Key Engineering Materials Vols. 611-612

Abstract: The present paper reveals one of the energy efficient ways of science investigation of materials for light construction purposes. The small hollow spheres made from different materials could change the weight of a construction part essentially, used as acoustic and thermal insulation and also as protection against vibrations. They can be used as a unit cell for big parts and alone filled with an inert gas, e.g. fusion targets. Pure tin shells were produced in transient (thixotropic) state of materials at elevated temperatures (close to the melting point of the pure tin melt) and several simulation steps were used, to determine the preferable boundary conditions. To one of them belongs the investigation of the temperature fields during the formation process. The formation force was determined theoretically. Also a theoretical assumption, that the solid material needs the same deformation force value or close to it, the numerical investigation was also carried out in FE-code QForm-3D.

Abstract: Commonly investigated problem on composite fabrication and forming for weight reduction in transportation and aerospace area is not completely cleared. The main difficulties on composites forming without building any defects caused new ways on process characterization due to the key parameters. In the paper two main problems were investigated, i.e. material fracture and material thinning during deep drawing. Through mechanical tests and numerical simulation the authors tried to couple the fracture with the technological boundary conditions of the deep drawing process and form a housing test part from a three-layer material.

Abstract: The success of semi-solid metal forming is dependent on a globular solid grain formation within a liquid phase. This paper presents experimental works concerning semi-solid metal processing of aluminium 7075 feedstock billets which were produced by direct thermal method. The flowability of feedstock billets was evaluated by an injection test processing unit. The feedstock billets were heated to a temperature of 620 °C by using a box furnace before transferred into a forming die. The formed feedstock billet was removed from the forming die after it was cooled to ambient temperature. Several analyses were conducted on the formed feedstock billets including dimensional measurement and microstructure analysis. The results show that the feedstock billets which contained highest amount of free secondary phase were most successfully formed. Microstructure analysis results also revealed the formation of more globular and larger α–Al solid grains in the same feedstock billets. In this experimental work, the feedstock billets with higher secondary (liquid) phase gives a significant effect to formability. It can be concluded that in order to get successful formability of direct thermal method feedstock billets, the billets need to have higher secondary phase content. Thus, the selection of proper feedstock billets is important to determine the success of the SSM processing.

Abstract: 800x600 The applying of burden materials containing titanium compounds in the blast furnace process and the processes of forming titanium carbides and nitrides has a directly impact on the physical and chemical properties of slag and pig iron. Thereby affecting the course of the process, its efficiency and economy. It is known that the dynamic viscosity coefficient of slag – with an increased titanium compounds content in the reducing conditions of the blast furnace - may rapidly change. The products of the reduction reaction, precipitation and separation of titanium compounds are responsible for the thickening effect of the slag and the problems of permeability of blast furnace, causing anomalies in the functioning of the unit. The presence of solid components (particles) in the melts determines the rheological character of the entire system.Authors have performed a rheological study of synthetic furnace slag concentration of TiO₂ in the range of 6% to 30%. The measurements were performed at temperatures in the range between 1310-1490^oC. The obtained results made it possible to analyze the rheological characteristics of liquid and semi-solid slag systems and produce flow curves. Identifying the rheological character of semi-solid slag systems provides opportunities for the development of a mathematical model of liquid phase flow in a dripping zone of the blast furnace, allowing for example to indentify the unstable parts of a metallurgical aggregate. Normal 0 21 false false false PL X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:Standardowy; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif";}

Abstract: In high temperature metal forming techniques, analysis of the material flow and deformation as well as wear distribution during forging are very important, because they are directly correlated to the quality of the final component and to the productivity and die life. In this paper a commercially available Finite Element Method based simulator, namely Transvalor Forge 2008^©, is used to numerically investigate on the effects of the various parameters on the mode of the failure of dies during hot forging. The exploration has the purpose to evaluate the possibility and related benefits of the advancement from a traditional hot forging process to a modern thixoforging one in the case study of steel-made steering pistons production. As a first step, the part related to the hot forging process is in detailed analyzed, in order to get an exhaustive description of the role of the different parameters. One step and two step solutions are proposed and discussed.

Abstract: Autoclave curing is a common practice to manufacture high temperature thermoset matrix composites in order to improve the mechanical properties of the final product. The cycle design i.e. the definition and optimization of the temperature-time curve is a key issue for a competitive production. In this paper a very fast and effective procedure, based on the coupling of a finite element thermochemical model of the process and an artificial neural network, is proposed to predict the evolution of temperature in predefined control points inside the processing material. The model has been tested against the imposed thermal cycle used as an input. The procedure is tested simulating the curing process of a three-dimensional double-curved shape. Obtained outcomes highlighted the remarkable capabilities of the implemented procedure in terms of reliability of temperature predictions and of drastic reduction of the computational time with respect to classic computational models.

Abstract: In the present paper, a numerical finite element model of the precipitation hardenable AA2024-T3 aluminum alloy, consisting of a heat transfer analysis based on the Thermal Pseudo Mechanical model for heat generation, and a sequentially coupled quasi-static stress analysis is proposed. Metallurgical softening of the material is properly considered and included in the calculations by means of the Myhr and Grong model, implemented as a user subroutine in ABAQUS. Numerical outcomes are compared with experimental results, highlighting the intriguing predictive capabilities of the model for both temperatures and residual stresses. The contour method is employed to map the longitudinal residual stress distribution on a transverse cross section of the joint. The influence of the applied boundary conditions and of the release of the clamping system on residual stresses is also assessed.

Abstract: In today's competitive business environment, it has become increasingly important to reduce manufacturing and raw materials cost. For this purpose, an innovative process of design and manufacturing railway axles is developed. It is based on forging hollow axles which allows a significant reduction in steel consumption. In this work, we tried to analyze how these modifications induced by this new process and design impact the service behavior and particularly the durability face to cyclic loadings that can lead to fatigue failure. In the present study, a numerical chain has been developed going from the simulation of the manufacturing process up to the analysis in fatigue. In the first step, the forging process is modeled in order to predict the residual stress field and the initial plastic strain. From this initial condition, the assembly operation of the wheel on the axle is simulated before the redistribution of stresses and strains under cyclic load. The final objective is to obtain the cyclic loadingpaths, in order to provide the data needed for the analysis of fatigue.

Abstract: Till now, the definition of cross wedge rolling dies requires know-how and important expertise from the designers. A decision-making methodology is being developed to provide sequential and logical steps to draw easier and faster the tool geometry. This methodology is based on designing rules found in literature that link the geometrical parameters of the desired rolled part and the geometrical parameters of the tool. Nevertheless, in the literature, the rules are not always consistent because the admissible domain for a parameter can differ from one author to another. In order to take into account this variability, a stability index is associated to each rule and to the designed tool. The methodology allows updating of the existing rules and the implementation of new rules. The set of parameters defining the geometry of the tool can be exported in the CAD/CAM software and FEM software. A case-study is presented to illustrate and validate the methodology.

Abstract: The behaviour of a closed top-hat section made of Dogal 800 DP subjected to stretch-bending is studied both experimentally and numerically. The top-hat section was made by forming of a sheet using a Flexform^TM fluid cell press and closed by a sheet using welding. Experiments were performed in a stretch-bending rig in two stages. During the first stage the profiles were bent under a constant horizontal stretch force. In the second stage the profiles were stretched back from the bent position. The force-displacement relations of the actuators involved in the experiments were recorded and the initiation and development of fracture during the stretching process after unloading of the die was detected by cameras. A finite element code was applied to model the forming operation and the stretch bending experiments including the unloading of the die and subsequent stretching of the profile. The elastic-plastic material model with calibrated parameters was adopted from previous studies on Dogal 800 DP, including the Cockcroft-Latham fracture criterion to detect initiation of fracture. The history variables were mapped from the forming model to the stretch-bending model. The forming process was simplified as a hydroforming operation and some deviations were observed regarding the thinning of the sheet between the model and the real process. The model of the stretch-bending experiment was able to capture the force-displacement relation during the first stage with reasonable accuracy. Some deviations between the experimental and simulated force-displacement relations were observed during the second stage, i.e. the stretch-back operation, but the initiation of fracture was well captured.