Eigenspannungsstabilität von Ti-6Al-4V Strukturkomponenten

Translated title of the contribution: Residual stress stability of Ti-6Al-4V structural components

Aleksandar Stanojevic

Research output: ThesisDoctoral Thesis


In the aircraft industry, the alloy Ti-6Al-4V is often used for structural parts due to its low density, high specific strength and fatigue limit, as well as excellent corrosion properties. In this context, the components must be designed to be as weight-optimized as possible while still meeting the high safety requirements. Mechanical surface treatment can improve the properties of the components through by inducing residual stresses and hardening the the surface, thus also improving the lightweight design aspect. Since residual stresses can relax as a result of service loads and components thus continuously lose the positive effects of surface treatment during the service life, knowledge about residual stress stability is essential. For this, the precise characterization of the residual stress and strain hardening state as well as its behavior as a result of thermal and mechanical loading is important. In this thesis, four surface states for the material Ti-6Al-4V were characterized by X-ray diffraction (XRD). To determine the depth and value of hardening, a method was developed which allows the iso-kinematic material parameters to be calculated directly from the XRD measurement signal. This forms the basis for the subsequent calculation of the residual stress stability. Thermal residual stress stability was investigated by ageing tests and downstream XRD measurements. The tests show stable residual stresses up to 200°C and strong relaxation in the temperature range of 370°C.To describe these processes, a constitutive model was developed to calculate the thermal residual stress stability based on the creep properties of the material. For this purpose, a creep model for the low-temperature range of Ti-6Al-4V was developed and parameterized by appropriate creep tests. The cyclic residual stress stability was determined by cyclic tests followed by XRD measurements. The tests show a complex dependence of the residual stress on the test parameters and the initial residual stress state. Most noticeable is the uniform relaxation of the residual stress at high mean stresses, as well as the abrupt relaxation at high stress amplitudes. The interaction between local loading condition and local material behavior determines the relaxation of the residual stress. The cyclic stability of the residual stresses is therefore calculated by a constitutive model, which determines the incremental residual stress relaxation by the inelastic increment of the local strain. The effect of a stable residual stress on the fatigue limit was determined by combining the residual stress relaxation model with further cyclic tests. At lower temperatures, it is clear that the fatigue limit can be improved by a factor of 50 due to residual stresses. The crack forms prematurely below the surface, which reduces the fatigue strength but has a positive effect on the fatigue limit. At higher temperatures, surfaces with high initial residual stresses exhibit lower fatigue limits than states with low residual stresses due to the faster residual stress relaxation. Thus, residual stresses cannot generally be recommended to increase the lightweight aspect, since overheating or overloads very quickly decrease the residual stresses. However, if it can be ensured that components made of Ti-6-4 are not heated above 200°C as well as have mean stresses below 700MPa, an increase in stress amplitude of 35% can be realized while maintaining the same service life. Finally, the developed models allow the representation of the surface condition as a digital twin along the value chain for the final component.
Translated title of the contributionResidual stress stability of Ti-6Al-4V structural components
Original languageGerman
Awarding Institution
  • Montanuniversität
  • Leitner, Martin, Assessor B (external)
  • Grün, Florian, Assessor A (internal)
Publication statusPublished - 2021

Bibliographical note

embargoed until null


  • Ti-6Al-4V structural components for aerospace
  • thermal-mechanical
  • cyclic residual stress stability
  • initial condition of residual stress and hardening state
  • residual stress measurement by x-ray diffraction
  • shot peening simulation
  • elasto-visco-plastic
  • local deformation behavior
  • low temperature creep
  • damage-based softening
  • residual stress sensitive fatigue limit

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