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1.
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
2.
A series of CNTs/SiO2/thiazole dye hybrid materials prepared via the sol-gel process is synthesized from carbon nanotubes (CNTs) and tetraethoxysilane
with heteroaryl 4-phenyl-2-amino-thiazole dyes. Heterocyclic 4-phenyl-2-aminothiazole dyes are processed with the hydrolysis-condensation
reaction at a constant ratio of vinyltriethoxysilane and tetraethoxysilane condensed with modified CNTs in appropriate proportion
under a catalyst. The structures of the CNTs/SiO2/thiazole dye hybrid materials are characterized by Fourier transform infrared spectroscopy (FTIR). Polytrimethylene terephthalate
(PTT) fabrics are used to evaluate the morphology structure by scanning electron microscopy (SEM). SEM images show that a
uniform dyeing on the PTT fabrics to confirm the reaction of hybrid materials with PTT fabrics. The washing fastness, color
evenness, water contact angle, air permeability, electric conductivity, and weatherability of PTT fabrics dyed with CNTs/SiO2/thiazole dye hybrid materials are evaluated, with results indicating improved conductivity and water-repellent. 相似文献
3.
In this paper, a multi-objective genetic algorithm based on the numerical simulation of the polymer flow is proposed to optimize the geometry parameters of the coat-hanger die with uniform outlet velocity and minimal residence time. The vector evaluated GA method is used to find the parameter values for obtaining the uniform outlet velocity and minimal residence time, where the manifold angle, the land height and the slot gap are chosen to be the design variables, the outlet velocity and the residence time are obtained by simulating the three-dimensional and isothermal polymer flow in the coat-hanger die. The stochastic universal sampling (SUS) is adopted to select the new population which is representative of a coat-hanger die. The optimal geometry parameters of the coat-hanger die achieved in the 30th generation among 20 individuals of each generation, which showed that the manifold angle and the gap slot were the most influencing design parameter on the coefficient of variation (CV) value of outlet velocity and residence time. 相似文献
4.
Air permeability is one of the most important utility properties of textile materials as it influences air flow through textile material. Air permeability plays a significant role in well-being due to its influence on physiological comfort. The air permeability of textile materials depends on their porosity. There are a lot of structural properties of textile materials also operating parameters (knitting+finishing) influencing air permeability and there are also statistically significant interactions between the main factors influencing the air permeability of knitted fabrics made from pure yarn cotton (cellulose) and viscose (regenerated cellulose) fibers and plated knitted with elasthane (Lycra) fibers. Two types of artificial neural networks (ANNs) model have been set up before modeling procedure by utilizing multilayer feed forward neural networks, which take into account the generality and the specificity of the product families respectively. A virtual leave one out approach dealing with over fitting phenomenon and allowing the selection of the optimal neural network architecture was used. Moreover this study exhibited that air permeability could be predicted with high accuracy for stretch plain knitted fabrics treated with different finishing processes. Within the framework of the work presented, ANNs were applied to help industry to adjust the operating parameter before the actual manufacturing to reach the desired air permeability and satisfy their consumers. 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.
The phase transformation of poly(trimethylene terephthalate) in crystalline state was simulated by atomistic modeling using
molecular mechanics technique. The crystalline structure of PTT was successfully prepared using the well-defined unit cell
structure of PTT and was satisfactorily verified by comparing that with the structure obtained from the x-ray diffraction
experiments. The basic elastic properties were predicted in this study, showing that the crystalline structure of PTT is very
pliable to the deformation at small strain. When the crystalline structure of PTT was stepwise deformed up to 50% of strain
in chain direction under uniaxial extension condition, the change in dihedral angle of trimethylene unit fromgg tott conformation was accompanied with a large increase of stress, indicating that the phase transformation of PTT in crystalline
state is difficult to occur. 相似文献
7.
The porosity of fibrous porous materials is an important factor to the thermal insulating performance of the material. This
paper considers both the optimum porosity of uniform fibrous battings and the optimum distribution of the porosity of non-uniform
fibrous battings for thermal insulation. The former was determined by an approximate analytical solution and a numerical simulation
by using finite volume method, and the latter was studied by applying simulated annealing method. The study showed that the
optimum porosity of uniform fibrous porous materials is very much dependent on fiber emissivity, and fiber radius, but little
influenced by the temperature difference of the boundaries. For non-uniform fibrous materials, there can be an optimum distribution
of porosity, which can be predicted by applying the simulated annealing method. 相似文献
8.
Nurlindah Hamrun Bahruddin Talib Muhammad Ruslin Hasminar Pangeran Mochammad Hatta Erni Marlina Andi Sitti Hajrah Yusuf Takashi Saito Keng-Liang Ou 《Marine drugs》2022,20(1)
This study aimed to investigate the potential use of brown algae Sargassum polycystum as irreversible hydrocolloid (alginate) impression material. Potassium alginate extracted from Sargassum polycystum was prepared in three different compositions (14%, 15%, and 16%) and mixed with other standard components to form an alginate impression material. Prior to that, the purity of potassium alginate was quantified with Fourier Transform Infrared Spectroscopy (FTIR) analysis. As a control material, the alginate impression material from a commercially available product was used. All alginate impression materials were then applied to a die stone model. Dimensional accuracy was measured by calculating the mesiodistal width of incisors in the generated dental cast using a digital caliper 0.01 accuracy (five replications). In addition, to evaluate the dimensional stability, the impression results were poured at four different periods (immediately, 5 min, 10 min, and 15 min). An independent t-test was performed to compare the measurement results with p < 0.05 considered significant. Analytical results confirm that the impression material containing 15% potassium alginate gives the best dimensional accuracy similar to control (p > 0.05). Meanwhile, the optimal dimensional stability was produced in the impression material containing 16% potassium alginate. Our study suggested that brown algae Sargassum polycystum has a promising potential to be used as an alginate impression material in clinical application. 相似文献
9.
The melt-blowing technique is usually used for thermoplastic resins, not for non-thermoplastic materials. In this study, nonwoven fabric was successfully obtained by a cellulose solution through melt-blowing technique. The solution was prepared by a twin-screw extruder after mixing cellulose pulp with 1-Allyl-3-methylimidazolium Chloride ([AMIM]Cl). Nonwoven fabric exhibited typical characteristics of those from melt-blown thermoplastic resins. Some aspects of meltblowing process are discussed, such as cellulose concentration, temperature of extrusion die and hot air pressure. In experimental range, to obtain nonwoven web, cellulose concentration was below 15 wt%. Temperature of extrusion die and hot air pressure had great influence on the fabric. With the increasing of temperature of extrusion die and hot air pressure, the fiber changed thin and the fiber web became better, while the fiber diameter became thicker after increasing the cellulose concentration. Elevating the temperature of extrusion die, the degree of polymerization decreased, and the quality of the fiber webs declined. 相似文献
10.
C. N. Herath 《Fibers and Polymers》2013,14(8):1339-1346
In this research work, air permeability variations of core spun cotton/spandex single jersey and 1×1 rib knitted structures were studied under relaxation treatments. Results are compared with similar fabrics made from 100 % cotton material. Even though cotton/spandex fabrics knitted with same stitch lengths, their structural spacing and stitch densities vary with the progression of treatments. Similar behavior was also observed with 100 % cotton knitted structures. Under higher machine set stitch lengths (i.e., lower fabric tightness factor), higher structural spacing and lower stitch densities were resulted and those variations significantly affected on the air permeability variations of knitted structures. 1×1 rib knitted structures showed significantly higher air permeability than single jersey structures and it is more prominent with cotton rib structures. However, cotton/spandex 1×1 rib and single jersey structures have not showed such significant deviations. Air permeability of cotton/spandex and 100 % cotton rib and single jersey knitted structures decreased with lower machine set stitch lengths (i.e., at higher fabric tightness factors). There was a correlation with fabric tightness, air permeability, areal density and fabric thickness such as knitted fabrics became tighter, their weight and thickness were higher, while their air permeability was lower. Thus, fabric areal density and fabric thickness are positively correlates to machine set stitch length?1 (fabric tightness factor). Air permeability of a knitted structure depends on material type, knitted structure, stitch length, relaxation treatment, structural spacing and stitch density. 相似文献
11.
Lightweight reinforced thermoplastic (LWRT) is a newly developed porous material. The low density, high rigidity, design flexibility and sound absorption of LWRT facilitate its application in the automotive industry. Fibers are bonded with a matrix and air is imported by deconsolidation, which is not only economical but also environmentally friendly. In this work, film stacking and non-woven methods were employed as the impregnation techniques to manufacture LWRT. The molded thickness and surface density of LWRT were varied to study their influences on the structures and mechanical properties. Different lengths of fibers in LWRT were selected and 7 % PP-g-MAH was added to the matrix and compared with unmodified matrix. The mechanical properties decreased with the increase in molded thickness and the decrease in surface density. With higher fiber length, the strength and stiffness increased, while the toughness exhibited a maximum value at 80 mm fiber length. The strength and stiffness of LWRT were also enhanced when 7 % PP-g-MAH was added. 相似文献
12.
13.
Thermal protection of firefighter protective clothing is greatly influenced by the air gap entrapped and moisture in clothing. In this paper, the effects of air gap size and position on thermal protective performance exposed to 84 kW/m2 heat source were investigated. Water was also added to thermal liner to understand the effect of air gap coupled with moisture on thermal protection. It was indicated that the TPP of fabrics system increased with the air gap size. The air gap position also greatly influenced the heat transfer during exposure to flash fire. Moisture added weakened the positive effect of air gap size when the air gap exists far from heat source, and almost eliminated the favorable effect of air gap position. However, when there is no air gap or small air gap between outer shell fabric and moisture barrier, moisture increased the thermal protection performance of multilayer fabrics system. The results obtained suggested that certain air gap entrapped in fabrics system and clothing microclimate could improve thermal protection, and the complicated effect of moisture should also be considered. 相似文献
14.
Soo Jin Baek Seong Yun Kim Seung Hwan Lee Jae Ryoun Youn Sung Hee Lee 《Fibers and Polymers》2008,9(6):747-754
In order to investigate effects of injection molding conditions on viscoelastic behavior and thermal deformation of film insert
molded (FIM) parts, injection molding was performed with various conditions such as injection speed, melt temperature, and
packing time. It was shown that variation of the warpage was decreased monotonically with increasing injection speed and exhibited
a bell-shaped curve as a function of melt temperature. Warpage variation was not affected by the packing time significantly
and the proportional relationship between warpage of the film insert molded part and shrinkage of the injection molded part
without film was observed. The FIM specimens produced with unannealed films showed the warpage reversal phenomenon (WRP) during
annealing and the magnitude of reversed warpage was affected significantly by the injection parameters and the extent of thermal
shrinkage of the unannealed film. Warpage of the FIM specimen was predicted by three dimensional numerical flow and stress
analyses and the predicted values showed a good agreement with the experimental results. 相似文献
15.
Kyung Hwa Hong 《Fibers and Polymers》2016,17(12):1963-1968
The purpose of this study was to develop an effective potential wound dressing material based on a polyvinyl alcohol (PVA) and tannic acid (TA) composite film. To prepare the PVA/TA films, PVA and TA blended aqueous solutions were cast into film form by spreading the solutions and drying them. Then the films were heat treated at 155 oC for 3 min to promote esterification between the PVA and TA. After removing un-crosslinked moieties from the films by rinsing and drying, the films were investigated by swelling behavior, FTIR spectroscopy, XRD and TGA. And, the antibacterial and antioxidant abilities of the films were also examined in this study. Through this investigation it was discovered that TA effectively acts as a functional antibacterial and antioxidant agent as well as crosslinker in the PVA/TA system. Thus, the PVA/TA composite films prepared by the casting and heat treatment method proposed in this study are expected to be used for topical medication, such as wound dressing material. 相似文献
16.
Oktay Yilmaz Emre Kısasöz F. Seniha Guner Cagri Nart Kadir Kirkkopru 《Fibers and Polymers》2014,15(1):84-90
Several restrictions which are related to extruder machinery and nature of process material exist in the design of plastic extrusion dies. To this respect, it is very important to consider design criteria and limitations in order to operate extrusion dies at desired production rate and temperature. In the current study, flow field characteristics through a conical spiral mandrel die are analysed in detail by 3D Computational Fluid Dynamics (CFD) simulations. The effects of operating conditions such as production rate and temperature on pressure drop through the spiral mandrel die and the occurence of melt fracture are investigated. The temperature dependent viscosity versus shear rate data for grade QB79P (CarmelTech) polypropylene (PP) melt under study are measured by use of rotational and capillary rheometers. Stress terms in the momentum equations are modeled by Generalized Newtonian Fluid (GNF) Model. For this, Bird-Carreau Model is employed as the viscosity model for the polymer melt. 3D CFD analyses provide comprehensive data and understanding with regard to flow behaviour through complex extrusion dies. 相似文献
17.
18.
为探究越冬期不同的覆盖材料对茶园土壤温度及茶叶产量、品质的影响,寻求效果佳的防冻材料,研究采用稻草、白膜、黑膜、稻谷壳和防草布等5种材料在茶园行间进行地表覆盖,比较不同材料覆盖后对土壤温度和茶叶产量、品质,以及春茶萌发时间的影响。结果表明,相较于未进行覆盖的对照,5种覆盖处理均能提高土壤温度,平均增温1.5~2.9℃,且覆盖后可使茶叶产量提高4.3%~13.6%,春茶萌发时间提早2~4 d,其中增温效果稻草和稻谷壳优于其他材料。使用稻草和稻谷壳覆盖后,茶叶水浸出物、咖啡碱、茶多酚、氨基酸含量均有所提高。综合比较来看,稻草和稻谷壳的增温效果较黑膜、白膜和防草布更好,而且能提高茶叶产量与品质,更适合作为茶园越冬期防冻的覆盖材料。 相似文献
19.
Nazire Deniz Yilmaz Nancy B. Powell Pamela Banks-Lee Stephen Michielsen 《Fibers and Polymers》2012,13(7):915-922
The effects of the material and treatment parameters on airflow resistivity and normal-incidence sound absorption coefficient of alkalized three layered nonwoven composites have been studied. The material parameters included fiber size and porosity. The treatment factors included the temperature, duration and concentration. The alkalized composite was a three-layered nonwoven sandwich structure consisting layers of Polypropylene/Hemp/Polypropylene. Alkalization treatment has been found to result in a loss of basis weight and a decrease in air flow resistivity. Among treatment factors, only temperature was found to be a statistically-significant factor on air flow resistivity. Higher-temperature alkalization leads to higher air flow resistivity compared to the lower-temperature treatment. Alkalization at higher temperature and higher concentrations gives better results in normalized sound absorption performance compared to lower-temperature and lower-concentration treatments, respectively. 相似文献