PSI - Issue 68

Aleksa Milovanović et al. / Procedia Structural Integrity 68 (2025) 922 – 928 A. Milovanović et al. / Structural Integrity Procedia 00 (2025) 000–000

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2. Materials and Methods Experimental tests were performed at room temperature in laboratory air conditions according to the ASTM D5045 standard for plane-strain fracture toughness assessment on SENB specimens using a Shimadzu AGS-X machine (Shimadzu Corp., Kyoto, Japan) loaded with a proprietary 3-point bending test rig and a load cell of 1 kN capacity. The specimens are 88x20x10 mm in bulk, with an 80 mm distance between the centers of supporting rollers. The notch was additively manufactured, as recommended by Valean et al. (2020) with 8 mm depth and 1 mm width. Pre crack length is approx. 2 mm (see Fig. 1). This conference paper encompasses only a fraction of the whole research regarding layer height and infill percentage influence on fracture properties of PLA thermoplastic. Here, only four infill cases are presented (100%; 70%; 40%; 10%) for the 0.1 mm layer resolution. The whole research includes 10 infill cases from 10 to 100% for 0.3 mm, 0.2 mm, and 0.1 mm layer configurations. Each specimen group contains three SENBs, and the loading pin speed is set to 5 mm/min (as recommended in the standard).

Fig. 1. SENB specimen engineering drawing (units in mm).

The tests strictly follow the recommendations from ASTM D5045-14 standard. From the load-deflection data, a straight line was drawn along with a 5% greater compliance on the linear part of the curve (see Fig. 2-Left). Unfortunately, some of the presented results don’t meet the P max / P Q < 1.1 requirement, and have to be presented using different methods. For simplicity, this conference paper includes J max values calculated from the total absorbed energy U t until the load reaches P max , subtracted by indentation energy U i until the corresponding P max (see Fig.2-Right). Namely, separate indentation tests with the same loading conditions were performed on intact SENBs for all considered infill cases, as suggested in the ASTM D6068-10 standard. In this case, the bottom supports were placed next to each other, to minimize the specimen bending. The J max values are used here not just for the interpretation of invalid results but also to compare all the tested SENBs.

Fig. 2. Load-deflection diagram for: Left- K IC calculation; Right- J max calculation.