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Additive Manufacturing and Characterization of Polylactic Acid (PLA) Composites Containing

Metal Reinforcements

Lily Kuentz1, Anton Salem2, M. Singh3, M.C. Halbig4, J.A. Salem4

1Lake Ridge Academy, North Ridgeville, OH 440392Hawken School, Gates Mill, OH 44040

3Ohio Aerospace Institute, Cleveland, OH 441424NASA Glenn Research Center, Cleveland, OH 44135

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https://ntrs.nasa.gov/search.jsp?R=20160010284 2020-02-21T06:13:22+00:00Z

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Additive Manufacturing

• 3D printing– 3D CAD files are sliced– Filament is heated and

extruded

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3D Printing Materials

• Main 3D printer filaments– PLA– ABS

• Composite materials– Contain metal powders– Various fibers

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Polylactic Acid (PLA)

• Benefits– Environmentally friendly– Does not release toxic fumes/safe for

people

• Disadvantages– Does not last as long

as other plastics.– Not as tough as ABS,

based on fracture toughness testing

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Applications of Polylactic Acid

• Films– Food packaging– Plastic bags

• Fibers– Upholstery– Disposable garments

• Biomedical applications

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Objectives

Determine the properties of the new PLA composite materials

• Microscopy• Tribology• Tensile Strength• Fracture Toughness

Compare the properties of the PLA with the PLA composites

• Are the PLA composites an improvement on the plain PLA materials?

• In what ways are these PLA composite materials an improvement?

• Thermogravimetric analysis

• Differential Scanning Calorimetry

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Materials Used in Present Study

• PLA (Polylactic acid)• Bronze fill PLA• Copper fill PLA• Magnetic Iron PLA• Stainless Steel PLA

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3-D Printed Materials

• The test samples were printed at several different layer heights seen below:

− Tensile bars - 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm− Wear test samples - 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm− Fracture toughness bars - 0.1 mm, 0.3 mm− Microscopy samples - 0.1 mm, 0.3 mm

• Three samples per conditionASTM D638

ASTM D5045

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0.1mm 0.2mm

0.3mm 0.4mm

Macrostructure

.4mm

..1mm

.3mm

.2mm

• Print resolution– Prints of different layer heights exhibit different

structures. Different mechanical properties?

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Density• Metal Composite PLA vs. Pure PLA

– The metal filled materials had much higher densities than the pure PLA; correlate to metal mass content.

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Thermogravimetric Analysis

Filament Metal Weight Percentage Metal Volume Percentage

Bronzefill PLA 80.35% 36.02%

Copperfill PLA 80.57% 36.41%

Stainless Steel PLA 58.87% 18.09%

Magnetic Iron PLA 48.33% 11.05%

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0

20

40

60

80

100

120

0 100 200 300 400 500 600 700 800

Weight %

Temperature

TGA Tungsten  N2

Thermogravimetric Analysis

Loss of PLA

Oxidation weight gain

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700 800

Weight %

Temperature

TGA GMASS Tungsten air

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MicrostructureM

agnetic Iron PLAB

ronze PLAC

oppe

r PLA

Stai

nles

s Ste

el P

LA

• Spheroidal Cu and bronze particles• Deformed stainless and iron particles; poor dispersion!

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Tensile Data

• PLA shows no layer height effect:

0

10

20

30

40

50

60

0.000 0.005 0.010 0.015 0.020 0.025 0.030

Stress (M

Pa)

Axial Strain (in/in)

PLA layer height of 0.1 to 0.4mm

PLA_0.1

PLA_0.2

PLA_0.3

PLA_0.4

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Tensile Data

• PLA shows the greatest strength:

0

10

20

30

40

50

60

0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040

Stress (M

Pa)

Axial Strain (in/in)

Metal Composite Systems for layer height of 0.3mm

PLA_0.3

MI_03.01

SS_0.3

Br_03.01

Cu_03.01

PLA

Magnetic Iron (11%)

Copper and Brass (36%)

Stainless (18%)

• As the concentration of metal in the filament increases, the strength decreases.

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Tensile Data

• Metal filled PLA show an effect of layer height:

• Lower strength and strain to failure.

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0

5

10

15

20

25

30

35

40

45

0 0.005 0.01 0.015 0.02 0.025

Stress

(MPa)

Axial Strain (in/in)

Stainless 0.2 Build Height

0

5

10

15

20

25

30

35

40

45

0 0.005 0.01 0.015 0.02 0.025Stress (M

Pa)

Axial Strain (in/in)

Stainless 0.4 Build Height

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Young’s Modulus

• Young’s modulus follows the V% of metal - porosity.• Still stiffer than premium ABS.• Poisson’s ratio was ~0.33.

ECu = 117 GPa(higher porosity)

EBz = 96-120 GPa

Cu

BZ

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3,145 

5,400 

4,494 

3,910 

3,637 

2,098 

PLA BZ,  36%

CU,  36%

SS,  18%

MI,  11%

PABS

YOUNG'S M

ODU

LUS (M

PA)

METAL  FILLED  PLA

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Fracture Toughness

• Generally, the fracture toughness follows the V% of metal.

• PLA has greater toughness than ABS, but metal additions can lower significantly (50% for Cu).

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3.39

1.7

2.0

3.1

3.4

2.7

PLA CU,  36%

BZ,  36%

SS,  18%

MI,  11%

PABS

FRAC

TURE

 TOUGHN

ESS, M

PA

METAL  FILLED  PLA

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Fracture Surfaces

• Do we have pictures?

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Tribology

0

0.2

0.4

0.6

0.8

1

0 100 200 300 400 500

PLA 0.3 mmPLA 0.1 mmCu 0.1 mmCu 0.3 mmBronze 0.1 mmBronze 0.3 mm

Fric

tion

Coe

ffici

ent

Distance (m)

• Friction Coefficient of metal filled PLA:

Related talk to be given on wear etc.

– The metal composite materials generally exhibit a higher coefficient of friction than pure PLA.

– Higher layer height exhibits lower friction.20

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Conclusions• PLA exhibits the greatest strength, with no dependence on

layer height.• Metal filled PLA is stiffer but weaker than unfilled; Good strain

to failure is usually exhibited. • SS filled PLA exhibits lower strain to failure – irregular powder

and higher % fill. Bonding? Distribution? Surface finish? Fractography!

• As the metal volume percentage increases, the porosity increases, and lower strength is exhibited.

• Young’s Modulus generally increase as the V% of metal increases.

• Fracture toughness decreases as metal content increases.• Higher coefficient of friction is exhibited by metal filled PLA’s.• Metal powder act as a weak interface thereby lowering strength

and toughness.21

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Future Work

• Continuing to process tests, and analyze these metal filled PLA materials.

• Characterization of new filaments.

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