Issue 24

A. V. Babushkin et alii, Frattura ed Integrità Strutturale, 24 (2013) 89-95; DOI: 10.3221/IGF-ESIS.24.09 93 For defying elastic modulus at three point bending of laminate composite material should be used refined dependencies, which consider influence of shear deformations and binding maximum flexure max  of the beam in the middle of brackets with applied force P, true elastic modulus at bending t f E and interlayer shear modulus G : 2 3 max 1 48 f i k f i E P l h E I l G                     (1) where k  – coefficient, which depends on cross section form of the beam (for rectangular 1.2 k   ); 3 12 bh I  – moment of inertia of beam cross section. True elastic modulus at bending t f E is bonded with fictitious modulus 3 max 48 i f P l E I      in the following ratio 2 1 1 1.2 t f f i h E E G l          (2) The higher ratio of thickness of the specimen to its length i h l and the higher degree of anisotropy of composite material, characterized by t f E G , the more different true elastic modulus from fictitious. With one test it is impossible to calculate elastic modulus by formula (1) as it has two unknowns f E and G . So for their determination are tested several specimens with different ratios i h l       and then was diagram made, where on the horizontal axis was put off value 2 i h l       and on the vertical axis – 1 f E . In this coordinates, relation (2) has to be represented as a straight line, which crosses the vertical axis at the point 1 t f E and slope of this line to the horizontal axis equal 1.2 G . Then value of t f E and G are determined by method of least square. D ISCUSSION OF RESULTS ension test results of highly filled fiberglass specimens (Direct "E" roving 0.7 - orthophthalic polyester resin 0.3) are in the Tab. 1. Temperature, °C Tensile strength at break  b MPa Young's modulus in tension E, GPa -30 922.1 34.2 0 980.2 36.8 +22 987.1 47.8 +40 690.5 38.8 +50 - 37.4 Table 1 : Unidirectional fiberglass (Direct "E" roving 0.7 - orthophthalic polyester resin 0.3) properties at tension test [3]. T