models. The objective of this paper is also improving and developing the soil-structure interaction analysis based on the experimental results and finite element method (FEM).
Evaluation of Elastic Structural Integrity of a 70 kW Class Lab-Scale PCHE Prototype under the Test Conditions of HELP
Authors: Song Kee Nam , Hong S.D.
Published: September 2013

The IHX (Intermediate Heat Exchanger) of a VHTR (Very High Temperature Reactor) transfers 950°C heat generated from the VHTR to a hydrogen production plant. The Korea Atomic Energy Research Institute (KAERI) has manufactured a 70 kW class lab-scale PCHE (Printed Circuit Heat Exchanger) prototype made of SUS316L under consideration as a candidate. In this study, as a part of a structural integrity evaluation of the lab-scale PCHE prototype, an elastic structural analysis including structural analysis modeling and a thermal/elastic structural analysis was carried out under the test conditions of a helium experimental loop (HELP). In addition, a structural integrity evaluation considering the weld material properties was conducted.
J Integral Computation for Repaired Cracks with Bonded Composite Patch in Aircraft Structures
Authors: Benyahia F. , Albedah A. , Bachir Bouiadjra Bel Abbès , Belhouari Mohamed
Published: September 2013

In this study, the three-dimensional and nonlinear finite element method is used to estimate the performances of bonded composite repairs of metallic cracked aircraft structures by analyzing the J integral and at the crack tips of repaired cracks for single and double symmetric patches. Several calculations have been realized to extract the plasticized elements around the crack tip. The obtained results show that composite repair reduces significantly the J integral at the crack tip which can improve the fatigue life of aircraft structures. It was also shown that the double symmetric patch has a considerable beneficial effect on the repair performance compared to the single patch.
Crack Length Estimation from the Damage Modelisation around a Cavityi in the Orthopedic Cement of the Total Hip Prosthesis
Authors: Benbarek Smail , Sahli A. , Bouziane Mohamed Mokhtar , Bachir Bouiadjra Bel Abbès , Serier B.
Published: September 2013

In orthopedic surgery and particularly in the total hip arthroplasty, the stem fixation is performed in general using a surgical cement which consists essentially of polymer (PMMA). Fracture of cement and prosthesis loosening appears after a high-stress level. This phenomenon origin is due to the presence of micro-cavities in the PMMA volume. The focus of our study is the modeling using the finite-element method of the cement damage around these cavities, the cavities' sizes and shapes effect on the damage risk, and the crack length estimation due to this damage. A small Fortran schedule was incorporated with the Abaqus code to calculate the damage zone. Results show that the presence of a cavity in the cement increases the damage parameter. The damage appears when the cavity is located in cement on the loading axis. If the cavity changes its shape from circular to elliptical, the size of the damage zone increases. One can predict the initiation of a crack in cement with a maximal length of 70μm.Keywords: total hip prosthesis, crack, bone cement, biomechanics, damage.
Microtensile Video Tester for Observation of Banana and Abaca Reinforced Composites Failure
Authors: Ortega Z. , Monzón M.D. , Benítez A.N. , Tcharkhtchi A. , Farzaneh S.
Published: September 2013

This research focus on the characterization of banana and abaca reinforced composites obtained by rotational molding process. These composites were fully characterized by means of DSC and mechanical tests (tensile, flexural, impact and DMA), as well as by optical microscopy. Tests presented in this paper aim to the observation of failures occurred in composites, in comparison with those observed in pure polyethylene. This equipment consists in a microtensile tester, equipped with an optical microscope, a camera and specific software for images capture. Tests have been carried out with test samples obtained from rotomoulded parts, at a rate of 1000 μm/min. Differences between both types of fiber have been observed, showing different compatibility of these fibers with the polymeric matrix; treated fiber also shows different failure process. Banana and treated abaca fibers break in the PE matrix, while pull-out effect was observed for abaca fiber.
Analytical Design of Gigacycle Fatigue Specimens for Size Effect Evaluation
Authors: Tridello A. , Paolino D.S. , Chiandussi G. , Rossetto Massimo
Published: September 2013

Research activities on gigacycle fatigue properties of materials have recently focused on the influence of specimen size used for ultrasonic fatigue tests. In order to increase the volume of material subjected to the maximum stress (risk volume) a new specimen shape with a Gaussian profile is proposed. An approximation of the Gaussian profile with an arc of circle is presented in the paper, in order to simplify the Gaussian specimen manufacturing process. The effect of the approximation is evaluated analytically and through a finite element analysis.
Modelling Microstructural Effects on the Mechanical Behaviour of a Friction Stirred Channel Aluminium Alloy
Authors: Vidal Catarina , Infante Virgínia , Lage Yoann , Vilaça Pedro
Published: September 2013

Friction stir channelling (FSC) is a relatively new solid-state manufacturing technology able to produce conformal channels in a monolithic plate in a single step. During the FSC process the metal workpiece material is softened by the heat energy generated from dissipation during: plastic deformation, internal material flow and frictional work between the tool and the metal workpiece. The mechanical performance of a friction stirred channel aluminium alloy is affected by microstructure surrounding the channel. A new methodology that simulates a realistic 2D microstructure from experimental metallographic characterization and tensile tests was developed using the commercial software ABAQUS to study the mechanical behaviour of the friction stirred channel 5083-H111 aluminium alloy. Fourpoint bending tests were simulated and compared with experimental results. The RambergOsgood model was also adopted in the finite element analysis. It is seen from this investigation that microstructure can significantly affect the bending strength of friction stirred channel plates.
The Role of Methane Hydrates in the Failure of a Gas Pipeline
Authors: Caputo Francesco , Cascetta F. , Lamanna Giuseppe , Rotondo G. , Soprano Alessandro
Published: September 2013

Gas hydrates are known to form plugs in pipelines. Gas hydrates are crystalline compounds that form when hydrocarbons such as methane come in contact with water under thermodynamical opportune conditions, as high pressure and low temperature. Hydrates, like any obstruction in a pipeline, reduce flow, increase back pressure in the system and increase the differential pressure across the obstruction. When the line section is obstructed by a plug, the differential pressure can put the hydrate in movement and quickly accelerate it up to a speed approaching that of sound; in this case, the moving mass can cause serious mechanical damages at downstream locations where the plug can also meet restrictions or obstacles such as valves, elbows or tees. In this paper a real case of a gas pipeline failure, due to the presence of a moving mass of methane hydrate, has been investigated by considering an analytical and numerical modeling of the motion of the hydrates, as well as of their impact against the pipes.
Experimental Investigation of Corrosion Processes on Weathering Steel Structures
Authors: Křivý Vit , Urban Viktor , Fabián Lukáš
Published: September 2013

This paper introduces the experimental corrosion tests that are carried on the existing weathering steel structures in the Czech Republic. The influence of the position and location of the surface in the structure on the resulting corrosion rates can be evaluated using this experimental testing. Typical surfaces of steel bridges are tested, e.g. webs of main girders, upper and lower surfaces of flanges, surfaces affected by leaking salt solutions. Results of the corrosions tests are used for the specification of corrosion prediction model.
Influence of Reinforcement Particle Sizes on the Joining Strength of the FSSWed PVC Joint Compounded SiC Particle in Welded Area
Authors: Kurabe Yohei , Miyashita Yukio , Hori Hisashi
Published: September 2013

In Order to Improve the Joining Strength of Friction Stir Spot Welded PVC Joint, Sic Particle was Compounded by the Stirring in the Welding Process. the Influence of Sic Particle Sizes on the Joining Strength was Investigated in this Study. in Case of the Specimen Compounded Sic Particle with Size of 14.6μm, Heat Generated during the Process Significantly Increased and Resulted in Increasing Width of Welded Region. however, According to Result of Hardness Test, Excessive Heat Generated during the Process Led to Degradation of Mechanical Property of the Welded Area in the Specimen Compounded Sic Particle with Size of 14.6μm. on the other Hand, in Case of the Specimen Compounded Sic Particle with Size of 6.5μm, Width of Welded Area was Smaller than that of the Specimen Compounded Sic Particle with Size of 14.6μm and was Similar as that of the Specimen Compounded Sic Particle with Size of 0.5μm. it was Observed that Hardness of the Welded Area was Uniformly Higher in the Joint Compounded Sic Particle with Size of 6.5μm. Specimen Compounded Sic Particle with Size of 6.5μm Showed the Highest Strength among the Joints Tested. it is Considered that the Joining Strength was Affected by both Width and Mechanical Property of the Welded Area.
Nonlinear Thermo-Mechanical Coupled Modeling for the Analysis of Stress Distribution in Air-Plasma-Sprayed Thermal Barrier Coatings
Authors: Chen Yu Hui , Zhong Shun Cong , Yang Xiao Xiang
Published: September 2013

Thermo-mechanical coupled modeling of air-plasma-sprayed (APS) thermal barrier coatings (TBCs) on Ni-based alloy was investigated. In the computational models, the stress distribution in the depth direction of the TBCs and also the influence of mechanical properties in heating, dwelling and cooling thermal cycles, were investigated. Nonlinear relationship (e.g., convective heat transfer between surrounding environment and coatings, and thermal transfer between the different layers etc.) was considered in the modeling. The results showed that the stress significantly reduced in the dwelling stage because of stress relaxation. The maximum stress occurred in the peak at the BC/TGO interface and it was amplified at the cooling stage. Moreover, the internal stress in the BC and TGO layer had a slight increase when TGOs thickness increased whilst the stress in the TBC and Sub were essentially unchanged. In the present work, the cracks in BC coating and the BC/TGO interface cracks were simulated as well. The failure mechanism I/II of TBCs had been investigated and the results showed that there was no stress concentration in the vicinity of cracks near the peak at the top coating layer, however, due to crack propagation, factures happened near the peak at the BC/TGO interface.
Effect of Triaxiality and Lode Angle on the Plasticity Behaviour of a Ti-6Al-4V Titanium Alloy
Authors: Gilioli Andrea , Manes Andrea , Giglio Marco , Allahverdizadeh Nima
Published: September 2013

The widespread Von Mises plasticity model fails to take the hydrostatic and the Lode angle effects into account and the assumption of this model is not valid for all types of metallic alloys. Hence in the present work the applicability of the Von Mises plasticity model in applications on a Ti-6Al-4V Titanium alloy have been analysed. A virtual test methodology, combination of experiments and numerical analysis have been developed. For this purpose various tensile tests on different specimen shapes have been carried out experimentally. These tests have been subsequently numerically reproduced to calibrate a constitutive law which fits every single test best, highlighting the possible effect of triaxiality and Lode angle on plasticity (strain hardening behaviour). An analysis of the specimen fracture surfaces have been carried out to evaluate possible effect of triaxiality and Lode angle down to a microscopic level.
Evaluation of Torsional Rigidity for Micro-Lattice Plates
Authors: Ushijima K. , Chen Dai Heng , Cantwell Wesley J
Published: September 2013

In this paper, the torsional rigidity of micro-lattice plates is investigated using a FE analysis. In particular, the effect of the overall length of the plate and the unit-cell geometry on the torsional rigidity are discussed. Also, a theoretical approach, based on classical beam theory, for predicting the rigidity is proposed, and its effectiveness is verified by comparing with FE results.
Effect of Processing Layer on Fatigue Strength of Extruded AZ61 Magnesium Alloy
Authors: Miyashita Yukio , Kushihata Kyohei , Kakiuchi Toshifumi , Kiyohara Mitsuhiro
Published: September 2013

Fatigue Property of an Extruded AZ61 Magnesium Alloy with the Processing Layer Introduced by Machining was Investigated. Rotating Bending Fatigue Tests were Carried out with the Specimen with and without the Processing Layer. According to Results of the Fatigue Tests, Fatigue Life Significantly Increased by Introducing the Processing Layer to the Specimen Surface. Fatigue Crack Initiation and Propagation Behaviors were Observed by Replication Technique during the Fatigue Test. Fatigue Crack Initiation Life of the Specimen with the Processing Layer was Slightly Longer than that of the Specimen without the Processing Layer. Higher Fatigue Crack Growth Resistance was also Observed when the Fatigue Crack was Growing in the Processing Layer in the Specimen with the Processing Layer. the Longer Fatigue Life Observed in the Fatigue Test in the Specimen with the Processing Layer could be Mainly due to the Higher Crack Growth Resistance. it is Speculated that the Fatigue Strength can be Controlled by Change in Condition of Machining Process. it could be Effective way in Industry to Improved Fatigue Strength only by the Cutting Process without Additional Surface Treatment Process.
Experiments Method Design Applied to Optimization of Patch Repairs for Cracked Plates
Authors: Belhouari Mohamed , Fekih S.M. , Kouider Madani , Amiri A. , Bachir Bouiadjra Bel Abbès
Published: September 2013

The optimization of the patch shape of bonded composite repair in aircraft structures is an efficient way to improve the repair performance. In this study the three-dimensional nonlinear finite element method is used to determine the J integral variation along the front of repaired crack with bonded composite patch in aircraft structures. The experimental design method was applied to optimize the patch shape and size in order to determine the most influencing dimension on the repair efficiency.
Dynamic Crack Analysis in Layered Piezoelectric Composites under Time-Harmonic Loading
Authors: Wünsche Michael , García-Sánchez Felipe , Zhang Chuan Zeng , Sáez Andrés
Published: September 2013

In this Paper, Time-Harmonic Dynamic Crack Analysis in Two-Dimensional (2D), Layered and Linear Piezoelectric Composites is Presented. A Frequency-Domain Symmetric Galerkin Boundary Element Method (SGBEM) is Developed for this Purpose. the Piecewise Homogeneous Sub-Layers of the Piezoelectric Composites are Modeled by the Multi-Domain BEM Formulation. the Frequency-Domain Dynamic Fundamental Solutions for Linear Piezoelectric Materials are Applied in the Present BEM. the Boundary Integral Equations are Solved Numerically by a Galerkin-Method Using Quadratic Elements. an Iterative Solution Algorithm is Implemented to Consider the Non-Linear Semi-Permeable Electrical Crack-Face Boundary Conditions. Numerical Examples will be Presented and Discussed to Show the Influences of the Location and Size of the Crack, the Material Combination of the Sub-Layers, the Piezoelectric Effect and the Time-Harmonic Dynamic Loading on the Dynamic Intensity Factors.
A Parametric Investigation of Surface Initiated Rolling Contact Fatigue Using the Asperity Point Load Mechanism
Authors: Hannes Dave , Alfredsson B.
Published: September 2013

Rolling contact fatigue (RCF) will eventually become an issue for machine elementsthat are repeatedly over-rolled with high contact loads and small relative sliding motion. Thedamage consists of cracks and craters in the contact surfaces. Asperities on the contact surfacesact as local stress raisers and provide tensile surface stresses which can explain both initiationand propagation of surface initiated RCF damage. A parametric study was performed to inves-tigate the contribution of surface roughness, friction and a residual surface stress to the RCFdamage process. The eﬀects on initiation, crack path and fatigue life at both early and devel-oped damage were examined for a gear application. Both a one-parameter-at-a-time approachand a 2-level full factorial design were carried out. Surface roughness and local friction prop-erties were found to control crack initiation, whereas the simulated crack path was primarilyaﬀected by the residual surface stress, especially for developed damage. Reduced surface rough-ness, improved lubrication and a compressive residual surface stress all contributed to increasethe simulated fatigue life. The asperity point load model could predict eﬀects on RCF that areobserved with experiments. The results further support the asperity point load mechanism asthe source behind surface initiated RCF.
Inner Damage and External Dent in Composite Structures after Impact – Part I: Experimental Observations
Authors: Espinosa Christine , Ruiz-Ayuso Miriam , Lachaud Frédéric
Published: September 2013

The damage tolerance methodology is used here to compare impact damage from experimental testing and virtual (numerical) testing. The first part of the study aims to identify links between experimental internal (delaminated area) and external measurable damage (dent depth) for a typical aeronautical T800S/M21e laminate. Effects of the mass/velocity ratios at some level of impact energy are evaluated. It is shown that a big mass generates denser and larger delamination with about the same dent than a small mass, which is a critical case for damage tolerance analysis. A relation between the external dent depth and internal delaminated area is proposed.
Thermographic Determination Methodology: Application on Fatigue Limit of AL 2024 for R=-1
Authors: Seitl Stanislav , Klusák Jan , Fernández Pelayo , Canteli Alfonso Fernández
Published: September 2013

The application of infrared thermography to obtain the external surface temperature during the application of cyclic loading, allows to evaluate the dynamic behavior of an element and to determine the fatigue limit. In this contribution, the reliability of the fatigue limit provided by the Risitano et al. and Canteli et al. methodologies is investigated in order to check their validity for practical applications. With this aim, an experimental program on aluminium specimens (AL 2024) under load control using a stress ratio minus one is performed. The fatigue limit for AL 2024 is derived, first from the Wöhler curve and then, compared with both Risitano et al. and Canteli et al. methodologies.
Fracture Characterisation of Reactor Core Graphite under Biaxial Loading
Authors: Liu Dong , Mostafavi M. , Flewitt Peter E.J. , Marrow T. James , Smith David John
Published: September 2013

The role of stress state on the fracture properties of a quasi-brittle material are explored using reactor core Gilsocarbon graphite. The objective of the experiment was to study the initial propagation of cracks. Cruciform specimens have been tested by a biaxial flexural loading method. Pre-slots of 10 mm width and up to a quarter of the depth of the specimen were introduced at the centre of the specimen by electric discharge machining. The slots are located between two through-thickness holes, which are designed to guide crack propagation. A loading jig has been designed and built that allows a range of biaxial loading states to be applied by variation of the length of the loading arms. Clip gauges are used to measure the crack mouth opening displacements. Preliminary tests have studied the fracture of specimens under different loading conditions.
High Accurate Solutions of Nonlocal Elasticity for Sphere
Authors: Wen P.H. , Huang X.J. , M.H.Aliabadi Ferri
Published: September 2013

The analysis of sphere nonlocal elasticity is carried out by using the improved point collocation method. The approach is based on the Eringen’s model and two and three dimension problems are transformed to one dimension problems considering the polar symmetry. One dimension second order differential equation in terms of radial displacement is derived with domain integral. Due to the excellent accuracy of the point collocation method to one dimension differential equation using the radial basis function interpolation, the numerical solutions can be used as benchmarks. This approach can be easily extended to dynamic nonlocal elasticity and plasticity for sphere.
Studying the Effects of Internal and External Microstructure on Fatigue Strength of Materials by Electromagnetic Excitation Technique
Authors: Syed Mujtaba , Ahmed Imtiaz , Müller Claas , Wilde Jürgen
Published: September 2013

A fatigue testing setup based on electromagnetic excitation was built to apply cyclic stresses to the specimens near their resonance frequency. A test near the resonance frequency has the advantage that higher stresses can be applied to test specimens at a reduced input power. Stress amplitude up to 1000 MPa can be applied to the test specimens and up to four specimens can be tested simultaneously. The setup can test specimens at high fatigue cycle regime i.e. 100 million stress cycles can be achieved in 48 hours.The setup has been used to study the effects of internal and external microstructure on the fatigue strength of materials. Specimens especially stainless steel-304 was prepared by different techniques i.e. electric discharge machining EDM, etching and laser cutting. Specimens prepared by these techniques were tested and their fatigue strengths were compared. To probe the material endurance limit, tests were also performed on the above mentioned steel specimens in very high stress cycle regime i.e. > 109 cycles. In order to investigate the effect of internal microstructure on fatigue strength of material, CuZn37 fabricated by etching was tested and the effect of different grain size on fatigue strength was compared. SN curves have been plotted for materials with no prior fatigue strength data. Stainless steel-1.4404 specimens prepared by Rapid Prototyping (RP) has been tested for fatigue analysis. The test results showed higher degree of scattering when compared to the traditionally manufactured steel. Fractography revealed the existence of inherent material flaws which was the main reason of higher degree of test point scattering. In addition to these data, the SN curve was plotted for Innolot which is an important soldering alloy and prompts to fatigue failure in electronic assemblies.
Contact Behaviour of Composite Laminate under Quasi-Static Indentation Load
Authors: Shen Z. , Xu Y.G. , Chrysanthou Andreas
Published: September 2013

A viable solution to the ever-demanding weight-saving target in aerospace industry is the replacement of conventional engineering alloys with composite materials in primary structures. A major concern to the effective use of composite laminates is the substantial reduction in the compressive strength when the contact force has exceeded the delamination threshold load (DTL). This paper focuses on the study of the contact behavior of composite laminates under quasi-static indentation (QSI) forces. The effect of damage initiation and growth on contact behavior has been investigated via detailed assessment of the relation between the indentation force and the dent depth. Different phases corresponding to undamaged, local damage, global damage, and final failure of the laminate have been identified. A modification to the classical Hertz contact law has been proposed to account for the matrix material resistance to plastic deformation.
Influence of the Die Bearing Length on the Hydrogen Embrittlement of Cold Drawn Wires
Authors: Toribio Jesús , Lorenzo Miguel , Aguado Leticia , Vergara Diego , Kharin Viktor
Published: September 2013

Prestressing steels, obtained by cold drawing, are highly susceptible to hydrogen embrittlement (HE) phenomena. Stress and strain fields produced by cold drawing play an essential role in this process since they affect hydrogen diffusion. Therefore, variations of such fields due to changes in drawing conditions could modify life in-service of these structural components. In this work the effect on HE of a parameter of the wire drawing process, the bearing length, is analyzed by means of diverse numerical simulations by the finite element method (FEM). The results of this work allow the definition of a characteristic value of the die bearing length equal to the wire radius, and demonstrate that the effects of stress-strain fields produced by wire drawing on HE are reduced when the bearing length exceeds such a characteristic value, so that the optimum cold drawing process is that with a bearing length higher than the wire radius.
The Study on Damage Failure of Pipeline under Flood Using Entropy Identification Method
Authors: Liu Miao , Wang Zhi Yin , Wang Xin
Published: September 2013

The buried pipeline will be spanning and subject to dynamic load under flooding, which may induce a damage failure of pipeline. In this paper, a mechanical analysis model of spanning pipelines is established under different levels of flood load. The mechanical response and the information entropy based on strain energy of the pipeline are calculated through global analytical searching method. In addition, the recognition of damage failure of pipeline is achieved according to the value of strain energy entropy of pipeline under different flood levels. The study shows that the strain energy entropy varies with the change of deformation reflects the damage failure feature of pipeline well, which can be used as a new method to identify the failure of pipeline.
Investigation of Bearing Strength of Single-Bolt Double-Lap Joints in Composite Laminate
Authors: Cheng Li Nan , Zheng Xi Tao , Tan Chun Yang
Published: September 2013

Based on the Upper Bound Theory, a Simplified Engineering Approach is Presented to Determine the Ultimate Strength of a pin-Loaded Composite Laminate in this Papaer. According to the Upper Bound Theory, the Displacement Rate in a Given Ply is Divided into Two Zones: the Moving Zone and the Static Zone. the Applied Load Q that Associated with Displacement must be Less than the Maximum Resistance of the Laminate. in this Paper we have Discussed the Failure Region, Failure Type of each Ply and Simplified the Tsai-Wu Failure Criterion. Experiments of Single-Bolt Double-Lap Joints have been Conduncted According to ASTM D5961 Test Standard. Finally, we can Observe that the Engineering Approach is in Good Agreement with the Test Results.
Fracture Toughness of Large Forgings for Power Producing Industry
Authors: Mentl Václav
Published: September 2013

The steam turbine rotors represent large components both in radial and axial directions. Their local properties generally differ from one forging to another, or if we compare head and bottom parts of the original ingot, or central and circumferential localities of one rotor body respectively, or if we compare the properties of separate discs e.g. in the case of welded rotors. These differences stem from both even slight changes in the chemical composition (of separate heats or even within one ingot) and thermo-mechanical treatment and in the differences in technology with respect to the real shape and size of the forgings in question. In the paper, the consequences of the differences in fracture toughness characteristics in various rotor localities are discussed with respect to the rotors operational safety taking into account the existence of cracks and material degradation.
Effect of Tearing Strength by Variations in Amount of Adhesive in Laminated Film for Liquid Package
Authors: Machida Yukihiko , Shimamoto Akira , Aoki Hiroyuki
Published: September 2013

Plastic film assumes a large role as packaging material in our life. Especially, by lamination which is pasting some kind of simple substances together, plastic films are able to have many kind of function on demand of usage. It is considered that enough high peel strength and tensile strength are needed for liquid package material. And it is considered that low tearing strength is needed for easy open package too. Adhesive existing at interlayer of laminated film, and the amount of adhesive may have effect on these physical properties. In this study, we changed amount of adhesive about laminated film, measured peel strength, tensile strength and tearing strength. And we investigated best suited amount of interlayer adhesive.
Skin Stringer Debonding Evolution in Stiffened Composite Panels under Compressive Load: A Novel Numerical Approach
Authors: Riccio Aniello , Raimondo A. , Scaramuzzino F.
Published: September 2013

In this paper, a numerical study, on the compressive behaviour of stiffened composite panels with skin-stringer debonding has been carried out. The analysis has been performed by adopting a novel robust (mesh and time step independent) finite elements based numerical model on a single stiffener panel with an artificial debonding. In order to prove the effectiveness of the proposed numerical tool, the results in terms of debonded area growth and compressive load versus applied displacement, have been compared with experimental data available in literature.
Molecular Dynamics Studies of Spalling and Melting in Shocked Nanocrystalline Pb
Authors: Xiang Mei Zhen , Hu Hai Bo , Chen Jun
Published: September 2013

The mechanisms of spalling and melting in nanocrystalline Pb under shock loading are studied by molecular dynamics simulations. Our results show that grain boundaries have significant influences on spalling behaviors in cases of classical spallation and releasing melting. In these cases, cavitation and melting both start on grain boundaries, and they display mutual promotion: melting makes the voids nucleate at smaller tensile stress, and void growth speeds melting. Due to grain boundary effects, the spall strength of nanocrystalline Pb varies slowly with the shock intensity in cases of classical spallation. In cases of releasing melting and compression melting, spall strength of both single-crystalline and nanocrystalline Pb drops dramatically as shock intensity increases.
The Deflection of Donut Type Hollow Slab Considering Crack Behaviors
Authors: Chung Joo Hong , Choi Hyun Ki , Lee Seung Chang , Choi Chang Sik
Published: September 2013

Recently, various types of slab systems which can reduce self-weight of slabs have been studied as the height and width of building structures rapidly increase. A hollow slab system is widely known as one of the effective slab system which can reduce self-weight of slab. According to previous studies, the hollow slab with donut type hollow sphere had enough flexural strength. On the other hand, there were some differences in flexural stiffness and deflection between general RC slab and donut type hollow slab. The deflection of hollow slab was influenced by the shapes of hollow spheres due to its different second moment of inertia and amount of concrete surrounding bottom re-bar. Especially, the cracking behaviors also influence the deflection of slab. General RC slab deflection has been sufficiently investigated and some models to consider the crack behavior such as crack width, crack space, tension stiffening effect, bond-slip relationship. However, there is no study about the crack behavior on the hollow slab. Therefore, the purposes of this paper are to presents the cracking behavior of donut type hollow slab and to evaluate the deflection considering the crack behavior under flexural load.
Comparison between Fracture Behaviour of Pipe-Line Ring Specimens and Standard Specimens
Authors: Gubeljak Nenad , Likeb Andrej , Predan Jožef , Matvienko Yu. G.
Published: September 2013

Thethin walled structures as pipe-line are often unsuitable for standard testingof fracture toughness. One possibility is applying non-standard modifiedspecimens with simple testing procedure, but measured fracture behaviour isconsequence of loading conditions and geometry of specimen. In this paper thedifferences in fracture behaviour of single edge notch bending (SENB) and ringpipe-line bended specimens are discussed. Especially uneven fatigue crack frontas consequence of complex fatigue loading caused different fracture behaviour,than standard single edge notch bending (SENB) specimens. The stress-strainconditions at the crack tip are analysed by finite element modelling. Thecritical crack tip opening displacement has been determined as a crack tipsurface strain-relaxation by using stereo-optical grading method. Comparisonbetween CTOD-R curves of both types of specimens shows difference in crackdriving force.
Modelling of Impact Behavior of Concrete Subjected to Shock Loading
Authors: Sun Yuan Xiang , Xu Lin
Published: September 2013

This paper presents a coupled model of damage and plasticity to describe the complex behavior of concrete subjected to shock loading. Comparison with the test results shows that the proposed model can give consistent prediction of the impact behavior of concrete.
Damage Imaging of Pipes in Nuclear Power Plants Using Torsional Guided Wave Modes
Authors: Wei Zhao Xiang , Xu Hong , Li Hong Yuan
Published: September 2013

Ultrasonic guided waves can propagate a long distance in pipeline with little attenuation. This means the damage in nuclear power plant can be detected from a remote single position. In the paper, the propagation of the guided waves are analyzed for the nuclear power plant pipes, and the axisymmetric torsional mode T(0,1) is chosen as the detection mode. An imaging method based on the synthetic focusing algorithm is used to obtain the damage information. The method is then verified by the finite element model. Results illustrate that the damage can be detected and located accurately by the damage imaging method. Not only the axial position, but also the circumferential position can be located simultaneously.
The Influence of Cycling Frequency to Response Loading in Fatigue Tests for Sandwich Beam with Viscoelastic Core
Authors: Xue Qi Chao , Zou Guang Ping , Xue Tao
Published: September 2013

In 3-point bending fatigue experiments of sandwich plate with visoelastic core and steel faceplates, it is found that response loading of specimen is very sensitive to cycling frequency. From fatigue test, different loading response of sandwich beam obtained in various cycling frequencies. Based on viscoelastic theory, responses of deformation of sandwich plate in cyclic square load wave are calculated. And an explanation of influences of cycling frequency is elaborated.
Effect of Crystallinity on Mechanical Properties of Carbon Fiber Reinforced Polypropylene
Authors: Katogi Hideaki , Takemura Kenichi
Published: September 2013

In this study, effect of crystallinity on mechanical properties of carbon fiber reinforced thermoplastics (CFRTP) was investigated. Polypropylene (PP) and maleic anhydride modified polypropylene (MAPP) were used as matrix. The crystallinity of PP was controlled by using heat treatment after hot press molding of CFRTP. The range of crystallinity of PP and MAPP were from 26% to 40%. Flexural tests and izod impact tests of CFRTP were conducted based on Japanese Industrial Standard (JIS) K 7074 and JIS K 7110, respectively. As a result, flexural property and izod impact value of CFRTP using PP increased with an increase of crystallinity. However, flexural property and izod impact value of CFRTP using MAPP almost did not change with an increase of crystallinity.
Mechanical Characterization of Bamboo Fiber-Reinforced Green Composites
Authors: Takagi Hitoshi , Fujii Toshihiro
Published: September 2013

This paper deals with the mechanical behavior of bamboo fiber-reinforced biodegradable composites (green composites). A starch-based, dispersion type biodegradable resin was used as matrix polymer, and this matrix was reinforced by long bamboo fibers which were extracted by a steam-explosion method. The experimental results showed that the developed green composites possessed the flexural and tensile strength of 263 MPa and 270 MPa, respectively. The mechanical properties of the green composites were evaluated as a function of fiber content. It is found that the observed tensile strength was slightly lower than that of estimated values from the rule of the mixture. This discrepancy might be related to the misorientation of the bamboo fiber in the composites and to that the final fracture of composites is also governed by the presence of weak bamboo fiber.