Papers by Keyword: Composite Materials

Abstract: The use of composite materials and specifically of Fiber Reinforced Polymers (FRP) is continuously increasing in structural applications due to their high strength-to-weight ratio. From an environmental perspective, composites still face relevant challenges due to impactful petroleum-based matrices and large amounts of waste generated during manufacturing processes. This study proposes the reuse of FRP machining waste as filler in Masked Stereolithography (M-SLA) 3D printing. Scraps from FRP laminates, obtained during drilling operations, were incorporated into a photocurable resin and used to print tensile and flexural specimens with increasing filler contents (0–5 wt%) and mechanical characterization tests were carried out. A cradle-to-grave Life Cycle Assessment (LCA) was performed to quantify the potential environmental benefits associated with the reduced use of virgin resin. Results show that the use of recycled FRP waste leads to a loss of tensile strength and stiffness (up to 61% and 21% respectively) but it also provides a reduction in Global Warming Potential (about 2% at 5 wt% filler). This demonstrates that the proposed strategy can improve the sustainability of 3D-printed components, especially for non-structural applications.

Abstract: This study presents a static finite element analysis of the milling of a flexible unidirectional glass fiber–reinforced polymer (UD-GFRP) plate. The workpiece is modeled as a clamped–free cantilever, with cutting forces evaluated independently of structural deflections and applied along the machined edge. SC8R continuum shell elements are employed to accurately represent through-thickness loading and bending behavior. A mesh sensitivity analysis is conducted to determine a suitable discretization, leading to a 64 × 56 × 8 element mesh. For the investigated configuration (, mm/tooth), the out-of-plane displacement reaches approximately 120 µm near the free end of the plate, whereas in-plane displacements reach up to-75 µm. These in-plane displacements are greater than or equal to the nominal feed per tooth, indicating a highly significant influence on chip formation. This work provides a basis for understanding the structural response of flexible composite plates during trimming and emphasizes the need for coupled force–deformation formulations.

Abstract: This work presents a theoretical and numerical study on the nonlinear free vibrations of orthotropic laminated composite beams, with a focus on different material orientations such as cross-ply, balanced, and woven configurations. Based on the Euler-Bernoulli beam theory and Von Karman’s geometric nonlinearity, we develop an analytical and matrix formulation using Hamilton’s principle. The novelty lies in the use of a homogenization approach to derive equivalent stiffness properties, allowing the comparison between symmetrical and asymmetrical composite beams. Despite limitations inherent to Euler-Bernoulli assumptions, results show the significant influence of layer orientation on the nonlinear frequency and displacement behavior. This study is valuable for structural applications in aerospace and mechanical systems.

Abstract: This paper investigates the application of polymer materials for low-temperature, pressure-less thermal storage in Czech district heating systems integrated with high-performance heat pumps. A dynamic simulation was conducted for a residential building of 180 occupants, equipped with a 32 kW heat pump, 10 kW photothermal panels, and 200 m³ of stratified water storage divided into preheating and high-temperature sections. Composite tanks for thermal storage can provide lower cost per cubic meter of storage, superior structural resilience under thermal cycling, and competitive environmental performance relative to polypropylene alternatives. The findings highlight composite storage as a technically and economically viable pathway for enhancing flexibility, efficiency, and decarbonization in Czech district heating networks.

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: This research focuses on optimizing ultrasonic welding technology for joining 3D printed metal composites. The study investigates the influence of various welding parameters, including ultrasonic frequency, amplitude, pressure and welding time, on the quality and strength of the welded joint. The research aims to identify the optimal welding conditions that ensure robust and reliable bonding of these complex materials, given their unique microstructural and mechanical properties. The findings will contribute to the development of efficient and reliable joining techniques for 3D printed metal composites, expanding their applicability in various engineering applications.

Abstract: In general, composite materials are widely used in many industries. A composite material is a material composed of two or more components. Such a composite material differs in its properties from the individual components of the entire composite. This contribution is aimed at evaluating the parameters of selected composite materials - wood fiber boards, carbon prepreg boards and epoxy boards. The measured quantities that were investigated on the given materials were the modulus of elasticity, the loss modulus and the tan delta angle. To evaluate the properties of the given composite materials, a dynamic-mechanical analysis using the DMA Q800 device from TA Instruments was used. Three samples were measured from each material. From the measured values, it is demonstrable for the modulus of elasticity that the greatest mechanical disturbance began to occur gradually due to the influence of temperature and frequency with three materials in this order: fiber board - carbon prepreg board - epoxy board. From the obtained values ​​of the loss modulus, it was proven that the sample - wood fiber board - had the lowest glass transition temperature. Finally, regarding the measured values ​​of the glass transition temperature for the loss angle (tan delta), it can be said that the wood fiber board also has the lowest damping ability.

Abstract: Determining interlayer shear modulus of composite materials by the method of three-point transverse bending is considered, and Timoshenko approaches to estimating the shear strains in this type of loading are assessed. It is shown that these approaches make it possible to determine the shear component of beam deflection with an accuracy acceptable for practice in testing them in three-point transverse bending, but only for isotropic materials. For anisotropic materials, they are unacceptable. These approaches are also unacceptable for determining the shear modulus of isotropic and anisotropic materials. Based on the data obtained as a result of the study, a simple and economical method for determining the shear moduli in the three-point transverse bending is proposed. This method was tested on both isotropic and composite materials with different reinforcement structures. Results showed a good agreement between the calculated and experimental values of the shear moduli for all the materials considered, which confirmed that the method proposed method can be used in practice.

Abstract: The growing issue of light expanded clay aggregate (LECA) disposal has become a pressing environmental concern globally, underscoring the need for swift and effective solutions. To mitigate this issue, the construction industry is increasingly adopting sustainable alternatives to traditional concrete. One such innovative approach involves incorporating these waste materials into construction materials, primarily concrete. This study aimed to create a novel, eco-friendly concrete material utilizing recycled LECA, engineered to float on water. The investigation employed a range of polyvinyl alcohol (PVA) fiber volume fractions (0, 0.15, 0.25, 0.35, and 0.45%) to assess their impact on the strength properties of lightweight foamed concrete (LWFC). The combination of LECA and polyvinyl alcohol (PVA) fibers resulted in compressive strengths ranging from 3.51 to 4.15 MPa, accompanied by densities between 600 and 750 kg/m³. Furthermore, ultra-lightweight foam floating concrete (ULWFFC)-P5 demonstrated enhanced load capacity, with a buoyancy force of 26.5 N. This innovation presents a groundbreaking opportunity for the construction sector, offering a sustainable and effective solution for complex projects in building and offshore marine environments.

Abstract: Natural fibers are widely used as reinforcement in composites and undergo development in the surrounding environment. However, natural fibers have a water-absorbing property that reduces the strength of the composite. The objective of this research was to analyze the percentage increase in water absorption of resin epoxy composite reinforced with woven ramie fibers. In this research, bisphenol a-epichlorohydrin resin epoxy and polyaminoamide hardener epoxy were utilized as the matrix with a volume fraction of 60:40. Various additions of cerepol pigment pastes (CPP) were made to the resin, specifically 5%, 7.5%, and 10%. The composite was fabricated using the hand layup method, molded in a mold with dimensions of 250mm x 250mm x 4mm, and immersed in seawater for 12 days. The results of the study indicated that the woven ramie fibers reinforced composites, both without CPP and with 5% CPP, and 10% CPP, experienced the highest percentages of water absorption, which were 1.34%, 1.28%, and 1.10%, respectively, while the lowest percentages of water absorption were 0.7%, 0.6%, and 0.75%.