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Issue link: https://ct.epubxp.com/i/178128
Work in Progress 110 mm 7.6 mm thick Pi preform C-leg L-shape (7.2 mm thick) Pi base Pi leg C-leg 300 mm Adhesive Layer (3.0 mm thick) Balsa core 50 mm (12.4 mm thick) Shear web skin (3.8 mm thick) Adhesive layer (3.0 mm thick) Flange (8.1 mm thick) Balsa core (12.4 mm thick) Shear web skin (3.8 mm thick) 3TEX tested I-beams made with a conventional joint design (C-beam plus L-shaped braces, at left) vs. its new joint design using a 3-D woven Pi preform (right). Adhesive Layer (2.5 mm thick) 42.5 mm Flange (4.2 mm thick) 25 mm 200 mm 200 mm blind mating, including excessively thick bondlines, voids, nonvertical alignment of the Pi legs or joint structure within the Pi, and even peel plies that are not removed before bonding. Second, a Pi joint, despite its complexity, can be preformed in an automated process. 3TEX R&D; director Dr. Keith Sharp says his company's 3D Weaving process "lends itself to easy manufacture of Pi joint preforms. We simply design a textile with z-direction yarns penetrating completely through the thickness for the center portion and then only halfway through the thickness for the outer edges, allowing these lengths to be folded up to form the two legs of the Pi." Te dry preform is reportedly easy to co-infuse with the blade shell so the legs of the Pi align vertically to receive and locate the shear web. Tis permits the blade manufacturer to use a simple fat plate for the web — C-shapes and L-braces are no longer necessary. Terefore, blind mating of the joint surfaces is vastly simplifed. Co-infused Pi joint and blade skin Source | 3TEX (8.1 mm thick) by distributor LBI Inc. (Groton, Conn.). Te Pi joints and web were infused with Rhino 1401-21/4101-21 epoxy resin supplied by Rhino Linings (San Diego, Calif.). When the Pi joints and web were bonded, the Pi joint slot was 2.5 mm/1 inch wider than the web to allow sufcient space for the Rhino 405 Structural Epoxy Gel adhesive. Te conventional I-beam used in the test replicated the construction of a 13m/43-f long commercial wind blade from Heartland Energy Solutions (Mount Ayr, Iowa). Te C-shape shear web was made with two faceskins of triaxial E-glass fabric (0˚/±45˚ with 0˚ oriented along the beam length), each measuring 3.8-mm/0.15-inch thick, on each side of a 12.4-mm/0.5-inch thick balsa wood core. Te material suppliers and infusion process were the same as those previously described. Te top and bottom fanges of the C-beam were formed by extending the two faceskins at 90o to the cored section. Te C-beam measured 7.6-mm/0.3-inch thick, and its height was 50 mm/1.97 inches. Two 7.2-mm/0.28-inch thick L-beams were Pi Progress CT oCTober 2013 Both types of 2.7m/8.9-ft beams were clamped and cantilever-loaded to simulate wind blade service, during tests conducted at the Constructed Facilities Laboratory at North Carolina State University. Source | 3TEX In a presentation at the 2012 SAMPE conference in Baltimore, Md., 3TEX reported that preliminary performance testing was done by fabricating composite I-beams made with the 3TEX 3-D woven Pi preform joint and a conventional joint (C-beam plus L-shaped braces, see top images, this page). Te I-beams were 2.7m/8.9f long by 0.3m/1-f tall, with 0.2m/0.7-f wide fanges, matching the dimensions of the spar cap width and thickness and the shear web height of a 13m/42.7-f long commercial wind blade at the 10m/33-f station. Te fanges were 8.1-mm/0.3-inch thick E-glass/ epoxy laminate. A test apparatus was developed that clamped a standard I-beam at one end and applied an upward load at the other end to simulate the dominant type of loading on a wind blade. For the Pi joint I-beams, Pi preforms were woven as a single E-glass fabric and split to form two 4.2-mm/0.2-inch thick legs, each measuring 42.5 mm/1.7 inches in length and separated by an 8.1-mm/0.3-inch thick central section that was 25-mm/1-inch wide. Te 110-mm/4.3-inch wide preform had 54 percent total fber volume fraction with equal amounts of fber in both in-plane directions and 1.5 percent in the z-direction. A 20-mm/0.8-inch wide fat plate shear web was made, using 3.8-mm/0.2-inch thick faceskins of triaxial E-glass fabric from SAERTEX USA LLC (Huntersville, N.C.) on each side of a 12.4-mm/0.5-inch thick balsa wood core, supplied 17