The Magnitude and Origin of Residual Stress in Ti-6Al-4V Linear Friction Welds: An Investigation by Validated Numerical
- PDF / 1,544,221 Bytes
- 12 Pages / 593.972 x 792 pts Page_size
- 84 Downloads / 148 Views
CTION
LINEAR friction welding (LFW) is an important technology for the latest generation of aeroengines because it is required for the fabrication of bladed discs—known colloquially as blisks—which allow significant savings in weight, fuel use, and CO2 emissions to be achieved.[1] Titanium alloys such as Ti-6Al-4V have proven to be suitable for joining using this method.[2] LFW involves the localized heating caused by the reciprocating action of two surfaces bought into contact at high frequency, under an applied load.[2–4] Unfortunately, because this is a relatively new joining method, the physical processes occurring in the vicinity of the joint are not yet fully understood. Research is needed to allow the full benefits of linear friction welding to be exploited. In the work presented in this article, numerical modeling has been used to predict the residual stress resulting from the LFW of a joint in Ti-6Al-4V and to investigate its source. Residual stress is to be expected as a result of the large deformation during LFW and because of the thermal strain resulting from the steep temperature gradients local to the weld line. Recent work using R. TURNER, Research Fellow, is with the Department of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, U.K., and with Rolls-Royce plc, Derby DE24 8BJ, U.K. Contact e-mail: [email protected] R.M. WARD, Lecturer, and R.C. REED, Director, are with the Department of Metallurgy and Materials, University of Birmingham. R. MARCH, Team Leader, is with Solid State Welding, Rolls-Royce plc. Manuscript submitted July 1, 2011. Article published online September 7, 2011. 186—VOLUME 43B, FEBRUARY 2012
synchrotron X-ray diffractometry[5,6] has confirmed that significant residual stress is indeed present after processing; however, its precise evolution is not yet known. As a result of the operating requirements of aeroengines and the importance of stress on component lifetime estimation, it is of considerable interest to understand the origin and magnitude of the residual stress from LFW.
II.
METHOD: MODEL DESIGN
The model used to support the work here follows the approach for analysis of LFW reported in Reference 7. Typically, three distinct phases can be identified during LFW[2,3]: the initial phase, the equilibrium (burn-off) phase, and the deceleration phase. Here, only the equilibrium phase (in which the work done by the reciprocating action is balanced against the enthalpy of the flash) is modeled, followed by an estimation of the heat transfer occurring during cooling to ambient temperature. The material properties were obtained from stress/strain curves measured at temperatures of up to 1773 K (1500 °C). The finite element (FE) method was used to calculate the thermal and mechanical behavior using Forge 2008 software.[8] For full details, the reader is referred to Reference 7. The axis definitions are presented in Figure 1, consistent with those used by other authors. The origin is located at the geometrical center of the specimen, on the weld line. As the aim of
Data Loading...
