PSI - Issue 14

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

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A summary of the here considered mechanical properties are summarized in Tab. 2. The GFRP specimens serve as reference and their specific results are set to be . As a matter of this benchmark the authors recommend to choose a silane primer for their intrinsic hybrid laminate made up by GFRP and steel.

Tab. 2. Benchmark of hybrid laminates Test Conditions DCB – static (fracture toughness) T = RT

#GB

#GFRP

#Si

#Ti

68 %

100 % 100 % 100 % 100 % 100 % 100 %

143 %

225 %

- -

aged, T = RT

34 % 22 %

18 % 31 %

T = 80 °C

EST – static (Shear strength ) T = RT

64 % 51 % 69 %

87 % 87 % 92 %

78 % 36 % 80 %

aged, T = RT

T = 80 °C

EST – cyclic (Cyclic shear strength

)

- -

T = RT

100 % 100 %

80 % 80 %

80 %

T = 80 °C

-

3

Ranking:

1

2

The EST according to Weidenmann et al. (2015), which has been set up for GFRP specimens, has to be carefully applied to the here used hybrid samples. A fracture analysis of the cyclically tested hybrid specimens reveals that always a cohesive failure occurs within the resin. However, the cyclical shear strength is significantly smaller by compared to the reference #GFRP samples. A detailed FEM analysis shows a non-homogeneous stress distribution of the shear stress . A hotspot of the shear stress appears at the contact zone of GFRP to the pressure plate. For the #GFRP reference the maximum shear stress at the hotspot is compared to the nominal shear strength of the #GFRP reference. For the hybrid specimens the shear stress at the hotspot is . The mechanical root canse for this phenomenon is unclear yet. Furthermore, the FEM reveals that the shear stress distribution at the interface is nonhomogeneous as well. However, the maximum shear stress at the interface is much smaller than . If the strength of the interface is sufficient, the hybrid laminate will fail at the hotspot in the GFRP constituent. Only for severely reduced strengths at the interface, e.g. in the aged #Ti specimens, a failure occurs in the interface. Since the maximum shear strength of the #GFRP reference is smaller than for the hybrid laminate , the #GFRP specimens exhibit higher shear nominal strengths. Generally, the shear actual strength are underestimated by means of the EST. 6. Acknowledgement This work is funded from the European Union as a part of the competition “Neue Werkstoffe” EFRE.NRW. Further, the authors gratefully acknowledge the co-operation partner Mubea Fahrwerksfedern GmbH. ASTM D 5528-01: Standard Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites. ASTM International, 2010. Both, J. C.: Tragfähigkeit von CFK-Metall-Laminaten unter mechanischer und thermischer Belastung. Dissertation, München, 2014. Brandt, R.; Busch, A.: Fracture Toughness and Strength of the Interface of A GFRP-Steel-Laminate, Proceedings Hybrid, Bremen, 2018, pp. 56-61. Busch, A.; Brandt, R.: Characterization of the Bonded Connection in Hybrid-Steel-GFRP-Laminates, KEM 742, 2017, pp. 408 – 415. Monden, A.; Sause, M. G. R.; Horn, S.: Surface modified Steel/Epoxy-based CFRP hybrid Laminates under Mode I, Mode II and mixed-mode Load Conditions, ECCM17 - 17th European Conference on Composite Materials, München, 2016. Monden, A.; Sause, M. G. R.; Hartwig, A.; Hammerl, C.; Karl, H.; Horn, S.: Evaluation of Surface Modified CFRP-Metal Hybrid Laminates, References