Papers by Author: Andrzej Rosochowski

Abstract: The paper describes a finite element method in 2D and 3D to simulate the super plastic forming of a demonstrator jet engine fan blade made from Titanium alloy sheet. The fan blade is an assembly of three sheets in which a single inner (core) sheet is diffusion bonded to the two outer (skin) sheets at prescribed zones, which is then super-plastically formed to a desired fan profile. In the model, the diffusion bonded zones between the core and skin sheets are simulated using tied interfaces. The thickness of each skin sheet is not uniform and significant change in thickness can occur over a short distance as well as gradually over the entire skin sheet. The thickness of the core sheet which is smaller than the thickness of each skin sheet remains uniform. The paper describes the design for a scaled-down demonstrator fan blade and model build process. Selected results and evaluations of finite element simulations are presented and discussed.

Abstract: This paper examines the effect of friction and back pressure on the formability of superplastically formed aluminium alloy AA7475 sheet at the temperature of 517 °C. Several experiments with lubrication and back pressure are performed using a simple box shape tool cavity. The coefficient of Coulomb friction between the formed sheet and tool has been determined indirectly using a finite element model to simulate superplastic forming of the box shape. Typical values determined for all lubricant conditions tested are in the range 0.1 < μ < 0.2. The void growth with strain was determined directly from measurements as a function of back pressure. The results show the application of back pressure at 1 MPa reduces the growth of voids from 7% to 0.3% void volume fraction at a logarithmic thickness strain of 0.65. This paper reports back pressure has a significantly greater role than friction in enhancing the formability of the alloy.

Abstract: Creating a small amount of ultrafine grained metals by severe plastic deformation, for example using equal channel angular pressing, is possible in many research laboratories. However, industrial production of these materials is lagging behind because of the lack of industrially viable severe plastic deformation processes. One attempt to change this situation is based on the concept of incremental equal channel angular pressing developed by the University of Strathclyde and Warsaw University of Technology. The paper describes the path the researchers took to develop the process starting from finite element simulation, through tool design and process implementation, to material characterisation. Examples of various process configurations, which enable obtaining UFG bars, plates and sheets are given and possible future developments discussed.

Abstract: Equal channel angular pressing (ECAP) is the most popular severe plastic deformation process used to refine grain structure of metals. However, its application exhibits inherent problems of low productivity and poor utilization of material. In order to address these problems, the ECAP channel with two-turns can be used. Historical examples and current applications of this configuration are provided including route BC version of the process. Route C version of two-turn ECAP is illustrated with a scaled-up process used for processing square inch cross section aluminium billets. To address another problem, that of short billets, it is suggested that future applications of two-turn ECAP are based on the new process of incremental ECAP; it enables decoupling feeding of the material and its deformation and thus reduces dramatically the feeding force for billets, plates and sheets.

Abstract: Batch SPD processes have a limited scope for being used on an industrial scale. More feasible are continuous processes among which the new SPD process of Incremental ECAP (IECAP) is an attractive option. In this paper, a double-billet version of I-ECAP, which doubles process productivity, is presented. The concept of the process is first checked using the finite element (FE) method. FE simulation results are the basis for the design of an experimental rig. Trials of nanostructuring of 10x10x200 Al 1070 billets are carried out with the forces on the reciprocating die and the feeder measured. Metallurgical samples after 4 and 8 passes of I-ECAP (route BC) are investigated using TEM. Tensile properties after 8 passes are established. All these results show that the new SPD process of I-ECAP gives the results comparable to those obtained by a classical batch ECAP with the added capability of dealing with much longer (possibly infinite) billets.

Abstract: Batch severe plastic deformation (SPD) processes are mainly used for laboratory purposes. More industrially oriented are continuous processes among which the new SPD process of Incremental Equal Channel Angular Pressing (I-ECAP) is an attractive option. This paper investigates the feasibility of using I-ECAP for nanostructuring of plates rather than bars. First, a 3D finite element simulation has been performed which shows the importance of restricting material flow in the direction of plate width. A laboratory rig has been designed, which converts the vertical movement of the machine crosshead into an oblique movement of the reciprocating punch. Preliminary trials of I-ECAP have been carried out on a 4x30x100mm Al 1070 plate. Metallurgical samples after 4 and 8 passes of I-ECAP (route A) have been investigated using TEM. In conclusion, the new SPD process of I-ECAP is capable of processing plates, which opens up new possibilities of nanostructuring metals on an industrial scale.

Abstract: This paper explains the concept of 3D-ECAP with “in-die rotation” and presents the results of experiments for two sets of tooling with channel passages orientated at 90° and 120°. The results for aluminium 1070 are compared in terms of the process force, billet end effects, mechanical properties and structure of the material.

Abstract: Severe plastic deformation (SPD) is used to convert traditional coarse grain metals and alloys into ultrafine-grained (UFG) materials. UFG materials possess a number of improved mechanical and physical properties which destine them for a wide commercial use. However, any attempt to use SPD technology commercially requires a better insight into the mechanics and practicality of SPD processes. This paper looks into historical development of SPD processes and focuses on such aspects of SPD as material flow, role of hydrostatic pressure, friction, geometry of tools, billet and feeding considerations, technical feasibility, etc. The discussion of these topics sets a background for decisions concerning further research and commercialisation of SPD.