[en] The main contribution of this Ph.D. is the development of a finite element based procedure to predict machinability considering the effect of lamellar ferrite-pearlite microstructures. The findings of this study give support to the understanding of the machinability of ferrite-pearlite steels. To cover a wide range of ferrite-pearlite microstructures, the analysis was focused on four steels with different carbon content: 16MnCr5, 27MnCr5, C45 and C60. Based on an Arbitrary Eulerian Lagrangian formulation, an orthogonal cutting Finite Element model in conjunction with a tool wear simulation strategy was provided for the prediction of scientific (cutting forces, tool temperatures, chip formation, etc.) and industrial relevant outcomes (machinability/tool wear). The required inputs that describe the flow stress of the workpiece material, the friction behavior in the tool-workpiece interface, and the tool wear rate were defined as functions dependent on microstructure and composition properties. Based on rheological characterization tests, a new material constitutive model was proposed to represent the behavior of ferrite-pearlite steels (MSB model). The main contribution of this model is that the strain hardening behavior of the ferrite-pearlite steels was modeled as a function of the chemical composition, and the microstructure parameters of pearlite fraction, interlamellar spacing and ferritic mean grain size. Frictional behavior was also identified as dependent on the ferrite content and the relative sliding velocity at the interface. In addition, a unique wear rate equation was identified to predict the wear on the rake and flank faces of the tool, based on specially designed orthogonal tests. This was set out as uncoupled mechanical and thermally activated wear phenomena, in which the mechanical wear was identified as an equation dependent on the carbon content of the steels and the sliding distance. The thermal wear was modeled by an Arrhenius type equation, in which the activation energy required for thermal wear to occur was found to be the same for all the tested ferrite-pearlite steels. The trends observed in the simulations were in good agreement with the orthogonal cutting tests as regards both scientific and industrial relevant outputs. The values of crater depth (KT) and flank wear land (VB), and the scientific variables of cutting forces (Fc), chip thickness (t2) and tool temperature were predicted with an error in the range of 5-20%. The major limitation of the developed model was found in the prediction of contact length (lc) or crater length (KB) and feed forces (Ff ), which were underestimated by 25-60%. In addition to the numerical approaches, two original empirical strategies were developed in the course of this research. One concerned the establishment of a direct relationship between the radiation of the tool surface and the real surface temperature without the need of characterizing the emissivity of the tool. The other was focused on the orthogonal cutting procedure in which fundamental variables were linked to tool wear. The combination of these two setups permitted the accurate characterization of the wear behavior of the steels, and demonstrated that the wear evolution on both the rake and flank faces could be modeled with the same wear rate equation.

[eu] Tesiaren ekarpen nagusia mekanizagarritasuna eta higaduraren eboluzioa aurreikustera bideratuta dagoen elementu finituetan oinarritzen den prozedura garatzea da, ferrita eta perlitazko lamelez osatutako altzairuen mikroestrukturaren eragina kontuan hartuta. Gainera, lortutako emaitza esperimentalak laguntzen du altzairu horien makinagarritasuna ulertzeko. Ferritaperlitazko mikroestruktura mota zabalean garatutako modeloa balioztatzeko, karbono-eduki desberdina duten lau altzairu hautatu dira: 16MnCr5, 27MnCr5, C45 eta C60. Lagrangiar Euleriar Arbitrario formulazioan oinarrituta, elementu finituen modelo bat garatu da, higadura simulazio estrategiakin batera aldagai zientifikoen (ebaketa indarrak, tenperaturak, txirbilaren formazioa) eta garrantzizko aldagai industrialak (makinagarritasuna eta herraminten higadura) aurreikusteko. Beharrezkoak diren sarrera parametroak, hau da, materialaren tentsiodeformazio deskribatzen duen modeloa, erreminta eta piezan harteko marruskadura eta higadura modeloa, propietate mikroestrukturalen eta konposizioaren arabera definitu dira. Reologia esperimentuetan oinarriturik, altzairu ferritiko-perlitikoen portaera errepresentatzen duen material modelo berria proposatu da (MSB modeloa). Konposizioan, perlita ehunekoan, perlitaren distantzia interlaminarean eta ferritaren batez besteko ale-tamainaren arabera materialaren deformazioren aurkako gogortasuna deskribatzea da modeloaren kontribuzio nagusia. Marruskadura legea, ferrita ehunekoaren arabera eta pieza eta erremintaren arteko abiadura erlatiboaren arabera definitu da. Azkenik, higadura lege bakar bat planteatu da erremintaren flanko eta krater higadura errepresentatzeko gai dena. Lege honek, higadura fenomeno desakoplatu mekaniko eta aktibazio termikoen bitartez deskribatzen du, non atal mekanikoa altzairuaren karbonoaren edukian eta irristatze luzeeran oinarritzen den. Fenomeno termikoari dagokion higadura Arrhenius motako ekuazio batekin modelatzen da, zeinean aktibazio energetikoa berdina dela aurkitu da aztertutako altzairu guztientzat. Emaitza enpirikoek zein simulaziokoek, joera berdinak lortzen dituzte aldagai zientifiko eta industrialak astertzerakoan. Krater sakoneraren (KT) aurreikuspena, flankoaren higadura luzera (VB), ebaketa indarra (Fc) eta txirbil lodiera (t2) %5-20ko akatsa lortu dute ebaketa ortogonalaren emaitza esperimentalekin alderatuta. Kontaktu luzera (lc) eta aitzinamendu indarra (Ff ) aurreikustean da modeloaren muga handiena, emaitzak %25-60 txikiagoak izanik. Elementu finituen modeluaz gain, bi ikerketa-estrategia enpiriko garatu dira ikerketan zehar. Lehenengoak, erremintaren gainazalak duen tenperatura erreala eta igortzen duen erradiazioaren arteko lotura zehazten du, erremintaren emisibitatea karakterizatu beharrik gabe. Bigarren prozeduran, modu sinkronizatuan funtsezko aldagaien eboluzioa eta erremintaren higadura lortzen dira ebaketa ortogonaleko prozesuan. Bi estrategia enpiriko hauen bitartez, ferritaperlita altzairuen higadura mekanismoak karakterizatu egin dira eta horren bidez, kraterraren eta flankoaren higadura errepresentatzeko gai den lege bakarra ezarri da.