對稱 二重 板狀 表面龜裂의 相互干涉에 對한 硏究

崔鎔湜,梁源鎬,金永鎭,金在元 成均館大學校 科學技術硏究所 1988 論文集 Vol.39 No.2

In this paper, the authors experimentally investigated interaction effects of twin surface cracks on crack growth rate in the process of fatigue fracture. Because of convenience of measuring crack length toward the thickness direction, transparent PMMA plate specimens with twin circular arc type notches were used for the experiments. Fatigue tests were performed on the specimens with crack aspect ratio b/a=0.267 varying the width and thickness of the specimen. From the test results, the interaction effects of twin surface cracks on fatigue crack growth rate were evaluated, and crack growing aspects during fatigue crack growth process were examined as well. The followings were obtained fromm the experimental analyses. Regardless of the specimen thickness, it was found that the crack growth rate around the surface crack tip increased in the region of crack distance ratio λ{=(a + a*) /e} ≥ 1.0 according to the interaction effect of the twin surface cracks. The magnitude of the fatigue crack growth rate became larger in the following order; (1) the internal crack-tip points, (2) the deepest points of the crack-tip, and (3) the external crack-tip points. During the fatigue process, the varying crack aspect ratios (b/a) of colinear surface cracks appeared to be smaller than those of the single surface crack.

Mixed Mode Crack Initiation 에서의 Fracture Criterion 에 관한 연구 (Ⅰ)

최용식,구재민 成均館大學校 科學技術硏究所 1987 論文集 Vol.38 No.2

This paper has clarified that minimum strain energy density criterion (SED) is of use in the uniaxial tension, but not in the uniaxial compression concerning with the crack extension angle of the slit crack. The proposing concept of maximum Smin is solved with the problem of the Smin selection. This concept is that crack extends to the direction that sign (σ_θ)·Smin has a maximum value. Its result is very excellent. In the mixed mode crack propagation, σ_r seems to be an important factor, and it is clarified that Williams' stress solution neglecting non-singular terms isn't useful and Swedlow's modified solution with the transverse stress, σ_t is useful in the compression of slit cracks, and also Swedlow's of a friction coefficient has a good result.

R-Curve에 의한 破壞靭性 K_RC 결정에 관한 기초적연구

최용식,김재원 成均館大學校 科學技術硏究所 1983 論文集 Vol.34 No.2

The crack extension resistance curve (R-curve) is a plot of material resistance values (K_R) versus crack extension values (Δa). It is considered that for a given material, the R-curve depends only on temperature and specimen thickness. As was suggested by Irwin, the critical avlues K_RC and Δa_c at instability point are defined as the coordinate values of the tangential point between the R-curve and the crack extension force curve appropriate for the specific loading method. This paper covers the determination of critical resistance value K_RC for fracturing of Aluminum Alloy 2024-F by R-curves using the compact tension specimen. Conclusions are summarized as follows: (1) The shape of R-curve of a material having a given thickness does not depend on the initial crack length. (2) The value of critical stress intensity factor K_RC of a material having a given thickness and size does not depend on the initial crack length but retains a constant value. For Aluminum Alloy 2024-F, K_RC value is found to be around 165-170kg.mm^(3/2) (3) As the load increases, the curve of compliance EB2V_1/P vs. a/W has a steep positive slope. (4) The fracture appearances of the compact tension specimen are presented in two shapes in the process of fracturing, plane stress condition is considered to be prevailing in the specimen.

對稱 二重 表面缺陷의 疲勞龜裂成長擧動에 對한 硏究

崔鎔湜,金在元 成均館大學校 科學技術硏究所 1988 論文集 Vol.39 No.1

This paper is concerned with the fatigue crack growth behavior for twin surface cracks. PMMA was selected for the specimen material because PMMA is transparent and the crack length of thickness direction can be measured exactly. Tension specimens having twin circular arc-shaped notch were used in the testing process. The results obtained from a series of experiments are summarized as follows: 1. The fatigue crack propagation of shallow-type surfacs cracks such as the case of crack aspect ratrio c/a = 0.151 initiated at the deepest point of the crack. Therefore, stress intensity factor at this point is estimated to be maximum value. 2. The fatigue crack growth race of the width direction was larger than that of the thickness direction. 3. The interaction behavior between two surface cracks was obseved in the fatigue crack growth rates toward the thickness direction as well as in those in the width direction, particularly, in the latter was greater than in the former. The more surface crack-tips approache closely, the greater the fatigue crack growth rate increases rapidly by the crack-tip interaction effect. 4. During the stable fatigue cracks are propagating, two surface cracks keep the feature approximately semi-elliptical cracks having major axis to minor axis length ratio of 3/2.

단독표면균열재의 피로수명 예측 해석

최용식,양원호,김영진,김재원 成均館大學校 科學技術硏究所 1990 論文集 Vol.41 No.1

Recent studies have shown that the fatigue growth behavior of semi-elliptical surface crack cannot be adequately predicted solely by the stress intensity factor analysis. The variation in constraint along the crack border, from plane stress condition at the plate surface to plane strain condition at the point of maximum crack depth, must be an important factor affecting the fatigue crack growth behavior. In this paper, an analysis on the fatigue life prediction of a semi-elliptical surface cracked body was performed, accounting for the variation in constraint along the crack border. That is, the fatigue life for a surface cracked body was predicted using linear elastic fracture mechanics concepts that were modified to account for crack closure behavior. The model for the fatigue life prediction in consideration of crack closure phenomenon was developed, and then the predicted fatigue lives using the model were compared with test data from PMMA specimens. The predicted results appeared to be conservative.

2個의 對稱表面龜裂의 相互干涉擧動 解析과 龜裂形狀變化 豫測 解析

崔鎔湜,金在元 成均館大學校 科學技術硏究所 1991 論文集 Vol.42 No.1

2個의 對稱表面龜裂에 대한 應力擴大係數는 아직 數式化된 形態가 存在하지 않기 때문에, 먼저 2個의 對稱表面龜裂을 갖는 PMMA 板材를 試驗片材料로 選擇하여 一定振幅 引張-引張形 疲勞試驗을 遂行한 後, 表面龜裂이 成長함에 따라 隣接한 두 龜裂의 間隔變化에 의한 干涉擧動을 解析하여, 單獨表面龜裂의 應力擴大係數에 대한 2個의 對稱表面龜裂의 應力擴大係數의 比로 定義되는 相互作用係數(Interaction Factor)를 9次 多項式으로 數式化하였다. 이때 表面龜裂의 疲勞成長擧動을 適切하게 單純化시켜서, 두 表面龜裂間에 相互干涉效果가 있는 最近點에서의 相互作用係數를 구하였는데, 이 相互作用係數는 다른 硏究者들의 解析結果와 比較되어 妥當性이 立證되었다. 單獨表面龜裂材에 대한 龜裂形狀變化 豫測 모델이 이 相互作用係數에 適用되어 2個의 對稱表面龜裂을 갖는 材料의 龜裂形狀變化를 豫測하는 節次를 設定하였다. 이 節次에 따라 2個의 對稱表面 龜裂을 갖는 PMMA 板材試驗片에 대하여 龜裂形狀變化를 豫測하여 實驗結果와 比較하였다. 2個의 對稱表面龜裂의 形狀變化 豫測節次過程에서는 두 表面龜裂間의 相互干涉效果와 合體條件 등이 單純化되어 適用되었으며, 이러한 單純한 假定에 의하여도 상당히 精密度 좋게 龜裂의 形狀變化가 豫測되었다. 또한 單獨表面龜裂의 形狀變化 豫測에서, 낮은 應力水準 즉, σ_max<0.2σ_YS의 範圍에서 龜裂形狀變化를 精密度 좋게 豫測하기 위하여 導入된 補正係數 F_s의 有效性이, 2個의 對稱表面龜裂의 形狀變化 豫測에서도 立證되었다. An analysis scheme for predicting the crack aspect pattern of materials which contain twin surface cracks was developed. Fatigue tests were performed on twin surface cracked PMMA plate specimens to obtain the interaction factor accounting for the interference effect of adjacent cracks. Here, the interaction factor is defined as the ratio of the stress intensity factor for twin surface cracks to that for a single surface crack. From the analysis of the fatigue test results, the interaction factor was presented as the ninth-order polynomial expression having a function of dimensionless crack spacing ratio. Then the polynomial expression was incorporated into the prediction program of the crack aspect pattern for twin surface cracked materials. And, the interaction effect and the coalescence condition of adjacent cracks were simplified in the newly developed prediction scheme of the crack aspect pattern. The predicted crack growth pattern using the prediction scheme was compared with test data from PMMA specimen. The predicted pattern agreed well with the test data.

Direct Stiffness Matrix에 의한 線型트러쓰 構造物의 解析

尹載殖,崔外鎬 全北大學校 1969 論文集 Vol.11 No.-

The direct stiffness matrix method has gained prominence in the last decade decade mainly for determining internal forces and displacementsof highly redundant strctures. A computerized analytical approach, using the direct stiffness matrix method, is developed for plane and space truss andtwo examples are solved for each truss. This method is more concise than the other matrix methods. Therefore the computer program data input are greatly simplfied.

表面龜裂의 疲勞成長擧動에 대한 破壞力學的 解析(Ⅱ) : 單一 表面龜裂材의 殘餘壽命豫測과 貫通擧動 Life Prediction and Through Thickness Behavior for Single Surface Cracked Specimens

崔鎔湜,梁源鎬,金永鎭,金在元 成均館大學校 科學技術硏究所 1989 論文集 Vol.40 No.1

Different methods of prediction for the remaining life and the aspect ratio variation w growing surface fatigue cracks in PMMA plates were compared with experimental data. The purpose of the study was to find out the most credible method. The methods evaluated in the present study included 'our assumptions based on the Newman-Raju solution of the stress intensity factor of surface cracks. In the low stress level of σ_max<0.2σ_Y, the assumption m_a≠m_b, C_a≠C_b based on the former experimental data appeared to be in excellent agreement with the present study, and the assumption m_a=m_b, (C_a)^x = C_b, x = (m_a)^0.04 proposed by the authors appeared to be in good agreement with experimental data and to be useful in predicting fatigue life of surface cracks under cyclic tension.

沃化水銀 (Hgl_2)半導體 放射線檢出器 製作에 關한 硏究

田載植,張忠根,吳熙弼 충남대학교 기초과학연구소 1983 연구논문집 Vol.4 No.-

As a preliminary study of fabricating semiconductor gamma-ray detector for practical use at room temperature, α-phase HgI_2 single crystals were grown by means of statical evaporation after appropriate purification of commercially available chemical grade HgI_2 powder. For the crystals grown, examination or measurements of such physical properties as thermal resistivity, photoconductivity and band gap energy including an evaluation of spectrometric characteristics, were carried out. The band gap energy were found to be 2.11eV. Results are summarized and illustrated in graphical forms. Throughout the study it is concluded that a priori purification of HgI_2 condition of crystal growing, polishing the surface and ohmic contact in fabricating a detector are particularly important parameters on which quality of the detector is largely dependent.

競爭과 協力 : 韓·日·中의 蹴球競技를 通하여 본 3國人의 文化心理 A study on the cultural Psychological of Korean, Japanese and Chinese on Soccer Games

강재식 경희대학교 체육대학 한국체육과학연구소 2002 體育學論文集 Vol.30 No.-

'This thesis is focused on cultural psychology investigated through Soccer games among three Countries of North Eastern Asia. Those nations are Korea, Japan, and China. They have shared long history. Sometimes peaceful, and sometimes they had horrible moment from their relationship in history. Now, what I would like to see is a possibility of communication of these different cultures who still share similar memories. Soccer game is very popular in these days. And the World Cup 2002 was, we can say, a climax, we have noticed that these countries had special attitude towards soccer game. It was not just a game. They were not just a spectators. They were identified themselves with those soccer players who were running on the ground sweating all over to win the game. They were there as 12th Soccer Team player who has played their role on the stand. Each team has special group of young people named. 'Red Devil' for Korea, 'Ultra Nippon' for Japan, and 'Cheer Leaders of Soccer' for China. These young people do not share their historical experience with their parents' generation, nor with their ancestors. Mostly what they care is about 'what now'. What these different cultural understanding of young generation indicated was possibility of communication and cooperation through a similar culture-cultural psychology which also could lead us to a cultural, economical, and even political cooperation. Now we live in a global world with high level of information technology. we could share any ideas and cultures through network regarles where you are and who you are. Would this be a big leap if I say we can expect more chances of cooperation amond these countries through the power of network and the similar cultural psychology.