SAMPE Journal - March/April 2011 - 37

pattern, namely 45° and 90°. Two layers are interwoven, which could be described as [(-45/45)/(90/0)]S and [(-45/90)/(45/0)]S. To let the machine place the desired pattern, a points file is created in Matlab and Excel which is used as input for the Fibre Placement Manager software. This Figure 1. A woven pattern created using fibre placement. creates the file with trajectories, head orientations and cutting in Figure 1 is created by placing a group of fibre bands in one commands for the Automated Dynamics Corporation direction, leaving a gap of exactly one bandwidth in between. automated fibre placement machine of the National A second group of fibre bands is placed in a second direction, Aerospace Laboratory NLR. Large 500 x 550 mm plates are creating the pattern shown in Figure 1b. Next the empty manufactured from which the specimens are cut. spaces shown in Figure 1a are filled up by a second group of The thermoset material used is Hexcel AS4/8552 prepreg fibre bands in the first direction shifted over one bandwidth. slit tape, supplied as 1/8” slit tape and 4 tapes placed Finally in Figure 1d the second direction is filled up creating together resulting in a bandwidth of ½” or 12.7 mm. As a two-ply laminate with a uniform thickness. this material has a cured ply thickness of 0.18 mm the In this example only two layers are interwoven, whereas in laminates were built up from 24 layers, resulting in a laminate theory an arbitrary amount of layers with different angles can thickness of 4.3 mm. The autoclave cycle recommended by be interwoven. Also instead of this 90 degree angle between the supplier is 60 minutes at 110°C followed by 120 minutes the two plies, any angle is possible. A photo example of one at 180°C. possible configuration with a 45 degree pattern is shown For the thermoplastic specimens the Automated Dynamics in Figure 2. Depending on the application and preferred Corporation fibre placement machine was fitted with the layup, this can be varied. Any layup can be created with this thermoplastic processing head. Again, the AS4 fibre was approach, and the location of the interwoven layers can be used, but this time in a pre-preg with Cytec APC-2 PEEK chosen at will, even combining unidirectional plies and AP- thermoplastic resin, supplied as 1/2 inch tape with a final plies. Finally the width of the bands used determines the resolution of the pattern, which influences the homogeneity of the laminate, performance and production time. As this fibre architecture does not involve curved fibre paths it does not have to deal with the gap and overlap issues often encountered in new fibre placement concepts4. Manufacturing For the compression after impact tests, specimens were manufactured according to ASTM standard 71365. Several options exist to make the prescribed quasi-isotropic laminate with a thickness of 4 mm. Two widely used lay-ups are [45/45/90/0]S and [-45/90/45/0] S, which are also described in the ASTM standard. These are well suited for the proposed pattern and allow for two different interface angles in the

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Figure 2. Example of one of the possible patterns.
SAMPE Journal, Volume 47, No. 2, March/April 2011

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SAMPE Journal - March/April 2011

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