Behavior Of Aluminum Alloy Sheets Research Articles

Study on the buckling behavior of aluminum alloy sheets - before and after repaired with composite patches

In this paper, the compressive buckling behavior of aluminum alloy plates with an elliptical hole of various sizes is investigated. In order to improve the stability of these thin plates, T700/QY8911 composite laminate is used as a patch to repair the hole. The study included an analysis of the critical and post-critical behaviour using experimental and numerical methods. Experiments focus on buckling loads, post-buckling behavior and the relationship between sizes of holes and buckling load. Meanwhile, the buckling load and buckling mode are determined by finite element analysis, using linear analysis of eigenvalue problems modes, and then, the nonlinear analysis of structures with initiated geometrically imperfection is carried out, studying its post-buckling behavior, damage behavior and transfer of load. The results show that the buckling load of the open-hole specimen is related to size of opening. The existence of patch has a significant influence on stress distribution, and the buckling capability of repaired specimens is noticeably improved to the plate without a hole. And the compression experimental results are consistent with the numerical results, revealing that the developed finite element model of the structure is correct.

Investigation on damage evolution and acoustic emission behavior of aluminum alloy sheet during blanking process

Investigation on damage evolution and acoustic emission behavior of aluminum alloy sheet during blanking process

Mechanical properties and interfacial microstructures of magnetic pulse welding joints with aluminum to zinc-coated steel

In this study, the relations between interfacial microstructure and mechanical behavior of aluminum alloy sheets and zinc-coated steel sheets magnetic pulse welding (MPW) joints were characterized systematically. MPW joints of aluminum alloy and ungalvanized steel sheets were prepared for comparative analysis. Results showed that some of zinc layer on the galvanized steel was washed away to form metal jet under the high-speed collision. The change of failure mode from interfacial failure to base material fracture due to interfacial microstructure evolution was the fundamental reason for different mechanical behavior of two MPW joints. Because of the difference in element content and the severe plastic shear at the interface, the crystalline grain morphologies and sizes of aluminum and zinc in the transition zone changed. Amorphous structure was also found in the transition zone. The existence of the zinc layer would form brittle and hard phases on the interface, resulting in the generation of welding defects, thereby reducing mechanical properties of the joint.

Numerical simulation of deformation behavior of aluminum alloy sheets under processing by groove pressing method

The results of theoretical estimation of capabilities of the material structure modification of 1560 aluminum alloy sheets under processing by severe plastic deformation are presented in this paper. Severe plastic deformation of flat specimens is effected by the constrained groove pressing method in original dies with trapezoidal teeth. The numerical simulation results of the sheet specimen treatment process by severe plastic deformation were used for dies designing. The stress-strain state of flat aluminum alloy specimens and the steel dies at high processing temperature, support reaction force during pressing and the degrees of plastic strain accumulation at the optimum mode of pressing were estimated. The main numerical result is the value of accumulated plastic strain in the specimen per one pressing cycle which is about 1.14. Large degrees of strain are the reasons of grain structure and material texture changes, which leads to inevitable change of its physical-mechanical properties. Increasing the number of pressing cycles leads to proportional increase of the degree of accumulated plastic strain.

Numerical simulation of deformation behavior of aluminum alloy sheets under processing by groove pressing method

Numerical simulation of deformation behavior of aluminum alloy sheets under processing by groove pressing method

평면 응력 조건에서 정의된 비이차 비등방 변형률 속도 포텐셜

본 연구를 통하여 비이차 비등방 항복 응력 포텐셜들의 근접 짝되는 변형률 속도 포텐셜들에 대해서 정리하고 Yld2000-2d의 근접 짝되는 Srp2003-2d에 대해서 상세 설명하였다. 제안된 비이차 비등방 변형률 속도 포텐셜 Srp2003-2d 식 형태가 소개 되었고, 볼록성이 증명되었다. 아울러 이방성 상수를 구하는 방법이 제시되었다. Srp2003-2d의 소성 거동을 살펴보기 위하여 자동차 용 알루미늄 합금 판재 AA6022-T4와 항공재료용 알루미늄 합금 AA2090-T3에 응용되었다. Srp2003-2d는 항복 응력 포텐셜 Yld2000-2d와 거의 흡사한 짝됨을 보여 주었으며, 알루미늄 판재의 비등방성을 적절히 묘사하였다. Srp2003-2d는 알루미늄 판재의 성형 공정의 모사를 위하여 이상 공정 이론을 비롯한 강소성체 재료에 대한 정식화에 적절히 응용될 수 있을 것이다. A non-quadratic anisotropic strain rate potential was introduced as a conjugate potential of the yield stress potential Yld2000-2d to describe anisotropic behavior of sheet metals, in particular, aluminum alloy sheets under plane stress state. This strain-rate potential takes into account the anisotropic yield stresses and R-values measured along the directions measured at 0, 45 and 90 degrees from the rolling direction, as well as the balanced biaxial yield stress and strain-rate ratio. The convexity of the strain-rate potential was completely proven. The strain-rate potential was applied for two anisotropic aluminum alloy sheets, AA6022-T4 and AA2090-T3. The results verified that the strain rate potential properly described the anisotropic behavior of aluminum alloy sheets and was closely conjugate of Yld2000-2d under the plane stress state.

Numerical simulation of ductile fracture behavior for aluminum alloy sheet under cyclic plastic deformation

A numerical analysis of mechanical behavior of aluminum alloy sheet under cyclic plastic deformation was investigated. Forming limit at fracture was derived from Cockcroft-Latham ductile damage criterion. The strain path of bending center of incremental roller hemming could be accepted as a kind of plane strain bending deformation process. Incremental rope roller hemming could be used to alleviate ductile fracture behavior by changing the stress state of the hemming-effected area. SEM observation on the fracture surface indicates that cyclic plastic deformation affects ductile fracture mechanism.

Stress integration method for a nonlinear kinematic/isotropic hardening model and its characterization based on polycrystal plasticity

Sheet metal forming processes generally involve non-proportional strain paths including springback, leading to the Bauschinger effect, transient hardening, and permanent softening behavior, that can be possibly modeled by kinematic hardening laws. In this work, a stress integration procedure based on the backward-Euler method was newly derived for a nonlinear combined isotropic/kinematic hardening model based on the two-yield’s surfaces approach. The backward-Euler method can be combined with general non-quadratic anisotropic yield functions and thus it can predict accurately the behavior of aluminum alloy sheets for sheet metal forming processes. In order to characterize the material coefficients, including the Bauschinger ratio for the kinematic hardening model, one element tension–compression simulations were newly tried based on a polycrystal plasticity approach, which compensates extensive tension and compression experiments. The developed model was applied for a springback prediction of the NUMISHEET’93 2D draw bend benchmark example.

Modeling of aluminum alloy sheets based on new anisotropic yield functions

New anisotropic models (Yld2000-2d, Barlat et al. [F. Barlat, J.C. Brem, J.W. Yoon, K. Chung, R.E. Dick, S.H. Choi, F. Pourboghrat, E. Chu, D.J. Lege, Plane stress yield function for aluminum alloy sheets, Int. J. Plastic. 19 (2003) 1297–1319]; Yld2004-18p, Barlat et al. [F. Barlat, H. Aretz, J.W. Yoon, M.E. Karabin, J.C. Brem, R.E. Dick, Linear transformation-based anisotropic yield functions, Int. J. Plastic. 21 (2005) 1009–1039]) that accurately describe the anisotropic behavior of aluminum alloy sheets were implemented in a finite element code, LS-DYNA User MATerial subroutine (UMAT). The Yld2004-18p especially, requires sufficient experimental input taken every 15° from the rolling direction. As planar anisotropic behavior, earing simulation was carried out in order to show the capability of Yld2004-18p to predict more than four ears. A general automotive panel simulation which covers forming, trimming and springback was performed to show the generality and efficiency of the two new yield functions. The simulation results led to the excellent predictions.

알루미늄 합금박판 비등온 성형공정 스프링백 해석용 유한요소 프로그램 개발 (2부 : 이론 및 해석)

The implicit, finite element analysis program for analyzing the springback in the warm forming process of aluminum alloy sheets was developed. For the description of planar anisotropy in warm forming temperatures, Barlat`s yield function is employed, and the power law type constitutive equation is used in terms of working temperatures for the depiction of work hardening in high temperatures. Also, Jetture`s 4-node shell elements are introduced for reflecting the mechanical behavior of aluminum alloy sheet and the non-steady heat balance equations are solved for considering heat gain and loss during the forming process. For the springback evaluation, Newton-Raphson iteration method is introduced for overcoming the geometric nonlinearlity problem. In order to verify the validity of the FEM program developed, the stretching bending and springback processes are simulated. Though springback analysis results are slightly bigger than experimental ones, they have the same trend of the decreasing springback as the forming temperature increases.

Plane stress yield function for aluminum alloy sheets—part II: FE formulation and its implementation

A recently proposed plane stress yield function [Yld2000-2d; Int. J. Plasticity 19 (2003) 1297—part I of this work] that well describes the anisotropic behavior of aluminum alloy sheets was implemented in a finite element code. A short review of the Yld2000-2d relevant features was provided and the complete formulation for the yield function implementation was proposed for its convenient use. Yield surface shapes, yield stress and r-value directionalities predicted with Yld2000-2d for Al–5 wt.% Mg and 6016-T4 alloy sheet samples were compared with those of previously suggested yield functions. Simulations of the cup drawing process for the Al–Mg binary sheet were performed to compute the cup height profiles (earing profiles) with different yield functions. The predicted profiles were compared to experimental data and it was shown that the simulation using Yld2000-2d led to the best agreement between theoretical and experimental results. The drawing and redrawing processes of a circular cup using the NUMISHEET'99 (Gelin, J.C., Picart, P., 1999. In: Gelin, J.C., Picart, P. (Eds.), Proceedings of NUMISHEET'99, Vol. 2. 13–17 September, Besancon, France) conference geometry and specifications for a 6111-T4 aluminum alloy sheet sample were also simulated. The predicted load-punch displacement curves and sheet thickness profiles along different radial directions of the cup were shown to be in excellent agreement with experimental data.

面内２軸引張応力下におけるアルミニウム合金板材の変形挙動

A biaxial tensile testing was conducted using cruciform specimens made of an aluminum alloy sheet of the 6000 series, and the testing was successfully kept up to a large deformation in its plastic region. Then, the work hardening exponent n* (n* value) in the central region of the specimens under in-plane biaxial stress was calculated using the strain and the measured value of the load from the device equipped for the testing. Thus, the biaxial tensile testing with cruciform specimens has an advantage over the biaxial testing with a semi-spherical rigid punch, such as the load value can be measured correctly without being affected by bending or friction. Yet, it is very difficult to make the cruciform specimens that make it possible to measure a large strain in plastic region, and there are few reports on the studies about the biaxial stretch forming area using cruciform specimens. In this study, how to make the cruciform specimens which enable the measurement of a large strain, and how to calculate the n* value is explained. Also, the deformation behavior of aluminum alloy sheets of the 6000 series in biaxial stretch forming was attempted to be researched by the experiment on the three stages of strain ratio using the cruciform specimens and two types of devices: a hydraulic type stress control machine and a mechanical type strain control machine.

Acoustical Society of America Meeting

In this study, the relations between interfacial microstructure and mechanical behavior of aluminum alloy sheets and zinc-coated steel sheets magnetic pulse welding (MPW) joints were characterized systematically. MPW joints of aluminum alloy and ungalvanized steel sheets were prepared for comparative analysis. Results showed that some of zinc layer on the galvanized steel was washed away to form metal jet under the high-speed collision. The change of failure mode from interfacial failure to base material fracture due to interfacial microstructure evolution was the fundamental reason for different mechanical behavior of two MPW joints. Because of the difference in element content and the severe plastic shear at the interface, the crystalline grain morphologies and sizes of aluminum and zinc in the transition zone changed. Amorphous structure was also found in the transition zone. The existence of the zinc layer would form brittle and hard phases on the interface, resulting in the generation of welding defects, thereby reducing mechanical properties of the joint.

Ａｌ‐Ｍｇ合金板の一軸及び二軸変形における塑性挙動

The uniaxial deformation behavior of aluminum alloy sheets containing 1 to 6%Mg was determined through a tensile test, and the biaxial deformation behavior, through hydraulic bulging, rigid punch forming with scribed circle and Erichsen cupping tests. The anisotropy of the sheets changes with magnesium content. The planar anisotropy parameter Δr is positive for 1 to 3%Mg, almost zero for 4%Mg and negative for 5 to 6%Mg. The average values in the uniaxial test are correlated fairly well with those in the biaxial test for fracture strength, strength coefficient K and work hardening exponent n. For the strain to failure, however, no correlation is found between the average uniaxial values and the biaxial ones.