[en] The substitution of metals by thermoplastic materials is increasing in structural applications in which lightness is essential. In many of these applications impact behaviour is a key factor, because impact produces the catastrophic rupture of components, risking the physical integrity of users. The complex impact behaviour of these materials makes difficult the use of engineering design methods like finite element method, that alow to reduce manufacturing costs and deadlines. This problem has two main facts: on one hand, the lack of routine tests methods for measuring material properties in impact conditions, required as input data by finite element codes. on the other hand, most of the constitutive models available in finite element codes have been developed for other materials that don't show the features of thermoplastics in impact conditions. In the present work a new characterisation method of impact behaviour of thermoplastics has been proposed, based on instrumented tensile-impact experimental tests. This method has allowed the determination of the stress/strain curves of polypropylene at constant strain rates. This information has been introduced in a finite element code through simple constitutive models available in it. The characterisation tensile-impact tests have been simulated, as well as indentation-impact tests. The correlation of numerical and experimental results show that the method is valid for predicting the evolution of force signal in time, as well as the minimum energy value for producing the rupture of samples in tensile impact configuration. Moreover, it has been demonstrated to be a great difference between the impact behaviour of the material in tensile-impact and indentation-impact configurations. The correlation of numerical and experimental displacement-time curves in both configurations has permitted to detect some main facts to be considered: the unloading behaviour of the material, as well as the dependency of Young's modulus and elastic limit with strain rate, must be taken into account both in the charaterisation method and constitutive modelling.

[eu] Termoplastikoak geroz eta gehiago erabiltzen dira metalen ordezkotzat, arintasuna funtsezko duten aplikazio estrukturaletan. Horietako askotan talka portaera oso garrantzitsua da, iharduera mota honek osagaien ezusteko apurketa sortu dezakeelako, erabiltzaileen segurtasuna kolokan gerta daitekeelarik. Materiale mota hauek daukaten talkarekiko portaera konplexuak, fabrikazio kostu eta epeak gutxitzeko lagungarri diren iginerutzako diseinu metodoen erabilera zailtzen du, adibidez elementu finitoen metodoarena. Arazo honek bi adar garrantzitsu ditu: alde batetik, ez dago elementu finitoen programetan sarrera datu bezala erabilgarriak izan daitezkeen termoplastikoen talka propietateak lortzea uzten duten araututako karakterizazio protokolorik. beste alde batetik, elementu finitoen programetan erabilgarri dauden materiale ereduak, termoplastikoak ez diren beste materiale batzurentzat garatu dira, hauek talka baldintzetan dauzkaten berezitasunak deskribatzeko gaitasunik ez dutelarik. Lan honetan, trakzioko konfigurazioan eginiko talka instrumentatuko teknika experimentalean oinarritutako termoplastikoen karakterizazio metodo berri bat proposatu da. Metodo honen bitartez polipropilenoaren tentsio-deformazio kurbak lortu dira deformazio abiadura konstantean. Informazio hau elementu finitoen programa baten sartu da programak berak dituen materiale eredu sinpleak erabiliz. Karakterizazioan egindako trakzioko talka saiakuntzak, eta baita indentazio konfigurazioan egindako beste talka saiakuntza batzuk ere, simulatu dira. Emaitzen korrelazio numeriko-esperimentalak frogatzen du proposatutako metodoa gai dela iragartzeko, bai indarraren aldaketa denboran, eta baita probeten apurketa sortzeko beharrezkoa den energia minimoa ere. Horrez gain, materialak trakzio eta indentazio konfiguraziotan egindako talketan erakusten duen portaera desberdintasun nabarmena ere agerian geratu da. Bi konfigurazio hauetan lortutako desplazamentu-denbora kurben korrelazio numeriko-esperimentalak kontutan hartzekoak diren funtsezko gai batzuk nabarmendu ditu, hala nola, materialak deskargatzerakoan duen portaera, eta elastizitate moduloak eta limite elastikoak deformazio abiaduran duten menpekotasuna, bai karakterizazioan eta baita materiale ereduan ere adieraztearen beharra.