A. Andrade-Campos

Development of an Optimization Framework for Parameter Identification and Shape Optimization Problems in Engineering

The use of optimization methods in engineering is increasing. Process and product optimization, inverse problems, shape optimization, and topology optimization are frequent problems both in industry and science communities. In this paper, an optimization framework for engineering inverse problems such as the parameter identification and the shape optimization problems is presented. It inherits the large experience gain in such problems by the SiDoLo code and adds the latest developments in direct search optimization algorithms. User subroutines in Sdl allow the program to be customized for particular applications. Several applications in parameter identification and shape optimization topics using Sdl Lab are presented. The use of commercial and non-commercial (in-house) Finite Element Method codes to evaluate the objective function can be achieved using the interfaces pre-developed in Sdl Lab. The shape optimization problem of the determination of the initial geometry of a blank on a deep drawing square cup problem is analysed and discussed. The main goal of this problem is to determine the optimum shape of the initial blank in order to save latter trimming operations and costs.

Mechanical Behaviour and Springback Study of an Aluminium Alloy in Warm Forming Conditions

This study deals with the mechanical behaviour and material modelling of an AA5754-O alloy at elevated temperature. Experimental shear tests were performed from room temperature up to 200°C, and the material behaviour has been identified with both shear and tensile tests, as a function of temperature. To analyse the influence of temperature during forming over springback, a split-ring test is used. Experimental results are obtained and compared to numerical simulations performed with the finite element in-house code DD3IMP. The numerical process of ring splitting is performed with the in-house code DD3TRIM. The main observed data are force-displacement curves of the punch during forming, cup thickness at the end of forming, and ring gap after splitting. It is shown that all these parameters are strongly dependent on the forming temperature. A correlation is obtained between experimental data and numerical simulation for the evolution of punch force and opening after springback as a function of temperature. The distribution of the tangential stress in the cup wall is the main factor influencing the springback mechanism in warm forming condition.

Energy Recovery in Water Networks: Numerical Decision Support Tool for Optimal Site and Selection of Micro Turbines

AbstractEnergy efficiency plays a large role in the sustainability effort of water utilities. In gravity-fed pipe networks that present excessive pressures, the installation of micro turbines or pu...

On the Development and Computational Implementation of Complex Constitutive Models and Parameters’ Identification Procedures

Nowadays, the automotive industry has focused its attention to weight reduction of the vehicles to overcome environmental restrictions. For this purpose, new materials, namely, advanced high strength steels and aluminum alloys have emerged. These materials combine good formability and ductility, with a high tensile strength due to a multi-phase structure (for the steel alloys) and reduced weight (for the aluminum alloys). As a consequence of their advanced performances, complex constitutive models are required in order to describe the various mechanical features involved. In this work, the anisotropic plastic behavior of dual-phase steels and high strength aluminum alloys is described by the non-quadratic Yld2004-18p yield criterion, combined with a mixed isotropic-nonlinear kinematic hardening law. This phenomenological model allows for an accurate description of complex anisotropy and Bauschinger effects of the materials, which are essential for a reliable prediction of deep drawing and springback results using numerical simulations. To this end, an efficient computational implementation is needed, altogether with an inverse methodology to properly identify the constitutive parameters to be used as numerical simulation input. The constitutive model is implemented in the commercial finite element code ABAQUS as a user-defined material subroutine (UMAT). A multi-stage return mapping procedure, which utilizes the control of the potential residual, is implemented to integrate the constitutive equations at any instant of time (pseudo-time), during a deformation process. Additionally, an inverse methodology is developed to identify the constitutive model parameters of the studied alloys. The identification framework is based on an interface program that links an optimization software and the commercial finite element code. This methodology compares experimental data with the respective results numerically obtained. The implemented optimization process aims to minimize an objective function, which defines the difference between experimental and numerical results using the Levenberg-Marquardt gradient-based optimization method. The proposed integrated approach is validated in a number of benchmarks in sheet metal forming, including monotonic and cyclic loading, with the goal to infer about the modelling of anisotropic effects.

Numerical optimization strategies for springback compensation in sheet metal forming

The industrial sheet metal forming process is known for being influenced by undesired effects such as springback, fracture, or wrinkling, leading to a lack of quality of the final part. Springback is a critical problem, particularly in the automotive industry where mass production is frequently used and geometric inaccuracies result in heavy economic losses. Therefore, when designing a forming process, it is mandatory to take into consideration the springback behavior of the part in order to compensate or reduce it, through the adjustment of the process parameters such as external forces or tools geometry. The aim of this work is to discuss efficient strategies to compensate springback. To this end, two different approaches are compared: the Finite Element Method Updating and the Metamodeling Optimization. These approaches can use distinct solution evaluation strategies, namely Experimental and Finite Element Analyses, using both implicit and explicit time integration schemes. These solution evaluations are used to quantify the efficacy of the solution for the springback compensation problem, which is then used as input in the optimization algorithms to obtain new designs for the forming process. Considerations are also given regarding the use of different forming tools’ parameterizations in the springback compensation problem: NURBS versus classical geometrical parameterization. All different approaches are applied to the springback compensation problem of the U-shaped rail, a benchmark that shows large elastic recovery after the tool removing. The results are also compared with the ones obtained by other authors, highlighting that, even for this simple example, metamodeling optimization requires a large number of evaluations.

A new approach for the prediction of speed-adjusted pump efficiency curves

ABSTRACT Researchers and engineers commonly rely on modelling and simulation computer programs to improve the management, design and operational efficiencies in water supply systems. The reliability of some efficiency measures, however, is known to be highly dependent on the modelling accuracy of the selected modelling/simulation tool. Although a number of papers have been recently published related to the use of variable-speed pumps in water networks, there are no relevant studies on the analysis and improvement of the methods used to model the behaviour of these pumps. Consequently, the present work focuses on the methods used to model efficiency curves of variable-speed pumps. A new approach for the prediction of the speed-adjusted curves is proposed and preliminary results using two distinct pumps are presented and discussed. The proposed method is capable of satisfactorily predicting the behaviour of the pumps, demonstrating its potential to be effectively used in modelling tools.

Design of a mechanical test to characterize sheet metals - Optimization using B-splines or cubic splines

Nowadays, full-field measurement methods are largely used to acquire the strain field developed by heterogeneous mechanical tests. Recent material parameters identification strategies based on a single heterogeneous test have been proposed considering that an inhomogeneous strain field can lead to a more complete mechanical characterization of the sheet metals. The purpose of this work is the design of a heterogeneous test promoting an enhanced mechanical behavior characterization of thin metallic sheets, under several strain paths and strain amplitudes. To achieve this goal, a design optimization strategy finding the appropriate specimen shape of the heterogeneous test by using either B-Splines or cubic splines was developed. The influence of using approximation or interpolation curves, respectively, was investigated in order to determine the most effective approach for achieving a better shape design. The optimization process is guided by an indicator criterion which evaluates, quantitatively, the strai...

Analysis of Steel Phase Transformations Using a Multiscale Transient Model

Multiphase steels offer impressive mechanical properties. However, their characterization still represents a challenge. In a quenching processes, phenomena such as undesirable strains or residual stress are inevitable and can be the cause for non-admissible final parts. Microstructural phase transformations generally magnify the problem. This fact leads to the need of numerical tools capable of quantifying these residual stresses, due to the non-existence of efficient non-destructive experimental procedure capable of measuring them. In this work, a numerical multiscale transient model, that uses the Asymptotic Expansion Homogenisation (AEH) method combined with finite element method (FEM), is proposed. The implementation of the AEH method is carried out using the commercial program Abaqus, considering an uncoupled and quasi-static transient problem with implicit time integration. Within the homogenisation method, the existence of two distinct scales is assumed, defining a micro and a macroscale. Within the smaller scale, the evolution of a steel periodic microstructure is analysed in detail and an equivalent homogeneous material model is established for macroscopic use. However, the microstructural evolution leads to the need of new equivalent homogeneous models in order to predict the macro response. Consequently, several mechanical, thermomechanical and transient thermal homogenization procedures are carried in order to establish different equivalent homogeneous models.

The Geometry Definition Influence in Inverse Analysis—Application to Carter Forming Process

Nowadays, industrial and scientific communities are confronted with extremely complex mechanical engineering problems. Therefore, to try to reduce this complexity and allow the simulation of different mechanical situations the investigation of the inverse engineering is increasing. Distinct inverse problems can be formulated, being one of the categories the initial geometry optimization, which is not extensively described in the literature. The aim of this kind of problems is to estimate the initial shape of a specimen or a blank in order to achieve the desired geometry after the forming process. In this work, the superplastic forming of a carter is described and studied. After the forming it is possible to verify that strain fields are not uniform in the whole carter surface, leading to a non‐homogeneous thickness distribution in the final geometry. To avoid this problem, a non‐uniform thickness of the initial undeformed blank can be found in order to obtain a regular final thickness of the sheet even wi...

Numerical analysis of triaxial residual stresses in quenched 316H stainless steel

Residual stress fields can cause creep damage in thermally aged components, even in the absence of working loads. In order to study this issue, the authors present a numerical study on the development of triaxial residual stresses in stainless steel specimens. A mechanical model dedicated to the analysis of heat treatment problems is described. The presented formulations are implemented incrementally with a non-linear constitutive model, adequate to the simulation of a wide range of thermal processes. The flow rule is a function of the equivalent stress and the deviatoric stress tensor, of the temperature field and of a set of internal state variables. The thermomechanical coupled problem is solved with a staggered approach. Spray water quenching was used to generate residual stress fields in solid cylinders and spheres made from 316H stainless steel. Finite element simulations were performed to find out how process conditions and specimen geometry influence the resulting residual stress distributions. The results show that compressive residual stresses are developed near the surfaces of the cylinders and spheres while tensile residual stresses occur near the centre. The level of residual stresses was found to be dependent on the heat transfer coefficient.