PSI - Issue 37

Mohammed Algarni et al. / Procedia Structural Integrity 37 (2022) 676–683 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

678

3

SN MN LN S UTS σ min σ max R

sharp notch specimen medium notch specimen large notch specimen

load ratio

ultimate tensile strength

minimum stress maximum stress

stress concentration factor notch sensitivity factor fatigue notch factor

K t Q K f S a N f η

stress triaxiality amplitude stress

number of fatigue life cycles to full fracture equivalent stress amplitude at zero mean stress

S ao

2. Experimental Details Three different notch radii were tested to study the influence of notch size on fatigue life: sharp notch (SN), medium notch (MN), large notch (LN) specimens. The dimensions are shown in the detailed drawing in Figure 1 and Table 1. They were printed using a commercial open source Creality 3D printer model Ender-3. The filament was made of PLA material manufactured by eSUN® with Young’s modulus of 2.1 GPa, a flexural strength of 75.1 MPa, ultimate tensile strength S UTS of 65 MPa, fracture strain of 8%, and density of 1.246 g/cm3. The diameter of the PLA filament polymer was 1.75 mm and was extruded through a 0.4 mm brass nozzle diameter. Printer settings included a nozzle temperature of 206°C, build plate temperature of 60°C, infill layer thickness of 0.12 mm, and infill density of 100%. The printing speed was set to 18 mm/s, and the raster angle was 0°, which is in the direction of the applied axial load. The specimens had smooth lateral surfaces, and the contour shell thickness was 0.4 mm. The specimen dimensions were rechecked to ensure a tolerance range of ±0.25 mm, which indicated that the 3D printer was consistently printing with high accuracy and quality. The fatigue tests were performed at room temperature by an electromechanical testing machine at a sinusoidal frequency of 10 Hz. The specimen S UTS values were determined by testing under monotonic loading (Table 1). Next, the specimens were tested under cyclic loading with load ratios ( R = σ min /σ max ) R = -1, 0.1, and 0.3. The fatigue tests were stopped after the fracture of each specimen occurred (failure criterion). Twenty specimens of each design were tested under each load ratio, resulting in a total of 180 tests.

Table 1: Specimen main dimensions and fatigue parameters Notch type a (mm) t (mm) r (mm) S UTS (MPa)

Ω

η

K t

q

K f

SN

1.2 1.2 1.2

3 3 3

2.2 5.5

30.6 34.0 44.2

1.32 1.14 1.00

0.78 0.86 0.97

1.24 1.12 1.00

0.54 0.21 0.04

0.47 0.42 0.35

MN

LN

32.5