PSI - Issue 13

Wenbo Sun et al. / Procedia Structural Integrity 13 (2018) 1020–1025 Author name / Structural Integrity Procedia 00 (2018) 000–000

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will be widely used in aviation structure in the future. During processing of SLM, a layer is stacked on the other layer, so there are some pores presented between the interlayers. This will cause that the mechanical properties of the titanium alloy manufactured by SLM are affected by the building direction (2015,2017). With increasing of SLM application in aircraft structure, it is urgent to study the effects of building direction on fatigue performance of SLM titanium alloy. The fatigue properties of SLM materials have been studied by several researchers, and it is shown that the porosity (2017,2016) and post treatment (2017,2018) are the main factors that affect the fatigue performance of structure built by SLM. Amanda studied the influence of porosity on the fatigue properties of additive manufactured titanium alloy (2017), and he focused on the effects of pore shape, size, position, and quantity on fatigue life. Some other scholars have also studied the fatigue property of the additive manufactured titanium alloy fabricated by different techniques (2018,2010), and their results are similar to those of SLM technology. Based on the multi-scale damage mechanism, Wan established a meso-model considering the effects of building direction and porosity, and then predicted the fatigue life of Ti-6Al-4V titanium alloy (2016). Based on the high cycle fatigue test data, Eric set up a numerical model to analyze the fatigue properties of the additive manufactured Ti-6Al-4V (2014). Lamellar structure can be clearly seen in microscopic image along the forming direction. This layered structure is bound to affect fatigue properties. Xie found that the building direction affected the stress intensity factor transition point, and the value of vertical building direction sample is 5% higher than that of the horizontal direction sample (2018). Jiao studied the influence of the stress ratio on the fatigue crack growth behavior under different temperatures (2017). In order to study the effects of the building direction on the fatigue crack growth behavior of Ti-6Al-4V titanium alloy manufactured by SLM, three kinds of C(T) specimens with different building directions were designed and fatigue crack growth rate tests were performed. 2. Sample design Based on ASTM-E647, C(T) specimens were designed and the size is shown in Fig. 1. The initial crack length is 10.0 mm.

Fig. 1. Compact C(T) Specimen

C(T) sample with three building directions (0 ° ,45 ° and 90 ° ) were designed. The deposition layer of 0 ° direction sample is parallel to the direction of the crack growing, while 90 ° sample is perpendicular to the direction of crack growing. Building directions of sample are defined and shown in Fig. 2 (The red arrow is the building direction). All the specimens were built by the BLT-S300 machine, and the fatigue crack growth test was carried out after post heat treatment process.