Papers by Keyword: Bending

Abstract: Metallurgy and heavy engineering construction, which are considered the most energy-intensive industries, place great focus on complex shaped thick-gage plate metal items of equipment with wall thickness exceeding 40 mm and diameter/width of up to 4000 mm. Such items of equipment include large machine parts manufactured by means of hot plate stamping, such as bodies of rotation (for example, the segment of the radial surface of converter shell, the bottom part of degassing unit, etc.) utilized as pressure-operated devices, vessels, tanks and other facilities by metallurgical, petrochemical, oil and gas, and nuclear industries. Presently known manufacturing methods of such items of equipment, for instance, stamping methods, have a number of technological problems. In the present paper, creation and development of the theory and technology of manufacturing different large bodies based on the combination of plate rolling and stamping processes, as well as the combination of asymmetric rolling and plastic bending processes, are proposed. The goal was to develop a cost-effective technology of producing large-size bodies of rotation in the conditions of a thick-plate mill. The rolling of the package forms the basis of the first stage of the new process. The package consists of the upper (punch) base, the lower (matrix) base, and the blank plate situated between them. The economic benefit from installing the developed technology based only on the combination of asymmetric rolling and plastic bending processes was more than 1 million dollars. Casings on two converters were produced and installed in the oxygen-converter plant.

Abstract: The hot stamping of α+β titanium alloy sheet into U shape with concave bottom using resistance heating were performed. Since both edges of the sheet in contact with a pair of electrodes were not heated, cracks occurred around the corners of the bottom due to the partially high flow stress. The cracks were prevented by slitting both edges before resistance heating because of the elongation of the edges. In addition, the hot stamping of titanium alloy sheet into joggle using partial resistance heating were performed. The distortion of sheet was reduced by reduction in area of resistance heating

Abstract: This paper focuses upon zigzag-shape bending for suppression of defects, including dent and springback. A series of finite element analyses was carried out in order to optimize the bending condition for suppression of these defects. As a result, it was clarified that a diagonal movement of the upper die was effective for suppression of dents while a rather vertical movement of the upper die was effective for suppression of springback. In order to suppress dent and springback at the same time, this paper proposes another method of bending method, whereby the upper die with special shape moves in a diagonal way. Moreover, the stability of the method against variation of tool dead position, which would be caused by elastic deformation of supporting members, was studied by FEM, followed by experimental verification.

Abstract: The combination of different types of deformation can create a continuous method that ensures the formation of ultrafine-grain structure in medium carbon steel wire. The method is based on drawing operation combined with torsion and bending. Tools and equipment applied in the wire and cables manufacturing are used for the implementation of this method. As a result of the combined strain effect the ultrafine homogeneous structure is formed in the medium carbon steel wire. The wire has increased strength while maintaining the plastic properties when compared with the corresponding properties after drawing.

Abstract: The effect of fibre reinforcement on Load Induced Thermal Strains (LITS) has not yet been significantly investigated up to now. Creep is becoming a key research topic only in the last few years. A semi-empirical model able to take into account both the thermo-mechanical damage associated to coarse aggregates and the thermo-chemical damage induced in the matrix and calibrated on the basis of the main results on plain concrete available in the scientific literature is presented. Some tests in uniaxial compression on Fibre Reinforced Concrete (FRC) cylinders characterized by a long age – 11-years-old – have been investigated and compared with the model to highlight fibre effects, if any. The uniaxial compressive strength at 28 days of the SFRC was 75 MPa; the specimens after 11 years showed a compressive strength exceeding 110 MPa. A strong increase of SLS residual strength was observed in post-cracking tension due to the long aging, while ULS residual strengths weakly increased. The cylindrical specimens were exposed to a maximum temperature of 200°C and 400°C and loaded with two load thresholds corresponding to 20% and 40% of the compressive strength detected at 28 days of aging, that means about 12.5% and 25% of the 11-years-old specimens. Two paths were investigated: pre-heated specimens up to 200°C or 400°C, then loaded with a compression stress equal to 0.2f_c,28 and 0.4f_c,28; and pre-loaded specimens up to 0.2f_c,28 and 0.4f_c,28 and then heated up to 200°C or 400°C. The duration of each test did not exceed 12 hours. Two main fibre effects were observed: a significant reduction of irreversible strains when the specimens were loaded and then heated and cooled and a different evolution in LITS passing from 200°C to 400°C, characterized by a significant reduction of the expected deformation.

Abstract: As a key component of high-voltage power lines, aluminium clad steel reinforced (ACSR) conductors must have adequate mechanical properties that ensure running safety. This paper presents the results of experimental and theoretical analysis of spiral stranded conductors that consist of a core with two layers of steel wires and three layers of aluminium wires. Tests were performed using two ACSR conductors of the same type, one new and the other 40-year-old, used for a 220 kV power lines. In service, the conductors can be subjected to additional stresses, which may lead to accelerated deterioration and premature failure. In order to provide reliable results, the tests were performed in similar conditions and using the same equipment for both strands. Comparison of results highlighted the influence of the service time on the mechanical properties.On the other hand, the degradation was decisively influenced by the position of the layer. The mechanical properties of the aged conductor are adequate even after 40 years in service. The most advanced degradations are near the clamping area, therefore intensive inspection and maintenance are recommended.

Abstract: Stringer sheets are bifurcated parts that possess, compared to flat sheet metal parts, a higher stiffness due to their higher geometrical moment of inertia. Currently, the common way of forming spatially curved stringer sheets is hydroforming. This article shows the feasibility of forming stringer sheets by using solid tools with short process times, which is more relevant for the industrial application. A die-bending process with a slot in the punch for the stringer is investigated. Since buckling of the stringer is one of the occurring failure modes, depending on the stringer height, an analytical estimation of the critical stringer height is carried out while considering the bending angle, bending radius and sheet thickness. The subsequent numerical and experimental investigations show a good agreement with the analytical estimation. Finally, a stiffness test is carried out with stringer sheets of different stringer heights. The result of this test underlines the motivation of forming buckling-free stringer sheets with stringers as high as possible. The normalized stiffness increases with rising stringer height until buckling occurs. At this point the stiffness values begin to fall with growing stringer height.

Abstract: This paper deals with the flexural stiffness of sandwich structures based on fiberglass and polymeric foams. The influence of geometrical and material parameters on the resulting effective flexural stiffness of the sandwich structure is being studied experimentally, analytically and using FEM models. The effective elasticity module of the sandwich-structured element is being studied and it’s theoretical and model dependencies on the stiffness of the foam core are being investigated. These dependencies are then compared with experimentally observed values. This study shows it is necessary to pay special attention to the issue of flexural stiffness of walls when designing sandwich shell products in order to prevent possible failures in the practical applications of these types of structures.

Abstract: Measuring deep brain neural activities with a microelectrode is of greatest importance in uncovering the mechanism of various brain disorders. In this operation, a microelectrode needs to be accurately inserted into deep the brain. However, a microelectrode of high flexibility would bend at encountering a layer of tough tissue during insertion, which would lead to deflection and impaired targeting accuracy. To deal with this problem, a rotational insertion method has been developed in this paper for deflection-free insertion. Rotation helps generate a dynamic anti-bending force to prevent buckling, and this force becomes larger with the increase of rotational speed. Thus, by controlling the rotational speed at which insertion is carried out, deflection-free insertion of a microelectrode deep into brain can be realized. The effectiveness of this method has been experimentally confirmed.

Abstract: SPH is a Lagrangian based computational method that can be used for solving fluids and solid mechanics problems. In this work, SPH is utilized to solve the two dimensional Navier’s equation for linear elastodynamics problems. The SPH technique computes the discrete particle properties using a smoothing distribution function, which takes into account the effect of neighboring particles. To investigate the performance of the developed method in solving solid mechanics problems, the problem of plate bending was simulated. The results show good agreement between the simulation and analytical solution. Additionally, the study found an indication that the current method of enforcing boundary conditions produces boundary effects at locations where the plate is attached to the wall and at the end of the plate.