PSI - Issue 77

Bastian Roidl et al. / Procedia Structural Integrity 77 (2026) 119–126 Bastian Roidl / Structural Integrity Procedia 00 (2025) 000 – 000

120

2

There are many parameters that affect fatigue properties. From these the effect of geometry and related size effect on fatigue performance of additively manufactured specimens is discussed in this paper. In the case of AM-products, Chen et al. showed that an increase in specimen size leads to lower fatigue resistance [7]. Dong et al. found out that smaller diameters of the specimens lead to lower tensile properties and to an increase in porosity [8]. Test parameters are another key factor influencing the results of fatigue life tests. Among others, the load ratio, defined as the ratio between minimum and maximum stress in the cycle, affects the results of the fatigue life tests. Load ratios define the value of the mean stress that is achieved during testing. Indeed, mean stresses have an impact on crack propagation and crack initiation [9] and thus on the fatigue life of components. Tensile mean stresses have negative effects on fatigue strength [9], [10] as they support crack initiation and propagation by opening the crack root [10]. In contrast, compressive stresses retard the crack formation and propagation [10]. To compare the results obtained with different load ratios or to use a test series with a specific mean stress to draw conclusions about other mean stresses, different equations or models can be used [11]. For aluminum alloys, Papuga et al. showed [12] that the SWT method is remarkably accurate for evaluating the mean stress effects. The aim of this paper is to investigate the fatigue behavior of AlSi10Mg produced by Laser-Powder Bed Fusion (L-PBF). The research addresses two key aspects: the size effect across three distinct geometries and the influence of mean stress on one geometry under both push-pull and tension-tension loading conditions, providing valuable insights into how geometry and mean stress affect the fatigue resistance of L-PBF AlSi10Mg.

Nomenclature A / G / H

Designations of specimen designs Laser Powder Bed Fusion (L-PBF)

L-PBF

Load ratio defined as minimum load to maximum load

R

Low-cycle fatigue High-cycle fatigue Kohout- Věchet model

LCF HCF K&V σₐ N f m σ m , UTS ∆ SWT

Parameters of the Kohout- Věchet regression

a KV , C, B, β

Applied stress amplitude [MPa] Number of cycles to failure mean stress sensitivity Applied mean stress [MPa] Equivalent stress amplitude [MPa] Ultimate tensile stress [MPa]

Fatigue index error

Smith-Watson-Topper model of mean stress effect

2. Fatigue strength analysis 2.1. Description of specimens This study investigates the fatigue behavior of additively manufactured AlSi10Mg specimens produced via Laser Powder Bed Fusion (L-PBF) with printing parameters as depicted in Table 1. The specimens used in this study were treated with T240 heat treatment, which is recommended by the manufacturer. By applying T240 heat treatment, the specimens are heated to 240 °C and held for 6 hours in the furnace, followed by two steps of cooling, first cooling in the furnace until a temperature of 100 °C is reached, and second, cooling in air. Three types of fatigue specimens were manufactured (see Fig. 1) to fit into two different machines. The surface of A and G specimens was left in the unmachined as-built state. For specimens of type H, the outer surface was machined, while the hole visible in Fig. 1 also remains in the unmachined as-built state. The specimens designated with A have a critical cross-sectional area of 63.6 mm². The G series has an area of 10.2 mm², and the H series has an area of 30.5 mm². However, the geometries G and H were specifically designed so that the crack propagation length remains similar for these specimens.