The paper presents the assessment of the possibility and reliability of the digital image correlation (DIC) system for engineering and scientific purposes. The studies were performed with the use of samples made of the three different materials—mild S235JR + N steel, microalloyed fine‑grain S355MC steel, and high strength 41Cr4 steel subjected to different heat‑treatment. The DIC studies were focused on determinations of dangerous zones with large stress concentrations, plastic deformation growth, and prediction of the failure zone. Experimental tests were carried out for samples with different notches (circular, square, and triangular openings). With the use of the DIC system and microstructure analyses, the influence of different factors (laser cutting, heat treatment, material type, notch shape, and manufacturing quality) on the material behavior were studied. For all studied cases, the stress concentration factors (SCF) were estimated with the use of the analytical formulation and the finite element analysis. It was observed that the theoretical models for calculations of the influence of the typical notches may result in not proper values of SCFs. Finally, the selected results of the total strain distributions were compared with FEM results, and good agreement was observed. All these allow the authors to conclude that the application of DIC with a common digital camera can be effectively applied for the analysis of the evolution of plastic zones and the damage detection for mild high‑strength steels, as well as those normalized and quenched and tempered at higher temperatures.
The presented study is related to the application of the composite overlays used in order to decrease the effect of the stress concentrations around the cut-outs in structural metal elements. The proposed approach with the application of the digital image correlation extends the recently presented studies. Such structural elements with openings of various shapes have been accommodated for a wide range of industrial applications. These structures exhibit certain stress concentrations which decrease their durability and strength. To restore their strength, various reinforcing overlays can be used. In the present paper, the flat panel structure without and with the composite overlays made of HEXCEL TVR 380 M12/26%/R-glass/epoxy is under the experimental and the numerical study. Particular attention is paid to the investigation of the samples with the rectangular holes, which for smooth rounded corners offer a higher durability than the samples with the circular hole of the same size. The experimental results are obtained for the bare element and are reinforced with composite overlay samples. The experimental results are obtained with the use of the Digital Image Correlation method, while the numerical results are the product of the Finite Element Analysis. In the numerical analysis, the study of the shape, size and fiber orientation in applied overlays is done. The reduction of the stress concentration observed in opening notches has confirmed the effectiveness of the overlay application. In the investigated example, the application of the square composite overlay increased the structure strength even by 25%.
Wood pellets play an important role among biomass materials used as fuel. At the same time, today’s economic, environmental, political and social realities, as well as other circumstances related to fuels used for heat generation, mean that there is demand for increasingly efficient and environmentally friendly combustion sources. As is well known, each combustion source has a different efficiency due to its intended use, design, principle of operation and the type and composition of the fuel burned. The amount of pollutants emitted into the environment during combustion also largely depends on these factors. The aim of this study was to compare the flue gas emissions and efficiency of two pellet burners of different design, burning certified A1 wood pellets from different suppliers. The emission requirements were met during the combustion of wood pellets in a boiler with the two burners tested (one with a moving grate and an overfed burner). The analyses and studies carried out aim to improve the capability of managing the efficiency and environmental performance of the heat source (i.e., a boiler or a burner) and the fuel (type of wood pellets). This is done in the context of demonstrating a better combustion source when selecting the right burner and fuel in terms of efficiency and emissions. In this paper, comparisons of flue gas emissions are presented along with characteristics in the form of graphs, as well as thermal and combustion efficiencies for the corresponding solid fuel used in the form of wood pellets. After comparing the emissions, it was found that the statistical averages of CO, NOx, dust and VOCs were similar for combustion at full power using the burners tested. Taking into account the pollution levels at combustion, it can be said that the difference in CO emissions at full and minimum combustion is lower for the experimental burner compared with the moving grate burner (reference burner). In summary, it can be concluded that the experimental overfed burner under consideration can be successfully used as a solid fuel boiler to burn wood pellets.
The stress concentration observed in the vicinity of cut-outs and holes in structural elements significantly influences the fatigue endurance of machines subjected to cyclic loads. Numerous studies have been made so far to improve this situation and increase the structure lifetime. Several design recommendations have also been worked out to avoid the problem of premature failure. The proposed article illustrates the influence of the composite overlays applied around the cut-outs made in flat steel constructional elements subjected to axial tension. The detailed study concerns the reinforcement made from the FRP (fibre reinforcement polymer) composite applied around the notches. Two types of composite materials were used, namely: TVR 380 M12/R-glass (glass fibres embedded in epoxy resin matrix) and AS4D/9310 (carbon fibres embedded in epoxy resin matrix). In the first step, the detailed numerical studies (finite element analysis) were performed for the steel samples (with no overlays added) with cut-outs made in the form of circle, square and triangle hole (the last two with rounded corners). The results of these studies were compared with the existing analytical solutions with respect to the stress concentration factors (SCF) estimation. The relatively good conformity was observed when using dense meshes of finite elements placed around the void vicinity. In the next step, the composite overlays were applied around cut-outs and their influence on the stress concentration was investigated. The influence of the fibre orientation, numbers of layers, sizes of the composite overlay used were considered. It was proved that the application of composite overlays evidently decreases the stress concentration around the notches.
In the paper, the authors focused on the environmental problems of pollution emissions caused by households using batch boilers fired with solid fuels. The aim of this study is to analyse the course of changes in the actual efficiency and emission of a solid fuel updraft boiler, the most popular type of batch boilers used in Poland in recent years. The subject of analysis is the comparison of the values of atmospheric emissions of harmful substances depending on the type of wood burnt in the boiler. The investigation comprises the combustion characteristics of three types of woody biomass (in billets), i.e., pine, birch, and beech. Based on the carried out research of all billets, the beech has the lowest values of CO (3497 mg/m3) and particulate matter (116.9 mg/m3). Despite this, obtained results exceed the current permissible limits based on the standard PN:EN 303-5:2012. The highest efficiency (54.13%) was obtained for birch billets, the lowest for pine (45.13%). The research has shown that the real heating efficiency during the combustion of wood, irrespective of the type of wood being burnt, is low. To summarise, the outdated installations contribute to air pollution several times higher, which indicates the need to replace inefficient heat sources using solid fuels with modern equipment that meets the most stringent standards.
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