bluuebunny/crossref_metadata_2025 huggingface dataset:
Microscopic Interlaminar Stress Analysis of CFRP Cross-Ply Laminate Using a Homogenization Theory
Authors: Matsuda Tetsuya , Okumura Dai , Ohno Nobutada , Kawai Masamichi
Published: March 2009

Microscopic stress distributions at an interlaminar area in a CFRP cross-ply laminate are
analyzed three-dimensionally using a homogenization theory in order to investigate microscopic
interaction between 0°- and 90°-plies. It is first shown that a cross-ply laminate has a point-symmetric
internal structure on the assumption that each ply in the laminate has a square array of long fibers. Next,
the point-symmetry is utilized to reduce the domain of homogenization analysis by half. Moreover, the
substructure method is combined with the homogenization theory for reducing consumption of
computational resources. The present method is then employed for analyzing stress distributions at an
interlaminar area in a carbon fiber/epoxy cross-ply laminate under in-plane off-axis tensile loading. It is
thus shown that microscopic shear stress significantly occurs at the interface between 0°- and 90°-plies.
It is also shown that the microscopic interaction between two plies is observed only in the vicinity of the
interface.
Application of Time-Temperature-Stress Superposition Principle to Nonlinear Creep of Poly(methyl methacrylate)
Authors: Luo Wen Bo , Wang Chu Hong , Zhao Rong Guo
Published: March 2009

The uniaxial tensile creep of a commercial grade Poly(methyl methacrylate) was
measured for 4000 seconds under various temperatures and stress levels ranging from 14 oC to
26 oC and 6 MPa to 32 MPa. The resultant creep compliance curves depart from each other for
stresses beyond a critical value which varies with temperature, indicating nonlinear viscoelastic
behavior. The time-temperature-stress superposition principle (TTSSP) was used to construct a
smooth master compliance curve with a much longer time-scale interval from the short-term tests at
higher stresses and temperatures. It is shown that the master curve covers a period of over 290 days,
which is nearly 3.9 decades longer than the test duration. Moreover, it is verified that the
time-temperature shift factors are dependent on stresses at which the shifts are applied, and that the
time-stress shift factors are dependent on reference temperatures.
Mechanical Properties of Bulk Glassy Metal after Deformation under High Temperature Conditions
Authors: Yoshikawa Takamasa , Tokuda Masataka , Inaba Tadashi
Published: March 2009

Bulk glassy metal is an alloy with the vitreous amorphous structure. Because of various
excellent properties, this material is expected to use as an alternative structural material for several
engineering applications very well. Although bulk glassy metal is very little deformed plastically in
the room temperature, it shows the huge super-plastic behavior over the high temperature. However,
there is not many reports mentioned about the mechanical properties of bulk glassy metal after plastic
deformation under high temperature condition. From the above point of view, in this study, we have
investigated the lower bound of temperature at which Zr55Cu30Al10Ni5 bulk glassy metal can be
plastically deformed in uniaxial tensile load. Furthermore, it is focused on the strength property of
bulk glassy metal in the room temperature after deformed under various high-temperature conditions.
In the experimental result, when this material was heated at temperature of 685[K] or higher, this
material crystallized and the mechanical strength in room temperature drastically decreased to
200[MPa], although this material as cast had the strength over 1500[MPa]. However, this material
showed sufficiently the plastic deformation at temperatures of 643[K] and the strength in room
temperature after cooling was equal to as cast. It is supposed that the strength depend on its atomic
structure, i.e., amorphous or crystalline, and the change of its structure is affected strongly by heating
process.
Research on the Failure Process of Rocks under Tensile Loading Using Elasto-Plastic CA Model
Authors: Pan Peng Zhi , Feng Xia Ting , Zhou Hui
Published: March 2009

A series of numerical experiments are conducted by the Elasto-Plastic CA model, which
was successfully used to simulate the rock failure process under uniaxial compression in previous
work by the authors, to obtain the failure processes of heterogeneous rocks as well as the stress-strain
relation and strain-AE relation under tensile loading at meso level. The model can consider the
heterogeneity of the materials conveniently, and has the advantages of localization, parallelization
etc. By constructing some local simple rules, the model can perfectly simulate the self-organization
process of rock failure process. In this paper, the domain is discretized into the system composed of
cell elements which are assumed to conform to the constitutive laws of elasto-brittle-plasticity. The
Weibull’s stochastic distribution is introduced to represent the heterogeneity of rock materials, and
Mohr-Columb criterion with tension cut-off is considered as the yield criterion. The process of crack
initiation, propagation and coalescence is well simulated and the results obtained reproduce the main
features known of rock behavior, both at meso and overall stress-strain levels.
Shape Memory Composite of SMA and SMP and its Property
Authors: Tobushi Hisaaki , Hoshio Kazumasa , Hayashi Shunichi , Miwa Norio
Published: March 2009

The shape-memory composite belt with a TiNi-SMA wire fiber and a polyurethane-SMP sheet
matrix was fabricated. The bending actuation characteristics of the belt were investigated by the
thermomechanical tests. The results obtained can be summarized as follows. (1) Residual deflection close to
the maximum deflection is obtained by cooling under constant maximum deflection. The residual deflection
disappears by heating under no load. Both the rate of shape fixity and the rate of shape recovery are close to
100%. (2) Recovery force appears by heating under constant residual deflection. The recovery force is 93-94%
of the maximum force. The development of high functionality of shape-memory composite elements is
expected by various combinations of SMAs and SMPs.
The Influence of the Fluctuation of Micro-Polar Boundary Conditions on the Evolution of Shear Strain Localization in Granular Materials
Authors: Bauer Erich , Tantono Sendy F. , Huang Wen Xiong
Published: March 2009

In this paper the interface behavior between an infinite strip of a granular mate-
rial and a rough boundary under plane shearing is numerically investigated using a micro-polar
continuum approach. Particular attention is paid to the influence of a fluctuation of micro-polar
boundary conditions along the interface on the evolution of shear strain localization within the
granular material. The mechanical behavior of the cohesionless granular material is described
with a micro-polar hypoplastic model. The evolution equations for the stress and the couple
stress are non-linear tensor valued functions which model inelastic behavior. The investigations
show that the micro-polar boundary conditions have a strong influence on the location and
thickness of the zone of strain localization when relative displacements within the interface are
excluded.
Unified Three-Dimensional Revision of Modified Cam Clay Model
Authors: Li Hang Zhou , Liao Hong Jian , Sassa Kyoji , Wang Gong Hui
Published: March 2009

According to unified strength parameters obtained from unified strength theory, the slope
of critical state line is modified to reflect critical states of different geomaterials under general stress
states. Yield function that can consider the effect of the third deviatoricic invariant is proposed, and
an elasto-plastic constitutive model is established by adopting non-associated flow rules;
furthermore, methods of overcoming singular points on the yield surface are discussed. The
proposed model is verified by true triaxial tests of clay, and results show that the model can well
predict stress-strain relationships.
Stringer Stiffened Cylinders on Local Supports – The Plastic Buckling Behavior
Authors: Vanlaere Wesley , Van Impe Rudy , Lagae Guy , De Strycker Maarten
Published: March 2009

The buckling behavior of locally supported cylinders is a topic that is still the subject of
many investigations. Adequate design rules have yet to be incorporated into the codes. In this
contribution, the plastic buckling behavior of a stiffened cylinder on local supports is studied. Our
research consists of two principal components, i.e. experiments on scale models and numerical
simulations. Here the numerical simulations are discussed. Firstly the effect of the yield stress is
investigated. In order to find a design rule, a large parametrical study has to be performed. In this
contribution, the characteristics and the results of this study are described. The simulations show
that for a radius to thickness ratio of the cylinder equal to 250, the optimal stiffener dimensions
correspond with a plastic buckling phenomenon and a failure stress that is larger than the yield
stress. For larger values of the ratio, the elastic instability of the stiffeners precedes the plastic
buckling and this shows that the stiffener configuration is not suitable for these values of the radius
to thickness ratio.
Second-Order Elasto-Plastic Analysis of Frames by Differential Quadrature Element Method
Authors: Nie G.J. , Zhong Zheng
Published: March 2009

A new differential quadrature element model is presented for the second-order
elasto-plastic analysis of frames in this study. The new model is based on the differential quadrature
method (DQM) and the finite-cut technique. Firstly the basic equilibrium differential equations of
members, the compatibility conditions of joints and the equilibrium equations of joints for the
second-order analysis of frames are established. The differential quadrature method is used to
discretize the basic equations and then the stiffness equations of the whole structure can be derived.
While the corresponding boundary conditions are considered, the mechanical behavior of frames can
be obtained. The yielding development along the axis of the member can be taken into consideration
by selecting several discrete points and simultaneously the yielding development across the section
can be considered using the layered approach. The full historical second-order elasto-plastic analysis
is achieved by the incremental iterative algorithm. According to the new model derived in this paper,
the interrelated structural calculating program is worked out. The results of numerical examples
demonstrate the validity of the differential quadrature element model (DQEM). The new model can
be used in the second-order elasto-plastic analysis of arbitrary frames.
Study on Calculation Method of Press Straightening Stroke Based on Straightening Process Model
Authors: Li Jun , Xiong Guo Liang
Published: March 2009

It is difficult to determine straightening stroke precisely for automatic straightening
machines. The existing calculation method of straightening stroke is based on straightening curvature
equation. Because the initial curvature is obtained by curve fitting method, the method is inconvenient
to use and its accuracy is not well. In this paper, a method to calculate straightening stroke based on
straightening process model is put forward. So the mathematic load-deflection model of straightening
process must be established at first. The straightening process model for shafts is developed according
to the elastic-plastic mechanics theory. By using the model, the straightening stroke can be calculated
directly according to the initial deflection of the bent part. It is advantageous to use and to decrease
errors. Comparing with FEM results and experimental results, the calculation results by the model are
exact and the errors are small. So the validity and the accuracy of the method are verified. It will be
helpful to the development of automatic straightening machines.
The Occurrence Limit of Strain Nonuniformity in Thin-Walled Cylinders Subjected to Cyclic Torsion
Authors: Kobayashi Masami , Uetani Koji , Mikami Tomohiro
Published: March 2009

The symmetry limit theory for 3-D continua developed by the authors, is applied to
predictions of the occurrence limit of nonuniform strain in cylinders subjected to cyclic torsion.
Bifurcation analysis of a steady-state path, which was defined as a continuous sequence of steady
states generated under continuous increasing amplitude cyclic loading, is performed for the cylinder
model. The deformation mode with very short wavelength in the circumferential direction is
obtained, analogous to that in the internal buckling of a rigidly confined continuum shown by Biot.
It is shown that this circumferential short-wave mode occurs at much smaller amplitude than the
bifurcation under monotonic torsion.
Forming Limits Prediction of FCC Sheet Metal Adopting Crystal Plasticity
Authors: Lee Wing Bun , Chen Yi Ping , To Sandy
Published: March 2009

A rate-dependent crystal plasticity constitutive model together with Marciniak-
Kuczynski(M-K) approach is employed to perform numerical simulations of forming limits
diagrams(FLDs). An initial imperfection in terms of a narrow band is adopted to initialize the sheet
necking. Homogeneous deformations inside and outside the band are assumed and the enforcement
of compatibility and equilibrium conditions is required only on the band interface. Constitutive
computations are carried out on two aggregates of FCC crystal grains, with each representing one of
the two zones, respectively. Taylor homogenization assumption is employed to establish the link of
stress between single crystal and polycrystal, and to derive an average response of the aggregates.
The same initial texture is imparted to the two aggregates and their evolutions will be traced in the
necking process. Factors affecting the FLDs prediction, such as imperfection intensity, initial
texture, strain rate sensitivity and crystal elasticity will be taken into account. The above procedure
will be applied to an annealed aluminium alloy sheet metal
Multiscale Modeling and Simulation of Crystal Plasticity Based on Dislocation Patterning in Polycrystal
Authors: Yamaki Naoshi , Aoyagi Yoshiteru , Shizawa Kazuyuki
Published: March 2009

A multiscale model on dislocation patterning of cell structure and subgrain for
polycrystal is newly developed on the basis of reaction-diffusion theory. A FD simulation for
dislocation patterning and a FE one for crystal deformation are simultaneously carried out for a
FCC polycrystal at large strain. Reflecting stress value on stress-effect coefficients, it is numerically
predicted that the evolution of dislocation pattern in a polycrystal is different in response to the
stress condition of each grain.
New Physical Interpretation of Incompatibility and Application to Dislocation Substructure Evolution
Authors: Aoyagi Yoshiteru , Hasebe Tadashi
Published: March 2009

Physical interpretations of the incompatibility tensor are extensively discussed and applied
to model several practically-important dislocation substructures in metallic materials. This paper
firstly performs a tangible decomposition of the incompatibility tensor into the two types of defects by
introducing Nye’s contortion tensor, and also clarifies the interrelationship with expressions given
based on differential geometry. The effects on the evolutions of intra-granular substructures like cells
and geometrically-necessary type bands are examined based on finite element simulations on
multi-grain models under tension and simple shear with several representative orientations.
Tensile Mechanical Properties of AM50A Alloy by Hopkinson Bar
Authors: Shu Dong Wei , Zhou Wei , Ma Guo Wei
Published: March 2009

An ultralight magnesium alloy AM50A has been investigated for its potential to be used
in aerospace and automotive industry. The dynamic stress strain relation of aluminum 6061 T6 and
the magnesium alloy AM50A have been obtained by using the Hopkinson bar apparatus. The strain
rates range between 600 s-1 and 1300 s-1. The Al 6061 T6 results tally well with those in literature.
The magnesium alloy AM50A displays about 50% higher tensile stress at the strain rate of about
1300 s-1 than at static.
Improvement of Measurement Accuracy of Non-Coaxial Hopkinson Bar Method
Authors: Umeda Tsutomu , Mimura Koji , Makino Masaki
Published: March 2009

The high measurement accuracy in dynamic tension testing is required for designs and
numerical simulations based on the accurate modeling of stress-strain relations at various strain-rates.
The non-coaxial Hopkinson bar method (NCHBM) is one of the recently proposed methods for dynamic
tension tests. In this study, the accuracy of the stress-strain relations obtained on the basis of NCHBM
was investigated by the analysis based on FEM and by experiment. The FE models of NCHBM
apparatus and plate-type specimens of various dimensions were made in detail. The target materials
employed in this study were mild steel and SUS316 stainless steel. The effects of the rising, the
dimensions of specimen, and the strain rate were examined systematically. The results calculated for the
specimens of SUS316 were compared with those obtained by experiment. At last, the improving
methods of the specimen fixation were proposed.
Solid Shell Element and its Application in Roll Forming Simulation
Authors: Li Da Yong , Luo Ying Bing , Peng Ying Hong
Published: March 2009

Solid shell element models which possess only translational degrees of freedom and are
applicable to thin structure analyses has drawn much attention in recent years and presented good
prospect in sheet metal forming. In this study, a solid shell element model is introduced into the
dynamic explicit elastic-plastic finite element method. The plane stress constitutive relation is
assumed to relieve the thickness locking and the selected reduced integration method is used to
overcome volumetric locking. The assumed natural strain method is adopted to resolve shear
locking and trapezoidal locking problem. Two benchmark examples and a stage of roll forming
process are calculated, and the calculating results are compared with those by solid element model,
which demonstrates the effectiveness of the element.
Dynamic Mechanical Behaviors of Aluminium Foam Filled Circular Tubes under Transverse Compressive Load
Authors: Zhang Xiao Qing , Huang Xiao Qing , Liu Yi Ping , Tang Li Qun , Liang Shan Li
Published: March 2009

The experimental studies on the static and dynamic mechanical properties of aluminium
foam material are presented first. Finite element models of four structures, including circular tube
filled and bonded with aluminium foam, circular tube filled but unbonded with aluminium foam,
single aluminium foam column and empty aluminium tube, under dynamic transverse compression
are established by FEMB code. The dynamic mechanical behaviors of the structures are analyzed
using LS-DYNA finite element code. The simulating results at certain cases are compared with
experimental measurements and the satisfying consistency confirmed the validity of the model. The
further numerical simulations are carried on the dynamic mechanical behaviors of four structures
with outer tubes of different wall-thickness. It is found that aluminium foam filling can greatly
improve the load-bearing capacity and energy-absorbing efficiency of structures. On the other hand,
the effect of the aluminium outer tube on the structure is obvious compared with single aluminium
foam column, in spite of the foam core and the tube are bonded together or unbonded. Another
result can be seen that the bonding between the foam and outer tube affects the structure weakly for
both thinner and thicker tubes. Finally, the simulating results show that the thicker wall of tube can
improve the load-bearing capacity and energy-absorbing ability of the structure.
Compressive Properties of Porous Metals with Homogeneous Pore Characteristics
Authors: Hakamada Masataka , Asao Yuuki , Kuromura Tetsumune , Yamada Yasuo , Chen Y. , Kusuda Hiromu , Mabuchi Mamoru
Published: March 2009

Spacer method is excellent technique of processing porous metals with well-controlled
pore characteristics such as porosity (up to 90%) and pore size (as small as several hundred
micrometers). Compressive properties of porous aluminum fabricated by the spacer method are
investigated. They were subjected to monotonic compression tests at room temperature, and showed
less fluctuated flow stress during their compressive deformation than conventional porous aluminum
alloy, reflecting their homogeneous pore characteristics. Also, shortening behavior of the porous
aluminum fabricated by the spacer method during cyclic compression was significantly differed from
that of conventional porous aluminum alloy. Therefore, it can be concluded that the homogeneity of
pore characteristics is responsible for compressive properties of porous metals. Monotonic
compression tests on porous copper specimens with various porosities, which were made by the
spacer method, were also conducted. The yield stress of the porous copper with high porosity (or low
relative density) depended on the relative density more strongly than that of the porous copper with
low porosity (or high relative density). It is presumed that porous metals with high porosity and ones
with low porosities have different deformation mechanisms.
A Study on the Application Infrared Thermography Camera for the 7FA Gas Turbine Blade Covering Crack Detecting
Authors: Choi Choul Jun , Kim Jae Yeol , Yang Dong Jo , Song Kyung Seok , Ahn Yeon Shik
Published: March 2009

In this investigation, we evaluated diagnoses of a defect concerning coating of land-base
gas turbine using infrared thermography camera. In this camera method has a strong point which is
able to save time and costs compared with former method. Because it can be long field acquire
temperature distribution by using non-contact method. But it has a week point that method applies
thermal load about inspection sample. Presently, Method used widely in detection of crack is
ultrasonic inspection. But this method, There is problem in application in place that uneven surface.
In order to check cracks on a blade coating of a gas turbine, a part with cracks in a waste blade
disposed after having been used in the field was extracted to produce a sample. So we apply the
method by a infrared thermography camera to the produced sample, the sample was heated by means
of a halogen lamp. In this paper, we want to describe production of land-base turbine sample, a
method of applying thermal load at produced sample, infrared thermography camera technique, an
analysis technique of thermography, a defect analysis of coating of land-base gas turbine blades.
Analyses of Cavitation Instabilities in Ductile Metals
Authors: Tvergaard Viggo
Published: March 2009

Cavitation instabilities have been predicted for a single void in a ductile metal stressed
under high triaxiality conditions. In experiments for a ceramic reinforced by metal particles a single
dominant void has been observed on the fracture surface of some of the metal particles bridging a
crack, and also tests for a thin ductile metal layer bonding two ceramic blocks have indicated rapid
void growth. Analyses for these material configurations are discussed here. When the void radius is
very small, a nonlocal plasticity model is needed to account for observed size-effects, and recent
analyses for the influence of such size-effects on cavitation instabilities are presented.
When a metal contains a distribution of micro voids, and the void spacing compared to void size
is not extremely large, the surrounding voids may affect the occurrence of a cavitation instability at
one of the voids. This has been analyzed for a material containing a periodic distribution of
spherical voids with two different void sizes, where the stress fields around larger voids may
accelerate the growth of smaller voids. Another approach has been an analysis of a unit cell model
in which a central cavity is discretely represented, while the surrounding voids are represented by a
porous ductile material model in terms of a field quantity that specifies the variation of the void
volume fraction in the surrounding metal.
Study on Metal Forming by Macro-Micro Combine Numerical Analysis
Authors: Zhang Shao Rui , Li Da Yong , Yin Zhong Wei , Peng Ying Hong , Zhou Fei
Published: March 2009

It has long been found that the crystal orientations would induce macroscopic anisotropy
during deformation process, and then affect the deformation properties of sheet metal. So it is very
important to find the true relation between texture distribution and macroscopic anisotropy. In this
paper, the anisotropy coefficients of the yield function are fitted by Taylor factor and crystal plastic
model. Metal flow is assumed to occur by crystallographic slip on given slip systems within each
crystal. Then this simulation results are compared with those of microscopic crystal plastic method.
Analysis of the Process of AA-6201 Feedstock Using Continuous Casting and Extrusion
Authors: Zhou Tian Guo , Jiang Zheng Yi , Wen Jing Lin , Xie Hai Bo , Tieu A. Kiet
Published: March 2009

Effects of the extrusion ratio, on-line solution temperature and cooling speed on the
microstructures, mechanical properties and conductivity of AA-6201 feedstock have been
investigated. Experimental results show that the size of the grain of the feedstock grows slowly with
an increase of on-line solution temperature, the size of strengthening phase becomes smaller and the
density becomes bigger with an increase of extrusion ratio. The tensile strength of AA-6201
feedstock after T-6 treated increases with an increase of extrusion ratio, on-line cooling speed, and
with a decrease of solution temperature, and the conductivity is a little penalty. Under the conditions
of the extrusion ratio 16.5, on-line solution temperature 793.15K and ageing temperature 423.15K,
the tensile strength, elongation and conductivity are 324 MPa, 10.1 % and 53.0% IACS respectively.
A feedstock with high quality can be produced by a method of continuous casting and extrusion.
Modelling of Dynamic Recrystallization in Hot Working
Authors: Xu Bing Ye , Qu Jie , Jin Quan Lin , Huang Han Xiong
Published: March 2009

Dynamic recrystallization, on which grain size of the final forging depends mainly, is one of
the most important microstructure evolution processes in moderate-to-low stacking fault energy metals. In
this paper, the process of dynamic recrystallization is simulated by numerical method. The paper first gives a
visco-plastic model considering dynamic recrystallization in detail; secondly gives the applied finite element
formulation and compiles an finite element program in Visual Fortran 6.5 based on the updated Lagrangian
formulation rigid-plastic finite element; thirdly the material parameters are identified through inverse
analysis, based on the compiled finite element program and the developed global optimization method; at
last, the compiled finite element program is applied to simulate the microstructure evolution caused by
dynamic recrystallization, the calculated result agrees with the experimental result relatively well.
Plasticity as a Lifesaver in the Design of Cardiovascular Stents
Authors: De Beule Matthieu , Mortier Peter , Belis Jan , Van Impe Rudy , Verhegghe Benedict , Verdonck Pascal
Published: March 2009

A common treatment to restore normal blood flow in an obstructed artery is the
deployment of a stent (i.e. small tube-like structure). The vast majority of stents are crimped on a
folded balloon and laser cut from 316L stainless steel tubes. Although, several numerical studies
(exploiting the Finite Element Method) are dedicated to the mechanical behaviour of balloon
expandable stents, there seems to be no consensus regarding the mechanical properties to describe
the inelastic material behaviour of SS316L. Moreover, as the typical dimensions of stent struts (e.g.
100 μm for coronary stents) are of a similar order of magnitude as the average grain size in stainless
steel (i.e. 25 μm), continuum approaches relying on macroscopic material properties may be
questionable. In addition, an experimental study on stainless steel stent strut specimens showed a
size-dependency of the failure strain. In this study the impact of the magnitude of the yield stress on
the stent expansion behavior is examined. An increase in the yield stress (from 205 N/mm² to 375
N/mm²) results in an increase of the pressure (from about 0.3 N/mm² to approximately 0.4 N/mm²)
which the clinician needs to exert for the balloon to unfold and to reach its cylindrical expanded
shape. Furthermore, the effect of the size dependency behavior of the material is studied by
monitoring the nominal strain during stent expansion. The maximum value of the nominal strain in
the expanded stent (e.g. εn = 23 %) does not exceed the critical value of the failure strain, (i.e. εn =
33 %), moreover the critical values are nowhere exceeded in the whole stent during the expansion.
Our numerical results - accounting for the presence of the balloon in its actual folded shape -
correspond very well with pressure/diameter data supplied by the manufacturer. Consequently, this
study shows that the free expansion of new generation balloon-expandable stents can be studied
accurately with computational analysis based on the Finite Element Method (FEM) and relying on
macroscopic material properties. In this context, there is no need to implement a size-based
constitutive material model, but before accepting the results of the study, one should check in any
case the maximum strain against the limit as shown above.
An Anisotropic Constitutive Model for a Directionally Solidified Superalloy
Authors: Yaguchi Masatsugu , Yamamoto Masato , Ogata Takashi , Ohno Nobutada
Published: March 2009

The monotonic tensile and creep deformations of a directionally solidified (DS)
superalloy are investigated for several loading directions. The material exhibits remarkable
anisotropy under elastic and creep loading conditions, whereas it shows isotropy under loading
conditions of high strain rates. Tension-torsion creep tests are also conducted to investigate the
deformation under multiaxial stress conditions. Referring to the observed behavior, a unified
constitutive model, which has two features, is developed for the DS superalloy. One is a static
recovery term of back stresses that is prescribed as a transversely isotropic property, which is
supposed to have an effect on the deformation behavior under creep loading conditions. The other is
the division of inelastic strain into two components, which represent octahedral and cubic slip
system deformations, so as to describe multiaxial creep deformation. Calculation results obtained
using the constitutive model are compared with the uniaxial and multiaxial experimental results to
evaluate the validity of the model.
Micromechanical Study on High-Temperature Behavior of ZrO2 Particle-Dispersed Ni Composites
Authors: Tsukamoto Hideaki , Kotousov Andrei G.
Published: March 2009

This paper aims to investigate high temperature behavior of ZrO2 particle-dispersed Ni
composites. The tension-compression tests under constant stress rates as well as creep tests
including stress-dip tests were performed using a high-temperature material testing set up, which
consists of an electric-hydraulic fatigue testing machine, electric furnace and extensometer with a
laser sensor. ZrO2 particle-dispersed Ni composites were fabricated by using the powder
metallurgical methods. The results obtained from the experimental study show that ZrO2 particles
remarkably strengthen the composite and there exists a reasonable correlation between the tensioncompression
stress-strain relation and the creep behavior. In addition, the creep behavior has been
examined based on the micromechanical concept, which takes into account the diffusional mass
flow at the interface between the particles and matrix. Some numerical analysis based on this
concept demonstrates that even a little amount of ZrO2 particles can effectively increase the creep
resistance of the composites
Dislocation-Grain Boundary Interactions by the Quasicontinuum Method
Authors: Shimokawa Tomotsugu , Kinari Toshiyasu , Shintaku Sukenori
Published: March 2009

The interactions between edge dislocations and the grain boundary have been studied
by using quasicontinuum simulations. With an increase in the shear strain, dislocation pile-up is
created and local stress concentration occurs at the head of the pile-up. The relationship between
the stress concentration and the number of dislocations in the pile-up is discussed.
In Vitro Evaluation of Poly ε-Caprolactone/Hydroxyapatite Composite as Scaffolds for Bone Tissue Engineering with Human Bone Marrow Stromal Cells
Authors: Heo S.J. , Kim S.E. , Hyun Yong Taek , Kim D.H. , Lee Hyang Mi , Hwang Yeong Maw , Park S.A. , Shin Jung Woog
Published: March 2009

This study evaluated the potential of the PCL (poly -caprolactone)/HA(Hydroxyapatite)
composite materials as a scaffold for bone regeneration. For this, we fabricated scaffolds utilizing
salt leaching method. The PCL/HA composite scaffolds were prepared with various HA contents
(20wt%, 40wt%, 60 wt %). To ensure the potential for the scaffolds, porosity tests were conducted
along with SEM observations. The porosity decreased with the increase of the contents of HA
particles. The porosity of the composite with the highest contents of HA was still adoptable (~85%).
In addition, the PCL/HA composite scaffolds were evaluated for their ability of osteogenic
differentiation with human bone marrow stromal cell (hBMSC) in vitro. Alkaline phosphatase
(ALP) activity, markers for osteoblastic differentiation, and total protein contents were evaluated in
hBMSCs following 14 days of cultivation. The addition of HA particles enhanced proliferation of
hBMSC during the test. Also, the differentiation ability of the cells was increased as HA particles
were added. In this study, we concluded that PCL/HA composite scaffolds has great potential as a
scaffold for bone tissue engineering.
Crash Behaviour of Various Modern Steels Exposed to High Deformation Rates
Authors: Laumann Till , Pfestorf Markus , Beil Andreas , Geiger Manfred , Merklein Marion
Published: March 2009

The increasing call for significant safety improvements of new cars requires, among other important
relevant aspects, the application of high strength materials for the body in white. Quenchable
manganese boron alloyed steels like 22MnB5 offer superior strength values, complex shapes and
enhanced accuracy. For the evaluation of the crash appropriateness specimens in different annealed
states are deformed in a so called drop test bench and hereupon judged in terms of absorbed energy,
maximum deformation and other aspects like wrinkling behaviour. Microscopic analysis
complements the evaluation of crash-appropriateness.
Finite Element Simulation of Forming, Joining and Strength of Sheet Components
Authors: Chenot Jean Loup , Bouchard Pierre Olivier , Chastel Yvan , Massoni Elisabeth
Published: March 2009

A 3-D solid finite element simulation of sheet forming processes is briefly discussed.
Examples of cold or warm deep-drawing and sheet hydro forming are presented. Sheet work-pieces
can be assembled to produce complex components by using different techniques: such as welding or
mechanical fastening. They must also be simulated in order to evaluate and optimise the quality of
the parts; examples of hemming and of self piercing riveting are described. Structural computation
allows us to evaluate the strength of a component and especially the strength of the joining. In the
future, more precise optimization of the components will be possible by the transfer of data from
the previous stages of sheet forming and joining, to the structural computation code. This input data
will be firstly the distribution of residual stresses, the evolution of local properties such as elastic
limit, damage and anisotropy. An example of structural computation on a system of two sheets
assembled by a single rivet is presented.
FEM in Plate Bending
Authors: Grizelj Branko , Barisic Branimir , Math Miljenko Dino
Published: March 2009

The paper is concerned with the numerical method of determination bending force and
calibration force in plate bending. For numeric procedure the finite element method is used.
Calibration force is determined when bending force and calibration coefficient are known.
Significant factors for determination of bending force are: material of the circular plate, bending
radius circular plate, diameter of the circular plate, thickness of the circular plate and method of
loading of the circular plate. The calibration coefficient is determined by experiment. The analysis
of bending plate is limited to the facts and figures used so far in the fabrication of spherical tanks,
i.e. for deformations up to 1 %.
Application of Blank Optimization Method in Deep Drawing of Rectangular Magnesium Alloy Cups under Non-Isothermal Condition
Authors: Zheng W.T. , Sorgente Donato , Palumbo G. , Tricarico Luigi , Ren Li Mei , Zhou L.X. , Zhang Shi Hong
Published: March 2009

Using the optimum blank in sheet metal forming process not only can decrease the
material wasting but also avoid possible defects such as local severe thinning, wrinkling and
fracture. Since it is practical technology for industrial production, many blank optimization methods
have been proposed and their validity was verified by some forming tests of typical or complicated
components. However, all the forming tests were carried out at room temperature or under
isothermal condition. In present work, a blank optimization method was employed to evaluate its
efficiency in deep drawing of rectangular magnesium alloy cups under non-isothermal condition. It
is proved by experiment that the employed blank optimization method can predict successfully the
optimum initial blank shape for the component with specified shape and dimension.
Computer Aided Modeling of Deep-Drawing
Authors: Pişkin Mehmet Ali , Kaftanoğlu Bilgin
Published: March 2009

Deep-drawing operations are performed widely in industrial applications. It is very
important for efficiency to achieve parts with no defects. In this work, a finite element method is
developed to simulate deep-drawing operation including wrinkling. A four nodded five degree of
freedom shell element is formulated. Isotropic elasto-plastic material model with Von Mises yield
criterion is used. By using this shell element, the developed code can predict the bending behavior
of workpiece besides membrane behavior. Simulations are carried out with four different element
sizes. The thickness strain and nodal displacement values obtained are compared with results of a
commercial finite element program and results of previously conducted experiments.
Sheet Hemming with Rolling Tools: Analysis and Optimization of the Part Quality
Authors: Ceretti Elisabetta , Aldo Attanasio , Fiorentino Antonio , Giardini Claudio
Published: March 2009

The present paper is the continuation of a research conducted on hemming operations by
using rolling tools. Sheet hemming is a joining operation widely used in automotive industry when
it is necessary to join two sheet parts (such as the engine hood or the door panels with their internal
frame) by plastic deformation of the edge of the outer part. The whole process is characterised by a
90° sheet flanging, a pre-hemming (up to approximately 135°) and the final hemming where the
outer sheet edge is bended up to 180° clamping the inner sheet. Hemming processes are normally
performed using rigid dies in series production and manually in pre-series and small batch
production, due to the high cost of the dies. Nowadays, rollers moved by robots are becoming an
interesting alternative to the manual operations especially when flexible productions are required.
Even if the process time is higher, this solution can help in minimizing set-up times and costs. The
required equipments are a support and a blocking system for the sheets together with the rollers
mounted on a CNC machine or on a robot. The production flexibility is guaranteed by changing the
3D tool path using a CAD/CAM system. Authors are dealing with this technique having conducted
many experiments studying the influence of the hemming process parameters such as flange
geometry (edge height, fillet radius), distance of the inner panel from the flange, tool path sequence,
along straight paths on steel sheets. The goal of the present research is to study the material
behaviour and the produced parts quality when working on aluminium sheets. In particular, both
experimental tests and simulations will be carried out in order to optimize the process.
Non Deterministic Approach in Metal Forming Springback Simulation
Authors: Del Prete Antonio , Primo Teresa , De Vitis Antonio A.
Published: March 2009

An uncertain approach has been evaluated to analyze the finite element analysis
responses for the springback evaluation on a stamped part. In the Metal Forming and Springback
simulations a deterministic approach does not take in account uncertain physical variations related
to material characteristics, friction conditions, tools active surfaces status, etc. Then, if one of the
purposes of the process design it is its reliability, a CAE study in aleatory conditions is the only way
to evaluate the process robustness. A study case has been defined and the explicit simulation was
performed for the forming stage while, the implicit simulation was performed for the springback
phase. Subsequently, a stochastic problem was solved to found the aleatory influence of process
parameters such as: anisotropy coefficient, Young modulus and friction between blank and tools to
evaluate their effect on the component springback. The evaluation of finite element models in
uncertain conditions can be considered like a CAE usage in order to obtain a “Robust Design” for
the examinated problem.
Analytic, Numerical, and Stochastic Comparison of Forming Force Modeling at Deep Drawing and Backward Extrusion on the Same Al 99.5 F7 Parts
Authors: Barisic Branimir , Math Miljenko Dino , Grizelj Branko
Published: March 2009

In order to determine the forming force in deep drawing and backward extrusion
processes (on Al 99.5F7 specimens) the analytical, numerical and stochastic modeling and analysis
of forming force on the basis of the Box-Wilson’s multi factorial experimental designs by use of
rotatable experimental design were carried out. The goal of the paper is to predict the force in these
different forming processes giving identical parts by means of different modeling approaches. This
study will seek to compare the results of these modeling solutions with experimental results serving
to check the correction and the verification of analytic, stochastic and numerically obtained results.
Also, the scope of the present paper is to evaluate different parameters affecting these processes and
to examine some experimental procedures in laboratory scale for the listed material in order to give
more useful information in numerical and stochastic computations and also, to define the
correlation among the parameters of these processes in order to improve the existing one and to
raise it to a higher techno economic level. The increasing tendency for industrial parts cost
reduction, quality improvement, materials savings, and the shortening of design and manufacturing
time is more focused on this way of analysis of processes. These investigations are a basis for
general conclusions about the forming force and they have a direct application in the projecting of
these processes, tools and forming systems.
Multi Shape Sheet Hydroforming Tooling Design
Authors: Del Prete Antonio , Papadia Gabriele , Manisi Barbara
Published: March 2009

In order to value the process of variables influence in sheet metal hydroforming, a special
hydroforming cell has been developed. Generally, sheet hydroforming is obtained using appropriate
press tooling. This option requires large investments completely dedicated to this technology of
production. As an alternative, conventional hydraulic presses can be used for sheet hydroforming in
combination with special hydraulic tooling named “hydroforming cells”. A special “hydroforming
cell” concept has been developed to perform experimental analysis for different shapes using the
same tooling set up. CAE tools had a strategic role just to develop the best layout and to find the
optimum solutions for the process variables. FEA has been used to define the distribution of the
blank holder variable forces: a solution which implies the use of twelve independent actuators have
been implemented. The position and the load path of each one of them has been chosen for each
formed shape, in accordance with the FEA results. Customized actuators have been used to solve
interferences between mechanical parts of the hydroforming cell. For this specific aspects the
virtual 3D design was necessary for the appropriate decisions. The developed process system is
very effective so that is possible to set up experimental campaigns for sheet hydroformed
components.
Modeling Flexforming (Fluid Cell Forming) Process with Finite Element Method
Authors: Hatipoğlu H. Ali , Polat Naki , Koksal Arif , Tekkaya A. Erman
Published: March 2009

In this paper, the flexforming process is modeled by finite element method in order to
investigate the operation window of the problem. Various models are established using explicit
approach for the forming operation and implicit approach for the unloading one. In all analyses the
rubber diaphragm has been modeled revealing that the modeling of this diaphragm is essential.
Using the material Aluminum 2024 T3 alclad sheet alloy, three basic experiments are conducted:
Bending of a straight flange specimen, bending of a contoured flange specimen and bulging of a
circular specimen. By these experiments the effects of blank thickness, die bend radius, flange
length and orientation of the rolling direction of the part have been investigated. Experimental
results are compared with finite element results to verify the computational models.
Strain in Shear, and Material Behaviour in Incremental Forming
Authors: Emmens Wilko C. , van den Boogaard Ton
Published: March 2009

This paper discusses some consequences of forming by shear, a situation that is sometimes
claimed to occur in incremental forming. The determination of the principal strains and principal
directions is discussed in detail. Two methods are presented: using a circular grid (although
simulated on the computer), and by deriving formulae from the theory; both yield identical results.
The strains assuming forming by shear are found to be (much) higher than in situations of forming
by stretch. This affects notably more fundamental studies on material behaviour in incremental
forming. The effects are illustrated using experimental data obtained with pre-stressed material.
Feature Based Approach for Increasing the Accuracy of the SPIF Process
Authors: Verbert Johan , Duflou Joost R. , Lauwers Bert
Published: March 2009

One of the main issues of the single point incremental forming (SPIF) process is still the
achievable accuracy. A number of methods have been suggested to increase this accuracy, but many
of these contain a significant drawback. Reprocessing the workpiece can increase the accuracy but
also significantly increases the manufacturing time and leads to a worse surface finish of the part.
Other methods iteratively correct the toolpath based upon the deviations measured on the previously
manufactured parts. This method is not very well suited for one of a kind products, since instead of
one part, multiple parts need to be manufactured before the desired accuracy can be reached. Our
method proposes to use feature detection to split the workpiece in a configuration of planes, edges,
freeform surfaces and other features. For each of these features an optimised toolpath strategy can
be determined and the toolpath in that zone can be adjusted for this strategy. The proposed method
generates a single pass toolpath that leads to more accurate parts compared to the standard CAM
toolpaths. This paper describes the feature based optimised toolpath generation method (FSPIF)
and contains the results of experiments performed to validate this method.