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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1. Introduction Apart from being able to produce more complex structures in terms of geometry, AM also excels over conventional manufacturing processes in its capacity to manipulate the internal structure of manufactured components. This is very useful for the production of lightweight parts with sufficient structural integrity in the automotive and aerospace industries, as stated by Alami et al. (2023), as well as for certain applications in the biomedical field (as stated by DeStefano et al. (2020)). For example, if the internal structure of orthopedic and fixation plates is manipulated, in addition to having the function of fixing bone fragments, they can also serve as drug carriers. Such applications include biocompatible and biodegradable polymer materials, which should withstand dissolution over a certain period and then gradually release the drug. Also, being biodegradable, the need for another operation to remove the plate becomes unnecessary. PLA material is probably the most suitable material for such applications, as stated by Farah et al. (2016). The final components’ mechanical properties are affected by the AM process parameters. A thorough analysis of process parameter influence on tensile properties of PP thermoplastic material was conducted by Milovanović et al. (2022a), and the following Milovanović et al. (2023) research was enhanced with statistical analysis using the ANOVA method with Tukey post hoc test. Namely, both research articles discussed the influence of infill density, layer height, and raster orientation. A comprehensive analysis of infill density and pattern on tensile properties of PLA material was performed by Pandžić et al. (2019). Here, the 13 different infill patterns were included in 10 different infill sets, from 100 to 10%. A gradual decline in all tensile properties was recorded from high-to-low infill percentage. In addition to the evaluation of fundamental mechanical properties, fracture mechanics principles are also an established practice in the testing of AM materials. For example, Linul et al. (2020) and Stoia et al. (2020) investigated the Mode I and Mode II fracture properties of materials manufactured by SLS using SENB specimen geometry. As for FDM technology, Marsavina et al. (2022) researched the AM process parameter effect on PLA material’s fracture toughness values. Namely, the influence of build orientation, layer, and specimen thickness were considered. Also, there is a report in Valean et al. (2020) on the advantages of directly printing a notch, versus preparing it on the milling machine. The effect of outer wall number on K IC results was investigated by Milovanović et al. (2022b), thereby stating that for acceptable results outer wall thickness should not be greater than a pre-crack length. Another example is the Ayatollahi et al. (2020) research which considers the different raster angles and their influence on fracture properties. An interesting study was conducted by the Arbeiter et al. (2018) group which saw the limitations of LEFM while using ASTM D5045 standard namely, their SENB specimens exhibited non-linear deformation before fracture. Hence, the application of EPFM methods was necessary for the evaluation of fracture properties, which led them to use J integral. Some of the results from this research cannot be interpreted using LEFM methods and will follow the recommendations from Arbeiter et al. (2018).

Nomenclature ANOVA Analysis of variance AM

Additive manufacturing Crack tip opening displacement Digital image correlation Elastic-plastic fracture mechanics Fused deposition modeling maximum J-integral value mode I fracture toughness Linear elastic fracture mechanics

CTOD

DIC

EPFM FDM

J max K IC

LEFM

PLA P max

Polylactic acid

maximum load value

PP P Q

Polypropylene

conditional load value Single edge notched bending Selective laser sintering

SENB

SLS