Complex machine parts are characterized by different shapes, material characteristics and working loads. The simultaneous theoretical optimization of shape and material properties is difficult because the single objective functional with a unique physical interpretation is unknown for these two features. The optimization is the multi-criteria procedure or the functional is a weighted average of partial criteria with the assumed weight values. Therefore, the structure and material characteristics are optimized numerically. The main goal of the article was to model and optimize the stress distribution inside the composite plates subjected to complex load. The advanced material composition was made of four different materials: steel, ductile iron, E-glass fibers and carbon fibers. The stress distributions were optimized for the homogeneous plate, the sandwich composite made of metal and textile layers, and the plate with additional stiffening elements (ribs and another plate along the neck portion). Based on the numerical simulations, the optimal structural shapes and material arrangements were determined.

The combination of kinematic and isotropic hardening models makes it possible to model the behaviour of cyclic elastic-plastic steel material, though the estimation of the hardening parameters and catching the influence of those parameters on the material response is a challenging task. In the current work, an approach for the numerical simulation of the low-cycle fatigue of AISI316L steel is presented using a finite element method to study the fatigue behaviour of the steel at different strain amplitudes and operating temperatures. Fully reversed uniaxial LCF tests are performed at different strain amplitudes and operating temperatures. Based on the LCF test experimental results, the non-linear isotropic and kinematic hardening parameters are estimated for numerical simulation. On comparing, the numerical simulation results were in very good agreement with those of the experimental ones. This presented method for the numerical simulation of the low-cycle fatigue on AISI316 stainless steel can be used for the approximate prediction of the fatigue life of the components under different cyclic loading amplitudes.

The integrity of the nuclear power plants components has to be guaranteed under operation and emergency conditions. It is necessary to evaluate all possible degradation mechanisms that could impact the structural integrity of the nuclear power plant structures such as pipelines and other components of the cooling systems. One of the dangers degradation mechanisms is the environmental fatigue which has a significant influence on the lifetime of various steel components operating in water. Exploring of non-codified methods for more precise assessment of fatigue phenomena can pave the way for the development of safer nuclear power plants with longer operational lifetimes. This is very important as the global demand for cleaner energy is increasing. This research study deals with numerical investigation of the low cycle fatigue behavior of the steel used for those nuclear reactor components where environmental fatigue plays a major role. The numerical simulation methodology is proposed to study the dependency of the kinematic hardening parameter on the strain amplitude to investigate the low cycle fatigue behaviour of AISI304L steel for the prediction of the fatigue curves that can be used for the estimation of the nuclear power plant safety and its lifetime.The experimental data was used to estimate the parameters required to define the material model for the numerical simulation and to validate the results of numerical simulation of the low cycle fatigue behaviour. The presented methodology can be used for fully reversed constant-amplitude strain loading low cycle fatigue simulations for various strain ranges to predict the low-cycle fatigue behavior of steel under repetitive loading.