SAMPE Journal - November/December 2019 - 32

FEATURE / ADDITIVE MANUFACTURED TOOLSET PARTS

Figure 21. Photodiode
data processed by
PathCoverage.

The levels of qualifications are coupon (e.g., coins),
element (e.g., dog-bone), detail (Comb/NIST), and
AM part.
Experimental and Simulation Results for
Porosity in AlSi10Mg
Figure 23 shows the effect of different values of laser
power and speed on density of AlSi10Mg specimens
and their porosity (data is provided by University
of Dayton Research Institute). Microscale porosity
was simulated, and experimental data and
numerical results are compared in Figure 24 for
different values of laser power and speed.
Mount Ring Virtual Quality Assessment
In the virtual quality assessment AM simulations
were performed that showed warpage and the
problems were fixed through simulation and
minimal prints (3) (Figure 25). These initial
part simulation validations were important in
establishing a baseline for further optimization
design of experiments.

Prediction of inter-granular/trans-granular void nucleation/growth,
surface roughness, residual stress, and oxidation using diffusional creep and
grain boundary sliding was performed. In collaboration with Imperial College
of London, the ASC team developed a practical engineering multi-scale
approach to estimate the performance of defect afflicted and as-built metal
specimens based on fracture mechanics diffusion creep crack nucleation and
growth capability. This capability is currently being used in high temperature
materials for nuclear industry7. The methodology of diffusion creep crack
growth is coupled with non-linear elastic fracture mechanics (LEFM) with the
assumption of defects considered as initial cracks. Local material modeling
integrated with commercial FEM is performed to determine the trans-granular
and intergranular crack formation under thermal-mechanical conditions
during powder-based additive manufacturing process. The bi-axiality of the
stresses results in intergranular cracks while the triaxiality of the stresses leads
to surface roughness. Figure 26a shows the zone of lowest margin being fed
into local grain models (Figure 26b). Figure 27a shows voids from path coverage
mapped to simulation models. Figure 27b shows the processed void scatter.
Figure 28a shows simulation of a comb base post plate removal deflections
and comparisons with test. Figure 28b shows the net shape simulations
compared with scans of an actual part.

Table 2. Steps and Criteria for Part Qualification.
Steps

32

|

Qualification Category

Description

1

AM Micro defects

Micro voids/Density during thermal history, super melting
sintering and solidification

2

AM Macro defects

Macro porosity: Printing error around hole and boundary

3

Surface roughness

Diffusional creep, Triaxial stress

4

Intergranular cracks

Diffusional creep, Biaxial stress

5

Scatter in material properties

6

Fracture control plan

7

Warpage

Evaluation of support, Residual stress

8

Net shape

Residual stress, Baseplate removal

9

As-built part performance

In-service loading

10

Post heat treatment

Grain growth, lower strain; thermal analysis

SAMPE JOURNAL

|

Stress-strain relation (yield stress, ultimate/plastic strain)
due to voids (micro/macro) and cracks
Characterization of fracture properties, fatigue crack
growth, stress intensity curve

N OV E M B E R / D E C E M B E R 2 0 1 9

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SAMPE Journal - November/December 2019

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