PSI- Issue 9

Khadija Kimakh et al. / Procedia Structural Integrity 9 (2018) 243–249 Khadija. KIMAKH / StructuralIntegrity Procedia 00 (2018) 000–000

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1. Introduction The lifetime prediction of mechanical structures has become a major subject in many industrial sectors: aeronautics, automotive... Many factors other than the mechanical proprieties of the material affect its ability to resist fatigue phenomenon. Besides these factors, the manufacturing process has a significant role in the fatigue strength. In fact, these methods including the machining are often associated with significant thermo-mechanical stresses that may result in heterogeneous properties in the materials. The impact of these properties, usually generated in surface and subsurface of the machined parts, could significantly affect the behavior of mechanical component subjected to fatigue loads. The fatigue cracks are generally initiated from free surfaces. The surface of a piece has two important aspects that have to be defined and controlled. The first aspect is geometric irregularities on the surface, and secondly the metallurgical alterations of the surface and the subsurface. This second aspect has been termed surface integrity. Several researchers have been interested in investigating the influence of cutting conditions on fatigue life. Ming Zhang (2016) proves that surface roughness has a significant effect on VHCF properties of FV520B-I, and VHCF properties of FV520B-I impeller can be improved by reducing surface roughness. D. Novovic et al. (2004) attest that both surface integrity and surface topography have a significant effect on fatigue performance of machined parts. It has been testified that for low surface roughness the fatigue lifetime depends on surface roughness. But for surface roughness higher than Ra = 2.5 µm, the fatigue performance depends on residual stress. Guoliang Liu et al. (2016) analyzed the modifications generated by cutting operation on surface integrity (residual stress, microstructure and surface roughness). The influence of surface roughness on the fatigue performance could be overshadowed by other surface integrity characteristics. Monchaï Suraratchaï et al. (2005, 2008) investigate the influence of machined surface on the fatigue life of 7010 aluminum alloy. They proposed a model, based on surface topography to predict fatigue lifetime. D P Davies et al. (2014) interested in Critical Helicopter Components. Different manufacturing methods were carried out to enhance the fatigue performance. Our work aims to identify a relationship between turning process parameters and fatigue behavior of the mechanical component. An experimental study is carried out to analyze this relationship. The cylindrical specimen for fatigue testing was released in CNC lathe Alpha 1530XS with 3 different values of feed rate. After specimen’s preparation, fatigue testing is accomplished to determine the fact of feed rate on fatigue lifetime. The results obtained are presented through S-N curves which highlighted the impact of feed rate on the fatigue life of parts.

Nomenclature Re 0.2% Yield strength Rm Tensile strength A Elongation E

Elasticity modulus

R f ɛ σ

Stress ratio Feed rate

strain Stress

Maximum stress

σ max

Number of cycles failure

N f