3TEX (United States)

This paper presents the use of distributed fiber optic sensing to achieve centimeter level resolution strain data along the entire length of a large composite beam. A 6.5 meter long composite beam, designed for use in a corrosive flue gas desulfurization (FGD) unit, was instrumented. A section of optical fiber was embedded into a fiberglass rope, which in turn was embedded into the composite beam during the manufacturing process. The beam was experimentally tested in four-point bending at the North Carolina State University Constructed Facilities Laboratory, and the strain profile along the entire length was measured using the embedded optical fiber. Strains of up to 6500 microstrain were measured at over 300 unique positions along the span by monitoring changes in the spectral shift of the Rayleigh scatter in the optical fiber using optical frequency domain reflectometry (OFDR). The fiber used in this test was optically equivalent to standard telecommunication fiber, allowing for low-cost, high-density strain measurements on large structures. The experiment confirms the potential of embedded fiber optic distributed sensing to be used for real-time health monitoring, or as a process feedback in an instrumented structural system. Benefits of employing distributed fiber optic sensing in structures such as the composite FGD unit include the ability to monitor and detect deterioration and damage, minimize the chance of unplanned downtime or failure, and limit exposure to consequences such as environmental contamination.

Composites based on laminates of uniaxial or biaxial fiber reinforcements exhibit low through-thickness thermal conductivity, due to low matrix thermal conductivity and the number of interfaces in the thermal path. For applications near heat-generating components, the use of laminate composites in the surrounding structure can be limited by this inability to transport heat through the thickness. Three-dimensional orthogonal weaving provides an efficient, cost-effective method of placing high thermal conductivity yarns in the through-thickness Z direction of a preform to yield structural composites with high through-thickness thermal conductivity and with in-plane strength or stiffness comparable to laminates. Three basic research efforts investigated the efficacy of this approach: 1) weaving trials to determine the ability to three-dimensional orthogonal weave pitch carbon fibers and plied copper wires in the Z direction of the preforms, 2) through-thickness thermal conductivity testing of composites based on three-dimensional preforms, and 3) thermal modeling to describe several of the phenomena observed during thermal conductivity tests. During the testing, composites based on the three-dimensional orthogonal preforms with Z fiber volume fractions of only 5.5% measured a 12-fold increase in through-thickness thermal conductivity over a laminate composite, 8.4 versus 0.7 W/m K.

This paper presents the design and analysis for a spar cap for a wind turbine rotor blade. The cap is formed of an integral, unitary 3D woven material (3WEAVE®) having constant thickness; spar cap weight is varied and controlled by appropriately tapering the cap width from the blade root to tip. This analysis is employed for 24-m and 37-m rotor blades. These studies are conducted parametrically, examining a range of 3WEAVE® materials incorporating varying fractions of glass and carbon fibers, and hence exhibiting a range of structural properties and material costs. These parametric studies are used to determine the impact on blade weight and cost resulting from the various materials studied. Detailed results are presented in the form of tables to enable candidate materials to be evaluated as they are developed.

On the dynamic collapse of circular and square tubes under axial impact On analysis of axisymmetric crushing of tubes and frusta Crushing strength of ship structures On the side impact of hollow composite rail body shells Multibody systems dynamics methodologies for crashworthiness On the numerical simulation of the progressive collapse of polymer composite sandwich beams under impact loading Simplified analysis of square plates under explosion loading Ballistic penetration and perforation of steel plates - an experimental and numerical investigation Dynamic behavior of large-scale structures due to a low speed impact Dynamic response and failure of free-free beams under impact or impulsive loading Failure behaviour of prestressed concrete beams under high-speed and impact loadings.

A brief overview of 3-D braiding technology and its two major branches, “row and column” and “rotary” braiding, opens the paper. An innovative 3-D braiding process that has been recently patented and implemented in a fully automated multi-modular industrial scale machine is introduced next. The machine enables producing complex, continuously variable shape preforms for composite structures. Each module of the machine incorporates some number of horngears with four yarn carriers placed on each of them. A novel gate switch mechanism, based on the gripping fork controlled rotation, provides smooth transfer of yarn carriers between adjacent horngears. Each gripping fork is controlled individually, thus allowing fabricating practically unlimited variety of complex cross section 3-D braided preforms. Examples of manufactured braided products include rectangular bars, T-, I- and J-stiffeners, box-beams, hollow tubes, etc. Results and discussion of mechanical characterization of 3-D braided carbon and E-glass composites conclude the paper.