DESIGN OF CFRP WITH FIBERS PLACED BY USING AN EMBROIDERY MACHINE K. - PDF document

18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS DESIGN OF CFRP WITH FIBERS PLACED BY USING AN EMBROIDERY MACHINE K. Oka 1 , T. Ikeda 2 *, A. Senba 2 , T. Ueda 1 1 Department of Aerospace Engineering, Nagoya University, Nagoya, Japan, 2 Composite Engineering Research Center, Nagoya University, Nagoya, Japan * Corresponding author (ikeda@nuae.nagoya-u.ac.jp) Keywords : CFRP, Optimization, Tailored fiber placement, Embroidery machine 1 Introduction 2 Design method for composites with fibers placed along optimal path Mechanical properties of composite laminates significantly depend on the fiber orientation of each 2.1 Optimal fiber path layer. Accordingly, if the fibers can be placed along Continuous optimal path, along which fibers are desired orientations within a layer, a composite placed by an embroidery machine, is obtained as structure can be designed so as to be optimized for follows. First, the target plate is divided into finite some properties. To this end some tailored fiber elements to predict quantities, such as displacements, placement (TFP) methods were suggested [1, 2]. stress, and strain, in an objective function or Tatting and Gurdal [1] used prepregs for processing constraints of an optimization method by using an the laminates, while Tosh and Kelly [2] used dry FEM. The optimal fiber angle  in each element is tows placed on a substrate by using an embroidery estimated by using combination of the FEM and an machine and this preform was impregnated with optimization method. The paths of the fibers in the resin. The latter method is expected to be lower-cost plate are determined if initial points of the paths because the prepregs themselves and their storage along the edge of the plate are determined. In this are costly. paper the initial points are obtained by a streamline To find the optimal orientations of the fibers an analogy [5]. optimization method, such as the first order Since a value of a stream function  does not vary optimization method (FOO) [3], the particle swarm along a streamline, optimization (PSO) [4], and the method that the         x y fibers are placed along the principal stress direction        (PSD), can be applied. FOO has good convergence, s x s y s . (1) although the obtained solutions may be in local          cos sin 0 solutions. PSO can find global solutions, although   x y much iteration may be needed to get global solutions. The coordinate along the streamline is defined as s , PSD is better than the other methods with respect to and the x - y coordinates and the fiber angle  are the computational cost, although PSD is not always illustrated in Fig. 1. If the slope along the normal to good method, when multiaxial stress condition or  dynamic problems are considered. the streamline is assumed to be constant , along n In this paper, a method to design composites with the edge on which the initial points are located;         optimal fiber orientations for an objective is x y   established. The embroidery-based TFP is adopted      n x n y n and a stiffness property of a plate to which a load is , (2)     applied around a corner is optimized.        sin cos , n   x y the initial points are determined by

    Table 1. Elastic constants       sin    x   PWCF E 54 . 9 [ GPa ], 0 . 28   , n   , (3)       cos     EPOXY E m 3 . 17 [ GPa ], 0 . 35      y m    TFP E 101 . 8 [ GPa ], E E 5 . 62 [ GPa ] for a certain constant d  . The coordinate along the 11 22 33    normal to the streamline is defined as n . G G 1 . 76 [ GPa ], G 1 . 94 [ GPa ] 12 31 23       2.3 Process of the composites 0 . 28 , 0 . 45 , 0 . 02 12 23 31 A carbon fiber dry preform is made by the embroidery machine as shown in Fig. 2, where the 3.2 Optimization results dry carbon fiber bundles are placed along the optimal paths on a substrate of a plain woven carbon The optimized fiber angles for the three fabric (PWCF). The preform is impregnated with optimization methods are shown in Figs. 4 (a), (b), epoxy resin by using the vacuum assisted resin and (c). These figures show a similar distribution of transfer molding (VaRTM) method. the fiber angles except for the distribution around the free end edge opposite the clamped edge for the 3 Results PSD in Fig. 4 (c). This region is, however, not 3.1 Bending-torsion problem important in this case because the region is located within the free end edge and the load point and no To verify availability of the above mentioned stress are generated there in the material. procedure, it was applied to a bending-torsion The fiber paths obtained from the fiber angle problem shown in Fig. 3. In this case, TFP layers of distribution optimized by FOO is shown in Fig. 5. the plate were divided into 15 regions in the x - The width between the neighbor fiber paths is not direction and the fiber angles in the regions were uniform along the streamline, that means the volume optimized by three optimization methods; FOO, fraction of the fiber is not uniform. PSO, and PSD. The optimization problem was given The numerical and experimental results of the by     bending-torsion stiffness defined as z F divided by the θ Find: [ ] 1 15 load are shown in Fig. 6. Laminate plates with layers which minimalizes: z F of straight fibers placed in 0 o or  45 o direction (4)       subject to constraints: 90 90 i instead of the optimized layers were also processed        15 , ( i 1 15 )  and their stiffness was compared with that of the i 1 i plate with the optimized layers. It is seen that there z F is the displacement of the load point shown in Fig. is no difference among the optimization methods 3 and it is calculated by using a commercial FEM and that the stiffness can be improved by 13% program ANSYS. compared to the plate with 0 o layers and by 95% to The stacking sequence of the laminates was the plate with  45 o layers. [PWCF(0 o , 90 o )/TFP layer/PWCF(0 o , 90 o )/PWCF(0 o , 90 o )] sym . The dry carbon bundles (Toho Tenax 4 Discussion HTS40-12K) were placed on the PWCF (Toho The stiffness obtained by the calculation is much Tenax W-3101) by inputting the optimized paths of higher than that obtained from the measured data as the fiber bundles into the embroidery machine shown in Fig. 6. This is because the mathematical (Tajima TCWM-101) shown in Fig. 2. The preform model does not include the embroidery effects such was impregnated with epoxy resin (West System as the damage by the sewing needle and the Z105 /Z206). thickness distribution due to the non-uniform width The thickness of the PWCF layer and TFP layer between the paths. were assumed to be 0.22 mm and 0.54 mm, When the carbon fiber bundles are placed on the respectively. The elastic constants were set at values PWCF by the embroidery machine, they are shown in Table 1. damaged by the embroidery needle. Accordingly, the stiffness of the laminate plates decreases. To