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Fiber Architecture
Published in P. K. Mallick, Processing of Polymer Matrix Composites, 2017
Another process for making a 3D architecture is called z-pinning. In this process, metal or pultruded composite pins with a diameter between 0.2 and 1 mm are inserted through the thickness of a stack of uncured prepreg layers or dry woven fabrics to provide reinforcement in the thickness direction (z-direction) (Figure 2.19). Ultrasonically assisted z-pinning or UAZ is the most common process for inserting the pins [10]. In this process, the pins are first arranged on a foam carrier, which is placed on top of the prepreg stack. The pins are driven from the foam carrier into the stack using an ultrasonically actuated tool. Under the compressive waves created by the tool, the foam carrier collapses as the pins enter the stack. Heat generated at the interface of the tool and the prepreg softens the resin, which helps in the insertion process. The collapsed foam carrier is then removed using a blade. The prepreg stack with the z-pins is then cured using vacuum bagging and autoclaving.
Future Prospective and Challenges
Published in Ramesh Kumar Nayak, Bankim Chandra Ray, Dibyaranjan Rout, Kishore Kumar Mahato, Hydrothermal Behavior of Fiber- and Nanomaterial-Reinforced Polymer Composites, 2020
Ramesh Kumar Nayak, Bankim Chandra Ray, Dibyaranjan Rout, Kishore Kumar Mahato
Presently, various modes of modifications for improving the properties, especially the out of the plane strength of the FRP composites, are being tested. Matrix modification, starting off with the addition of ceramic-based nanofillers and presently with carbon-based nanofillers carbon nano Fiber [CNF], carbon nano Tube [CNT], , graphene) is gaining ground as an effective process to increase properties of FRP composites, at various temperatures. On the other hand, modification of the fiber promises improvements likewise. This approach focuses on coating the surface of the fiber in order to enhance the fiber-matrix interfacial properties. Fiber surfaces with higher surface area, wettability, and an affinity for a matrix warrant superior stress transfer to the reinforcements. Sizing, electrochemical method, plasma treatment, and hybrid fibers are promising modification methods. Out of these, electrophoretic deposition of nanofillers on conductive fiber like carbon fibers is an interesting option. The electrophoretic deposition (EPD) technique has been extensively adopted for surface alterations to develop nanoparticle-reinforced materials. EPD stands apart from other techniques because of several advantages like ease of controlling the film thickness, better homogeneity of surface, and high rate of deposition. Z-pinning, a process where reinforcements are inserted along the Z direction of continuous long fiber composites dramatically improves resistance to delamination. The following challenges can be highlighted in contrast to the development of FRP industries: Availability of quality raw materialsThe rising cost of raw materials and high price sensitivity of the marketLack of skilled laborLack of awareness in the industrial worldQuality assurance and standardization are further issues which concern manufacturersLack of concrete regulatory bodies/frameworkA finite number of scientific publicationsLack of recycling policy of FRP waste and end of life productsThe necessity to develop quality consciousness among small-scale FRP/GFRP composites manufacturersNew products and applications need to be developed at a faster rateModerate implementation of the automated FRP fabrication process
Experimental failure strengths of composite single-lap joints reinforced with I-Fiber stitching process
Published in Advanced Composite Materials, 2022
Woo-Jin An, Uy-Hhwa Seo, Geon-Hyeong Kim, Dong-Hwan Yoon, Jin-Ho Choi
The conventional stitching process can be applied to flexible fibers, such as aramid, carbon, or glass fiber, because the top and bottom fibers are knitted together and bent to an angle greater than 180°. The z-pinning method uses a pre-processed pin (metal or composite), which after being inserted supports the material only by the shear force of the z-pin. The I-Fiber stitching process (Figure 1) is a method that complements the z-pinning and conventional stitching processes. Discontinuous fibers are inserted into the dry preform or prepreg, and the remaining fibers from the I-shaped head at the top and bottom of the laminate after curing. The ‘head’ increases the reinforcement effect by acting like a nut of a bolt. Kim et al. and An et al. describe the stitching process using an in-house-built automatic stitching machine [10–12].
Experimental and numerical assessment of the effect of transverse reinforcing of AL-GFRP single lap adhesive joint using Z-pins under tensile loading
Published in The Journal of Adhesion, 2022
A. Mirzaei, A.H. Darbandi, M. Ramzaninezhad, M. Rezvaninasab, M. H. Alaei
In the following step, using a scanning electron microscope (SEM), the fracture surface was observed more accurately. There are various methods for z-pinning which each of them have adverse effects on the microstructure of z-pinned composites, such as resin-rich zones, fiber waviness, or broken fibers. Figures 9a and 9b show the schematic and microscopic views of fiber waviness defect caused when z-pins fail to align entirely with longitudinal fibers, respectively. It happens in one of the usual methods called the Ultrasonically Assisted Z-pinning (UAS), in which pin insertion is assisted by the use of heat and ultrasonic vibration through a hand-held gun, and as a possible result, one of the z-pins would have offset a little to the right of the nominal pin-line, and the adjacent z-pin would have offset to the left. It has been seen that fiber waviness lessens both in-plane tension and compression properties such as strength and modulus of z-pinned composites .[17,47,48] The z-pinning technique used in this study and explained in section 2.1 have eliminated this imperfection as z-pins are fixed in a PMMA plate, and fabrics are laid on them by hand. In this method, composite plies are placed on the top of the PMMA plate, which acts as a mold and holds the z-pins, so the fibers are arranged around the z-pins, and the z-pins penetrate the fabric layers throughout the thickness with minor fiber damage or fiber waviness. Then, the composite is cured using the vacuum bagging method. The microscopic view of this phenomenon is shown in Figure 10. As it can be observed from the failure surface of the joint, there is no fiber misalignment in the composite adherend. In addition, fiber broken, delamination, and stress concentrations, which usually happens in the method of drilling holes for z-pins, [48] does not exist in the method used in this research.
Influence of manufacturing process and GFRP pin loading on shear and dynamic behaviour of composite joints
Published in The Journal of Adhesion, 2023
Thulasidhas Dhilipkumar, Murugan Rajesh
Furthermore, adhesively bonded composite joints fail suddenly due to higher stress concentrations at overlap ends. As a result, adhesively bonded joints have been unable to meet general aviation’s requirement for damage tolerance. To address the shortcomings of adhesive joining, researchers developed various through-thickness reinforcement techniques such as stitching, tufting, and Z-pinning.[21,22] One of the promising techniques for improving the performance of adhesively bonded joints is Z-pinning. The Z-pinning pin involves the embedding of small rods in the bonding area of composite adherents. Generally, a small volume of pins (0.5% to 4%) is sufficient to enhance the resistance against out of plane loading and joint strength.[23,24] Chang et al.[25] reported that embedding a 0.5% volume fraction of carbon fibre pins increased the single-lap joint’s shear properties and fatigue strength. Li et al.[26] examined the impact of Z-pin insertion on the mechanical properties of the fastened composite joints. Results showed that inserting Z-pins around the bolted region improved the composite joint’s bearing stiffness, load-carrying ability, and ultimate failure strength by 9.6%, 12.8%, and 9.8%, respectively. The study also reported that the presence of Z-pins reduced the formation of cracks around the bolted region due to effective bridging, which includes debonding and pin sliding in the damaged region. Mouritz et al.[27] compared the effectiveness of metallic and composite pin reinforcement on mode I fracture toughness of carbon fibre reinforced epoxy laminate. Results confirmed that insertion of Z-pins improved the composite’s fracture toughness and fatigue strength due to effective bridging of delamination cracks. Lobel et al.[28] examined the tensile properties of double-lap composite joints after embedding stand-alone and edge stapled pins. The results showed that stand-alone pins increased tensile strength by 28% due to lower peel stress and axial fixation, whereas edge stapled pinning increased tensile strength by 23% compared to unpinned composite joints.