• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.936-938
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• 2017

본 논문에서는 발사체 및 무기체계의 연소관 등에 적용되고 있는 복합재의 볼트체결부에 대한 점진적 파손 해석을 수행하였다. 해석에 사용된 Hashin 파손 판정식은 복합재 파손모드에 따라 섬유 인장 파손 모드(Fiber tensile failure mode), 섬유 압축 파손 모드(Fiber compressive failure mode), 기지 인장 파손 모드(Matrix tensile failure mode), 기지 압축 파손 모드(Matrix compressive failure mode)의 4가지 모드로 고려되었으며, 이를 이용해 user subroutine인 UMAT을 개발하였다. 점진적 파손 해석을 통해 복합재 볼트체결부에 대한 파손강도를 예측 하였으며, 이를 시편 시험 결과와 비교하였다.

• Steel and Composite Structures
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• 제21권6호
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• pp.1327-1345
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• 2016

$Al_2O_3$/SiC particulate reinforced (Metal Matrix Composites) MMCs which were produced by using stir casting process, bending strength and hardening behaviour were obtained using an analysis of variance (ANOVA) technique that uses full factorial design. Factor variables and their ranges were: particle size $2-60{\mu}m$; the stirring speed 450 rpm, 500 rpm and the stirring temperature $620^{\circ}C$, $650^{\circ}C$. An empirical equation was derived from test results to describe the relationship between the test parameters. This model for the tensile strength of the hybrid composite materials with $R^2$ adj = 80% for the bending strength $R^2$ adj = 89% were generated from the data. The regression coefficients of this model quantify the tensile strength and bending strengths of the effects of each of the factors. The interactions of all three factors do not present significant percentage contributions on the tensile strength and bending strengths of hybrid composite materials. Analysis of the residuals versus was predicted the tensile strength and bending strengths show a normalized distribution and thereby confirms the suitability of this model. Particle size was found to have the strongest influence on the tensile strength and bending strength.

• Advances in concrete construction
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• 제8권1호
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• pp.21-31
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• 2019

The rich recipe of ultra high performance concrete (UHPC) offers the higher mechanical, durability and dense microstructure property. The variable like cement/sand ratio, amount of supplementary cementitious material, water/binder ratio, amount of fiber etc. alters the UHPC hardened properties to any extent. Therefore, to understand the effects of these variables on the performance of UHPC, inevitably a stage-wise development is required. In the present experimental study, the effect of sand/cement ratio, the addition of finer material (fly ash and quartz powder) and, hybrid fiber on the fresh, compressive and microstructural property of UHPC is evaluated. The experiment is conducted in three phases; the first phase evaluates the flow value and strength attainment of ingredients, the second phase evaluates the efficiency of finer materials (fly ash and quartz powder) to develop the UHPC and the third phase evaluate the effect of hybrid fiber on the flow value and strength of ultra high performance hybrid fiber reinforced concrete (UHP-HFRC). It has been seen that the addition of fly ash improves the flow value and compressive strength of UHPC as compared to quartz powder. Further, the usage of hybrid fiber in fly ash contained matrix decreases the flow value and improves the strength of the UHP-HFRC matrix. The dense interface between matrix and fiber and, a higher amount of calcium silicate hydrate (CSH) in fly ash contained UHP-HFRC is revealed by SEM and XRD respectively. The dense interface (bond between the fiber and the UHPC matrix) and the higher CSH formation are the reason for the improvement in the compressive strength of fly ash based UHP-HFRC. The differential thermal analysis (DTA/TGA) shows the similar type of mass loss pattern, however, the amount of mass loss differs in fly ash and quartz powder contained UHP-HFRC.

• Journal of Welding and Joining
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• 제14권4호
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• pp.99-108
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• 1996

The microstructure and bond strength are examined on the SiC/SiC and SiC/mild steel joints brazed by the Ag-Ti based alloys with different Ti contents. In the SiC/SiC brazed joints, the thickness of the reaction layers at the bond interface and the Ti particles in the brazing alloy matrices increase with Ti contents. When Ti is added up to 9 at% in the brazing alloy. $Ti_3SiC_2$ phase in addition to TiC and $Ti_5Si_3$ phase is newly created at the bond interface and TiAg phase is produced from peritectic reaction in the brazing alloy matrix. In the SiC/mild steel joints brazed with different Ti contents, the microstructure at the bond interface and in the brazing alloy matrix near SiC varies similarly to the case of SiC/SiC brazed joints. But, in the brazing alloy matrix near the mild steel, Fe-Ti intermetallic compounds are produced and increased with Ti contents. The bond strengths of the SiC/SiC and SiC/mild steel brazed joints are independent on Ti contents in the brazing alloy. There are no large differences of the bond strength between SiC/SiC and SiC/mild steel brazed joints. In the SiC/mild steel brazed joints, Fe dissolved from the mild steel does not affect on the bond strength of the joints. Thermal contraction of the mild steel has nearly no effects on the bond strength due to the wide brazing gap of specimens used in the four-point bend test. The brazed joints has the average bond strength of about 200 MPa independently on Ti contents, Fe dissolution and joint type. Fracture in four-point bend test initiates at the interface between SiC and TiC reaction layer and propagates through SiC bulk. The adhesive strength between SiC and TiC reaction layer seems to mainly control the bond strength of the brazed joints.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 추계학술발표대회 논문집
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• pp.25-28
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• 2003

Carbon nanotubes(CNTs), since their first discovery, have been considered as new promising materials in various fields of applications including field emission displays, memory devices, electrodes, NEMS constituents, hydrogen storages and reinforcements in composites due to their extra-ordinary properties. The carbon nanotube reinforced nanocomposites have attracted attention owing to their outstanding mechanical and electrical properties and are expected to overcome the limit of conventional materials. Various application areas are possible for carbon nanotube reinforced nanocomposites through the functionalization of carbon nanotubes. Carbon nanotube reinforced polymer matrix nanocomposites have been fabricated by liquid phase process including surface functionalization and dispersion of CNTs within organic solvent. In case of carbon nanotube reinforced polymer matrix nanocomposites, the mechanical strength and electrical conducting can be improved by more than an order of magnitude. The carbon nanotube reinforced polymer matrix nanocomposites can be applied to high strength polymers, conductive polymers, optical limiters and EMI materials. In spite of successful development of carbon nanotube reinforced polymer matrix nanocomposites, the researches on carbon nanotube reinforced inorganic matrix nanocomposites show limitations due to a difficulty in homogeneous distribution of carbon nanotubes within inorganic matrix. Therefore, the enhancement of carbon nanotube reinforced inorganic nanocomposites is under investigation to maximize the excellent properties of carbon nanotubes. To overcome the current limitations, novel processes, including intensive milling process, sol-gel process, in-situ process and spark plasma sintering of nanocomposite powders are being investigated. In this presentation, current research status on carbon nanotube reinforced nanocomposites with various matrices are reviewed.

• International Journal of Concrete Structures and Materials
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• 제18권2E호
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• pp.97-102
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• 2006

In this study, the effect of supplementary materials(GGBS, PFA, SF) on sulfuric acid corrosion resistance was assessed by measuring the compressive strength, corroded depth and weight change at 7, 28, 56, 91, 180 and 250 days of immersion in sulfuric acid solution with the pH of 0.5, 1.0, 2.0 and 3.0. Then, it was found that an increase in the duration of immersion and a decrease in the pH, as expected, resulted in a more severe corrosion irrespective of binders: increased corroded depth and weight change, and lowered the compressive strength. 60% GGBS mortar specimen was the most resistant to acid corrosion in terms of the corroded depth, weight change and compressive strength, due to the latent hydraulic characteristics and lower portion of calcium hydroxide. The order of resistance to acid was 60% GGBS>20% PFA>10% SF>OPC. In a microscopic examination, it was found that acid corrosion of cement matrix produced gypsum, as a result of decomposition of hydration products, which may loose the structure of cement matrix, thereby leading to a remarkable decrease of concrete properties.

• 한국분말재료학회지
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• 제1권2호
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• pp.159-166
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• 1994

The variation of the microstructures and the mechanical properties with varying vacuum hot pressing temperature and pressure was investigated in PyM processed 20 vol%) SiCw/ 2124Al composites. As increasing the vacuum hot pressing temperature, the aspect ratio of whiskers and density of composites increased due to the softening of 2124Al matrix with the increased amount of liquid phase. The tensile strength of composite increased with increasing vacuum hot pressing temperature up to $570^{\circ}C$ and became saturated above $570^{\circ}C$, To attain the high densification of composites above 99%, the vacuum hot pressing pressure was needed to be above 70 MPa. However, the higher vacuum hot pressing pressure above 70 MPa was not effective to increase the tensile strength due to the reduced aspect ratio of SiC whiskers from damage of whiskers during vacuum hot pressing. A phenomenological equation to predict the tensile strength of $SiC_w$/2124AI composite was proposed as a function including two microstructural parameters, i.e. density of composites and aspect ratio of whiskers. The tensile strength of $SiC_w$/2124AI were found more sensitive to the porosity than other P/M materials due to the higher stress concentration and reduced load transfer efficiency by the pores locating at whisker/matrix interfaces.

• Design & Manufacturing
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• 제14권4호
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• pp.11-16
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• 2020

In this study, forming of carbon composite parts was performed using an injection/compression molding process. An impregnation of matrix is determined by ability of wet and flow rate between the matrix and reinforcement. The flow rate of matrix passing through the reinforcements is a function of permeability of reinforcement, a viscosity of matrix and pressure gradient on molding, and the viscosity of the matrix depends on the mold temperature, molding pressure and shear strain of matrix. Therefore, compression molding experiment was conducted using a heating mold in order to confirm the possibility of matrix impregnation. The impregnation of the matrix through the porosities between the woven yarns was confirmed by the cross-sectional SEM image of compression molded parts. An injection molding process was also performed at a short cycle time, high molding pressure and low mold temperature than those of compression experiment conditions. Deterioration of impregnation on the surface of molded parts were caused by these injection conditions and it could be the reason of decreasing the maximum tensile strength. In order to improve impregnation of matrix on the surface, injection/compression molding and insert-over molding were applied. As a result of applying injection/compression molding and insert-over molding, it was shown that the improvement of impregnation on the surface and the maximum tensile strength was increased about 2.8 times than the virgin matrix.

• 한국신뢰성학회지:신뢰성응용연구
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• 제1권1호
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• pp.17-33
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• 2001

The characteristics of Weibull distribution are investigated as a function of shape parameter. The statistical estimation methods of the shape parameter and statistical comparison methods of two or more shape parameters are studied. Assuming Weibull distribution, statistical analysis of bending-strength data of alumina titanium carbide ceramic matrix composites machined two different methods are performed.

• The Journal of Advanced Prosthodontics
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• 제8권6호
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• pp.433-438
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• 2016

PURPOSE. The aim of this in vitro study was to evaluate the mechanical properties (bending strength and hardness) of seven different fiber reinforced composite posts, in relation to their microstructural characteristics. MATERIALS AND METHODS. Two hundred eighty posts were divided into seven groups of 40, one group for each type of post analyzed. Within each group, 15 posts were subjected to three-point bending strength test, 15 to a microhardess meter for the Knoop hardness, and 10 to Scanning Electron Microscope in order to determine the diameter of the fibers and the percentage of fibers embedded in the matrix. To compare the flexural strength in relation to the type of fiber, matrix, and the hardness of the posts, a Kruskal-Wallis H test was used. The Jonckheere-Terpstra test was used to determine if the volume percent of fibers in the post influenced the bending strength. RESULTS. The flexural strength and the hardness depended on the type of fibers that formed the post. The lower flexural strength of a post could be due to deficient bonding between the fiber and the resin matrix. CONCLUSION. According to the results, other factors, besides the microstructural characteristics, may also influence the mechanical properties of the post. The feature that has more influence on the mechanical properties of the posts is the type of fiber.