Issue 28

P.Valentino et alii, Frattura ed Integrità Strutturale, 28 (2014) 1-11 ; DOI: 10.3221/IGF-ESIS.28.01 9 The stiffness values, numerically calculated, show good agreement with the corresponding experimental ones in both the considered cases, i.e. experimental and standardized, φ f =50%, fibre volume content. In particular, the stiffness determined by the FE-analyses lies in the range of the secant modulus E s.0.5% and the tangent modulus E t.0.1% . As an exception the numerical results for the stiffness of the twill weave 1/3 in fill direction yield slightly lower values than the experimental ones. Experimentally determined strengths and corresponding failure modes Tensile strength values σ z.B , based on the experimental results, have been calculated, according to [22] and [12], and shown in Fig. 12, respectively. In particular the experimental values related to the twill weave 2/2 reinforcement are higher than the ones calculated by the indicated values in the data sheets, while a good agreement has been observed for the twill weave 1/3 reinforcement. With the aim to provide a proper interpretation of the experimental tensile tests a careful analysis on the failure modes and crack pathpropagationhas been carriedout. In particular, in Fig. 11 is shown a depiction of a typical fracturemode of a specimenwith twill weave 2/2 reinforcement. Woven fabric with 0°-90° and 90°-0° orientation exhibited analogous failuremodes. The crack started in the gauge length andproceeded perpendicularly to the applied load. Figure 11 : Fractured specimen with twill weave 2/2 fabric reinforcement in the warp direction. The area enclosed in the square box show details of the damagemechanism. InFig. 13 is shown a depictionof a typical fracturemode of a specimenwith twill weave 1/3 reinforcement. Similar to the previous case study, the orientation of the woven fabric did not affect the failuremode and the crack started in the gauge length. However, the crack path is inclinedof approx. 45° to the applied load axis. Figure 12: Calculated tensile strengths of the respective textile semi-finished products standardized to a fibre volume content of φ f =50%.