PSI - Issue 56

Estera Vălean et al. / Procedia Structural Integrity 56 (2024) 58 – 64 Estera Vălean et al./ Structural Integrity Procedia 00 (2023) 000 – 000

60

3

material, the application of the SED method cannot disregard the determination of the control volume characteristic length. Due to the independency of the control volume characteristic length and of the SED critical value on the geometry, both can be determined if the loads to fracture are known for the same material according to two different geometrical conditions. This led to the development of analytical solutions for the determination of such as the following ones that gives for static conditions as a function of the ultimate tensile strength and of the fracture toughness, , (Lazzarin et al. 2005; Yosibash et al. 2004):

2

  

  

 K

(1 )(5 8 ) 4     

R

plane strain



IC

(2)

0

UTS

2

     K

  

(5 3 ) 4  

R

plane stress



C

(3)

0

UTS

The concepts presented in the above constitute the basic idea of the method; for further insights on the method analytical framework and applications, we recommend the works of Radaj et al. 2013 and Berto et al. 2014. 3. Materials and methods The materials considered in this work are polylactic acid (PLA, Silver - Prusa Polymers) and carbon fiber reinforced polylactic acid (PLA-CF, Sunlu - containing short CF (<20%)). Prusa MK3 printer was used to realize the specimens. 3D printing software was used to set the printing parameters, such as raster angle, head speed, temperature and so on. The temperature of the nozzle and the built platform was controlled at around 60°C and 215°C, respectively. An infill density of 100% is defined in the printing software with raster angles of ±45 degrees for the infill, while the orientation position of the part on the built platform was 0°. The tests have been carried out in displacement control mode (2 mm/min) using an electromechanical testing machine (Model: Z wick Roell 005) with a maximum load of 5 kN. The Young’s modulus , E , ultimate tensile strength, , and strain at break, , were obtained considering three smooth specimens per material according to ISO 527-1 (2012) while the fracture loads were o btained for notched specimens with changing the notch opening angles 2α, as reported in Fig. 1, considering five specimens per geometrical condition and material.

Fig. 1. Geometries of the test V-notched specimens tested under tension. All specimens are 4 mm thick.