This study investigates the impact of infill density on the mechanical properties of fused deposition modeling (FDM) 3D-printed polylactic acid (PLA) and PLA reinforced with carbon fiber (PLA+CF) specimens, which hold industrial significance due to their applications in industries where mechanical robustness and durability are critical. Exposure to cooling lubricants is particularly relevant for environments where these materials are frequently subjected to cooling fluids, such as manufacturing plants and machine shops. This research aims to explore insights into the mechanical robustness and durability of these materials under realistic operating conditions, including prolonged exposure to cooling lubricants. Tensile tests were performed on PLA and PLA+CF specimens printed with varying infill densities (40%, 60%, 80%, and 100%). The specimens underwent tensile testing before and after exposure to cooling lubricants for 7 and 30 days, respectively. Mechanical properties such as tensile strength, maximum force, strain, and Young’s modulus were measured to evaluate the effects of infill density and lubricant exposure. Higher infill densities significantly increased tensile strength and maximum force for both PLA and PLA+CF specimens. PLA specimens showed an increase in tensile strength from 22.49 MPa at 40% infill density to 45.00 MPa at 100% infill density, representing a 100.09% enhancement. PLA+CF specimens exhibited an increase from 23.09 MPa to 42.54 MPa, marking an 84.27% improvement. After 30 days of lubricant exposure, the tensile strength of PLA specimens decreased by 15.56%, while PLA+CF specimens experienced an 18.60% reduction. Strain values exhibited minor fluctuations, indicating stable elasticity, and Young’s modulus improved significantly with higher infill densities, suggesting enhanced material stiffness. Increasing the infill density of FDM 3D-printed PLA and PLA+CF specimens significantly enhance their mechanical properties, even under prolonged exposure to cooling lubricants. These findings have significant implications for industrial applications, indicating that optimizing infill density can enhance the durability and performance of 3D-printed components. This study offers a robust foundation for further research and practical applications, highlighting the critical role of infill density in enhancing structural integrity and load-bearing capacity.

This study aims to investigate the influence of thermal modification (TM) on the physical and mechanical properties of wood. For this purpose, the experimental part focused on selected influential parameters, namely temperature, residence time, and density, while the four-point bending strength is obtained as the output parameter. The obtained experimental data are stochastically modeled and compared with the model created by genetic programming (GP). The classical mathematical analysis obtained treatment parameters in relation to the maximum bending strength (T = 187 °C, t = 125 min $\rho$ = 0.780 g/cm³) and compared with the results obtained by genetic algorithm (GA) (T = 208 °C, t = 122 min, and $\rho$ = 0.728 g/cm³). It is possible to obtain models that describe experimental results well with stochastic modeling and evolutionary algorithms.

This study aimed to evaluate the impact of thermal modification on the physical and mechanical properties of three different wood species from Bosnia and Herzegovina, namely beech wood (Fagus sylvatica L.), linden wood (Tilia cordata), and silver fir wood (Abies alba). The samples underwent thermal modification at five different temperatures (170 °C, 180 °C, 195 °C, 210 °C, and 220 °C) for varying durations (ranging from 78 to 276 min). After treatment, they were exposed to outdoor conditions for twelve months. The study examined the four-point bending strength, tensile force, color change, and surface quality of the modified and unmodified samples. The results showed that outdoor exposure negatively impacted the mechanical properties of the unmodified samples, especially in the linden wood which was 41% and the beech wood which was 42%. Additionally, outdoor exposure caused significant surface cracks in the thermally modified linden and beech wood. The study also found prominent color changes in the modified and unmodified samples during twelve months of exposure. The roughness of the samples was determined with a confocal laser scanning microscope, which showed that the roughness increased on both the axial and the longitudinal surfaces after weathering. The highest roughness for the fir wood was determined to be 15.6 µm. Overall, this study demonstrates the importance of wood modification and its impact on the use-value of wood products.

Optimization of thermal modification of wood by genetic algorithm and classical mathematical analysis | Redžo Hasanagić | Agricultural Journals

The paper presents the modeling of tension force on a solid wood, which is coupled with a toothed connection, using methods of genetic programming. Experimental tests were performed on beech and oak test tubes. The experimental research consisted force measuring for various input parameters, such as type of wood, width, tubes, thickness and others. After the experimental part, the measurement data were collected in a form suitable for mathematical modeling, which defined the input parameters (predictors) of the experiment which formed the geometric relationship of the teeth l / p, the ratio of the width and thickness of the b / h elements, the wood density ρ and the humidity of the test W(%). As the output variable, the medium stretch force is defined, Fist. The obtained experimental data are divided into two parts: the first part of the experimental results was used to train and obtain a tensile force model, while the other part of the data was used to test and validate the model. After the model was formed, the analysis of the results and evaluation of the model were made. The analysis and discussion of the results showed that the method of genetic programming can be successfully used in the modeling of such experimental research.

The paper presents the development of the mathematical model of joint parameters impact, during solid wood lengthening with a mini tooth, on the joint strength. Impact parameters are wood density (ρ), ratio of wood element width and thickness (b/h) and geometrical size of mini tooth expressed as ratio of length and distance between width of the tooth (l/p). This paper presents an example of how the process of joining solid wood can be optimized prior to the production process to avoid exploitation testing and increased costs of the process. Based on the obtained model (F), force optimization was performed as a function of the maximum tensile force. The results of the conducted research indicate that mathematical modelling and optimization can be successfully used to define the tensile break force and technological parameters of solid wood elements lengthened by finger joint.