PSI - Issue 2_B

F.Sacchetti et al. / Procedia Structural Integrity 2 (2016) 245–252 247 F.Sacchetti, W.J.B. Grouve, L.L. Warnet, I. Fernandez Villegas/ Structural Integrity Procedia 00 (2016) 000 – 000 3

2. Experimental methods

The present section describes the preparation of the materials as well as the DCB and mandrel peel test procedures. The DCB tests were carried out according to the ISO 15024 standard. As no standard exists for the mandrel peel test, the test was carried out based on an ESIS protocol [Kawashita (2005)]. The influence of test speed and specimen width on mandrel peel toughness was characterized experimentally as well.

2.1. Materials

One Carbon/PEEK 5 harness satin weave laminate from TenCate with a [(0/90)/(0/90) r ] 4s lay-up was press consolidated in a Pinette press at 10 bar and 380 °C for 10 min. For the crack initiation region, a 12.5  m thick Polyimide film (Upilex S) was inserted prior to the consolidation process. The film was added in different positions to obtain both the DCB and the mandrel peel specimens from the same laminate. In one half of the laminate the film was inserted between the two first plies in order to obtain the peel specimens, while in the other half the same film was added at the mid-plane of the laminates to obtain the DCB specimens. The repetitive unitcell of 5 harness carbon/PEEK has a dimension of 7 mm. Peel samples of width 10 mm and 18 mm were cut from the first half of the laminate. The 10 mm wide specimens contain slightly more than one unit cell of the weave pattern in the width of the specimen, while the 18 mm specimens contain more than two unit cells in the width direction. Specimens of 20 mm width were cut from the laminate to obtain the DCB specimens. The dimension of the DCB samples follow the ISO 15024 standard. The double cantilever beam test was performed according to the ISO 15024 standard. The specimens were tested in a servo-hydraulic Instron 8500 universal testing machine equipped with a 200 N force cell. The crack length was measured using an automated camera system, engineered to follow the crack tip during the test, mounted on the universal testing machine. The camera was fitted with a lens having a 20x magnification. The applied force ( F ), the displacement ( δ ) as well as the crack length ( a ) was measured during the test, performed at a displacement rate of 1.2 mm/min. The obtained data was reduced using the corrected beam theory (CBT). As the delamination length is measured directly using the horizontal displacement of the traveling camera system, there is no need for a correction to be applied to the measurements. All DCB samples showed unstable crack propagation, the fracture toughness was calculated only for re-initiation values. The mandrel peel setup used in this work has a mandrel with a radius of 10 mm and a width of 18 mm. A constant displacement rate was applied using a Zwick universal testing machine in which the peel set up is fixed. The alignment force F a , necessary to conform the peel arm to the mandrel, was applied using a pneumatic actuator. It was kept constant at approximately 60 N for the 10 mm wide tapes and 108 N for 18 mm tape. Two 200 N force transducers were used to measure the alignment and peel force F p . The test consists of two steps. First, the top ply is peeled from the laminate. The critical energy rate can be calculated from the measured forces using Equation 1. = 1 ( (1 − ) − ) (1) However, the friction present in the setup μ is not known. Therefore, as a second step, the test is performed again on the previously peeled specimen for which G c is equal to zero. Consequently, the friction coefficient can be obtained from Equation 1 as: = − (2) 2.3. Mandrel peel test 2.2. Double cantilever beam test