This master thesis is written in an act of cooperation between the Institute of Mechanics from the Montanuniversität Leoben and Hoerbiger GmbH. The aim of this master thesis is to create a finite element model using a python script to determine the maximum possible clearance between cylinder and piston of double acting piston compressors. On the one hand, decreasing clearance leads to decreasing stresses, strains and deformations in the cylinder ring, on the other hand, the wear between piston and cylinder increases. A large clearance leads to less wear between piston and the cylinder, but result in an increase of stresses, strains and deformations of the cylinder ring. This thesis uses a linear elastic material model to check how well the results of an axisymmetric model match those of a three dimensional model. Since all results are in a comparable range, thus only the axisymmetrical model is included in the following sections. Using the material data of Hoerbiger, a viscoelastic material model, which accounts for time, temperature, load as well as load rate dependency is developed. Linear viscoelastic parameters are functions of temperature and time. A non-linear viscoelastic material model also takes the influence of the non-linear relationship between stresses and strains at higher stress values into account. This is not considered in the linear viscoelastico-elastic material model. However, since polymeric materials have a very small linear elastic range or linear viscoelastic range, a non-linear viscoelastic model appears to be the best choice for further investigations. In the third part of this master thesis, a parameter study is carried out to determine the influence of temperature, time, pressure, load rate and geometry on the deformation behaviour of the cylinder rings. It also includes the creep strain of the material. The final section deals with finding a suitable criterion to determine the maximum possible clearance between cylinder wall and piston. The creep strains that occur are small and therefore not decisive for failure. In the case of the cylinder rings a classical fatigue strength problem is to be dealt with. The permissible cylinder ring protrusion is assessed in analogy to the FKM guideline with the help of degrees of utilisation. The stresses are evaluated at the critical point. The maximum mean stress and stress amplitude that occur during a load cycle are taken from the FE results. The cylinder ring protrusion is varied until the maximum degree of utilisation is reached. This is repeated for other load levels. Since no fatigue strength data is available for the material used, the fatigue strength data and the fatigue strength curves are approximated using estimation formulas. This also includes the further evaluations. The results show that the permissible cylinder ring protrusion can be significantly increased depending on the pressure difference without reaching the maximum allowable degree of utilisation.
|Translated title of the contribution||Finite Elemente Analyse zur Optimierung kunststoffbasierter Zylinderringe reziprokierender Kolbenkompressoren|
|Award date||21 Oct 2022|
|Publication status||Published - 2022|
Bibliographical noteno embargo
- Cylinder rings
- creep behaviour
- fatigue strength