Fatigue and short crack assessment of powder bed fusion laser-based fabricated AlSi10Mg miniature specimens under alternating bending load

Abstract

Al-Si alloys are commonly used in the automotive and aircraft industry because of their excellent strength-to-weight ratio. Due to the laser powder bed fusion manufacturing process, inhomogeneous cooling affects the microstructure as well as defect distributions. Within this paper, the uniform fatigue damage tolerance assessment was further qualified for (miniature) bending specimens with different loaded volumes based on the concepts according to Murakami (√area) and Shiozawa for an initial defect-based model. These approaches were used to calculate defect-related fatigue life curves, in which the cyclic stress intensity factor (ΔK) at the initiating defect (√area) was used to represent local stress concentration at the crack tip instead of nominal stress-based S-N curves. Results of S-N curves did not allow a precise lifetime prediction due to increasing effect of manufacturing-related defect distributions, while fracture mechanical approaches enable a uniform fatigue lifetime description of different testing volumes. The calculated fatigue limit and short crack threshold value suggested by Noguchi based on the extended approach of Murakami need to be compared and validated experimentally. Furthermore, the effects of miniaturization and crack propagation have been identified and considered. Uniform fatigue life predictions and efficient materials testing have been combined and show potential for future research.

Keywords

• Al-Si alloy
• Additive manufacturing
• Fracture mechanical approach
• Bending
• Miniaturization