Measurement and Modeling of Residual Stress in Ti-6Al-4V Linear Friction Welds

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1 TWI Conference, Cambridge UK March 19, 2015 Daira Legzdina/Vincent Chung Clement Buhr/ Paul Colegrove Measurement and Modeling of Residual Stress in Ti-6Al-4V Linear Friction Welds

2 Honeywell.com Outline Motivation Test specimens Measurement methods Neutron diffraction Contour method Comparison Residual stress modeling presented by Clement Buhr /Cranfield University Page 1

3 Honeywell.com Motivation Titanium alloys are popular for aerospace applications Structural members Turbine engine bladed disks/rotors Advanced joining methods allow for more efficient manufacture Linear friction welding (LFW) Linear friction welding Two surfaces forced into contact Repeated linear rubbing Advantageous for titanium because carried out in air Page 2

4 Honeywell.com Test specimen Test specimen construction Two blocks of Ti-6Al-4V Join using LFW Remove flash Page 3

5 Honeywell.com Measurement details Goal: quantify residual stress in weld region Two measurement methods: Neutron diffraction measurements along line Measurement performed at Los Almos National Lab SMARTS beam line 2 mm x 2 mm x 2 mm gage volume Contour measurement over plane Measurement performed by Hill Engineering Page 4

6 Residual Stress (MPa) Honeywell.com Neutron diffraction results Summary of residual stress measured using neutron diffraction High magnitude tensile stress near LFW plane Largest in long direction Decreases to near-zero at approximately 5 mm Neutron diffraction Szz Syy Sxx Distance from LFW center (mm) Page 5

7 Honeywell.com Contour method overview- Hill Engineering Contour method can generate a 2D map of residual stress normal to a plane Contour method steps (illustrated for 2D body) Part contains unknown RS (a) Cut part in two: stress release deformation (b) Measure deformation of cut surfaces Apply reverse of average deformation to finite element model of body (c) Map of RS normal to surface determined Cut measure FEM residual stress Page 6

8 Residual Stress (MPa) Honeywell.com Contour method results Summary of results from contour method measurement 2D map of long-direction stress High magnitude tensile stress near LFW joint Near-zero stress elsewhere yy-component Distance from LFW center (mm) Page 7

9 Residual Stress (MPa) Honeywell.com Comparison Neutron diffraction Single line, 3 stress components Contour method 2D map, single stress component Compare region of overlap Similar peak magnitude (800 MPa vs 750 MPa) Contour method is slightly lower Similar peak width 1000 Neutron Diffraction 800 Contour 600 yy-component Distance from LFW center (mm) Page 8

10 Residual Stress (MPa) Honeywell.com Effect of thermal stress relief Additional measurement on different (but similar) specimen Post weld thermal stress relief Compare with non-stress relieved Significant reduction in tensile magnitude (750 MPa vs 100 MPa) As welded Thermal stress relief As welded Thermal stress relief yy-component (contour method) Distance from LFW center (mm) Page 9

11 PhD Project Outline Residual stress prediction for 3D linear friction welded coupons Experiments : Time consuming Expensive Parametric studies difficult Solution Modelling Modelling complementary to experiments Page 10

12 State of Art Very few publications on modelling RS for LFW components Existing models : 2-D - Long solution times Model the oscillations - 3-D model hard to achieve Page 11 Hypothesis: Oscillations are not critical in predicting RS; it is the thermal profile during cool-down which drives the RS

13 Modelling Approach ABAQUS finite element package was used 2-D model considered Material used: Ti-6Al-4V Sequentially coupled thermal stress analysis was used: Transient analysis to model the heating and cooling stages and get the evolution of the thermal profile -Heat flux applied at the weld interface during the heating stage then deactivated for the cool down Stress analysis to investigate the presence of RS in the welded structure Note: Due to symmetric conditions, only a quarter of the coupon was actually modelled Page 12

14 120 Thermal Analysis: Validation 40 Page 14

15 X-Symm Stress Analysis Boundary conditions: Symmetry is applied on two edges to account for the whole coupon Thermal profile of the cool down applied (duration 100s) then the coupon is brought to the temperature of 20 C (duration 100s) Plane-strain elements used Page 15 Y-Symm

16 Stress Analysis Page t=0s t=10s t=200s

17 Stress Analysis (MPa) Dimensions: 10x20x30mm Dimensions: 20x40x120mm Page 17 R. Turner (2011) et al The Magnitude and Origin of Residual Stress in Ti-6Al-4V Linear Friction Welds: An Investigation by Validated Numerical Modeling Abaqus

18 Stress Analysis 1 Δx=5.4mm R. Turner (2011) 2 Abaqus Page 18

19 Conclusion & Further Work Initial work indicates that it is feasible to predict residual stresses without: A fully coupled model Modelling the oscillations Page 19 Improvement of the model : Heat flux distribution, 3-D model Study of the influence of the flash on the residual stress distribution Modelling the heat treatment stress-relief process