Sukhoon Pyo

3D-Damage Model for Fiber-Reinforced Brittle Composites with Microcracks and Imperfect Interfaces

A three-dimensional (3D) micromechanics-based evolutionary damage model is proposed to predict the effective elastic behavior of continuous fiber-reinforced brittle matrix composites with microcracks and imperfect interfaces. Eshelby’s tensor for a circular cylindrical inclusion with slightly weakened interface is adopted to model continuous fibers with imperfect interfaces. The nucleation of microcracks is simulated by employing the continuum damage model. A multilevel damage modeling process in accordance with Weibull’s probabilistic function is incorporated into the micromechanical framework to describe the sequential evolution of imperfect interfaces in the composites. Numerical examples corresponding to uniaxial loadings in the longitudinal and transverse directions are solved to illustrate the potential of the proposed damage model. Furthermore, the present prediction is compared with available experimental data in the literature to highlight the applicability of the proposed model.

Experimental Investigation of Multi-mode Fiber Laser Cutting of Cement Mortar

This study successfully applied multi-mode laser cutting with the variation of the laser cutting speed to cement mortar for the first time. The effects of the amount of silica sand in the cement mortar on laser cutting are tested and analyzed. The kerf width and penetration depth of the specimens after laser cutting are investigated. As the laser cutting speed increases, the penetration depth decreases for both cement paste and cement mortar, whereas the kerf width becomes saturated and increases, respectively, for cement paste and cement mortar. Cross sections of the specimens are compared with illustrations. Top-view images of the cement mortar with indicators of the physical characteristics, such as re-solidification, burning, and cracks are examined, and the possible causes of these characteristics are explained. The optical absorption rates of cement-based materials are quantified at wide ranges of wavelength to compare the absorption rates in accordance with the materials compositions. The chemical composition variation before and after laser cutting is also compared by EDX (Energy Dispersive X-Ray) analysis. In addition to these observations, material removal mechanisms for cement mortar are proposed.

Effect of Laser Speed on Cutting Characteristics of Cement-Based Materials

The results of an experimental investigation on the physical and chemical characteristics of cement-based materials under laser interactions are presented. The laser cutting tests were conducted using a multi-mode continuous fiber laser with a laser power of 1 kW. The experimental variables were laser speed, water to cement ratio, and material compositions including cement paste, cement mortar, and ultra high-performance concrete (UHPC). In order to evaluate the mass removal mechanisms of cement-based materials under laser interactions, the effect of laser cutting was evaluated in terms of kerf width, penetration depth, and chemical composition changes before and after the interaction with laser using EDX analysis. The test results reveal that adding silica sand in cement-based materials leads to decreasing penetration depth and increasing kerf width. Unlike the cement paste and cement mortar series, UHPC specimens showed no discernible crack observed by the naked eye after laser interaction due to its high strength. Furthermore, the chemical analysis indicates that chemical composition changes were caused by various mechanisms including dehydration of calcium hydroxide and thermal decomposition of calcium carbonate.

Review of Standards on Railway Noise and Suggestions on Directions for the Development of Sound Absorbable High Strength Concrete

본 연구에서는 최근 그 중요성이 날로 증대되고 있는 철도소음과 관련한 세계 주요나라의 기준들을 비교 · 검토하였다. 증가하는 철도의 고속화 수요증대와 이에 따른 유지보수 비용저감을 위해 기존 자갈궤도 대신 콘크리트 슬래브궤도의 도입이 늘고 있는 추세인데, 콘크리트 슬래브궤도는 음을 반사시키는 특성으로 소음레벨을 높이는 단점을 가지고 있다. 이에 따라 철도 소음을 효과적으로 대응할 수 있는 방안중의 하나로 소음저감형 콘크리트 슬래브궤도 개발을 위한 주요 검토사항들을 제시하였다. 높은 흡음성능을 갖는 콘크리트의 개발을 위해 공극률 측정방법, 실내에서 측정할 수 있는 흡음률 측정방법, 단일지수로 흡음계수를 표현할 수 있는 평가방법들을 비교·검토하였다. 또한 흡음률 예측모델들을 저자들에 의해 최근에 개발된 흡음콘크리트의 시험결과들과 비교 · 분석 하였다.