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Chapter 6 Machining-Induced Surface Integrity and Its Effect on Fatigue

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Chapter 6 Machining-Induced Surface Integrity and Its Effect on Fatigue SURFACE INTEGRITY EVALUATION AND THE EFFECT OF MACHINING-INDUCED SURFACE INTEGRITY CHARACTERISTICS ON PART’S PERFORMANCE by QUANREN ZENG A thesis presented in fulfilment of the requirements for the degree of Doctor of Philosophy Centre for Precision Manufacturing Department of Design, Manufacture and Engineering Management University of Strathclyde Glasgow, Scotland, UK February 2015 ABSTRACT Surface integrity (SI) is the integrated surface behavior and condition of a material after being modified by a manufacturing process; it describes the influence of surface properties and characteristics upon material functional performance. As the leading-edge field of manufacturing research, SI finishing/machining and the consequent machining-induced complex combination of surface roughness, residual stress, work-hardening, macro and microstructure transformation, strongly affect the fatigue and stress behavior of machined parts. This kind of influence is particularly sensitive and pronounced in the difficult-to-machine materials, which are typically chosen for the most critical applications in the automobile, aerospace and nuclear industry. Thus, well-designed SI processing requirement and accurate SI evaluation model are essential to control and ensure the surface quality and functional performance for these key parts. In this thesis, an SI descriptive model for quantitative characterization and evaluation of surface integrity is proposed based on five principal SI characteristics. Considering the nature of surface integrity, a conceptual framework of an SI model for machined parts is established, in which the SI model is constructed based on the correlations between SI manufacturing processes, SI characteristics and final functionality. This model offers a theoretical basis and guideline for controlling SI characteristics and improving fatigue properties for machined parts. An empirical model for estimating the SI-characteristics-caused effective stress concentration factor (SCF) is established with fatigue life as the evaluating indicator. For a typical difficult-to-machine material, GH4169 superalloy, usually used in internal combustion engines, its grindability and the influence of processing parameters on the five principal SI characteristics are investigated in detail. The correlations between the processing parameters and the SI characteristics, between the processing parameters and the fatigue properties, and between the SI characteristics and the fatigue properties, are analyzed based on an orthogonally-designed grinding experiment and corresponding rotary bending fatigue testing for GH4169 samples within the selective range I of grinding processing parameters. The feasibility and effectiveness of the proposed model for estimating the SI effective SCF are also validated by the experimental results, and this has actually offered an equivalent and convenient means for evaluation of SI and fatigue properties. Finally, the conclusions and contribution of the research are discussed, and potential future work to build on this research is identified. II ACKNOWLEDGEMENT I’d like to say I have been very lucky to start my Phd research in the precision manufacturing field at the Department of Design, Manufacture and Engineering Management, University of Strathclyde. The multiple disciplines involved have enabled me to learn so much out of my original expectation before I began this journey. At the beginning of my odyssey, I was like a piece of “raw material” to be manufactured to some extent. The research process has gradually developed and equipped me with some ‘fabricated tools’ that have the ability to shape and finish this piece of work. Thanks to all the “craftsmen” who have helped me throughout this process. The one I should especially thank is my supervisor at the University of Strathclyde, Professor Yi Qin, the chief craftsman who makes me as a competent and independent researcher. Words are not enough to express my appreciation and feeling. I am indebted to his professional supervision, encouragement and patience. What I learned from him will benefit me all my life, especially his attitude and way to manage the academic research activities in everyday life. My thanks are due to the local supervisor at Northwestern Polytechnical University, Professor Geng Liu, for his persistent support and trust in my research decisions. Thanks to Professor Xiutian Yan and Mrs Youhua Li who helped me to get the chance to start my joint Phd journey at the University of Strathclyde. Thanks to the Asia-link project for funding the first year of my Phd study. It would be impossible for me to finish this work without their support. I would also like to express my sincere appreciation to Dr Xinchun Huang and Professor Jinxin Ren for their help in experiment design and instructive discussion in my thesis research. Thanks are also extended to emeritus Professor Frank Travis for thesis checking and proofreading. My thanks are also due to the staff in DMEM. Thanks to the secretaries and IT staff in the Department and all the people that were or are still in the Leonardo Centre, especially III Alasdair Downs, Barry, Dino Bertolaccini and so on. Thanks to my former and current office colleagues Dr Wendan Wang, Dr Wenjuan Wang, Dr Gang Zhang, Dr Jie Zhao and Dr Peipei Wu and so on for helped me to find a pleasant life in Glasgow. Finally, to my dear mum, Shuiqing Lu, dad, Sanyuan Zeng, sister, Zirong Zeng, and my girlfriend Jinying Sun. Thank you all for your pure-hearted love and unselfish support to me, which had warmed me so much in this cold season in Glasgow. IV PUBLICATIONS RELATING TO MY PHD RESEARCH 1. Q. Zeng, et al. Influence of machining-induced 3D surface roughness on component’s performance (In preparation and intending to submit to Wear). 2. Q. Zeng, et al. Investigation into grindability of a superalloy and effects of grinding parameters on its surface integrity. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture. 2015, Vol. 229, pp. 238-250 (first published online on April 29, 2014) 3. Q. Zeng, et al. Characterisation of the relationship between surface texture and surface integrity of superalloy components machined by grinding. Edited by Essam Shehab, Peter Ball, Benny Tjahjono. Advances in Manufacturing Technology XXVII, Proceedings of the 11th International Conference on Manufacturing Research (ICMR2013), p.239-244. September 19-20, 2013, Cranfield University, UK 4. Feng, J., Qin, Y., Zeng, Q., et al. Parameterised FE modelling of the surface-systems with coatings which considers the cracking of the coatings and influences of the case-hardening of the substrate, Journal of Multiscale Modelling, 2011, Vol. 3, No. 1-2, pp. 1-22 5. Q. Zeng, et al. Surface texture’s role in assessing surface integrity of machined parts. Applied Mechanics and Materials, 2010, Vols. 34-35, pp. 1145-1148 6. Q. Zeng, et al. Framework of surface integrity model for machined components. Advanced Materials Research, 2010, Vols.139-141, pp.167-171 V CONTENT ABSTRACT ................................................................................................................................. I ACKNOWLEDGEMENT ............................................................................................................ III PUBLICATIONS RELATING TO MY PHD RESEARCH .................................................................... V CONTENT ................................................................................................................................ VI LIST OF FIGURES ..................................................................................................................... X LIST OF TABLES ................................................................................................................... XIII NOMENCLATURE ................................................................................................................. XIV CHAPTER 1 INTRODUCTION ...................................................................................................... 1 1.1 SCOPE OF THE WORK .................................................................................................. 1 1.2 AIM & OBJECTIVES ..................................................................................................... 3 1.3 ORGANIZATION OF THESIS ......................................................................................... 4 REFERENCES ..................................................................................................................... 7 CHAPTER 2 LITERATURE REVIEW .......................................................................................... 10 2.1 INTRODUCTION ......................................................................................................... 10 2.2 CHARACTERIZATION AND EVALUATION OF SURFACE INTEGRITY ........................... 12 2.3 SURFACE AND SUBSURFACE RESIDUAL STRESS ....................................................... 15 2.4 MICROSTRUCTURE AND MICROHARDNESS .............................................................. 18 2.5 SURFACE TEXTURE AND ROUGHNESS PARAMETERS ............................................... 21 2.5.1 2D Surface Roughness Characteristic Parameters ......................................... 27 2.5.1.1 2D surface amplitude parameters ........................................................ 28 2.5.1.2 2D surface amplitude distribution parameters .................................... 30 2.5.1.3 2D surface slope
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