Lebensdauerbewertung von Mikroporen in Aluminiumgussbauteilen auf Basis lokaler Beanspruchungsanalysen

Translated title of the contribution: Fatigue assessment of micropores in cast aluminium structures based on local stress and strain analysis

Wolfgang Schneller

Research output: ThesisMaster's Thesis


The industrial importance of aluminium is based on its lightweight engineering potential, especially within the manufacturing process of automotive components. Modern casting processes feature the economic design of complexly shaped components. The inherent properties of such castings possess are strongly linked to the manufacturing process and affect their mechanical properties. Thus, it is of utmost technological relevance to assess the effect of these microstructural properties such as mircopores or gas shrinkage cavities. This master thesis focuses on the effects of the aforementioned inherent microstructural casting properties concerning the fatigue strength of aluminium components. The fatigue assessment bases on a local finite element numerical analysis and facilitates further an elaborated method to calculate the fatigue strength analytically. In order to detect pores within a test specimen, a computer tomography scan needs to be carried out first. Subsequently, the shape and position of internal microstructural defects such as shrinkage or gas pores can be determined thus generating a voxel cloud. Originating from this point data, a surface is derived and a spatial simulation applicable model of the pore, embedded in an aluminium matrix, is created. Tensile tests were carried out to provide material-specific stress-strain curves to support the set-up of an elastic-plastic simulation. The presented methodology for evaluating the effect of micropores regarding fatigue strength enables the assessment of fatigue life based on the elasto-plastic notch stress and strain values. A fatigue test with variable amplitude loading and a successive metallographic analysis of the fracture surface using electron microscopy scanning evaluates the crack propagation rate. In addition, the ratio of crack initiation to crack growth is determined. The experimentally obtained service strength is in accordance with the results of an analytical comparative fatigue life calculation. Finally, the effect of the position of microporosities on the stress intensity and –concentration factor is studied. A Monte-Carlo simulation enables a statistical judgement of the local stress intensity factor for varying pore geometry based on the proposed numerical tools. The results show a characteristic behaviour dependent on the defects distance to the surface as well as the pores equivalent circle diameter. The stress intensity increases with a decreasing ratio of surface distance to effective pore diameter. Summing up, the presented findings contribute to an improved local fatigue assessment of cast aluminium structures, which supports further optimization of lightweight components in respect to manufacturing and application-oriented dimensioning.
Translated title of the contributionFatigue assessment of micropores in cast aluminium structures based on local stress and strain analysis
Original languageGerman
Awarding Institution
  • Montanuniversität
  • Leitner, Martin, Co-Supervisor (internal)
  • Stoschka, Michael, Supervisor (internal)
  • Aigner, Roman, Co-Supervisor (internal)
Award date23 Mar 2018
Publication statusPublished - 2018

Bibliographical note

embargoed until 13-02-2023


  • fatigue assessment
  • micropores
  • numerical analysis
  • cast aluminium
  • stress intensity factor

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