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In this paper we build some composite materials reinforced with needles from fir trees. In order to build the samples, we have firstly created some strips in this way: we put the pines, continuously, on a sheet of paper where we apply a thin layer of resin (we have used epoxy and polyester ones). We have made 10 strips and we have glued them together by using the same synthetic resins (epoxy and polyester). In the end we have obtained some composites reinforced with strips from fir trees needles and paper sheet, and the matrix is made from epoxy and polyester resins. From the obtained plate, we have cut some samples in order to study their free vibrations. We have placed an accelerometer at about 10 mm from the free edge and we have clamped the samples on several free lengths. The accelerometer is connected to a signal conditioner NEXUS which is also connected to a data acquisition system SPIDER 8. The data acquisition system is connected to a notebook through USB port. From the samples free vibrations, we have determined: the eigenfrequency, the damping factor per unit mass, damping factor per unit length, dynamic stiffness, dynamic Young modulus and loss factor.

Dynamic behaviour of composites reinforced with needles from fir trees