Multi-scale Progressive Failure Analysis of Triaxially Braided Textile Composites

Geleta, Tsinuel N.,Woo, Kyeongsik The Korean Society for Aeronautical and Space Scie 2017 International Journal of Aeronautical and Space Sc Vol.18 No.3

In this paper, the damage and failure behavior of triaxially braided textile composites was studied using progressive failure analysis. The analysis was performed at both micro and meso-scales through iterative cycles. Stress based failure criteria were used to define the failure states at both micro- and meso-scale models. The stress-strain curve under uniaxial tensile loading was drawn based on the load-displacement curve from the progressive failure analysis and compared to those by test and computational results from reference for verification. Then, the detailed failure initiation and propagation was studied using the verified model for both tensile and compression loading cases. The failure modes of each part of the model were assessed at different stages of failure. Effect of ply stacking and number of unit cells considered were then investigated using the resulting stress-strain curves and damage patterns. Finally, the effect of matrix plasticity was examined for the compressive failure behavior of the same model using elastic, elastic - perfectly plastic and multi-linear elastic-plastic matrix properties.

Molecular Marker Development and Gene Cloning for Diverse Disease Resistance in Pepper (Capsicum annuum L.): Current Status and Prospects

Geleta Dugassa Barka,이준대 한국육종학회 2020 Plant Breeding and Biotechnology Vol.8 No.2

The production of chili pepper (Capsicum annuum L.) is hindered by several biotic factors even though stridingprogresses were made in genetic improvement in the last two decades. Among the advancements were the fast-track geneticimprovement of disease-resistant varieties by the use of marker-assisted selection (MAS) and the conventional breeding-based introgressionof major resistance genes. Marker development, marker-based identification and fine mapping have revealed a large numberof resistance genes, from which cloning of some candidate genes demonstrated the applicability and versatility of map-based cloningfor disease resistance. In some of the recent fine mapping of disease resistance QTLs, closely linked DNA markers were identified,which in turn resulted in the rapid introgression of target gene(s) into breeding lines. Also, progresses were made on the characterizationand map-based cloning of resistance genes conferring broad-spectrum resistance. As the number of identified and characterizedresistance genes and the DNA markers linked to resistance genes are steadily generated, the development of multiple/durable resistanceto major chili pepper diseases is accelerated by MAS. In the present review, the development of molecular markers, marker-basedmapping of genes conferring resistance to ten major chili pepper diseases were discussed, focusing on the recent advancements in majorand QTL-spanning resistance gene mapping. The review provides up-to-date insights into the development of DNA markers linked todisease resistance genes and the cloning of resistance genes, which are all so crucial in pepper breeding for disease resistance.

Delamination Behavior of L-Shaped Laminated Composites

Geleta, Tsinuel N.,Woo, Kyeongsik,Lee, Bongho The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.2

We studied the delamination behavior of L-shaped laminated composites numerically and experimentally. In finite-element modeling, cohesive zone modeling was used to simulate the delamination of plies. Cohesive elements were inserted between bulk elements at each interlayer to represent the occurrence of multiple delaminations. The laminated composite models were subjected to several types of loading inducing opening and shearing types of delamination. Numerical results were compared to those in the literature and of experiments conducted in this study. The results were carefully examined to investigate diverse delamination initiation and propagation behaviors. The effect of varying presence and location of pre-crack was also studied.

Prediction of Effective Material Properties for Triaxially Braided Textile Composite

Geleta, Tsinuel N.,Woo, Kyeongsik,Lee, Bongho The Korean Society for Aeronautical and Space Scie 2017 International Journal of Aeronautical and Space Sc Vol.18 No.2

In this study, finite element modeling was used to predict the material properties of tri-axially braided textile composite. The model was made based on an experimental test specimen which was also used to compare the final results. The full interlacing of tows was geometrically modelled, from which repeating parts that make up the whole braid called unit cells were identified based on the geometric and mechanical property periodicity. In order to simulate the repeating nature of the unit cell, periodic boundary conditions were applied. For validation of the method, a reference model was analyzed for which a very good agreement was obtained. Material property calculation was done by simulating uniaxial and pure shear tests on the unit cell. The comparison of these results with that of experimental test results showed an excellent agreement. Finally, parametric study on the effect of number of plies, stacking type (symmetric/anti-symmetric) and stacking phase shift was conducted.

Antioxidant Activity and Mineral Content of Unripe Apples Grown in Gangwon-Do

Birtukan Geleta,Do-Hoon Lee,Jae-Yun Heo 한국원예학회 2022 한국원예학회 학술발표요지 Vol.2022 No.11

Antioxidant Activity and Mineral Content of Unripe Apples Grown in Gangwon-Do

Birtukan Geleta,Do-Hoon Lee,Jae-Yun Heo 한국원예학회 2022 한국원예학회 학술발표요지 Vol.2022 No.11

Inclined Adhesive Composite Joint Analysis with Cohesive Zone Modeling

Tsinuel Nurilligne Geleta(찌누엘 누릴린 젤레타),Kyeongsik Woo(우경식),Yunsun Choi(최윤선) 한국항공우주학회 2015 한국항공우주학회 학술발표회 논문집 Vol.2015 No.11

본 연구에서는 경사진 접착 조인트의 응력과 파괴 거동을 전산해석을 통하여 연구하였다. 응집요소모델링을 이용하여 접착부의 균열 발생과 성장을 모사하였다. 조인트는 라미네이트 웹, 웨지 블록, 그리고 접착부로 구성되어 있으며, 2 차원 평면 응력 상태로 모델링 되어 있다. 본 연구에서는 접착부 필렛 형상, 접착부 필렛 사이즈, 접착부 두께, 라미네이트 웹의 꺽김 반경, 그리고 웨지 블록 각도에 따른 조인트의 강도를 비교하였다. 또한, 실험상에서 나타날 수 있는 접합부의 결함에 의하여 발생할 수 있는 거동을 조사하였다. In this study, the stress and failure behavior of adhesive joints has been examined using FEA. Cohesive zone modeling has been used to simulate the crack initiation and propagation through the adhesive. First, a joint assembly consisting of laminated web, wedge block and adhesive was modeled using 2-dimensional finite elements in plane stress condition. Then, five of the geometric parameters, namely, adhesive fillet shape, adhesive fillet size, adhesive thickness, laminate bend radius and wedge block angle have been examined for their effect on the strength of the joint assembly. Furthermore, examination of flaws within the adhesive and at the interface with the adherend was done.

The Cement Industry in Ethiopia

DURE MULATU GELETA,LULIT HABTE EKUBATSION,안지환 한국에너지학회 2018 에너지공학 Vol.27 No.3

The cement industry is one of the rapidly growing industry in Ethiopia. The average per capita cement consumption of the country has increased from 39kg to 62kg. However, this is still way below than the global average per capita consumption of 500kg. The Ethiopian government is planning to expand its cement industry by upgrading the current cement plants and also opening of new cement plants in order to meet the future demand of the country. Currently, the number of cement plants in Ethiopia has reached to 20. By the year 2025, per capita cement consumption is expected to increase to 179kg. Recently, Ethiopia has become one of Africa’s largest market for the cement industry. In addition, Ethiopia has become the major exporter of cement in the Sub-Saharan African region. The Ethiopian cement industry is highly dependent on the use of imported energy sources for its production. This situation has a significant amount of impact on the high production costs of the industry. This paper will try to review the history, production, available resources, the technologies and energy use of the Ethiopian cement industry.

Effect of Material Type, Support Condition and Cutouts on Rectangular Plate Frequency Analysis

( Tsinuel N. Geleta ),( Kyeongsik Woo ) 충북대학교 건설기술연구소 2016 建設技術論文集 Vol.35 No.1

단순 사각형 평판의 진동문제는 보다 복잡한 구조물의 진동거동을 이해하는데 유용하다. 본 연구에서는 3종류의 재료와 2종류의 경계조건, 그리고 3종류의 컷아웃을 고려한 사각형 평판의 진동해석을 수행하였다. 평판형상은 중앙, 에지 및 모서리에 컷아웃이 있는데 이를 4절점 쉘요소로 모델링 하였다. 등방성과 직교이방성 재료에 따른 효과를 알아보기 위하여 강철 및 알루미늄과 T300/에폭시 적층 라미네이트 재료를 고려하였다. 해석결과 재료의 물성치는 진동형상보다는 진동수에 더 큰 영향을 미치고 있음을 알 수 있었다. 또한 컷아웃이 없는 형상에 비해 모서리 컷아웃을 가진 형상이 진동수 및 진동형상의 관점에서 가장 큰 변화를 보였다. Vibration of simple rectangular plates can be used to get insight of the vibration behavior of more complicated structures. In the present work, frequency analyses were performed in which three types of materials were considered with two types of support condition and three types of cutout positions. Finite element modeling with four node shell elements was used to model the plate. The materials used are steel, aluminium and T700/Epoxy unidirectional laminated composite to demonstrate the effect of isotropic material against orthotropic. For the Cutouts, circular cutouts at the center, edges and corners were placed. The results showed that effect of material type was more significant on the natural frequency than the mode shapes. In terms of the cutouts, the corner cutout had the highest effect on both natural frequency and mode shape change from the pristine model.

Prediction of Effective Material Properties for Triaxially Braided Textile Composite

Tsinuel N. Geleta,Kyeongsik Woo,Bongho Lee 한국항공우주학회 2017 International Journal of Aeronautical and Space Sc Vol.18 No.2

In this study, finite element modeling was used to predict the material properties of tri-axially braided textile composite. The model was made based on an experimental test specimen which was also used to compare the final results. The full interlacing of tows was geometrically modelled, from which repeating parts that make up the whole braid called unit cells were identified based on the geometric and mechanical property periodicity. In order to simulate the repeating nature of the unit cell, periodic boundary conditions were applied. For validation of the method, a reference model was analyzed for which a very good agreement was obtained. Material property calculation was done by simulating uniaxial and pure shear tests on the unit cell. The comparison of these results with that of experimental test results showed an excellent agreement. Finally, parametric study on the effect of number of plies, stacking type (symmetric/anti-symmetric) and stacking phase shift was conducted.