The problem of crack propagation in viscoelastic materials is of great interest given the numerous engineering applications of such materials. Due to viscoelasticity, even the study of the basic Mode I opening represents a tricky theoretical challenge. Indeed, existing theories adopt important approximations such as i) simplistic constitutive behaviour, ii) steady-state crack propagation, iii) infinite domain of the system. In this work, we revise the theory of Persson & Brener for systems of infinite domain; specifically, we propose a solution to take into account size effects in a viscoelastic plate. The theory allows to consider the realistic constitutive behaviour of viscoelastic materials and to predict the dependence of the energy release rate with the crack tip speed. Comprehensive experimental investigations are performed to corroborate our theoretical predictions. First, dynamic mechanical analysis (DMA) is performed to characterize the complex viscoelastic modulus of PolyTetraFluoroEthylene (PTFE). Second, tensile tests are carried out on cracked PTFE samples, and pictures are recorded with an image acquisition system. Moreover, a point tracking algorithm is developed to measure the crack length and opening displacement. Moving from small to high crack tip speeds, the fracture process becomes less ductile and an increase in the maximum load is observed. In addition, experimental data show that the inclusion of finite-size effects in the theory is crucial for accurately estimating the energy release rate.

A model is presented that predicts the amount and location of oxide inclusions in steel castings. A number and size distribution of inclusions, defined about a mean diameter, enters the casting system at its inlet during the filling process and are transported to their final locations in the casting. Model parameters for inclusion density, drag and wall friction are used to calculate the motion and locations of the oxide particles. Model results are presented to study the effects of casting shape and surface orientation on the final inclusion locations and distributions within castings. These results are compared with inclusion tracking experiments where the geometry of the gating system and orientation of casting cope surfaces affect the final distribution of inclusions in the castings. Measured and simulated inclusion area percent coverage, inclusion count and mean diameter are compared for a range of modelling parameters and inclusion size distributions. The size and number distribution at the casting system inlet, and other model parameters, are determined which provide the best agreement between measured and simulated inclusion area, count, and size.

The analysis, characterization, and comparison of modern and ancient mortars provide fundamental (by tracing the change in the raw materials and recipes used from the past to the present) and practical (obtaining modern mortars compatible with the ancient) knowledge. This work aimed to characterize modern and ancient mortars by investigating their phase composition, binder-to-aggregate ratio, hydraulicity, and hygroscopic properties. The used methods for analyses were powder X-ray diffraction, Fourier transforms infrared spectroscopy, and thermal analysis. A modern mortar (sample A) preparation was with a binder of white Portland cement and an aggregate of river sand. Ancient mortar samples (sample B - cocciopesto and sample C - lime mortar) collection were from Bulgarian archaeological sites allocated within the Roman period. The results define investigated sample A as pozzolanic mortar with hygroscopic properties, sample B - as hydraulic lime mortar with hygroscopic properties, and sample C – as lime mortar without any hygroscopic properties. Obtained results with these, achieved for phase composition and binder-to-aggregate ratio, show that modern mortar is not compatible with the Romans and is not suitable for reconstruction and conservation of masonry from these archaeological sites.

Recently, interest has shifted towards developing multijunction or tandem solar cells due to their high potential to generate higher efficiency than traditional single-junction solar cells. Cadmium telluride (CdTe) and silicon (Si) solar cell materials have demonstrated significant potential in photovoltaic energy generation as tandem structures if fully developed. One approach for optimising CdTe/Si is to develop an effective tunnel junction that can electrically and optically interconnect the cadmium telluride and silicon cells with minimal loss. The wxAMPS 3.0 numerical simulation was used in this work to develop CdTe/Si tandem using zinc telluride/aluminium doped zinc oxide (ZnTe/AZO) as a tunnel junction (TJ). The result obtained shows an optimum efficiency of over 36 % with Voc = 1.945 V, Jsc = 21.519 mA/cm², and FF = 86.823 % utilising the optimal 200 nm CdTe and Si absorber thickness of 300 μm. An analysis of the demonstrated results suggests that ZnTe/AZO tunnel junction will significantly contribute to the realisation of the CdTe/Si tandem solar cell. Hence, upon inserting a 40 nm highly doped ZnTe/AZO tunnelling junction to a CdTe/Si tandem configuration, the solar cell's performance was enhanced by 48.190%.

In the search of an adequate real time strain measurement method in aluminum casting, the use of Fiber-Bragg-Grating ( FBG ) is being investigated with great interest. In order to do so, the behaviour of glass fiber sensors in a liquid aluminium alloy at temperatures up to 750°C is experimentally analysed in a laboratory environment. For better process understanding a simulation of the fiber alloy composite is conducted. FBG is an optical measurement method, which uses engraved Bragg reflectors in a 125 µm in diameter thick glass fiber. This reflector transmits most of the wavelengths but only reflects one specific wavelength. This specific wavelength can be measured and changes due to the axial strain on the grating by the fluid alloy reaction and by the changes in temperature. Using a so-called mirror furnace, several experiments with the fiber alloy composite are evaluated. These measurements are also the basis for the further understanding of hot tearing. The data gathered during the measurement campaign - both numerical and experimental - is used to parameterize a simulation. As a result, the understanding of the fiber alloy composite behaviour is expanded and a digital twin is modeled with MATLAB's partial differential equation toolbox.

Transport pneumatic systems (TPS) are widely used in various branches of industries. The transportation of crushed material in such systems is carried out due to the air flow. In the woodworking industry, there are technological processes that are often accompanied by the formation of dust and other small air pollutants. Studying the movement of particles in polluted air makes it possible to transport or separate such particles, while spending less energy. In this paper, the mathematical model of the movement of dusty air containing separate solid particles (production waste) was worked out, and based on it, solution will allow to separate and capture crushed wood particles and to reduce the cost of consumed electricity for transportation is proposed.