bluuebunny/crossref_metadata_2025 huggingface dataset:
Large Deformation Modeling of a Re-Entrant Honeycomb under Tensile Load
Authors: Zhang Jian Jun , Lu Guo Xing , Ruan Dong , Wang Zhi Hua
Published: December 2016

This work studies the large deformation behaviors of a re-entrant honeycomb subjected to the quasi-static tensile loading by employing the finite element (FE) package ABAQUS 6.11-2. The size effect of FE models is firstly investigated. Then, the deformation mechanism and stress-strain curve of a re-entrant honeycomb are discussed. Finally, the plastic Poisson’s ratio is calculated from the true strain and presented.
Large Deflection Response of Rectangular Metal Sandwich Plates with Functionally Graded Foam Core Subjected to Blast Loading
Authors: Xiang Chun Ping , Qin Qing Hua , Wang Fang Fang , Wang Ming Shi , Yu Xue Hui , Wang Tie Jun
Published: December 2016

A theoretical research is carried out to study the large deflection response of a fully clamped rectangular metal sandwich plates with functionally graded foam core subjected to blast loading. Using a new yield criterion for sandwich cross-section with graded foam core, we obtained the analytical solutions for the dynamic response of rectangular sandwich plates. Finite element simulations with gradient layers foam core model are performed to study the dynamic response of the sandwich plates with graded foam core subjected to blast loading. The results of the analyses seem to predict well the deflections that are given numerically.
A New Design of Energy Absorbing Bolt
Authors: Liu Si Cong , Lu Guo Xing , Shu Dong Wei , Zhou Ying Xin , Zhao Zhi Ye
Published: December 2016

Rock movement caused by external explosion loading can damage the nearby tunnel or cavern.To avoid damage, energy absorbing bolts with high load-displacement and large energy absorptioncapacities are required. The deformation and friction of the bolt absorb energy during the rock movementand preventing the structure from damage. To maximize the energy absorption capacity in the limitedspace inside the borehole, we developed a new bolt that utilizes the friction and plastic deformation ofthe sleeve. To develop the new bolt, FE simulation in Abaqus was used to improve designs beforefabrication. Two prototypes of the new design was fabricated and tested by static pull test. The resultsshowed the bolts yielded in the desired way. The experimental results prove the new bolt is capable ofabsorbing large amount of energy and accommodating large displacement.
Impact Combined Shear-Compression Testing of Honeycombs Using a Rotatable Hopkinson Bar
Authors: Hou B. , Tan S.B. , Xiao R. , Zhao Han
Published: December 2016

This paper presents a new method based on the split Hopkinson pressure bar (SHPB) to perform impact combined shear-compression test for cellular materials. For this purpose, a bevelled end is cemented to the input bar and the output bar are rotatable to be parallel to the inclined plane of the bevelled end. The system uses the friction between the specimen and the pressure bars to apply the combined shear compression loading on the honeycomb specimen. Such a testing method is validated by the simulation of the whole loading system (split bar + specimen) using ABAQUS code. It shows that this combined shear-compression test provides a quite accurate measurement. Tests on the 5052 aluminium honeycombs are performed. The shear stress-strain behaviour and the compressive behaviour are separated. The experiment result confirms previous testing results and reveals that the shear component will weaken the compressive strength of the honeycomb at high strain rate.
Crystal Plasticity Analysis of Change in Active Slip Systems of α-Phase of Ti-6Al-4V Alloy under Cyclic Loading
Authors: Kawano Yoshiki , Mayama Tsuyoshi , Kondou Ryouji , Ohashi Tetsuya
Published: December 2016

In this paper, we investigated changes in active slip systems of α-phase of Ti-6Al-4V alloy under a cyclic plastic loading using a crystal plasticity finite element method. In the analyses, a bicrystal model was employed, and the crystallographic orientations were set so as that prismatic  or basal slip system was the primary slip system in each grain. The results showed that there was a mechanism where the basal slip systems could reach the stage of activation under the cyclic plastic loading even though the condition was that the prismatic  slips initially operate. The reason for the activity changes was due to the changes in the incompatibility between the grains by the work hardening, and the effect of the incompatibility on activities of slip systems appeared even in the perpendicular arrangements of the grains to the loading direction.
Dislocation Dynamics Simulation of Interaction between Prismatic Dislocation Loops and Voids in Irradiated Thin Films
Authors: Cai Ying Ying , Guo Jia Pei , Chen Yi Ping
Published: December 2016

At the microscopic scale fast neutron irradiation brings about a high density of small point defect clusters in the form of dislocation loops and voids. And such radiation damage is of primary importance for materials used in nuclear energy production. In the present investigation emphasis is placed on the understanding of the mechanisms involved in the evolution of prismatic dislocation loops by glide in the presence of external free surfaces and those of the voids and in the interaction between dislocation loops and voids within irradiated thin films, so as to simulate in situ Transmission Electron Microscopy (TEM) images of dislocations, which is an indispensable tool for extracting information on radiation damage. By employing 3D dislocation dynamics based on isotropic elacticity and principle of superposition, the calculation results show that the image force is determined by the distance of the dislocation loop from the external and void surfaces and scales with the film thickness; the dislocation glide force is determined by the image stress as well as the loop–loop interaction stress which is in turn governed by the loop spacing. It is also shown that the presence of voids in the thin films has a strong influence on the behaviours of prismatic dislocations.
Subsequent Yield Behavior of Hexagonal Metal with Rolling Texture
Authors: Tadano Yuichi
Published: December 2016

The subsequent yield surface of a rolling textured polycrystalline hexagonal metal sheet is computed using homogenization-based crystal plasticity. Hexagonal metals, such as magnesium and titanium, generally shows poorer formability compared to than cubic metals. The subsequent yielding behavior of a polycrystalline metal strongly affects the formability. The abrupt strain path change method is used to evaluate the direction of plastic flow, allowing the non-normality effect of the hexagonal metal to be quantitatively determined. The homogenization-based crystal plasticity model is used for representing the polycrystalline behavior of a HCP metal. The role of each slip system in the subsequent yield behavior is investigated. The mechanism of subsequent yielding of the HCP metal, which induces the non-normality effect, is discussed.
High Temperature Deformation of Cast ZW11 Magnesium Alloy with Very Large Grain Size
Authors: Rao Kamineni Pitcheswara , Bagheripoor M. , Dieringa Hajo , Hort N.
Published: December 2016

Magnesium (Mg) alloys are considered for biomedical applications due to their matching bone density and biodegradable/abioabsorable nature. Mg-1% Zinc-1% Yttrium (ZW11) alloy was cast using a direct chill slow cooling process to obtain dense ingot with uniform composition. However, the resultant alloy developed a very coarse grained microstructure with a grain size in the range of 2,600 to 4,000 μm (2.6-4.0 mm). The hot working behavior of ZW11 alloy has been investigated using compression tests in the temperature and strain rate ranges of 340-540 °C and 0.0003 – 10 s-1 to evaluate the optimum processing parameters. A processing map has been developed on the basis of the flow stress data. The processing map reveals a window of workability in the temperature and strain rate ranges of 460-540 °C and 0.0003-10 s-1 and regimes of flow instability. The microstructures of the deformed alloy provided support to the processing map.
Development of Simulation Technology for Production of Porous Polymeric Membranes
Authors: Nada Hironori , Kudo Masakazu , Takahashi Junichi , Yamamoto Toshiharu , Hara Hideyuki , Shizawa Kazuyuki
Published: December 2016

Porous polymeric membranes are used for ion exchange membranes, membrane filter and separators of batteries owing to its micro-porous structure. Extension method is one of the inexpensive processes of such membrane. However, any suitable stability condition of the process has not yet been clarified. In this study, SEM (Scanning Electron Microscope) observations in production process are carried out and the simulation technology for production is developed for improvement in productivity. In this simulation model, the evolution equation of microscopic damage, constitutive equation depending on microscopic damage and the homogenization method are used for representation of evolution of micro-porous structure of crystalline polymer. It is indicated that numerical results obtained here are in good agreement with the SEM observations.
Thermo-Mechanical Cyclic Plastic Behavior of 304 Stainless Steel at Large Temperature Ranges
Authors: Ohno Nobutada , Yamamoto Ryohei , Okumura Dai
Published: December 2016

Thermo-mechanical cyclic experiments on 304 stainless steel were performed at several temperature ranges which had maximum temperatures ranging from 350°C to 1000°C and a minimum temperature of 150 °C. Related isothermal cyclic experiments were also performed. Temperature-history dependent cyclic hardening significantly occurred under thermo-mechanical cyclic loading with maximum temperatures around 600°C, whereas almost no cyclic hardening was observed when the maximum temperature was 1000°C. The observed thermo-mechanical cyclic plastic behavior in the saturated state of cyclic hardening was then simulated using a cyclic viscoplastic constitutive model, leading to the following findings. It was difficult to predict the saturated thermo-mechanical cyclic behavior using only the isothermal cyclic experimental data. The saturated thermo-mechanical cyclic behavior was simulated well by introducing a cyclic hardening parameter depending on the maximum temperature. This means that the cyclic hardening parameter should not change with temperature but depend on the maximum temperature in the saturated state of cyclic hardening under thermo-mechanical cyclic loading.
Estimation of Residual Stress Change due to Cyclic Loading by Classical Elastoplasticity Model and Subloading Surface Model
Authors: Higuchi Ryota , Okamura Kazuo
Published: December 2016

The subloading surface model has been formulated and applied to the prediction of cyclic loading behavior. The material function prescribing elastic-plastic transition in the original subloading surface model has been extended so as to describe the inverse and reloading behavior and the strain accumulation in cyclic loading more accurately for steel. In the present paper, the extended subloading surface model was applied to the prediction of the change of the residual stress due to cyclic loading. The four-point cyclic bending test was performed for the specimen that had initial residual stress. The distributions of the residual stress before and after cyclic loading were measured by the X-ray stress measurement method. The simulation to the experiment was performed by the extended subloading surface model. The stress distribution after cyclic loading simulated by the extended subloading surface model was in good agreement with measured one, and was more accurate than that by the nonlinear isotropic/kinematic hardening model.
Estimation of Plastic and Creep Strain Development of SAC Solder under Cyclic Loading by Using Stepped Ramp Waves
Authors: Ohguchi Ken-Ichi , Sasakir Katsuhiko
Published: December 2016

The fatigue tests under both loading conditions of the Fast-Slow and the Slow-Fast were conducted to discuss validity of an inelastic strain analysis method which was proposed previously. The development behaviors of plastic and creep strains during the tests were analyzed by employing the stepped ramp wave (SW) loading. Using the analysis results, the difference of the development behaviors of plastic and creep strains between the Fast-Slow condition and the Slow-Fast condition was clarified. Then, the fatigue failure surfaces obtained from the tests were observed by using SEM to clarify the difference of the fracture surface between the Fast-Slow condition and the Slow-Fast condition. By correlating the aspect of fracture surface with the development behavior of plastic and creep strain, the validity of the proposed inelastic strain analysis method was discussed.
Thermo-Elasto-Plastic Analysis of Pearlitic Transformation Plasticity under Combined Bending-Tensile Loading
Authors: Hamdam M. Arif , Takahashi Kazuki , Tateoka Hayata , Oshita Kenichi , Nagaki Shigeru
Published: December 2016

In a previous study, we showed the anisotropy of plastic strain due to the pearlitic transformation and proposed a hydrostatic pressure-dependent constitutive equation to describe this phenomenon. In the present study, we assess the validity of this model using a bending-tensile loading system to experimentally and numerically analyze and characterize the pearlitic transformation plasticity. First, the maximum bending deflections due to the austenite-pearlite transformation were measured under different loadings and then transformation-plasticity coefficients were determined. Furthermore, as was done for bending-tensile loading tests, the pearlitic transformation plasticity was simulated using Abaqus Standard under the same austenitization and loading conditions as in experiments, and the calculated results for pearlitic-transformation plastic deformation are compared with the experimental results. The results show that the transformation plastic deflection due to the pearlitic transformation decreases with increasing applied tensile stress. In addition, this behavior can be described by a hydrostatic pressure-dependent model in large-deformation theory.
Evaluation of Very High Cycle Fatigue Properties of β-Titanium Alloy by Using an Ultrasonic Tensile-Compressive Fatigue Testing Machine
Authors: Kasahara Reo , Nishikawa Masato , Shimamura Yoshinobu , Tohgo Keiichiro , Fujii Tomoyuki
Published: December 2016

β-titanium alloy has been developed recently because β-titanium alloy has better cold workability, proof stress, and tensile strength. In order to use β-titanium alloy for automobile parts subject to cyclic loading, very high cycle fatigue properties of β-titanium alloy should be investigated. In this study, very high cycle fatigue properties of β-titanium alloy Ti-22V-4Al were evaluated by using an ultrasonic fatigue testing method, which allows us to reduce a fatigue testing period to 1/100 − 1/1000 of that by using conventional testing methods. An S-N diagram and fracture morphology of Ti-22V-4Al in the very high cycle region were investigated. Fatigue failure was observed and subsurface fracture occurred in the very high cycle region.
Improvement of Corrosion Fatigue Strength for TiNi Shape Memory Alloy
Authors: Yamada Kazuki , Matsui Ryosuke
Published: December 2016

In this study, we enhanced the corrosion fatigue life of a TiNi shape-memory alloy wire using a thermal oxidation treatment technique that can generate a passive layer on the wire surface. We followed the following procedure for the thermal oxidation treatment. First, the as-received material with an oxide film was mechanically polished to remove the film using an abrasive paper and a buffing compound. Second, the material was heat-treated in an electrical furnace filled with an N2-20 vol% O2 gas for 1 h at 673 K. Subsequently, the material was allowed to cool in the furnace. The results of this treatment are summarized as follows. (1) A passive layer was uniformly generated on the surface of the TiNi shape-memory alloy wire via thermal oxidation on a macroscopic scale; this significantly improved its corrosion resistance. (2) Thermal oxidation extended the corrosion fatigue life of the treated material more compared with HT in air. In addition, we found that the layer generated via the thermal oxidation treatment can maintain adhesion to the base material even when subjected to a bending strain greater than 1%.
First Principles Calculations of Stress-Induced Structural Changes of Supercooled Borosilicate Glass
Authors: Mylvaganam Kausala , Liu Wei Dong , Zhang Liang Chi
Published: December 2016

Unlike the traditional silicate glasses, borosilicate glasses behave differently because of the addition of boron atoms. Extensive studies have been carried out to understand the abnormal function of boron in glass network. However, it is not clear how the atomic structure of borosilicate glass changes under loading. This paper investigates the behaviour of borosilicate glass under uniaxial compression with the aid of ab initio simulations. Sodium borosilicate glass having 160 atoms and a mass density of 2.51 g/cm3 with composition 3Na2O-B2O3-6SiO2 were equilibrated first at 3500K, then at 2500K, 1500K, 1200K, 1000K, 825K and 625K. Structural analysis showed that at higher temperatures the sodium borosilicate liquid does not have a specific structure. At around 825 K (i.e. around Tg), boron network and silicon network form and remain stable even at a temperature of 625 K. When the supercooled sample at 825K was subjected to uniaxial compression, the stress along the compression direction first increases and then decreases with a change in boron structure, which could modify the behaviour of the borosilicate glass.
Strain Gradient Plasticity: An Application to Plastic Flow Localization Analysis
Authors: Kuroda Mitsutoshi
Published: December 2016

In this paper, strain gradient plasticity theory is extended to include the corner-like effect that is inherent in crystal plasticity. The predictive feature of the extended theory is examined via finite element analysis of a constrained simple shear problem and a plane-strain tension problem involving plastic flow localization. Numerical issues with respect to finite element formulations are also discussed.
Effects of Blowing Ar on Inclusion and Properties of AZ61 Magnesium Alloy
Authors: Lu Yan Qing , Zhu Xue Jin , Hu Xiao Dong , Yao Yao , Cai Han
Published: December 2016

Magnesium alloys have low density, light weight, strength, stiffness, high heat resistance, good shock absorption, convenient recycling use and other characteristics, which make it have the potential of widely using in aerospace, transportation, weapons, 3C products and other fields. AZ61 magnesium alloy melt was purified by using composite refining technology. The AZ61 micro-structure and mechanical properties were studied after casting, rolling and annealing. Using SF6 and Ar mixed gas to protect melting AZ61 magnesium alloy, the effect was good, and size of inclusion was all blow 50μm. The effect of blowing Ar on inclusion removal was obviously. The inclusion contents were decreased from an initial 1.37% to a final 0.58%. Alloy elongation was increased obviously, which was from an initial 4.02% to a final 7.09%.
Temperature Dependent Plastic Deformation Behavior of AZ31 Magnesium Alloy in Uniaxial and Biaxial Compressions
Authors: Shimizu Ichiro
Published: December 2016

Metal forming of magnesium alloys often performed at elevated temperature, because magnesium alloys exhibit peculiar stress-strain relation and inferior ductility compared to conventional metals at room temperature. In the present study, deformation behavior and formability of cast and extruded AZ31 magnesium alloys under uniaxial and biaxial compressions at room temperature and at elevated temperatures were investigated. The results revealed that the compressive stress-strain relation of AZ31 magnesium alloy changed not only with the initial texture but also with the deformation temperature. The temperature dependency of flow stress of the cast alloy was smaller than that of the extruded alloy probably because of less influence of pre-deformation. In addition, the influence of compressive deformation pattern upon flow stress of the extruded alloy remained even at elevated temperature to 523 K. The temperature dependency of compressive fracture was also discussed and it was found that the equi-biaxial condition improved the compressive formability at elevated temperatures.
Evaluation of Micro/Meso/Macro Thermal Properties of Plain-Woven Laminates
Authors: Sato Yoshihiko , Matsuda Tetsuya
Published: December 2016

In this study, thermal properties of plain-woven laminates are analyzed micro-, meso-and macroscopically based on a multiscale approach. For this, the effects of thermal expansion of constituents are incorporated into the micro/meso/macro homogenization method for plain-woven laminates developed by our research group. This method enables us to analyze thermal properties of not only fiber bundles in laminates but also fibers and matrix materials in fiber bundles, in addition to their macroscopic thermal properties. The present method is then applied to the thermal property analysis of plain-woven carbon fiber/epoxy laminates subjected to a macroscopic temperature change from 180°C to 20°C. Two types of carbon fibers, i.e. HTA and P75, are considered in the analysis. It is shown that quite high thermal residual stress can occur in fiber bundles, fibers and a matrix. It is also shown that the present method can predict the change of thermal properties of the laminates depending on the difference of fibers.
Characterizing Fracture Development in Ti-Alloy with I-Type Cracks Using Acoustic Emission and Thermal Infrared Imaging
Authors: Ouyang Hao , Shi Jian , Sakamoto Hidetoshi , Zhao Guang Hui
Published: December 2016

This paper discusses the plastic deformation and fracture development of Ti-alloy under uniaxial tension. The energy dissipation and transfer characteristics in the plastic deformation and fracture processes were analyzed using acoustic emission (AE), thermal infrared (TIR) imaging, and thermocouples. Uniaxial tension tests were carried out, during which TIR images were obtained and the AE energy was observed. The mechanical characteristics of Ti-alloy with I-type cracks were analyzed based on the TIR images, AE energy, and temperature. The plastic work of the Ti-alloy specimen was found to dissipate as thermal energy rather than AE energy. Moreover, the TIR images were correlated well with the AE energy observed during the plastic deformation and fracture processes of the material.
Bending Behavior to Fracture of an Aluminium Alloy Involving Pre-Strain
Authors: Pradeau A. , Thuillier Sandrine , Yoon Jeong Whan
Published: December 2016

The work associated to this abstract is focused on the modelling of an aluminium alloy under the shape of sheet. It characterizes the mechanical behaviour up to rupture of an AA6016 alloy, taking into account the anisotropy and the hardening of the metal. The mechanical tests on which the model is based on consist of uniaxial tension, simple shear and hydraulic bulging performed at room temperature up to rupture, except for the simple shear. The numerical model is constituted of three parts. The choice of the model is suited for ductile fracture and allows for high flexibility, thanks to a total of 21 material parameters. The material parameter identification is realised through an inverse methodology. The objective of such an approach is to minimize iteratively the gap between the experimental and numerical outputs.
Validation of the results is then done with the help of bending tests. The bending tests are performed with and without pre-strain in tension prior to the air-bending. Different amplitudes of pre-strain allows to reach rupture or not in bending, thus giving the possibility to find the value of the parameter controlling the non-linear accumulation of the damage. The correlation between experiments and simulations is proved to be successful and gives a very good representation of the mechanical behaviour of the aluminium alloy studied.
An Adaptive Triangle Mesh Generation for One Step Inverse Analysis
Authors: Liu Yong Cai , Bao Yi Dong , Chen Wen Liang
Published: December 2016

One step inverse analysis is widely used in sheet metal forming process, since its effective prediction in a short time. A non-linear equation about unknown displacements from final part to plane part is deduced in one step inverse analysis, and it is often solved by Newton-Raphson method. The initial value of the displacements is quite essential to convergence of Newton-Raphson method. An adaptive triangle mesh on 3D surface equipped with metric frame using advancing front method is presented in this paper to improve condition number of matrix and enhance the convergence rate. Numerical results are showed that one step inverse analysis has faster convergence when the initial displacement is solved by adaptive triangle mesh compared with the part mesh (more triangles on final part), and one step inverse analysis has a well distribution of thickness when initial displacement is solved by adaptive triangle mesh compared with tool mesh (bad-quality triangles on final part).
Effect of Optimisation Parameters in Topology Optimisation
Authors: Chiu Louis N.S. , Stojanov Daniel , Rolfe Bernard F. , Yan Wen Yi
Published: December 2016

The Bi-directional Evolutionary Structural Optimisation (BESO) method had been used by many authors for the optimisation of structures. This work sets out to investigate the effect of key optimisation parameters utilized in the BESO method, the evolution rate and the filter radius, on the outcome of the optimisation. An understanding of the interaction of these factors in the optimisation process enables a more efficient way to produce optimised components that can fully capitalise on the capabilities of additive manufacturing.
Investigation on Micro-Tensile Test System Platform Used for Test of the Weld
Authors: Ye Tian , Zhang Bu Shen , Liu Jie Jian , Suo Tao
Published: December 2016

In this paper, the mechanical properties of electron beam welding TC4 titanium alloy in different regions of the welded joint were studied by using the Micro-tensile test device and digital image correlation method. In the research, the problem of sample's gripping, strain measurement accuracy, load measurement and lens distortion verification are solved. The main work is as follows: The digital image correlation method, which is non-contact, full field measurement, simple, easy operation and high accuracy, is used to measure the strain of the micro tensile specimen, the fine speckle technique for micro mechanical property testing is developed, furthermore, the measurement accuracy of the digital image correlation method for the micro sample is discussed. Finally, the Micro-tensile test system platform is built which can be used to test the micro mechanical properties of the weld.
Effect of Material Anisotropies of Hot-Rolled High-Strength Steel Sheet on Localized Deformation Behavior in Hole Expansion - Part-I Experimental Consideration to Circular and Oval Hole
Authors: Suzuki Toshiya , Okamura Kazuo , Ishimaru Yuya , Hamasaki H. , Yoshida Fusahito
Published: December 2016

In this study, the effect of the material anisotropies of hot-rolled high-strength steel sheet on localized deformation behavior in hole expansion test has been investigated experimentally. First, the hole expansion test with the circular hole has been conducted to investigate the effect of anisotropies of material properties on the localized deformation behavior around the hole edge. Next, the hole expansion test with the oval hole has been conducted to investigate the effect of the major axis direction of the oval hole on the localized deformation behavior around the hole edge. As a result, it was clarified that the effect of anisotropies of r-value and n-value on the localized deformation behavior is strong, especially the anisotropy of n-value.
Study of Large-Expansion-Ratio Tube Hydroforming with Movable Dies
Authors: Hwang Yeong Maw , Hsieh Shin Yan , Kuo Nai Jung
Published: December 2016

In this paper, finite element codes LS-DYNA and DYNAFORM are used to analyze the plastic flow pattern of a tube hydroforming into a product with large expansion ratio and eccentric axes. Tube hydroforming with a movable die is proposed to enhance the forming capacity of tube hydroforming technology. The relative speed of the axial feedings to the movable die for obtaining a sound product is determined by a geometric analysis. The whole forming processes are divided into two stages. At the first stage, an internal pressure is applied on the inner surface of the tube and two axial feedings and a movable die move forward simultaneouly. At the second stage, one of the axial feedings keeps moving forward, whereas, the movable die moves backward. With this forming schedule for the axial feedings and movable die, products with more uniform thickness distributions are obtained. Finally, experiments of tube hydroforming with a movable die are conducted. Low-carbon steels are used as the tube specimen in the experiments. The simulation results of the product shape and thickness distributions are compared with experimental results to verify the validity of the finite element modeling and the proposed forming schedules.
Research on Stability of Panel Ultrasonic Peening Forming
Authors: Lu Shi Hong , Zhang Wei , Wu Tian Rui , Zhou You Liang , Zhou Zhen
Published: December 2016

Ultrasonic peening forming (UPF) is a newly developed sheet metal forming technology which has been applied in the aerospace engineering. It has the advantages of low equipment cost, portability, no pollution and excellent comprehensive performance of the material after being formed. It will have a broad application in local forming and sizing of airplane wing panel. When the panel is relatively thinner, there will be two different types of instability in the panel surface after being formed, one is a local instability, and the other is a global instability. As to the local instability, an equal ratio partial structure of the wing panel was chose as the experiment research subject, which has the same thickness and local area dimension. The simulation of the ABAQUS software showed the variation of arc height for different thickness panel under different impact amplitude, the results showed that arc height changed negatively when the impact amplitude reached a specified value, namely global instability. When the thickness is up to 3.2mm, the arc height of panel increased linearly implied the global instability stopped. As to the local instability (spherical bulge phenomenon), a partial component with the same proportion substituted for typical complex flat panel. Control variable method is used to study the spherical bulge deformation in local panel region, the relationship between shot peening time and impact amplitude was established. The result showed that he larger impact amplitude, the smaller the impact time was when the local instability occurs. The research results have great guiding significance over the practical manufacturing process.
Asymmetric-Shaped Bending of Adhesively Bonded Sheet Metals
Authors: Tokuda Taro , Uemori Takeshi , Yoshida Tetsuya , Takiguchi Michihiro , Yoshida Fusahito
Published: December 2016

In sheet metal industries, press-formed sheet elements are usually adhesively bonded together at the final stage of assembly. Instead of such a conventional process, the present authors proposed a new technique that first flat sheets are adhesively bonded together and then press-formed into the final products. In previous study, the problem of the die-bending (V-bending and hat-shaped bending) with symmetrical shape has studied. In this study, asymmetric-shaped bending of adhesively bonded sheet metals was investigated by experiments and FEM analysis method. In the case of asymmetric-shaped bending, it was found that the timing of contact from the die corner to the die hypotenuse is early in the press-forming process compared with symmetrical bending (V-bending and hat-shaped bending). For the FEM analysis results, the maximum shear strain in asymmetric-shaped bending was smaller than that in symmetric-shaped bending at the hat-shaped side. Thus, the shape of the die has a large influence on the die-bending of adhesively bonded sheet metals.
Pulsed Laser Surface Treatment for Improvement of Machinability
Authors: Inoue Takuya , Yamada Keiji , Sekiya Katsuhiko , Tanaka Ryutaro , Yamane Yasuo
Published: December 2016

The surface of worn dies are often machined to remove the worn layer and then to re-form its shape. But, in machining operations for hardened materials, the high cutting force sometimes yields bending deflection of low stiffness tools, and results the decrease in productivity and accuracy.In this study, surface treatment by pulsed laser is applied for the high hardness materials to improve the machinability in the machining operation. Die steels are used as work material machined with ball endmills of carbide in the experiments where the cutting force and the actual depth of cut are measured to obtain the specific cutting energy and to evaluate the machinability. In endmilling operations of the nitrided die steels, the actual depth of cut is decreased by the bending deflection of endmill. However, the surface treatment with laser moderates the decreasing of the actual depth of cut. It is confirmed that the surface of workpiece pre-treated with laser has larger roughness than un-treated ones, and the specific cutting energy is decreased by laser surface pre-treatment.
Residual Stress Analysis Considering Phase Transformation and Transformation Plasticity for Heat-Treated Large Size Shaft
Authors: YANAGISAWA Yusuke , Kishi Yasuhiro , Sasakir Katsuhiko
Published: December 2016

The residual stress distributions of the forgings after both water-cooling and air-cooling were measured experimentally. The residual stress occurring during the heat-treatment was also simulated considering the phase transformation and the transformation plasticity. A comparison of the experiments with the simulations showed a good agreement. These results shows that the transformation plastic strain plays an important role in the heat treatment of large forged shafts.
A Computational Investigation on Small Punch Test for Evaluating Fracture Toughness of TRIP Steel at Higher Deformation Rate
Authors: Pham Hang Thi , Iwamoto Takeshi
Published: December 2016

It is considered that fracture toughness of TRIP steel can be evaluated by means of the small punch (SP) test. However, a mechanism of improving fracture toughness in the SP test for TRIP steel under the impact condition might not be clarified through merely experimental works because the effect of strain-induced martensitic transformation (SIMT) coupled with temperature in TRIP steel becomes quite complicated at high deformation rate. Therefore, a computational simulation on the SP test for an evaluation of the mechanism is indispensable. Since the specimen in the SP test will be fractured at a certain level of deformation, it is necessary to express the fracture by incorporating damage model into constitutive equation of the material in simulation of the SP test. In the present study, a finite element analysis is performed for the SP test with a specimen made of type-304 austenitic stainless steel by an inclusion of damage parameter and its evolution equation. After showing the validity of the computation, the effects of deformation rate, temperature, and SIMT on the force-deflection curve and deformation behavior are examined. Then, the mechanism of rate-sensitive fracture toughness in TRIP steel is challenged to be clarified.
Effects of Aging Process in Hot Forming with Synchronous Cooling on Properties of AA2024
Authors: Chen Ming He , Chen Guo Liang , Wang N.
Published: December 2016

Aging treatment is an important process of a new hot forming technology with synchronous cooling (HFSC) for heat-treatable, high-strength aluminum alloys. In this paper, it were carried out respectively experimental research both the artificial aging and natural aging, and subsequent performance testing and microstructure analysis were implemented to investigation the effect of different aging process on the final mechanical properties of AA2024. Research results show that, under the condition of forming temperature range from 475°C to 495°C, the mechanical properties of AA2024 which made by HFSC and after nature aging for 96 hours: yield strength, tensile strength and elongation ratio was up to 499.0MPa, 306.5 MPa and 19.1% respectively; For the artificial aging, at aging temperature of 190°C, aging time of 4～8 hour, its yield strength, tensile strength and elongation ratio was up to 515.0MPa, 398.0 MPa and 11.1% respectively.
A Measurement of Volume Resistivity in Fe-Based Shape Memory Alloy under Tensile Deformation and its Evaluation of Strain Rate Sensitivity
Authors: Cao Bo , Moriyama Yutaro , Fujita Kazuki , Iwamoto Takeshi
Published: December 2016

Fe-based shape memory alloy (Fe-SMA) shows the smaller shape memory effect (SME) compared with the widely-used NiTi alloy. However, because its production cost is much lower than the NiTi alloy, Fe-SMA is challenged to be applied in civil engineering fields such as vibration absorbers and joints. A key of the SME is stress-induced martensitic transformation. Thus, it is important to evaluate an amount of martensite, which can control such excellent performance of Fe-SMA, for increasing a reliability of the Fe-SMA. However, until now, it is quite hard to find studies to evaluate the amount of martensite in Fe-SMA experimentally during deformation at various strain rates, especially during high speed deformation. Instead of the evaluation, it is convenient to capture change in volume resistivity, which has a correlation with the amount of martensite, at various strain rates. In the past, the volume fraction of α’ martensite is evaluated by using a resistance measurement based on the four point-probes method. The advantages of the method are quite simple and relatively high precision, however, its disadvantages are a requirement of strictly-precise reference resistor and power supply, and it is easily affected from noise. In this study, at first, a circuit of Kelvin double bridge with a higher precision is assembled. Then, the rate sensitivity of volume resistivity in Fe-28Mn-6Si-5Cr alloy, which is a kind of Fe-SMA, is experimentally estimated by using the assembled circuit of Kelvin double bridge during tensile testing at various strain rates.
Frangibility Study of Natural Fiber Reinforced Composite Laminates
Authors: Pushparaja Pushparaja , Balaganesan G. , Velmurugan Ramachandran
Published: December 2016

Biodegradable composites are highly encouraged to replace the traditional composites to promote the frangibility and environmental sustainability. In this paper, impact response of natural fiber reinforced composites is carried out by using drop mass set-up. Sisal and coir fibers are reinforced in epoxy matrix and the laminates are made by compression moulding process. Experiments are conducted to predict energy absorption and peak contact force during impact of 6 kg mass. Results are analyzed to find suitability of natural fiber reinforced composites in order to derive the suitable materials for frangibility application.
Analysis of the flooding event of October 22-23, 2005 in a small basin in the province of Bari (Southern Italy)
Authors: Bisantino Tiziana , Pizzo Vincenzo , Polemio Maurizio , Gentile Francesco
Published: December 2016

In the province of Bari the hydrographic network consists of ephemeral streams called lame. In these watercourses the absence of runoff for long periods contributed to unfounded beliefs concerning the hydraulic safety of the landscape and therefore uncontrolled changes in streambeds and floodplains. In these streams high water discharges can occur during heavy rainfalls, as demonstrated by the floods that hit the city of Bari in the late nineteenth and early twentieth century. The flooding event of October 22-23, 2005 can be considered catastrophic as it resulted in six deaths, numerous injuries and substantial damage sustained by road and railway infrastructures at the intersection with the hydrographic network. This study aims to analyse the severity of the event in terms of the response of the landscape with reference to the case of the lama Scappagrano basin, where a Eurostar train derailed due to the collapse of the railway embankment. Coupled hydrological and two-dimensional hydraulic modelling was performed to reconstruct the flood hydrograph and water depths on the upstream side of the embankment. The results were used to set the boundary conditions to analyse the internal stability of the embankment using a finite element method.
Organizational Infrastructure in the Collegiate Athletic Training Setting, Part III: Benefits of and Barriers in the Medical and Academic Models
Authors: Eason Christianne M. , Mazerolle Stephanie M. , Goodman Ashley
Published: December 2016

Context: Academic and medical models are emerging as alternatives to the athletics model, which is the more predominant model in the collegiate athletic training setting. Little is known about athletic trainers' (ATs') perceptions of these models.

Objective: To investigate the perceived benefits of and barriers in the medical and academic models.

Design: Qualitative study.

Setting: National Collegiate Athletic Association Divisions I, II, and III.

Patients or Other Participants: A total of 16 full-time ATs (10 men, 6 women; age = 32 ± 6 years, experience = 10 ± 6 years) working in the medical (n = 8) or academic (n = 8) models.

Data Collection and Analysis: We conducted semistructured telephone interviews and evaluated the qualitative data using a general inductive approach. Multiple-analyst triangulation and peer review were completed to satisfy data credibility.

Results: In the medical model, role congruency and work-life balance emerged as benefits, whereas role conflict, specifically intersender conflict with coaches, was a barrier. In the academic model, role congruency emerged as a benefit, and barriers were role strain and work-life conflict. Subscales of role strain included role conflict and role ambiguity for new employees. Role conflict stemmed from intersender conflict with coaches and athletics administrative personnel and interrole conflict with fulfilling multiple overlapping roles (academic, clinical, administrative).

Conclusions: The infrastructure in which ATs provide medical care needs to be evaluated. We found that the medical model can support better alignment for both patient care and the wellbeing of ATs. Whereas the academic model has perceived benefits, role incongruence exists, mostly because of the role complexity associated with balancing teaching, patient-care, and administrative duties.
Early numeracy performance of South African school beginners
Authors: Aunio Pirjo , Mononen Riikka , Ragpot Lara , Törmänen Minna
Published: December 2016

Early numeracy skills are highly relevant for children’s mathematics learning at school, especially in the initial years when much mathematics learning relies on early numeracy competence. The aim of this study was to investigate the level of early numeracy skills in a sample of South African children in the first months of formal schooling. In this cross- sectional study, there were 443 first graders (206 girls and 237 boys) from Gauteng Province schools. The mean age of the children was 81.61 months (6 years 10 months) (SD 5.40 months). Their early numeracy skills were measured with the ThinkMath Scale. The main finding of this study was that there were statistically significant differences in early numeracy skills between the children when they started first grade. The differences were related to the home language of the first graders in the English medium schools, as well as the type of school (public vs. private). This article concludes that the numeracy competence of the children from the sample was notably varied in the beginning of their formal schooling, which has implications for teaching in the vastly different classroom populations that are all served by one national curriculum.
Problem-based Learning vs Lectures—Comparison of Academic Performances among Dental Undergraduates in India: A Pilot Study
Authors: Markose Joji , Eshwar Shruthi , Rekha K , Naganandini S
Published: December 2016

Introduction

Effective teaching is critical for student learning, especially in professional field, such as dentistry. To cope with the dynamic state of society, the changing pattern of diseases, a clear understanding of the links between basic sciences, technology, and health care systems are crucial. Future health care provider's education system should encourage the development of learning characteristics, such as critical thinking and problem-solving. Problem-based learning (PBL) is one such method.

Aims and objectives

To evaluate the efficacy of PBL vs lecture method of teaching among the final-year dental undergraduates.

Materials and methods

A comparative study with 38 finalyear dental students, 19 students in PBL and 19 students in lecture groups were undertaken. The PBL group was further divided into three smaller groups. Both the groups were given a topic from the undergraduate curriculum of Public Health Dentistry prescribed by Dental Council India (DCI) and were assessed for their academic performances through an internal assessment examination.

Results

Both the groups consisted of higher number of females. Mean marks obtained by PBL group was 6.63 ± 1.80, which was significantly higher as compared with the lecture group which was 4.84 ± 1.17 (p = 0.001**).

Conclusion

Students in PBL group showed better academic performance as compared with students in the lecture group.

How to cite this article

Rekha K, Naganandini S, Eshwar S, Manvi S, Markose J. Problem-based Learning vs Lectures— Comparison of Academic Performances among Dental Undergraduates in India: A Pilot Study. World J Dent 2017; 8(1):59-66.
Communicative and Psychologic Management Protocol for Aggressive Periodontitis
Authors: Rajeev Vini , Arunachalam Rajeev
Published: December 2016

Introduction

Wakefulness about periodontal disease as of today is more than ever before. In spite of advancements in periodontal therapy, limitations do occur. Aggressive periodontitis being the most intricate as the etiopathogenesis is not clearly understood. Effective management of the disease is challenging during the advanced stages of the disease, and with the current therapeutic choices, it seems to be rather incomplete. Coping the patient to the situation is perhaps the least acknowledged and the most undervalued aspect in generalized aggressive periodontitis. As depression/stress influences the immune system and also alters the behavioral habits, it is extremely important to psychologically prepare the patient. Referral to appropriate professional for assistance and counselling should be included in the protocol for periodontal management. Adjustment, adaptation, and confrontation strategies need to be overlooked when preparing the patient. The quality of dentist—patient communication is a key determining factor in patient satisfaction, participation, and compliance with therapeutic planning. This paper aims to think through ways in which communication and incorporation of counselling as part of treatment protocol could improve the experience for the patient and allow better treatment by the team. Henceforth, psychotherapy promotes active participation of the patient rather than a passive receiver of the therapy.

How to cite this article

Arunachalam R, Rajeev V. Communicative and Psychologic Management Protocol for Aggressive Periodontitis. World J Dent 2017;8(1):67-70.
Update to Assessing Economic Damages in Personal Injury andWrongful Death Litigation in Florida
Authors: Williams David R.
Published: December 2016

Current changes in personal injury and wrongful death litigation in the state of Florida.