The research that introduced in this thesis can be further extended into many research directions as follows:
Microstructure prediction and phase transformation model integration: For the materials which the microstructure has a significant effect on the mechanical performance, it is important to predict the microstructure of the materials during the deposition process and integrate the phase transformation model into the FE mechanical model in order to get accurate residual stress and distortion. This can be done in the FE models through developing a subroutine in the FE software which describes the interactions among temperature, microstructure and its corresponding mechanical properties. The integration of the phase transformation model into the FE models will provide the accurate thermo-mechanical predictions to a wider range of materials.
Hybrid FE model for wider range of WAAM structures: The efficient FE approaches overcome the application bottleneck of the huge computational time required for the transient model. However, the application of steady-state based approach is currently only utilised to large scale and straight wall based structures. The constrains and limitations of this approach need to be investigated in the future. On the contrast, the transient model has the advantage of analysing small scale and complicated structures. Therefore, a hybrid FE model can be considered in the future that can combine the advantages of steady-state based approaches and the transient model to enable the thermo-mechanical prediction for a wider range of WAAM structures.
Residual stress and distortion mitigation process: The current research in this thesis did not consider the mitigation methods of residual stress and distortion using additional facilities. However, there
tensioning, etc. FE models can be developed on the efficient FE approaches that proposed in this thesis to help generating better methods for minimising the residual stresses and distortions of the WAAM process.
Development of an automatic WAAM building planner: In the current research stage complicated WAAM structures need to be divided manually into many simple walls and the building sequence is decided based on the experience and results from experimental or FE trials. An automated CAD-guided building planner need to be developed in the future research which can automatically divide the complicated geometries into multiple and easy-to-handle sub-structures. Advanced optimisation techniques and algorithms need to be developed for this planner which uses the optimal building strategies based on the knowledge gained from the research of the RUAM team. The efficient FE models that introduced in this thesis can be integrated in the building planner to provide thermo-mechanical information for deciding the best building strategy.
[Page left intentionally blank]
REFERENCES
Abaqus User’s Manual. (2010), HKS Co. USA.
Alberg, H. and Berglund, D. (2003), Comparison of plastic, viscoplastic, and creep models when modelling welding and stress relief heat treatment, Computer Methods in Applied Mechanics and Engineering, vol. 192, no. 49-50, pp. 5189-5208.
Alimardani, M., Toyserkani, E. and Huissoon, J. P. (2007), A 3D dynamic numerical approach for temperature and thermal stress distributions in multilayer laser solid freeform fabrication process, Optics and Lasers in Engineering, vol. 45, no. 12, pp. 1115-1130.
Almeida, P (2012), Process control and development in wire and arc additive manufacturing. PhD Thesis, Cranfield University. U. K.
Altenkirch, J., Steuwer, A., Peel, M. J., Richards, D. G. & Withers, P. J. (2008), The effect of tensioning and sectioning on residual stresses in aluminium AA7449 friction stir welds. Materials Science and Engineering A, vol. 488, pp.
16-24.
Altenkirch, J., Steuwer, A., Withers, P. J., Williams, S. W., Poad, M. & Wen, S.
W. (2009), Residual stress engineering in friction stir welds by roller tensioning.
Science and Technology of Welding and Joining, vol. 14, pp.185-192.
Baker, R. (1925), Method of Making Decorative Articles, US Patent 1,533,300, filed Nov. 12 1920, patented 14th April 1925.
Baufeld, B., Biest, O., Gault, R. (2010), Additive manufacturing of Ti-6Al-4V components by shaped metal deposition: Microstructure and mechanical properties.
Baufeld, B., Brandl, E., Biest, O. (2011), Wire based additive layer manufacturing: Comparison of microstructure and mechanical properties of Ti–
deposition. Journal of Materials Processing Technology, vol. 211, no. 6 pp.
1146-1158.
Benzley, S., Perry, E., Merkley, K., Clark, B. and and Sjaardema, G. (1995), A Comparison of All-Hexahedral and All-Tetrahedral Finite Element Meshes for Elastic and Elasto-Plastic Analysis, October 1995, pp. 179.
Berglund, D., Alberg, H. and Runnemalm, H. (2003), Simulation of welding and stress relief heat treatment of an aero engine component, Finite Elements in Analysis and Design, vol. 39, no. 9, pp. 865-881.
Bouchard, P. J. (2009), The NeT bead-on-plate benchmark for weld residual stress simulation, International Journal of Pressure Vessels and Piping, vol. 86, no. 1, pp. 31-42.
Boyer, R., Welsch, G. and Collings, E. W. (1994), Materials properties handbook : titanium alloys, .
Brice, C.A., Rosenberger, B. T., Sankaran, S. N., Taminger, K. M. (2009), Chemistry control in electron beam deposited titanium alloys, Materials Science Forum, Gold Coast, QLD. pp. 155-158.
Brust, F. W., and Kim, D. S. (2005), Mitigating welding residual stress and distortion, in: Z. Feng (Eds.), Processes and mechanisms of welding residual stress and distortion, Woodhead.
Camilleri, D., Comlekci, T., Grey, T. G. F. (2004), Computatinoal prediction of out-of-plane welding distortion and experimental investigation, The Journal of Strain Analysis for Engineering Design, vol. 40, no. 2, pp. 161-176.
Camilleri, D. and Gray, T. G. F. (2005), Computationally efficient welding distortion simulation techniques, Modelling and Simulation in Materials Science and Engineering, vol. 13, no. 8.
Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, vol. 221, pp. 235-249.
Cao, W. and Miyamoto, Y. (2006), Freeform fabrication of aluminium parts by direct deposition of molten aluminium, Journal of Materials Processing Technology, vol. 173, no. 2, pp. 209-212.
Casalino, G. and Ludovico, A. D. (2008), Finite element simulation of high speed pulse welding of high specific strength metal alloys, Journal of Materials Processing Technology, vol. 197, no. 1-3, pp. 301-305.
Charles, C. (2008), Modelling microstructure evolution of weld deposited Ti-6Al-4V, PhD Thesis, Luleå University of Technology.
Cheng, W. (2005), In-plane shrinkage strains and their effects on welding distortion in thin-wall structures, PhD Thesis, Ohio State University, U. S.
Chen, X. L., Yang, Z., Kim, D. S. (2005), Modeling distortion and residual stress during welding: practical applications, in: Z. Feng (Eds.), Processes and mechanisms of welding residual stress and distortion, Woodhead.
Chin, R. K., Beuth, J. L. and Amon, C. H. (2001), Successive Deposition of Metals in Solid Freeform Fabrication Processes, Part 1: Thermomechanical Models of Layers and Droplet Columns, Journal of Manufacturing Science and Engineering, vol. 123, no. 4, pp. 623-631.
Chin, R. K., Beuth, J. L. and Amon, C. H. (2001), Successive Deposition of Metals in Solid Freeform Fabrication Processes, Part 2: Thermomechanical Models of Adjacent Droplets, Journal of Manufacturing Science and Engineering, vol. 123, no. 4, pp. 632-638.
Chin, R. K., Beuth, J. L. and Amon, C. H. (1996), Thermomechanical modeling of molten metal droplet solidification applied to layered manufacturing, Mechanics of Materials, vol. 24, no. 4, pp. 257-271.
Chiumenti, M., Cervera, M., Salmi, A., Saracibar, C., Dialami, N., Matsui, K.
(2010), Finite element modeling of multi-pass welding and shaped metal deposition processes, Computer Methods in Applied Mechanics and Engineering, vol. 199, no. 37-40, pp. 2343-2359.
Choi, J. and Chang, Y. (2005), Characteristics of laser aided direct metal/material deposition process for tool steel, International Journal of Machine Tools and Manufacture, vol. 45, no. 4-5, pp. 597-607.
Colegrove, P., Ikeagu, C., Thistlethwaite, A., Williams, S., Nagy, T., Suder, W., Steuwer, A., Pirling, T. (2009), Welding Process Impact on Residual Stress and Distortion, Science and Technology of Welding and Joining, vol.14, pp. 717-725.
Costa, L., Vilar, R., Reti, T., Deus, A. M. (2005), Rapid tooling by laser powder deposition: Process simulation using finite element analysis, Acta Materialia, vol. 53, pp. 3987-3999.
Cozzolino, L., Coules, H., Colegrove, P., Wen, S. (2011), Modelling distortion reduction on pre-and post-weld rolled gas metal arc welded plates, Proceeding of International Workshop on Thermal Forming and Welding Distortion, Bremen, Germany, pp. 169-179.
Das, S. (2003), Physical Aspects of Process Control in Selective Laser Sintering of Metals, Advanced Engineering Materials, vol. 5, no. 10, pp. 701-711.
Dann, J. A., Daymond, M. R., Edwards, L., James, J. A., Santisteban, J. (2004), A comparison between Engin and Engin-X, a new diffractometer optimized for stress measurement, Physica B, vol. 350, pp. 511-514.
Deng, D. and Murakawa, H. (2008), Prediction of welding distortion and residual stress in a thin plate butt-welded joint, Computational Materials Science, vol. 43,
Deng, D. (2009), FEM prediction of welding residual stress and distortion in carbon steel considering phase transformation effects, Materials and Design, vol. 30, pp. 359-366.
Deng, D. and Murakawa, H. (2006), Numerical simulation of temperature field and residual stress in multi-pass welds in stainless steel pipe and comparison with experimental measurements, Computational Materials Science, vol. 37, no.
3, pp. 269-277.
Deng, D., Murakawa, H. and Liang, W. (2008), Prediction of welding distortion in a curved plate structure by means of elastic finite element method, Journal of Materials Processing Technology, vol. 203, no. 1-3, pp. 252-266.
Deng, D., Murakawa, H. and Liang, W. (2007), Numerical simulation of welding distortion in large structures, Computer Methods in Applied Mechanics and Engineering, vol. 196, no. 45-48, pp. 4613-4627.
Deo, M. V., Michaleris, P., Sun, J. (2003), Prediction of buckling distortion of welded structures, Science and Technology of Welding and Joining, vol. 8, no.
1, pp. 55-61.
Domack, M.S., Taminger, K.M.B., Begley, M. (2006), Metallurgical mechanisms controlling mechanical properties of aluminum alloy 2219 produced by electron beam freeform fabrication, Materials Science Forum, Vancouver, pp. 1291-1296.
Dong, P. (2005), Residual stresses and distortions in welded structures: a perspective for engineering applications, Science and Technology of Welding and Joining, vol. 10, no. 4, pp. 389-398.
Elcoate, C., Bouchard, P., Smith, M. (2003), 3-Dimensional Repair Weld Simulation – Based on Plate Comparison, ABAQUS World User’s Conference, Munich.