Estudo do desalinhamento das fibras nas propriedades mecânicas de compósitos estruturais de pás eólicas / Study of fiber misalignment effects on the mechanical properties of wind blades structural composites

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

This work presents the study of waviness influence on the mechanical properties of wind blades structural components fabricated by vacuum infusion. For this purpose, out-of-plane waviness, which is a common manufacturing defect, was induced on glass and carbon reinforced plastics (GRP and CRP) and compared with control laminates without waviness (wave-free control specimens). With a special device, different severities varying from 2,5 to 20 % were intentionally induced in the laminates Specimen families with different severities were machined for statics longitudinal tensile test (0°, load applied on fiber direction) and longitudinal compression test (0°), and tensile-tensile fatigue dynamic test, R = 0,1. ISO 527-5, ISO 14126 and ASTM 3479 norms were respectively used for the tests. Both static and dynamic tests were performed on servo-hydraulic machines. Elongation, load and cycles number until brake were acquired and used to determine the tensile strength, the compression strength, the strain at break and fatigue life. During the longitudinal tensile test it was possible to determine the Young modulus and the Poisson coefficient using strain gauges extensometers. The waviness on GRP and CRP affects negatively the tensile strength, with a reduction of 25 % for GRP with S = 20 %, and of 13 % for CRP with S = 12,5 %. The drop of compression strength was significant due to the fact that the fiber misalignment leads to a buckling compression failure. Comparing the control laminate with the S = 20 % one, this reduction was 84 % for GRP and 70 % for CRP. The fatigue analysis proved that the out-of-plane waviness reduces substantially the composite life time under severe strengths. For an applied load of 65 % of control glass laminate tensile strength, the fatigue life for the control group was 60.000 cycles. Applying the same load, the fatigue life was reduced to 30.000 cycles for S = 10 % family and to 1.500 for S = 20 %. The mechanical tests results showed the negative influence of the waviness on the composite mechanical properties, and demonstrated the existence of a catastrophic and premature failure, localized on the central region of the wave, which can turns in a potential area for crack initiation of a structural component with severe load. In summary, this study allowed quantifying the effects of out-of-plane waviness on the mechanical properties of wind blade structural components.

ASSUNTO(S)

compósitos propriedades mecânicas pás eólicas reforço de vidro e carbono matriz epóxi composites mechanical properties wind blade glass and carbon reinforced materials epoxy matrix

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