Issue34

S. Keck et alii, Frattura ed Integrità Strutturale, 34 (2015) 371-378; DOI: 10.3221/IGF-ESIS.34.41 372 At first, materials and specimens are explained. Then experimental investigations and numerical computations are described. Later on the identified crack paths and fatigue crack growth curves are illustrated. Finally, conclusions of the obtained results and an outlook are given. M ATERIAL AND SPECIMENS n this work the composite is reinforced with flax-fibres, which are semi-finished products (yarn and twisted yarn). Their density is about 1,450 kg/m³ [1]. For the polymer matrix an epoxy resin is used. The fibres get rolled on a frame to achieve a unidirectional alignment (Fig. 1). Due to the orthotropic behaviour of the fibres and the unidirectional alignment the composites are orthotropic, too. Unnotched specimens and compact tension specimens were taken from plates (geometric dimensions: 500 mm x 470 mm x 10 mm). The size of an unnotched specimen is 150 mm x 15 mm x 10 mm. The geometric dimensions of the compact tension specimens (Fig. 2) are chosen according to the ASTM standard E647-13 [2]. Due to the smaller mechanical properties (Fig. 3) compared to metallic materials the drill holes are reduced. The specimen depth is set to 10 mm. A post- curing process provides a higher strength of the polymer matrix. For each compact tension specimen the pre-crack initiation is produced with a razor blade (razor sawing). Figure 1 : Semi-finished product consisting of flax. Figure 2 : Geometric dimensions of the investigated compact tension specimen (dimensions in mm). I

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