• 한국안전학회지
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• 제28권6호
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• pp.57-63
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• 2013

This paper discusses 2D models of beams for simulating the fracture of brittle materials. A simulation of an experiment on a concrete beam subjected to bending, in which two overlapping cracks occur, is used to study the effect of individual beam characteristics and different arrangements of the beams in the overall network mesh. It was found that any regular orientation of the beams influences the resulting crack patterns. Methods to implement a wide range of poisson's ratios are also developed, the use of the mesh to study arbitrary micro-structures is outlined. The crack pattern that are obtained with mesh are in good agreement with the experimental results. Also, numerical simulations of the tests were performed by means of a model, and non-integer dimensions were measured on the predicted mesh damage patterns.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 춘계학술대회 논문집
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• pp.287-292
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• 1998

In this study behavior of fatigue crack and fatigue fracture is observed under rotary bending fatigue testing in friction welded dissimilar materials. Fatigue fracture most occurred in SM15C heat affected zone around Interface. In case of fatigue test, stress is reduced the position of fracture gradually moves to the welded Interface. Micro crack of heat affected zone surface on SM15C is observed at any different stress.

• Computers and Concrete
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• 제2권2호
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• pp.165-176
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• 2005

This paper discusses 2D lattice models of beams for simulating the fracture of brittle materials. A simulation of an experiment on a concrete beam subjected to bending, in which two overlapping cracks occur, is used to study the effect of individual beam characteristics and different arrangements of the beams in the overall lattice. It was found that any regular orientation of the beams influences the resulting crack patterns. Methods to implement a wide range of Poisson's ratios are also developed, and the use of the lattice to study arbitrary micro-structures is outlined. The crack patterns that are obtained with lattice are in good agreement with the experimental results. Also, numerical simulations of the tests were performed by means of a lattice model, and non-integer dimensions were measured on the predicted lattice damage patterns.

• 대한기계학회논문집A
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• 제32권11호
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• pp.943-950
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• 2008

A novel nondestructive testing (NDT) system, which is able to detect a crack with high speed and high spatial resolution, is urgently required for inspecting small cracks on express train wheels. This paper proposes a high speed scan type magnetic camera, which uses the multiple amplifying circuits and the crack indicating pulse output system. The linearly integrated Hall sensors are arrayed in parallel, and the Hall voltages from each sensor in the scanning direction are obtained and amplified. High-speed NDT can be achieved by using the exclusive analog-digital converter and micro-processor because the ${\partial}\;V_H/\;{\partial}$ x value, which provides the most important crack information, can be obtained by buffering and calculating. The effectiveness of the novel method was verified by examine using cracks on the wheel specimen model.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.747-749
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• 2006

SMS Meer GmbH, formerly Mannesmann and today part of the SMS Group, has been building powder presses since the early 1950s. The patents developed here in this field have long since documented the pioneering work carried out for the PM industry. The paper focuses on the challenge of reconciling the contradictory demands in the production of highly complex and crack-free PM parts. The process employed with the patented Controlled Punch Adapter (CPA) [1] counters possible cracking reliably and directly at the source. In this way is it possible to develop new and highly complex parts to series production maturity in a minimum of time even without simulation of the press cycle [2]. The quality data achieved in the production series, almost 100% crack and micro crack-free green parts with optimum density distribution over all press levels is unrivalled and thus gives the user a clear lead over the competition.

• 한국정밀공학회지
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• 제18권1호
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• pp.201-212
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• 2001

If defects are located far apart, fatigue cracks are independently initiated from them and gradually approach other cracks so that the fatigue life becomes influenced by the crack growth behavior of those interacting cracks. In this study, the effect of the stress interaction between defects on the fatigue crack propagation behavior is investigated experimentally and these results are verified by finite element method. In addition, fatigue crack propagation behaviors under micro hole interaction field are studied.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.976-979
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• 2002

This research presents the new method to fabricate small features through applying chemical mechanical micro machining(C3M) for Al5052 and single crystal silicon. To improve machinability of ductile and brittle material, reacted layer was formed on the surface before micro-drilling process by chemical reaction with $HNO_3$(10wt%) and KOH(10wt%). And then workpieces were machined to compare conventional micro-drilling process with newly suggested one. To evaluate whether or not the machinability was improved by the effect of chemical condition, surface defects such as burr, chipping and crack generation were measured. Finally, it is confirmed that C3M is one of the feasible tools for micro machining with the aid of effect of the chemical reaction.

• 한국정밀공학회지
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• 제32권5호
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• pp.463-470
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• 2015

Solar cell is typical representative of renewable green energy. Silicon wafer contributes about 66 percent to its cost structure. In its manufacturing, micro-cracks are often occurred due to manufacturing process such as wire sawing, grinding and cleaning. Their detection and classification are important to process feedback information. In this paper, a classification method of micro-cracks is proposed, based on the fusion of principal component analysis(PCA) and neural network. The proposed method shows that it gives higher results than single application of two methods, in terms of shape and size classification of micro-cracks.

• Computers and Concrete
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• 제24권6호
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• pp.499-511
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• 2019

In this paper, wave propagation of double-bonded Cooper-Naghdi micro sandwich cylindrical shells with porous core and carbon nanotube reinforced composite (CNTRC) face sheets are investigated subjected to multi-physical loadings with temperature dependent material properties. The governing equations of motion are derived by Hamilton's principle. Then, the influences of various parameters such as wave number, CNT volume fraction, temperature change, Skempton coefficient, material length scale parameter, porosity coefficient on the phase velocity of double-bonded micro sandwich shell are taken into account. It is seen that by increasing of Skempton coefficient, the phase velocity decreases for higher wave number and the results become approximately the constant. Also, by increasing of the material length scale parameter, the cut of frequency increases, because the stiffness of micro structure increases. The obtained results for this article can be used to detect, locate and quantify crack.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.239-245
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• 2006

초음파를 이용한 추진기관의 비파괴검사는 X-ray 검사에 비하여 경제성이 우수하고, X-ray 검사시 취약한 dis-bond, damage 등의 결함 검출이 우수한 편이다. 그리고 전용시설의 필요없이 현장에서 실시간으로 검사가 가능하며 방사선 작업에 비하여 안전한 방법이다. 본 논문에서는 고체 추진제에 대한 초음파 특성을 분석하고, 추진제/라이너 미접착에 대한 내측과 외측 검사 방법 및 추진제 damage에 의한 미세 크랙검출에 대하여 실험 및 분석하였다. 실험 결과, 추진제에서의 초음파 감쇠는 $6\sim8db/cm$로 비교적 큰 감쇠를 보였으며 추진제/라이너 미접착에 대한 내 외측 검사에 있어서도 제한된 조건이지만 검출 가능성을 보였다. 그리고 damage에 의한 추진제 미세 크랙도 초음파의 감쇠특성을 이용하여 검출 가능함을 보였다.