A numerical and experimental study on the mechanical characteristics of sheet material by the hydraulic bulge test and uniaxial tensile tests

Quoc-Tuan Pham(팜콕투완),Jin-Jae Kim(김진재),Young-Suk Kim(김영석),Seong-Jin Kwon(권성진) 한국자동차공학회 2016 한국자동차공학회 부문종합 학술대회 Vol.2016 No.5

Unixaial tensile test is the most common method used to identify the mechanical characteristics for sheet materials. However, several sheet forming processes lead to large plastic deformation in which the plastic strain is over the maximum uniform elongation of uniaxial tensile test, for instance, clinch forming, hydroforming, stamping and deep drawing. Therefore, post-necking behavior of sheet materials is a currently attractive research topic where these studies focus on the behavior of metals beyond the uniaxial tensile elongation. This study aims to determine the flow curves and yield locus of aluminum 5052 sheets by performing the hydraulic bulge test and uniaxial tensile tests. To obtain this goal, firstly, a series of uniaxial tensile tests are performed in order to evaluate the yield stress and anisotropic plasticity coefficients in three orientations 0°, 45° and 90° respect to the rolling direction. Secondly, the hydraulic bulge test is carried out to achieve biaxial stress-strain curve. From this curve, biaxial yield stress and biaxial anisotropic plasticity coefficients are derived. Moreover, a new strain hardening function is proposed to perfectly describe stress-strain relation of studied material in term of uniaxial tensile test and predict the post-necking behavior of this material. The biaxial stress-strain curve is transformed into an effective stressstrain curve, then this curve is compared with the fitting results of new strain hardening function in rolling direction to highlight the accuracy of post-necking prediction of proposed equation. Thirdly, the parameters of Yld2000 yield function are derived from above-mentioned mechanical properties to describe yield locus of aluminum 5052 sheets. Finally, the achieved effective stress-strain curve and yield locus are imported into a FE analysis code to simulate the hydraulic bulge test of this material. The simulation results match well with the experiment records and it is reasonable to conclude that the novel approach to determine the mechanical characteristics achieved from this study can be applied for other sheet materials.

[특별세션]DIC 액압벌지실험을 이용한 순 티타늄 판재의 소성유동곡선에 관한 연구

김진재(Jinjae Kim),김영석(Youngsuk Kim),권성진(Seongjin Kwon) 한국자동차공학회 2016 한국자동차공학회 부문종합 학술대회 Vol.2016 No.5

In this paper, the plastic flow curve of commercially pure titanium sheet (CP Ti) has been evaluated using Tensile test and Hydraulic bulge test. The plastic flow curve known as hardening curve is a key on factor needed in conducting finite element analysis for the forming process of sheet material. However, several sheet forming processes lead to the large plastic deformation of which the plastic strain is over the maximum uniform elongation of uniaxial tensile test, for instance, clinch forming, hydroforming, stamping and deep drawing. Therefore, we have performed tensile and a hydraulic bulge test for CP Ti sheet. We also have used and evaluated three method that convert from hydraulic bulge flow curve to tensile flow curve. The measured true flow curve from the hydraulic bulge test can be fitted well by the hardening equation known as Kim-Tuan model.

유압벌지실험을 이용한 순 티탄늄 판재의 소성유동곡선 평가(제2보)

김영석(Kim, Young-Suk),김진재(Kim, Jin-Jae) 한국산학기술학회 2016 한국산학기술학회논문지 Vol.17 No.4

본논문에서는대형 선박의 판형열교환기등에 널리 이용되고있는 순 티타늄판재의소성변형을 유한요소해석하기 위한 기초 데이터로서 순 티타늄 판재의 유동곡선을 평가하였다. 순 티타늄 판재의 프레스 가공 시에 판재에는 국부적으로 큰 소성변형이 발생하고 있다. 그러나 기존의 단축 인장실험에서 얻을 수 있는 소성변형률이 낮아서 티타늄 판재의 가공공정 설계를 위한 유한요소해석의 정밀도를 떨어뜨리는 경우가 있다. 본 연구에서는 큰 소성변형률 까지 안정적으로 성형이 가능한 유압벌지실험을 수행하여 재료의 소성변형에서 가공경화특성을 나타내는 유동곡선으로써 진응력-진변형률 선도를 구하였고 그 결과를 인장실험 결과와 비교하였다. 순 티타늄 판재의 유압벌지실험에서 재료의 변형률은 3D 디지털 영상 상관법을 이용한 ARAMIS 시스템으로 실시간 측정된다. 이 유압벌지실험으로부터는 소성 변형률이 0.65 이상 까지도 안정적으로 재료의 소성유동곡선을 얻을 수 있었으며 그 결과는 Kim-Tuan 이 문헌 17[Y.S. Kim, J.H. In, Korean Acadmia-Ind. Coop. Soc.,(be in print), 2016] 의 연구에서 제안한 가공경화식으로 잘 핏팅됨을 알 수 있었다. In this study, the plastic flow curve of commercially pure titanium sheet (CP Ti) actively used in the plate heat exchanger etc., was evaluated. The plastic flow curve known as hardening curve is a key factor needed in conducting finite element analyses (FEA) for the forming process of a sheet material. A hydraulic bulge test was performed on the CP Ti sheet and the strain in this test was measured using the DIC method and ARAMIS system. The measured true stress-true strain curve from the hydraulic bulge test (HBT) was compared with that from the tensile test. The measured true stress-true strain curve from the hydraulic bulge test showed stable plastic flow curve over the strain range of 0.7 which cannot be obtained in the case of the uniaxial tensile test. The measured true stress-true strain curve from the hydraulic bulge test can be fitted well by the hardening equation known as the Kim-Tuan model.

Identification of the Plastic Deformation Characteristics of AL5052-O Sheet Based on the Non-Associated Flow Rule

Quoc Tuan Pham,김영숙 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.2

This study aims to determine the plastic deformation characteristics of aluminum 5052-O based on non-associatedflow rule. To achieve this goal, a new strain hardening model named as Kim-Tuan hardening modelis proposed to perfectly describe the stress-strain relation of the studied material in terms of the uniaxial tensiletest and to predict the material’s post-necking behavior. Additionally, the plastic behaviors of AL5052-O sheetare described by two approaches: the associated flow rule with YLD2000-2d yield function and the nonassociatedflow rule with Hill's quadratic function (NAFR-Hill48). The parameters of these functions werederived from the material properties that were obtained from uniaxial tensile tests and bulge test. The flow curvebased on Kim-Tuan model and plastic behaviors obtained from two above-mentioned approaches were importedinto a finite element analysis code to simulate the hydraulic bulge test for this material to confirm the precisionof material characteristics achieved before. The simulation results based on the NAFR-Hill48 match wellwith the experiment results of bulge test while the YLD2000-2d provides highly accurate predictions foranisotropy of this material.

Mechanical Behavior of Embossed AA1050-O Sheets Subjected to Tension and Forming

사비르므졸리,Carl Labergere,Marion Martiny,Mohamad Jrad,Guillaume Robin,김흥수,Francois Choquart 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.10

In this paper, experimental characterization of embossed aluminum sheets is performed using extensive mechanical tests. Rotary embossing is performed on these sheets in order to obtain a periodic hill-and-valley structure. The experimental program consists of realizing mechanical tests such as tension, deep drawing, and hydraulic bulge tests using embossed samples in order to build a database that can be used for future finite element modeling tasks. The tensile tests are performed using digital images correlation (DIC) for total displacement measurements and for detailed strain maps. The hydraulic bulge and deep drawing tests are conducted on embossed circular samples to study their formability. A comparison was made with the plane (non-embossed) sheets to explain the contribution of the embossed structure either in both cases of uniaxial and multiaxial loadings.

Deformation behaviours of SS304 tubes in pulsating hydroforming processes

Lianfa Yang,Ninghua Wang,Yulin He 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.60 No.1

Tube hydroforming (THF) under pulsating hydraulic pressures is a novel technique that applies pulsating hydraulic pressures that are periodically increased to deform tubular materials. The deformation behaviours of tubes in pulsating THF may differ compared to those in conventional non-pulsating THF due to the pulsating hydraulic pressures. The equivalent stress-strain relationship of metal materials is an ideal way to describe the deformation behaviours of the materials in plastic deformation. In this paper, the equivalent stress-strain relationships of SS304 tubes in pulsating hydroforming are determined based on experiments and simulation of free hydraulic bulging (FHB), and compared with those of SS304 tubes in non-pulsating THF and uniaxial tensile tests (UTT). The effect of the pulsation parameters, including amplitude and frequency, on the equivalent stress-strain relationships is investigated to reveal the plastic deformation behaviours of tubes in pulsating hydroforming. The results show that the deformation behaviours of tubes in pulsating hydroforming can be well described by the equivalent stress-stain relationship obtained by the proposed method. The amplitude and frequency of pulsating hydraulic pressure have distinct effects on the equivalent stress-strain relationships-the equivalent stress becomes augmented and the formability is enhanced with the increase of the pulsation amplitude and frequency.

Springback Prediction in U-draw/bending of DP and TRIP Steel Sheet

Jeong Yeon Lee(이정연),Myoung-Gyu Lee(이명규),Frederic Barlat 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5

U-draw/bending experiment and simulation have been employed to investigate the characteristics of springback in sheet metals, because they can represent the deformation of material in forming processes with simple but robust manner. Finite element method is frequently used for the simulation of springback, but the prediction is strongly influenced by the constitutive models such as yield criteria and hardening laws. In the present study, springback of DP and TRIP steel sheets in U-draw/bending was predicted with a finite element analysis. Various constitutive models were considered: the von Mises isotropic and Hill’s anisotropic yield models for the yield criteria; isotropic and non-linear kinematic hardening models for the hardening laws. Especially, to characterize the hardening behavior, both uniaxial tensile test and balanced biaxial tensile test (by hydraulic bulge test) were carried out. The prediction was greatly influenced by the choice of hardening model, while slightly affected by the choice of yield criterion. It was found that the kinematic hardening model provides better prediction than the isotropic hardening model for the particular model materials. The use of flow curve from hydraulic bulge test seems to be more reliable than the use of uniaxial tensile flow curve owing to extended measurable strain range.

유압벌지시험을 이용한 순타이타늄 판재의 물성거동 평가

팜콕투안(Q. T. Pham),김진재(J. J. Kim),박기철(K. C. Park),김영석(Y. S. Kim) 한국소성가공학회 2018 한국소성가공학회 학술대회 논문집 Vol.2018 No.5

비연합유동법칙에 기반한 왜곡-경화 모델을 이용한 순 티타늄 판재의 유압벌지시험시 재료의 소성변형거동 예측

김진재(J. J. Kim),XiaoXiao,김영석(Y. S. Kim) 한국생산제조학회 2021 한국생산제조시스템학회 학술발표대회 논문집 Vol.2021 No.7