Different approaches towards numerical modelling of bolt bearing

Magistrsko delo obravnava postopke za numerične simulacije pritiska vijaka na pločevine v vijačenih spojih do trenutka porušitve. Pritisk vijakov v območju kontakta s pločevinami rezultira v velikih plastičnih deformacijah, te pa lahko vodijo v porušitev materiala. Modeliranje obnašanja tega območja ni trivialno, zato smo predstavili možnost uporabe naprednih materialnih modelov, ki jih ponuja Abaqus, komercialni program za numerično modeliranje. Opisan problem nosilnosti vijaka v vijačenih spojih smo analizirali s statično, eksplicitno in povezano Euler-Lagrange analizo. Model porušitve materiala sloni na principu akumuliranja škode in zmanjševanja togosti končnih elementov do točke, ko ne nudijo več nobene odpornosti in so odstranjeni iz modela, ali pa ostanejo na svojem mestu z zanemarljivo majhno togostjo. Opisan model je odvisen od odnosa med razmerjem napetosti (hidrostatičnim delom napetostnega tenzorja in Von Mises napetostjo), plastično deformacijo in plastičnim pomikom do porušitve. Omenjene parametre smo ocenili s pomočjo eksperimentalnih testov. Simulirali smo več različnih vijačenih spojev z dvema različnima materialoma. Materialni model smo definirali na podlagi testov z različnimi porušitvami in rezultate analiz nato primerjali s preostalimi eksperimentalnimi testi. Preučili smo tudi možnosti in prednosti uporabe modela z Eulerjevo mrežo končnih elementov, saj je pri klasičnih modelih lahko simuliranje kontakta v območju velikih plastičnih deformacij problematično. Povezana Euler-Lagrange analiza kombinira oba pristopa tako, da za telesa, pri katerih pričakujemo velike deformacije, uporabimo Eulerjev pristop, pri ostalih pa konvencionalen Lagrangejev. Primerjali smo različne materialne modele, tipe končnih elementov, časovne korake in modele optimizirali za čim boljše rezultate in hitrosti analize.This thesis focuses on the procedures for numerical analysis that allow numerical modelling of bolt bearing up to fracture. Bolt bearing is characterized by large plastic deformations that occur mainly near the contact between bolts and plates and may possibly lead to fracture. Numerical modelling of such behaviour is not trivial. The commercially available software Abaqus was used for this purpose, taking the advantages of built-in material models and numerical procedures without introducing the user subroutines. The problem of bolt bearing is assessed using static stress analysis, explicit analysis and coupled Eulerian-Lagrange analysis. The fracture model considered is based on stress modified fracture model and relies on the accumulating damage and on the reducing stiffness of finite elements to the point, where they offer no resistance and can be either removed from the model or are left with negligible stiffness. The required parameters (stress triaxiality, equivalent plastic strain to failure and displacement to failure) were determined from the experimental data. A few different bolted connections with different types of failure are analysed with full failure model and the results are compared with experiments. The advantage of Eulerian meshing is considered where excessive plastic deformations lead to contact problems. Coupled Eulerian-Lagrange analysis with model parts expected to have large deformations were modelled with Eulerian approach and the rest with more conventional Lagrange approach. Diverse material models, element options, time step and their impact on numerical simulation were compared and optimized for speed and accuracy