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Carvelli V.,Polytechnic of Milan | Gramellini G.,Polytechnic of Milan | Lomov S.V.,Catholic University of Leuven | Bogdanovich A.E.,3TEX, Inc. | And 2 more authors.
Composites Science and Technology | Year: 2010

The paper studies tension-tension fatigue behavior of a single-ply non-crimp 3D orthogonal weave E-glass composite and of a laminated composite reinforced with four plies of a standard plain weave fabric. Both composites have same total thickness and very close fiber volume fraction. The paper presents the description of the materials, the results of quasi-static tensile and of tension-tension fatigue tests, including the damage development during fatigue tensile loading. The non-crimp 3D woven fabric composite, loaded in both principal in-plane directions (warp and fill), shows the best quasi-static tensile properties and, when loaded in the fill direction, exhibits much longer fatigue life than its laminated plain weave counterpart. During both quasi-static and fatigue loading, the latest damage initiation is observed for the 3D woven composite in both in-plane directions. The PW laminate develops delamination between the plies for each maximum stress in the cycle considered. Contrary to that, the 3D composite is not affected by delamination neither under quasi-static nor under fatigue loading conditions. © 2010 Elsevier Ltd.

Bilisik K.,3TEX, Inc.
Journal of the Textile Institute | Year: 2010

Multiaxis 3D-woven carbon preforms are fabricated using prototyped multiaxis weaving. The fabricated preform has structural instability at thickness. For this reason, the structural parameter and processing parameters were evaluated to make uniform preform and to understand the preform-process relations. The important process parameters are identified and described to enhance the preform and unit cell architecture. Also, preform structural parameters are analyzed in terms of fiber cross-section and fiber tow size, bias angle, and fiber waviness. The useful recommendation is also to make uniform multiaxis 3D-woven preform for composites. © 2010 The Textile Institute.

Karahan M.,Catholic University of Leuven | Karahan M.,Uludag University | Lomov S.V.,Catholic University of Leuven | Bogdanovich A.E.,3TEX, Inc. | And 2 more authors.
Composites Part A: Applied Science and Manufacturing | Year: 2010

Measurements of the internal geometry of a carbon fiber non-crimp 3D orthogonal woven composite are presented, including: waviness of the yarns, cross sections of the yarns, dimensions of the yarn cross sections, and local fiber volume fraction. The measured waviness of warp and fill yarns are well below 0.1%, which shows that the fabric termed here "non-crimp" has nearly straight in-plane fibers as-produced, and this feature is maintained after going through all steps of fabric handling and composite manufacturing. The variability of dimensions of the yarns is in the range of 4-8% for warp and fill directions, while the variability of the yarn spacing is in the range of 3-4%. These variability parameters are lower than respective ranges of variability of the yarn waviness and the cross-sectional dimensions in typical carbon 2D weave and 3D interlock weave composites, which are also illustrated in this work for comparison. © 2010 Elsevier Ltd. All rights reserved.

Karahan M.,Catholic University of Leuven | Karahan M.,Uludag University | Lomov S.V.,Catholic University of Leuven | Bogdanovich A.E.,3TEX, Inc. | Verpoest I.,Catholic University of Leuven
Composites Science and Technology | Year: 2011

An experimental study of the in-plane tension-tension fatigue behavior of the carbon fiber/epoxy matrix composite reinforced with non-crimp 3D orthogonal woven fabric is presented. The results include pre-fatigue quasi-static test data, fatigue life diagrams, fatigue damage progression, and post-fatigue quasi-static test data for the warp- and fill-directional loading cases. It is revealed that the maximum cycle stress corresponding to at least 3. million cycles of fatigue life without failure, is in the range of 412-450. MPa for both loading directions. This stress range is well above the static damage initiation threshold and significantly above the first static damage threshold (determined by the onset of low energy acoustic emission). The second static damage threshold, determined by the onset of high energy acoustic emission and related to the appearance of local debonds and intensive transverse matrix cracking falls within this range. The established correlation between a 3000,000. cycle fatigue stress limit on one side and the second static damage threshold stress on the other is of a high practical importance, because it will significantly reduce the amount of future fatigue tests required for this class of composites. Surprisingly, for equal maximum cycle stress level, the fatigue life under fill-directional loading appears about three times shorter than that under warp-directional loading. The 100,000. cycle, 500,000. cycle and 1000,000. cycle fatigue loading with 450. MPa maximum cycle stress has resulted in so high variations of post-fatigue static modulus, strength and ultimate strain, that no consistent and statistically meaningful trends could have been established; further extensive experimental studies are required to reliably quantify this effect. © 2011 Elsevier Ltd.

Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 999.37K | Year: 2010

Wind blades are complex constructions of composite materials. As with all composite structures, forming joints between the various elements has long been problematic, since composites cannot easily be bolted, fastened, or welded together. Current manufacturing methods result in thick adhesive layers that have varying dimensions and which are the most common failure area in wind blades during operation in the field. Integral Pi shaped (shaped like the Greek letter p) and

Agency: Department of Homeland Security | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 332.52K | Year: 2010

  Based on the results of the Phase I project, it was shown that 3TEX`s unitary 3D woven E-Glass billet reinforced composite panels have excellent potential to be used as blast mitigating material for protecting buildings. Fibers and resins used in the Phase I were selected with affordability and fire resistance as the major considerations. In the Phase II effort proposed, the same fiber and resin will be used. The 3D woven billet preform design will be optimized and, based on the new geometry, predictive analysis will be conducted to determine that performance under shock loading is still at the same level found in Phase I or better. The new material will be produced and tested in the University of Rhode Island (URI) shock tube for validation. Large scale blast testing of mock-up concrete walls will be conducted using three different mounting approaches. An innovative attenuator will be used to reduce the shock load transmitted through the mounting bolts to the wall. A patented coupler will also used to simulate the joining of two panels in a vertical installation. At the end of the Phase II, a complete technical data package (TDP) for the materials and methods used, will be developed.

Agency: Department of Defense | Branch: Air Force | Program: STTR | Phase: Phase I | Award Amount: 100.00K | Year: 2010

A novel method of fabricating carbon nanotube (CNT) reinforced polymer matrix composites is proposed. It includes growing super-aligned carbon nanotube arrays on a flat substrate, using NCSU proprietary shear pressing method to compress the grown arrays into a layer of densely packed, highly aligned CNTs inclined at an angle of several degrees to the substrate, separating the produced CNT sheet from the substrate, infusing polymeric resin into the sheet to fabricate an uncured prepreg, laying up the prepreg plies at desired orientations, and finally curing the laminate. This manufacturing process will result in a thick, high CNT volume fraction reinforced laminate with unique in-plane and out-of-plane reinforcement architectures. This kind of laminates can be used for relatively small size aerospace structures, where special combinations of high mechanical strength, high electrical conductivity and high thermal conductivity are required. Experimental validation and scaling up this technological approach will include increasing CNT length and their array growth area, building computer controlled apparatus for precise shear pressing of the grown arrays, developing special means for aerospace grade resin infusion into CNT sheets, ply lamination and cure. Initial experimental studies will include in-plane tensile testing and measurements of through thickness electrical and thermal conductivities. BENEFIT: Aerospace industry may be primarily interested in using these novel CNT reinforced prepregs and composite laminates for unique structures which require low weight and high strength combined with high electrical and/or high thermal conductivity. Immediate applications may include light-weight composite structures for housing various aircraft electronic systems. Currently available composite laminates are not applicable due to their low through-thickness thermal and electrical conductivities. In the proposed CNT prepregs and laminates, with long CNTs extending through the whole ply thickness, these properties will be elevated to a much higher level, at least an order of magnitude. The development of integrated manufacturing cycle for these materials and their structural components will enable to supplying them in large volumes for the next generation unmanned aircraft and surveillance platform structures, as well as for the future civil transport systems.

Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase I | Award Amount: 99.98K | Year: 2011

A novel method of manufacturing complex unitized composite structures reinforced with 3D non-crimp orthogonal woven fabric (serving as self-sustained single-ply skin preform) and 3D braided fabrics (serving as self-sustained unitary preforms for stiffeners, Pi-joints or other similar elements) is proposed. The method uses two consecutive steps: high temperature cure resin infusion and room temperature cure resin infusion into the same skin preform via high temperature and room temperature VARTM processes respectively. The 3D braided preforms are attached to the skin preform and co-infused in vacuum bag at room temperature. The skin preform can be a hybrid of PAN-based and pitch-based carbon fibers; the former type fiber is used for the inner part and the latter type faces elevated temperatures. Special attention is paid to the interface between two distinct matrix materials occupying different parts of the skin and to the interfaces between skin and stiffener (Pi-joint). Special methods of interface strength enhancement using sprayed carbon nanotubes and creating porous regions will be studied. Non-destructive evaluation and initial mechanical testing will be conducted. BENEFIT: The proposed out-of-autoclave manufacturing approach will enable production of complex unitary composite structures suitable for future supersonic transport applications. This will be achieved by a relatively simple process and equipment, with minimal labor involvement and at significantly reduced manufacturing cost. The use of thick self-sustained integrally woven and braided 3D fabric preforms is a key: it will completely eliminate the steps of stitching multiple layers of thin fabrics for the skin and stiffeners, Pi-joints, frames, etc. By use of different carbon fiber types and combining high temperature and room temperature cure resins in the same preform, it will become possible to optimize the whole complex of thermo-mechanical properties of this new type of unitary composite structures.

Bogdanovich A.E.,3TEX, Inc. | Bradford P.D.,North Carolina State University
Composites Part A: Applied Science and Manufacturing | Year: 2010

Macroscopic textile preforms were produced with a multi-level hierarchical carbon nanotube (CNT) structure: nanotubes, bundles, spun single yarns, plied yarns and 3-D braids. The 3-D braided preform was the first of its kind produced by textile processing technique and used as a composite reinforcement consisting solely of carbon nanotubes. Four different epoxy systems that possessed a wide range of mechanical properties (owed to an added modifier) were infused into the CNT yarns and 3-D braids. Mechanical characterization of the resulting composites was conducted through the use of tensile testing. It was found that the tensile strength, stiffness and, especially, strain-to-failure values for each preform type were close regardless of the properties of the matrix whose strain-to-failure values ranged from 3.6% to 89%. This is hypothetically attributed to the nano-scale interaction between individual nanotubes and polymeric macromolecules in the composites. This hypothesis is validated by the Dynamic Mechanical Analysis results in Part II. © 2009 Elsevier Ltd.

Bradford P.D.,North Carolina State University | Bogdanovich A.E.,3TEX, Inc.
Composites Part A: Applied Science and Manufacturing | Year: 2010

Macroscopic textile preforms were produced with a multi-level hierarchical carbon nanotube (CNT) structure: nanotubes, bundles, spun single yarns, plied yarns and 3-D braids. In tensile tests, reported in Part I, composites produced from the 3-D braids exhibited unusual mechanical behavior effects. The proposed physical hypotheses explained those effects by molecular level interactions and molecular hindrance of the epoxy chains with individual carbon nanotubes occupying about 40% of the composite volume. Dynamic mechanical analysis was used in this Part II to study the molecular transitions of neat epoxy resin samples and their corresponding CNT yarn composite samples with varying matrix properties. Dramatic effects on the intensity and temperature at which α-transitions occured, were recorded, as well as a marked effect on the smaller segmental motions, or β-transitions. These changes in the matrix assist in explaining the mechanical test data presented in Part I and the proposed physical explanation of those data. © 2009 Elsevier Ltd.

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