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1

Finite element modelling of the fracture behaviour of surface treated Ti-6Al-4V alloy

Ziaja W.

Archives of Computational Materials Science and Surface Engineering

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2009

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Vol. 1, nr 1

53-60

EN

Purpose: Surface treatments of the titanium alloys are frequently applied in order to modify the surface layer microstructure and to improve tribological properties or resistance to high temperature oxidation of the alloy. Various surface engineering techniques can be used to increase the surface hardness, e.g. deposition of the coatings composed of metallic carbides, nitrides or more recently DLC. The stiffness and strength properties of the coating and substrate materials differ significantly. Cracking of the usually brittle coating leads to stress concentration and localized plastic deformation of the substrate which can facilitate propagation of microcracks into the substrate. This can result in premature failure of the hard coated component. In the paper the crack penetrating hard coating was analysed and the influence of coating and substrate properties on crack driving force was numerically investigated. Design/methodology/approach: Two dimensional finite element analysis of the four point bending test of surface modified titanium alloy with the crack penetrating hardened layer was carried out. Findings: The effect of the coating thickness and stiffness, residual stresses in the coating, yield strength of substrate material and yield properties of diffusion hardened layer on crack driving force was determined. Research limitations/implications: Some extension of the numerical model should be introduced in order to take into account the interactions of the crack with microstructure of the material. Practical implications: The results could be used for selection of parameters of surface layer with complex structure in the process of the design of load bearing components against fracture. Originality/value: The fracture behaviour of hard coated materials was most frequently studied for indentation and friction conditions and considerably less concern was devoted to coated systems under tension or compression.

2

Effect of the cutting speed on the chip morphology and the cutting forces

Daymi A., Boujelbene M., Ben Salem S., Hadj Sassi B., Torbaty S.

Archives of Computational Materials Science and Surface Engineering

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2009

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Vol. 1, nr 2

77-83

EN

Purpose: The aim of this research is to make a first experimental analysis of the effect of the cutting speed on the chip morphology, and of the cutting forces in the orthogonal turning process of the titanium alloys Ti-6Al-4V. Design/methodology/approach: The methodology has consisted of proving a series of parameters combinations: f, feed rate, Vc, cutting speeds are explored in a range from 50 to 250 m/min, and is analyzing the different types of chips and the evolution cutting forces appeared during each one them, and determined the analytical model of plastic deformation ratio. Findings: Tests achieved have shown three main types of chips: Continuous chip at 50 m/min, Flow chip for speeds ranging around 100 m/min, and Shear localized chip starting from the transition speed of 125 m/min and above. The modification of the mechanism of chip formation is associated with the appearance of shearing instability. Chip segmentation by shear localisation is an important process which is observed within a certain range of cutting speeds. This phenomenon might be desirable in reducing the level of the cutting forces by improving chip's evacuation. Research limitations/implications: A possible future work would be the development of a general the phenomenal of the thermo mechanical of the cutting high speed machining. The behavior is of the thermo - visco - plastic studies are planed in the future. Practical implications: The relationship found between high speed machining and chip morphology and the cutting forces and work piece surface finish has an important practical implication since it allows selecting the best cutting condition combination from the points of view both the security and the economy for the established requirements in each case. Results are of great importance in for aerospace, biomedical and automotive industry. Originality/value: The paper is original since the bibliographical review has allowed testing that, although works about these themes exist, none approaches the problem like it has been made in work.

3

Study of the milling strategy on the tool life and the surface quality for knee prostheses

Boujelbene M., Abellard P., Bayraktar E., Torbaty S.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 31, nr 2

610-615

EN

Purpose: The aim of this research is to make a study about the influence of the tool trajectory's generation on its tool life and the improvement of the surface quality in multi-axis milling at high speed machining of the knee prostheses. The material used for this study is the titanium alloy Ti-6Al-4V ELI (TA6V ELI) for implant. Design/methodology/approach: The methodology has consisted on proving a serie of parameters combinations with various machining configurations and various programs of the tool trajectory's generation in three and five axes (the axis of the tool is maintained normal on the machined surface by rotation around Y axis; the axis of the tool is maintained according to axis Z; the axis of the tool is tilted around the Y axis). And determined the influence of the machining strategy over of the tool life. Findings: The knee prostheses are constructed with important mechanical resistance materials with complex form, which require high performance cutting tools and high cost. The good generation's trajectory of the cutting tool in multi-axes milling permits to minimize flank wear. High speed Machining offers a considerable profit in the capacity of surface quality, duration of the machining and polishing operations and consequently in improvement productivity. But the choice of the cutting speed must be recommended by the couple tool-materials. Research limitations/implications: A possible future work would be the development of a general the phenomenal of the residual stress of various machining configurations and various programs of the tool trajectory's generation and the knee protheses life. The behaviour of the residual stress studies are planed in the future. Practical implications: The relationship found between the milling strategy on the tool life and surface quality work piece has an important practical implication since it allows selecting the best cutting condition for knee prostheses. Results are of great importance in the quality of articulation surface so the cartilage in medicine industry. Originality/value: The paper is original since the bibliographical review has allowed testing that, although works about these themes exist, none approaches the problem like it has been made in this work. This paper could be an interesting source of information for engineers and researchers who work with machining knee prostheses.