PSI - Issue 34

J. Gil et al. / Procedia Structural Integrity 34 (2021) 6–12

9

4

J. Gil et al. / Structural Integrity Procedia 00 (2019) 000–000

2.5

1

2 5 0.5

12

5 14

0.5

2

75

20

z

45°

y

x

50

5

10

7

Fig. 3. Prism dimensions in millimetres.

Fig. 2. Benchmark bridge dimensions in millimetres.

The second approach, approach #2, is indeed more complex as it models the spread of powder in a new layer before it undergoes the melting process, and the laser trajectory in each layer besides computing the thermal history and mechanical outputs. The heat source was modelled with a Goldak spatial distribution, whose governing equation is given in Equation 2.

6 √ 3 η P f π √ π abc

exp − 3

z 2 c 2

x 2 a 2 −

y 2 b 2 −

(2)

Q =

3

Both of the approaches model the interaction between the component and substrate as a contact surfaces.

3. Experimental setup

Two physical components were additively manufactured through LPBF, experimentally studied and subsequently simulated: a simple 50 × 10 × 20mm (where latter measure coincides with the build direction) prism which will hence forth be named prism , and a more complex geometry developed by the National Institute of Standards and Technology (NIST) henceforth called benchmark bridge . The latter was specially designed with the aim of highlighting the influ ence of residual stresses on component distortion. Both of the aforementioned geometries are schematically shown in Figures 2-3. Besides their di ff erent geometry, the components’ constituent material, process parameters and scanning strategies are di ff erent, with the former being made out of AISI 316L stainless steel and the latter 18Ni300 Maraging steel - although the original NIST bridge is made out of Inconel 625; the process parameters are shown in Table 1, and the scanning strategies are described as follows: • Prism: line zig-zag pattern that repeats at every three layers, starting with a 0° angle between the material deposition direction and the x axis described in Figure 3; the second layer is deposited with a 120° angle in relation to the first in the counter-clockwise direction, and the third with a 240° angle; • Bridge: line zig-zag pattern that repeats at every two layers, starting with a 90° angle between the material deposition direction and the x axis; the second layer is deposited with a 0 angle in relation to the x axis. The residual stresses in both components were measured by x-ray di ff raction (XRD): the 316L prism was measured with Mn- K α radiation, and the 18Ni300 bridges were measured with Cr- K α radiation, with each stress measurement’s exposition time being 30 s. The measurements were conducted in the component’s surface. These two geometries serve as the basis for three distinct analysis employed: residual stress analysis in the prism, residual stress in the benchmark bridge and deflection analysis after bridge leg separation from the baseplate, with the latter being physically achieved through wire electrical discharge machining. The vertical deflection was measured through a Nikon Three-Axis Coordinate Measuring System with Renishaw PH10T-Plus Head of spherical tip.