Effect of Cutout Orientation on Stress Concentration of Perforated Plates with Various Cutouts and Bluntness

Woo, Jin-Ho,Na, Won-Bae Korean Society of Ocean Engineers 2011 International journal of ocean system engineering Vol.1 No.2

Perforated plates with cutouts (or holes) are widely used in structural members. These cutouts provide stress concentration in plates. Extensive studies have been carried out on stress concentration in perforated plates, which consider cutout shapes, boundary conditions, bluntness of cutouts, and more. This study presents stress concentration analyses of perforated plates with not only various cutouts and bluntness but also different cutout orientations. Especially, the effect of cutout orientation on stress concentration is emphasized since structural members have become more complicated recently. To obtain stress concentration patterns, a finite element program, ANSYS, is used. For the designated goal, three parameters are considered as follows: the shapes of polygonal cutouts (circle, triangle, and square), bluntness (a counter measure of radius ratio, r/R), and rotation of cutouts (${\theta}$). From the analyses, it is shown that, in general, as bluntness increases, the stress concentration increases, regardless of the shape and rotation. A more important finding is that the stress concentration increases as the cutouts become more oriented from the baseline, which is the positive horizontal axis (+x). This fact demonstrates that the orientation is also a relatively significant design factor to reduce stress concentration. In detail, in the case of the triangle cutout, orienting one side of the triangle cutout to be perpendicular to the applied tensile forces is preferable. Similarly, in the case of the square cutout, it is more advantageous to orient two sides of square cutout to be perpendicular to the applied tensile force. Therefore, at the design stage, determining the direction of a major tensile force is required. Then, by aligning those polygon cutouts properly, we can reduce stress concentration.

Is Stress Concentration Relevant for Nanocrystalline Metals?

Kumar, Sandeep,Li, Xiaoyan,Haque, Aman,Gao, Huajian American Chemical Society 2011 Nano letters Vol.11 No.6

<P>Classical fracture mechanics as well as modern strain gradient plasticity theories assert the existence of stress concentration (or strain gradient) ahead of a notch tip, albeit somewhat relaxed in ductile materials. In this study, we present experimental evidence of extreme stress homogenization in nanocrystalline metals that result in immeasurable amount of stress concentration at a notch tip. We performed in situ uniaxial tension tests of 80 nm thick (50 nm average grain size) freestanding, single edge notched aluminum specimens inside a transmission electron microscope. The theoretical stress concentration for the given notch geometry was as high as 8, yet electron diffraction patterns unambiguously showed absence of any measurable stress concentration at the notch tip. To identify possible mechanisms behind such an anomaly, we performed molecular dynamics simulations on scaled down samples. Extensive grain rotation driven by grain boundary diffusion, exemplified by an Ashby–Verrall type of grain switching process, was observed at the notch tip to relieve stress concentration. We conclude that in the absence of dislocations, grain realignment or rotation may have played a critical role in accommodating externally applied strain and neutralizes any stress concentration during the process.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2011/nalefd.2011.11.issue-6/nl201083t/production/images/medium/nl-2011-01083t_0006.gif'></P>

주의집중력이 스트레스와 정서반응에 미치는 영향

위오기,지성구,왕위 한국경영컨설팅학회 2017 경영컨설팅연구 Vol.17 No.3

본 연구는 대학생들의 주의집중력이 스트레스와 정서에 미치는 영향과‚ 스트레스가 집중력과 정서에 미치는 영향을 검증하고자 하는 연구 목적을 설정하였다. 충남권 소재 대학에 재학중인 대학생 235명을 대상으로 연구한 결과는 다음과 같다. 첫째‚ 집중력은 스트레스에 부정적 영향을 미쳤다. 둘째‚ 스트레스는 부정 정서에 긍정적 영향을 미쳤다. 셋째‚ 집중력은 긍정 정서에 긍정적 영향을 미치고, 부정 정서에 부정적 영향을 미쳤다. 이러한 연구결과를 바탕으로 시사점을 제시하였다. 첫째‚ 대학생들이 집중력을 증대시키는 훈련에 참여하거나, 대학교에서 집중력 훈련 프로그램 등을 학생들에게 제공하면 긍정적 효과를 기대할 것으로 보인다. 둘째‚ 대학생들의 스트레스를 효과적으로 감소시킬 수 있는 단기특강이나 정규 학점 과정의 개설을 제안한다. 셋째‚ 대학들은 교양과목으로 명상과목을 도입하여 운영하는 것도 하나의 방안이 될 수 있다. 그리고‚ 이 연구의 한계와 미래 연구의 방향도 제시하였다. The purpose of this study was to investigate the effect of concentration of university students on stress and emotion, and the effect of stress on concentration and emotion. The results of the study are as follows: 235 college students in Chungnam area. First, concentration has a negative effect on stress. Second, stress affects positive emotions negatively, but negative emotions positively. Third, concentration had a positive effect on positive emotions and negative affect on negative emotions. Based on the results of this study, implications are suggested. First, if college students participate in training to increase their concentration, they will be helped in stress and emotional management. It is also expected that the university will have a positive effect if it provides students with concentration training programs. Second, universities propose the establishment of short-term lectures or regular credit courses that can effectively reduce the stress of college students. Third, universities can introduce meditation courses as a liberal arts subject and operate them. And the limitations of the research and future research directions are suggested.

Strain-Rate Effect on the Stress and Strain Concentration in a Visco-Plastic Plate With An Elliptic Hole

Yanqiu Chen,Jin Zhang,Peishi Yu,Jian Wu,Weibo Wang,Junhua Zhao 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.4

The stress and strain concentration in some component has been a signifi cant topic for structural safety assessment. However, the evaluation of the stress and strain concentration based on the widely existing solutions for linear elastic material under static loading would lead to remarkable errors when the material undergoes the dynamic loading, since the coupling eff ect induced by the nonlinearity of the stress–strain relationship and the strain-rate strengthening could be of signifi cant infl uence. Here we analyzed the strain-rate dependent concentration of stress and strain for a visco-plastic plate with an elliptic hole subjected to dynamic loading. The three-dimensional stress and strain are calculated by fi nite element analyses based on a rate-dependent Johnson–Cook model in which the material constants are set according to a typical visco-plastic standard 45 carbon steel. Our results show that both the plastic stress and strain concentration factors signifi cantly depend on not only the strain but also the strain rate. With the increment of the remote strain rate, the stress concentration monotonically increases, while the strain concentration shows decreasing tendency.

Interfacial Stress Concentrations of Vertical Through-plate to H-beam Connections in CFT Column

Choi, Insub,Chang, HakJong,Kim, JunHee Council on Tall Building and Urban Habitat Korea 2020 International journal of high-rise buildings Vol.9 No.4

This paper aims to evaluate the interfacial stress concentrations on connection between vertical through-plate and H-beam in CFT column. Full-scale experiments were performed on three specimens with varying thickness of the vertical through-plate to investigate the interfacial stress concentration factor in the connections. The specimens underwent brittle failure at the location where the steel beam is connected to the vertical through-plate before the steel beam reached its plastic moment. The strain data of the part were analyzed, and the sectional analyses were conducted to determine appropriate residual stress models. In addition, the stress concentration factor was quantified by comparing the analytical local behavior in which the stress concentration is not reflected and the experimental data reflecting the stress concentration. The results showed that the maximum reduction of the stress concentration factor due to an increase in the thickness of the vertical through-plate is 50.3%.

뇌교육 기반 인성프로그램이 초등학생의 스트레스 및 집중력에 미치는 영향

이정민,오미경 사단법인 인문사회과학기술융합학회 2019 예술인문사회융합멀티미디어논문지 Vol.9 No.9

The purpose of this study was to investigate the effects of brain education based personality program on stress and concentration of elementary school students. The subjects were selected from 15 classes of 4th grade in elementary school and 363 students were assigned to experimental group (219 students in 9 classes) and control group (144 students in 6 classes). For the study design, pre - post test control group design was applied. In the experimental group, the brain education based personality program was performed for 12 weeks, once a week, for 40 minutes per session. ANCOVA (Analysis of Variance) method was used for data analysis. The analysis showed that stress and concentration were significantly improved in the experimental group with brain - based toughness program compared to the control group. The brain-based personality program has shown to reduce elementary school students' stress and improve their concentration. The results of this study suggest that brain - based personality programs, which can integrate physical, cognitive, and emotional development, By changing children's perceptions of stress situations, they reduced the stress of children and it gives motivation for the purpose of studying, it develops the power to choose and execute by oneself, and improves concentration. 본 연구는 뇌교육 기반 인성프로그램이 초등학생의 스트레스와 집중력에 미치는 영향을 파악하고자 하였다. 연구대상은 초등학교 4학년 15개 학급 363명을 대상으로 하였으며, 실험집단(9개반 219명)과 통제집단(6개반 144명)으로 구분하였다. 연구설계는 사전-사후 통제집단 실험설계를 적용하였으며, 실험집단에는 12주간, 주 1회, 회당 40분씩 뇌교육 기반 인성프로그램을 실시하였다. 자료분석은 ANCOVA 방식을 사용하여 분석하였다. 분석결과, 뇌교육 기반 인성프로그램을 시행한 실험집단에서 통제집단 대비하여 스트레스와 집중력이 유의미하게 향상된 결과가 나타나 뇌교육 기반 인성프로그램은 초등학교 아동의 스트레스를 감소시키고 집중력을 향상시키는 것으로 밝혀졌다. 이러한 연구결과는 신체, 인지, 정서의 통합적 발달을 체험할 수 있는 뇌교육 기반 인성프로그램은 스트레스 상황을 지각하는 아이들의 관점을 변화시켜 스트레스를 감소시키고, 공부하는 목적에 대한 동기부여를 통해 스스로 선택하고 실행하는 힘을 키워 집중력을 향상시킨 것으로 본 연구결과를 설명할 수 있다.

고온 환경하 응력 확산에 의한 금속시편내 격자결함 재분포

윤선진,조용무,Yoon, Seon-Jhin,Cho, Yong-Moo 한국금형공학회 2018 한국금형공학회지 Vol.12 No.1

In this study, we calculated the redistribution of vacancy concentration in metal specimens induced by stress-induced diffusion at a high temperature. To deduce the governing equation, we associated the unit volume change equation of strains with a differential equation of vacancy concentration as a function of stress using the stress-strain relationship. In this governing equation, we considered stress as the only chemical potential parameter to stay in the scope of this study, which provided the vacancy concentration equation as of stress gradient in metals. The equation was then mathematically delineated to derive a analytical solution for a transient, one-dimensional diffusion case. With the help of Korhonen's approximation and the boundary conditions, we successfully deduced a general solution from the governing equation. To visualize the feasibility of our solutions, we applied the solution to two different stress-induced cases - a rod with fixed concentrated stresses at both ends and a rod with varying concentrated stresses at both ends. Although it is necessary to legitimatized the model in the future for improvement, our results showed that the model can be used to interpret the location of structural defects, the formation of vacancy, and furthermore the high temperature behavior of metals.

Generalized multifield variational formulation with interlaminar stress continuity for multilayered anisotropic beams

Dhadwal, Manoj Kumar,Jung, Sung Nam Elsevier 2019 Composites Part B, Engineering Vol.168 No.-

<P><B>Abstract</B></P> <P>Classical finite element (FE) beam theories are based on displacement formulation requiring derivatives to obtain the stress components which leads to a large number of FEs and depend on nodal averaging techniques for achieving sufficient accuracy. In this work, a new multifield variational based FE formulation is proposed within the cross-sectional framework of multilayered composite beams for accurate and efficient predictions of sectional stiffness constants and stresses. The interlaminar stress continuity is not assumed a priori and inherently incorporated using the Hellinger-Reissner principle along with a global stress equilibrium constraint, directly computing the stresses at nodal locations. The three-dimensional (3D) stresses and warping deformations are considered as primary variables which inherently incorporate elastic coupling effects related to transverse shear and Poisson deformations. The formulation results in a generalized fully-coupled 6 × 6 sectional stiffness matrix considering elastic couplings. The efficacy of the present analysis is substantiated for thin-walled composite beams with elastic couplings. An excellent correlation is achieved for the elastostatic response as compared with the 3D FE and experimental results. The stresses obtained by the multifield analysis are in accord with detailed 3D FE solutions for various loading conditions while computed at a much reduced computational cost. Improved predictions of interlaminar stresses and stress concentrations are achieved compared to displacement-based approach along with the correct identification of continuity across layer interfaces. The effect of fiber orientation on the interlaminar stresses is also shown to be significant which can be useful for damage analysis of composite beams.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A multifield variational finite element analysis developed for anisotropic beams. </LI> <LI> •3D stresses with interlaminar continuity modeled as unknowns without a priori assumptions or post-processing technique. </LI> <LI> •Excellent correlation obtained as compared with 3D finite element analysis while predicting interlaminar stresses and stress concentrations at corners correctly. </LI> <LI> •Influence of fiber angles on interlaminar stresses demonstrated for coupled beams. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Shot peening 가공에 의한 노치재의 응력분포와 피로강도의 개선

이승호,김희송 한국공작기계학회 1998 한국생산제조학회지 Vol.7 No.5

Second step shot peening was applied on both smooth specimen and U-notch specimen in order to investigate the stress distribution and the improvement in fatigue strength. Various experiments and measurements such as rotary bending fatigue test and the measurement of compressive residual stress were performed. The results showed that the fatigue strength of second step shot peened specimens increased by 34 percent compared to that of unpeened ones. Compressive residual stress also considerably increased, which resulted in the increase of fatigue strength. Finite element analysis showed that shot peening is effective decreasing the bending stress by external force. The effectiveness of shot peening reducing the compressive residual stress was anticipated by the superposition of the concentrated stress and the compressive residual stress.

적외선 열화상 응력측정법에 의한 동적 응력집중계수 예측

최만용(Man Yong Choi),강기수(Ki Soo Kang),박정학(Jeong Hak Park),안병욱(Byung Wook Ahn),김경석(Koung Suk Kim) Korean Society for Precision Engineering 2008 한국정밀공학회지 Vol.25 No.5

Structural components subjected to high frequency vibrations, such as those used in vibrating parts of gas turbine engines, are usually required to avoid resonance frequencies. Generally, the operating frequency is designed at more than resonance frequencies. When a vibrating structure starts or stops, the structure has to pass through a resonance frequency, which results in large stress concentration. This paper presents the transient thermoelastic stress analysis of vibrating cantilever beam using infrared thermography and finite element method (FEM). In FEM, stress concentration factor at the 2nd resonance vibration mode is calculated by the mode superposition method of ANSYS. In experiment, stress distributions are investigated with infrared thermography and dynamic stress concentration factor is estimated. Experimental result is agreed with FEM result within 10.6 %. The advantage of this technique is a better immunity to contact problem and geometric limitation in stress analysis of small or micro structures.