J.F. Caseiro

Thermomechanical Modeling of Multiphase Steels: Classical and Modern Engineering Analyses

This chapter presents the thermodynamic foundations for the analysis of multiphase steels and some conventional approaches used in the analysis of these materials, including classical constitutive equations. Afterwards, the standard strategies for modeling multiphase metals are introduced as well as some examples. The new assumptions and today’s modeling strategies, that include complex numerical simulation methods such as the finite element method, finite volume, finite differences and phase-field methods, are also presented and compared with the previous approaches, with the aid of examples and research results.

On a New Optimization Approach for the Hydroforming of Defects‐Free Tubular Metallic Parts

In the hydroforming of tubular metallic components, process parameters (internal pressure, axial feed and counter‐punch position) must be carefully set in order to avoid defects in the final part. If, on one hand, excessive pressure may lead to thinning and bursting during forming, on the other hand insufficient pressure may lead to an inadequate filling of the die. Similarly, an excessive axial feeding may lead to the formation of wrinkles, whilst an inadequate one may cause thinning and, consequentially, bursting. These apparently contradictory targets are virtually impossible to achieve without trial‐and‐error procedures in industry, unless optimization approaches are formulated and implemented for complex parts. In this sense, an optimization algorithm based on differential\evolutionary techniques is presented here, capable of being applied in the determination of the adequate process parameters for the hydroforming of metallic tubular components of complex geometries. The Hybrid Differential Evolutio...

On the thermomechanical modelling of multiphase materials during heat treatments and subsequent forming

In multiphase materials, such as steels, the metallurgical composition is achieved during the manufacture process and depends directly on the thermal path undergone by the material. This multiphase composition, as well as certain mechanical properties, can be changed through heat treatments. In these heat treatments (e.g. quenching), residual stresses typically arise during the cooling of the material. In this work, the thermomechanical modelling of multiphase materials is discussed. In the first part, a multiphase thermo‐elastoplastic‐viscoplastic model is presented and applied to simulate several quenching heat treatments. The model uses the Johnson‐Mehl‐Avrami‐Kolmogorov (JMAK) equation to describe the diffusion transformation and the Koistinen‐Marburger model to characterize the diffusionless martensitic transformation in non‐isothermal kinetics. This allows the observation of the evolution of the different steel phases during the cooling process. However, it isn’t possible to determine the residual s...

Optimisation of Tubular Hydroforming Processes for Wrinkling and Thinning Control

This paper is focused on the development and implementation of an innovative optimisation algorithm for the wrinkling and thinning control during the hydroforming of complex metallic parts. A straightforward numerical algorithm for simultaneous tracking and evaluation of the initiation of wrinkling/thinning defects was implemented, together with a numerical simulation program based on the Finite Element Method (FEM). After undesirable wrinkling/thinning patterns are identified during FEM simulation, the developed optimisation procedure (called Hybrid Differential Evolution Particle Swarm Optimisation - HDEPSO) is responsible to automatically correct the process input parameters, in order to achieve the successful forming of the desired part. In the end, the combined procedure (optimisation methodology + FEM) proved to be able to lead to a suitable numerical simulation and design tool for industrial hydroformed metallic tubular parts.

An evolutionary-inspired optimisation algorithm suitable for solid mechanics engineering inverse problems

In this work, a direct search optimisation algorithm based on differential and evolutionary methods, as well as in the behaviour of animals is developed. This algorithm is applied to inverse engineering problems. Firstly, the developed algorithm is validated and compared with existing optimisation algorithms using a set of composite functions specially design for that purpose. In the second phase, the algorithm is applied to engineering and computational mechanics problems. The 120-bar dome truss problem that is solved using the finite element method (FEM) is analysed. Subsequently, the compression of a cylindrical billet and the plate with a central cut-out problems are analysed. In these two problems, the function to minimise is given by a commercial FEM code. Finally, the algorithm is applied to a constitutive model parameter identification problem. The develop algorithm obtains good results and a good convergence rate.