PSI - Issue 76

Davide D’Andrea et al. / Procedia Structural Integrity 76 (2026) 151–158

152

1. Introduction Selective laser sintering (SLS) is one of the Additive Manufacturing (AM) techniques adopted for the production of polymeric materials, obtaining components having complex geometries with mechanical properties compatible for various engineering applications such as automotive, aerospace and medical. SLS process consists of layer-by-layer laser sintering of powder particles over the platform of a printing bed.. Traditionally, components had to be designed with manufacturing constraints in mind, relying on subtractive methods, like milling, turning, and drilling, which limited the ability to create complex geometries. On the other hand, AM allows to obtain complex shapes by printing parts slice by slice rapidly. The increasing global focus on a sustainable industry focused on reducing the environmental impact of products and production cycles, as well as minimizing resource waste, has driven the development and adoption of innovative materials, such as compostable materials. Polyamide 12 (PA12) is the most used powder in the Selective Laser Sintering (SLS) process. According to EN ISO 10993-1, parts produced from PA12 are both chemically and physically durable, as well as biocompatible. In addition to SLS, PA12 can also be used in other AM technologies such as FDM, when available in filament form, and HP Multi Jet Fusion, a powder-based process developed by HP (Khorasani et al., 2024). Its mechanical properties make PA12 an ideal matrix to be reinforced by materials such as carbon fibres (Danilo D’Andrea et al., 2025; Jansson and Pejryd, 2016) and glass fibres (Hao et al., 2019; Kohutiar et al., 2025). While its mechanical properties are well investigated in literature, there are a few works focused on its fatigue properties (Avanzini et al., 2022; Rosso et al., 2020), which are strictly related to printing parameters such as build orientation and velocity, layer thickness, position in the printing chamber and energy level (Stoia et al., 2020). Other researchers (Chen et al., 2018; Koh et al., 2023) demonstrated also that PA12 printed by powder processes is affected by ageing phenomena; for this reason, rapid methodologies to obtain fatigue limit should be used. Thermographic Methods (TMs), traditionally used for the rapid assessment of fatigue properties in engineering materials such as steels produced by conventional manufacturing processes, in recent years has been increasingly applied to investigate the mechanical properties of AM components, including those made from steels, polymers, and carbon fibre-reinforced composites. In particular, Risitano’s Thermographic Method (RTM) was used to obtain fatigue limit and S-N curve as explained in (Fargione et al., 2002; La Rosa and Risitano, 2000), while Static Thermographic Method (STM) (Risitano and Risitano, 2013) was applied to identify a critical stress value, referred to as the “limit stress” , which should not be exceeded to avoid failures under fatigue load conditions. In the present work, two sets of SLS PA12 specimens were tested adopting RTM and STM, retrieving information regarding the fatigue limit and the S-N curve of the material. The results were validated through a conventional constant amplitude (CA) fatigue test campaign showing a good agreement between the estimated values.

Nomenclature E

Young’s Modulus [MPa] testing frequency [Hz] inverse slope of the SN curve

f

k

N, N f

number of cycles, number of cycles to failure

R

stress ratio

ΔN Δσ ΔT ΔT st

Number of cycles block length

stress increase of a stress-controlled stepwise fatigue test [MPa]

temperature variation [K] stabilization temperature [K] ultimate strain yield strain Energy Parameter [Cycles ⋅ K] limit stress from STM [MPa] equivalent stabilization temperature [K]

ΔT st eq

ε u ε y Φ

σ lim