• Tunnel and Underground Space
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• v.22 no.4
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• pp.284-295
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• 2012

Abrasiveness of rock plays an important role on the wear of rock cutting tools. In this study, Cerchar abrasiveness tests were carried out to assess the abrasiveness of 19 different Korean rocks. Cerchar abrasiveness test is widely used to assess the abrasiveness of rock because of its simplicity and inexpensive cost. This study examines the relationship between Cerchar Abrasiveness Index (CAI) and mechanical properties (uniaxial compressive strength, Brazilian tensile strength, Young's modulus, Poisson's ratio, porosity, shore hardness of rock), and the effect of quartz content, equivalent quartz content, which was obtained from XRD analysis. As a result of test, CAI was more influenced by petrographical properties than by the bonding strength of the matrix material of rock. CAI prediction model which consisted of UCS and EQC was proposed. CAI decreased linearly with the hardness of the steel pin. Numerical analysis was performed using Autodyn-3D for simulating the Cerchar abrasiveness test. In the simulations, most of pin wear occurred during the initial scratching distance, and CAI increased with the increase of normal loading.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.32 no.4
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• pp.447-456
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• 1996

본 논문은 선박 기관사의 실무 능력 평가를 위한 CAI 시스템의 설계와 구현에 관한 것이다. 지금까지 실무 기관사들을 위한 평가 시험은 주로 필답 시험과 구두 시험에 의존해 왔지만, 컴퓨터를 이용할 CAI 시스템을 사용함으로써 평가에 걸리는 시간을 단축할 뿐만 아니라 효율적인 평가를 할 수 있다. 시스템의 구성은 영역 지식, 질문, 예제 등으로 구성되어 있으며 13 관련 분야에 바탕을 두고 있다. 이 시스템의 사용자는 교사, 실습생, 학생, 선박관련 전문가들이 될 수 있다. 또한 이 시스템을 Client/server 환경으로 확장하기 위하여 Oracle 7.3과 PowerBuilder 5.0을 이용한 실험적인 환경을 설계하고 대표적인 Client page를 보여주고 있다.

• Composites Research
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• v.16 no.4
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• pp.66-73
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• 2003

The importance of understanding the response of structural composites to impact and CAI cannot be overstated to develop analytical models for impact damage and CAI strength predictions. This paper presents experimental findings observed from quasi-static lateral load tests, low velocity impact tests. CAI strength and open hole compressive strength tests using 3 mm thick composite plates($[45/-45/0/90]_{3s}$- IM7/8552). The conclusion is drawn that damage areas for both quasi-static lateral load and impact tests are similar and the curves of several drop weight impacts with varying energy levels(between 5.4 J and 18.7 J) follow the static curve well. In addition, at a given energy the peak force is in good agreement between the static and impact cases. It is identified that the failure behaviour of the specimens from the CAI strength tests was very similar to that observed in laminated plates with open holes under compression loading. The residual strengths art: in good agreement with the measured open hole compressive strengths. considering the impact damage site area, an equivalent hole. The experimental findings suggest that simple analytical models for the prediction of impact damage area and CAI strength can be developed on the basis of the failure mechanism observed from the experimental tests.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.1
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• pp.62-67
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• 2011

Nanoparticles-coated and impact-damaged carbon-fiber reinforced plastics(CFRP) laminates were tested under compression-after-impact(CAI) mode and the propagation of damage due to compressive loading has been monitored by acoustic emission(AE). The impact damage was induced not by mechanical loading but by a simulated lightning strike. CFRP laminates were made of carbon prepregs prepared by coating of conductive nano-particles directly on the fibers and the coupons were subjected to simulated lightning strikes with a high voltage/current impulse of 10~40 kA within a few microseconds. The effects of nano-particles coating and the degree of damage induced by the simulated lightning strikes on the AE activities were examined, and the relationship between the compressive residual strength and AE behavior has been evaluated in terms of AE event counts and the onset of AE activity with the compressive loading. The degree of impact damage was also measured in terms of damage area by using ultrasonic C-scan images. From the results assessed during the CAI tests of damaged CFRP showed that AE monitoring appeared to be very useful to differentiate the degree of damage hence the mechanical integrity of composite structures damaged by lightning strikes.

• Composites Research
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• v.16 no.2
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• pp.33-40
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• 2003

In order to overcome one of the most pronounced shortcomings of conventional laminated composites, such as the low damage tolerance due to delamination, the thermoplastic materials and 3D (three-dimensional) preforms have been utilized in the manufacture of composite materials. From the newly developed process termed as the co-braiding, hybrid yarns of the thermoplastic fibers (PEEK) and reinforcing fibers (carbon) have been fabricated. In order to further enhance the delamination suppression, through thickness fibers have been introduced by way of 3D weaving technique in the fabrication of textile preforms. The preforms have been thermoformed to make composite materials. Complete impregnation of the PEEK into the carbon fiber bundles has been confirmed. For the comparison of mechanical performance of 3D woven composites, quasi-isotropic laminates using APC-2/AS4 tapes have been fabricated. Tensile and compressive properties of both the composites have been determined. Furthermore. the open hole, impact and CAI(Compression After Impact) tests were also carried out to assess the applicability of 3D woven textile reinforced thermoplastic composites in aerospace structures.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.110-114
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• 2009

This study is for the evaluation of compressive strength restoration of sandwich composite laminates with adhesively bonded scarf patches. It was used in this study that the sandwich composite laminate with an aluminum honeycomb core and CF1263 woven fabric carbon/epoxy faces was applied to the car body structure for Korean tiling train. In this study, it was damaged by low velocity impact and repaired using scarf repair method. Then, the compressive strength restoration of assessed by compressive after impact (CAI) test. From the test, it could be known that the compressive strength was restored up to 72% by only scarf repair method and 91% applied by an extra ply over the undamaged one.

• Korean Journal of Materials Research
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• v.7 no.11
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• pp.974-980
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• 1997

SiC$_{p}$/AI 합금 복합재료에 있어서 동적 및 정적파괴인성시험을 실시하고 파괴거동에 미치는 부하조건의 영향을 검토하였다. 동적파괴인성시험은 CAI시스템을 이용하여 1.5m/sec의 부하속도로 실시하였고, 정적파괴인성시험은 만능시험기를 이용하여 0.3 mm/min의 부하속도로 실시하였다. 또한 파괴과정을 명확히 해석하기 위하여 동적부하조건에 대해서는 stop block법을, 정적부하조건에 대해서는 복수시험편법을 이용하였다. 균열의 발생 및 성장은 부하조건에 의해 크게 영향을 받으며, 변위량에 대한 균열의 발생은 정적부하조건에서 더 빨리 일어나고, 균열의 성장은 동적부하조건에서 더 급격하다. 또한 부하조건은 파괴의 형태에도 크게 영향을 미치며, 동적부하조건하에서는 정적부하조건하에 비하여 균열이 입자부분(입자의 파단 또는 박리)을통과해 가는 경향이 크고 비교적 많은 편향을 반복해서 진행해 가지 때문에 파괴인성치도 크다.다.

• Journal of the Korea Society of Computer and Information
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• v.13 no.6
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• pp.69-76
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• 2008

The biggest strength of the Internet is to enable to access information without any limitation of time and space. As the Internet and IT technologies have been developed, various kinds of teaching ways in education field such as remote lectures, video lectures, and CAI(Computer Adapted Instruction) have emerged. In terms of education, evaluation can be a basic foundation to help teach students in the next learning stage according to each student's level. In addition, it is able to give the information of students'abilities and provides proper learning programs to teach students on a case-by-case basis. The purpose of the paper is to establish evaluation system on the WWW(World Wide Web) that can reflect learning activities part of students in their evaluation scores based on the two important learning theories, Behaviorism and constructivism, which are mainly used in evaluation procedures to judge learning ability of students. This system will give information about learners, and analyze the learning interest of learners. The proposed system enables teachers to evaluate learning ability of students through various kinds of information of learners, and to execute level-based education.

• Composites Research
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• v.18 no.3
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• pp.38-46
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• 2005

In order to characterize the outstanding performance of three-dimensional (3D) composites, the low velocity impact test has been carried out. 3D fiber structures have been achieved by using the automated tape placement (ATP) process and a stitching method. Materials for the ATP and the stitching process were carbon/epoxy prepreg tapes and Kevlar fibers, respectively. Two-dimensional composites with the same stacking sequence as 3D counterparts have also been fabricated for the comparison of damage tolerance. For the assessment of damage after the impact loading, specimens were subjected to C-Scan nondestructive inspection. Compression after impact (CAI) tests were conducted to evaluate residual compressive strength. The damage area of 3D composites was greatly reduced $(30-40\%)$ compared with that of 2D composites. Although the CAI strength did not show drastic improvement for 3D composites, the ratio of retained strength was $5-10\%$ higher than 2D samples. The effect of stitching on the impact performance was negligible above the energy level of 35 Joules.

• Journal of the Korean Society for Railway
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• v.15 no.2
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• pp.109-115
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• 2012

In order to evaluate the effect of structural degradation of a GFRP composite bogie frame due to ballast-flying phenomena, the impact test and residual compression test after impact was conducted for glass fiber/epoxy 4-harness satin woven laminate composites applied to skin part of a bogie frame. The impact test was performed using a instrumented impact testing system with energy levels of 5J, 10J, and 20J, and the impactor was designed to have various ballast shapes such as sphere, cube, and cone to consider the ballasted track environments. The residual compression strength was tested to evaluate the degradation of mechanical properties of impact-damaged laminate composites. The results showed that the damage area and the degradation of residual compressive strength after impact for laminate composites was increased with increase of impact energy for all ballast shapes, and was particularly most influenced by ballast shape of cone.