Key Engineering Materials Vols. 651-653

Abstract: Finite element models optimizing cold forged products have to incorporate the complete manufacturing pathway. Virtual process design as a method based on a multistep operation approach can describe interacting phenomena. Thus, inheritance effects like residual stress and damage evolution can be tracked throughout the processing chain. Besides the influence of the deformation direction (Bauschinger Effect) on material flow can be predicted. Using intermediate step optimization may also extend geometrical limits. Furthermore it may increase life time and improve material efficiency for a given component. The exploitation of these coupling effects may also form a basis for further product and process innovations.

Abstract: Forming processes usually involve irreversible plastic transformations. The calculation in that case becomes cumbersome when large parts and processes are considered. Recently Model Order Reduction techniques opened new perspectives for an accurate and fast simulation of mechanical systems, however nonlinear history-dependent behaviors remain still today challenging scenarios for the application of these techniques. In this work we are proposing a quite simple non intrusive strategy able to address such behaviors by coupling a separated representation with a POD-based reduced basis within an incremental elastoplastic formulation.

Abstract: A new efficient updated-Lagrangian strategy for numerical simulations of material forming processes is presented in this work. The basic ingredients are the in-plane-out-of-plane PGD-based decomposition and the use of a robust numerical integration technique (the Stabilized Conforming Nodal Integration). This strategy is of general purpose, although it is especially well suited for plateshape geometries. This paper is devoted to show the feasibility of the technique through some simple numerical examples.

Abstract: There have been many efforts to investigate and develop a numerical damage and failure models during metal forming process of lightweight alloys. Due to the difficulties experienced during experimental determination of the incurred damage during forming of lightweight alloys, many researchers have sought to predict the damage, failure and forming limit curves using numerical simulations. Conventional finite element analysis of metal forming processes for lightweight parts which have been subjected to a nonlinear strain history often breaks down due to numerical difficulties. Many scientific research works have attempted to use different mathematical methods to model the damage progression and failure of alloying material under large deformation. The damage initiation, progression and also failure of alloys are a result of accumulated damage under plastic deformation [1-3]. These models (single and multi-damage parameters) are generally based on energy and constitutive equations to simulate the fracture and failure processes in metal alloys. However, these methods have serious short comes in predicting the damage and failure in metal forming process with strain rate effects. In the present study, following the in-depth study of damage initiation and progression in lightweight alloys, a frame work has been setup to develop a numerical model for damage accumulation during forming process. Based on the existing damage theory, a mathematical extension for damage initiation and also damage accumulation under wide range of stress triaxiality (including near pure shear) has been developed. An experimental program has also been carried out using samples made from lightweight alloys. One of the main contributions of this paper is to show the advantages of using plasticity-based modified damage models to investigate the damage accumulation in cast aluminium alloys.

Abstract: The objective of this work is the study of the mechanical behaviour of a sandwich structure, composed by two out layers in aluminium sheets, separated by a core in metal foam also in aluminium, by penetration of a spherical punch. Considering a structure composed by these two different materials, each one presents a different mechanical behaviour separately [1, 2].The set up used in the present experimental work is composed by a punch, with a radius r, which imposes a displacement/force to a specimen fixed in its boundary.In these tests, specimens with four different length were considered; 25 mm, 50 mm, 75 mm and 150 mm. The values of force/displacement of the punch were registered.

Abstract: Forming, press hardening and welding are a well-established production processes in manufacturing industry, but predicting the finished geometry and the final material properties of the processed parts is still a major issue. In particular, deformations caused by welding are often neglected in the virtual process chain, although they have to be compensated for in order to fulfill the requirements on shape tolerance. This presentation will give an overview on novel features of LS-DYNA implemented particularly for welding simulations.To begin with, new keywords will be presented that allow applying the heat generated by the weld torch. LS-DYNA offers a very convenient way to define the well-known Goldak heat source, but it is also possible to define arbitrarily shaped torch geometries.In order to obtain a predictive model for welding simulations, specific material models have been devised in LS-DYNA. The properties of filler material in weld seams are accounted for by a ghost material approach. Material is initialized as ghost material and is activated, i.e. it is given base material properties, when the temperature reaches the melting point. This approach has been implemented for a relatively simple thermo-elasto-plastic material formulation *MAT_CWM as well as for the more complex material law *MAT_UHS_STEEL. The latter has initially been implemented for press hardening simulations and is able to predict the microstructure of steel alloys including phase transformations and the resulting mechanical properties.In this contribution, details of the material formulations and novel features are presented. Examples will demonstrate how these features can be applied to multistage processes including several forming and welding stages.

Abstract: The multiscale modelling of the behaviour of metal alloys during processing is often limited by the computing power required to run them. The Agile Multiscale Methodology was conceived to enhance the designing and controlling of complex multiscale models through an automatic run-time adaptation of its constitutive sub-models. This methodology is used to simulate the behaviour of an 6082 aluminium alloy during its thermomechanical treatment. The macroscopic deformation, the work-hardening and the state of precipitation are computed in different modules, allowing the coupling of several software solutions (DEFORM^TM2D and © MatCalc) through an external storage of the relevant data.

Abstract: Over the past years engineering has established itself in many areas of production technology on the basis of simulation methods. Efficient tools and software applications for the development and planning of products, machines and systems have been developed which allow virtual analyses especially for critical areas, e.g. micro structural analysis’s, forming processes or joining applications. However, these are often isolated solutions which only cover one particular aspect and are not complete calculation tools. This is often caused by data transfer between simulation programs. There are hardly any automatic links between software tools which often come from different providers. Often data formats have to be converted first and then transferred manually. Therefore, interdependencies can only be taken into consideration to a small extent and with a high expenditure of resources. This affects the quality of numerical results and hence the development and optimization process. Consequently, the necessity of a process chain simulation which covers all production steps similar to a virtual factory becomes obvious. This automatic simulation should make it possible to consider the numerical results from micro structure calculation to the manufacturing of the composite tools successively and thus contribute to having a nearly fault-free perfected process for the real factory.

Abstract: The aim of this paper is to study the simulation of cogging process using a thermo-mechanical partitioned algorithm. The thermal and mechanical problems are solved separately. The mechanical problem is based on the balance equation whereas the thermal problem is based on the heat equation. The two physics are coupled trough the mechanical parameters that depends on the thermal problem and vice versa. The results obtained using the software Forge3 show that the mechanical deformation is high inside the zone of deformation and negligible outside whereas the temperature is high overall the mesh with a gradient at the zone of contact between the dies and the work piece.

Abstract: The paper deals with the identification of material model based on the internal variable. The model with one internal variable, which was average dislocation density, was considered. Identification was performed using inverse analysis (IA) of uniaxial compression tests. In this work IA was transformed to an optimization task and the goal function was defined as difference (in Euclid's norm) between measured and calculated parameters: loads in plastometric tests (used to identify flow stress) and stresses in stress relaxation tests (used to identify recrystallization kinetics). Exploring a possibility of making the identification more reliable by application the Sensitivity Analysis (SA) was the main objective of the work. The IA was preceded by SA of the model output with respect to the model parameters to select an efficient optimization algorithm and/or eliminate local minima. Selected results of identification for different materials are presented in the paper, as well.