PSI - Issue 42

Liviu Marsavina et al. / Procedia Structural Integrity 42 (2022) 1259–1265 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1260

2

wide range of plastic materials like polylactic acid (PLA), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), poly phenyl sulfone (PPS), polyethylene terephthalate glycol (PETG) and polyamide (PA) can be used for printing Ayatollahi et al. (2020), Bahrami et al. (2020).

Nomenclature a

crack lengrh

A B C E

fitting parameter for linear regression

width of the specimen

fitting parameter for linear regression

Young modulus maximum load

F max

c f

effective size of fracture process zone

G f M i

energy release rate bending moment radius of the specimen

R

R 0

transitional size half of the span nominal stress

S

 N  N0

fitting stress parameter The FDM works with specialized 3D printers and production-grade thermoplastics to build strong, durable and dimensionally stable parts with good accuracy and repeatability. Nowadays, there is a tendency to increase the size of the printed components and to produce big dimensional components and structures. However, there are no studies up to now to investigate the size effect on such components. In recent years the fracture toughness of FDM printed components was investigated by Arbeiter et al. (2018), Ahmad and Susmel (2018, 2019), Valean et al. (2020), which shows that the Linear Elastic Fracture Mechanics (LEFM) could be applied for these type of materials and components. Depending on the process parameters values the mode I fracture toughness of PLA between 3.5 to 7 MPa m 0.5 were obtained, Arbeiter et al. (2018), Ahmad and Susmel (2018). Also, the mode II fracture toughness of PLA was obtained between 2.4 to 3.6 MPa m 0.5 using Single Edge Notched Specimens loaded asymmetric, Marsavina et al. (2022). The size effect is in detail presented in Bazant and Planas (1998), Bazant (2002) and successfully applied for different type of materials like concrete and rocks, metal Bažant (1984), Bazant and Kazemi (1990), polymeric foams Zdenek et al. (2003), Marsavina et al. (2014). This paper represents an attempt to apply the asymptotic matching to investigate the size effect in two type of polymeric materials PLA and PETG obtained using FDM. 2. Experimental investigations In present study the size effect was investigated on Semi Circular Bend Specimens (SCB) samples, Fig. 1 made of PLA and PETG printed specimens using FDM technology. Four specimen sizes were considered with radius R = 10, 20, 30 and 40 mm, named S, M, L and XL, all with the same thickness of 6 mm. The ratio between crack length a and radius R was maintained constant a/R =0.5. The specimens were manufactured using a PRUSA printer. The manufacturing parameters are shown in Table 1. The specimens were loaded in three point bending maintaining the ratio between half of the span S and radius R of 0.8 ( S/R = 0.8). The static three point tests were performed on the Strength of Materials Laboratory from the University Politehnica Timisoara using the Zwick Proline Z005 (5 kN) static testing machine, Fig. 2. Tests were performed at room temperature (22±2ºC) with a loading speed of 2 mm/min. Five tests where carried on for each specimen size.