Wyniki wyszukiwania - BazTech

1

Artificial neural networks and evolutionary algorithms in engineering design

Velsker T, Eerme M, Majak J., Pohlak M., Karjust K.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 44, nr 1

88--95

EN

Purpose: Purpose of this paper is investigation of optimization strategies eligible for solving complex engineering design problems. An aim is to develop numerical algorithms for solving optimal design problems which may contain real and integer variables, a number of local extremes, linear- and non-linear constraints and multiple optimality criteria. Design/methodology/approach: The methodology proposed for solving optimal design problems is based on integrated use of meta-modeling techniques and global optimization algorithms. Design of the complex and safety critical products is validated experimentally. Findings: Hierarchically decomposed multistage optimization strategy for solving complex engineering design problems is developed. A number of different non-gradient methods and meta-modeling techniques has been evaluated and compared for certain class of engineering design problems. The developed optimization algorithms allows to predict the performance of the product (structure) for different design and configurations parameters as well as loading conditions. Research limitations/implications: The results obtained can be applied for solving certain class of engineering design problems. The nano- and microstructure design of materials is not considered in current approach. Practical implications: The methodology proposed is employed successfully for solving a number of practical problems arising from Estonian industry: design of car frontal protection system, double-curved surface forming process modeling, fixings for frameless glazed structures, optimal design of composite bathtub (large composite plastics), etc. Originality/value: Developed numerical algorithms can be utilised for solving a wide class of complex optimization problems.

2

Material parameters identification by use of hybrid GA

Majak J., Toompalu S., Pohlak M.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 27, nr 1

63-66

EN

Purpose: of this paper is to develop material parameters identification algorithm for yield criterion BBC2003 using global optimization techniques. Design/methodology/approach: An algorithm proposed is based on use of error minimization function, which allows considering over-constraining. Due to strong nonlinearity of the problem considered a number of solutions is available. In order to determine global extreme two stage GA (global optimization technique) is treated. Findings: Numerical material parameters identification algorithm is developed. An approach provided allows reducing significantly the dimension of the nonlinear system before its numerical solution. Convergence to global extreme can be expected due to global optimization technique employed. Research limitations/implications: An analysis is done by keeping formability analysis in mind and only material parameters involved in yield criterion in space of principal stresses are considered. Thus the results can be generalized by including terms corresponding to shear stresses. Practical implications: Advanced yield criteria like BBC2003 are still not used extensively due to the complexities accrued: increasing number of material parameters (additional tests), a complex non-linear programming problem. An algorithm proposed simplifies the material parameters identification process for considered yield criteria BBC2003. The formability analysis of the 6000 series aluminium alloy sheet AA6181-T4 is considered as a case study and used for testing the algorithm proposed. Originality/value: In the case of posed optimization problem the dimension of the design space is reduced from six to two. Over-constraining and under-constraining are considered in algorithm (situations, where number of unknown parameters is not equal with the number of given constraints, are covered).

3

Technology design of composite parts

Karjust K., Küttner R., Pohlak M.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 22, nr 2

23-26

EN

Purpose: Purpose of this paper is to optimize the design of the manufacturing technology process of large composite plastic products. One of the key problems is how to integrate computer-based product design and planning of the technology process. Design/methodology/approach: In the current study the Neural Network meta-modelling technique has been used. The optimization of the plastic sheet and its strengthening layer thickness has been performed using the surrogate design model. For modeling and structural analysis of derivative products CAE (ANSYS) and CAD (Unigraphics) systems are used. The Finite Element Analysis simulation was performed with optimal thickness values to verify the prediction accuracy of a surrogate model. Findings: The optimization model is proposed to control and analyze the calculated technology planning route, the optimal vacuum forming processes, the technology of post-forming operations, strengthening and assembling operations. The design of the new products is tightly integrated with manufacturing aspects. The product family of the large composite plastic products together with the derivate products and their production technologies is designed using proposed methodology. The optimization of the plastic sheet and its strengthening layer thickness has been performed. Practical implications: The most of the methods described in this study are now under development and industrial testing. Development of manufacturing (operation) plans for a product family is of great practical importance with many significant cost implications. In design of derivative products for the product family, the nonlinear optimization is used and the detailed description of the product is established. The proposed approach is exemplified by the development of a family of products in Wellspa Inc. Originality/value: Value of this paper is that developed optimization model controls and analyzes the calculated technology planning route.

4

Incremental sheet forming process modelling - limitation analysis

Pohlak M., Majak J., Küttner R.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 22, nr 2

67-70

EN

Purpose: of this paper is incremental sheet forming (ISF) process modelling. Main attention is paid to limitation analysis. Two kinds of risks are considered: material failure and tool failure. Aim of the current study is to minimize both risks i.e. provide limits for safe manufacturing. Design/methodology/approach: Experimental, numerical and theoretical investigation is performed. The test procedures are designed for determining FLD and forming force components in ISF process. The ISF process is modelled using FEM software LS-DYNA (fully integrated shell elements). In numerical analysis the plastic anisotropy is considered (Hill's second and Barlat's higher order yield criteria). Findings: The influence of plastic anisotropy on two formability characteristics - FLD and forming load components is studied. In both cases the effect of plastic anisotropy is found to be significant. It is shown that variation of the Lankford coefficient(s) in range 0.5 - 3.0 may cause changes on the formability characteristics over ten percent. Research limitations/implications: Limitations on forming angle, complications with considering elastic spring-back. Practical implications: The estimates on forming load components can be used for tooling selection in order to avoid tool failure. The FLD can be used in order to separate safe and unsafe forming areas in ISF process. Originality/value: An approximate theoretical model is proposed (based on Iseki's model). Incremental sheet forming strategies for determining forming limit diagram (FLD) are pointed out.

5

A simple algorithm for formability analysis

Majak J., Pohlak M., Küttner R.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 22, nr 1

57-60

EN

Purpose: of this paper is to develop a simple algorithm for local and diffuse necking analysis, which covers different yield criteria and strain hardening laws. Design/methodology/approach: Theoretical study, application of plasticity theory. Numerical analysis, FLD determination. Experimental verification (material parameters and FLD). Comparison of obtained results with the results available in literature. Both, stress and strain based FLD-s are considered. Findings: The dimensionless in stability tensors are introduced. The plastic instability criterion in tensor notation is derived. The capabilities of the derived instability criteria are improved using different anisotropic yield criteria from Hill48 up to BBC2003. A test procedure for determining material properties and forming limits in plane strain condition for sheet metal is performed. Reseach limitations/implications: The study is based on classical instability conditions. The stress-strain behavior of the material is described with empirical equation (the strain rate and also temperature dependence of the flow stress are not considered). Practical implications: The forming limit curve determined defines boundary between elastic or stable plastic deformation (below curve) and unsafe flow (above curve). The risk of failure is determined by the distance between the actual strain condition in the forming process and the forming limit curve. Originality/value: A simple algorithm for local and diffuse necking analysis is proposed. The dimensionless instability tensors introduced can be used for theoretical improvements.