PSI - Issue 53

Martin Matušů et al. / Procedia Structural Integrity 53 (2024) 29 – 36 Author name / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction Temperature measurement can be taken as an additional parameter for assessing fatigue performance for various alloys. The thermographic method showed its high potential for various steels and other materials in previous works. Not only to establish the fatigue limit [1; 2; 3; 4; 5; 6], but also to predict sections of the S-N curve on a smaller number of specimens [7; 8; 9] than the traditional fatigue tests (e.g., by ASTM E739-10 [10]) would request. The temperature increase observed during cyclic loading and used by this method is called the self-heating (SH) effect [11; 12]. This phenomenon which is highly affected by the testing frequency, load amplitude, and stress ratio occurs usually in three phases (see Sec. 2.3. Thermal response). Within the SH test setup, only the stress amplitude is changed. This allows the authors to investigate the temperature evolution throughout the High Cycle Fatigue (HCF) domain. In this paper, the thermographic method for fatigue life prediction, number of cycles to failure, is used to analyze the fatigue behavior of four different configurations of additively manufactured AlSi10Mg using L-PBF [13]. Four different heat treatments (HT) are used to evaluate their effect on fatigue strength, fatigue limit transition, and tensile properties.

Nomenclature Θ

Stabilized temperature increase

Thermoelastic effect

S t

Time constant for thermal exchange between the specimen and its surroundings

τ

Thermal dissipation Initial temperature rate Final temperature rate Number of cycles Number of cycles till failure Theoretical fatigue limit Young’s modulus of elasticity Yield strength at 0.2% of strain

d 1 R o R γ N N f

σ FL

E

R p0,2

R m Ultimate tensile strength R a , R z Roughness parameters (arithmetic average and maximum peak to valley height, respectively) ρ ,c Material’s density and materials specific heat

2. Fatigue strength analysis 2.1. Fatigue strength analysis

This study investigates the fatigue behavior of AlSi10Mg additively manufactured aluminum alloy using L-PBF technology. Hourglass-shaped fatigue specimens were used for the fatigue experiment, see Fig. 1a. M18x1 threaded heads of fatigue specimens were used to fix them into Amsler HFP resonant pulsator with a 100 kN load cell. The load ratio R =0.1 was applied only in tension. Tensile specimens with a critical cross-section of 6x3 mm were used for static tests, see Fig. 1b.

b)

a)

Fig. 1. (a) Fatigue test specimen; (b) Static tensile specimen with specimen thickness of 3 mm.

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