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Residual stresses were predicted by a flow analysis in the mold cavity and residual stress distribution in the injection molded
product was measured. Flow field was analyzed by the hybrid FEM/FDM method, using the Hele Shaw approximation. The Modified
Cross model was used to determine the dependence of the viscosity on the temperature and the shear rate. The specific volume
of the polymer melt which varies with the pressure and temperature fields was calculated by the Tait’s state equation. Flow
analysis results such as pressure, temperature, and the location of the liquid-solid interface were used as the input of the
stress analysis. In order to calculate more accurate gap-wise temperature field, a coordinate transformation technique was
used. The residual stress distribution in the gap-wise direction was predicted in two cases, the free quenching and the constrained
quenching, under the assumption that the shrinkage of the injection molded product occurs within the mold cavity and that
the solid polymer is elastic. Effects of the initial flow rate, packing pressure, and mold temperature on the residual stress
distribution was discussed. Experimental results were also obtained by the layer removal method for molded polypropylene. 相似文献
2.
Kwang Seok Lee Seok Won Lee Jae Ryoun Youn Tae Jin Kang Kwansoo Chung 《Fibers and Polymers》2001,2(1):41-50
To determine three-dimensional fiber orientation states in injection-molded short fiber composites a CLSM (Confocal Laser
Scanning Microscope) is used. Since the CLSM optically sections the composites, more than two cross-sections either on or
below the surface of the composite can be obtained. Three dimensional fiber orientation states can be determined with geometric
parameters of fibers on two parallel cross-sections. For experiment, carbon fiber reinforced polystyrene is examined by the
CLSM. Geometric parameters of fibers are measured by image analysis. In order to compactly describe fiber orientation states,
orientation tensors are used. Orientation tensors are determined at different positions of the prepared specimen. Three dimensional
orientation states are obtained without the difficulty in determining the out-of-plane angles by utilizing images on two parallel
planes acquired by the CLSM. Orientation states are different at different positions and show the shell-core structure along
the thickness of the specimen. 相似文献
3.
Ji Hoon Kim Myoung-Gyu Lee Kwansoo Chung Jae Ryoun Youn Tae Jin Kang 《Fibers and Polymers》2006,7(1):42-50
In this paper, elasto-plastic constitutive equations for highly anisotropic and asymmetric materials are developed and their numerical implementation is presented. Some engineering materials such as fiber reinforced composites show different material behavior in the different material directions (anisotropy) as well as in tension and compression (asymmetry). Although these materials have mostly been analyzed using the anisotropic elastic constitutive equations, the necessity of consideration of plastic properties has been frequently reported in the previous works. In order to include both the anisotropic and asymmetric properties of composite materials, the Drucker-Prager yield criterion is modified by adding anisotropic parameters and initial components of translation. The implementation procedure for the developed theory and algorithms is presented based on the implicit finite element scheme. The measured data from the previous work are used to validate the present constitutive equations. 相似文献
4.
Yun?Kyoung?Cho Young?Seok?Song Tae?Jin?Kang Kwansoo?Chung Jae?Ryoun?YounEmail author 《Fibers and Polymers》2003,4(3):135-144
Permeability of the preform is one of key factors in design of RTM (Resin Transfer Molding) mold, determination of processing
conditions, and modeling of flow in the mold. According to previous studies, permeability measured in the unsaturated fiber
mats are higher than that in the saturated fiber mats by about 20 % because of the capillary pressure. In this study, permeabilities
of several fiber preforms are measured for both saturated and unsaturated flows. A saturated experiment of radial flow has
been adopted to measure the permeability of anisotropic fiber preforms with high fiber content, i.e., circular braided preforms.
In this method, four pressure transducers are used to measure the pressure distribution. Permeabilities in different directions
are determined and the experimental results show a good agreement with the theory. Since permeability is affected by the capillary
effect, permeability should be measured in the unsaturated condition for the textile composites to be manufactured under lower
pressure as in the Vacuum Assisted Resin Transfer Molding (VARTM). 相似文献
5.
A finite element method is employed for a flow analysis of the melt spinning process of a non-circular fiber, a PET(polyethylene
terephthalate) filament. The flow field is divided into two regions of die channel and spin-line. A two dimensional analysis
is used for the flow within the die channel and a three dimensional analysis for the flow along the spin-line. The Newtonian
fluid is assumed for the PET melt and material properties are considered to be constant except for the viscosity. Effects
of gravitation, air drag force, and surface tension are neglected. Although the spin-line length is 4.5 m, only five millimeters
from the spinneret are evaluated as the domain of the analysis. Isothermal and non-isothermal cases are studied for the flow
within the die channel. The relationship between the mass flow rate and the pressure gradient is presented for the two cases.
Three dimensional flow along the spin-line is obtained by assuming isothermal conditions. It is shown that changes in velocity
and cross-sectional shape occur mostly in the region of 1mm from the die exit. 相似文献
6.
Won Ho Lee Seok Won Lee Tae Jin Kang Kwansoo Chung Jae Ryoun Youn 《Fibers and Polymers》2002,3(4):159-168
Polyurethane foams were produced by using a homogenizer as a mixing equipment. Effects of stirring speed on the foam structure
were investigated with SEM observations. Variation of the bubble size, density of the foam, compressive strength, and thermal
conductivity were studied. A hybrid foam consisting of polyurethane foam and commercial polystyrene foam is produced. Mechanical
and thermal properties of the hybrid foam were compared with those of pure polyurethane foam. Advancement of flow front during
mold filling was observed by using a digital camcorder. Four types of mold geometry were used for mold filling experiments.
Flow during mold filling was analyzed by using a two-dimensional control volume finite element method. Variation of foam density
with respect to time was experimentally measured. Creeping flow, uniform density, uniform conversion, and uniform temperature
were assumed for the numerical simulation. It was assumed for the numerical analysis that the cavity has thin planar geometry
and the viscosity is constant. The theoretical predictions were compared with the experimental results and showed good agreement. 相似文献
7.
Myoung-Gyu Lee Ji Hoon Kim Hansun Ryou Kwansoo Chung Jae Ryoun Youn Tae Jin Kang 《Fibers and Polymers》2006,7(3):276-285
Development and numerical implementation for an elastoplastic constitutive model for anisotropic and asymmetric materials
are presented in this paper. The Coulomb-Mohr yield criterion was modified to consider both the anisotropic and asymmetric
properties. The modified yield criterion is an isotropic function of the principal values of a symmetric matrix which is linearly
transformed from the Cauchy stress space. In addition to the constitutive equation, the numerical treatment for the singularity
in the vertex region of yield surface and stress integration algorithm based on elastoplasticity were presented. In order
to assess the accuracy of numerical algorithm, isoerror maps were considered. Also, extension of a strip with a circular hole
was simulated and results compared with those obtained using the (smooth) Mises yield criterion to validate stress output
for a complex stress state. 相似文献
8.
Lee Wonoh Kim Ji Hoon Shin Heon-Jung Chung Kwansoo Kang Tae Jin Youn Jae Ryoun 《Fibers and Polymers》2003,4(2):77-83
The cell modeling homogenization method to derive the constitutive equation considering the microstructures of the fiber reinforced
composites has been previously developed for composites with simple microstructures such as 2D plane composites and 3D rectangular
shaped composites. Here, the method has been further extended for 3D circular braided composites, utilizing B-spline curves
to properly describe the more complex geometry of 3D braided composites. For verification purposes, the method has been applied
for orthotropic elastic properties of the 3D circular braided glass fiber reinforced composite, in particular for the tensile
property. Prepregs of the specimen have been fabricated using the 3D braiding machine through RTM (resin transfer molding)
with epoxy as a matrix. Experimentally measured uniaxial tensile properties agreed well with predicted values obtained for
two volume fractions. 相似文献
9.
Ever since the ideal forming theory has been developed for process design purposes, application has been limited to sheet
forming and, for bulk forming, to two-dimensional steady flow. Here, application for the non-steady case was made under the
plane-strain condition. In the ideal flow, material elements deform following the minimum plastic work path (or mostly proportional
true strain path) so that the ideal plane-strain flow can be effectively described using the two-dimensional orthogonal convective
coordinate system. Besides kinematics, schemes to optimize preform shapes for a prescribed final part shape and also to define
the evolution of shapes and frictionless boundary tractions were developed. Discussions include numerical calculations made
for a real automotive part under forging. 相似文献
10.
To better understand the formation of necking in drawing processes of fibers, strain distributions during drawing processes
have been analyzed. For simplicity, one-dimensional incompressible steady flow at a constant temperature was assumed and quasi-static
model was used. To describe mechanical properties of solid polymers, non-linear visco-plastic material properties were assumed
using the power law type hardening and rate-sensitive equation. The effects of various parameters on the neck formation were
mathematically analyzed. As material property parameters, strain-hardening parameter, visco-elastic coefficient and strain-rate
sensitivity were considered and, for process parameters, the drawing ratio and the process length were considered. It was
found that rate-insensitive materials do not reach a steady flow state and the rate-sensitivity plays a key role to have a
steady flow. Also, the neck formation is mainly affected by material properties, especially for the quasi-static model. If
the process length changes, the strain distribution was found to be proportionally re-distributed along the process line by
the factor of the total length change. 相似文献
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