Effect of residual stress on the bending of aluminium

Journal of Manufacturing Processes

Detrimental residual stresses that occur in welded joints can be removed by rolling the weld seam. In this study we show that rolling could be applied to much thicker-section welds than has previously been attempted. A residual stress field introduced by localised rolling of an aluminium alloy specimen was studied to establish whether the plastic deformation caused by rolling would be sufficient to treat thicksection welds. It was modelled using finite element analysis and characterised using detailed neutron diffraction measurements. During rolling, plastic deformation occurs through the entire thickness of the specimen and strongly compressive residual stresses are created in the rolled area. Some features of the three-dimensional residual stress field, such as a region of tensile stress beyond the end of the rolled area, could be detrimental to structural integrity. It is recommended that these should be taken into account in the design of rolling-based weld treatment and surface treatment processes.

2016

This study elaborates the bending process of Al 6061 aluminium alloy using three-point bend test. The permanent deformation takes place on the sheet metal strip as a result of severe plastic strain. One of the major issues in the sheet metal bending process is that the formation of spring back during unloading. This study involves combined design of experiment and finite element analysis to understand the bending and spring back behaviour of sheet metal. The elasto-plastic behaviour is studied by parametric numerical simulations. The static mechanical behaviour at ambient temperature is investigated for various thickness and radius of punch to achieve its correlations. The systematic approach is carried by developing numerical models of three-point bending of aluminium strips.

2018

During the optimal design and simulation of machining or forming processes, detailed simulation of structural response is typically required for use in Finite Element Analysis (FEA). In this study, the bulk temperature and rate dependent resistance to deformation of strip formed aluminium alloys is modelled using the Mechanical Threshold Stress model. The model is characterised to AA5182 alloy data and used in the FEA simulation of a strip rolling process. The effects of element choice, dynamic or quasi-static simulations and the use of particular modelling algorithms on the computational cost and overall accuracy associated with each simulation have to be considered. Given the correctly implemented material tangent, an implicit analysis is illustrated to allow larger stable time-steps. Dynamic and quasi-static solutions are very similar for the simulated process meaning inertia effects are negligible. It is further demonstrated that great care be given to the maximum allowable time...

Materials & Design, 2011

Sheet metal forming involves planar stress states, in the sheet plane, like in tension and simple shear, or stress states characterized by a gradient in the thickness, like in bending. In this latter case, material limit prediction derived from an instability criterion is no longer valid. In this work, a criterion based on a critical void volume fraction, identified from macroscopic tests, is applied to the case of bending of square samples of aluminium alloy AA6016-T4. Mechanical tests are performed at two aging times to quantify its influence on the mechanical behaviour and only the hardening law is modified to take it into account. It is shown that a good correlation is obtained between the critical void volume fraction obtained from tension on notched samples and biaxial expansion, and the onset of crack development in the bent zone. Moreover, macroscopic load recorded during bending is sensitive to ductile damage, which makes this test particularly interesting for damage investigation.

Journal of Materials Engineering and Performance, 2019

In a number of sheet metal stamping and joining processes, the material undergoes large plastic deformation exceeding the range of plastic strain achievable in a standard tensile test prior to material plastic instability. In order to extend the range of effective strains, the multistep rolling process was employed which enabled prestraining of aluminum sheet above 2.0 of true strain. Tensile testing of rolled samples was used to identify the flow stress corresponding to the level of prestrain: By varying the prestrain level, several data points were obtained for the studied flow curve. The numerical simulation using Abaqus software for the cold rolling process of aluminum strips confirmed that majority of the strip is deformed in plane strain compression condition. Performed simulation of the LDH test determined that earlier fracture might occur if the curve obtained via rolling-tensile testing approach is used versus traditional power law approximation and Voce law approximation. The results of simulation for the multistep drawing of a cylindrical cup revealed possible wrinkling in the die entry area during redrawing stage of the process if the rollingtensile testing flow curve is employed.

Mérnöki és informatikai megoldások, 2022

The current as well as the future industrial market for Aluminium (Al) is huge and various research is being under work regarding the usability of Aluminium. However, during the deep drawing of Aluminium several issues can be developed and some of them are originated from the fundamental material properties. One of these factors is the material texture, which is the preferred orientation of the constituent polycrystalline Al, and the characteristic texture is affected by different rolling and annealing recipes. To investigate the material texture, symmetric and asymmetric rolling trials were performed on a commercially available Al 1050 sample. Energy-dispersive X-ray Spectroscopy (EDX), and Electron Backscatter Diffraction (EBSD) scanning has performed to determine the material composition and the crystallographic orientations of the investigated samples.

International Journal of Material Forming, 2009

The investigation of bendability of sheet metal alloys is of great importance for the evaluation of process robustness in production of hemmed sheet metal assemblies. Furthermore, material cracks due to bending can also occur at deep drawing operations. This contribution focuses on the experimental determination of material's formability at deep drawing, the characterisation of bendability especially for hemming operations and the determination of formability under combined deep drawing and bending loads, respectively. Keywords Forming limit curve. FLC. Bending limit curve. BLC. Failure mix. Combined bending and stretching Abbreviations BLC bending limit diagram FLC forming limit curve FLD forming limit diagram M correlation function for combined load conditions r i inner bending radius α strain path orientation β bending indicator ϕ 1 major strain ϕ 1,1 major strain of pre-strain ϕ 1, res major strain of pre-strain inclusive subsequent bending ϕ 2 minor strain ϕ b bending strain (outer fiber) ϕ 1, planar major strain component of planar forming limit description ϕ M major forming limit strain component for combined load conditions ϕ b strain tensor for bending operations ϕ d strain tensor for deep drawing operations ϕ strain tensor for all possible states of strain

Metals

Rolling is one of the most employed industrial processes which can be used at multiple manufacturing stages, allowing different geometries such as plates, rods, profiles, billets, slabs, tubes, and seamless tubes to be obtained. However, rolled products develop anisotropy due to the preferential orientation of crystals in the rolling direction. Thus, some process configurations and different processing parameters (e.g., thickness reduction per rolling pass, deformation routes, roll diameters, and strain rate) have been proposed to deal with the desired anisotropy. In this context, this investigation evaluates and compares the effect of symmetrical and asymmetrical rolling on an aluminum alloy sheet deformed until a 38% thickness reduction using multiple rolling passes. The asymmetrical process displayed larger texture and microstructure gradients across the sheet thickness than the symmetrical one, manifested as more grain refinement and more intense shear texture components close t...

Specimens of pre-strained and severely deformed aluminum alloy AA1350 are undergone rolling and heat treatment at 125, 200 and 275 1C on their final processing history. The combined effect of rolling and post-annealing on the mechanical properties and microstructural evolutions is investigated. The main effort is focused on the ductility of specimens tolerating duplex straining paths. Results show that adequate annealing can effectively enhance ductility without noticeable decrease in the strength of the specimens at 200 1C and before recrystallization starts. During microstructural evolutions, no rapid grain/crystallite growth is observed at lower temperatures; however, treatment at 275 1C considerably changes mechanical characteristics by equiaxing the lamellar structure. According to the examinations, it is concluded that pre-straining through constrained groove pressing with the strain of 1.16 and subsequently imposing rolling strain up to the strain of 1.23 results in aluminum having extremely limited ductility and ultra-fine microstructure free of micro-cracks. By annealing at 200 1C, the considerable recovery of elongation (up to 4.6%) is achieved and this is noticeable compared to the ductility of non-heat treated and severely deformed aluminum (approximately 1%).

2006