Abstract
Cantilever-type rotating bending fatigue tests were conducted under a very high cycle fatigue regime using conventionally manufactured Ti-6Al-4V specimens having drilled artificial defects with different sizes. The relationship between fatigue limit and defect size was defined as a fatigue limit design curve considering the transition from the fracture-mechanics dominating area to the fatigue-limit dominating area. A conventional Murakami’s equation was applicable as a design curve of additively manufactured Ti-6Al-4V with defects at 107 cycles. However, conventional equation gave un-conservative predictions for the fatigue limit at 108 cycles. Therefore, two kinds of modified Murakami’s equation were proposed as fatigue limit design curves for the very high cycle fatigue regime. Simple parallel shift of Murakami’s equation gave a conservative fatigue limit, whilst better result was obtained by changing the slope of Murakami’s equation. The proposed design curve was valid for the defect sizes ranging from 10 to 500 μm.
Highlights
Additive manufacturing (AM) has been attracting large attention due to its many advantages
It has been reported that hot isostatic pressing (HIP) could reduce the size and number of pores [8,9]
It is considered that the residual stress of AM-Ti is small because the fabrication process is electron beam melting, in which the energy input is larger than selective laser melting
Summary
Additive manufacturing (AM) has been attracting large attention due to its many advantages. Near-net-shape and complicated-shape components can be fabricated by AM using hard-to-work materials, such as high-strength steels, titanium (Ti) alloys and so on [1,2]. Ti-6Al-4V is widely used as aerospace components and one of the hard-to-work materials. One of the major drawbacks of AM is the formation of pore-like defects during AM process, which have a significant effect on the fatigue performances [4,5,6,7]. That is because pore-like defects could be assumed as fatigue crack starters. It has been reported that hot isostatic pressing (HIP) could reduce the size and number of pores [8,9]. As-built components with defects are sometimes used from the viewpoint of reducing costs, indicating the importance of quantitative evaluation of the effect of defects on fatigue properties
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