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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3.3. Cyclic Shear Strength

The setup for the load-controlled, cyclic shear test is similar to that of the static shear test. Maximum loads of , , and are straining the GFRP reference specimens and , , and the hybrid specimens, respectively, at a stress ratio . At least three specimens have been tested at each load level at a frequency .

Fig. 2. Test setup of the EST-Test.

4. Results

4.1. Fracture Toughness

by means of

The DCB test according to the modified beam theory serves to evaluate the fracture toughness

the energy release rate

(1)

where d denotes the crack opening displacement (s. Fig. 1). is a correction value individually determined for each specimen. The average energy release rate , made up by at least three measurements per crack length, is fitted by a power law approach , (2) compensates for the units. The fitting parameters and , the detailed diagrams of the energy release rate as well as the fractographic details have been described and documented in Busch et al. (2017) and Brandt et. al. (2018). A limitation of the experimental setup allows only for the analysis of the fracture toughness according to Eq. (2) by an extrapolation of to denoted as . The variation of at , which is the crack length closest to , approximately defines the variation of at . Fig. 3 shows the results. The value for #GFRP at RT is . It increases for , and is highest for the aged specimens. The #Si specimens show the highest value at RT and a significant drop at as well as for the aged specimens. The value of specimen #Ti at RT shows the highest energy release rate of all specimens. In contrast to that, the aged variant and the test at exhibit a significantly reduced shear strength. The mechanically treated specimens exhibit a rather small fracture toughness at RT. The early failures of the specimens of the aged variant as well as for where and are fitting parameters, and