PSI - Issue 42

Ralf Lach et al. / Procedia Structural Integrity 42 (2022) 3–8 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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considered specially at B = 4 mm. Specimens were also machined from 4 mm thick compression-moulded plates for comparison. 3. Fracture Mechanics Methods The calculation of elastic – plastic fracture mechanics values of thermoplastic polymers at impact bending loading is described in very detail in the MPK standard (Grellmann, 2016). For testing the instrumented Charpy impact tests was applied (ICIT; modified pendulum impact testing machine of company ZwickRoell GmbH & Co. KG, Ulm (Germany); pendulum hammer speed: 1 m/s; standard climate).

B

L 1

a

W

L 2

mini-CT specimens L 1 = L 2 = 25 mm

B = 4 mm a/W ~ 0.5

Fig. 1. Fracture mechanics mini-CT specimens manufactured using 3D printing of ABS.

Besides the crack resistance curve concept, also the concept of Essential Work of Fracture (EWF concept) has also been performed to characterize the stable crack initiation and crack propagation behaviour of ductile materials (Clutton, 2001). Here for example, double-edge notched specimens (differently deep and sharply notched 10 mm wide DENT specimens as used in this study) are loaded at tensile loading up to fracture and the load – displacements diagrams are recorded (universal testing machine Z020 of company ZwickRoell GmbH & Co. KG, Ulm (Germany); traverse speed: 2 mm/min; standard climate). The applicability of the EWF concept is particularly depending on whether full plastification of the specimen ligament occurs before crack initiation and on whether the load – displacements diagrams are self-similar (Lach, 2005). In this case, the total work of fracture U can be split into two components, where U p is the dissipated work inside the plastic zone and U e is the work of crack growth inside the process zone. With U e = w e · L·B and U p =  ·w p ·L 2 ·B the specific work of fracture w f = U/(L·B) is obtained with w f = w e +  ·w p ·L, where w e is the essential work of fracture (EWF) as measure of the resistance against stable crack initiation and  ·w p is a measure of the resistance against stable crack propagation (L is the ligament length with L = 2...8 mm;  is the shape factor of the plastic zone). Furthermore, crack resistance (R) curves were measured using compact tension specimens (mini-CT specimens, see Fig. 1) (universal testing machine Z020 of company ZwickRoell GmbH & Co. KG, Ulm (Germany); traverse speed: 2 mm/min; standard climate). To investigate the evolution of strain fields close to the crack tip during loading and crack propagation the digital image correlation was applied ((the system used was the Q400 measuring system manufactured by the company LIMESS Messtechnik und Software GmbH, Krefeld (Germany)). 4. Results and Discussion Fig. 1 gives an overview of the results of uniaxial tensile testing (tensile strength: Fig. 1a and elastic modulus: Fig. 1b) of ABS and PC. The processing parameters (printing speed and building direction) don’t have an effect (or