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Efficiency enhancement of sheet metal forming analysis with a mesh regularization method
No full text학위논문(석사) - 한국과학기술원 : 기계공학전공, 2003.2, [ vii, 65 p. ]성형해석 기법과 도구가 발달함에 따라 해석에 대한 신뢰도가 높아졌으며 이에 따라 보다 복잡한 형상을 갖는 구조물의 성형이나 다단계 성형 해석이 많아지게 되었다. 그러나 이러한 복잡한 형상을 갖는 구조물의 경우 국부적인 변형으로 인해 전체 구조물의 성형 해석 시간을 증가시키고 수렴성을 저하시킨다. 또한 다단계 해석의 경우, 1단계 성형 해석으로부터 얻어진 격자 구조를 다음 단계에 적용할 경우 1차 성형 해석으로 인한 격자의 왜곡과 변형이 심하여 이러한 효과가 다음 단계의 해석에 영향을 미치게 된다. 지금까지는 이러한 문제점을 보완하기 위하여 최종 성형물의 형상을 알고 있을 경우 전문가의 판단과 수작업에 의해 양질의 격자 구조를 재 구성하고 여기에 각종 변형률 값과 응력 값을 mapping 하여 다음 단계 해석에 적용하고 있으며 또 다른 방법으로는 성형해석 도중에 단계별로 격자의 왜곡을 측정하여 격자를 세분화해 가는 h-adaptivity 방법이 널리 쓰이고 있다. 그러나 이는 해석 시간이 급격히 늘어나고 분열된 다른 요소 사이에 제약이 가해진다는 단점이 생기게 된다.
본 논문에서는 성형 해석 도중에 발생하는 격자 구조의 국부적인 왜곡을 찾아 이를 그룹으로 생성하여 각각의 patch 로 만들고 patch 단위로 돌아가며 그 위에 놓인 격자 구조를 개선하게 된다. 또한 형성된 patch는 3차원 상에 자유 곡면을 이루고 있으므로 형상 차이를 최소화 하기 위하여 patch를 근사하는 NURBS 곡면을 생성하고 곡면 위의 영역에서 절점을 이동시켜 격자의 질을 향상 시키게 된다.한국과학기술원 : 기계공학전공
Strain hardening model of pure titanium considering effects of deformation twinning
No full textThis paper is concerned with the effect of deformation twinning on the strain hardening behavior of commercially pure titanium during the compressive loading. In accordance with many studies on titanium, the strain hardening behavior of titanium during compression has different characteristics from those of general metallic materials. It has been reported that the strain hardening rate of titanium during compression can be divided into three stages. In the first stage, the strain hardening rate decreases as the strain increases due to dynamic recovery. Following the first stage, however, a sudden increase in the strain hardening rate is observed in the second stage. It is well known that the occurrence of the second stage is due to the generation of deformation twinning. After the second stage, the strain hardening rate decreases again as the strain increases in the third stage. In this paper, a strain hardening model that can represent the three stages of strain hardening is proposed based on the investigated effect of deformation twinning on the strain hardening behavior of titanium. The electron backscatter diffraction (EBSD) analyses are conducted to quantify the twin volume fraction with increase of compressive plastic strain, which provide fundamental frame of the hardening model for titanium
Bending History in Finite Element Inverse Analysis of Deep Drawing Processes
No full textThis paper introduces a new approach to take account of bending history in finite element inverse analysis of a sheet metal forming process. A modified membrane element was adopted for finite element inverse analysis so that bending–unbending energy was additionally imposed on the total plastic energy. Bending–unbending regions were predicted from the geometry of the final shape and tools. The proposed method was applied to deep drawing processes of a cylindrical cup. The blank shape and the distribution of the thickness strain were compared with those obtained from the incremental finite element analysis to evaluate the effect of the bending history. The proposed method reduced the difference between the results of the inverse analysis and those of the incremental analysis. The analysis was also carried out changing the thickness of the initial blank to investigate the effect of bending deformation. The results showed that the difference was remarkably reduced as the thickness of the initial blank increased. This indicates that the suggested method is useful to obtain more accurate results especially when bending effects are significant
Failure Elongation of Steel Sheets for an Auto-body at the High Strain Rate
No full textThis paper presents the dynamic failure elongation of conventional mild steels and advanced high strength steel sheets such as TRIP and DP steels. The failure elongation has been obtained from the high speed tensile testing machine with various strain rates ranged from 0.003/s to 200/s. The experimental result demonstrates that the tensile elongation does not simply decrease as the strain rate increases, but it decreases from the quasi-static state to the strain rate of 0.1 or 1/s and increases again up to the strain rate of 100/s. Furthermore, some high strength steels have the tendency that the tensile elongation increases as the strain rate increases. This tendency has varieties depending on the microstructure and forming history of sheet metal. Moreover, the localized strain rate hardening in the necking region induces the increase of elongation. This phenomenon is very important not only in sheet metal forming but also in the crashworthiness evaluation to predict the fracture of sheet metal member
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Strain-rate potential based elastic/plastic anisotropic model for metals displaying tension-compression asymmetry
No full textTheoretical description of plastic anisotropy requires the definition of either stress potentials or plastic strain-rate potentials. In general, strain-rate potentials are more suitable for process design. Existing strain-rate potentials (phenomenological or texture-based) are applicable only to the description of the plastic behavior of materials with cubic crystal structure. Very recently, Cazacu et al. [9] have developed an orthotropic strain-rate potential applicable to metals that display tension-compression asymmetry when subjected to monotonic loading (e.g. hexagonal metals). This strain-rate potential is the exact work-conjugate of the anisotropic stress potential of Cazacu et al. [8]. In this paper, an elastic/plastic formulation based on the proposed strain-rate potential and a fully implicit time integration algorithm for this potential are presented. Finite-element tube bending simulation results demonstrate the capabilities of the model to represent the effects of the anisotropy and tension-compression asymmetry of the material on its mechanical response. If a material has the same yield in tension and compression, the strain-rate potential reduces to that proposed by Hill [17]. Further, validation of the robustness and accuracy of the integration algorithm is performed by using this new model and Hill [17] to simulate a circular cup drawing test of a steel plate. �� 2011 Elsevier B.V.Partial support for this work provided by NSF through grant CMMI- 0800197 and by AFOSR through grant FA9550-10-1-042 is gratefully acknowledged. Appendix
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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