PSI - Issue 19

Christian Schneider et al. / Procedia Structural Integrity 19 (2019) 370–379 Ch. Schneider et al / Structural Integrity Procedia 00 (2019) 000 – 000

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Afterwards, two different types of specimen, following the simulation, were cut out. The geometry was 250 × 25 × 1.6 mm (length × width × thickness) for the EMB090 and 250 × 25 × 2 mm for the UD90. Two different end tabs were glued on the specimen. Following the simulation results, tabs made of GFRP with fibre direction of ±45°, a taper angle of 14° and a thickness of 1 mm were manually glued on EMB090. To compare the results of the UD90 specimen to previous works and literature, Aluminum tabs of 1 mm thickness were glued on them (Brunbauer et al. 2015; Gaier et al. 2017). The geometry details are shown in Fig. 5.

EMB090

UD90

Fig. 5: Geometry details (in mm) of the two different types of specimen (left); Specimen with the glued-on tabs (right).

4. Experimental procedure

4.1. Quasi-static tensile tests

For the quasi-static tests, several specimen of each type were produced and named with Carbon-Epoxy-Static Tension (CEST), the specimen type (01 = EMB090, 02 = UD90) and a running letter. The Quasi-static tensile tests were performed with both types of specimen on a universal testing machine Zwick Z250 equipped with a load cell and mechanical grips of 250 kN by Zwick GmbH & Co.KG (Ulm, Germany). For strain measurement in and transverse to test loading direction, a digital image correlation (DIC) system by GOM (Braunschweig, Germany) was used. The test speed for tensile tests at EMB090 was 2 mm/min and – because of expected lower forces – 1 mm/min for UD90. The specimen´s longitudinal Young´s modulus E xx and Poisson´s ratio ν xy were evaluated between 0.0005 and 0.0025 absolute strain according to (ÖNORM EN ISO 527-1) (2012). For the fatigue tests, the specimen were labeled by Carbon-Epoxy-Fatigue-Tension (CEFT), the specimen type (01 = EMB090, 02 = UD90) and a running letter. A servo-hydraulic test machine MTS 322 equipped with a loadframe and a load cell of 250 kN by MTS Systems Corporation (Minnesota, USA) was used. Fatigue tests were performed at three different stress levels depending on the layup. For EMB090, stress levels of 40 %, 45 % and 50 % of the static strength were chosen. The chosen stress levels for UD90 were 30 %, 35 % and 40 %. Test frequency f was chosen between 1 – 10 Hz depending on the load level. To detect hysteretic heating, an infrared (IR) sensor measured the surface temperature of the specimen throughout the whole test. All fatigue tests were performed at the R-ratio (defined as minimum stress σ min divided by maximum stress σ max ) of 0, which means σ min = 0 and the amplitude stress σ a = σ max /2. Fatigue tests were analysed statistically according to (ASTM E739 - 91). An additional optical camera system CV-X100 by Keyence Corporation (Osaka, Japan) was used to record crack initiation and growth at the edge of the specimen. The pictures were taken regularly with machine triggered count of cycles. 4.2. Fatigue tensile tests