| Abstract | Određivanje mehaničkih parametara materijala pri smičnom opterećenju od velike je važnosti za proizvodne industrije kod kojih se primjenjuje tehnologija oblikovanja deformiranjem. Sve većom primjenom numeričkih metoda u svrhu modeliranja i optimiranja konačnih proizvoda, raste potreba za definiranjem pouzdanijih parametara materijala kako bi se moglo što vjerodostojnije opisati elastoplastično ponašanje metalnih materijala. Postojeće metode mehaničkih ispitivanja na jednostavni i čisti smik tijekom ravninskog opterećenja tankih limova konstantno se poboljšavaju s ciljem smanjenja fenomena izvan ravninskih pomaka u promatranoj zoni ispitnog uzorka koje degradiraju realni odziv materijala. Najčešće metode mehaničkog ispitivanja na smik provode se pomoću Iosipescu i Arcan ispitnih uređaja na ispitnim uzorcima leptirastog oblika. Geometrija predloženih ispitnih uzoraka sastoji se ploče\lima s dva simetrična V zareza čija je svrha osiguravanje homogenog stanja smicanja. Tijekom ispitivanja mjerenje deformacija nije moguće provesti primjenom klasičnim ekstenzometara, već se primjenjuju mjerne trake koje se postavljaju na pretpostavljena kritična mjesta ispitnog uzorka. Štoviše, razvitkom optičkih metoda mjerenja cijelog polja pomaka, omogućena je analiza odziva materijala u cijeloj promatranoj zoni interesa. Najčešće korištena optička mjerna metoda u eksperimentalnoj mehanici je metoda korelacije digitalne slike (eng. Digital Image Correlation - DIC), kod koje se razlikuju lokalni i globalni DIC pristup. U okviru ovog diplomskog rada, primijenjen je globalni pristup stereo korelacije digitalne slike čija se kalibracija temelji na unaprijed poznatoj (tj. definiranoj) geometriji CAD modela eksperimentalnog postava. U ovom radu provedena su četiri ispitivanja na smik primjenom modificiranog Arcan prihvata na jednoosnom elektro-mehaničkom ispitnom uređaju Beta 50-5 (Messphysik, Austrija). Mehanička ispitivanja provedena su na leptirastim ispitnim uzorcima izrađenim iz čelika C60 debljine 1 mm. Tijekom ispitivanja korišten je mjerni sustav Aramis pomoću kojeg su zabilježene digitalne slike promatrane zone interesa tijekom mehaničkog ispitivanja. Registrirane slike korištene su za detaljnu analizu cijelog polja pomaka primjenom globalnog stereo korelacijskog algoritma EikoTwin. Validacija eksperimentalnog postava provedena je na tri leptirasta ispitna uzorka kod kojih je narinuto monotono smično opterećenje. Navedena statička ispitivanja razlikovala su se s obzirom na konfiguraciju eksperimentalnog postava koja je ovisila o preddefiniranoj krutosti Arcan prihvata te dodatnoj potpori promatrane zone interesa koja ne dozvoljava izvijanje ispitnog uzorka. Analizom rezultata pokazano je kako je neophodno smanjiti krutost Arcan prihvata i postaviti dodatnu potporu s ciljem sprječavanja izvan ravninskih pomaka koji uzrokuju fenomen izvijanja kod tankih limova. Osim toga, provedeno je dodatno cikličko ispitivanje s ciljem potvrđivanja unaprijeđenog eksperimentalnog postava za mehanička ispitivanje tankih limova.Određivanje mehaničkih parametara materijala pri smičnom opterećenju od velike je važnosti za proizvodne industrije kod kojih se primjenjuje tehnologija oblikovanja deformiranjem. Sve većom primjenom numeričkih metoda u svrhu modeliranja i optimiranja konačnih proizvoda, raste potreba za definiranjem pouzdanijih parametara materijala kako bi se moglo što vjerodostojnije opisati elastoplastično ponašanje metalnih materijala. Postojeće metode mehaničkih ispitivanja na jednostavni i čisti smik tijekom ravninskog opterećenja tankih limova konstantno se poboljšavaju s ciljem smanjenja fenomena izvan ravninskih pomaka u promatranoj zoni ispitnog uzorka koje degradiraju realni odziv materijala. Najčešće metode mehaničkog ispitivanja na smik provode se pomoću Iosipescu i Arcan ispitnih uređaja na ispitnim uzorcima leptirastog oblika. Geometrija predloženih ispitnih uzoraka sastoji se ploče\lima s dva simetrična V zareza čija je svrha osiguravanje homogenog stanja smicanja. Tijekom ispitivanja mjerenje deformacija nije moguće provesti primjenom klasičnim ekstenzometara, već se primjenjuju mjerne trake koje se postavljaju na pretpostavljena kritična mjesta ispitnog uzorka. Štoviše, razvitkom optičkih metoda mjerenja cijelog polja pomaka, omogućena je analiza odziva materijala u cijeloj promatranoj zoni interesa. Najčešće korištena optička mjerna metoda u eksperimentalnoj mehanici je metoda korelacije digitalne slike (eng. Digital Image Correlation - DIC), kod koje se razlikuju lokalni i globalni DIC pristup. U okviru ovog diplomskog rada, primijenjen je globalni pristup stereo korelacije digitalne slike čija se kalibracija temelji na unaprijed poznatoj (tj. definiranoj) geometriji CAD modela eksperimentalnog postava. U ovom radu provedena su četiri ispitivanja na smik primjenom modificiranog Arcan prihvata na jednoosnom elektro-mehaničkom ispitnom uređaju Beta 50-5 (Messphysik, Austrija). Mehanička ispitivanja provedena su na leptirastim ispitnim uzorcima izrađenim iz čelika C60 debljine 1 mm. Tijekom ispitivanja korišten je mjerni sustav Aramis pomoću kojeg su zabilježene digitalne slike promatrane zone interesa tijekom mehaničkog ispitivanja. Registrirane slike korištene su za detaljnu analizu cijelog polja pomaka primjenom globalnog stereo korelacijskog algoritma EikoTwin. Validacija eksperimentalnog postava provedena je na tri leptirasta ispitna uzorka kod kojih je narinuto monotono smično opterećenje. Navedena statička ispitivanja razlikovala su se s obzirom na konfiguraciju eksperimentalnog postava koja je ovisila o preddefiniranoj krutosti Arcan prihvata te dodatnoj potpori promatrane zone interesa koja ne dozvoljava izvijanje ispitnog uzorka. Analizom rezultata pokazano je kako je neophodno smanjiti krutost Arcan prihvata i postaviti dodatnu potporu s ciljem sprječavanja izvan ravninskih pomaka koji uzrokuju fenomen izvijanja kod tankih limova. Osim toga, provedeno je dodatno cikličko ispitivanje s ciljem potvrđivanja unaprijeđenog eksperimentalnog postava za mehanička ispitivanje tankih limova. |
| Abstract (english) | Determination of the mechanical parameters of the material at the shear loading regime is of great importance for the manufacturing industries where metal forming technology is applied. Increasing application of the numerical methods for modelling and optimizing final products, demands more reliable material parameters in order to describe the elastoplastic behavior of metal materials in a more predictable way. The existing experimental methods considering in-plane pure and simple shear loading on thin sheets are constantly improved in order to improve the reduction of the out-of-plane displacements in the region of interest. The reported out-of-plane displacements are degrading the realistic response of the material. The most commonly used fixtures for the shear test methods are conducted with Iosipescu and Arcan rigs on the butterfly-shaped samples. The geometry of the proposed test specimens is a plate/sheet with two symmetrical V-notches whose purpose is to ensure a homogenous shear state. The deformation measurement during the mechanical test cannot be carried out by the application of the classical extensometers. The measuring gauges can be mounted on the assumed critical locations of the test sample. With the development of the optical measurement methods, the observation of the full-field displacement maps are enabled. Furthermore, with the proposed methods it is possible to identify the material response in the zone of interest. The most commonly used optical measurement method in experimental mechanics is Digital Image Correlation (DIC). The full-field measurement can be resorted by local and global DIC approaches. Within this master thesis, a global stereo digital image correlation approach is applied, whose calibration is based on the previously known (i.e., defined) geometry (i.e., CAD model) of the experimental setup. In this work, four shear experiments were carried out using a modified Arcan fixture on the uniaxial electro-mechanical testing device Beta 50-5 (Messphysik, Austria). Mechanical tests were carried out on the 1 mm thick butterfly test specimens made of C60 steel. During the experimental investigation, the optical measurement system Aramis was used to record the series of digital images of the observed region of interest during the change of mechanical loading. Registered images were used for detailed analysis of the full displacement fields using the global stereo correlation algorithm EikoTwin. The validation of the experimental setup was carried out on three butterfly test samples in which a monotone shear loading was applied. These static tests are conducted with differentDetermination of the mechanical parameters of the material at the shear loading regime is of great importance for the manufacturing industries where metal forming technology is applied. Increasing application of the numerical methods for modelling and optimizing final products, demands more reliable material parameters in order to describe the elastoplastic behavior of metal materials in a more predictable way. The existing experimental methods considering in-plane pure and simple shear loading on thin sheets are constantly improved in order to improve the reduction of the out-of-plane displacements in the region of interest. The reported out-of-plane displacements are degrading the realistic response of the material. The most commonly used fixtures for the shear test methods are conducted with Iosipescu and Arcan rigs on the butterfly-shaped samples. The geometry of the proposed test specimens is a plate/sheet with two symmetrical V-notches whose purpose is to ensure a homogenous shear state. The deformation measurement during the mechanical test cannot be carried out by the application of the classical extensometers. The measuring gauges can be mounted on the assumed critical locations of the test sample. With the development of the optical measurement methods, the observation of the full-field displacement maps are enabled. Furthermore, with the proposed methods it is possible to identify the material response in the zone of interest. The most commonly used optical measurement method in experimental mechanics is Digital Image Correlation (DIC). The full-field measurement can be resorted by local and global DIC approaches. Within this master thesis, a global stereo digital image correlation approach is applied, whose calibration is based on the previously known (i.e., defined) geometry (i.e., CAD model) of the experimental setup. In this work, four shear experiments were carried out using a modified Arcan fixture on the uniaxial electro-mechanical testing device Beta 50-5 (Messphysik, Austria). Mechanical tests were carried out on the 1 mm thick butterfly test specimens made of C60 steel. During the experimental investigation, the optical measurement system Aramis was used to record the series of digital images of the observed region of interest during the change of mechanical loading. Registered images were used for detailed analysis of the full displacement fields using the global stereo correlation algorithm EikoTwin. The validation of the experimental setup was carried out on three butterfly test samples in which a monotone shear loading was applied. These static tests are conducted with different configurations of the experimental setup. The setup configurations differ by the predefined installation stiffness of the Arcan rig and the application of the additional support of the zone of interest. The novel support does not allow the buckling of the test sample. Hence, the analysis of the measured displacement and strain fields showed that it is necessary to reduce the stiffness of the Arcan rig and testing device connection. Moreover, the additional support prevents the out-of-plane displacements which cause the buckling phenomena on thin sheets. In addition, a cyclic mechanical test was performed to verify the upgraded experimental setup for mechanical testing of the metal thin sheets.configurations of the experimental setup. The setup configurations differ by the predefined installation stiffness of the Arcan rig and the application of the additional support of the zone of interest. The novel support does not allow the buckling of the test sample. Hence, the analysis of the measured displacement and strain fields showed that it is necessary to reduce the stiffness of the Arcan rig and testing device connection. Moreover, the additional support prevents the out-of-plane displacements which cause the buckling phenomena on thin sheets. In addition, a cyclic mechanical test was performed to verify the upgraded experimental setup for mechanical testing of the metal thin sheets. |
