Key Engineering Materials Vols. 651-653

Abstract: The detection of process failures in earlier design stages is essential for preventing high additional costs and a loss of time. Here, the finite element analysis (FEA) is an inherent part of the process design. This work represents numerical and experimental investigations, which were carried out in order to identify factors that influence the fold formation in an upsetting process of hollow parts, i.e. different forging velocities, different materials or the friction. The experimental results were compared with the numerical simulations. Based on these investigations, an automatic optimization model was created, which is the focus of this work. It allows varying and optimizing the experimentally determined process parameters, influencing the fold formation, automatically with the aim to produce a workpiece free of folds. For this purpose the commercial Software-System Forge (Transvalor) was used. The results of this work provide basic information for the development of complex processes. It can be shown that the automatic numerical optimization is an indispensable tool for the process design. It helps determining optimal process parameters individually and avoiding extensive trial and error investigations and hence a loss of time and costs.

Abstract: The temperature of forging dies has a high influence on the wear development of the tool surface. To reduce the thermal impact on tool life cooling lubricants are used in many manufacturing processes. They perform two functions: tool cooling and reduction of friction. Cooling lubricants must always meet these two requirements. Within this article the separation and the particular optimization of both functions is presented.As an alternative to a graphite-water-mixture, boron nitride is the medium of choice for lubrication purposes, since it features excellent lubricant properties. For a high wettability it is applied by electrostatic coating.As an alternative approach to removing heat from a forging die, the usage of heat pipes is for the first time investigated in this paper. These passive elements are able to transport heat without using external energy. They will be varied in form and volume. This cooling method will be qualified for the use in forging dies.

Abstract: Based on experimental studies of the complex mechanical properties and microstructure, as well as simulation of rails rolling modes made from different steel manufacturers are shown the main technological approaches to obtain rails with high operational reliability . Found that, under the current production technology of domestic steel rails the adjustment of the chemical composition, temperature-deformation modes of rolling and cooling speed rate of the rails is suitable for reducing the negative free ferrite influence on rails durability.

Abstract: X-ray micro computed tomography (Micro-CT) is a non-destructive technique that can provide information on the internal structure of materials. The purpose of micro-CT is to assess the presence of defects as well as characterizing internal structures and potential damage present in the produced part. Simple shear is an interesting deformation mechanism for woven fabric draping. The internal structure change of the carbon fibre twill fabric after shear deformation is chosen as a subject of this paper. Parameters of the mesoscopic internal structure of the woven fabric like cross section, shape, area, and middle line coordinates can be obtained from micro-CT images through image processing procedures. Details of the image data processing for sheared fabric cross sections are discussed. This paper illustrates the possibilities of micro-focus computer tomography in materials research, namely for defining geometrical properties of textile. Image processing is also used for the recognition of fibre direction in the yarns. Described methodology can be applied for determining structure of a fabric, and the results can be used for further micromechanical modelling. Identification of the fibres orientation is important for estimation of the mechanical properties of composites and can be achieved with image processing techniques.

Abstract: Most suspension descriptions nowadays employed are based on the Jeffery's model andsome phenomenological adaptations of it that do not take into account size effects, that is, the kinematicsand stresses do not introduce a micro-mechanical characteristic length and thus, the rheologicalproperties become independent of the rod length. New models able to enrich first gradient kinematicsas well as to activate rod-bending mechanisms (needed for explaining the mild elasticity experimentallynoticed) are needed. In this paper we propose a second gradient description able to activate rods bending.

Abstract: The increasing use of finite element simulation in the field of composite material forming involved in the past few years a large amount of research on the constitutive modelling of textile material at the mesoscopic scale (i.e. the scale of individual fiber tow). Up to now, the community interest was focused on a consistent shape prediction. Moreover, the large amount of contacts between yarns imposed the use of dynamic explicit approaches for numerical efficiency reasons. Recent advances in contact algorithms make now possible the use of implicit schemes. The present paper shows how a constitutive equation written and implemented in the dynamic explicit scheme with ABAQUS/Explicit is adapted to implicit one (i.e. ABAQUS/Standard), for large displacement analyses.Validation and perspectives are illustrated on a weaving operation.

Abstract: Thin structures are commonly designed and employed in engineering industries to save material, reduce weight and improve the overall performance of products. The finite element (FE) simulation of such thin structural components has become a powerful and useful tool in this field. For the last few decades, much attention and effort have been paid to establish accurate and efficient FE. In this regard, the solid–shell concept proved to be very attractive due to its multiple advantages. Several treatments are additionally applied to the formulation of solid–shell elements to avoid all locking phenomena and to guarantee the accuracy and efficiency during the simulation of thin structures. The current contribution presents a family of prismatic and hexahedral assumed-strain based solid–shell elements, in which an arbitrary number of integration points are distributed along the thickness direction. Both linear and quadratic formulations of the solid–shell family elements are implemented into ABAQUS static/implicit and dynamic/explicit software to model thin 3D problems with only a single layer through the thickness. Two popular benchmark tests are first conducted, in both static and dynamic analyses, for validation purposes. Then, attention is focused on a complex sheet metal forming process involving large strain, plasticity and contact.

Abstract: The ability of a draping simulation to accurately predict the outcome of a forming process mainly depends on the accuracy of the input parameters. For pre-impregnated composites, material must be characterised in the same conditions as forming occurs, i.e. in temperature regulated environment. Given the issues encountered while testing specimens enclosed in a thermal chamber and mounted on a tensile testing machine, new test methods have to be developed. A new approach using a Dynamic Mechanical Analysis system is presented for the investigation of tensile properties perpendicular to fibre direction of unidirectional pre-impregnated composites. Analyses are focused on a unidirectional carbon fibre thermoplastic tape reinforced polyamide 6 in its molten state. Quasi-static tests are performed at forming temperature for different loading rates with specimens of different geometries in order to assess the reproducibility of the test method.

Abstract: The bending deformation of thermoplastic prepregs is one of the key deformation modes in the thermoforming due to its crucial role in the wrinkling occurrence. The influence of temperature is of main importance because the viscous effect of resin is temperature dependent and prepregs thermoforming is usually performed closed to resin’s melting point. The currently available bending test devices are not adapted for thermoplastic prepregs since these devices can only be operated at room temperature. To solve this problem, a new cantilever test with an optical measuring performed in an environmental chamber is proposed. The bending properties of PPS-carbon satin prepregs are measured at a series of high temperatures. It’s shown that the bending stiffness of the fore-mentioned pepregs is strongly affected by the temperature and shows a non-linear bending behaviour. The measured bending properties are used to simulate a thermoforming process. The influence of bending properties on the simulation results, especially to the wrinkling is presented as well.

Abstract: A methodology to calculate surface strains from a rectangular grid placed on a forming blank is introduced. This method consists of treating the grid points as nodes of a finite element (FE) model and assigning elements to the grid. The strains are then computed following FE analysis. If higher order elements are used, also more information within the element can be obtained which allows a coarser grid without loss of accuracy. This is the major advantage of the approach presented herein.