금속재료 응력-변형률 곡선의 수학적 표현들

현홍철(Hong Chul Hyun),이진행(Jin Haeng Lee),이형일(Hyungyil Lee) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.1

본 연구에서는 인장과 압축실험 데이터를 사용하여 재료의 응력-변형률 곡선을 얻었다. 시편에 네킹현상이 발생하기 전에는 인장실험의 결과를 토대로 각 재료의 영률값과 항복강도를 찾았다. 이후 비선형 거동은 압축실험의 데이터를 이용해나타냈다. 이렇게 얻어진 재료의 실제응력-변형률 곡선을 구간 멱함수법을 사용해 변형률 구간별로 회귀하였다. 회귀하여 구한 곡선과 실제 재료의 응력-변형률 곡선을 비교해 최적 회귀방법과 상응하는 변형률 회귀구간을 찾았다. 하나와 두 변수에 의한 회귀를 혼용하면 가장 적절한 회귀 방법이 얻어진다. 우선 두 변수들로 회귀하여 항복강도를 찾는다. 뤼더변형률이 없는 재료의 항복강도를 예측에는 초기구간 데이터만을 이용해야 오차를 최소화 할 수 있다. 한편 뤼더변형률이 재료들은 곡선의 후반부 데이터를 사용해야 정확한 물성치를 찾아낼 수 있다. 이어 항복강도가 구해진 상황에서 응력-변형률 곡선의 전체 데이터를 사용해, n 을 단일변수로 하여 회귀한다. 여기서 얻은 항복강도와 n 을 이용하면 실제 실험응력-변형률 곡선을 가장 유사하게 따라가는 회귀곡선을 얻을 수 있다. Stress-strain curves based on Ramberg-Osgood and Hollomon relations are strongly dependent upon the regressed range of strain. This work investigates mathematical expressions of true stress-strain curves of metallic materials. We first observe the variation of yield strength, strain hardening exponent and stress-strain curve with regressed range of stain. Based on sectional regression and expression using one or two parameters, we propose an optimal strain range for which yield strength and nonlinear material behavior are quite appropriate.

STS301L 용접이음재의 피로설계에 관한 연구

백승엽(Seungyeb Baek) 한국자동차공학회 2010 한국 자동차공학회논문집 Vol.18 No.4

STS 301L 필렛 용접이음재의 피로설계에 관한 연구

백승엽(Seung yeb Baek) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.5

용접부는 일반적으로 잘 알려져 있는 바와 같이, 외력에 의한 응력 집중원(stress concentration source)이 되는 것은 물론 용접과정에서의 입열(heat input)로 인한 성분과 조직의 변화에 의해 반복하중에 대한 피로강도(fatigue strength)가 모재의 그것에 비해 훨씬 떨어져서 피로균열(fatigue crack)의 발단이 되고 있다. 따라서, 본 연구에서는 실제로 철도차량에 적용되는 가스용접 이음재 가운데 대표적인 형상시편들을 재질별로 피로실험을 수행하여 피로하중범위-피로수명(ΔP-Nf) 관계를 도출하여 비교·평가하였다. 또한, 수치 해석적 유한요소법을 이용하여 용접이음재의 응력분포를 해석한 후, 용접이음부에 발생하는 최대주응력으로 (ΔP-Nf) 관계를 Δσ-Nf 관계로 재정리하였다. 이상의 결과들을 바탕으로, 가스용접이 적용된 철도차량 차체의 경제적이고 합리적인 피로설계를 위한 기초정보로 사용하고자 하였다. Stainless steel sheets are widely used as structural materials for the manufacture of railroad cars and commercial vehicles. These kinds structures used stainless steel sheets are commonly fabricated by using the gas welding. For the fatigue design of gas welded joints such as fillet joints and plug joints, it is necessary to obtain information on the stress distribution at the weldment and the fatigue strength of the gas welded joints. Moreover the influence of the geometrical parameters corresponding to the gas welded joints on the stress distribution and fatigue strength must be evaluated. ΔP-Nf curves were obtained from the data recorded in fatigue tests. Using these results, the ΔP-Nf curves were rearranged according the relation between Δσ-Nf and the maximum stress at the edge of the fillet welded joint.

관통구를 갖는 판구조물의 강도평가 방법에 관한 연구

김을년,장준태 대한조선학회 2017 大韓造船學會 論文集 Vol.54 No.6

The purpose of this paper is to verify the structural integrity of a region with numerous penetration-holes in offshore structures such as semi-submersible rig and FPSO. In order to effectively check the yielding and buckling strength of plate members with penetration-holes, a screening analysis program was developed with the FE analysis tool to generate fine meshed model using the theoretical and analysis methods. When a hole is appeared in the plate structure members, the flow of stress is altered such that concentrations of stress form near the hole. Stress concentrations are of concern during both preliminary and detail design and need to be addressed from the perspectives of strength. To configure the geometrical shape, very fine meshed FE analysis is needed as the most accurate method. However, this method is practically impossible to apply for the strength verifications for all perforated plates. In this paper, screening analysis method was introduced to reduce analysis tasks prior to detailed FE analysis. This method is applied to not only the peak stress calculation combined stress concentration factor with nominal stress but also nominal equivalent stress calculation considering cutout effects. The areas investigated by very fine meshed analysis were to be chosen through screening analysis without any reinforcements for penetration-holes. If screening analysis results did not satisfy the acceptance criteria, direct FE analysis method as the 2nd step approach were applied with one of the coarse meshed model considering hole or with the very fine meshed model considering the hole shape and size. In order to effectively perform the local fine meshed analysis, automatic model generating program was developed based on the MSC/PATRAN which is pre-post FE analysis program. Buckling strength was also evaluated by Common Structure Rule (CSR) adopted by IACS as the stress obtained from very fine meshed FE analysis. Due to development of the screening analysis program and automatic FE modeling program, it was able to reduce the design periods and structural analysis costs.

인장속도가 ETFE 막재의 역학적 특성에 미치는 영향

김재열(Kim Jae-Yeol),강주원(Kang Joo-Won) 대한건축학회 2010 大韓建築學會論文集 : 構造系 Vol.26 No.5

Uniaxial tensile tests of strip ETFE foil specimens (thickness: 250μm) are carried out for six kinds of tensile speeds (tensile strain speeds: 10%, 25%, 50%, 100%, 200%, 500% min?¹). The tensile strength, the tensile strain at break, the yield stress and the Young’s modulus under different tensile speeds are obtained from the tests. According to the results of the tests, with the increase of the tensile speed: the tensile strength of ETFE membrane increases slightly while the tensile strain at break decreases; the yield stress of ETFE membrane increases a little but the second yield stress increases little; the yield strain of membrane increases too but the second yield strain decreases slightly. It is also found that the tangent and the second Young’s modulus of ETFE membrane present a descending trend while the secant and the third Young’s modulus have no obvious change when the tensile speed increases. By analyzing the results of the tests, the linear fitting formulas to calculate the mechanical parameters of ETFE membrane are presented through using the logarithm of tensile strain speed as the variable.

철근커플러 소재에 대한 내구성 시험

신상훈(Shin Sang Hun),권태웅(Tae Woong Gwon),강승규(Seung Gyu Kang) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

Ultimate Strength Formulation for Steel Plated Structure

Joo-Shin, Park,Bong-Jae, Kim,Ki-Bok, Jang,Yong-Suk, Suh,Joo-Hyeon, Kim,Jae-Myeong, Lee 한국해양환경·에너지학회 2012 한국해양환경·에너지학회 학술대회논문집 Vol.2012 No.5

A ship structure is basically an assembly of stiffened panel elements and an estimation of the maximum load carrying capacity or the ultimate strength of these members is of the highest importance task for the safety assessment and rational design of the structure, In general, thin plates are often used in cruise ship/high speed vessel structures, for example at deck plating, side shell plating and inside structure, It has been known that reducing the thickness of plating dramatically reduces the buckling strength of a steel plate subjected to irv?plane compression and shear loading, and the ultimate strength of it is also expected to decrease. In the present paper, to clarify and examine the fundamental buckling and progressive collapse behaviors of thin plates subjected to in-plane compression and in-plane edge shear load, a series of elastic and elastoㅡplastic large deflection analyses are performed applying nonlinear FEM codes, MSC Patran/Nastran, On the basis of the numerical results, influences of yielding stress, thickness of plating, slenderness ratio, loading condition on the characteristics of the buckling/ultimate strength and progressive collapse behavior of steel plates, are discussed, It is shown that the ultimate strength formula developed for a flat plate can give a reasonable estimate of strength, when the newly defined double beta parameter considering the change of yield strength as well as slenderness ratio, It is our hope that the obtained ultimate strength formulation would be used as practical design guideline to predict ultimate strength of steel flat plates in the field of ships and offshore structures.

베벨각도에 따른 피로수명 평가

신상훈(Sang Hun Shin),권태웅(Tae Woong Gwon),김상희(Sang Hee Kim),이승갑(Seung Kap Lee) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

Brittle Fracture of welded structure without warning abruptly occurs, and brings about human and material loss. It is matter of grave importance that designing welded structure quite predicts fatigue crack propagation life to mostly taking time fatigue crack growth on fatigue life of structures. Chamfer effect and Chamfer angle have an impact on fatigue life of specimens of Fillet Welding Type performed fatigue test. As a result, fatigue life was no effect on chamfer effect and chamfer angle for the specimens.

부유식 크레인을 이용한 침몰 선박 인양 작업을 위한 인양력 및 해저면 이탈력에 관한 수치 연구

김동민(Dong-Min Kim),김정석(Jeong-Seok Kim),박효진(Hyo-Jin Park),남보우(Bo Woo Nam),최혁진(Hyuck-Jin Choi) 한국해양환경·에너지학회 2022 한국해양환경·에너지학회 학술대회논문집 Vol.2022 No.11

방공호용 방폭 밸브의 구조해석 및 성능에 관한 연구

이정빈,김기선,양동학,김성육,이정국 한국기계기술학회 2015 한국기계기술학회지 Vol.17 No.3

A Blast valve is the device that is used in the air intake and the exhaust vent of CBRN(Chemical, Biological, Radiological and Nuclear warfare) protection facility. The valve is automatically closed when explosion pressure is applied from the outside of equipment. This study is investigated on the structural design and the performance of blast valve. After modeling the entire of blast valve and spring assembly, the data for the spring parameter is obtained through the finite element method and the operating limits of the valve are derived. Also, a prototype is made to determine the relationship between the load and the opening closing amount of valve through the load cell test. The performance of prototype at analysis as blast valve is agreed well with that at experiment. It is verified that the blast valve proposed in this paper is designed with the structure to endure the explosion pressure.