Effect of induced plastic strain on the porosity of PA12 printed through selective laser sintering studied by X-ray computed micro-tomography

Abstract

3D printing is a widespread technology in different fields, such as medicine, construction, ergonomics, and the transportation industry. Its diffusion is related to the ability of this technique to produce complex parts without needing for assembly of different components or post-processing. However, the quality of the parts produced by additive manufacturing could be affected by the fabrication process, thus leading to the development of different kinds of defects such as porosity or inclusions. Understanding the role played by these defects and promoting strategies that could help reduce their occurrence represents a key point to allow using 3D printing for structural applications. In this work, 3D printed parts have been subjected to porosity characterization by using experimental tests on Dogbones samples subjected to plastic deformation. In particular, X-ray computed micro-tomography (µ-CT) has been employed as an investigation tool for the identification of fabrication defects and for analyzing the crack growth mechanism that occurs after subjecting samples to quasi-static loading conditions.

Additive Manufactured Parts Produced Using Selective Laser Sintering Technology: Comparison between Porosity of Pure and Blended Polymers

“…Moreover, the authors found a skin that appears to be significantly denser compared to the internal region. Similar results were obtained by Ajoku et al [40], by Rouholamin and Hopkinson [41], and by Morano et al [42].…”

“…As an example, Figure 4a reports a comparison between the porosity values obtained by various authors (Stichel et al [25], Dewulf et al [36], Morano et al [42], and Pavan et al [47]) with approximately equal ED values (ED = 3.4 ± 0.1 J/cm 2 ), while, in Figure 4b, the contribution of pores with a specific diameter on the total porosity can be observed. The average value of the measured porosity is equal to 3.5 ± 0.3%.…”

“…Morano et al [42] analyzed the change in the shape and distribution of the pores during quasi-static loading conditions, inducing plastic strain, by employing X-ray micro tomography. The authors found a significant variation in the porosity percentage by increasing the residual deformation.…”

Effect of Strain Rates and Heat Exposure on Polyamide (PA12) Processed via Selective Laser Sintering

“…Moreover, the mechanical properties are also dependent on the internal structure of the sample, e.g., porosity or inner defects [ 36 , 37 ]. It is well known that parts obtained by additive manufacturing are characterized by the occurrence of internal porosity [ 38 , 39 , 40 , 41 , 42 ]. In a previous work by the authors [ 40 ], the inner morphology of 3D-printed dogbones fabricated using PA12 was examined, revealing a significant level of porosity at approximately 3%.…”

“…Moreover, observable unmelted powder particles were believed to have a substantial influence on the porosity formation process. Typically, pores originate during the SLS printing process, as testified by different works [ 40 , 44 , 45 ]. Moreover, some big dimples originate after fracture due to the detachment of unmelted particles [ 43 ].…”