• Composites Research
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• v.17 no.3
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• pp.1-7
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• 2004

In the vacuum assisted RTM (VARTM) process that has become the center of attention for manufacturing massive composite structures, a good evacuation of air in the fiber preform is recognized as the prime factor. The microvoids, or the dry spots, are formed as a result of improper gate/vent locations and the mold geometry. The non-uniform resin velocity at the flow front leads to the formation of microvoids in the fibers, whereas the air in the microvoids can migrate along with the resin flow during mold filling. The residual air in the internal voids of a composite structure may cause a degradation of the mechanical properties as well as the structural failure. In this study, a unified macro- and micro analysis methods were developed to investigate the formation and transport of air in resin during VARTM process. A numerical simulation program was developed to analyze the three-dimensional flow pattern as well as the macro- and microscopic distribution of air in a composite part fabricated by VARTM process.

• Journal of the Korean Geosynthetics Society
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• v.23 no.1
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• pp.17-25
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• 2024

The Voids in the Mineral Aggregate (VMA) within asphalt mixtures play a crucial role in defining the mixture's structural integrity, durability, and resistance to environmental factors. Accurate prediction and optimization of VMA are essential for enhancing the performance and longevity of asphalt pavements, particularly in varying climatic and environmental conditions. This study introduces a novel machine learning framework leveraging ensemble machine learning model for predicting VMA in asphalt mixtures. By analyzing a comprehensive set of variables, including aggregate size distribution, binder content, and compaction levels, our framework offers a more precise prediction of VMA than traditional single-model approaches. The use of advanced machine learning techniques not only surpasses the accuracy of conventional empirical methods but also significantly reduces the reliance on extensive laboratory testing. Our findings highlight the effectiveness of a data-driven approach in the field of asphalt mixture design, showcasing a path toward more efficient and sustainable pavement engineering practices. This research contributes to the advancement of predictive modeling in construction materials, offering valuable insights for the design and optimization of asphalt mixtures with optimal void characteristics.

• International Journal of Highway Engineering
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• v.7 no.4 s.26
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• pp.79-89
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• 2005

Field and laboratory investigations were performed for concrete pavement of the Yeongdong Expressway located in western part of the Kangwon Province where lots of the substantially large spatting distresses were found. The spatting distresses were investigated to the naked eye in the field, and splitting tensile strength, air void, and neutralization tests were performed for the cores obtained from the pavement. In addition, load transfers at joints and dynamic bearing capacities at slab centers were measured to identify the lowering of the structural capability of the pavement. It was judged that the investigated concrete slabs were affected by freezing and thawing action because the air voids of the cores were substantially low. Therefore, it was concluded that the low air voids affected the lots of the large spatting distress in the pavement located in the region of cold winter.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.4
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• pp.191-197
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• 2018

This paper details the development of an isotropic elastic-damage constitutive model for polymeric foam based on irreversible thermodynamics to consider the growth and coalescence of voids. The constitutive equations describe the material behavior sustaining unilateral damage. To facilitate finite element analysis, the material properties for specific types of polymeric foams are applied to the developed model; the model is then implemented in ABAQUS as a user-defined material subroutine. To validate the developed damage model, the simulated results are compared to the results of a series of tensile tests on various polymeric foams. The proposed damage model can be utilized to further research on continuum damage mechanics and finite element analysis of polymeric foams in computational engineering.

• Korean Journal of Materials Research
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• v.18 no.1
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• pp.38-44
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• 2008

The micro-structural changes, strength characteristics, and micro-fractural behaviors at the joint interface between a Sn-4.0wt%Ag-0.5wt%Cu solder ball and UBM treated by isothermal aging are reported. From the reflow process for the joint interface, a small amount of intermetallic compound was formed. With an increase in the isothermal aging time, the type and amount of the intermetallic compound changed. The interface without an isothermal treatment showed a ductile fracture. However, with an increase in the aging time, a brittle fracture occurred on the interface due mainly to the increase in the size of the intermetallic compounds and voids. As a result, a drastic degradation in the shear strength was observed. From a microshear test by a scanning electron microscope, the generation of micro-cracks was initiated from the voids at the joint interface. They propagated along the same interface, resulting in coalescence with neighboring cracks into larger cracks. With an increase in the aging time, the generation of the micro-structural cracks was enhanced and the degree of propagation also accelerated.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.375-382
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• 1999

The use of compaction grouting system(C.G.S) evolved in the 1950's to correct structural settlement of buildings. Over the almost 50 years, the technology has developed and is currently used in wide range of applications. Compaction Grouting, the injection of a very stiff 'zero-slump' mortar grout under relatively high pressure, displaces and compacts soils. It can effectively repair natural or man-made soil strength deficiencies in variety of soil formations. Major uses of Compaction Grouting include densifying loose soils or fill voids caused by sinkholes, poorly compacted fills, broken utilities, improper dewatering, or soft ground tunneling excavation. Other application include preventing liquefaction, re-leveling settled structures, and using compaction grout bulbs as structural elements of minipiles or underpinning. So, on the basis of the case history constructed in recent year, a study has been performed to analyze the basic mechanism of the Compaction Grouting and verify the effectiveness of the ground improvement.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.04a
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• pp.406-413
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• 1998

The distinct element method is improved to consider the charateristics of stress wave propagation in media involving the discontinuous faces. The distinct element method has many advantages to analyse the characteristics of the reflection, refraction and deflection of the waves in nonhomogeneous media. The double-suing connection system is adopted instead of the single-spring connection system because the distinct element cannot be used for analysing the contact behavior between the different materials by only one contact spring. For the verification of the improved code, the results of the numerical analysis are compared with that of the photoelastic experiments which are one or two dimensional wave propagation problem of the nonhomogeneous media including the different accoustic impendence material or voids. It is shown that the characteristics of the stress wave propagation in nonhomogeneous media can be simulated appropriately using the improved distinct element method.

• Geomechanics and Engineering
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• v.16 no.5
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• pp.559-567
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• 2018

Technological innovations in sustainable materials for soil improvement have attracted considerable interest due to energy crisis and environmental concerns in recent years. This study presents results of a comprehensive investigation on utilization of nanocarbons in reinforcement of a residual soil mixed with 0, 10 and 20% bentonite. Effects of adding proportionate quantities (0, 0.05, 0.075, 0.1 and 0.2%) of carbon nanotubes and carbon nanofibers to soil samples of different plasticities were evaluated. The investigation revealed that the inclusion of nanocarbons into the soil samples significantly improved unconfined compressive strength, Young's modulus and indirect tensile strength. It was observed that carbon nanofibers showed better performance as compared to carbon nanotubes. The nanosized diameter and high aspect ratio of nanocarbons make it possible to distribute the reinforcing materials on a much smaller scale and bridge the inter-particles voids. As a result, a better 'soil-reinforcing material' interaction is achieved and desired properties of the soil are improved at nanolevel.

• Journal of the Korean Society of Clothing and Textiles
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• v.20 no.1
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• pp.157-169
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• 1996

Polyester yarns and fabrics containing three levels of $TiO_2$ delusterant were hydrolyzed with NaOH and examined for physical and morphological changes. The mechanical propertis and hand values of alkaline hydrolyzed polyester fabrics were measured using KES-FB system. Also, the relationship between the morphology and the mechanical property of alkaline hydrolyzed polyester fabrics was analyzed. The results are as follows: 1. At an initial stage of alkaline treatment, the concentration of $TiO_2$ did not affect the weight loss of the treated yarns. But by increasing treatment time, the effect of the concentration of $TiO_2$ on the weight loss of the fiber became more pronounced. The weight loss were increased in the following order; fulldull> semidull> clear 2. The effect of hydrolysis on yarn tensile strength seems to be more related to the size of the pits on the fibers rather than the number of pits. 3. Axially oriented pits occurred along the hydroyzed, delustered fiber surfaces, while such pitting was absent on hydrolyzed fiber containing no $TiO_2$. The number of voids across the surface of a fiber increased with an increase in the amount of TiOa incorporated into the fibers. The size of the voids depended on the treatment time of hydrolysis rather than the concentration of TiOa. 4. The mechanical properties and hand values of polyester fabrics were changed by alkaline treatment but were identical regardless of the concentration of TiOa. While the mechanical properties of polyester fabrics depended on the structural change of the fibers and the yarns within the fabrics as the fiber diameter became progressively smaller rather than the size and number of pits.

• Structural Engineering and Mechanics
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• v.71 no.4
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• pp.433-444
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• 2019

Shear studs are often used to connect steel girders and concrete deck to form a composite bridge system. The application of precast concrete deck to steel-concrete composite bridges can improve the strength of decks and reduce the shrinkage and creep effect on the long-term behavior of structures. How to ensure the connection between steel girders and concrete deck directly influences the composite behavior between steel girder and precast concrete deck as well as the behavior of the structure system. Compared with traditional multi-I girder systems, a twin-I girder composite bridge system is more simplified but may lead to additional requirements on the shear studs connecting steel girders and decks due to the larger girder spacing. Up to date, only very limited quantity of researches has been conducted regarding the behavior of shear studs on twin-I girder bridge systems. One convenient way for steel composite bridge system is to cast concrete deck in place with shear studs uniformly-distributed along the span direction. For steel composite bridge system using precast concrete deck, voids are included in the precast concrete deck segments, and they are casted with cast-in-place concrete after the concrete segments are erected. In this paper, several sets of push-out tests are conducted, which are used to investigate the heavier of shear studs within the voids in the precast concrete deck. The test data are analyzed and compared with those from finite element models. A simplified shear stud model is proposed using a beam element instead of solid elements. It is used in the finite element model analyses of the twin-I girder composite bridge system to relieve the computational efforts of the shear studs. Additionally, a parametric study is developed to find the effects of void size, void spacing, and shear stud diameter and spacing. Finally, the recommendations are given for the design of precast deck using void for twin I-girder bridge systems.