[en] Fretting wear is one of the main degradation mechanism produced in steel wire ropes. This phenomenon leads to produce wear scars between the contacting thin steel wires reducing considerably the fatigue life of these components. The complex assemblage of the wires in the wire rope systems make difficult the experimental characterization of this phenomenon, being economically costly and too much time consuming. With the aim to reduce these disadvantages and increases the knowledge of this phenomenon in complex components such as the wire rope systems, in this thesis a fretting wear simulation methodology for predicting wear scars in thin steel wires has been developed. The complex multicontact problem presented in wire rope systems, has been simplified with the development of an individual crossing cylinder model, in which the severity of the wear scars can be analysed under the range of the different geometrical and operational parameters appeared in each contact. In order to define the frictional and wear behaviour of the thin steel wires, in terms of the coefficient of friction and the wear coefficient, fretting wear tests have been carried out under different conditions (loads, strokes and number of cycles). Firstly in a more common tribological system of 90° crossed cylinder arrangements and secondly with different crossing angles, which are a more realistic configuration to that one presented in wire ropes. This study has reported the influence of the contact pressure and the wear debris in the wear behaviour. Thus two wear mechanisms have been derived from this type of tests, a more aggressive wear mechanism in the beginning of the test and a stable wear mechanism in the remaining part of the test. The developed wear simulation methodology is based on the Archard's wear law applied in a local perspective. So that the wear simulation is an iterative process in which the Archard's local equation is solved according to the contact pressures and slip distributions obtained by the finite element model, as many times as sliding increments needed to reach the desired sliding distance or, in the case of fretting wear, the desired number of cycles. Nevertheless this process requires high computational time, which increases in the case of the 3D problem presented in the thin steel wires. Therefore an optimized methodology for modelling any tribological system has been proposed, based on the optimization of the main parameters involved in the wear modelling (mesh size, sliding increment and speed factor). This methodology has been applied first in a cylinder on plane sliding wear 2D FE model and then was adapted to the 90° crossed cylinder 3D fretting wear FE model. Finally this approach has been implemented in the crossing angle 3D FE model, in which the parameterization of all the geometrical parameters and meshes that form the model has been introduced, in order to reduce the time required for modelling all the type of contacts presented in the wire rope systems. It has been demonstrated that following this methodology it can be defined the optimum parameters for modelling fretting wear of 3D problems in terms of the minimum computational time with the minimum difference in the final wear scar. The optimized wear simulation methodology has been finally validated following an exhaustive validation methodology. To this end the specific wear coefficients obtained in the fretting wear thin steel wires tests have been used. The validation consisted of three steps: wear scar dimensions, wear scar depth (profile) and wear scar volume comparison. This procedure has shown the accurate validation of the entire wear scar shape in both top and bottom specimens. The proposed methodology has been used then to study the severity of the wear scars under the different geometrical and operational parameters presented in the wire ropes contacts. The analysis of the severity of the wear scars has been done in terms of the percentage of resistant area loss and the stress concentration factor, concepts that are in relation with the catastrophic rupture of the wire and the fatigue life reduction of the wire, respectively. To develop this study the methodology of design of experiments (DOE) has been used. The great influence of the diameter and the crossing angle was derived from this study. Finally the effect of fretting wear on the fatigue life reduction of thin steel wires has been analysed. For this purpose the frictionally-induced multiaxial contact stresses obtained from the 90° thin steel wires FE model have been used. The fatigue life prediction model uses a critical-plane SWT (Smith-Watson-Topper) approach in a 3D crossed cylinder problem. A new damage accumulation methodology for the adaptive mesh simulation in 3D problems, based on the cyclic material removal, has been developed. The effect of the contact pressure and stroke has been analysed and contrasted with the results obtained experimentally. Guidelines for developing a more robust methodology were proposed in the end of this research work.

[eu] Kable metalikoen barnean gertatzen den degradazio fenomeno garrantzitsuenetako bat da fretting-a. Gertaera honek dakar kablearen neke bizitza murriztea, hariz osatutako kableetan pitzadurak sortuaz. Altzairuzko harien muntai konplexuak fenomeno honen karakterizazio esperimentala oztopatzen du, batez ere ikerkuntzaren luzapenean eta koste ekonomikoan. Desabantaila hauek ahal diren einean gutxitzeko batetik, eta kable metalikoa bezalako sistema konplexuetan fenomeno honi buruzko ezagutza handitzeko bestetik, fretting fenomenoa sortutako pitzadurak iragartzeko higadura simulazio metodologia garatu da tesi honetan. Kableetan sortzen den harien arteko multi-kontaktu arazoa zaila suertatzen dela jakinda, bi zilindrok gurutzatzean sortzen duten kontaktu bakarreko modelo bat eraiki da. Modelo honek, kableetan agertzen diren kontaktu bakoitzeko pitzaduren larritasuna neurri geometriko edo funtzionamenduen ondorioz aztertzeko gaitasuna dauka. Fretting saiakuntza tribologikoak baldintza ezberdinetan egin dira (indar normala, deslizamendu anplitudea eta ziklo-kopurua) marruskadura eta higadura portaerak ezagutzeko. Saiakuntzak hasieran, 90°ko angeluz gurutzatuta dauden zilindroen konfigurazio arrunt batean egin dira, ondoren, kableetan agertzen diren benetazko angelu ezberdinetan izan direlarik. Azterketa hauetan, harien arteko presioa eta higaduraren ondorioz sortzen diren partikulen eraginak aztertu dira, bi higadura mekanismo nagusi bereiztuz: higadura oldarkorra (saiakuntzaren hasieran) eta higadura egonkorra. Tesi honetan garatu den higadura simulazioren metodologia, Archard higaduraren legea maila lokalean aplikatzean datza. Higadura-simulazioa prozesu iteratiboa izanik, Archarden ekuazio lokala ebazten da elementu mugatuen (FE) modelotik lortutako presio kontaktu eta deslizamendu erlatiboa erabiliz, behar diren deslizamendu erlatibo gehikuntza adina errepikatuz, distantzia osoa bete arte, Fretting-aren kasuan ziklo kopuru osoa bete arte. Tesi honetan aztertu den altzairuzko hariaren 3D simulazioak denbora konputazional handia eskatzen duela jakinik, edozein tribosisteman higadura simulatzeko metodologia optimizatua proposatu da, higadura simulazioan parte hartzen duten parametro garrantzitsuen optimizazioan oinarrituta (sare tamaina, irrista gehikuntza eta higadura bizkorgailua). Metodologia hau, zilindro-plano 2D FE modelo batean aplikatu da lehenik eta 90° zilindro gurutzatuta dauden 3D FE modelo batera egokitu da ondoren. Azkenik, metodologia hau angelu ezberdinez gurutzatzen diren zilindroen 3D FE modeloan inplementatu da. Modelo honek gainera parametro geometriko eta sarearen parametrizazioa dakar, kableetan agertzen diren kontaktu mota guztiak modelatzeko behar den denbora murrizteko. Metodologia honen erabilerarekin fretting higadura simulatzeko parametro optimoak identifikatu daitezkeela frogatu da, bai 2D modeloetan, baita 3D modeloetan, denbora konputazional txikiena eta pitzaduran diferentzia txikiena erabiliz. Higadura simulatzeko metodologia optimizatua balioztatu da, balioztatzeko prozesu zehatz bat jarraitu ondoren. Hau lortzeko hariekin egindako fretting saiakuntzen ondorioz lortutako higidura koefizienteak erabili dira. Balioztapen hau, pitzadurekin erlazionatuta dauden hiru alderdietan oinarritu da: pitzaduraren dimentsioak, pitzaduraren sakonera (erdiko profila) eta bolumena. Pitzaduren larritasuna aztertzeko proposatu den higadura simulatzeko metodologia, kableetan agertzen diren parametro geometriko eta funtzionalen pean erabili da. Hariaren larritasunaren azterketa, azalera erresistenteren portzentai galera eta tentsio kontzentrazioa baliatuz aztertu da. Bi parametro hauek hariaren apurtzeko ahalmenarekin eta nekearen bizitza murrizteko ahalmenarekin loturik daude. Beraz, azterketa hau garatzeko esperimentu diseinuaren metodologia (DOE) erabili da. Azterketa honetan diametro eta angelu gurutzatuen bizitza murrizteko ahalmena ikusi da. Azkenik, Fretting fenomenoak altzairuzko harien neke bizitza murriztean duen efektua aztertu da, horretarako, 90°-ko higadura simulatzeko modelotik, marruskaduraren ondorioz agertzen diren kontaktuzko tentsio multiaxialak erabili dira. Neke-bizitza aurreikusteko metodologia, planu kritiko eta SWT (Smith-Watson-Topper) neke eredua 3Dko zilindro gurutzatu modeloaren inplementazioan datza. Horretaz gain, 3D modeloen higadura ziklikoa kontutan hartzeko, kaltea pilatzeko modelo berri bat gehitu zaio. Azkenik, kontaktu presioaren eta deslizamendu anplitudearen eragina aztertu da, fretting saiakuntzan lortutako emaitzekin alderatuz. Tesi honen amaieran fretting fenomenoaren eraginez altzairuzko hariz osaturik dauden kable metalikoen neke bizitza aurreikusteko metodologia sendoagoa garatzeko jarraibideak proposatu dira.