• Journal of the Korean Society for Precision Engineering
• /
• v.28 no.2
• /
• pp.219-225
• /
• 2011

Silicone resin is recently used as encapsulant for high-power LED module due to its excellent thermal and optical properties. In the present investigation, finite element analysis of cure process was attempted to examine residual stress evolution behavior during silicone resin cure process which is composed of chemical curing and post-cooling. To model chemical curing of silicone, a cure kinetics equation was evaluated based on the measurement by differential scanning calorimeter. The evolutions of elastic modulus and chemical shrinkage during cure process were assumed as a function of the degree of cure to examine their effect on residual stress evolution. Finite element predictions showed how residual stress in cured silicone resin can be affected by elastic modulus and chemical shrinkage behavior. Finite element analysis is supposed to be utilized to select appropriate silicone resin or to design optimum cure process which brings about a minimum residual stress in encapsulant silicone resin.

• Composites Research
• /
• v.30 no.6
• /
• pp.410-415
• /
• 2017

This paper predicted deformation due to thermal residual stress in composites using finite element analysis. Temperature cycle, Model shape, Laminate angle, Stacking sequence, chemical shrinkage of resin, and thermal expansion are affect composite deformation. Compare the results of the analytical model with the actual model of the same shape. This paper suggests that the analytical results can be applied to actual Model.

• Transactions of Materials Processing
• /
• v.11 no.7
• /
• pp.581-588
• /
• 2002

Among the processes to produce micro lens, the process using press molding is a new technology to simplify the process, but it contains many unknown variables. The press-molding process proposed in this paper was simplified into two step process, the first step is the pressing to design the preform for glass element, the second step is the annealing to reduce the residual stress. It is important to estimate the amount of shrinkage of glass gob and the residual stress during process. It Is difficult to evaluate the process variables as mentioned above through the experiment. The influences due to process variables was evaluated by using FEM parametric analysis. The results in this paper can be applicable to produce micro lens.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.3
• /
• pp.126-135
• /
• 2013

Recently, mass concrete with high flowability are widely used to improve the quality and constructability in the longer span construction of prestressed concrete bridges, but it may induce nonstructural cracks due to the hydration heat and autogenous shrinkage etc. The stresses in concrete were evaluated by various experiments and numerical analysis. The tensile stress in mass concrete was increased in connection with the accumulation of hydration heat. Moreover, large amount of autogenous shrinkage from powder type admixture could add the tensile stress to mass concrete near anchorage zone. The tensile stresses in anchorage zone by heat and autogenous shrinkage exceeded the tensile strength of early stage of concrete, and small amounts of stress increasement were shown in other parts of PSC girder.

• Korean Journal of Materials Research
• /
• v.9 no.7
• /
• pp.735-739
• /
• 1999

In this study we investigated stress development and shrinkage of thickness for a single $PbTiO_3$(PT) layer prepared by sol-gel processing. Changes of microhardness for multideposited PT layers with temperatures are also monitored to understand the densification of thin films. Single PT layer shrank rapidly from room temperature to$ 220^{\circ}C$ yielding 83% of total shrinkage observed up to $500^{\circ}C$. A tensile stress of ~75MPa developed in an as-spun layer, and increased steadily beyond $130^{\circ}C$ until it reaches the maximum value of 147MPa at $250^{\circ}C$. The significant decrease of tensile stress in the film beyond $370^{\circ}C$ indicates that thermal expansion mismatch between the film and the substrate dominates the stress behavior in this temperature range. Microhardness of the multideposited coatings also increased rapidly above $300^{\circ}C$ regardless of the pyrolysis temperatures used. Large amount of perovskite phase formed in multideposited coatings after $550^{\circ}C$ may be due partly to enhanced homogeneous nucleation in the thicker coating.

• Textile Coloration and Finishing
• /
• v.10 no.3
• /
• pp.10-19
• /
• 1998

This paper investigates the change of mechanical properties and thermal shrinkage in commercial multi-filament PET(polyethylene terephthalate) , namely, regular yarn, POY, DTY and composite yarn. To determine changing the effects of processing steps, these were examined at three steps process simulation conditions. The first step is sizing simulation$(S-1\;step\;:\;130^\circ{C}\times2\;min$., hot air treatment under 0.1 gf/d load), the second step is scouring simulation$(S-2\;step\;:\;100^\circ{C}\times20\;min$., boiling water treatment under free tension)and final step is setting simulation$(S-3\;step\;:\;180^\circ{C}\times2\;min$., hot air treatment under free tension). Regular yarn in multi-step treatment showed higher shrinkage at S-3 step and DTY showed higher in at S-1 step. While POY was relaxed at S-1 step, composite yarn showed different shrinkage properties depending on composite yarn type. Mechanical properties showed good relationship with shrinkage : high shrinkage makes initial modulus decrease and bleating strain increase. It also makes decreasing yield strain and yield stress decrease.

• Journal of the Korea Concrete Institute
• /
• v.16 no.3 s.81
• /
• pp.425-431
• /
• 2004

This paper describes an experimental investigation of how time-dependent deformations of high strength concretes are affected by maximum size of coarse aggregate, curing time, and relatively low sustained stress level. A set of high strength concrete mixes, mainly containing two different maximum sizes of coarse aggregate, have been used to investigate drying shrinkage and creep strain of high strength concrete for 7 and 28-day moist cured cylinder specimens. Based upon one-year experimental results, drying shrinkage of high strength concrete was significantly affected by the maximum size of coarse aggregate at early age, and become gradually decreased at late age. The larger the maximum size of coarse aggregate in high strength concrete shows the lower the creep strain. The prediction equations for drying shrinkage and creep coefficient were developed on the basis of the experimental results, and compared with existing prediction models.

• Textile Coloration and Finishing
• /
• v.16 no.6
• /
• pp.35-43
• /
• 2004

This study surveys the physical properties of ATY produced with FDY and POY. ATY is made with 70d Nylon FDY and 80d Nylon POY using AIKI air jet texturing machines, respectively. The processing parameters such as air pressure and yam speed are varied, and air pressure is varied ranging with 8.5bar, l0.5bar and 1l.5bar, and yarn speed is varied ranging with 400m/mim, 450m/mim, and 500m/min. The various physical properties of ATY made by POY and FDY denier, wet shrinkage, dry shrinkage, tensile properties, thermal stress and instability are measured and discussed with air pressure and yam speed. The shrinkage simulation of ATY is performed for analysing the process shrinkage on the dyeing and finishing processes.

• Magazine of the Korea Concrete Institute
• /
• v.2 no.1
• /
• pp.109-119
• /
• 1990

This study was accomplished to investigate the characteristics of hardening shrinkage and initial creep of epoxy resin concrete depending on the presence of filler. According to the test results, the hardening shrinkage was increased with increment of sLOrage temperature, and the ef¬feel of tempemture on the hardening shrinkage of epoxy resin concrete with 6% filler was more Significant than that of epoxy resin concrete without filler. Also, the initial creep strain was increased with loading times, stress--strength ratio and elastic strain, and the values for opoxy resin concrete with 6 % filler are higher than that for eposy resin concrete without filler.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2018.05a
• /
• pp.275-276
• /
• 2018

Ultra high performance concrete(UHPC) represents high early age autogenous shrinkage strain due to its low water-to-binder ratio(W/B) and high fineness admixture usage. It has been reported that fiber can control restrained tensile stress and crack. The purpose of the present study is, therefore, to investigate the autogenous shrinkage as well as mechanical properties including compressive strength, flexural strength and modulus of elasticity on the UHPC with fiber type and pre-mix of binder.