Papers by Keyword: Plastic Deformation

Abstract: In shot peening, bombarding the surface with steel shot propelled at high velocity causes plastic deformation of surface. The process with the characteristic deformation was applied to joining process. Our approach has been applied to the butt joining of the dissimilar metal sheets. In this method, however, the joint strength was lower than the flow stress of base metal. The modified joining processing was being carried out to improve the bondability. In the present study, the joining of dissimilar metal sheets using a shot peening process was investigated to improve the bondability. In the joined section, the edge of the joint area of the sheets were slit using a laser. In this method, the edges of the sheet are overlapped the other sheet. When the connection is peened, the material undergoes large plastic deformation near the surface due to the collision of shots. In this process, particularly noteworthy is the plastic flow near surface layer. The edges of the sheet are joined to the other sheet, thus two sheets can be joined each other. In the experiment, the shot peening treatment was performed by using an air-type peening machine. The shots used were made of high carbon cast steel. Air pressure was 0.6 MPa and peening time was in the range of 30-240s. The metal sheets were commercial low-carbon steel, stainless steel, pure aluminium, aluminium alloy, and pure copper. The effects of processing conditions on the bondability were mainly examined. It was found that the present method was effective for joining of dissimilar metal sheets.

Abstract: Rail-wheel contact problems have been analyzed by the use of the three-dimensional finite element models. Based on these models, the paper presents a study regarding the applicability of the Hertz contact to rail-wheel contact problems. Beside a standard rail, the study also considers a crane rail and a switching component. The bodies of the contact problem are the standard rail UIC60 and the standard wheel UICORE. The maximum contact pressure which the material can support in the elastic range in steady state conditions is known as the shakedown limit. With an operating contact pressure below the shakedown limit the rail would be expected to remain elastic a long period of its lifecycle. However, examination of rail cross-sections shows severe plastic deformation in a sub-surface layer of a few tens of microns thickness; the contact patch size is in tens of millimeters. Three-dimensional elastic-plastic rolling contact stress analysis was conducted incorporating elastic and plastic shakedown concepts. The Hertzian distribution was assumed for the normal surface contact load over a circular contact area. The tangential forces in both the rolling and lateral directions were considered and were assumed to be proportional to the Hertzian pressure. The elastic and plastic shakedown limits obtained for the three-dimensional contact problem revealed the role of both longitudinal and lateral shear traction on the shakedown results. An advanced cyclic plasticity model was implemented into a finite element code via the material subroutine. Finite element simulations were conducted in order to study the influences of the tangential surface forces in the two shear directions on residual stresses and residual strains. The Hertz theory is restricted to frictionless surfaces and perfectly elastic solids, but it is the best method for determining deformations and stress from pitch of contact. Form change due to wear and plastic deformation of a rail can reduce the service life of a track. The purpose of this investigation was to study the development of these damage mechanisms on new and three years old rails in a commuter track over a period of two years.

Abstract: Microstructure and mechanical properties of 2024 aluminum alloy flange semi-solid thixoforging by changing cavity was investigated. Theoretical calculation and forming test were adopted to study the preparation of flange. It is concluded that the influence factors of forming limit of flanges are radical load P, friction τ and thickness t by theoretical calculation. The results show that it is uniform in the process of forming. Microstructure and mechanical properties of flange have been improved significantly with the increase of the radical load. Way of variable cavity realized the real plastic deformation, which results in high mechanical properties of flange. The flange could obtain fine microstructure with grain sizes of 20~30μm, tensile strength of 433MPa and elongation of 10.1%, with changing amount of 30MPa. The results indicate that the microstructure and mechanical properties could achieve forging requirement and be controlled using changing cavity.

Abstract: Rigid-plastic finite element was used to investigate the effect of channel inner angle on aluminum ECAP processing. The simulation results demonstrate that distribution of maximum principal stress was non-homogeneous no matter with 90° inner angle or 120° inner angle. For the both inner angle values, material located at the front-end of workpiece flow easily and material located at the top of die channel corner flow difficultly, which were well agreed with plastic mechanics and experiment. The inhomogeneity of maximum principal distribution in ECAP workpiece processed with die channel inner angle of 90° was more severe than that with die channel inner angle of 120°.

Abstract: The superalloy parts in the aeronautical field demand high reliability, which is largely related to surface integrity. Surface integrity generally includes three parameters, such as geometric parameter, mechanical parameter and metallurgical parameter. The paper presents the influence of cutting speed on surface plastic deformation and white layer formation through orthogonal milling of FGH95 superally material. The influence of cutting speed on grain refinement of machined surface is also investigated. It is found that cutting speed has significantly effect on the surface metallurgical characteristic microstructure. The increasing of cutting speed creates severer plastic deformation. Surface plastic shear strain increases with the increasing of cutting speed, while the depth of plastic deformation decreases on contrary. White layer thickness is increased with the increasing of cutting speed. Through statistical analysis for grains number, it can be drawn that the higher the cutting speed, the more serious grains refinement.

Abstract: Experiments have shown that initial voids may exist in the manufacturing processes of pure aluminum, which adversely affect its mechanical properties. In this study, the process of plastic deformation around voids in pure aluminum was examined at atomic scale through molecular dynamics (MD) simulation. The Modified Embedded Atom Method (MEAM) was employed to characterize the atomic interactions in the pure aluminum with two voids. The calculation results revealed that the interaction of two voids endures three phases when the interval of the voids is increased: void coalescence, void coactions followed by the formation of a stress shield zone, and interaction vanishing. The critical parameters of the interval for the three phases were defined as well in this work. It was observed that crack initiated and further propagated near the voids along the slip systems of FCC crystal, which eventually caused structural failure. Meanwhile, the evolution of micro structure in the crack propagation process was investigated by means of Common Neighbor Analysis (CNA). The results showed that the phase transformation occurred near the voids during loading process.

Abstract: The aim of this work is to establish a correlation coefficient between the positron annihilation lifetime technique (PALS) and the Vickers hardness for the heat treatable aluminum alloys (6066, 6063).The potential of positron annihilation spectroscopy in the study of light alloys is illustrated with special regards to age hardening, severe plastic deformation, annealing and quenching in aluminum alloys. Vickers hardness is the standard method for measuring the hardness of metals, particularly those with extremely hard surfaces. Accordingly, a correlation coefficient of 90 % between τ and Hv is obtained. This correlation can help us to explain many behaviors of these alloys under deferent conditions.

Abstract: Combined with the pre-test results, homogenization, plastic deformation, aging and other processes of Mg-7.1Gd-4.6Y-1.3Nd-0.5Zr (EW75) magnesium alloy was studied in engineering tests. The results show that in engineering test the large ingots (Φ500×800~900mm) of the EW75 alloy using two-stage homogenization treatment had perfect homogenization effect and no burnt structure. After multi-directional forging and extruded deformation, the homogenized residual second phase particles were fully broken, and the structure was refined and uniform. The peak aged craft was 230°C×6h, with the aging time increasing, the tensile strength and elongation remained unchanged, showing a strong anti-aging ability. The two-stage homogenization treatment + multi-directional forging + direct extrusion deformation + peak aging treatment was used to prepare a high performance EW75 alloy and at longitudinal direction its ultimate tensile strength, yield strength and elongation were 450MPa, 385MPa, 12.0% respectively.

Abstract: mproving ductility in metals using friction stir processing (FSP) is a challenging effort and is made by means of a rotating tool inserted in a work piece providing heat transfer and plastic deformation. In this investigation, improving ductility during FSP was determined as a purpose and the microstructure and mechanical properties of nugget zone were investigated during friction stir processing (FSP) of pure copper. Ductility was measured using tensile elongations at a temperature of 20 °C. By varying the traverse speed from 40 to 100 mm/min at rotation speeds of 300 and 600 rpm, the ultrafine grain microstructure was achieved .Defects were observed in rotational speed of 300 rpm. By increasing traverse speed at constant rotational speed of 600 rpm grain size of the nugget zone decreased and ductility increased. Achievable ductility was limited by cavity formation due to lower heat input and deformation in samples with defects.

Abstract: This paper presents the conclusions of machinability tests on a Cast Iron GTW 35-04. The content of this article also focuses on the analysis of selected basic indicators of steel machinability: quality of the processed surface. The results of the article are conclusions for working theory and practice for drillng of cast iron. Based on the cutting tests, cutting speeds of 50 to 100 m/min, feed rate of 0.1 to 1.0 mm and screw drill carbide monolite.