Einfluss der Porosität auf die Betriebsfestigkeit von Al-Druckgussbauteilen

Translated title of the contribution: Influence of Porosity on the Fatigue Strength of High Pressure Die Cast Aluminium Components

Dawid Pawel Powazka

Research output: ThesisDoctoral Thesis

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Abstract

A possible way to achieve weight optimisation is by using light aluminium alloy castings. Typical examples of the functioning application of such materials are parts of the car body and chassis. Further advantages are low partial costs due to mass manufacture and production of complicated structures in only one working cut. However, to achieve the optimum layout of aluminium parts is difficult, because the fatigue strength of the casting components is very sensitive to the casting inclusions. The most common and dangerous inclusions are pores and blowholes. They influence the fatigue life very strongly and lead to unpredictable failure of the components. The material inhomogeneities are systematically diversified to evaluate their influence on the fatigue life of component. However the porosity evaluation in cast components is lately only statistically realizable, because an accurate prediction of pore location, topology and size in aluminium component is not possible. Microfocus computer tomography investigations render an estimation of characteristic variables of the pores topology. It delivers a precise three dimensional identification of individual pores as wells as a global evaluation of aggregate porosity. Based on these analyses, the influence of the pores on the local loading condition is investigated through FEM calculations. In these calculations different kinds of pores are taken into consideration, varying from ideal spherical shape to the real three-dimensional pore geometry extracted from computer tomography investigations. Examinations shows, that the local strain increase because of the pores. The concentration of strain depends on the size, form and location of the single pore as well as the relative location of the pores. The stress concentration factor is therefore much larger then the globally accepted form factor Kt,p=2,05 generated through ideal spherical pore. With this knowledge a porosity conditional form factor Kt,Pore is developed as a function of the degree of the porosity. Afterwards on the basis on this form factor and using the S/N curve of reference specimen with known degree of porosity a calculation model is generated which allows the assessment of the fatigue strength of Aluminium-Alloys with any arbitrary porosity. This derived calculation algorithm is finally verified on the basis of several aluminium alloys. The fatigue life calculation with consideration of the local porosity is carried out on the series-production high pressure die cast component, delivering an accurate prediction of the fatigue life.
Translated title of the contributionInfluence of Porosity on the Fatigue Strength of High Pressure Die Cast Aluminium Components
Original languageGerman
QualificationDr.mont.
Supervisors/Advisors
  • Eichlseder, Wilfried, Assessor A (internal)
  • Kaleta, Jerzy, Assessor B (external), External person
Publication statusPublished - 2009

Bibliographical note

embargoed until null

Keywords

  • Casting Defects Mechanical Properties Computed Tomography (CT) FEA

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