PSI - Issue 14

Robert Brandt et al. / Procedia Structural Integrity 14 (2019) 891–899 Robert Brandt/ Structural Integrity Procedia 00 (2018) 000 – 000

897

7

diagrams of the hybrid specimens. At RT the inclinations of the specimens are for the silane treated and for the titanium dioxide treated specimens. The cyclic shear strengths are for both specimens . For an elevated temperature , the inclination becomes for the silane and for the titanium dioxide treated specimens. All results are summarised in Tab. 1.

Tab. 1. The parameters of the Wöhler-type curves of the cyclic shear strength test #GFRP

#Si

#Ti

RT 25 9,5

80 °C

RT 20 7,4

80 °C

RT 20 8,4

80 °C

21

17

-

at

cycles [MPa]

10,6

6,5

10,0

inklination

5. Conclusion Our evaluation of the fracture toughness of #GFRP specimens reveal that neither an elevated temperature of nor an aging may harm the toughness of GFRP. However, the magnitude of the fracture toughness values has to be critically discussed considering the extrapolation method. Most commonly, the fracture toughness is evaluated at the point of nonlinearity (NL) in a δ -F diagram, according to Eq. (1). As a matter of the different method of analysis, the deviation between the NL-method and the extrapolation method are approximately up to , s. Fig 7. However, the

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

NL-Method

Extrapolation-Method

Fracture Toughness G I,50mm [N/mm]

#GFRP (T = RT)

#GFRP (aged)

#Si (T = RT)

#Si (aged)

#Ti (T = RT)

#Ti (aged)

Fig. 7. Comparison between the experimental NL-Method and the Extrapolation-Method

trend stays the same. Without any doubt, the fracture toughness of the intrinsic hybrid laminates suffers by the increased testing temperature or by an aging before testing. Severe drops of fracture toughness are clearly recognized in the range of up to in comparison to the reference. At RT, the fracture toughness of the intrinsic hybrid laminates even exceeds that of #GFRP. The static shear strength is less affected by an elevated testing temperature or aging. Even #GFRP specimens show a drop at detrimental conditions. Furthermore, the values for the #Si and #Ti specimens are always smaller than those for #GFRP. The cyclically tested specimens show the highest values for #GFRP at cycles. For a test at the cyclic shear strength of the reference is reduced by in comparison to RT. Both variants of the hybrid specimens show up a reduced shear strength of - in comparison to the reference. The influence of an elevated test temperature of is for #Si , which is close to the reference.