bluuebunny/crossref_metadata_2025 huggingface dataset:
Probing Temperature-Dependent Viscoelastic Properties of Glassy Materials Using Impact Induced Vibration - Theory and Experiments
Authors: Wang Jian Biao , Ruan Hai Hui
Published: December 2016

The viscoelastic properties of glass under different temperature are essential for the high-precision thermo-plastic-forming of glass. But it is exceptionally difficult to establish a quantitative relation between the thermal history and the viscoelasticity owing to the lack of constitutive model of glassy materials’ relaxation. The present work investigates the validity of Young’s modulus measurement in impulse excitation technology and then the viscosity predicted by Kelvin and Maxwell model. It is demonstrated that the classical Kelvin model, leads to the seemingly unphysical result that viscosity increases with temperature since the experimental loss rate of damped vibration increases with temperature. Although Maxwell model can be employed to explain the positive temperature dependence of loss rate, the magnitude is even smaller than the viscosity at glass transition temperature and is therefore also unreasonable. The further theoretical work suggests the intermediate zone of Kelvin and Maxwell model.
Low Velocity Impact Response of Composite/Sandwich Structures
Authors: Akshaj Kumar V. , Surya P. , Pandit M.K.
Published: December 2016

Dent resistance of structures is one of the important design parameters to consider in automotive, aerospace, packaging and transportation of fragile goods, civil engineering and marine industries. It is important to study the dynamic impact response of various combinations of skin and core materials which can provide desired fracture toughness and highest strength to weight ratio for such applications. This paper discusses the low velocity impact response of sandwich structures having unique combination of mild steel as skin material bonded to thermoplastics/PU foam as core material. HDPE, LDPE and polypropylene were the choice of thermoplastics and an optimum combination of materials for the sandwich structure was evaluated using drop-weight experimental set up. It is observed that LDPE is the best choice of core material for the sandwich structures considered.
Modelling of Instability and Fracture Effects in the Sheet Metal Forming Based on an Extended X-FLC Concept
Authors: Hora Pavel , Berisha Bekim , Gorji Maysam , Hippke Holger
Published: December 2016

The industrial necking prediction in sheet metal forming is still based on the Forming Limit Diagram (FLD) as initially proposed by Keeler. The FLD is commonly specified by the Nakajima tests and evaluated with the so called cross section method. Although widely used, the FLC concept has numerous serious limitations. In the paper the influences of bending on the FLC as well as postponed crack limits will be discussed. Both criteria will be combined to an extended FLC concept (X-FLC).
The new concept demonstrates that the Nakajima tests are not only appropriate for the evaluation of the necking instability, but also for the detection of the real crack strains. For the evaluation of the crack strains, a new local thinning method is proposed and tested for special 6xxx Al-alloys.
Numerical Study of the Effects of Strain Rate and Cell Geometry on Dynamic Behavior of Axial Crushing Honeycomb
Authors: Umeda Tsutomu , Kataoka Kohei , Mimura Koji
Published: December 2016

The axial crushing behavior of commercial metal honeycombs was studied with laying emphasis on the effects of strain rate and geometry on its characteristics as an energy absorber. To investigate the effect of strain rate on the energy absorption capacity, the honeycombs of some metal foil materials were numerically modeled by taking the plastic deformation and failure of adhesively-bonded joint between corrugated sheets and the initial imperfection into consideration. The relationship between the enhancement of mean buckling stress and the strain rate was discussed. Furthermore, A3003 honeycomb model was examined by changing its branch angle from 30° to 180° because the geometrical dispersion will also affect the energy absorption capacity. Typical calculated results under different strain rate and geometric conditions were compared with the corresponding experimental results. It was found that the effect of strain rate on the stress – strain relation of the honeycomb structure is greatly relaxed as compared with that of the material itself. The effects of the boundary condition on the crushing behavior of irregular honeycombs were also discussed.
The Evolution of the {110}<001> and {236}<385> Recrystallization Textures in Cu Alloys and High Mn Austenitic Steels with the Brass Rolling Texture
Authors: Lee Dong Nyung
Published: December 2016

The {110}<112> rolling texture of Cu-22%Zn and Cu-30%Zn sheets having relatively low stacking fault energy transforms into the {236}<385> texture after recrystallization. The 40°<111> relation is approximately satisfied between the {110}<112> and {236}<385> textures. The 40°<111> relation is often addressed as a token of the oriented growth theory for the recrystallization texture evolution. On the other hand, Cu-16%Mn and Cu-1%P alloys and high Mn austenitic steels such as Fe-18%Mn-0.6%C, Fe-18%Mn-1.5%Al-0.6%C, and Fe-18%Mn-3%Al-0.6%C sheets having relatively high stacking fault energy also have the {110}<112> rolling texture, which transforms into the {110}<001> texture after recrystallization. The 40°<111> relation is not established between the {110}<112> rolling texture and the {110}<001> recrystallization texture. The differences are attributed to differences in the stacking fault energies of the materials. The phenomena can be explained by defects that dominates the stored energy of the rolled materials. When the grain boundary energy dominates the stored energy, the {236}<385> texture evolves after recrystallization. On the other hand, when dislocation energy dominates the stored energy, the {110}<001> texture evolves after recrystallization. The {110}<001> recrystallization texture evolution is well explained by the strain-energy-release-maximization theory. The 40°<111> relation is believed to originate in the maximum mobility of <111> tilt boundaries at a rotation angle of 40°.
Anisotropic Elastic Field of 3D Prismatic Dislocation Loops in Bounded and Voided Single Crystal Films
Authors: Guo Jia Pei , Cai Ying Ying , Chen Yi Ping
Published: December 2016

Dislocations in a finite medium bring about image stresses. These image stresses play important roles in the dislocation behavior in finite sized systems such as thin films. Since the ratio of surface to volume is higher for thin films than for bulk materials, dislocation behaviors in thin films are greatly different from those in a corresponding infinite medium, which make it necessary to take into account the effects of free surfaces on the evolution of dislocations in thin films. In the investigations[4, 5], image stresses in an elastic cylinder and thin films are calculated by employing a Fourier transform (FFT) approach and isotropically elastic fields due to dislocations are adopted in their formulation. However, most crystals are anisotropic, and the anisotropic ratio changes with environment physical parameters, such as the temperature, moisture, electron field, magnetic field. A theorem based on anisotropic Stroh’s formula for calculating the image stress of infinite straight dislocations in anisotropic bicrystals has been developed by Barnett and Lothe[6]. Wu et al.[3] recently also make use of the FFT technique to investigate the general dislocation image stresses of cubic thin films, thus extending the formalism by Weinberger et al.[4,5] from isotropic to anisotropic thin films. It is clear that for the assumed in-plane elastic fields to be periodically defined within an unbounded region is an essential and indispensable prerequisite for the above FFT-based approach to be effectively implemented, thus ruling out the possibility of its being employed to analyse image stresses in bounded and/or voided thin cubic films. Our motivation here is then to make an further extension by first calculating the anisotropic elastic fields of dislocation loops in an unbounded thin film with cavities and then invoking FEM and the principle of superposition to seek the image stress solution.
Quantitative Evaluation of Deformation Twinning Behavior in Polycrystalline Pure Magnesium
Authors: Soeda Takeshi , Tadano Yuichi , Hagihara Seiya
Published: December 2016

A crystal plasticity analysis of polycrystalline pure magnesium is conducted to investigate deformation twinning behavior at the crystal grain scale. A dominant factor in the onset of deformation twinning is the resolved shear stress on a twinning system. More than one twin system may simultaneously be activated in a crystal grain, resulting from inhomogeneous stress distribution caused by constraints imposed by neighboring grains. In this study, a pure magnesium polycrystal is modeled using a fine finite element mesh and analyzed using the crystal plasticity model involving deformation twinning. The evolution of deformation twinning at the crystalline scale is numerically investigated, and the present approach demonstrates that two or more twinning systems are be activated in a single crystal grain because of the strong inhomogeneity in the grain.
Multiscale Simulation of Dynamic Recrystallization for α-Mg Phase in Mg/LPSO Alloys Based on Multi-Phase-Field and Dislocation-Based Crystal Plasticity Model
Authors: Kimura Yuichi , Kujirai Sho , Ueta Ryo , Shizawa Kazuyuki
Published: December 2016

Magnesium alloy with Long-Period Stacking Ordered Structure (LPSO) and α-Mg (ordinary HCP structure) phase is expected for a new structural material due to its excellent mechanical properties. Its materials strengthening arises from the kink band formation in LPSO phase and the grain refinement of α-Mg phase in the vicinity of LPSO phase because of recrystallization. In the present study, a multiscale and multiphysics computation for the dynamic recrystallization in α-Mg phase is carried out by coupling the dislocation-based crystal plasticity model for HCP crystals proposed previously by the authors with the multi-phase field model through dislocation density. In the present model, not only the environmental temperature-dependences of nucleation and nucleus growth but also a pinning effect of boundary migration of recrystallized grain boundary owing to existence and influence of additive elements are newly taken into account. Furthermore, grain size behaviors of recrystallized nuclei are investigated for various volume fractions of additive element and ratios of grain boundary segregation.
Numerical Biaxial Tensile Test of Aluminum Alloy Sheets Using Crystal Plasticity Model Implemented in Commercial FEM Software
Authors: Ochiai Shohei , Yamanaka Akinori , Kuwabara Toshihiko
Published: December 2016

To improve the accuracy of forming simulations for sheet metal, the use of material models calibrated by multiaxial material tests is essential. Adequate material models can be calibrated on the basis of the contours of equal plastic work obtained by multiaxial material tests. However, because the tests often require special experimental equipment, they are not widely used by the industry. This paper proposes a methodology for a numerical biaxial tensile test that uses ABAQUS, a popular commercial software package for finite element analysis. In numerical tests, an open-source user-defined material model (UMAT) is used to implement crystal plasticity models. In order to validate our methodology, we performed a numerical biaxial tensile test on a 6000-series aluminum alloy sheet, and the results were compared with those of biaxial tensile tests with a cruciform specimen. The results demonstrated that the proposed numerical biaxial tensile test provides a reasonable prediction of stress-strain curves and the contours of equal plastic work.
Application of Subloading Surface Model to Heat Treatment Simulation Based on Explicit Finite Element Method
Authors: Kawaragi Yusuke , Okamura Kazuo
Published: December 2016

The heat treatment simulation based on the explicit finite element method was developed. The subloading surface model considering the phase transformation was implemented in VUMAT of commercial FE code Abaqus/explicit. It is expected that the error of explicit analysis decrease in the stress integration, since the subloading surface model has an ability of pulling back stress state automatically to the yield surface in the plastic loading process. The formulation of subloading surface model in metallo-thermo-mechanics is presented, and the verification of the presented model is shown by the finite element quenching simulation. The deviation from the yield surface is less than that of the conventional explicit analysis, and the computation time is considerably less than that of the implicit analysis.
Evaluation of the Stress Distribution by the Stepped Load Indentation Test with Constant Depth
Authors: Takita Atsuko , Sasakir Katsuhiko , Ohguchi Ken-Ichi , Fujiki H.
Published: December 2016

For accurate evaluation of the reliability of electronic package, FEM analyses considering the creep deformation of solder joint in-situ should be conducted. It is well known that the indentation creep test has an advantage to evaluate the creep deformation in microscopic region although there are the problems. Authors already modified the indentation creep test and proposed the method to estimate the steady state creep deformation by the modified test. For lead free solders generally used for the solder joint, the transient creep deformation should be measured by the indentation test in addition to the steady state creep deformation. The transient creep strain occurs in the indentation process. Therefore, it needs to separate the strain into the elastic-plastic strain and the creep strain. In this paper, the method to obtain the stress-strain relation using the indentation test is proposed. New indentation test used the stepped load was proposed to obtained the stress variation during the indenter was pushed and conducted by the numerical test. The suitable measurement point to obtain the relationship between the stress and the strain was identified. The stress variation estimated by proposed area well coincides with the equivalent stress variation of the nodal solution. Therefore, if the method to obtain the strain variation during the indentation process by the indentation in future is developped, it may be possible to estimate the stress-strain curve expressed the uniaxial deformation in the microscopic region.
Biaxial Ratchetting Deformation of Solders Considering Halt Conditions
Authors: Tomizawa Yusuke , Suzuki Takehito , Sasakir Katsuhiko , Ohguchi Ken-Ichi , Echizenya Daisuke
Published: December 2016

Recently, Halt (Highly accelerated limit test) is widely employed for evaluation of reliability of electronic products. Halt condition is quite severe. The tested products are subjected to mechanical impacts, thermal shock, and vibration at same time. However, there has not been a reasonable and accurate evaluation method for Halt yet. To construct an accurate evaluation method of Halt, basic deformation mechanism of parts of the electronic products should be clarified from both experimental and theoretical points of view. In this paper, focusing on solder joints of circuit boards of electronic products, ratchetting deformation, especially, biaxial ratchetting deformation of solder joints is revealed from both experimentally and theoretically. The authors have already conducted biaxial ratchetting test combining axial and torsional cyclic loading using a tubular specimen of Type 304 stainless steel. However, as for solders, it is difficult to make tubular specimen. Since size of the solder joints is micron, a small size joint specimen of copper tube and solder is employed in this paper. First, to confirm the quality of the joint specimen such as boundary between copper and solder, both the tensile and cyclic loading tests are conducted at several temperatures using Sn-3Ag-0.5Cu. The basic characteristic of tensile and fatigue failure is obtained from these tests. After the confirmation of the accuracy of the joint specimen, biaxial ratchetting tests are conducted superposing the tensile load on cyclic torsion. The biaxial ratchetting tests are conducted using a biaxial loading testing machine developed for the joint specimens of solder and copper.
Study of Micro Deformation of Austenitic-Ferrite Duplex Stainless Steel by Nanoindentation Method
Authors: Guo Su Juan , Cui Yuan Yuan , Xuan Fu Zhen , Wang Xiao
Published: December 2016

Based on the technology of the nanoindentation, the basic mechanical properties and cyclic deformation behavior of the austenite phase and ferrite phase in an austenitic-ferritic duplex stainless steel was studied. Firstly, from the displacement monotonic indentation experiment, the differences between the basic mechanical properties (e.g. hardness and elastic modulus) of austenite phase and ferrite phase are compared. Then, with the incremental load controlled loading-unloading conditions applied, the indentation depth evolution rule and the indentation creep behavior was studied. Finally, with the load controlled cyclic indentation experiments being conducted, the cyclic evolution rule of displacement into surface were observed, and the influence of different load level on the micro cyclic deformation behavior of each phase were discussed.
Effect of the Non-Associativity of Plasticity Model on the Cyclic Behavior of Geomaterials
Authors: Oka Fusao , Kimoto Sayuri
Published: December 2016

The present paper proposed a cyclic plasticity model with a non-associativity parameter, i.e., the model includes non-associative flow rule and associative one. In the present model, the non-associative parameter controls the non-associativity. The model is derived based on the non-linear kinematical hardening rule with two hardening parameters for both the volumetric and deviatoric strains. From the simulation by the present model, we have found the strong non-associativity leads to the large decrease in the mean effective stress, i.e. almost zero mean effective stress during the cyclic deformations under undrained conditions while the model with associated flow rule is not.
Towards a Better Understanding of the Ratcheting Phenomenon
Authors: Taleb Lakhdar , Keller Clément
Published: December 2016

In this work our goal is to better understand the origin of the cyclic accumulation of the inelastic strain (often called ratcheting) observed in 304L SS subjected to uniaxial cyclic stress control at room temperature. Recent works performed in the frame of small strain assumption attribute this phenomenon essentially to creep [1]. However, outside this frame, it seems that creep is not the only contributor in this phenomenon [2]. New experiments are performed here in order to investigate the role played by creep, cyclic softening, fatigue damage and ratcheting in this observation.
Elastic and Plastic Analysis of O-Ring Seal for Reactor Pressure Vessel
Authors: Shao Xue Jiao , Zheng Lian Gang , Zhang Li Ping , Fu Xiao Long
Published: December 2016

The elasto-plastic analysis for Reactor Pressure Vessel seal is necessary because of nuclear safety is actively demanded. The existed work based on simplified way to simulate the seal ring, such as uniform stress, spring elements, is too conservative. Therefore, it is necessary to simulate seal ring using 3D solid model considering the elasto-plastc deformation. In this paper, the two-dimensional model is adopted to simulate the compressing and springback character of inconel 718 O-ring using nonlinear isotropic hardening constitutive model and contact algorithm. The simulation approach and constitutive model are validated according to the deformation of seal ring using ANSYS. The seal analysis for reactor pressure vessel is achieved by considering complex loads, such as bolt pre-tightening force and temperature/pressure transient with the usage of an elasto-plastic constitutive model. It is found that the deformation of seal ring obtained by finite element is close to true value. The application of 3D solid model can reduce excessive conservatism effectively and improve the precision of seal analysis compare to the simplified method.
Description of Closure of Cyclic Stress-Strain Loop and Ratcheting Based on Y-U Model
Authors: Yoshida Fusahito , Hamasaki H. , Uemori Takeshi
Published: December 2016

This paper proposes a cyclic plasticity model to describe the closure of a cyclic stress-strain hysteresis loop based on the Y-U model. In this model, the backstress moves in a cyclic memory surface following a newly proposed kinematic hardening law. For this model just the same Y-U parameters can be used, and no additional material parameters are needed. By using a supplementary rule, this model is also able to describe ratcheting.
Relaxation Oscillation in the Viscous Flow of Borosilicate Glass
Authors: Liu Wei Dong , Zhang Liang Chi
Published: December 2016

Relaxation oscillation is a nonlinear dynamic phenomenon, commonly observed in viscous-plastic deformation of materials. However, it is the first time that we observed this phenomenon in the viscous flow of borosilicate glass in its super-cooled liquid region. Our investigation identified that the oscillation is caused by the particular microstructure of borosilicate glass. Specifically, the structure of borosilicate glass consists of borate-rich and silicate-rich networks. During the viscous flow, the fast deformation in borate network tends to be localized. However, the network mixing reaction between the borate-rich and silicate-rich networks can slowly relax the fast localized deformation. These two processes occur simultaneously and as a result bring about the relaxation oscillation. Based on this mechanism, the study established a physical constitutive model to predict the relaxation oscillation during the compression of borosilicate glass.
Deformation Properties of 3D Printed Shape Memory Polymer
Authors: Takeda Kohei , Hayashi Shunichi , Ueki Kazunori
Published: December 2016

Recently, the 3D printer which can make products in a short time without cutting or casting has been attracted worldwide attention. If we use the 3D printer, it is possible that a customized product which is well suited to the individual is fabricated with low cost and in a short time. On the other hand, in the intelligent materials, shape memory polymer (SMP) has been practically used. In SMP, shape fixity and shape recovery appear based on the difference of properties of molecular motion between above and below the glass transition temperature in temperature variation. The thermomechanical property of SMP is close to that of the human body around glass the transition temperature. Since SMP has these characteristics, it can be applied to the elements coming into contact with body as a nursing-care robot in the medical field. Hence, if we make a product with SMP using the 3D printer, the new device which is well suited to the individual can be developed. In the present paper, the deformation properties of SMP made by the fused deposition modeling (FDM) 3D printer were investigated. The results obtained are as follows. (1) The deformation resistance and recovery strain in unloading of the 3D printed SMP under a low printing rate are higher and larger than these of the high printing rate. (2) If we heat the 3D printed SMP under a high printing rate, it does not recover the original shape perfectly since the residual stress appears during printing.
Super-Elastic Behavior Analysis of Shape Memory Alloy Vascular Stent
Authors: Tao Liang , Luo Chang , Li Wei Xuan , Zhang Yao Jiang
Published: December 2016

NiTi shape memory alloy (SMA) vascular stent, with good bio-compatibility and super-elastic properties, has become an important medical device in clinical treatment of cardiovascular or cerebrovascular diseases. The free expansion of stent in vessel involves the mechanical behavior of geometric large deformation related to the structure of super-elastic. In this paper, the nonlinear mechanical model for the substructure of NiTi shape memory alloy vascular stent is established, and the displacement deformation equation is derived. The geometric non-linearity of the structure is proved. Furthermore, the geometric nonlinear mechanical model is verified by numerical method. The mechanical analysis model of NiTi shape memory alloy vascular stent is widely used in the field of tracheal stent and so on.
Elasto-Viscoplastic Analysis of Slanting-Weft Woven Fabric Composites Based on Homogenization Theory
Authors: Goto Keita , Tomioka Takuya , Arai Masahiro , Matsuda Tetsuya
Published: December 2016

The elasto-viscoplastic behavior of slanting-weft woven laminates, the fiber bundles of which are not crossed at a right angle, is investigated both macroscopically and microscopically. For this, an analysis model for the [±θ] slanting-weft woven laminate with a cross angle ±θ and its diamond-shaped unit cell are considered. Then, a basic cell, which is quarter of the unit cell, is defined as an analysis domain by considering the point-symmetry of the internal structure. For the basic cell, the homogenization theory for nonlinear time-dependent composites with point-symmetric internal structures is applied. Using the present method, the elasto-viscoplastic analysis of the [±θ] slanting-weft woven laminates subjected to an in-plane uniaxial tensile load is performed. From the analysis results, the macroscopic elasto-viscoplastic behavior and the microscopic stress and strain distributions of the laminates are investigated.
Effects of Two Scaling Exponents on Swelling-Induced Softening of Elastomers under Equibiaxial and Planar Extensions
Authors: Okumura Dai , Mizutani Masahiro
Published: December 2016

We study the effects of two scaling exponents on the mechanical properties of swollen elastomers under equibiaxial and planar extensions. Two scaling exponents are introduced to extend the Flory-Rehner free energy function, and are adjusted based on the previous study. Results show that swelling-induced strain softening is apt to occur under equibiaxial extension compared to uniaxial extension. The additional tensile stress in a lateral direction enables it to occur in relatively poor solvents, and accelerates the onset point. Planar extension shows more complicated responses because the stress in the constrained direction changes dramatically depending on the combination of two scaling exponents and the Flory-Huggins interaction parameter.
Atomistic Model Analysis of Deformation of Carbon Nanotubes under Axial Compression
Authors: Sato Masanobu , Umeno Yoshitaka
Published: December 2016

We carried out molecular dynamics (MD) simulation and atomistic instability (ASI) analysis with carbon nanotubes (CNTs) under axial compression to reveal the mechanism of buckling. We investigated the development of instability mode until buckling of structure. For single-walled carbon nanotubes (SWCNTs), Euler-type buckling was found in relatively thin and long nanotubes, while buckling with deformation change of cross-sectional shape (radial buckling) was found in thick and short carbon nanotubes. The crossover between the Euler-type buckling modes and radial buckling modes was clearly seen in the ASI analysis.
Computational Simulation of Scale-Dependent Non-Uniform Deformation Behavior of Polymer Foam
Authors: Uchida Makoto , Suzuki Keita , Kaneko Yoshihisa
Published: December 2016

Polymer foam is widely used in the engineering field because of various functions such as lightweight, shock absorbing, insulation and so on. However, the strength of the material dramatically decreases with the increase in the volume fraction of the foam. Furthermore, deformation behavior of the material strongly depends on the microscopic heterogeneous structure consisting of foam and polymer wall. In the present study, a micro-to macroscopic deformation behavior of polymer foam is modeled using the rate-form second-order homogenization method. To model the microscopic structure consisting of foam and polymer wall, a hexagonal shape periodic structure was used, and the molecular chain network theory was used to represent an elastic-viscoplastic deformation behavior of polymer wall. The effect of the sizes of macroscopic and microscopic structures on the mechanical behavior of LDPE foam was investigated by computational simulation of bending of cantilever. The bending resistance, in other words, resistance to the strain gradient clearly depended on the comparative size between microscopic and macroscopic structures. For smaller foam model, the strain distributions were point symmetry, and those for different sizes of specimens were same. On the other hand, in larger foam model, strain field was not symmetry, and the magnitude of the asymmetry was emphasized for small specimen. Large difference in the macroscopic strain increasing with the microscopic size induced these asymmetry, and it caused size-dependent bending resistance of the LDPE foam.
Plastic Limit Analysis of Piping with Local Wall-Thinning under Elevated Temperature
Authors: Du Xian He , Liu Ying Hua
Published: December 2016

In order to evaluate the safety and integrity of piping with local wall-thinning at elevated temperature, a numerical method for plastic limit load of modified 9Cr-1Mo steel piping is proposed in the present paper. The limit load of piping at high temperature is defined as the load-carrying capacity after the structure has served for a certain time period. The power law creep behavior with Liu-Murakami damage model is implemented into the commercial software ABAQUS via CREEP for simulation, and the Ramberg-Osgood model is modified to consider the material deterioration effect of modified 9Cr-1Mo steel by introducing the creep damage factor into the elasto-plastic constitutive equation. For covering the wide ranges of defect ratios and service time periods, various 3-D numerical examples for the piping with local wall-thinning defects, and creep time are calculated and analyzed. The limit loads of the defected structures under high temperature are obtained through classic zero curvature criterion with the modified Ramberg-Osgood model, and the typical failure modes of these piping are also discussed. The results show that the plastic limit load of piping containing defect at elevated temperature depends not only on the size of defect, but also on the creep time, which is different from the traditional plastic limit analysis at room temperature without material deterioration.
Application of Uncoupled Damage Models to Predict Ductile Fracture in Sheet Metal Blanking
Authors: Canales Cristian , Boman Romain , Ponthot Jean Philippe
Published: December 2016

The use of uncoupled damage models has been widely used over the years for the prediction of ductile fracture in engineering applications. Nevertheless, its applicability in the prediction of failure has been shown to be limited in the wide range of loading conditions encountered in different manufacturing processes. In order to enhance the formulation of former damage models, the Lode angle has been recently used to characterize the stress states along with the stress triaxiality. This new family of damage models has been demonstrated to give excellent results when proportional loading paths are considered, but its efficiency in more complex applications still need further analysis. To this end, a comparative study of former and recently developed uncoupled damage models is performed in this work. The identification of material parameters is done considering simple mechanical tests under different conditions. Then, the models are used to predict the onset and propagation of cracks during blanking, where numerical predictions are compared with experimental results. Finally, the selected damage models presented a remarkable overall performance in the range of clearances under study.
The Refinement Algorithm of Blank Outline Based on One-Step Inverse Analysis
Authors: Zhou Jia Kai , Bao Yi Dong , Zhou Wan Lin , Cui Jing , Wang Hui Ting
Published: December 2016

Blank dimensions and outlines can be obtained in one-step inverse analysis. Applying more accurate mesh will achieve more precise outlines while usually lead to the increase of computation time. To ensure operation efficiency, this paper proposes a new blank outline refinement algorithm based on one-step inverse analysis. Firstly, the initial configuration is obtained from the final configuration by one-step inverse analysis. Secondly, all outline nodes is projected to the nearest element in the final configuration. Thirdly, according to the position of projected nodes in the element, the coordinate of outline nodes in the initial configuration is achieved through mapping. Finally the number of outline nodes is increased in rounded corners, the coordinate of added nodes are calculated through interpolation. At last all outlines corresponding to characteristic lines of part surface are acquired. Using A-pillar as an example, outlines are calculated by the refinement algorithm and commercial software. It proves that under the same mesh quality, outlines obtained by refinement algorithm become more accurate and smooth, especially in rounded corner. The results can contribute to judge the rationality of blank shape and improve the final part forming property. This algorithm refines the accuracy of outlines and ensures the efficiency of one-step inverse analysis.
Warping Behavior of Thin Strip with Single-Drive Rolling
Authors: Baba Wataru , Miyake Masaru , Yanagimoto Jun
Published: December 2016

For the manufacture of good quality strips by rolling processes, the bending residual stress of the strip is one of the most important qualities to be controlled. Most reports on strip bending behavior have focused on thick plates produced under batch rolling conditions [1, 2], and few reports have examined continuous rolling of thin plates. In this report, we conducted a single-drive rolling test with a strip having the thickness of 0.23mm and a 2Hi test mill with work rolls 410mm in diameter. We also calculated the pressure distribution and warping curvature. The model used here was based on the Orowan model constructed by Morimoto and Yanagimoto [3]. In this calculation, the roll bite was separated into 3 sections, i.e., forward slip region, backward slip region and cross shear region. In the calculation results, the pressure distribution showed the existence of a pressure well in the cross shear region, as also reported by Zorowski et al. [4] The curvature in the calculation result increased as the reduction ratio increased up to 10%, but decreased with increasing reduction ratios larger than 10%. This tendency was the same as the measured curvature in the experiment, and was considered to be caused by the moment by friction force at the cross shear region and also the aspect ratio of the cross shear region.
Numerical Investigation on Mini Internal Gear Forging Process
Authors: Chen Chang Cheng , Wu Bo Heng
Published: December 2016

Gear transmission system is closely related to the consumer electronics products, factory automation industry, science and technology toys, medical equipment, electric hand tools, home appliances and the low-speed high torque applications of automotive industry. In the past, the almost manufacturers produced the metal gear of transmission system mostly by machining method. The gear machining tools of relative processing are mired in difficulties when the gear was miniaturized. In terms of the way of micro forging to produce the gear transmission components, not only a high accuracy and production rate being much times of gear machining, which achieves a significant competitive advantage. This study aims to conduct a research for a mini internal gear forging formability. For this purpose, the finite element method was used to analyze the mini internal gear forging process based on a die set of involute gear profile model. From the simulation results, the characteristic of flowing field of material filled into the gear mold and the induced strain and stress distribution were observed. All findings can be significantly provided to develop the manufacturing process of mini gear forging.
Springback Analysis of Aluminum Alloy Sheet Metals by Yoshida-Uemori Model
Authors: Uemori Takeshi , Fujii Kento , Nakata Toshiya , Narita Shinobu , Tada Naoya , Naka Tetsuo , Yoshida Fusahito
Published: December 2016

During the last few decades, the enhancement of prediction capability of the sheet metal forming have been increasing dramatically. High accurate yield criteria and wokhardening model (especially, non-linear kinematic hardening model) have a great importance for the prediction of the final shapes of sheet metal. However, the predicted springback accuracy of aluminum alloy sheet metal is not still good due to their complicated plastic deformation behaviors.In the present research, the springback deformation of aluminum alloy sheet metals were investigated by finite element calculation with consideration of initial anisotropy and the Bauschinger effect. In order to examine the effect of the initial and deformation induced anisotropy on the springback deformation, several types of high accurate yield function and hardening rules are utilized in the present research. The calculated springback by Yoshida 6th yield function [1] and Yoshida-Uemori model [2] shows an excellent agreement with the corresponding experimental data, while the other models underestimate the springback.
An Experimental and Numerical Study on Forming Force, Fracture Behavior, and Strain States in Two Point Incremental Forming Process
Authors: Wang Chen Hao , Daniel William J.T. , Lu Hai Bo , Liu Sheng , Meehan Paul Anthony
Published: December 2016

Two-point incremental sheet forming process (TPIF) is an emerging and promising manufacturing process for the production of complex geometries or customized functional sheet components. In this study, the single-pass TPIF process is investigated using experimental and numerical approaches to study the forming force evolution, fracture behavior and strain states with a varied wall angle hemisphere shape. It can be concluded that both the peak force and fracture depth increases with tool diameter and incremental depth in TPIF process. It seems the deformation mechanism or the failure mechanism is strongly dependent on particular forming conditions based on a failure parts morphology observation. FEM simulation results indicated that the major plastic strain is positive while the minor plastic strain is negative in the TPIF process on a hemiphere shape. it can be concluded that the strain increment and total equivalent plastic strain is affected by both tool diameter and incremental depth.
Effect of Material Anisotropies of Hot-Rolled High-Strength Steel Sheet on Localized Deformation Behavior in Hole Expansion - Part-II Simulation and Evaluation of Anisotropic Yield Function
Authors: Okamura Kazuo , Suzuki Toshiya , Ishimaru Yuya , Hamasaki H. , Yoshida Fusahito
Published: December 2016

In this study, the circular hole expansion process of high-strength steel sheet is numerically simulated using FE analysis with Hill48 quadratic, Gotoh’s fourth order, Yld2000-2d and Yoshida’s sixth order polynomial yield function. The effects of anisotropic yield functions on local reduction of thickness are evaluated. The thickness distribution around the circular hole edge at just before necking depends on the initial hole diameter. When the initial hole diameter is relative large, the simulation results give almost same thickness distribution among different yield functions. While the initial hole is relative small, individual characteristics of yield function becomes clear and the sixth order yield function gives the best prediction.
An Experimental Evaluation of Energy Absorption of TRIP Steel by Small Punch Test
Authors: Hayashi Asuka , Iwamoto Takeshi
Published: December 2016

TRIP steel possesses high strength and excellent ductility. In addition, it is possible that TRIP steel indicates high energy absorption so that TRIP steel is expected to apply to automotive members. To design the members made of TRIP steel, it is important to clarify its energy absorption characteristic at various deformation rates. In the previous study, the energy absorption characteristic of TRIP steel is evaluated by J-integral under quasi-static to dynamic condition by using a thick specimen based on ASTM standard. However, by using such thick specimens, it is difficult to conduct the three-point bending test under impact condition because of high ductility in TRIP steel. A small punch (SP) test is the experimental method which can evaluate fracture parameters such as J-integral. By using a conventional use of small specimen in the SP test, it is possible to evaluate J-integral of TRIP steel under impact deformation. In this study, energy absorption characteristic of TRIP steel is investigated by SP test under different deflection rates. Then, the relationship between the values of J-integral obtained by previously conducted three-point bending test and the SP test of TRIP steel is discussed.
Development of a Rubber Diaphragm Forming Simulation System Based on ABAQUS
Authors: Jin Xia , Zhuang Lu Wei , Bao Yi Dong , Han Yong Kun
Published: December 2016

Rubber diaphragm forming is one of very important manufacture method in aircraft manufacturing. In order to achieve the purpose of precise forming and high efficient simulation of the rubber diaphragm forming for the aircraft sheet metal parts in CAE software of ABAQUS, first the blank design module is developed and embedded into ABAQUS in the use of one step inverse finite element method because there is no blank design algorithm in ABAQUS. Then according to the characteristics of the rubber diaphragm forming, development technology on ABAQUS is applied to develop a rubber diaphragm forming simulation system based on combining Graphical User Interface GUI and the scripting language of Python. In this system, the parameter definition plug-in and finite element modeling module are designed to save a lot of tedious steps, so the blank parameters and process parameters can be defined rapidly and the simulation process can be simplified in ABAQUS, which can greatly improve the analysis speed and improve the efficiency of the finite element method. Finally the accuracy and effectiveness of the rubber diaphragm forming simulation system are verified by the simulation of a typical part that is a door frame bracket of aircraft.
Improvement of Shape Accuracy in Press-Formed Parts of High-Strength Steel by Springback-Root-Cause Analysis
Authors: Hiramoto Jiro , Urabe Masaki , Ishiwatari Akinobu , Yoshida Fusahito
Published: December 2016

Springback is one of the most serious problems in high-strength steel-sheet forming to produce automotive body parts. A springback-root-cause analysis method was developed to identify the areas of stresses at the bottom dead point, which are the most influential in springback. The analysis method of using springback driving stresses, that is, the difference between stresses before and after springback, is more accurate to eliminate the effect of the residual stresses on springback. This analysis method was applied to both a simple model and the forming of an actual part to verify this analysis method. The areas of stresses that have a major impact on springback were identified. A countermeasure against the actual part springback based on this result was devised and it was clarified that the countermeasure is effective on the springback.
Study on Magnesium Alloy Thin Sheet by Symmetric Rolling and Asymmetric Rolling Process
Authors: Wang Zhen Ming , Zhao Hong Yang , Hu Xiao Dong , Lu Yan Qing , Ju Dong Ying
Published: December 2016

Magnesium alloy is honored as green engineering material for its low density, high specific strength, high specific rigidity, well cutting processing property, well electromagnetic shielding property, heat conduction and easy to recycle. In this paper, AZ31 Magnesium alloy sheet at difference thickness were prepared by symmetric and asymmetric rolling employed with six-roller mill. Microstructure of the two kinds of rolling magnesium alloy thin sheets at 0.5mm thickness were investigated. The grain distribution of AZ31magnesium alloy sheets made by asymmetry rolling at room temperature are more uniform than those made by symmetry process. The grains made by asymmetry are more tiny and the tensile strength and elongation increased obviously and the mechanical properties got better. At room temperature, value of n increased. Large value of n benefit to stamping forming. At room temperature, the value of LDR of asymmetry rolling sheets is 1.26, which was higher than symmetry rolling. So asymmetry rolling benefits to stamping forming.
Effect of Stress Relaxation on Springback of Steel Sheet in Warm Forming
Authors: Saito Naoko , Fukahori Mitsugi , Hisano Daisuke , Hamasaki H. , Yoshida Fusahito
Published: December 2016

Springback of a high strength steel (HSS) sheet of 980 MPa grade was investigated at elevated temperatures ranging from room temperature to 973 K. From U-and V-bending experiments it was found that springback was decreased with increasing temperature at temperatures of above 573 K. Furthermore, springback was decreased with punch-holding time because of stress relaxation. In this work, the stress relaxation behavior of the steel was experimentally measured. By using an elasto-vicoplasticity model, the stress relaxation was described, and its effect on the springback of sheet metals in warm forming was discussed theoretically.
Determination of the Anisotropic Hardening of Sheet Metals at Large Strain from Stretch Bending Test
Authors: Capilla Gustavo , Hamasaki H. , Yoshida Fusahito , Suzuki Toshiya , Okamura Kazuo
Published: December 2016

The present study aims to determine stress-strain curves at large strains of sheet metals under the uniaxial stress state by using the in-plane stretch-bending test. The combined Swift-Voce model, which describes the large-strain work-hardening of materials by means of a weighting coefficient μ, was used for FE simulation of the stretch-bending. The coefficient μ was determined by minimizing the difference in punch stroke vs. bending strain responses between the experimental data and the corresponding experimental results. By using this inverse approach, stress-strain curves of two levels of high-strength steel sheets of a precipitation hardening type, 590R and 780R, in three sheet directions (0, 45 and 90o from rolling direction), were determined.
On the Scale Dependence of Micro Hydromechanical Deep Drawing
Authors: Sato Hideki , Manabe Kenichi , Furushima Tsuyoshi , Wei Dong Bin , Jiang Zheng Yi , Alexandrov Sergei
Published: December 2016

Tooling feature size to minimum thickness becomes small in micro scale products and its ratio affects the deformation behavior in micro sheet forming significantly. In this study, the effect of this relative tooling feature size on drawing characteristics and effects to improve the drawability, such as friction holding effect, hydrodynamic lubrication effect and compression effect by blank edge radial pressure, in micro hydromechanical deep drawing (MHDD) are investigated using plasticity theory and numerical simulation. The results show that the micro drawing characteristics in MHDD can be improved by applying counter pressure. However, the required fluid pressures for friction holding and hydrodynamic lubrication effects increase as the relative punch diameter and/or die shoulder radius to thickness decrease, although the compression effect by radial pressure on the blank edge is independent of the relative tooling feature size.