Modeling of Spot Weld with Failure for Crash Simulations

Examensarbete för masterexamen
Master Thesis
Automotive engineering (MPAUT), MSc
Rajalakshmi, Adhinathan Srinivasan
Shafiq, Tishko
With increasing number of vehicles around the globe, one of the current focus of automotive industry has been vehicle safety. Modern technical advancements in computation field has led to extensive improvements in crash simulation. Spot welds, despite being relatively small in size, contributes hugely to vehicle safety as they hold vehicle body together. The behaviour of spot welds during crash play a vital role and thus, appropriate modelling of spot weld and prediction of failure is essential. Alongside accurate prediction of failure, an added necessity is to save computational time. The project is carried out in partnership with CEVT AB, where MF GenYld + CrachFEM material model (reference model) is utilised to predict failure of spot weld. The scope of the project is development of a model that reduces computational time, yet achieving results of reference model. In this project, two approaches are dealt with for achieving the aforementioned objective. Three coupon tests (peel, lap shear and u-tension) are taken as standard test to validate the developed models. One of the approaches is developing a model that represents spot weld as beams. The results for the 5-beam, 8-beam, 9-beam method were varying. The stiffness curve (force-displacement curve) of the model matched reference stiffness curve either for shear or the other two tests. There were no results obtained where the stiffness curve would match for all three coupon tests. No advantageous change in computation time was observed, but carrying an advantage of no added mass to the model. Another approach is modification of the material card to suit the reference model. The material model considered is General Incremental Stress-State dependent Damage Model (GISSMO). The GISSMO material card was developed by another master thesis project and suitability of the model to spot welds is investigated in this project. The approach provided promising results, where the resulting stiffness curve closely represented reference model and also, significant decrease in computational time. The reference model reproduces damage model on the heat affected zone (HAZ) but not on the actual spot weld. Modelling with beams are valid only when beams represent the reference mesh pattern. The GISSMO model represents reference model closely and it can be used in early modelling stages to save computational time.
Materialvetenskap , Transport , Innovation och entreprenörskap (nyttiggörande) , Annan materialteknik , Materials Science , Transport , Innovation & Entrepreneurship , Other Materials Engineering
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