PSI - Issue 79

Daniel Hofferberth et al. / Procedia Structural Integrity 79 (2026) 313–321

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microstructure, but they demand clean, well ‑ characterized end ‑ of ‑ life magnets and robust pretreatment (demagnetization, coating removal, size classification). A pragmatic alternative is to reuse magnet powders in bonded composites: shredded NdFeB is embedded in an organic matrix to form near ‑ net ‑ shape parts at low cost that can be produced by, e.g., injection molding. While bonded magnets typically exhibit reduced magnetic properties compared to sintered NdFeB and have lower thermal stability, they can be tailored via binder selection (thermoplastic vs. thermoset), particle orientation, and filler fraction. Crucially, performance must be assessed beyond magnetic metrics: tensile and compressive strength, stiffness, creep and fatigue behavior, thermal aging, moisture resistance, and corrosion protection determine reliability in service. Optimized composite design (e.g., reinforced binders, controlled porosity, surface treatments) and standardized characterization protocols are needed to close the gap between recycled bonded magnets and high ‑ performance applications. A rigorous comparison of routes – considering property retention, cost, energy footprint, and scalability – will guide materials selection and design ‑ for ‑ disassembly strategies that unlock truly sustainable magnet supply chains. In the field of tension between these challenges, the presented investigations focus on mechanical properties and especially on the fatigue strength of recycled magnets. The influencing parameter temperature and humidity is additionally regarded, leading to valuable insights that help to design reliable and sustainable motors or generators.

Nomenclature K t

Stress concentration factor Highly Stressed Volume Mean Stress Sensitivity Slope of the S-N curve Probability of Survival

V 90%

M

k

P s

r

notch radius

d

specimen inner width specimen outer width

D

p q

axial correction factor according to Neuber axial correction factor according to Neuber

2. Material and experimental procedure In total, three different types of ISO specimens were used for this investigation: one unnotched and one slighty notched specimen, Fig. 1 as well as one notched specimen with a notch radius of R = 0.9 mm radius, Fig. 2a. The recipe for compounding was composed of 91.6 wt.% of NdFeB (MQP B+) + 7.4 wt.% PA12 + 1 wt.% additives. All specimens were produced with commercial NdFeB powder in the injection molding process by KOLEKTOR, a partner of the HARMONY project. Based on literature, the moisture absorption of PA12 is low which makes it useable for different kinds of automotive and offshore applications, as well as for magnets. Because of this behavior of PA12, a selected amount of each type of specimens was stored/aged at three different environmental conditions. 1) Aging under ambient conditions (20°C with 50 % - 60 % humidity), 2) Aging at a temperature of 40°C and 10 % humidity 3) Aging at 60°C and 10 % humidity. The aging time was set to at least 4 weeks. The elevated temperature levels have been chosen to allow a moisture release of PA12. Before starting the fatigue investigation, the geometrical dimensions (width and height) of all specimens were measured to apply a consistent nominal stress amplitude for each specimen. For fatigue testing, a fully electric testing device, type Instron E10000, equipped with pneumatic clamping for flat specimen was used for the investigation at ambient temperature. The clamping force was optimized by adapting the