Aluminium high pressure die-castings have become essential elements of a modern carbody in recent years. The high pressure die-casting method enables to produce thinwalledcomponents of complex geometries. This advantage is used to create structuralnodes and connector elements as one-piece components. These components are subjectedto extreme loads such as in crash situations and expected to maintain the structuralintegrity of the car body. Numerical models are required to analyse the structural behaviourof aluminium high pressure die-casting components and to guarantee their structuralreliability.The material ductility in aluminium high pressure die-casting components is stronglyinfluenced by casting defects. Typical casting defects are shrinkage pores, gas pores andoxide films. These casting defects are caused by the casting system and fluctuations duringthe casting process. As a result, the casting defects are varying within a component.Moreover, the variation can be separated into a global systematic variation depending onthe casting system and a local pseudo-random variation caused by the process fluctuations.A casting defect can be considered as initial material damage which leads to a decreaseof the local material ductility. As a result, the material ductility exhibits a global systematicvariation and a local pseudo-random variation. The main objective of the presentwork is the experimental and numerical analysis of these two types of variation.The main objective of the experimental work was the investigation of the global systematicvariation and the local pseudo-random variation in the material ductility of analuminium HPDC alloy. Here, a generic high pressure die-casting component made ofan AlSi9Mn alloy in casting condition was considered. An extensive material characterisationwas performed using uniaxial tensile tests. The specimens were machined fromdifferent extraction positions as well as from duplicated extraction positions of the genericcasting component. Through this sampling approach, it was possible to analyse thesystematic variation as well as the local pseudo-random variation in the material ductility.The mechanical analysis of the tensile test results showed a reproducible strain hardeningbehaviour in duplicated extraction positions, but the failure strain varied between differentextraction positions and within duplicated positions. A detailed statistical analysis wasperformed on the tensile test results and hypothesis tests were applied to identify extractionpositions with comparable material ductility. Based on the results obtained from thehypothesis tests, it was concluded that the generic casting component can be separatedinto characteristic parts of comparable material ductility. Moreover, it was shown that thelocal pseudo-random variation of the material ductility can be described by a weakestlinkWeibull distribution. In addition, the fracture surfaces of selected specimens wereexamined by a SEM analysis and, as expected, casting defects were found on each fracturesurface and identified as the dominating factor for fracture. Besides material testing,bending tests and axial compression testswere carried out on the generic casting component.Especially, the experimental results obtained from the bending tests exhibited strong scatter. According to the results obtained from material testing, it was concluded that thestrong scatter is caused by the global systematic variation and the local pseudo-randomvariation in the material ductility.As a result, a probabilistic approach in failure modelling was considered in the numericalwork. Hence, it was possible to capture the local pseudo-random variation in thematerial ductility. The probabilistic failure model was based on the phenomenologicalCockcroft-Latham failure criterion and the weakest-link model by Weibull. The requiredquantities stress state and equivalent plastic strain were given by an isotropic hypoelasticplasticconstitutive model. The focus was put on the numerical prediction of the failureprobability of casting components. Usually, the failure probability is estimated froma Monte-Carlo simulation based on various finite element simulations using a pseudorandomlydistributed critical failure value. In the present work, an approach was presentedto predict the failure probability from a single finite element simulation. Both approacheswere compared in numerical analysis and it was shown that both approacheslead to the same prediction of the failure probability. The approach based on the directcomputation of the failure probability was applied in finite element simulations of thebending test and the axial compression test of the generic casting component. Accordingto the material characterisation, the FE model of the generic casting component waspartitioned into three parts. For each part the parameters of the constitutive model andthe probabilistic failure modelwere found from the corresponding experimental results. Itwas demonstrated that the numerically predicted failure probability and the experimentallyestimated failure probability are verywell correlated in both load cases. Consequently,the applied probabilistic failure model was considered as validated. Moreover, a novel approachfor the pseudo-random distribution of a critical failure value was presented andthe concept of the uncoupled modelling approach was introduced. Due the uncoupledmodelling approach, it was possible to perform mesh convergence studies on finite elementmodels using a pseudo-randomly distributed critical failure value. However, theprobabilistic failure model captured only the local pseudo-random variation in the materialductility. Hence, a through-process modelling approach was presented based on acasting simulation result and the definition of casting qualities. This approach was onlynumerically investigated.
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