Solid State Phenomena Vol. 382

Abstract: The paper presents the development of vacuum infusion technology for thermoplastic composites with a polymethyl methacrylate (PMMA) matrix and continuous fibre reinforcement. The study focuses on process optimization, including testing of various tool surface treatments, adjustment of infusion parameters, and modifications to the technological lay-up. Additionally, the influence of sampling location within the composite panels on test results was examined. Differences in thickness, glass transition temperature, and in-plane shear strength were observed between the different sections of the panels. High-quality impregnation of glass fabrics was achieved, and the feasibility of manufacturing functional demonstrators with complex geometries was verified. The findings confirm the potential suitability of PMMA-based composites for aerospace applications.

Abstract: The research is concerned with obtaining basic knowledge in the field of machining biocomposite materials with hemp fibers and a matrix in the form of a mixture of polyester and methyl methacrylate resin in a secret ratio. The research was focused on milling technology, or rather side milling. For the needs of the research, 3 milling tools were selected with which experimental measurements were performed. Each tool was different in its type of sharpened geometry, both standard and specialized, including one coated. The experimental measurements focused on the size and course of wear of the cutting edge of the tools, the roughness value of the machined surface and the size and type of delamination of the upper and lower layers of the biocomposite material under investigation. The obtained results helped to evaluate the machinability of the selected hemp biocomposite and at the same time determined the future direction of research with regard to the design of a suitable cutting geometry of the tool and the overall optimization of the machining process during side milling.

Abstract: Composite fiber products and components are widely used in various industries, from highly stressed structural elements in the aerospace industry to sports equipment. In order to achieve the desired final shape, these materials are often subjected to various machining methods. Due to the inhomogeneous structure of composites and the different physical and mechanical properties of the matrix and reinforcement, specific problems arise during machining, such as delamination, intensive tool wear, increased temperature in the cutting area, or poor surface finish.This work deals with the observation of delamination size, wear, and cutting forces when drilling holes in carbon composites with tools with different rake angles. The result of this work is a recommendation for the geometry of tools for drilling this type of carbon composite.

Abstract: This study evaluates the direct machining of internal threads in glass fiber-reinforced (GFRP) and carbon fiber-reinforced (CFRP) composite materials, comparing the performance of cutting taps, conventional thread milling, and orbital thread milling. GFRP and CFRP samples were prepared and drilled under optimized conditions to minimize delamination, followed by thread production using the three different technologies. Visual and microscopic inspections revealed that orbital thread milling consistently produced the highest thread quality with minimal fiber damage, while cutting taps resulted in the most defects. Tensile testing showed that, in GFRP, orbital thread milling achieved the highest maximum load (18.05 kN), only slightly exceeding other methods. In CFRP, thread strength was similar across all technologies for 4 mm thick samples (around 4 kN), but increasing the thickness to 8 mm nearly doubled the strength, regardless of the threading method. The results demonstrate that orbital thread milling is optimal for thread quality, but in CFRP, material thickness is the dominant factor influencing joint strength. Direct threading in composites is feasible when appropriate machining parameters and technologies are applied.

Abstract: External conditions such as strain rate and temperature influence the mechanical properties of materials. In this paper, the influence of strain rate on the tensile properties of an additive-manufactured polylactic acid (CR-Wood PLA) polymer is studied experimentally. The key mechanical properties, including tensile modulus, yield strength, and strain at fracture of the material are studied at the low (0.0091/s and 0.91/s) and the intermediate (1/s – 3.63/s) strain rate ranges. The experimental investigation revealed that the stress-strain relationship of the material is influenced by the strain rate, however, differently across the ranges. The yield strength improved with the increase in the strain rate until ἐ = 1.81⁄s. A further increment in strain rate slightly declined the yield strength. The tensile modulus showed a notable decrement, however, only near the transition between the low and intermediate ranges. On the other hand, the strain at fracture monotonically decreased with the strain rate at both ranges. The material underwent significant post-yield plasticity, and a stress whitening throughout the reduced section of the specimens during the low strain rate tests. At higher strain rates, the plasticity was limited, and the stress whitening was localized just at the fracture surfaces.

Abstract: Flax fibre–reinforced polymers (FFRPs) are attractive for lightweight structures due to their low density, favourable specific stiffness and partially bio-based origin. However, their performance is strongly affected by manufacturing route, porosity and moisture uptake, which are typically more critical than for conventional glass or carbon fibre composites. This study compares flax, glass, carbon and carbon–flax hybrid epoxy laminates produced by vacuum infusion, hand lay-up and autoclave prepreg processing. Fibre volume fraction and void content are determined from density measurements, optical microscopy and X-ray computed tomography. Tensile and flexural properties are measured according to EN ISO 527-4 and EN ISO 14125 in the dry state and after accelerated conditioning at 35 ± 2 °C and 100 % relative humidity. Infused unidirectional flax laminates reach a tensile strength of about 259 MPa and a specific tensile strength of approximately 0.21 MPa·m³·kg⁻¹, comparable to glass laminates. Moisture exposure increases thickness by 11.8–13.9 % for infused flax laminates and about 2.3 % for an infused carbon–flax hybrid laminate and leads to strength reductions up to roughly 30 % in flax-rich laminates, while autoclave-processed laminates show only minor losses. The results provide process-dependent design guidelines for FFRPs in moisture-exposed, weight-sensitive components.

Abstract: This study investigates the impact of voids on the precision and dimensional stability of bonded joints in hybrid CFRP–aluminum assemblies for optical applications. Six CFRP samples were fabricated using filament winding and bonded to anodized aluminum alloy sleeves with DP 190 epoxy. Four samples were cured at 70 °C and two at 20 °C. Dimensional stability was assessed through radial runout measurements at three stages: post-manufacture, after environmental conditioning (including thermal cycling between +70 °C and –40 °C and six thermal shock cycles), and following mechanical resistance tests (shock, bump, and vibration per ISO 9022-3:2015). X-ray computed tomography (CT) revealed frequent defects such as adhesive starvation at joint edges, overflow, and a significant number of voids introduced during mixing. Porosity analysis showed that the presence of voids with equivalent diameters ≥0.5 mm strongly correlated with increased changes in radial runout, suggesting reduced dimensional stability.

Abstract: The presented article focuses on the design of composite tank which consists of wound cylindrical part (manufactured by the means of filament winding) which is bonded together with domes (manufactured by spraying or light resin transfer molding - LRTM technology). Composite structure was manufactured from glass/polyester material system by company ACO Industries Tábor. The article describes the possibility of using a bonded joint on cylinder/dome interface. This possibility was experimentally tested on specimens and also numerical simulation of full-scale model (finite element method - FEM) was performed. Developed construction is used for underground water treatment application and it is loaded with both the weight of the retained water and the pressure of the soil and groundwater during its deep burying.

Abstract: This paper presents the collaboration of the members of the research team involved in the TAČR project TM03000010 (acronym CAFICO) [1-6]. Verification of the functional properties of current structural designs is a prerequisite for successful development and subsequent production of products in any industry. Current development, including innovation, cannot do without the use of simulation methods and CAE technologies. However, their use is based on the knowledge and experience of the research team, including respect for the results of physical experiments, without which proper product development cannot be achieved.