What triggers a microcrack in printed engineering parts produced by selective laser sintering on the first place?

Highlights: • Degree of particle melt (DPM) in SLS parts affect and control both crack initiation and propagation. • Assessment of fracture behaviour to investigate what is triggering a microcrack in the first instance. • It was found that un-melted particles proximity was the triggering effect in the onset of a microcrack. • A microcrack started invariably between the two closest un-melted particles. - Abstract: The proximity of un-melted particles within Selective Laser Sintered (SLS) printed engineering parts made of Nylon-12 is found as a major triggering effect for cracking and ultimately failure. The numerical investigation, by means of the eXtended Finite Element Method (XFEM), was performed over samples with different arrangements of un-melted particles obtained experimentally. The onset and propagation of microcracks was simulated. This included inherently how the degree of particle melt (DPM) in SLS parts affects and controls both crack initiation and propagation. The results evidenced that a microcrack started invariably between the two closest un-melted particles in all numerical tests performed considering different arrangements of un-melted particles.