Research - Summary

The application of complex materials with enhanced properties that achieve high efficiency at acceptable cost is a key issue in developing modern structures and machine components. In mechanical power transmissions of today, the powder metallurgy (PM) technology has shown considerable advantages over the conventional metallurgy due to relatively low manufacturing costs, environmental friendliness, a high utilization rate of material and a good noise reduction in exploitation. Here, sintered gears, which might become key components of mechanical power transmission in future machines, are considered. The gear load bearing capacity is limited by different kinds of ageing mechanisms, such as the bending fatigue in tooth root or pitting at teeth flank. In the sintered steel, interconnected pores cause strain localizations between particles, while isolated porosity induces overall deformations. To accurately predict a failure during the ageing process due to the fatigue, a detailed numerical analysis incorporating damage at the microstructural level is of great importance, which still represents a challenge in scientific community, with many unanswered questions.

The overall objective of the MultiSintAge project is the development of a computational framework for modelling ageing degradation of sintered materials and structures subjected to fatigue loading conditions. In the first phase of the research, a series of experimental studies to examine the influence of microstructure on the mechanical behaviour of powder metal used in the production of sintered gears will be conducted. The topology of the sintered material at the microlevel will be obtained from a comprehensive metallographic analysis, while nanoindentation tests will be carried out to determine the material properties of the matrix material. Based on the metallography and mechanical characterization, the Representative Volume Element (RVE) of the sintered material will be determined. The use of the RVE will enable the development of original multiscale micro-to-macro approaches for modelling the quasi-static and fatigue behaviour of a sintered material by a homogenization procedure.

In the next research phase, the influence of densification depth on the pitting of sintered mechanical components subjected to rolling and sliding fatigue contact conditions will be investigated. Here, the pitting phenomena will be experimentally studied on densified rollers by means of the Rolling Contact Fatigue (RCF) tests. Another key objective includes the development of micro-level numerical models for pitting, as well as the homogenization-based numerical approach for the modelling at the macro-structural level. Numerical homogenization procedures and models will be implemented into the FEA software ABAQUS by means of user subroutines. The homogenization-based numerical approach will be validated by comparison to the results obtained by RCF test and the Direct Numerical Simulation (DNS) analysis. This will prove the applicability of the developed homogenization procedures in engineering calculations, because this approach should be computational less expensive than the DNS model, while maintaining acceptable accuracy. After the examination of the experimental and numerical setup on a simple roller, the derived approach will be applied and validated on a more complex densified sintered gear. Herein, the tooth bending fatigue tests of densified sintered gears will be carried out on a Single Tooth Bending Fatigue test rig. In addition, the pitting and bending fatigue tests of densified sintered gears will be carried out on a closed mechanical power loop gear device. In the contrast to the existing numerical approaches for analysing structural integrity of sintered gears and other structural components, in the developed numerical methods the material properties of a sintered material at the macro-level will be obtained by means of material modelling at the microstructural level, whereby appropriate nonlocal numerical models and homogenization procedures will be proposed.

In further research, the developed numerical methods might be used for designing new sintered or porous materials with desired microstructure having enhanced properties. This could considerably contribute to achieving a long-desired goal of producing sintered structural components with a prolonged structural lifetime intended for withstanding heavy loads.