Papers by Keyword: CFRP

Abstract: The increasing use of fibre-reinforced composites raises critical issues related to sustainability and end-of-life management, particularly for thermoset-based systems. In this work, a non-conventional thermo-mechanical recycling strategy is proposed for hemp/carbon hybrid laminates, aiming at the recovery and reuse of intact reinforcement plies without destructive fibre-matrix separation. Full carbon, full hemp, and two hybrid laminate configurations with different stacking sequences were manufactured, recycled through controlled thermo-mechanical disassembly, and reprocessed into new laminates. The flexural and interlaminar shear behaviour of virgin and recycled materials was investigated to assess the influence of the recycling process on mechanical performance.

Abstract: Concrete, often conceptualized as an inert construction material, is fundamentally a dynamic composite that undergoes continuous physicochemical transformations throughout its service life, governed by natural degradation processes and mechanical aging. Despite its widespread utility, concrete’s quasi-brittle behavior, characterized by low tensile strength and susceptibility to abrupt failure under traction-dominated loading regimes, remains a critical limitation in structural engineering. To address these intrinsic vulnerabilities, the rehabilitation of concrete infrastructure has emerged as a pivotal research domain, with advanced retrofitting techniques focusing on enhancing tensile performance and transitioning failure modes from brittle to ductile. Among these, externally bonded reinforcement (EBR) using fiber-reinforced polymer (FRP) composites has gained prominence as a high-efficacy solution for augmenting load-bearing capacity and structural resilience. This study employs a parametric finite element analysis (FEA) framework in Abaqus/CAE to systematically evaluate the mechanical efficacy of two distinct carbon fiber-reinforced polymer (CFRP) retrofitting strategies: (1) externally bonded CFRP plates and (2) internally embedded CFRP reinforcement within the beam’s cross-section. The computational investigation quantifies the influence of reinforcement placement on critical performance metrics, including ultimate load capacity, deformation ductility, and failure mechanisms. Numerical results demonstrate that internally integrated CFRP reinforcement significantly enhances structural ductility and peak load resistance, while maintaining a marginal mass differential. These findings underscore the critical role of reinforcement topology in optimizing stress redistribution and crack mitigation, offering actionable insights for the design of next-generation retrofitting protocols that prioritize both strength and serviceability. The study advances the discourse on sustainable infrastructure rehabilitation by delineating a pathway for leveraging embedded composite systems to transcend the inherent limitations of conventional concrete matrices.

Abstract: Carbon fiber reinforced polymer (CFRP) bonded structures are widely used for their lightweight and high specific strength. However, research on durability of adhesively bonded lap joints under hygrothermal conditions remain insufficient. Therefore, the aging process and residual strength of CFRP-bonded lap joints with different adhesives were studied. Condition of hygrothermal aging tests were set, then moisture absorption behavior of CFRP plate and adhesive layer were analyzed, respectively. Based on the same aging period, residual tensile strength of acrylic-based specimens and epoxy-based specimens were compared. To evaluate their performance and clarify the failure mechanisms, Finite element method (FEM) simulations were conducted. Load-displacement curve was recorded and morphology of the failure surfaces was analyzed by using a microscope.

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: 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: The shift towards electric mobility needs extensive research into battery modules, particularly in relation to safety due to the high energy density of Li-ion batteries. Battery casings must be able to protect the module from external impacts while also containing any potential danger in the event of internal failure. This study presents a comprehensive qualitative screening of thermoset and thermoplastic carbon fiber-reinforced polymers (FRP) used in automotive and aerospace applications under thermal runaway (TR) conditions, to identify suitable materials for battery enclosures. The test setup is an adaptation of the UL 2596 standard with a hexagonal array of seven 21700-format cells. The results indicate that CF-PEEK, CF-PPS, and an aerospace-grade epoxy, CF-EP_str (primary structural material) effectively contain the TR with low damage using the current setup. Medium damage was observed in CF-PC, CF-bio-based phenolic, while non-structural CF-epoxy and CF-PA6 failed to contain the TR. This qualitative study serves as an initial screening process to narrow down materials for further in-depth analysis, emphasizing the need for reproducible TR events for accurate assessment.

Abstract: This study examines the feasibility of utilizing the press forming method on multi-layer, multi-orientation continuous CFRP preform produced by the additive manufacturing (AM) technique. The 5-layer preforms with fiber orientations of 45° and -45° impregnated in Nylon-6 resin layers were made by a 3D printer, and press-formed in varying temperatures and pressures. Optimal forming outcomes were determined by qualitative evaluations of the surface finish, fiber impregnation, resin flow, and quantitative observations on shape variations by comparison with the mold dimensions. Experimental results showed that the molding temperature of 220°C and pressure between 0.5MPa - 1MPa could produce preforms with optimal surface conditions. There was almost no void of bubble defects, no excess resin flow, and a smooth transition was established between the carbon fiber and the matrix resin layers while allowing the full mechanical strength properties to be realized. The formed preform evaluations confirmed that the press molding method is feasible on multi-layer, multi-orientation continuous CFRP with optimal surface conditions.

Abstract: This paper applies Flow Drill Screws (FDS) technology to the joining of composite materials and metal materials. It investigates the connection strength and mechanism between thermosetting carbon fiber reinforced composites and metal materials, as well as between thermoplastic carbon fiber reinforced composites and metal materials. The study includes shear tests and metallographic tests to analyze the two types of connections. The experimental results demonstrate the feasibility of using the FDS process for composite materials and metal materials. It is found that the FDS process is more suitable for connecting thermoplastic composites and metal materials compared to thermosetting composites and metal. This type of connection exhibits a smaller damage range at the interface and allows the thermoplastic matrix to effectively fill the threaded connection area after heating. Additionally, the micro-mechanical interlocks generated at the laminate interface can effectively increase the connection strength.

Abstract: Recently, the use of carbon fiber-reinforced plastic (CFRP) has been picking up in aerospace and automotive industries. However, machining of CFRP produces fine cutting chips, which disperse in the machining environment and can be hazardous to workers and machine tools. Therefore, a cutting-chip disposal technology is required to address this problem. This study investigated the chip dispersal behavior during the drilling of CFRP to identify the factors that affect the dispersal of cutting chips. The focus of this study was the airflow field generated by drill rotation. Therefore, a simulation analysis for around the drill edge was used. The results of the drill edge simulation and chip discharge behavior during CFRP drilling were validated experimentally. The results suggested that the airflow field around the drill edge caused by drill rotation did not significantly affected chip dispersal.

Abstract: One possible method for strengthening deteriorated concrete structures is to externally bond composite material plates to the concrete. The use of Carbon Fiber Reinforced Polymer (CFRP) laminates as an effective and versatile technique for strengthening reinforced concrete (RC) structures has developed into a sizable industry in recent years. To implement such rehabilitation, the nature of the bond between the composite plate and the concrete must be understood. The behavior of reinforced concrete beams strengthened in the negative moment region using CFRP strips is presented in this paper. The experimental program included strengthening and testing five half-scale, reinforced, simply supported rectangular cross section beams with an overhanging (cantilever) portion. One of the tested specimens was tested without any strengthening and considered as the control specimen. The rest specimens were strengthened with CFRP strips using different technique and then tested until complete failure. The effect of strengthening technique on deflection, failure load, strain, failure mode, and ductility are discussed. In addition, and due to local stress concentration at the plate ends, the influence of different type of CFRP fixation at both ends for proper bonding of the strips, and the strengthening pattern on the behavior of beams was examined. The ratio of absorbed energy at failure to total energy, or energy ratio, was used as a measure of beam ductility. The results generally indicate that the flexural strength of the strengthened beams is increased. It is also noted that, in addition to the longitudinal CFRP plates, the fiber oriented in the vertical direction forming a C or U-shape around the beam cross section significantly reduce beam deflections and increase beam load carrying capacity. However, all the strengthened beams experienced semi brittle failure, mandating a higher factor of safety in design. The results also indicate that plating reduced crack size in the beams and somewhat reduced their ductility.