Key Engineering Materials Vol. 684

Abstract: This paper presents a method for acquiring true stress–strain curves using engineering strain curves obtained from upset forging of cylindrical specimens. The main problem deals with determination the true strain in upset hot forging on hummers when the values of strain rates are differ in the range from 0 to 10^-3s. At such strain rates due to wave processes strain distribution in cylindrical specimen will be uneven. The purpose of this publication is to analytically determine the strain distribution in compressed cylindrical specimen.

Abstract: The evaluation of formability for sheet metals by means of different tests such as hole-expansion and forming limit tests is widely used in industry. The experimental efforts for these tests and the scatter of the results are much higher than those for the identification of the mechanical properties of various material charges for the same material grade in tensile test. Difficulties in accurate formability evaluation for new steel grades, such as AHSS, have necessitated a review of the existing prediction methods. Consequently, a new formability criterion was developed from the statistical relations of parameters for approximately fifty steel grades in various thickness ranges. The criterion considers the combination of mechanical properties from the tensile testing as the yield strength, tensile strength and total elongation and plastic deformation energy in a single value. The quality ranking of different charges and coils was made by using of the criterion as well as, for comparison, other well-known criteria which are currently used in the industry. The results obtained involving the new formability criterion seems to be accurate for a wide range of material grades and thicknesses, from the viewpoint of automotive design requirements.

Abstract: The present technical work reports on the formability and related behaviour of components during hot rolling of metal matrix composites (MMC) produced from powder. A new metal matrix composite based on TRIP (Transformation Induced Plasticity) austenitic steel AISI304 with varying amounts (10% and 20%) of homogeneously embedded zirconium dioxide (partially stabilized with Mg (Mg-PSZ)) was investigated by means of compression tests and rolling of wedge shaped samples at temperature of 900°C and 1100°C. Two different particle size distributions of Mg-PSZ powder were investigated: fine and coarse. Based on the experimental results, the deformation behaviour (arc of contact length, roll gap ratio, strain, strain rate), the microstructure evaluation (pore amount and their cross sectional area) and the formability (equivalent fracture strain) under different stress state conditions had been analyzed.

Abstract: The material flow in particle reinforced metal-matrix-composites (MMC) had been investigated. The composite consisted of TRIP steel and magnesium stabilized ZrO₂ particles (Mg‑PSZ) in volume fractions of 0 %, 5 % and 20 %. The basic materials were produced by hot-pressing and showed a very homogeneous particle distribution and a almost full density. Then the samples were cut to wedge shape and hot-rolled with a constant roll gap. Caused by the shape, the true strain increased over the length and reached a maximum of true strain of 0.6. The strain rate was set to be higher than 0.1 and lower than 10/ s. After rolling, it was possible to combine rolling force, true strain and the material flow due to the grid on the surface. With an increase in volume fraction of Mg‑PSZ the rolling force increases as well. Metallographic examinations were performed to determine and document the flow of particles within the composite due to true strain conditions. It was found that the particles flow with the base material and turn parallel to the rolling direction. This effect was measured using the degree of orientation of partially oriented linear structure elements Ω_12, according to ASTM E 1268-01. The index was increasing with increasing true strain value. Further microscopic examination showed debonding of the interface between particles and matrix-material. For MMC’s having a volume fraction of 20 % Mg-PSZ a true strain at fracture of 0.5 to 0.6 was determined.

Abstract: Abstract. Excellent combination of mechanical properties makes bainitic steels very attractive for commercial application. The most potential benefit of bainitic steels is found in the lightweight design of car bodies. The chemical composition, productions process and the austenite state control the properties of those steels. To reach the target of the correct component design it is important to focus on transformation kinetics. High carbon steels have been investigated, which contain approximately 0.5% C, 1.5% Si, 1.5% Mn, 0.9% Cr and 1.5% Cu. It’s expected to form a carbide free bainitic microstructure due to the Si addition. The residual austenite in the microstructure of high carbon bainitic steels ensures the forming ability besides the high strength. Maximum tensile strength is 1650 MPa and elongation is around 30%. Those steels can be used to produce large scale components.

Abstract: Natural frequencies of the four upgraded front searchlight designs were received in ANSYS software environment. In the first case serial front searchlight incandescent electric lamp was replaced by a LED group which was mounted on the one-piece cylinder backing. The second front searchlight design had the backing which was upgraded by a radial ribs and concentric rigidity ferrules. Analyze of the backing deformation character by vibrations with the natural frequencies established a number of design solutions which make it possible to raise front searchlight vibration resistance. By the front searchlight model were established that the natural frequencies of the searchlight with the one-piece backing appertain to the whole range of the train vibrations. Natural frequencies of the backing with perforation, rigidity ferrules, and radial ribs appertain to the low frequencies of the railway locomotive vibrations spectrum. On basis of devised methodology of analyze of the deformation and natural frequencies of the surface carrying a LED group the vibration-proof searchlight design was introduced and researched.

Abstract: This paper gives an overview of residual stresses problem after heat treatment of large scale forged parts as well as numerical study and simulations of different methods to reduce stresses. DEFORM software was used for Finite Element Method (FEM) simulations as one of the most capable simulation tools combining both forging and heat treatment processes analysis. The study is performed on the sample of large scale airspace part of aluminum AK6 (AlMgSiCu) alloy. The comparison of different quenching media is presented. Practical conclusions and recommendations are made to optimize the process and reduce residual stresses after the heat treatment. This paper provides numerical simulation and theoretical conclusions and needs to be amended by experimental measurement of residual stresses by one of available methods as part of the future work.

Abstract: The work considers some techniques for defining the stress state during computer modelling of metal-forming processes. A mathematical model of anisotropic elastoplastic material has been developed and an algorithm of computing the stress-strain behavior according to this model has been described.

Abstract: The article represents the theoretical basis for the generation of virtual material models with the given crystallographic orientation (CGO) of the structure in metals and alloys with the cubic crystal lattice. The obtained functional interrelations allow to take into consideration a metal sheet CGO in technological calculations of metal forming processes and, most significantly, a priori by means of calculations to determine the structure CGO meeting the requirements of increasing the materials formability and the product performance. It is given an example of the implementation of the calculated CGO of the structure while rolling can sheet from aluminum alloy 3104.

Abstract: Provided here is a mathematical model of the operation of backward extrusion in the mode of short-time creeping of thick-walled pipe blanks made out of orthotropic material with cylindrical anisotropy of the mechanical properties. Carried out was theoretical research of the operation of isothermal axisymmetric backward extrusion of thick-walled pipe blanks made out of anisotropic materials by conic point-tool in the mode of short-time creeping. Established were regularities regarding the change of material flow kinematics, regarding the stressed and strained condition of the blank, regarding force modes and limit possibilities of deformation depending on the technological parameters, on friction conditions on the contact surfaces of the operating tools and of the blank, regarding the geometrical dimensions of the blank and of the manufactured part, and of the anisotropy of the mechanical properties of the blank material, that on the basis of the developed mathematical model of isothermal non-radial flow of anisotropic material under conditions of axisymmetric stressed and strained conditions in the mode of short-time creeping. Experimental operations were carried out for isothermal backward extrusion of thick-walled pipe blanks made out of АМг6 aluminum and ВТ6С titanium alloys. Comparing the results of theoretical and experimental data for force modes of the operation of isothermal backward extrusion of thick-walled pipe blanks points to their satisfactory similarity (difference not exceeding 5% - 10%).