Key Engineering Materials
Vol. 350
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Vols. 348-349
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Vol. 344
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Vols. 340-341
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Vol. 339
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Vols. 334-335
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Key Engineering Materials Vols. 340-341
Paper Title Page
Abstract: Twin-roll thin strip casting process combines casting and hot rolling process into a single
step; in which melt and solid states exist in the casting region, so its deformation is more complex
than rolling process. In this paper, Anand’s model, a unified visco-plasticity constitutive model, was
employed to simulate the highly nonlinear behavior in the twin-roll casting process. Anand model’s
parameters were regressed based on compression tests at various temperature and strain rate for
magnesium alloy AZ31. To calculate the thermal mechanical stresses, the thermal flow of twin-roll
casting process was simulated firstly; then stresses were calculate, in which the temperature field
result of thermal flow was imposed as body load, and a small displacement load along roller
tangential direction was imposed simultaneously in order to simulate rolling action. The deformation
results can well describe the forward slip zone, backward slip zone and melt eddy zone in the casting
region. Based on the results, the applicability of Anand’s model on twin-roll casting process was
discussed.
877
Abstract: Biaxial compression tests with an abrupt strain path change have been performed on
polycrystalline aluminum to investigate the plastic deformation behavior under complex strain
histories. Attentions are paid especially to the rapid change in the normal stresses due to the abrupt
strain path change. The influences of the prestrain amplitude and the angular relation of sequential
strain paths on the stress changes were also studied. The results showed that the transient increase of
the normal stresses related to the latent hardening phenomenon with strain path change as well as the
plastic anisotropy increase with the pre-straining amplitude. The transient increase in the stress was
also affected by the strain histories in the sequential compression tests with the strain path change.
The transient stress increment became large to the maximum then decreases with the angle between
the sequential paths.
883
Abstract: This paper deals with experimental observations and modeling of plastic deformations of
a high strength steel sheet (HSS sheet) under biaxial stress conditions. Using a cruciform specimen
of a HSS sheet of 980MPa-TS, experiments of proportional and non-proportional loadings were
performed. Numerical simulations for the biaxial stress-strain responses were conducted using a
constitutive model of large-strain cyclic plasticity (Yoshida-Uemori model), and the results were
compared to the experimental data. The results of numerical simulation show a good agreement
with the experimental results, which is attributed to accurate modeling of the backstress evolution
of the anisotropic yield surface.
895
Abstract: 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.
901
Abstract: In this study, a linearization approach is used to develop an implicit integration scheme
for high-temperature inelastic constitutive models based on non-linear kinematic hardening. A
non-unified model is considered in which inelastic strain rate is divided into the transient and steady
parts driven, respectively, by effective stress and applied stress. By discretizing the constitutive
relations using the backward Euler method, and by linearizing the resulting discretized relations, a
tensor equation is derived to iteratively achieve the implicit integration of constitutive variables.
The integration scheme is then programmed as a subroutine in a finite element code and applied to a
lead-free solder joint analysis. It is thus demonstrated that the integration scheme affords the
quadratic convergence of iteration even for considerably large increments.
907
Processing Conditions and Mechanical Properties of Fine Grained Mg by Equal Channel Angular Pressing
Abstract: Mg and Mg alloys are promising materials for light weight high strength applications. In
this paper, grain refinement of pure Mg using severe plastic deformation was tried to enhance
mechanical properties of the hard-to-deform metallic material. The microstructure and the
mechanical properties of Mg processed by equal channel angular pressing (ECAP) at various
processing temperatures were investigated experimentally. ECAP of channel angle of 90o and
corner angle of 0o was successful without fracture of the samples at 300 oC. The hardness of the
ECAP processed Mg decreased with increasing ECAP processing temperature. The effect of
temperature on the hardness and microstructure of the ECAP processed Mg were explained by the
dislocation glide in the basal plane and non-basal slip systems and the dynamic recrystallization and
recovery.
913
Abstract: The nano/microstructure and mechanical/tribological properties of the eutectic regions in
thixo/rheo-cast A356 alloy parts were investigated using nano/micro-indentation and mechanical
scratching, combined with optical microscopy and atomic force microscopy (AFM). Most eutectic
silicon crystals in the A356 alloy showed a modified morphology as fine-fibers. The aging
responses of the eutectic regions in both the thixo/rheo cast A356 alloys aged at 150 0C for different
times (0, 2, 4, 8, 10, 16, 24, 36, and 72h) were investigated. Both Vickers hardness (HV) and
indentation hardness (HIT) test results showed almost the same trend of aging curves, the peak was
obtained at the same aging time of 10 h, and in tribological properties of thixo/rheo-cast, the friction
coefficient of thixo-cast was investigated lower than that of rheo-cast.
919
Abstract: Mechanical damping systems have been widely used to various industrial structures and are
mainly hydraulic and pneumatic devices nowadays. This article presents an experimental
investigation of a nano colloidal damper. Particularly for colloidal damper, the hydraulic oil is
replaced by a colloidal suspension, which is consisted from a nano-porous matrix with controlled
architecture and a lyophobic fluid. Nano colloidal damper test rig and the measuring technique of the
hysteresis were described in this study. Influence of the water volume and particle diameters upon the
nano colloidal damper hysteresis was investigated. As a result, the proposed nano colloidal damper
(NCD) is proved as an effective one, which can be replaced for the conventional hydraulic damper.
925