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Formability and hydroforming of anisotropic aluminum tubes
textThe automotive industry is required to meet improved fuel efficiency standards
and stricter emission controls. Aluminum tube hydroforming is particularly well suited in
meeting the goals of lighter, more fuel-efficient and less polluting cars. Its wider use in
industry is hindered however by the reduced ductility and more complex constitutive
behavior of aluminum in comparison to the steels that it is meant to replace. This study
aims to address these issues by improving the understanding of the limitations of the
process as applied to aluminum alloys.
A series of hydroforming experiments were conducted in a custom testing facility,
designed and constructed for the purposes of this project. At the same time, several levels
of modeling of the process, of increasing complexity, were developed. A comparison of
these models to the experiments revealed a serious deficiency in predicting burst, which
was found experimentally to be one of the main limiting factors of the process. This
discrepancy between theory and experiment was linked to the adoption of the von Mises
yield function for the material at hand. This prompted a separate study, combining experiments and analysis, to calibrate alternative, non-quadratic anisotropic yield
functions and assess their performance in predicting burst. The experiments involved
testing tubes under combined internal pressure and axial load to failure using various
proportional and non-proportional loading paths (free inflation). A number of state of the
art yield functions were then implemented in numerical models of these experiments and
calibrated to reproduce the induced strain paths and failure strains.
The constitutive models were subsequently employed in the finite element models
of the hydroforming experiments. The results demonstrate that localized wall thinning in
the presence of contact, as it occurs in hydroforming as well as other sheet metal forming
problems, is a fully 3D process requiring appropriate modeling with solid elements. This
success also required the use of non-quadratic yield functions in the constitutive
modeling, although the anisotropy present did not play as profound a role as it did in the
simulation of the free inflation experiments. In addition, corresponding shell element
calculations were deficient in capturing this type of localization that precipitates failure,
irrespective of the sophistication of the constitutive model adopted. This finding
contradicts current practice in modeling of sheet metal forming, where the thin-walled
assumption is customarily adopted.Aerospace Engineering and Engineering Mechanic
Computer aided design and optimization of bi-layered tube hydroforming process
Tube hydroforming is one of the unconventional metal forming processes in which high fluid pressure and axial feed are used to deform a tube blank in the desired shape. However, production of bi-layered tubular components using this process has not been investigated in detail in spite of the large number of research studies conducted in this area. Bi-layered tubing can be useful in complex working environments as it offers dual properties that a single layer structure doesnât have. Consequently, for wider implementation of this technology, a detailed investigation on bi-layered tube hydroforming is required.
In this research, both single and bi-layered tube hydroforming processes were numerically modelled using the finite element method (ANSYS LS-DYNA). Experiments were conducted to check the numerical models validation. In addition, Response Surface Methodology (RSM) using the Design-Expert statistical software has been employed along with the finite element modelling to attain a detailed investigation of bi-layered tube hydroforming in the X-type and T-type dies. The process outputs were modelled as functions of both the geometrical factors (tube length, tube diameter, die corner radius, and thicknesses of both layers.) and the process parameters (internal pressure coordinates, axial feed, and coefficient of friction.). Furthermore, the desirability approach was used in conjunction with the RSM models to identify the optimal combinations of each the geometrical factors and process parameters that achieve different objectives simultaneously. In addition, a different optimization approach that applies the iterative optimization algorithm in the ANSYS software was implemented in the process optimization.
The finite element models of single and bi-layered tube hydroforming processes were experimentally validated. A comparison of both processes was carried out under different loading paths. Also, response surface modelling of the bi-layered tube hydroforming process outputs was successfully achieved, and the main effects and interaction effects of the input parameters on the responses were discussed. Based on the RSM models, the process was optimized by finding the inputs levels at which the desired objectives are satisfied. Finally, a comparison of the RSM based optimization approach and the iterative optimization algorithm was performed based on the optimum results of each technique
EXPERIMENTS AND ANALYSIS OF ALUMINUM TUBE HYDROFORMING
This is a thesis on the development of an experimental table-top sized tube hydroforming machine at the University of New Hampshire. This thesis documents the design of the machine and the exploration of the forming envelope of the device via finite element modeling of the forming process. Several experiments on Al-6061-T4 tubes were used to evaluate the plastic behavior and strain limits of the tube in the axial and circumferential (hoop) directions. Two of these material tests, the uniaxial tension test and the ring hoop tension tests, were simulated with finite element models to refine the Al-6061-T4 plasticity curve, including the extrapolation of the hardening curve beyond the point of ultimate tensile stress. 2D and 3D finite element models of the hydroforming process were also used to evaluate potential tube materials, outer diameters, and wall-thickness for future experiments and research efforts
Virtual product development and testing for aerospace tube hydroforming industry : improved non-linear solid-shell element
Dans les recherches rĂ©alisĂ©es pour ce projet de thĂšse, il est dĂ©montrĂ© quâune traverse existante de train dâatterrissage dâhĂ©licoptĂšre Ă patins fabriquĂ©e par pliage et Ă©rosion chimique, pourrait ĂȘtre remplacĂ©e par une autre traverse, dont la forme innovante est fabricable par le procĂ©dĂ© dâhydroformage de tubes. Ce procĂ©dĂ© prĂ©sente par exemple lâavantage dâĂȘtre plus respectueux de lâenvironnement que le procĂ©dĂ© de fabrication actuel, car il ne nĂ©cessite pas lâutilisation de produits chimiques polluant. De plus, la mĂ©thodologie dĂ©veloppĂ©e dans le cadre des recherches rĂ©alisĂ©es permet de prendre en compte lâhistoire du matĂ©riau de la traverse dans toutes les Ă©tapes de son processus de fabrication. Les performances dâun train dâatterrissage Ă©quipĂ© de la nouvelle traverse ont Ă©tĂ© Ă©valuĂ©es numĂ©riquement. Des travaux, dĂ©veloppĂ©s avec le logiciel de calculs par Ă©lĂ©ments finis ABAQUS, ont permis de mettre en Ă©vidence lâintĂ©rĂȘt dâutiliser des Ă©lĂ©ments finis de coque solides fiables et prĂ©cis. Ces Ă©lĂ©ments sont en effet capables de prendre en compte le comportement dans lâĂ©paisseur de structures minces avec une seule couche dâĂ©lĂ©ments. Une nouvelle technique de lissage appelĂ© «Smoothed finite element method» ou «SFEM» a retenu lâattention pour sa simplicitĂ© de mise en Ćuvre et son insensibilitĂ© Ă la distorsion de maillage parfois rencontrĂ©e dans les simulations de formage de formes complexes. Un Ă©lĂ©ment de coque solide rĂ©sultant linĂ©aire dĂ©veloppĂ© en utilisant cette mĂ©thode SFEM pour traiter de la cinĂ©matique en membrane et en flexion a Ă©tĂ© testĂ© avec succĂšs au travers dâexemples classiques identifiĂ©s dans la littĂ©rature. Ce nouvel Ă©lĂ©ment a montrĂ© un niveau de prĂ©cision souvent supĂ©rieur Ă celui dâautres Ă©lĂ©ments dĂ©jĂ existants. En outre, un Ă©lĂ©ment de coque solide Ă intĂ©gration rĂ©duite, capable de fonctionner avec la plupart des lois de comportement en trois dimensions et cela mĂȘme en prĂ©sence de structures minces a Ă©tĂ© dĂ©veloppĂ©. Cet Ă©lĂ©ment, libre de tout blocage a montrĂ© un bon niveau de prĂ©cision par rapport aux Ă©lĂ©ments existants dans le cas de problĂšmes implicites gĂ©omĂ©triquement linĂ©aires et non-linĂ©aires. LâĂ©lĂ©ment a Ă©tĂ© Ă©tendu en formulation explicite puis couplĂ© avec une loi de comportement hyper Ă©lastoplastique en trois dimensions. Il a enfin Ă©tĂ© testĂ© dans une simulation dâhydroformage de tubes en prĂ©sence de pressions Ă©levĂ©es, de frottement et de grandes dĂ©formations.In the current work, it is shown that an existing helicopter skid landing gear cross tube, made by tube bending and chemical milling, could be replaced by another cross tube, whose innovative shape is producible by tube hydroforming. This method has for example the advantage of being more environmentally friendly than the current manufacturing process, because it does not require the use of hazardous chemicals. In addition, the methodology developed in this project takes into account the cross tube materialâs history throughout the manufacturing process. Moreover, the performance of a skid landing gear equipped with this new cross tube has been evaluated numerically. This thesis simulation work has been developed with the finite element analysis software ABAQUS. It highlights the potential gains of using a reliable and accurate solid-shell finite element which is capable to take into account the through-thickness behavior of thin structures with a single layer of elements. A new smoothing technique called «Smoothed finite element method» or «SFEM» has been considered for its simplicity and insensitivity to mesh distortion, sometimes encountered while simulating complex shapes forming. A new resultant linear solid-shell element using this SFEM to deal with membrane and bending kinematics has been developed and successfully tested through classical benchmark problems found in the literature. This new element has often shown much greater level of accuracy than other existing elements. In addition, a novel reduced integration solid-shell element, able to work with most three dimensions constitutive laws even in the presence of thin structures is also discussed. This element, free of locking, shows a good accuracy level with respect to existing elements in implicit geometrically linear and non-linear benchmark problems. Its extension to explicit formulation is coupled with a three dimensions hyper elastoplastic constitutive law and tested in a tube hydroforming simulation involving high pressures, friction and large deformations
Metal Micro-forming
The miniaturization of industrial products is a global trend. Metal forming technology is not only suitable for mass production and excellent in productivity and cost reduction, but it is also a key processing method that is essential for products that utilize advantage of the mechanical and functional properties of metals. However, it is not easy to realize the processing even if the conventional metal forming technology is directly scaled down. This is because the characteristics of materials, processing methods, die and tools, etc., vary greatly with miniaturization. In metal micro forming technology, the size effect of major issues for micro forming have also been clarified academically. New processing methods for metal micro forming have also been developed by introducing new special processing techniques, and it is a new wave of innovation toward high precision, high degree of processing, and high flexibility. To date, several special issues and books have been published on micro-forming technology. This book contains 11 of the latest research results on metal micro forming technology. The editor believes that it will be very useful for understanding the state-of-the-art of metal micro forming technology and for understanding future trends
Latest Hydroforming Technology of Metallic Tubes and Sheets
This Special Issue and Book, âLatest Hydroforming Technology of Metallic Tubes and Sheetsâ, includes 16 papers, which cover the state of the art of forming technologies in the relevant topics in the field. The technologies and methodologies presented in these papers will be very helpful for scientists, engineers, and technicians in product development or forming technology innovation related to tube hydroforming processes
Multi-objective Optimization of Tube Hydroforming Using Hybrid Global and Local Search
An investigation of non-linear multi-objective optimization is conducted in order to define a set of process parameters (i.e. load paths) for defect-free tube hydroforming. A generalized forming severity indicator that combines both the conventional forming limit diagram (FLD) and the forming limit stress diagram (FLSD) was adopted to detect excessive thinning, necking/splitting and wrinkling in the numerical simulation of formed parts. In order to rapidly explore and capture the Pareto frontier for multiple objectives, two optimization strategies were developed: normal boundary intersection (NBI) and multi-objective genetic algorithm (MOGA) based on the concept of dominated solutions . The NBI method produced a uniformly distributed set of solutions. For the MOGA method, a stochastic Kriging model was used as a surrogate model. Furthermore, the MOGA constraint-handling technique was improved, Kriging model updating was automated and a hybrid global-local search was implemented in order to rapidly explore the Pareto frontier. Both piece-wise linear and pulsating pressure paths were investigated for several case studies, including straight tube, pre-bent tube and industrial tube hydroforming. For straight tube hydroforming, the optimal load path was obtained using the NBI method and it showed a smaller corner radius compared to that predicted by the commercial program LS-OPT4.0. Moreover, the hybrid method coupling global search (MOGA) and local search (sequential quadratic programming: SQP) was applied for straight tube hydroforming, and the results showed a significant improvement in terms of the stress safety margin and reduced local thinning. For a commercial refrigerator door handle, the MOGA method was utilized to inversely analyze the loading path and the calculated path correlated well with the production path. For a hydroformed T-shaped tubular part, the amplitude and frequency of the pulsating pressure were optimized with MOGA. Thinning was reduced by 25% compared with experimental results. A multi-stage (prebent) tube hydroforming simulation was performed and it indicated that the reduction in formability due to bending can be largely compensated by end feeding the tube during hydroforming. The loading path optimized by MOGA showed that the expansion into the corner of the hydroforming die increased by 16.7% compared to the maximum expansion obtained during experimental trials
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